Development of Automotive Permanent Magnet Alternator with Fully Controlled AC/DC Converter

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Article Development of Automotive Permanent Magnet Alternator with Fully Controlled AC/DC Converter

Tareq S. El-Hasan ID

Electrical Engineering Department, Zarqa University, Zqrqa 13132, Jordan; [email protected]; Tel.: +962-777-747-230

Received: 18 November 2017; Accepted: 9 January 2018; Published: 24 January 2018

Abstract: This paper proposes the design of a three-phase axial flux permanent magnet alternator (AFPMA) that is characterized with an air-cored stator and two-rotor (ACSTR) configuration. The AFPMA is harnessed with fully controlled AC/DC converter using six bridge Insulated Gate Bipolar Transistor (IGBTs) capable to deliver a constant DC output power as an attempt to replace the Lundell alternator for automotive applications. First, the design methodology and analysis of the AFPMA is introduced. The most effective parameters, such as rotor diameter, magnet thickness, number of turns, and winding thickness are determined. A smart digital control which facilitates the comparison between the magnitudes of the three-phase input signals instead of finding the zero crossing points is developed. Moreover, custom design comparators are specially designed and developed to generate adaptive signals that are fed into an Arduino Uno microcontroller. Accordingly, the Arduino generates the timely precise pulses that are necessary to maintain the appropriate triggering of the IGBTs. This technique allows the IGBTs to conduct in an adaptive manner to overcome the problem of asymmetrical voltage outputs from the AFPM alternator. The system is also capable of handling the variation in the speed of the AFPMA via the rigor code in Arduino that detects the change in the supply frequency and voltages in a real time process. The system is first analyzed via simulations using MATLAB/Simulink and then experimentally validated at certain speed and loading conditions. The preliminary tests results indicate that such system is capable to provide an efficient solution to satisfy automotive electric power demands.

Keywords: automotive alternator; axial ﬂux permanent magnet alternator; air cored stator alternator; fully controlled AC/DC converter

1. Introduction When implementing electrical technology or components into vehicles, the size, weight, cost, performance, and efﬁciency are the major factors that need to be considered for successful integration. Steadily but surely, automobile manufacturers are looking to improve vehicle component performance and increasing their power density. Among these components is the on-board electrical power charging system which normally consists of the alternator, power converter, and battery. Such electrical systems are pushed to their limits as more and more vehicle’s components are replaced by electrically powered or electrically assisted items. In addition, the evolving customer demands, increasing car functionalities, and developing vehicle regulations and legislations have necessitated the development of the electrical power generating system to satisfy the increasing demands of electrical power in automobiles. For the last 50 years, the three-phase claw-pole alternators (or Lundell alternators) have been used for the generation of electric power in automotive applications. Until very recent years, this alternator was the most economic choice in vehicle technology due to its low manufacturing cost. However, Lundell alternators suffer from major drawbacks such as reduced efﬁciency, limited output power, and the need for continuous maintenance. This in turn has limited the utilization of such machines in

Energies 2018, 11, 274; doi:10.3390/en11020274 www.mdpi.com/journal/energies Energies 2018, 11, 274 2 of 28 modern vehicles due to the challenges initiated by increased power demands. Hence, other alternatives for electrical power generating systems have been considered to meet such challenges in motor vehicles [1–4]. To meet the increasing power demands in modern vehicles, automobile manufacturers have exploited the distinguished merits offered by the rare earth, high power, permanent magnets (PM) in the development of electrical power generator to replace the Lundell alternators. Alternators utilizing PM offer numerous attractive features over other conventional types of electrical machines, including higher efficiency, higher power density, no maintenance, and better reliability [5,6]. PMs can also improve the dynamic performance, and output quality of the machine. PMs are also becoming less expensive, which makes PM machines more prevalent. The recent advances in power electronic devices have led to better, easier, and cost effective control of PM machines, with the tendency of operating the machine over a large range of speeds while maintaining a reasonable efficiency. Several types of PM machines have been constructed based on their magnetic field direction. For example, PM machines with axial, radial, or transverse configurations have found their way into many applications, such as home appliances, industrial use, renewable energy, and automobiles [7–10]. Other benefits such as short length, ease of manufacturing and assembly, and modularity are realized by axial flux PM (AFPM) machines when compared to other configurations. Such machines have demonstrated their relative fitness in applications that are limited with confined spaces or those which require direct coupling of the machine with short overhang [11]. AFPM machines can be used for both low speed [12,13] and high speed applications [14–16]. Moreover, AFPM machines with ACSTR configurations are characterized with extra advantages such as lower cogging torque, reduced eddy current losses, better output wave (sinusoidal-like) generation, and less harmonics [15] as compared to other types of PM machines with cored stator configurations. Hence they have potential for use in wind energy applications [17–19] as well as automotive applications [20–23]. This paper introduces the design and optimization methodology for an AFPM alternator (AFPMA) as part of the integrated battery charging system in automobiles. The proposed AFPMA, which is intended to work as a replacement for the Lundell alternator diverges from the high speed version that has been previously developed for high speed applications [14–16]. The objective is to rebuild that AFPMA with minimal design effort to make it suitable for vehicle applications. This is achieved by redesigning the stator windings within the existing geometrical constraints and without jeopardizing the machine’s efficiency. To do so, the sizing equations for the machine are developed, and the machine performance is analysed using MATLAB/Simulink modelling. Moreover, a three-phase fully controlled AC/DC rectifier is developed and integrated with the AFPMA. The complete system is experimentally tested and simulation results are validated and results obtained are presented in detail in this paper. The ultimate goal is to design a suitable on-board electrical power system that can satisfy the full requirement of increasing demand of modern automotive industry. The machine shall be capable of providing the car with the necessary power to charge the battery and to turn all electrical and electronics loads whether the engine is running at idle speed or at full speed.

2. Description and Design Requirements of the AFPMA The machine under investigation has an air-cored stator and two-rotor (ACSTR) system with no iron core in the stator coils. Originally, the machine was designed for high speed applications [14]. Hence, the rotors were carefully designed to allow the machine to withstand high levels of centrifugal forces. The proposed AFPMA in this paper is depicted in Figure1. To redesign the machine for low to moderate speed applications, the rotor conﬁguration and dimensions are kept the same except the retainment ring which encapsulates the rotor magnets are selected from lower cost aluminium alloy instead of expensive, high strength maraging alloy. In addition, simpler manufacturing and assembly processes are performed which in turn reduces the machine cost. However, the stator is completely redesigned in order to achieve the automobile requirements. Still, the stator is air cored (ironless) Energies 2018, 11, x FOR PEER REVIEW 3 of 30 redesigned in order to achieve the automobile requirements. Still, the stator is air cored (ironless) in Energies 2018, 11, x FOR PEER REVIEW 3 of 30 orderEnergies to minimize2018, 11, 274 weight, losses, and cogging torque. Figure 2 shows the main parameters3 ofthat 28 are considered in the redesign process. These are: the outer radius of the coil which is similar to the redesigned in order to achieve the automobile requirements. Still, the stator is air cored (ironless) in outer radius of the PM disc, ( R ), inner radius of coil which is similar to the inner radius of PM disc in order to minimize weight, o losses, and and cogging cogging torque. torque. Figure Figure 2 shows the main parameters parameters that that are considered in the redesign process. These are: the outer radius of the coil which is similar to the ( Ri ),are number considered of winding in the redesign turns ( process.Nt ), axial These air are: gab the length outer (stator radius ofth theickness), coil which and ismechanical similar to the speed outerouter radius radius of theof the PM PM disc, disc, (R o(),R innero ), inner radius radius of coilof coil which which is similar is similar to theto the inner inner radius radius of PMof PM disc disc ( Nm ). The target is to reconstruct a mathematical model that can be used to design the stator (Ri), number of winding turns (Nt), axial air gab length (stator thickness), and mechanical speed (Nm). ( Ri ), number of winding turns ( Nt ), axial air gab length (stator thickness), and mechanical speed windingThe targetto fit isfor to reconstructthe AFPMA a mathematical to achieve the model machine that can requirements be used to design presented the stator in winding Table 1 to within ﬁt for the N existingthe( AFPMAconstraints.m ). The to target achieve is the to machinereconstruct requirements a mathematical presented model in Table that 1can within be theused existing to design constraints. the stator winding to fit for the AFPMA to achieve the machine requirements presented in Table 1 within the existing constraints.

(a) (b) (a) (b)

FigureFigure Figure1. AFPMA 1. AFPMA 1. AFPMA under under under consideration: consideration: consideration: (a (a)) 3D( 3Da) 3Dexploded exploded exploded viewview view of of ACSTR;of ACSTR; ACSTR; (b ) ((b assembledb)) assembled AFPMA. AFPMA. AFPMA.

FigureFigure 2. AFPMA 2. AFPMA rotor rotor and and stator stator main main parameters. parameters. Figure 2. AFPMA rotor and stator main parameters. TableTable 1. AFPMA 1. AFPMA Requirements. Requirements. AFPMATable 1. Set AFPMA Parameters Requirements.Value Unit AFPMA Set Parameters Value Unit AFPMARMS Set line–line Parameters voltage Value 17 Unit V RMS line–lineRated current voltage 17 40 V A RMS line–line voltage 17 V RatedRated current speed 40 5000 A RPM RatedRated current speed 5000 40 RPM A Rated power @ rated speed 1.2 kVA RatedRated power @speed rated speed 1.2 5000 kVA RPM 3. Design ConsiderationRated and Sizing power of @ the rated AFPMA speed 1.2 kVA 3. Design Consideration and Sizing of the AFPMA In order to facilitate the AFPMA for automobile applications, the machine shall be designed to 3. DesignIn Consideration order to facilitate and the Sizing AFPMA of the for automobileAFPMA applications, the machine shall be designed fit for the gasoline engine speed. However, coupling the alternator directly to the automobile engine to ﬁt for the gasoline engine speed. However, coupling the alternator directly to the automobile will require an increased number of stator winding turns to compensate for the low operating speed, engineIn order will to require facilitate an increasedthe AFPMA number for ofautomobile stator winding applications, turns to compensate the machine for theshall low be operating designed to thus increasing overall machine volume. Lundell alternators are therefore commonly run with a belt fit forspeed, the gasoline thus increasing engine overall speed. machine However, volume. coupling Lundell the alternators alternator are directly therefore to commonlythe automobile run with engine will requireratio ofan 3:1increased to obtain number a higher of statorrotational windin speed.g turns For theto compensateproposed AFPMA, for the alow belt operating ratio of 5:1 speed, is thus increasing overall machine volume. Lundell alternators are therefore commonly run with a belt ratio of 3:1 to obtain a higher rotational speed. For the proposed AFPMA, a belt ratio of 5:1 is

Energies 2018, 11, 274 4 of 28 a belt ratio of 3:1 to obtain a higher rotational speed. For the proposed AFPMA, a belt ratio of 5:1 is adopted to achieve higher rotational speed hence increasing the overall power density of the system. Accordingly the AFPMA shall be capable to operate in the range of 3750–15,000 rpm when coupled to an engine running in the range of idle speed of 750 rpm to the cruise speed of 3000 rpm. As far as the mechanical integrity is concerned, the AFPMA has its PMs encapsulated by a high strength retainment ring that is shrunk fit on the rotor disc. Mechanical integrity tests showed safe operation of the machine at rotational speeds in the excess 25,000 [16]. However, in this paper, and for the purpose of laboratory testing, the proposed machine is driven by a three-phase electric motor with a belt ratio of 1.7:1 which will limit the machine maximum speed of the AFPMA to 5100 rpm. Once the range of operating speed is known, it is possible to develop the necessary sizing equations and mathematical models that can be utilized for optimization purposes in order to determine the machine’s parameters within the competing demands to meet the system requirements. To derive the necessary equations, the induced voltage formula will be applied on the stationary conductors in the presence of a rotating magnetic field. The rotating magnetic field in the proposed machine is secured by the axially magnetized PM semicircular discs that are located alternately on both rotor sides. The induced voltage in the conductor relies on the flux density, conductor length, and relative velocity. Calculation of the flux density in the middle of the air gap relies on several parameters such as: magnet type/grade, magnet axial length Lm, magnet shape and air gap length Xg between the two PM rotors. In automotive applications, components in the engine compartment are fitted in confined spaces and often exposed to high ambient temperatures and insufficient cooling. Mounted near the engine, the alternator is exposed to high temperatures, thereby reducing its performance and lifetime. Therefore, PM alternators have to be designed with great care to avoid the risk of PM demagnetization, especially for the NdFeB which has a lower Curie temperature and lower working temperature. In automotive applications, the under hood temperature may vary in the range from 50 ◦C to 80 ◦C, adding more thermal stress on the PM alternator as it may increase the risk of PM demagnetization. Therefore, selecting the type and the grade of PM is a vital issue in the design process as one has to compromise between achieving higher power density and higher temperature operability. Among the recently developed PMs, comes the neodymium iron boron (NdFeB) magnet which has high remanence Br, high coercive force Hc, high energy production, and a high performance/cost ratio. As can be shown in Figure3, NdFeB magnets with grade N52 have the highest normalized energy product (with average remanence value of 1.45 T) which makes them the most powerful magnets among other grades. However, such magnets have a limited operating temperature of 80 ◦C which may degrade the performance of the proposed AFPM alternator when used for automotive applications. In this stage of research, it was decided to choose the type and grade of PM that provides the best magnetic characteristics in order to achieve the maximum possible power density of the AFPM alternator to perform as an advanced development model (ADM). The objective is to prove that the AFPMA would perform according to the requirements and interface well with other systems in terms of form, fit, and function (F3). Thanks to its simple shape and design, the ACSTR configuration of the proposed AFPMA allow for natural ventilation and heat removal with minimal effort. The NdFeB magnets are held by an Alumec carrier which in turn plays a crucial role in dissipating the heat that may transfer from the stator windings to the rotor surface. In addition, the rotating PM discs work as natural ventilators since they continuously expel the hot air surrounding their surfaces during rotation. Consequently, once the performance of the machine is experimentally validated, the engineering development model (EDM) of the AFPMA will consider the intended final materials and/or deployment of the necessary cooling arrangement to account for reliability, availability, and maintainability (RAM). Energies 2018, 11, x FOR PEER REVIEW 5 of 30

Energies 2018, 11, 274 5 of 28 Energies 2018, 11, x FOR PEER REVIEW 5 of 30

(a) (b)

Figure 3. Normalized energy product vs. different grades of NdFeB at their corresponding maximum operating temperatures: (a) calculated at 20 °C; (b) calculated at 80 °C. Based on available information from China YY Magnetics (Zhejiang, China) [24].

To account for temperature(a) effect on the energy product of the(b )PMs hence on the machine performance, B and H are calculated respectively as [25]: FigureFigurer 3. 3.Normalized Normalizedc energy energy product product vs. vs. different different grades grades of of NdFeB NdFeB at at their their corresponding corresponding maximum maximum operatingoperating temperatures: temperatures: (a ()a calculated) calculated at at 20 20◦ C;°C; (b ()b calculated) calculated at at 80 80◦ C.°C. Based Based on on available available information information fromfrom China China YY YY Magnetics Magnetics (Zhejiang, (Zhejiang, China) China) [24 [24].].  B  Br  Br 20 1 TPM  20 (1)  100  To account for temperature effect on the energy product of the PMs hence on the machine To account for temperature effect on the energy product of the PMs hence on the machine performance, B and H are calculated respectively as [25]: performance, Br andr Hc arec calculated respectively  as [25]:  H Hc  Hc20 1 TPM  20  (2) h α100B i  B = B 1 + B(T − 20) (1) r Br r20Br 20 1 PMTPM  20  (1)  100100  where Br 20 and Hc20 are the NdFeB gradeh 52 remanenceα andi coercive force respectively given at = + H ( − ) Hc Hc20 1   HTPM 20  (2) Hc  Hc20 1100 TPM  20 (2) 20 °C,  B and  H are the temperature coefficients 100 for Br and Hc and they are set to −0.12 and where Br20 and Hc20 are the NdFeB grade 52 remanence and coercive force respectively given at ◦ −0.6 respectively,20 C, αB and andαH areTPM the is temperature the PM coefﬁcientstemperature for Bwhichr and H cisand set they to arethe set maximum to −0.12 and operating where Br 20 and Hc20 are the NdFeB grade 52 remanence and coercive force respectively given at temperature−0.6 respectively,of 80 °C. Accordingly, and TPM is the PMthe temperature remanence which value is setand to theenergy maximum product operating are temperaturecalculated for N52 20 °C,◦  B and  H are the temperature coefficients for Br and Hc and they are set to −0.12 and at the maximumof 80 C. Accordingly, operating the temperature remanence value which and show energyed product a decrease are calculated in the for normalized N52 at the maximum energy product operating−0.6 respectively, temperature and which T showed is the aPM decrease temperature in the normalized which isenergy set toproduct the maximum by approximately operating by approximately 8%. The effectPM of temperature rise on the normalized energy product for several 8%.temperature The effect of of 80 temperature °C. Accordingly, rise on the the remanence normalized value energy and product energy for product several are grades calculated of NdFeB for N52 as grades ofcompared atNdFeB the maximum toas the compared energy operating product to temperature the of energy N52 based which product on show 20 ◦ Cofed is N52a presented decrease based in onthe Figure 20normalized 4°C. is presented energy product in Figure 4. by approximately 8%. The effect of temperature rise on the normalized energy product for several grades of NdFeB as compared to the energy product of N52 based on 20 °C is presented in Figure 4.

Figure 4. Degrading of the normalized energy product as a function of the temperature increase for Figure 4.Figure Degrading 4. Degrading of the of normalized the normalized energy energy product product as as a functiona function of the of temperaturethe temperature increase increase for for several grades of NdFeB. Based on available information from e-magnets UK (Hertfordshire, UK) [26]. several gradesseveral of grades NdFeB. of NdFeB. Based Based on available on available inform informationation from from e-magnets UK UK (Hertfordshire, (Hertfordshire, UK) [UK)26]. [26]. For simplification purposes, circular magnet shapes are considered to determine the magnetic For simpliﬁcation purposes, circular magnet shapes are considered to determine the magnetic For simplificationflux density in the purposes, air gap between circular the twomagnet PM rotors shapes. The are full consideredderivation of theto determinesizing equation the and magnetic ﬂux density in the air gap between the two PM rotors. The full derivation of the sizing equation and flux densityother in necessary the air gap equations between for the the AFPMA’s two PM paramete rotors.r Thedetermination full derivation and optimization of the sizing purposes equation are and other necessary equations for the AFPMA’s parameter determination and optimization purposes are shown in Appendix A. other necessaryshown in equations AppendixA .for the AFPMA’s parameter determination and optimization purposes are shown in Appendix A.

Energies 2018, 11, 274 6 of 28

4. Optimization of the AFPMA In order to optimize the machine design, two main characteristics will be investigated. These are machine efﬁciency and machine internal power factor, as will be described in detail in the following sections.

4.1. Machine Efficiency To predict the machine efficiency, the losses that are affected by the redesign process of the stator will be investigated. The two main losses that are seen to have major impact on the efficiency of the redesigned AFPMA these are the stator copper losses and the windage losses. The copper losses, Pcu, are calculated at the designed armature current, IA = 40 A as:

2 Pcu = 3IARW (3)

The windage losses of the machine is highly dependent on the rotor diameter and the rotational speed. If the rotor diameter is kept constant, then the only parameter that affects the windage losses is the rotor speed as: 3 5 5 PW = 0.5NRCf ρairωm Ro − Rsh (4) 3.87 Cf = √ (5) Re ρ ω R2 Re = air m o (6) µair where Cf is the coefficient drag for turbulent flow, Re is Reynolds number, NR is number of rotating 3 discs, ρair is the specific density of the surrounding air = 1.18 kg/m , µair is the coefficient of viscosity −5 of the air = 1.98 × 10 kg/m·s, and Rsh is shaft radius. Moreover, the amount of saving in windage losses is a critical aspect which may diversely affect the overall performance of the machine if precautions are not considered during the design. Hence, for fixed rotor geometry, the windage losses will only vary as a function of the rotor speed as:

2.5 PW = Kwdgωm (7)

The maximum windage losses PW,max are obtained at the maximum calculated speed, and minimum number of winding turns. i.e., at Nt= 2. Accordingly, the saving in the windage losses PW,sav can be calculated as:

PW,max − PW PW,sav = (8) PW,max

Assuming unity load power factor, and rated armature current of 40 A, the machine output power can be calculated as: Pout = 3Vϕ, f l IA (9)

Assuming the machine is operating at unity power factor, the full load phase voltage Vϕ, f l is calculated as: q 2 2 Vϕ, f l = Eϕ,rms − (IAXW ) − IARW (10) Other losses, such as rotor eddy current losses, are not considered in the investigation since the rotor geometry is not changed. Hence, the machine efﬁciency, η at the rated armature current and unity load power factor is calculated as:

P η = out × 100% (11) Pout + Pcu + PW Energies 2018, 11, x FOR PEER REVIEW 7 of 30

Other losses, such as rotor eddy current losses, are not considered in the investigation since the rotor geometry is not changed. Hence, the machine efficiency,  at the rated armature current and unity load power factor is calculated as:

Pout   100% (11) Pout  Pcu  PW

Energies 2018, 11, 274 7 of 28 4.2. Machine Internal Power Factor (cos φ)

The machine internal power factor (PFm) can be calculated as PF cos , where 4.2. Machine Internal Power Factor (cos ϕ) m     1 X W   tan  . Also, the voltage regulation of the machine can be calculated as: −1 XW The machine  internal power factor (PFm) can be calculated as PFm = cos ϕ, where ϕ = tan .  RW  RW Also, the voltage regulation of the machine can be calculated as: V ,nl V, fl VR  100% (12) Vϕ,nlV− Vϕ, f l VR = , fl · 100% (12) Vϕ, f l The no load voltage Vnl equals the per phase internal generated voltage of the machine E,rms . The no load voltage17 V equals the per phase internal generated voltage of the machine E . Hence, E   9.815nlV . ϕ,rms ,rms 17 Hence, E rms = √ =3 9.815 V. ϕ, 3 To performTo perform the the optimization, optimization, the the numbernumber of of turns turns per per pole pole per per phase phase Nt N ist variedis varied in steps in steps in in the rangethe range from from two two turns turns up up to to nine nine turns. turns. The The maximummaximum number number of ofturns turns is limited is limited with with the space the space betweenbetween the shaft the shaft and magnetand magnet inner inner radius. radius. For a For specific a specific number number of turns, of turns, the corresponding the corresponding rotational speed,rotational power speed, factor, power saving factor, in windage saving in losses, windag voltagee losses, regulation, voltage regulation, and efficiency and efficiency are calculated. are Usingcalculated. the set parametersUsing the set found parameters in Table found2, the in firstTable group 2, the offirst results group is of graphically results is graphically presented to showpresented the machine to show efficiency the machine and the efficiency internal and power the internal factor againstpower factor the change against in the number change of in turns number of turns (eventually the speed) as shown in Figure 5a. The second group of results are also (eventually the speed) as shown in Figure5a. The second group of results are also arranged to show arranged to show the saving in windage losses, voltage regulation, and rotational speed against the the saving in windage losses, voltage regulation, and rotational speed against the change in number of change in number of turns as shown in Figure 5b. Such graphs are utilized to assist in selecting the turnsbest as showncombinations in Figure of 5machineb. Such graphsperformance are utilized characteristics to assist hence, in selecting the calculated the best parameters combinations as of machine performance characteristics hence, the calculated parameters as summarized in Table3. It can summarized in Table 3. It can be seen from the results that the optimum design is obtained at Nt = 4 be seen from the results that the optimum design is obtained at Nt= 4 turns where PFm = 0.94 and turns where PFm = 0.94 and efficiency of 94% is achieved. Moreover, at this point the saving in efficiency of 94% is achieved. Moreover, at this point the saving in normalized windage losses is 93% normalized windage losses is 93% and the design speed ( N ) of 4814 rpm is achieved. The line–line and the design speed (N ) of 4814 rpm is achieved. The line–linem RMS output voltage is dependent RMS output voltage ism dependent on the AFPMA speed. Hence the machine voltage/speed constant on the AFPMA speed. Hence the machine voltage/speed constant mc which correlates the AFPMA mc which correlates the AFPMA line–line RMS output voltage to its rotational speed Nm can be line–line RMS output voltage to its rotational speed Nm can be found as mc = VLL/Nm. found as mc VLL / Nm .

(a) (b)

Figure 5. Optimization results for the AFPMA: (a) Machine efficiency and the internal power factor vs. Figure 5. Optimization results for the AFPMA: (a) Machine efficiency and the internal power factor vs. number number of turns; (b) Saving in windage losses, voltage regulation, and rotational speed vs. number of turns; (b) Saving in windage losses, voltage regulation, and rotational speed vs. number of turns. of turns.

Table 2. AFPMA Set Parameters.

AFPMA Set Parameters Value Unit Desired line–line RMS output voltage 17.6 V Number of phases (star connected) 3 - Air gap half-distance, Xg 10 mm Number of poles, p 8 - Axial thickness of PM, Lm 17 mm Inner radius of PM, Ri 27 mm Outer radius of PM, Ro 48 mm Remanence for NdFeB Grade 52, Br 1.45 T Wire diameter, dW 2.2 mm Energies 2018, 11, 274 8 of 28

Table 3. AFPMA Calculated Parameters.

AFPMA Calculated Parameters Value Unit

Number of winding turns per pole per phase, Nt 4 - Winding resistance per phase, RW 22.8 mΩ Winding inductance per phase, LW 4.14 µH Design speed, Nm 4814 RPM −3 No load machine voltage/speed constant, mc 3.537 × 10 V/RPM Generated frequency, f 320 Hz Air gap ﬂux density, Bg 0.546 T Voltage regulation, VR % 10.3 - Machine internal power factor (cos ϕ), PFm 0.94 - Machine power angle, δ 2 Deg Efﬁciency, η (%) 94 -

5. Modelling and Simulation of the AFPMA The AFPMA under consideration has its magnet topology designed to produce a sinusoidal ﬂux in its ironless stator. This implies that the induced voltages will be almost sinusoidal. MATLAB/Simulink R2012a (Mathworks, Galway, Ireland) [27], has a block that is already deﬁned in the SimPowerSystems which is called a permanent magnet synchronous machine (PMSM). This block is used to simulate the performance of the AFPMA under consideration after setting the corresponding parameters as shown in Figure6. Energies 2018, 11, x FOR PEER REVIEW 9 of 30

Figure 6. AFPMA MATLAB/Simulink model and parameter configuration. Figure 6. AFPMA MATLAB/Simulink model and parameter conﬁguration. The AFPMA equivalent circuit is depicted in Figure 7, whereas the corresponding mathematical modelThe of AFPMA the machine equivalent in rotor circuit reference is depicted frame (dq in-axis) Figure is 7summarized, whereas the in correspondingAppendix B. mathematical model of the machine in rotor reference frame (dq-axis) is summarized in AppendixB. d p d L i m Ld id d d R i Lqiq Rwid dt w d 2 dt i id d         p p m L i m q q V r V 2 d 2 q   (a) (b)

Figure 7. AFPMA equivalent circuit: (a) d-axis model; (b) q-axis model.

Once the parameters of the AFPMA are defined, MATLAB/Simulink model can be used to predict the machine performance at several conditions which can be further analyzed after experimental validation. The expected line–line rms voltages of the machine at no load and for several rotational speeds are represented in Figure 8.

Energies 2018, 11, x FOR PEER REVIEW 9 of 30

Figure 6. AFPMA MATLAB/Simulink model and parameter configuration.

Energies 2018The, 11 AFPMA, 274 equivalent circuit is depicted in Figure 7, whereas the corresponding mathematical 9 of 28 model of the machine in rotor reference frame (dq-axis) is summarized in Appendix B.

d p d L i m Ld id d d R i Lqiq Rwid dt w d 2 dt i id d         p p m L i m q q V r V 2 d 2 q   (a) (b)

Figure 7. AFPMA equivalent circuit: (a) d-axis model; (b) q-axis model. Figure 7. AFPMA equivalent circuit: (a) d-axis model; (b) q-axis model. Once the parameters of the AFPMA are defined, MATLAB/Simulink model can be used to predictOnce the the parameters machine performance of the AFPMA at areseveral deﬁned, conditions MATLAB/Simulink which can be model further can analyzed be used after to predict the machineexperimental performance validation. atThe several expected conditions line–line whichrms voltages can be of further the machine analyzed at no after load experimental and for validation.several Therotational expected speeds line–line are represented rms voltages in Figure of 8. the machine at no load and for several rotational speedsEnergies 2018 are, represented11, x FOR PEER in REVIEW Figure 8 . 10 of 30

Figure 8. Expected AFPMA line–line rms voltages at no load for several operating speeds. Figure 8. Expected AFPMA line–line rms voltages at no load for several operating speeds.

6. Development of the Controlled AC/DC Rectifier for the AFPMA 6. Development of the Controlled AC/DC Rectifier for the AFPMA Regulation of the output voltage is a key issue in automotive alternator. The output voltage of Regulation of the output voltage is a key issue in automotive alternator. The output voltage the alternator shall be maintained at about 14 V DC, which is the nominal charging voltage of a 12 V of the alternator shall be maintained at about 14 V DC, which is the nominal charging voltage of a lead–acid battery. The Lundell alternator regulates its output voltage by controlling the current 12 V lead–acid battery. The Lundell alternator regulates its output voltage by controlling the current supplied to the filed windings hence the magnetic flux inside the alternator. In PM machines where supplied to the filed windings hence the magnetic flux inside the alternator. In PM machines where the flux is relatively constant, the back-emf is only proportional to the alternator’s speed. Therefore, the flux is relatively constant, the back-emf is only proportional to the alternator’s speed. Therefore, driving the machine above the rated speed will generate a back-emf that is exceeding the rated driving the machine above the rated speed will generate a back-emf that is exceeding the rated output output voltage. Accordingly, at top speed the power electronic components in the converter shall be voltage. Accordingly, at top speed the power electronic components in the converter shall be capable capable to withstand both rated current and the considerable machine back-emf which may involve to withstand both rated current and the considerable machine back-emf which may involve increased increased power electronics cost and complexity. This could be solved by employing a DC-to-DC or power electronics cost and complexity. This could be solved by employing a DC-to-DC or controlled controlled AC-to-DC converter to maintain a constant output voltage. The separate converter can be AC-to-DC converter to maintain a constant output voltage. The separate converter can be mounted in mounted in a location where the temperatures and vibration levels are lower. When used together a location where the temperatures and vibration levels are lower. When used together with an IGBT with an IGBT based AC/DC converter, the alternator can respond in a fast manner to provide the based AC/DC converter, the alternator can respond in a fast manner to provide the required charging required charging current, at a stable voltage, over a large range of rotational speeds. current, at a stable voltage, over a large range of rotational speeds. The regulation and control of alternator’s output has been described in a number of studies [28–31]. Most of this work relies on using the Pulse Width Modulation (PWM) and boost rectifier technique. Published research on the integration and implementation of fully controlled AC/DC converter to PM generators is still scarce. In this paper, the description of the development of three-phase full wave fully controlled rectifier system using six IGBT bridge will be demonstrated to regulate the output of the AFPMA. As shown in Figure 9, the proposed system will utilize smart digital control using specially designed comparators interfaced with Arduino Uno to generate the required pulses to the gate of the IGBTs. The proposed system shall be capable to operate under several conditions such as variable input voltage, variable input frequency, various loading conditions. The objective is to supply a regulated DC voltage to a vehicle’s battery and loads under varying alternator speeds.

Energies 2018, 11, 274 10 of 28

The regulation and control of alternator’s output has been described in a number of studies [28–31]. Most of this work relies on using the Pulse Width Modulation (PWM) and boost rectiﬁer technique. Published research on the integration and implementation of fully controlled AC/DC converter to PM generators is still scarce. In this paper, the description of the development of three-phase full wave fully controlled rectiﬁer system using six IGBT bridge will be demonstrated to regulate the output of the AFPMA. As shown in Figure9, the proposed system will utilize smart digital control using specially designed comparators interfaced with Arduino Uno to generate the required pulses to the gate of the IGBTs. The proposed system shall be capable to operate under several conditions such as variable input voltage, variable input frequency, various loading conditions. The objective is to supply aEnergies regulated 2018, 11 DC, x FOR voltage PEER to REVIEW a vehicle’s battery and loads under varying alternator speeds. 11 of 30

Figure 9. 9. ProposedProposed automotive automotive electrical electrical powering powering system system using AFPMA using AFPMA harnessed harnessed with fully withcontrolled fully controlledAC/DC rectifier. AC/DC rectiﬁer.

The following main components form the corner stones of the fully controlled AC/DC converter: The following main components form the corner stones of the fully controlled AC/DC converter:  IGBT six-pack module (CM100TF-12H) •  IGBTMicrocontroller six-pack module (Arduino (CM100TF-12H) Uno) • MicrocontrollerComparator circuit (Arduino (voltage Uno) sensing). • ComparatorLC filter. circuit (voltage sensing). • LC filter. 6.1. Control Scheme 6.1. Control Scheme To obtain the required and regulated DC voltage, the IGBT switches have to be triggered at a properTo obtaintime and the sequence. required andThe regulatedvoltages DCof the voltage, three thephases IGBT from switches the AFPMA have to beare triggered measured at ainstantaneously proper time and to determine sequence. the The most voltages positive of phase thethree and the phases most fromnegative the phase AFPMA using are comparator measured instantaneouslycircuitry that is shown to determine in Figure the 10. most It compares positive phase two phases and the (AB, most AC, negative BC) amplitudes phase using and comparator generates circuitrya pulse at that the isoutput shown if inthe Figure phase 10 at. the It compares non-invert twoing phases input is (AB, higher AC, than BC) amplitudesthe phase at and the generatesinverting ainput. pulse The at the generated output ifpulses the phase are fed at theto Arduino non-inverting via a special input isconditioning higher than circuit the phase and atthen the a inverting decision input.is made The to generatedtrigger two pulses specific are switches fed to Arduino of the viaIGBT. a special The switching conditioning scheme circuit is andbased then on aa decisionspecific iscombination made to trigger sequence two as specific shown switches in Figure of 11. the To IGBT. keep Thethe output switching voltage scheme at a specific is based (preset on a specific value) combinationvoltage, the DC sequence output asfrom shown the filter in Figure is then 11. co Tompared keep the with output the voltage voltage set at apoint specific and (preset if the output value) voltage,voltage is the lower DC outputthan the from set point, the filter the isrectifier then compared will be activated with the accordingly. voltage set point and if the output voltage is lower than the set point, the rectifier will be activated accordingly.

Energies 2018, 11, 274 11 of 28 EnergiesEnergies 2018 2018, ,11 11, ,x x FOR FOR PEER PEER REVIEW REVIEW 1212 of of 30 30

VCCVCC

77 11 55 InputInput voltage voltage from from alternator alternator 33

3PH3PH 66 22

44 741741

VCCVCC

77 11 55

66 22

44 741741

VCCVCC

77 11 55

66 22

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FigureFigure 10. 10. Voltage Voltage measurementmeasurement measurement andand and comparatorcomparator comparator circuit.circuit. circuit.

FigureFigure 11. 11. IGBT IGBT switching switching sequence sequence forfor for controlledcontrolled controlled rectiﬁerrectifier rectifier operation.operation. operation.

6.2.6.2.6.2. Controlled Controlled RectifierRectifier Rectifier DesignDesign Design CalculationsCalculations Calculations TheTheThe threethree phase phase full fullfull wave wave fully fully controlled controlled rectif rectif rectifierierier is is is implemented implemented implemented using using using six six six IGBTs IGBTs IGBTs connected connected connected in in inthethe the formform form ofof of aa afullfull full wavewave wave bridgebridge bridge configuration.configuration. configuration. AllAll All thethe the sixsix six IGBTs IGBTs are areare controlled controlled switchesswitches whichwhichwhich areareare turnedturnedturned onon on atat at appropriateappropriate appropriate timestimes times byby by applyingapplying applying suitablesuitable suitable gategate gate triggertrigger trigger signals.signals. signals. TheThe The averageaverage average outputoutput output voltagevoltage voltage VVVdcdcdcof of of the the the rectifier rectifier rectifier can can can be be be calculated calculated calculated as as as [32 [32]: [32]:]: √ 33 22VVLL V = LLLLcos α (13) VVdcdc  coscos (13)(13) dc π where VLL is the rms line voltage from the three-phase AFPMA and α is the firing angle applied to the wherewhere VV is is the the rms rms line line voltage voltage from from the the three-phase three-phase AFPMA AFPMA and and  is is the the firing firing angle angle applied applied IGBT gate.LLLL  toto the theThe IGBT IGBT AFPMA gate. gate. output voltage is regulated by controlling the firing angle of the IGBTs. To otbain a constantTheThe AFPMA AFPMA output voltage,output output voltage avoltage feedback is is regulated regulated signal must by by controll becontroll sent toinging the the the controller firing firing angle angle to compare of of the the IGBTs. IGBTs. it with To To the obtain obtain preset a a valueconstantconstant of 14.3 outputoutput V to voltage, allowvoltage, for aa controlled feedbackfeedback signal batterysignal mustmust charging bebe sentsent operation. toto thethe controller Whencontroller the batterytoto comparecompare is fully itit with charged,with thethe thepresetpreset controller valuevalue of keepsof 14.314.3 the VV to firingto allowallow angle forfor at controlledcontrolled 90 degrees. battebatte Whenryry chargingcharging the battery operation.operation. charge goes WhenWhen below thethe the batterybattery preset isis level, fullyfully charged,charged, the the controller controller keeps keeps the the firing firing angle angle at at 90 90 degrees. degrees. When When the the battery battery charge charge goes goes below below the the presetpreset level,level, thenthen thethe controllercontroller triggerstriggers thethe IGBTIGBT withwith aa firingfiring angleangle belowbelow 9090 degreesdegrees whichwhich isis

Energies 2018, 11, 274 12 of 28 then the controller triggers the IGBT with a ﬁring angle below 90 degrees which is proportional to the voltage difference. The higher the voltage difference, the lower the ﬁring angle will be. The minim line–line RMS voltage VLL,min that is required to achieve the preset value of 14.3 V for the battery charger at α = 0 degree can be determined from (13) as: √ 3 2V 14.3 = LL,min (14) π

Rearranging for VLL,min 14.3π VLL,min = √ = 10.58 V (15) 3 2

The minim speed of the AFPMA, Nm,min that keeps the output voltage at the preset value while considering the machine constant value can be calculated as

V 10.58 = LL,min = = Nm,min −3 2997 RPM (16) mc 3.537 × 10

At the design speed, Nm = 4814RPM, the line–line RMS output voltage will be 17.6 V and the line-line peak output voltage, VLL,pk will be 24.89 V. Hence the maximum rectiﬁer output voltage, o Vdc at α = 0 will be 23.7 V. The predicted results for AFPMA voltage and rectiﬁer voltage with respect to speed are summarized in Table4.

Table 4. AFPMA and rectiﬁer output voltages at no load vs. speed at α = 0o.

AFPMA Speed, Nm VLL,rms VLL,pk Vdc (RPM) (V) (V) (V) Design speed = 4814 17.6 24.89 23.7 Minimum speed = 2997 10.6 14.9 14.3 Maximum speed 5000 18.29 25.8 24.7

7. Overall System Simulation The complete system that includes the AFPMA, integrated with the three-phase fully controlled AC/DC converter, LC ﬁlter, battery, load, and controller is modeled using MATLAB/Simulink as shown in Figure 12. The controller design relies on the measurement of the AFPMA output voltages where both most positive and negative phases are determined at a certain instant. Based on the feedback signal from the battery side, the controller generates the necessary pulses to trigger the IGBT switches accordingly. For simulation purposes, logic OR gates are used to implement the switching sequence that was presented in Figure8. The algorithm that is used to enable the controller is depicted in Figure 13. Whereas the controller output zero-one pulses are depicted in Figure 14. Energies 2018, 11, 274 13 of 28 Energies 2018, 11, x FOR PEER REVIEW 14 of 30 Energies 2018, 11, x FOR PEER REVIEW 14 of 30

Figure 12. Complete system simulation using MATLAB/Simulink model. Figure 12. Complete system simulation using MATLAB/Simulink model.

Figure 13. Algorithm used to enable the controller for simulation purposes. Figure 13. Algorithm used to enable the co controllerntroller for simulation purposes. In practice, charging system in an automobile shall be capable to operate at various loads and In practice, charging system in an automobile shall be capable to operate at various loads and variousIn practice, engine/alternator charging systemspeed whil in ane supplying automobile a shallregulated/fixed be capable vo toltage operate to battery at various terminals loads andand various engine/alternator speed while supplying a regulated/fixed voltage to battery terminals and variousany loads engine/alternator connected across speed the terminals. while supplying In the fo allowing regulated/ﬁxed section, simulations voltage to batteryfor different terminals scenarios and any loads connected across the terminals. In the following section, simulations for different scenarios anyare developed loads connected in order across to predict the terminals. the system In the behavior following at various section, operating simulations conditions. for different scenarios are developed in order to predict the system behavior at various operating conditions. are developed in order to predict the system behavior at various operating conditions.

Energies 2018, 11, 274 14 of 28 Energies 2018, 11, x FOR PEER REVIEW 15 of 30

Figure 14. Controller output pulses (zero–one).

7.1. System Simulation with Open Circuit In this scenario, the AFPMA speed is set to 5000 RPM, the load and the battery are disconnected from the rectifier rectifier terminals, terminals, and and the the firing firing angle angle α is is setset toto zero. The The six six pu pulselse rectified rectified output output as as a aresult result from from the the simulation simulation is is shown shown in in Figure Figure 15. 15 .The The AFPMA AFPMA line–line line–line peak peak voltage voltage is found to be

24.8 V,V, hencehence thethe rectiﬁerrectifier output output voltage voltageV dcVdcis foundis found to beto be 23.7 23.7 V. SuchV. Such initial initial simulation simulation results results are validatedare validated by comparing by comparing them them to the to analytical the analytical results results that arethat presented are presented earlier earlier in Table in 4Table. Hence 4. Hence other simulationother simulation scenarios scenarios can be can conducted be conducted with more with conﬁdence.more confidence.

Energies 2018, 11, 274 15 of 28 Energies 2018, 11, x FOR PEER REVIEW 16 of 30

Energies 2018, 11, x FOR PEER REVIEW 16 of 30

Figure 15. SimulationSimulation results results for for open open circuit circuit rectifier rectiﬁer output output voltage voltage at at 5000 5000 rpm rpm at at firing ﬁring angle angle α = 0. 0.

Figure 15. Simulation results for open circuit rectifier output voltage at 5000 rpm at firing angle  = 0. 7.2. System Simulation with Constant Load and Variable Speed 7.2. System Simulation with Constant Load and Variable Speed In this scenario, scenario, a a constant constant electrical electrical load load of of 0.7 0.7 Ω Ωis fittedis fitted across across the the battery battery terminals terminals while while the thespeed speed of AFPMA ofIn AFPMA this scenario, is ramped is ramped a constant up up fromelectrical from 3800 3800load RPM of RPM 0.7 toΩto is5100 fitted 5100 RPM across RPM throughthe through battery the theterminals simulation simulation while the runtime. runtime. speed of AFPMA is ramped up from 3800 RPM to 5100 RPM through the simulation runtime. Simulation results are depicted in Figure 16 where battery terminal voltage (after filter),filter), rectifierrectifier voltage Simulation(before filter), results and are loaddepicted current in Figure are captured16 where batteryin response terminal to voltagespeed (aftervariation filter), with rectifier respect to voltagevoltage (before (before filter), filter), and and load load current current are are captured captured in response response to tospeed speed variation variation with respect with respect to to time. The charging limit for the battery is set to 14.3 V. time. Thetime. charging The charging limit limit for the for the battery battery is is set set to to 14.3 14.3 V.

FigureFigure 16. Simulation 16. Simulation results results for for constant constant electricalelectrical load load and and variable variable AFPMA AFPMA speed. speed.

Figure 16. Simulation results for constant electrical load and variable AFPMA speed.

Energies 2018, 11, 274 16 of 28 Energies 2018, 11, x FOR PEER REVIEW 17 of 30

7.3.7.3. SystemSystem SimulationSimulation withwith ConstantConstantSpeed Speed and and Variable Variable Load Load InIn thisthisscenario, scenario, thethe speedspeed ofof AFPMAAFPMA isis setset to to 5100 5100 RPM RPM whilewhile thethe is is electrical electrical load load connected connected acrossacross thethe batterybattery terminalterminal isis decreaseddecreased from 3 Ω to 0.7 0.7 ΩΩ ofof through through the the simula simulationtion runtime runtime from from 0 0to to 1.5 1.5 s. s. Simulation Simulation results results are are depicted depicted in in Figure Figure 17 where batterybattery terminalterminal voltagevoltage (after(after filter),filter), rectifierrectifier voltagevoltage (before(before filter),filter), and and load load current current are are captured captured in in response response to to electrical electrical load load variation variation withwith respect respect to to time. time. The The charging charging limit limit for for the the battery battery is is set set to to 14.3 14.3 V. V.

FigureFigure 17.17.Simulation Simulationresults resultsfor forconstant constant speed speed and and variable variable electrical electrical load. load.

7.4.7.4. SystemSystem SimulationSimulation withwith VariableVariableSpeed Speed and and Variable Variable Load Load InIn this this scenario, scenario, both both speed speed of of AFPMA AFPMA and and electrical electrical load load are are varied varied simultaneously. simultaneously. The The speed speed is increasedis increased from from 3800 3800 RPM RPM to 5100 to RPM5100 whileRPM thewhile electrical the electrical load across load the across battery the terminal battery is terminal decreased is fromdecreased 3 Ω to from 0.7 Ω 3of Ω throughto 0.7 Ω theof through simulation the runtimesimulation from runtime 0 to 1.5 from s. Simulation 0 to 1.5 s. resultsSimulation are depicted results are in Figuredepicted 18 wherein Figure battery 18 where terminal battery voltage terminal (after voltage filter), rectifier(after filter), voltage rectifier (before voltage filter), (before and load filter), current and load current are captured in response to electrical load variation with respect to time. The charging limit for the battery is set to 14.3 V.

Energies 2018, 11, 274 17 of 28 are captured in response to electrical load variation with respect to time. The charging limit for the batteryEnergies 2018 is set, 11 to, x FOR 14.3 PEER V. REVIEW 18 of 30

Figure 18. Simulation results for variablevariable speedspeed andand variablevariable electricalelectrical load.load.

8.8. Testing andand ExperimentationExperimentation ofof thethe AFPMAAFPMA TheThe AFPMAAFPMA along along with with the the controlled controlled AC/DC AC/DC converter converter are are experimentally experimentally tested tested to obtain to obtain their performancetheir performance characteristics characteristics as shown as shown in Figure in Figure 19. As 19. an alternativeAs an alternative prime moverprime tomover the car to engine,the car aengine, three-phase a three-phase electrical electrical motor that motor is fed that from is fed three-phase from three-phase variable powervariable supply power is supply used to is drive used the to AFPMAdrive the at AFPMA several speedsat several through speeds pulleys through and pulleys belt. A an dummyd belt. A resistive dummy load resistive is used load to test is used the system to test underthe system various under loading various conditions. loadingThe conditions. three-phase The outputthree-phase from theoutput AFPMA from is the fed AFPMA to the electrical is fed to load the throughelectrical the load IGBT through which the is fullyIGBT controlled which is fully via the controlled controller via circuit. the controller The controller circuit. circuit The controller contains thecircuit comparator contains circuit,the comparator Arduino Uno, circuit, and theArduin IGBTo gateUno, driver and circuit.the IGBT To demonstrategate driver thecircuit. system To performancedemonstrate atthe several system operating performance conditions, at several the following operating tests conditions, are performed the as following described tests below. are performed as described below.

Energies 2018, 11, 274 18 of 28

Energies 2018, 11, x FOR PEER REVIEW 19 of 30

Figure 19. Experimental test rig; (1) Three-phase driving motor, (2) AFPMA, (3) controller circuit, Figure(4)19. IGBTExperimental six-pack module test CM100TF-12H, rig; (1) Three-phase (5) three-phase driving power motor, supply, (2) AFPMA, (6) dummy (3) resistive controller load, circuit, (4) IGBT(3a) comparator six-pack module circuit, (3b) CM100TF-12H, Arduino Uno, (5)(3c) three-phase IGBT gate driver power circuit. supply, (6) dummy resistive load, (3a) comparatorFigure 19. Experimental circuit, (3b) test Arduino rig; (1) Uno, Three-phase (3c) IGBT drivin gateg drivermotor, circuit.(2) AFPMA, (3) controller circuit, 8.1. No(4) LoadIGBT Tests six-pack module CM100TF-12H, (5) three-phase power supply, (6) dummy resistive load, (3a) comparator circuit, (3b) Arduino Uno, (3c) IGBT gate driver circuit. 8.1. No LoadIn this Tests section, the system is tested under no load condition with AFPMA initially is running at rated speed of 5000 RPM. The line–line output voltage from the AFPMA is captured and compared In8.1. this No Load section, Tests the system is tested under no load condition with AFPMA initially is running at with the simulation results obtained from MATLAB as shown in Figure 20. Results obtained show a rated speed of 5000 RPM. The line–line output voltage from the AFPMA is captured and compared with goodIn match this section,between the the system simulation is tested and experimentalunder no load re sults.condition The resultswith AFPMA of the three-phase initially is line-neutralrunning at the simulationratedvoltages speed are results ofcaptured 5000 obtained RPM. using The PicoScope from line–line MATLAB 3000output oscilloscope asvolt shownage from (Pico in Figurethe Technology, AFPMA 20. Results is capturedCambridgeshire, obtained and compared show UK) aas good matchwithdepicted between the simulationin theFigure simulation 21.results The obtainedquality and experimental of from the MATLABAFPMA results. voltageas shown The signal in results Figure is also of20. theanalyzed Results three-phase obtained where the line-neutralshow total a voltagesgoodharmonic are match captured distortion between using the(THD) simulation PicoScope is found and to 3000 experimental be close oscilloscope to 2% results. as (Picoshown The results Technology, in Figure of the 22. three-phaseCambridgeshire, The output line-neutral from the UK) as depictedvoltagesrectifier in Figure atare zero captured 21firing. The using angle quality PicoScope is also of captured the 3000 AFPMA oscilloscope in Figure voltage (Pico23. signalIt Technology, is shown is also from Cambridgeshire, analyzed the results where that UK) thethe as total harmonicdepictedrectified distortion outputin Figure voltage (THD) 21. The is is veryquality found close toof tothe be the closeAFPMA output to 2% voltageobtained as shown signal from inisthe also Figure simulation analyzed 22. The results. where output Itthe is total fromalso the rectifierharmonicshown at zero that distortion firingphase angleC has(THD) its is alsopeakis found captured line–line to be voltage inclose Figure to less 2% 23 than as. It shown isthe shown other in Figure two from phases 22. the The results by output1.5 volts. that from the This rectifiedthe is outputrectifierexplained voltage at by iszero the very firing fact close that angle tothethe is coil also output that captured is obtainedrespon insible Figure from for thephase23. It simulation isC isshown physically results.from locatedtheIt results is between also that shown the that rectified output voltage is very close to the output obtained from the simulation results. It is also phaseother C has two its phases peak line–linein the middle voltage of the less air thangap. Ther the otherefore, twoless magnetic phases by flux 1.5 density volts. Thisarrives is from explained PM by shownto that thatlocation, phase hence C has less its peakinduced line–line voltage voltage is produced less than in thethat other coil. twoThis phases makes bythe 1.5 output volts. voltage This is the fact that the coil that is responsible for phase C is physically located between the other two phases explainedasymmetrical by theand fact special that theprecautions coil that ishave respon to siblebe taken for phase into Cconsideration is physically whenlocated designing between the in theotherscheme middle two for ofphases the the controller airin the gap. middle of Therefore, the ofconverter. the air less gap. magnetic Therefore, flux less density magnetic arrives flux density from arrives PM to from that location,PM henceto less that induced location, voltagehence less is producedinduced voltage in that is coil.produced This makesin that coil. the outputThis makes voltage the output asymmetrical voltage and specialasymmetrical precautions and have special to be precautions taken into considerationhave to be taken when into designing consideration the schemewhen designing for the controller the of thescheme converter. for the controller of the converter.

Figure 20. AFPMA no load voltage (line-neutral) experimental results vs. simulation results at N = 5000 RPM. m Figure 20. AFPMA no load voltage (line-neutral) experimental results vs. simulation results at Figure 20. AFPMA no load voltage (line-neutral) experimental results vs. simulation results at N = 5000 RPM. Nm = 5000RPM.m

Energies 2018, 11, 274 19 of 28 Energies 2018, 11, x FOR PEER REVIEW 20 of 30 Energies 2018, 11, x FOR PEER REVIEW 20 of 30 Energies 2018, 11, x FOR PEER REVIEW 20 of 30

Figure 21. AFPMA no load three-phase line-neutral voltages tested at N = 5000 RPM. Figure 21. AFPMA no load three-phase line-neutral voltages tested atmNm = 5000RPM. Figure 21. AFPMA no load three-phase line-neutral voltages tested at Nm = 5000 RPM. Figure 21. AFPMA no load three-phase line-neutral voltages tested at Nm = 5000 RPM.

Figure 22. AFPMA phase voltage THD % experimental result at N = 5000 RPM. m Figure 22. AFPMA phase voltage THD % experimental result at N = 5000 RPM. Figure 22. AFPMA phase voltage THD % experimental result atmNm = 5000RPM. Figure 22. AFPMA phase voltage THD % experimental result at Nm = 5000 RPM.

Figure 23. Rectifier output voltage at zero firing angle at N = 5000 RPM. m Figure 23. Rectifier output voltage at zero firing angle at Nm = 5000 RPM. Figure 23. Rectifier output voltage at zero firing angle at Nm = 5000 RPM. Figure 23. Rectiﬁer output voltage at zero ﬁring angle at Nm = 5000RPM.

Energies 2018, 11, 274 20 of 28

TheEnergies controller 2018, 11, x FOR of the PEER AC/DC REVIEW converter is designed to deal with the voltages under asymmetrical21 of 30 conditions.Energies 2018 It, is 11 the, x FOR comparator PEER REVIEW that gives the controller the adaptively feature as it compares21 of 30 the most positiveThe signalcontroller with of thethe most AC/DC negative converter one. Therefore,is designed an to adaptive deal with pulse the is voltages generated under from the comparatorasymmetricalThe that controller isconditions. proportional of the It isAC/DC the to thecomparator differenceconverter that is between givesdesigned the the controller to two deal consecutive thewith adaptively the phases.voltages feature Evenunder as it in an asymmetricalcomparesasymmetrical situationthe conditions.most wherepositive It theis signal the three comparator with phase the voltages mostthat givesnegative are the not controllerone. balanced, Therefore, the the adaptively comparatoran adaptive feature pulse is capable as isit to generatedcompares fromthe most the comparatorpositive signal that withis proportional the most negativeto the difference one. Therefore, between an the adaptive two consecutive pulse is create the necessary pulse and send it to Arduino Uno to generate the necessary pulses for triggering phases.generated Even from in thean comparatorasymmetrical that situation is proportional where the to thethree difference phase voltages between are the not two balanced, consecutive the the appropriate switches in the IGBT module. For example, Figure 24 shows the output from the comparatorphases. Even is incapable an asymmetrical to create the situation necessary wher puelse the and three send phase it to voltagesArduino are Uno not to balanced,generate the comparatornecessarycomparator for pulses C is and capable for phases triggering to create A. When the the appropriate Cnecessary phase (blue switpulseches color) and in thesend is most IGBT it to positivemodule. Arduino thanFor Uno example, phase to generate A Figure (green the 24 color) the comparatorshowsnecessary the pulses output generates for from triggering the the appropriatecomparator the appropriate for pulse C switand (yellowches phases in color) the A. IGBT When throughout module. C phase For that (blue example, interval. color) Figure is The most 24 results also showpositiveshows thatthe than output the phase peak from A value(green the comparator of color) phase the A comparatfor is higherC andor phases thangenerates that A. theWhen for appropriate phase C phase C. As pulse(blue a result, color)(yellow anis color) most adaptive pulsethroughoutpositive is generated than that phase from interval. A the (green The comparator resultscolor) thealso witnessed comparat show thator bythe generates an peak increase value the ofappropriate in phase the pulses A is pulsehigher width (yellow than (yellow that color) for color). The outputphasethroughout C. from As thata theresult, interval. comparators an adaptive The results arepulse sentalso is generatedshow to Arduino that fromthe Unopeak the comparator wherevalue of the phase appropriatewitnessed A is higher by an train than increase ofthat pules for in are generatedthephase pulses andC. As sentwidth a result, to (yellow IGBT an adaptive gate color). driver Thepulse circuitoutput is generated fromfrom whichthe from comparators the the comparator IGBT are switches sent witnessed toare Arduino triggered by an Uno increase accordingly.where in the pulses width (yellow color). The output from the comparators are sent to Arduino Uno where As canthe be appropriate shown from train Figure of pules 25, are the generated six Arduino and pulses sent to haveIGBT different gate driver widths circuit to from allow which for adaptivethe IGBTthe appropriate switches are train triggered of pules accordingly. are generated As canand be se shownnt to IGBT from gate Figure driver 25, thecircuit six fromArduino which pulses the control of the AC/DC converter. haveIGBT differentswitches widths are triggered to allow accordingly. for adaptive As control can be of shown the AC/DC from converter.Figure 25 , the six Arduino pulses have different widths to allow for adaptive control of the AC/DC converter.

Figure 24. Phase C and A with adaptive pulse generated from the comparator at Nm = 5000 RPM. Figure 24. Phase C and A with adaptive pulse generated from the comparator at Nm = 5000RPM. Figure 24. Phase C and A with adaptive pulse generated from the comparator at Nm = 5000 RPM.

Figure 25. Arduino pulses with appropriate pulse widths to allow for adaptive control of AC/DC converter.Figure 25. Arduino pulses with appropriate pulse widths to allow for adaptive control of AC/DC Figure 25. Arduino pulses with appropriate pulse widths to allow for adaptive control of converter. AC/DC8.2. Load converter.Tests 8.2. Load Tests 8.2. Load TestsIn this section, the AFPMA and the AC/DC converter are tested under load conditions as shown in FigureIn this 26. section, First set the of AFPMA results andis obtained the AC/DC when conver the systemter are tested is connected under load to the conditions battery only.as shown The Insecondin Figure this set section, 26. of resultsFirst the set is AFPMAofobtained results whenis and obtained thethe system AC/DC when is the connected converter system tois aretheconnected battery tested toand under the a singlebattery load head conditionsonly. lamp. The as shownThesecond in third Figure set set of of26results results. First is isobtained set obtained of results when when isthe the obtained system system is when isconnected connected the systemto battery the battery is and connected twoand heada single to lamps. the head battery Results lamp. only. The second The third set set of of results results is obtained when when the the system system is connected is connected battery to and the two battery head andlamps. a singleResults head

Energies 2018, 11, 274 21 of 28 lamp. The third set of results is obtained when the system is connected battery and two head lamps.

Results obtainedEnergies 2018 for, 11 the, x FOR three PEER loading REVIEW conditions as compared to the no load condition are22 of summarized 30 in Table5. It is shown from the results that the controller was successful in maintaining almost obtained for the three loading conditions as compared to the no load condition are summarized in Table a constant output voltage close to 14 V DC with an average decrease of 2.7% for a 30% increase in Energies5. It is 2018shown, 11, x fromFOR PEER the REVIEWresults that the controller was successful in maintaining almost a constant22 of 30 load currentoutput and voltage 6.6% close decrease to 14 V inDC averagewith an average output decrease voltage of 2.7% for for 60% a 30% increase increase inin load load current current. Also, obtained for the three loading conditions as compared to the no load condition are summarized in Table when analyzingand 6.6% the decrease alternator’s in average output output waveforms,voltage for 60% itincrease is noticed in load that current. the Also, line–line when voltageanalyzing gets more 5. It is shown from the results that the controller was successful in maintaining almost a constant the alternator’s output waveforms, it is noticed that the line–line voltage gets more distorted as the distorted asoutput the controlledvoltage closeconverter to 14 V DC iswith processed an average to decrease provide of more2.7% for charging a 30% increase current in load while current the alternator controlled converter is processed to provide more charging current while the alternator running is running isand also 6.6% decreased decrease in as average can be output shown voltage in Figure for 60% 27 increase. in load current. Also, when analyzing also decreased as can be shown in Figure 27. the alternator’s output waveforms, it is noticed that the line–line voltage gets more distorted as the controlled converter is processed to provide more charging current while the alternator running is also decreased as can be shown in Figure 27.

Figure 26. Testing of AFPMA and AC/DC converter under charging process (battery and load connected). Figure 26. Testing of AFPMA and AC/DC converter under charging process (battery and load

connected). Figure 26. Testing of AFPMA and AC/DC converter under charging process (battery and load connected).

(a) (b) (c)

Figure 27. Distorted line–line output voltages due to increased load current; (a) without rectifier and no load at 5085(a )rpm; (b) with rectifier and no load(b at) 5032 rpm; (c) with rectifier and charging(c) current of 11 A at 4740 rpm. Figure 27. Distorted line–line output voltages due to increased load current; (a) without rectifier and Figure 27. Distorted line–line output voltages due to increased load current; (a) without rectifier and no loadTable at 5085 5. rpm;AFPMA (b) withand AC/DCrectifier converter and no load under at 5032 loading rpm; conditions (c) with rectifier vs. no andload charging condition current no load atof 5085 11 A rpm;at 4740 ( brpm.) with rectifier and no load at 5032 rpm; (c) with rectifier and charging current

of 11 A at 4740 rpm. Speed VLL,rms Vdc I dc Table 5. AFPMATest and AC/DCCondition converter under loading conditions vs. no load condition (RPM) (V) (V) (A) No load (rectifier only) 5032 18.41 24.15 0 Table 5. AFPMA and AC/DC converter underSpeed loading VLL, conditionsrms Vdc vs.I dc no load condition. TestBattery Condition only 5020 18.01 14.53 2.85 (RPM) (V) (V) (A) Battery and one head lamp 4876 16.89 13.57 7.62 No load (rectifier only) Speed 5032 V 18.41LL,rms 24.15V dc 0 Idc TestBattery Condition and two head lamps 4740 16.05 13.21 11.04 Battery only (RPM) 5020 18.01 (V) 14.53 (V) 2.85 (A) Battery and one head lamp 4876 16.89 13.57 7.62 9. Conclusions and Future Recommendations No loadBattery (rectifier and two only) head lamps 5032 4740 16.05 18.41 13.21 24.15 11.04 0 This paper exhibitedBattery the only design methodolo 5020gy and optimization 18.01 14.53of AFPMA2.85 having ACSTR 9.configuration ConclusionsBattery and and its Future and integration one Recommendations head with lamp three phase 4876 fully controlled 16.89 AC/DC 13.57 converter 7.62 as part of the onboard batteryBattery charging and two system head for lamps use in automobile 4740 applications. 16.05 The 13.21 necessary 11.04 sizing equations This paper exhibited the design methodology and optimization of AFPMA having ACSTR were developed, and optimization of the machine was performed based on parametric analysis. The configuration and its integration with three phase fully controlled AC/DC converter as part of the number of winding turns, hence machine design speed, were optimized against the machine onboard battery charging system for use in automobile applications. The necessary sizing equations 9. Conclusionsefficiency. and Analytical Future results Recommendations showed that the AFPMA having four turns per coil per phase is suitable were developed, and optimization of the machine was performed based on parametric analysis. The Thisnumber paper exhibitedof winding theturns, design hence machine methodology design speed, and optimizationwere optimized ofagainst AFPMA the machine having ACSTR configurationefficiency. and Analytical its integration results showed withthree that the phase AFPMA fully having controlled four turns per AC/DC coil per converterphase is suitable as part of the onboard battery charging system for use in automobile applications. The necessary sizing equations were developed, and optimization of the machine was performed based on parametric analysis. The number of winding turns, hence machine design speed, were optimized against the machine efficiency. Analytical results showed that the AFPMA having four turns per coil per phase is suitable to Energies 2018, 11, 274 22 of 28 run at nearly 4800 rpm to achieve an power output of 1.2 kW at rated line voltage of 17 and rated current of 40 A at an expected efficiency of 94%. The AFPMA was modeled using MATLAB/Simulink and the results obtained were close to analytical solutions. The response of the AFPMA while operating with a three-phase controlled rectifier using six IGBT bridge is modeled and experimentally tested, forming the basis for the design of a closed-loop controller to regulate the output voltage. The experimental performance of the closed-loop system is examined and evaluated. A custom design comparator circuit was developed to produce the necessary pulses for Arduino Uno and was capable of dealing with asymmetrical output voltage conditions from the AFPMA. The Arduino was used as a controller that generates the required pulses for triggering the IGBTs sequentially in a timely manner. The Arduino custom code enabled the production of a regulated DC output voltage across the battery via controlling the firing angle of the IGBT model in proportion to the amount of voltage difference between the battery voltage preset value and the measured value. The overall system was experimentally tested under partial loading conditions and results obtained showed the validity of the analytical as well as the simulation results within acceptable level. Experimental results demonstrated that the closed-loop controller was successful in regulating the output voltage close to 14 V DC while the alternator was operating in the range of the rated speed. Measurements showed a 2.7% decrease in average output voltage for a 30% increase in load current. It is worth mentioning that some amount of the voltage drop can be attributed to the drop in the alternator speed (approximately 2.9%) due to the increased load torque on the electrical motor that is driving the alternator. For accurate evaluation and assessment of the system performance, it is recommended to use alternative prime movers that can provide constant speed during load variations. Further investigations of the output power for the system using the controlled rectifier are also required at higher speed operation. Moreover, it was noticed that during the loading tests, that the machine voltage/speed constant (mc) tends to change under high current loading. This can be explained by the flux weakening that occurs in the middle of the air gap due to armature reaction. More experimental results need to be conducted to determine the exact relationship and to account for this change in the MATLAB/Simulink model. Also, preliminary laboratory tests showed a rise of 50 ◦C in the temperature of the stator winding above ambient temperature of 25 ◦C when the full load current of 40 A is drawn from the machine for a period of two hours without using integral fan. It is anticipated that the stator winding temperature may rise in the range of 100–130 ◦C when the AFPMA is tested in an engine compartment due to the elevated ambient temperature. This in turn may cause a temperature increase in the nearby magnets which may lead to demagnetization of the PMs. Therefore, the cooling aspect of the AFPMA needs to be considered in order to minimize the temperature rise by using an integral fan on the shaft or other methods of forced ventilation. More experimental tests are required to test the system under several full loading conditions. Using alternative grades of NdFeB can be decided once the machine is tested on-board of the vehicle at several loading conditions. In general, the preliminary results showed the potential capabilities of the AFPMA for meeting increasing power demands in automotive applications. In addition, a scaled up system can be also made in the future to satisfy higher power ratings of automobiles.

Acknowledgments: The author acknowledges that this research is funded by the Deanship of Research and Graduate Studies at Zarqa University/Jordan. The author also would like to extend his gratitude to the laboratory supervisor Eng. Mohammad Mosleh as well as to Eng. Basil Al Jamal and Eng. Yazan Shihab for their help in conducting the experimental work at the electrical engineering department of Zarqa University. Conﬂicts of Interest: The author declares no conﬂict of interest. Energies 2018, 11, 274 23 of 28

Nomenclature

Amg Air gap/magnet interface area Aw Winding cross sectional area Bg Air gap magnetic flux density Br Magnetic remanence Cf Coefficient drag for turbulent flow Cl Coil mean path length dW Wire diameter Eind Induced voltage in a conductor Per phase internal generated E rms ϕ, voltage f Electrical frequency of the voltage Hc Magnetic coercive force IA Armature current Id d-axis current Iq q-axis current Kg Machine geometrical constant Km Machine magnetic constant Lc Conductor length Ld d-axis inductance LL Per phase leakage inductance Lm Magnet axial length Lmg Total magnet air gap length Lq q-axis inductance Lw Winding Inductance LZ Magnetization inductance mc Machine voltage/speed constant Nm Mechanical speed Minim acceptable speed of the N m,min AFPMA NR Number of rotating discs Nt Number of winding turns p Rotor number of poles Pcu Copper losses p f Wire packing factor Internal power factor for the PFm machine Pout Machine output power PW Windage losses PW,max Maximum windage losses PW,sav Saving in the windage losses r Average radius of conductor R Centre point of the PM disc Re Reynolds number Reluctance of the path of the Req magnetising flux Ri Inner radius of the coil Ro Outer radius of the coil Rsh Shaft radius RW Winding resistance Te Electromagnetic torque → v Linear velocity vector

Vd d-axis voltage Vdc Rectiﬁer average output voltage VLL RMS line voltage Energies 2018, 11, 274 24 of 28

VLL,min Minim line-line RMS voltage VR Voltage regulation of the machine Vq q-axis voltage Vϕ, f l Full load phase voltage Vϕ,nl No load phase voltage Wl Total winding length Xg Air gap half-distance XW Winding reactance α Rectifier firing angle αB Temperature coefficient for Br αH Temperature coefficient for Hc δ Machine power angel η Efficiency of the machine λr Peak flux reaching the stator windings µair Coefficient of viscosity of the air ρair Specific density of the surrounding air ωm Mechanical angular velocity

Appendix A. Derivation of the Sizing Equations for the AFPMA The magnetic ﬂux density in the air gap between the two PM rotors (assuming circular PMs) is calculated as [33–36]:   Xg + Lm Xg Bg = Br q − q  (A1) 2 2 2 2 R + (Xg + Lm) R + Xg where R is center point of the PM disc which can be determined as:

R − R R = o i (A2) 2

Hence, the induced voltage in the conductors is given by:

→ → Eind = ( v × B g) · Lc (A3)

→ → Since v is perpendicular to B g, the magnitude of the induced voltage reduces to:

Eind = v · Bg · Lc (A4)

The tangential velocity of the conductor can be represented in terms of angular velocity ωm as:

v = ωm · r (A5) where r is the average radius of the conductor (m), also called the magnet centerline and can be found as:

R + R r = o i (A6) 2

The angular velocity ωm can be expressed in terms of mechanical speed of the rotor Nm as:

2π ωm = Nm (A7) 60

The average effective length of the winding conductor, Lc can be calculated as

Lc = 2(Ro − Ri) (A8)

Substituting (A7) into (A5) and then into (A4)

π · Nm E = r · Bg · Lc (A9) ind 30 Energies 2018, 11, 274 25 of 28

For number of turns Nt per phase and for number of poles p, substituting (A6) and (A8) into (A9) can be represented as: π 2 2 E = (R − R ) · Bg · Nm · N · p (A10) ind 30 o i t For three phase stator, the line-line rms induced voltage can be expressed as: √ π 3 2 2 ELL = √ (Ro − R ) · Bg · Nm · Nt · p (A11) 30 2 i

Hence, the number of turns can be found as: √ 30 2 · E N = √ LL (A12) t 2 2 π 3 · (Ro − Ri ) · Bg · Nm · p  q q  2 2 2 2 (Xg + Lm) R + Xg − Xg R + (Xg + Lm)   Bg = Br q q  (A13) 2 2 2 2 R + (Xg + Lm) · R + Xg  q q  2 2 2 2 R + (Xg + Lm) · R + Xg ELL 7.796   Nt =  q q  (A14) Nm p · Br 2 2 2 2 R · r · [(Xg + Lm) R + Xg − Xg R + (Xg + Lm) ]

The above equation can be reduced to:

ELL Nt = · Km · Kg (A15) Nm

" q √ # 2+( + )2· 2+ 2 7.796 R Xg Lm R Xg where Km = , and Kg = √ q are the machine magnetic constant and p·Br 2 2 2 2 R·r·[(Xg +Lm) R +Xg−Xg R +(Xg+Lm) ] geometric constant, respectively. The frequency of the generated voltage is determined by:

p · N f = m (A16) 120

The AFPMA under consideration has a non-salient rotor topography. Also the stator has an air-cored structure which enables sinusoidal ﬂux distribution. Hence, the inductance of the machine can be calculated as [37]: Lw = LL + LZ (A17) The per phase leakage inductance can be calculated as:

3 pNt Cl L = µo (A18) L 12 where Cl is the coil mean path length which can be determined based on the geometry of the coil as: 2π Ntdw Ntdw C = p Ro + + R − + 2(Ro − R + N dw) · p (A19) l p f 2 i 2 i t f

π π C = 2R + 1 + 2R − 1 + 2N d · p (A20) l o p i p t w f

Wl = p · Nt · Cl (A21) The winding resistance can be calculated as:

ρ · Wl RW = (A22) Aw where Wl is the total winding length, Aw is the winding cross sectional area, dw is the wire diameter, and p f is the wire packing factor and it can be deﬁned in the range between 1.2 and 1.3 depending on the wire diameter. Energies 2018, 11, 274 26 of 28

By performing magnetic circuit analysis, the reluctance of the PM and the coil can be calculated, hence the magnetizing inductance can be determined as:

2 pNt LZ = (A23) Req where Req is total reluctance of the path of the magnetising ﬂux and can be calculated as:

Lmg Req = (A24) µo Amg

Lmg = 2Lm + 2Xg (A25)

R2 − R2 A = π o i (A26) mg p where Xg is the air gap (axial length) half-distance, Lmg is the total magnet air gap length, and Amg is the air gap/magnet interface area. The per-phase synchronous reactance of the stator windings are calculated as:

XW = 2π · f · L (A27)

Appendix B. Simulink Mathematical Model of the AFPMA in Rotor Reference Frame (dq-Axis)

pωm d V = −Rwi + Lqiq − L i (A28) d d 2 d dt d

pωm pωm d Vq = −Rwiq − L i + λr − Lq iq (A29) 2 d d 2 dt The dq-axis currents can be described as

d −Vd − Rwid + 0.5pωm Lqiq id = (A30) dt Ld

d −Vq − Rwiq − 0.5pωm Ldid + 0.5pωmλr iq = (A31) dt Lq The coreless (ironless) stator of the AFPMA implies that the stator inductance as referred to the dq-axis does not vary with rotor position, which makes Ld = Lq = Lw. Hence the electromagnetic torque of the machine can be expressed as 3 Te = p iqλr (A32) 4

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