Research and Analysis of Permanent Magnet Transmission System Controls on Diesel Railway Vehicles

electronics

Article Research and Analysis of Permanent Magnet Transmission System Controls on Diesel Railway Vehicles

Lili Kang 1,2, Dongjie Jiang 2, Chaoying Xia 1,*, Yongjiu Xu 2 and Kaiyi Sun 2

1 School of Electrical and Information Engineering, Tianjin University, Tianjin 300072, China; [email protected] 2 CRRC Tangshan Co., Ltd., Tangshan 064000, China; [email protected] (D.J.); [email protected] (Y.X.); [email protected] (K.S.) * Correspondence: [email protected]

Abstract: As the energy crisis and environmental pollution continue to be a gradual threat, the energy saving of transmission systems has become the focus of railway vehicle research and design. Due to their high-power density and efﬁciency features, permanent magnet synchronous motors (PMSM) have been gradually applied in railway vehicles. To improve the efﬁciency of the transmission system of diesel railway vehicles, it is a good option to use PMSM as both a generator and traction motor to construct a full permanent magnet transmission system (FPMTS). Due to the application of the new FPMTS, some of the original control strategies for diesel railway vehicle transmission systems are no longer applicable. Therefore, it is necessary to adjust and improve the control strategies to meet the needs of FPMTS. We studied several key issues that affect the reliability and comfort of the vehicles. As such, this paper introduced the FPMTS control strategy, including the coordinated control strategy of the diesel and the traction motor, the two degrees of freedom (2DOF) decoupling current regulator, the maximum torque control of the standardized unit current, the wheel slip protection control, and the fault protection strategy. The experiment was carried out on the test platform and the test run of the diesel shunting locomotive equipped with the FPMTS. The results showed that the control strategy described in this paper met the operation characteristics of the FPMTS and that the control Citation: Kang, L.; Jiang, D.; Xia, C.; performance was superior. The study of FPMTS lays the foundation for the subsequent application Xu, Y.; Sun, K. Research and Analysis of permanent magnet motors in high-powered diesel locomotives and high-speed diesel multi-units. of Permanent Magnet Transmission System Controls on Diesel Railway Keywords: diesel transmission system; permanent magnet synchronous motor (PMSM); two degrees Vehicles. Electronics 2021, 10, 173. https://doi.org/10.3390/ of freedom (2DOF); maximum torque control; railway vehicles electronics10020173

Received: 11 November 2020 Accepted: 30 December 2020 1. Introduction Published: 14 January 2021 Diesel railway vehicles play a significant role in non-electrified railway operation, heavy-haul railway freight transport, emergency rescue, and vehicle deployment [1–3]. By Publisher’s Note: MDPI stays neu- the end of 2015, 52% of the world’s railway vehicles used diesel as their power source [4]. tral with regard to jurisdictional clai- The transmission system is one of the most critical systems in diesel railway vehicles, which ms in published maps and institutio- influence safety and energy-saving performance [5]. Since the 1980s, the transmission sys- nal affiliations. tem of diesel railway vehicles began to develop from the former direct current traction motor transmission system to an alternating current asynchronous traction motor transmission system. In recent years, researchers have begun to gradually apply a permanent Copyright: © 2021 by the authors. Li- magnet synchronous motor (PMSM) to the transmission systems of rail vehicles due to censee MDPI, Basel, Switzerland. the advantages of high-power density. France’s Alstom, the Japan Railway Corporation, This article is an open access article Germany’s Siemens, and the China Railway Rolling Stock Corporation (CRRC) all carried distributed under the terms and con- out technical research and commercial operations of PMSM. The results prove that PMSMs ditions of the Creative Commons At- have a smaller size, lighter weight, and higher efficiency than asynchronous motors and tribution (CC BY) license (https:// synchronous excitation motors [6–9]. Therefore, PMSM has become a new trend for railway creativecommons.org/licenses/by/ vehicle motors [6,10]. 4.0/).

Electronics 2021, 10, 173. https://doi.org/10.3390/electronics10020173 https://www.mdpi.com/journal/electronics Electronics 2021, 10, 173 2 of 18

Among the large amount of research into PMSM, some has concentrated on optimizing the structure of the traction system. Takuma Ito et al. tried to use one inverter to control three or four PMSMs [11]. In Reference [12], Kassem Roumani et al. investigated the influence of geometric design variables on the machine’s characteristics in a low voltage permanent magnet synchronous motor for in-wheel direct-drive application. Meanwhile, in order to make the PMSM traction system meet the railway vehicles’ requirements, a significant amount of research into PMSM control strategy has been completed. Yifa et al. put forward a novel field weakening method to modify the current by the angle between the constant torque and the degressive voltage curve direction, which would make the motor operate steadily along the field-weakening curve [13]. Calleja et al. proposed an optimized modified direct-self-control (M-DSC) method, which can obtain better dynamic performance [14]. Zhao et al. designed a nonsingular terminal sliding mode observer (NTSMO) to detect the demagnetization of the permanent magnet and proposed an accurate torque control method to improve the torque control accuracy of PMSM [15]. Taniguchi et al. proposed a control method for the PMSM drive system without a position sensor, which can estimate the initial position and the speed of the rotor when the vehicle slides across the whole speed range. This method can also be used when the back electromotive force (back-EMF) voltage is higher than the inverter DC link voltage [16]. Zhao et al. designed a control scheme based on the most torque per ampere (MTPA) strategy to obtain high power density and achieve smooth transitions between the constant torque mode and the constant power (field weakening) mode. In addition, they designed a novel low- frequency pulse width modulation (PWM) strategy for a smooth transition when changing the carrier frequency [17]. Some researchers have also studied the method for reducing the harmonic current of high-powered PMSM. In Reference [18], Zhang et al. analyzed the relationship between the load current of PMSM and the output voltage of the inverter using synchronous PWM, and they deduced the expression of current harmonics. A novel current harmonic distortion minimization PWM (CHMPWM) algorithm for the PMSM was constructed. In References [11,13–18], it can be seen that PMSMs are now widely adopted as traction motors in railway vehicles. However, research on PMSMs as generators has largely been ignored, especially the system structure in which the generator and traction motor use PMSMs at the same time. In order to improve the efficiency of the whole transmission system to a greater extent, taking PMSM as both a generator and traction motor to construct a full permanent magnet transmission system (FPMTS) is a feasible and attractive scheme. In the transmission system, the control of the generator and traction motor, as well as the coordinated control, are always the core problems in system control. In this paper, the design scheme of the FPMTS is applied, problems encountered in the design are demonstrated, and the corresponding solutions are provided. The original induction motors’ control methods and strategies are not fully adapted. Hence, a corresponding strategy needs to be studied. This paper makes a detailed analysis and introduction from the aspect of a coordinated control strategy of the diesel and the traction motor, the two degrees of freedom (2DOF) decoupling current regulator, the maximum torque control of a standardized unit current, the wheel slip protection control, and the fault protection strategy.

2. Constitution and Features of FPMTS The main circuit of FPMTS is shown in Figure1. The diesel drives the permanent magnet synchronous generator (PMSG) to generate a three-phase alternating current (3AC). Then, the alternating current (AC) is converted to a direct current (DC) using the uncontrolled rectiﬁer. After grounding detection, brake chopper, and auxiliary converter, DC is inverted 3AC to provide electric power for PMSM via four inverters. The auxiliary converter gets its power from the DC link, which provides the power for vehicle auxiliary loads. The FPMTS is controlled by the traction control unit (TCU) and the motor control unit (MCU), which are placed in the traction converter box. TCU receives the driver’s Electronics 2021, 10, x FOR PEER REVIEW 3 of 19

Electronics 2021, 10, 173 3 of 18

iary loads. The FPMTS is controlled by the traction control unit (TCU) and the motor control unit (MCU), which are placed in the traction converter box. TCU receives the driver’s commandcommand and andcontrols controls the thediesel diesel speed speed according according to the to themotor motor state, state, which which is is fed back fed back by theby theMCU. MCU. The The MCU MCU receives receives a torque a torque command command from from TCU TCU through through the the con- controller area troller area networknetwork (CAN) (CAN) bus bus and and drives drives the the PMSM. PMSM. Using Using the the pulse pulse width width modula- modulation (PWM) tion (PWM) method,method,the the inverter inverter converts converts the the DC DC into into variable variable voltage voltage variable variable frequency fre- (VVVF) AC, quency (VVVF)which, AC, thus,which, realizes thus, re thealizes vehicle’s the vehicle’s operation. operation.

FigureFigure 1. Main 1. circuitMain circuit of the offull the permanent full permanent magnet magnet transmission transmission system system (FPMTS). (FPMTS).

This project Thistakes project Cummins takes QSK19 Cummins diesel QSK19 as the diesel system as the power system source. power The source. diesel The diesel out- output powerput increases power increasesapproximately approximately linearly with linearly a speed with abetween speed between 900 rpm 900 and rpm 1300 and 1300 rpm, rpm, changingchanging only a little only from a little 1300 from rpm 1300 to 1800 rpm rpm. to 1800 The PMSM rpm. The operates PMSM at operatesa constant at a constant torque controltorque mode control under mode 510 rpm under and 510 at rpma constant and at power a constant control power mode control from mode 510 rpm from 510 rpm to to 2000 rpm.2000 Therpm. conversion The conversion between betweenthe constant the constant torque torquecontrol control mode modeand constant and constant power power controlcontrol mode mode is automatically is automatically adjusted adjusted according according to the to theDC DClink link voltage. voltage. Ac- According to cording to thethe characteristic characteristic of of diesel diesel and and th thee requirement requirement of ofthe the traction traction characteristic, characteristic, the main the main parametersparameters of FPMTS of FPMTS are aredecided decided (Table (Table 1).1 ).

Table 1. Main Tableparameters 1. Main of parametersthe full permanent of the full magnet permanent transmission magnet system transmission (FPMTS). system (FPMTS).

Parameter ParameterValue ValueParameter ParameterValue Value Diesel idle speedDiesel (r/min) idle speed (r/min) 900 900PMSM rated PMSM speed rated (r/min) speed (r/min) 510 510 Diesel rated Dieselspeed rated (r/min) speed (r/min) 1800 PM 1800SM maximum PMSM speed maximum (r/min) speed (r/min) 2000 2000 PMSG rated PMSGpower rated (kW) power (kW) 560 560 PMSM Rated PMSM torque Rated (Nm) torque (Nm) 1800 1800 PMSG rated current (A) 630 PMSM maximum torque (Nm) 3200 PMSG rated PMSGcurrent rated (A) voltage 630(V) PM 520SM maximum Inverter torque maximum (Nm) current 3200(A) 700 PMSG ratedDC voltage link rated (V) Voltage 520 (V) Inve 750rter maximum PMSM current stator resistance (A) (Ω 700) 0.013 DC link ratedPMSM Voltage rated (V) power (kW) 750 PMSM100 stator PMSM resistance d-axis inductance(Ω) (mH)0.013 0.72 PMSM rated PMSMpower rated (kW) current 100(A) PMSM 270 d-axis PMSM inductance q-axis inductance(mH) (mH) 0.72 1.54 PMSM rated current (A) 270 PMSM q-axis inductance (mH) 1.54 3. Control and Protection Strategy 3.1. Coordinated Control of Diesel and Traction Motor Fuel consumption and mechanical wear increase when diesel runs at high speeds and light loads for a long time. Therefore, it is required to adjust the diesel speed dynamically with the load changes. The FPMTS is also an active loading system. Improper loading processes will stop the diesel, especially in the process of diesel acceleration or deceleration.

Electronics 2021, 10, x FOR PEER REVIEW 4 of 19

3. Control and Protection Strategy 3.1. Coordinated Control of Diesel and Traction Motor Fuel consumption and mechanical wear increase when diesel runs at high speeds Electronics 2021, 10, 173 and light loads for a long time. Therefore, it is required to adjust the diesel speed4of dy- 18 namically with the load changes. The FPMTS is also an active loading system. Improper loading processes will stop the diesel, especially in the process of diesel acceleration or deceleration. Solving the coordinated control of the diesel and the traction motor is the Solving the coordinated control of the diesel and the traction motor is the main problem ofmain FPMTS. problem of FPMTS. InIn cruise mode, mode, the the system system only only needs needs to toensure ensure that that the thediesel’s diesel’s output output power power (i.e., (i.e.,the power the power for traction for traction motors, motors, excluding excluding other other auxiliary auxiliary power) power) is greater is greater than thanthe trac- the tractiontion power power required required for for traction traction motors, motors, and and that that the the diesel diesel is is controlled inin minimumminimum fuelfuel consumptionconsumption mode.mode. Nevertheless,Nevertheless, duringduring vehiclevehicle accelerationacceleration oror deceleration,deceleration, thethe tractiontraction powerpower changeschanges rapidlyrapidly withwith vehiclevehicle speed,speed, whichwhich will,will, thus,thus, exceedexceed thethe dieseldiesel maximummaximum outputoutput power,power, resultingresulting inin thethe dieseldiesel stopping.stopping. Moreover,Moreover, thethe energyenergy supplysupply system,system, composedcomposed ofof thethe dieseldiesel andand thethe PMSG,PMSG, isis aa largelarge inertialinertial systemsystem withwith aa limitedlimited capacitorcapacitor servingserving asas thethe energyenergy storagestorage inin thethe DCDC link.link. Therefore,Therefore, thethe DCDC linklink voltagevoltage changeschanges rapidly,rapidly, and and it it is is difﬁcult difficult to to regulate regulate it in it real-time.in real-time. Therefore, Therefore, the controlthe control program pro- mustgram detectmust detect the change the change process process of the of diesel the diesel and theand motor, the motor, and limitand limit the torquethe torque of the of motorthe motor automatically automatically when when necessary. necessary. ConsideringConsidering thethe output output characteristics characteristics of of the the diesel diesel and and motor, motor, we we propose propose the the follow- fol- inglowing method. method. When When the motorthe motor speed speed is fewer is fewe thanr 100than rpm, 100 rpm, the diesel the di speedesel speed increase increase from 900from rpm 900 to rpm 1300 to rpm. 1300 When rpm. theWhen motor the speed motor enhances speed enhances from 100 from rpm to100 510 rpm rpm, to the510 diesel rpm, speedthe diesel increase speed proportionally increase proportionally from 1300 rpm from to 1300 1800 rpm rpm. to The 1800 speed rpm. relation The speed curve relation of the dieselcurve andof the the diesel motor and is shownthe motor in Figureis shown2. Figure in Figure3 shows 2. Figure the control 3 shows ﬂow the chart control of theflow coordinatedchart of the coordinated control strategy. control strategy.

Speed/rpm

1800

Diesel speed Motor speed 1300

900

600 the difference between the 510 dies el speed and the motor speed

100 0 t/min FigureFigure 2.2. SpeedSpeed relationrelation forfor thethe dieseldiesel andand thethe motor.motor. 3.2. Design of the 2DOF Decoupling Current Regulator In order to reduce fuel consumption, when the vehicle is in cruise mode, diesel speed and vehicle speed (motor speed) are required to be decoupled. In extreme cases, when the diesel runs at 900 rpm, the DC link voltage is 320 V DC. When the PMSM runs at the maximum speed (2000 rpm), the traction motor needs a weak magnetic expansion speed, which is up to four times. The current loop needs a strong adaptability to voltage and has a wide bandwidth. For this reason, the 2DOF decoupling current regulator is adopted based on decoupling control of dq-axes. Then, all poles and zeros of the current loop are conﬁgured by introducing virtual resistance to achieve fast responses to current command, adjusting quickly to deal with back-EMF disturbance. In the dq reference frame of rotor permanent magnet orientation, the voltage equation of PMSM is as follows:

did Ld dt = ud − Rsid + ωeLqiq diq (1) Lq dt = uq − Rsiq − ωeLdid − ωeψf

where Ld and Lq are the dq-axes stator inductances, Rs is the stator resistance, ud and uq are the dq-axes stator voltages, id and iq are the dq-axes stator currents, ωe is the rotor electrical angular velocity, and ψf is the rotor permanent magnetic ﬂux linkage. ElectronicsElectronics 20212021, 10, 10, x, FOR 173 PEER REVIEW 5 of5 18of 19

Program starts

Get the diesel speed and motor speed ，then calculate their acceleration

Vary beyond the set range? No

Yes Cruise counter incremented by 1 Clear cruise counter

No Up to 20 seconds?

According the diesel speed and the maximum torque that the MCU feeds Yes back, TCU gives an execution torque to the MCU.

Go into cruise mode, the motor torque remains unchanged. TCU calculates the diesel's output power, Is it accelerating? No then gradually adjust the diesel speed to the working point of the optimal fuel consumption curve.

Yes

TCU calculates the minimum diesel TCU calculates the minimum diesel speed(Spmin) according to the diesel speed(Spmin) according to the diesel output power and motor current output power and motor current speed . speed .

Diesel speed Diesel speed Yes Yes is Spmin ？ is Spmin ？

No No

Diesel speed is Maximum Diesel Speed is idle Yes Yes (1800 rpm)? speed(900 rpm)？

No No

Increase diesel speed at a faster rate Decrease diesel speed at a faster rate

Finish

FigureFigure 3. 3. ControlControl flow ﬂow chart chart of the coordinatedcoordinated control control strategy. strategy.

3.2. Design of the 2DOF Decoupling Current Regulator In order to reduce fuel consumption, when the vehicle is in cruise mode, diesel speed and vehicle speed (motor speed) are required to be decoupled. In extreme cases, when the diesel runs at 900 rpm, the DC link voltage is 320 V DC. When the PMSM runs

Electronics 2021, 10, 173 6 of 18

The 2DOF current regulator is designed by introducing virtual resistance and cross- feedback decoupling control. ud and uq can be obtained from the following equation.

0 ud = u d − Radid − ωeLqiq 0 (2) uq = u q − Raqiq + ωeLdid + ωeψf

0 0 where Rad and Raq are the virtual resistances. u d and u q are the outputs of the dq-axes current proportional integral (PI) regulator. 0 kid u d = kpd + s (id,ref − id) (3) 0 kiq u q = kpq + s (iq,ref − iq)

Substituting Equation (2) into Equation (1) obtains the following.

did 0 Ld = u d − (Rs + Rad)id dt (4) diq 0 Lq dt = u q − (Rs + Raq)iq Thus, the decoupling of dq-axes current loop is realized. Let the design bandwidth of the current loop be ωb, taking the virtual resistance value as Rad = ωbLd − Rs, Raq = ωbLq − Rs, the parameter of PI regulator as kpd = ωbLd, kid = ωb(Rs + Rad), kpq = ωbLq, and kiq = ωb Rs + Raq). The obtained closed-loop transfer function of the PMSM current loop is shown below.

 kid  kpd+ s sL +R +R  d s ad 0  kid  k + s   1+ pd " ( ) # I (s) sLd+Rs+Rad Id,ref s d =    kiq  Iq(s)  kpq+ s  Iq,ref(s)  + +   0 sLq Rs Raq  kiq  k +  1+ pq s sLq+Rs+Raq  kid  (5) kpd+ s k 0  sL +R +R +k + id " ( ) #  d s ad pd s  Id,ref s =  k   k + iq  I (s)  0 pq s  q,ref kiq sLq+Rs+Raq+kpq+ s  ω  b 0 " I (s) # s+ωb d,ref =  ω  0 b I (s) s+ωb q,ref

In the above process, the d-axis and q-axis channels each have one pair of zeroes and poles equal to −ωb, which are canceled out. Moreover, each channel has one pole equal to −ωb. They all have fast convergence speed and good stability. For comparison, the traditional PI regulator parameter design method does not introduce virtual resistance (Rad = Raq = 0), and the canceled poles are the slow poles equal to −Rs/Ld and −Rs/Lq, which are much closer to the origin than −ωb. Using root locus analysis, it is easy to discern that, unless the dq-axes are decoupled accurately with the increase in the motor speed, there are two closed root trajectories that begin at the slow poles of the open loop. After two slow poles meet on the negative real axis, they change along the positive and negative direction of the virtual axis. The damping becomes smaller and smaller, and leads to a continuous low frequency current oscillation response. Although increasing the bandwidth of the current loop can signiﬁcantly reduce this oscillation, the bandwidth of the current loop is limited by the inverter modulation frequency. In this project, the power device is an insulated gate bipolar transistor (IGBT) of 1700 V and 1400 A. In order to limit the IGBT loss, the modulation frequency is 2000 Hz. Electronics 2021, 10, x FOR PEER REVIEW 8 of 19

Electronics 2021, 10, 173 In the practice, considering the delay of 1.5 modulation cycles from filling duty7 ofcy- 18 cle register to PWM output, the motor stator voltage in the static coordinate system is  10 On the basisu of the 2DOF decoupling design of the current regulator, the integral a − θω+−+ θω   21 3 cos(edTT ) sin( ed ) ud anti-saturation measuresu =× are added to the block diagram of the current regulator (Figure(6)4), b 32 2 sin(θω++TT ) cos( θω ) u where u is the maximum amplitude of theed motor stator voltage ed  vector,q and u and dq uc d max −−13 uq are the actual voltages applied to the motor stator. The algorithm ensures that the actual 22

applied voltage vector udq is limited within the voltage circle speciﬁed in udq and has where TT= 1.5 , T is the PWM modulation cycle, i.e., the regulator outputmax voltage the sameds direction ass u . When the voltage vector changes from the outside of the voltage dqω vectorcircle tohas the an inside, advanced this designedT electrical helps the angle. current loop recover smoothly and fast.

kpd

k id min()uu , × s ′ dq dq max id,ref ed ud ud ud ua ud 22+ uudq kpd + ω  id Riad d r Li q q 10  − 21 3× 1 32 2 ub  k −−13 pq  22 θω+−+ θω cos(edTT ) sin( ed ) θω++ θω k sin(edTT ) cos( ed ) iq min()uu , × s ′ dq dq max iq,ref eq uq uq uq uc uq uu22+ kpq dq i Ri−−ω Li ψ ω ω θ q aq q r d d r r r s

i i d cosθθ sin a ×  −sinθθ cos 3 0 2 i i q 1 b 2 2

FigureFigure 4. 4. DesignDesign scheme scheme of of the the current current regulator. regulator.

3.3. MaximumIn the practice, Torque consideringControl of a Standardized the delay of 1.5Unit modulation Current cycles from filling duty cycle registerIn order to PWM to improve output, the motorefficiency stator of voltagethe transmission in the static system, coordinate maximum system torque is per ampere (MTPA) is adopted before the PMSM entering the field weakening control mode.   1 0 In this project,ua maximumr torque√ control" cosof the(θ + standardizedω T ) − sin unit(θ + currentω T ) was# used. For 2  −1 3  e d e d ud interior PMSM,ub  = electromagnetic 2 2 torque × is expressed by Equation (7). (6) 3  √  sin(θ + ωeTd) cos(θ + ωeTd) uq uc −1 − 3 =+−ψ 2 2 TpiLLiimnfqdqqd[( )] (7) where T is the electromagnetic torque, i and i are dq-axes currents separately, where Tdm = 1.5Ts, Ts is the PWM modulationd cycle, i.e.,q the regulator output voltage vector T ψ Phasn is an the advanced number ωofe poled electrical pairs, and angle. f is the permanent magnet flux linkage. In order to obtain the maximum torque per unit current, i and i should be 3.3. Maximum Torque Control of a Standardized Unit Current d q satisfied.In order to improve the efficiency of the transmission system, maximum torque per ampere (MTPA) is adopted before the PMSM entering the field weakening control mode.

Electronics 2021, 10, 173 8 of 18

In this project, maximum torque control of the standardized unit current was used. For interior PMSM, electromagnetic torque is expressed by Equation (7).

Tm = pn[ψfiq + (Ld − Lq)iqid] (7)

where Tm is the electromagnetic torque, id and iq are dq-axes currents separately, Pn is the number of pole pairs, and ψf is the permanent magnet ﬂux linkage. In order to obtain the maximum torque per unit current, id and iq should be satisﬁed.

( ) ∂ Tm/is = 0 ∂id ( ) (8) ∂ Tm/is = 0 ∂iq q 2 2 Put Equation (7) and the motor stator current (is = id + iq) in Equation (8), then id can be expressed by Equation (9). s 2 ψf 1 ψf 2 id = ± + iq (9) 2 Lq − Ld 4 Lq − Ld

For the salient pole PMSM, Lq > Ld, id < 0, the sign before the root in Equation (9) should be negative. Finally, the relation between id and iq is expressed in Equation (10). s 2 ψf 1 ψf 2 id = − + iq (10) 2 Lq − Ld 4 Lq − Ld

According to a given torque command, Equations (7) and (10) obtains the value of id and iq via an iterative calculation. To avoid the iterative operation, the per unit value of current and torque can be expressed as idn = id/ib, iqn = iq/ib, and Tn = Tm/Tb [19]. The value of ib and Tb is as follows. ψf ib = − Lq Ld (11) Tb = pnψfib

Then, the per unit value of torque Tn can be expressed by the equation below. q 3 Tn = idn(idn − 1) h ( − ) i q (12) Tm iq Lq Ld iqn 2 Tn = = 1 − i = iqn[1 − i ] = 1 + 1 + 4i Tb ib ψf d dn 2 qn

By making and querying tables of Tn − idn and Tn − iqn, the per unit values of iqn and idn can be obtained. Finally, the reference values id and iq can be obtained when combined with parameters of the PMSM. In fact, as the motor current increases, the q-axis inductance changes due to the inﬂuence of the armature reaction [20–22]. The change of the permanent magnetic ﬂux and d-axis inductance is small. Therefore, the online adjust of q-axis inductance based on its changes is necessary.

3.4. Wheel Slip Protection Control Strategy Wheel slip protection is an essential function for railway vehicles, and prevents dam- age to the wheels and rails caused by wheel slips. Due to the MCU’s quick response ability, the focus of the wheel slip protection is to detects the slip state quickly and accurately. In this project, the slip state is judged by calculating the deviation of velocity and acceleration for motors. The MCU compares the real-time speed of each motor with the minimum value of the four motors. If the speed deviation exceeds the threshold, the MCU reduces the execution torque in proportion. The MCU compares the real-time acceleration of the motor with the Electronics 2021, 10, 173 9 of 18

Electronics 2021, 10, x FOR PEER REVIEW 10 of 19

given threshold. If the acceleration difference exceeds the threshold, the MCU reduces the execution torque in proportion as well. The greater the speed deviation, the greater the greater the decrease in the motor torque ratio. In extreme cases, the MCU rapidly reduc- decrease in the motor torque ratio. In extreme cases, the MCU rapidly reduces the motor es the motor torque to zero to prevent wheel slip. The MCU detects motor speed and torque to zero to prevent wheel slip. The MCU detects motor speed and calculates angular calculates angular acceleration every 10 ms. When the MCU exits the wheel slip protec- acceleration every 10 ms. When the MCU exits the wheel slip protection, the execution tion,torque the remains execution unchanged torque remains for a certain unchanged period offor time a certain (200 ms),period and of then time increases (200 ms), to and the thenaimed increases value given to the by aimed TCU. value given by TCU. TakingTaking the numbernumber 11 motormotor as as an an example, example, the the block block diagram diagram of of wheel wheel slip slip protection protec- tionis shown is shown in Figure in Figure5. 5.

n1 n1 T1ref n2 Δ nmax T nmin Δn ΔΔ1m 1 =×−na11 − n min TT11ref 11 3 Δ ΔΔna a1 max max n 4 Δ=nnn − 电动机转速11min

Δa amax max

Δ=aaa − 电动机转速11max

Figure 5. The block diagram of wheel slip protection. Figure 5. The block diagram of wheel slip protection.

In Figure5, n1, n2, n3, and n4 are the real-time speeds of the four motors. nmin is the In Figure 5, n , n , n , and n are the real-time speeds of the four motors. n minimum speed of1n1, n2 2, n33, and n44. ∆n1 is the difference between n1 and nmin. a1 is themin a Δ isacceleration the minimum of the speed number of 1n1 motor., n2 , n3max, andis then4 . reference n1 is the value difference of maximum between acceleration. n1 and a a a a a ∆n 1 .is a the is absolute the acceleration value of the of differencethe number between 1 motor.1 and a max is . the∆ 1 referenceis the value value of ∆ of1 aftermin the1 clipping algorithm. T is the motor torque givenmax by the TCU, and T is the Δ 1ref 1m maximumexecution torqueacceleration. of the numbera1 is 1the motor. absolute value of the difference between a1 and Δ Δ amax . ∆nmaxa1 isand the∆ avaluemax are of programmablea1 after the parameters,clipping algorithm. which can T1ref be modified.is the motor If the torque value of ∆nmax and ∆amax become smaller, the slip protection control effect becomes stronger. given by the TCU, and T1m is the execution torque of the number 1 motor. The flow chart of the algorithm is shown in Figure6, where nanti is the preset value of the Δn and Δa are programmable parameters, which can be modified. If the slip protectionmax counter.max Δ Δ value of nmax and amax become smaller, the slip protection control effect becomes 3.5. Fault Detection and Restart Control stronger. The flow chart of the algorithm is shown in Figure 6, where nanti is the preset The MCU is responsible for fault detection and system protection functions. The value of the slip protection counter. faults detected by the hardware detection circuit include the IGBT drive fault, IGBT fault, overcurrent, main circuit overvoltage, and control board under voltage. The faults detected by the software include system self-check fault, contactor fault, inverter overheating, motor overheating, over speed fault, and sensor faults. The faults are classified, according its type and severity level. When the fault occurs, the fault information is submitted to the TCU via the CAN bus. When the faults occur, they are detected by the hardware and the MCU immediately blocks the IGBT drive signal before de-energizing the DC contactor. If the inverter output current does not decrease to zero within the specified time, the AC contact is de-energized. When the faults occur, they are detected by the software and the MCU checks the sensor first. If the fault is not the sensor’s fault, the MCU provides a different treatment according to different situations.

Electronics 2021, 10, 173 10 of 18 Electronics 2021, 10, x FOR PEER REVIEW 11 of 19

Program starts

Calculate the variables in Figure 5

Slip protection ? Yes

No T1m>0.7T1ref? Δn 10.5−<1 ？ Δ Yes nmax Yes

No Add 1 to slip protection counter Δa 10.5−<1 ？ Yes Δ amax Slip Protection Set slip protection Yes Clear slip counter =nanti ? ， No flag clear slip Protection counter Protection counter No

Clear the T1m=0.7T1ref Slip protection flag

Perform the execution torque T1m

Finish

Figure 6. Control flow Figurechart of 6. wheelControl slip ﬂow protection. chart of wheel slip protection.

3.5. Fault Detection andThe Restart following Control is a brief description of the restart control strategy after the fault is The MCUcleared. is responsible After receiving for fault the detectio restartn command, and system the protection MCU resets functions. the PI regulator The and unlocks faults detectedthe by PWM.the hardware Before thedetection DC contactor circuit include is energized, the IGBT if the drive main fault, circuit IGBT voltage fault, is lower than overcurrent, mainthe threshold,circuit overvoltage, the motor operatesand control in an board electric under braking voltage. mode, The and faults the main de- circuit voltage tected by the issoftware pumped include to the supplysystem voltage. self-check The fault, electric contactor braking torquefault, inverter is very little,over- which does not heating, motoraffect overheating, the running over ofspeed the vehicle.fault, and When sensor the faults. demagnetization The faults are current classified, is established, the according its typevoltage and loop severity controls level. the When main circuitthe fault voltage occurs, to be the close fault to theinformation DC supply is voltage. After submitted to thethe TCU DC contactorvia the CAN is energized, bus. the program responds to the torque command and enters When thethe faults driving occur, state. they Then, are thedetect voltageed by loop the exitshardware and the and restart the MCU progress immedi- is finished. The flow chart of the restart control is shown in Figure7. ately blocks the IGBT drive signal before de-energizing the DC contactor. If the inverter In the above restart control process, if a serious fault occurs, the DC contactor should output current does not decrease to zero within the specified time, the AC contact is be de-energized as soon as possible. Only when the PWM signal is blocked and the stator de-energized. When the faults occur, they are detected by the software and the MCU current of the motor does not decrease to the preset value within the specified time, the checks the sensor first. If the fault is not the sensor’s fault, the MCU provides a different AC contactor is de-energized. Once the AC contactor is de-energized, the program is treatment according to different situations. considered unsuitable for the restart operation. The following is a brief description of the restart control strategy after the fault is cleared. After receiving the restart command, the MCU resets the PI regulator and unlocks the PWM. Before the DC contactor is energized, if the main circuit voltage is lower than the threshold, the motor operates in an electric braking mode, and the main circuit voltage is pumped to the supply voltage. The electric braking torque is very little, which does not affect the running of the vehicle. When the demagnetization current is established, the voltage loop controls the main circuit voltage to be close to the DC supply voltage. After the DC contactor is energized, the program responds to the torque com-

Electronics 2021, 10, x FOR PEER REVIEW 12 of 19

Electronics 2021, 10, 173 11 of 18 mand and enters the driving state. Then, the voltage loop exits and the restart progress is finished. The flow chart of the restart control is shown in Figure 7.

Program starts

Receive command to restart?

Yes

Unlock PWM, assign PI regulator

Main circuit voltage Motor operates in electric No is OK? braking mode

Yes

Close DC contactor, withdraw voltage loop automatically

Finish

FigureFigure 7. Flow chartchart of of the the restart restart control. control.

4. Simulation In the above restart control process, if a serious fault occurs, the DC contactor shouldWe be built de-energized a simulation as model soon for as the possible. motor control Only when system the in MATLAB/Simulink. PWM signal is blocked In and order to verify the system performance after using the 2DOF regulator algorithm, the 2DOF the stator current of the motor does not decrease to the preset value within the specified regulator and traditional PI regulator were applied to the system, respectively, and the time,results the of AC the twocontactor regulators is de-energized. were compared. Once The the motor AC parameters contactor areis de-energized, listed in Table1 .the pro- gramThe sampling is considered frequency unsuitable was 0.0005 for sthe and restart the bandwidth operation. of the current loop was 160 Hz (ωb = 1000 rad/s). Figure8a shows the current and torque responses controlled by the 4.traditional Simulation PI regulator when the motor accelerated and decelerated from 0 to 1000 rpm withWe an 800built Nm a load.simulation From Figure model8a, for it is the apparent motor thatcontrol good system performance in MATLAB/Simulink. was obtained. In orderFigure to8b verify shows currentthe system and torqueperformance responses after controlled using bythe the 2DOF traditional regulator PI regulator algorithm, the when the motor accelerated and decelerated from 0 to 2000 rpm with an 800 Nm load. As 2DOF regulator and traditional PI regulator were applied to the system, respectively, shown in Figure8b, there was marked oscillation when the motor operated at high speeds. and theIn orderresults to of solve the thetwo problem regulators of current were oscillationcompared. during The motor the motor’s parameters high-speed are listed in Tableoperation, 1. The we sampling adopted a 2DOFfrequency decouple was current0.0005 regulator.s and the Figure bandwidth9a shows of the the current current loop ω = wasand torque160 Hz responses ( b 1000 when rad/s). the motor Figure accelerated 8a shows ordecelerated the current from and 0 totorque 2000rpm responses with con- trolled800 Nm by loads. the traditional The 2DOF PI method regulator was adoptedwhen the without motor the accelerated decoupling and control decelerated of the from 0dq-axes. to 1000 Figure rpm9 withb shows an the800 current Nm load. and torque From responses Figure 8a, in the it sameis apparent operation that condition good perfor- but with the 2DOF method decoupling control of the dq-axes. By comparing Figure9a mance was obtained. Figure 8b shows current and torque responses controlled by the with Figure8b, it is clear that the current with the 2DOF method performed better than the traditionaltraditional PIPI method,regulator as therewhen was the no motor oscillation accelerated at high speeds.and decelerated By comparing from Figure 0 to 92000a rpm withwith an Figure 8009 b,Nm it canload. be seenAs shown that the in current Figure and 8b, torque there inwas the marked 2DOF method oscillation did not when the motorhave much operated of a difference at high speeds. with or without the decoupling of the dq-axes. Therefore, the superiority of the 2DOF method is clear, as it improves performance. Figure9c shows the current and torque responses for the 2DOF decoupling current regulator when the motor operated in the deep ﬂux. It weakened conditions in the constant power mode (500 Nm

Electronics 2021, 10, 173 12 of 18

Electronics 2021, 10, x FOR PEER REVIEW 13 of 19 output and 2000 rpm). As shown in Figure9c, the deep ﬂux weakening control made the motor current close to its maximum value.

n rpm

⋅ Tm Nm

iA A

t s

(a)

n rpm

⋅ Tm Nm

iA A

t s

(b)

Figure 8. Current and torque responses adopted a traditional proportional integral (PI) regulator: (a) the motor operates at Figure 8. Current and torque responses adopted a traditional proportional integral (PI) regulator: (a) the motor operates low-speed and (b) the motor operates at high-speed. at low-speed and (b) the motor operates at high-speed. Figure 10 shows a restart process when a fault was detected. The serious fault occurred atIn 0.05 order s, then to the solve PWM the was problem blocked, of and current the DC oscillation contactor was during de-energized. the motor’s The energyhigh-speed operation,stored in we the adopted three-phase a 2DOF inductance decouple of the curre tractionnt regulator. motor made Figure the DC 9a link shows voltage the rise current andfor torque a short responses amount of time,when and the then motor fall back accelerated gradually. or The decelerated system restarted from at 0 0.07 to s,2000 and rpm withthen 800 the Nm electric loads. brake The torque 2DOF was method generated was to maintainadopted thewithout DC link the voltage decoupling and establish control of thethe dq-axes. demagnetization Figure 9b current shows for the the current traction an motor.d torque The restart responses process in ﬁnishedthe same at 0.15operation s conditionand the torquebut with command the 2DOF responded. method As decoupli can be seenng fromcontrol Figure of the10, thedq-axes. system By designed comparing in this project quickly responded to failures and had a good restart performance. Figure 9a with Figure 8b, it is clear that the current with the 2DOF method performed better than the traditional PI method, as there was no oscillation at high speeds. By comparing Figure 9a with Figure 9b, it can be seen that the current and torque in the 2DOF method did not have much of a difference with or without the decoupling of the dq-axes. Therefore, the superiority of the 2DOF method is clear, as it improves performance. Figure 9c shows the current and torque responses for the 2DOF decoupling current regulator when the motor operated in the deep flux. It weakened conditions in the constant power mode (500 Nm output and 2000 rpm). As shown in Figure 9c, the deep flux weakening control made the motor current close to its maximum value.

ElectronicsElectronics 2021, 102021, x, FOR10, 173 PEER REVIEW 13 of 1814 of 19

n rpm

⋅ Tm Nm

iA A

t s

(a)

n rpm

⋅ Tm Nm

iA A

t s

(b)

n rpm

⋅ Tm Nm

iA A iA A

t s

(c)

Figure 9. Current and torque responses adopted two degrees of freedom (2DOF) regulator: (a) the motor operates at Figure 9. Current and torque responses adopted two degrees of freedom (2DOF) regulator: (a) the motor operates at high-speed without decoupling the dq-axis, (b) the motor operates at high-speed with a decoupling dq-axis, and (c) the high-speed without decoupling the dq-axis, (b) the motor operates at high-speed with a decoupling dq-axis, and (c) the motor operates in a deep ﬂux weakening condition. motor operates in a deep flux weakening condition.

Figure 10 shows a restart process when a fault was detected. The serious fault occurred at 0.05 s, then the PWM was blocked, and the DC contactor was de-energized. The energy stored in the three-phase inductance of the traction motor made the DC link voltage rise for a short amount of time, and then fall back gradually. The system restarted at 0.07 s, and then the electric brake torque was generated to maintain the DC link voltage and establish the demagnetization current for the traction motor. The restart process finished at 0.15 s and the torque command responded. As can be seen from Fig-

ElectronicsElectronics 2021, 202110, x, FOR10, x PEERFOR PEER REVIEW REVIEW 1515 ofof 1919

Electronics 2021 10 , , 173 ure ure10, 10,the thesystem system designed designed in inthis this project project quickly quickly responded responded to to failuresfailures andand had14 of a 18 goodgood restartrestart performance. performance.

n rpmn rpm

uDC V uDC V

iA,B,C A iA,B,C A

t s t s

Figure 10. Responses in the restart process. FigureFigure 10. 10. ResponsesResponses in in the the restart process.process. 5. Experiment 5. Experiment 5. Experiment InIn order order to to verify verify the correctnessthe correctness of the of theoretical the theoretical analysis analysis and system and performance, system perfor- themance,In system order the experiments systemto verify experiments werethe correctness carried were out oncarried of the th FPMTSe ou theoreticalt on test the platform FPMTS analysis (Figure test platformand 11). systemFigure (Figure 12 perfor-a 11). mance,showsFigure the current 12a system shows responses experiments current controlled responses were by carried acontroll traditional ouedt on by PI the a regulator traditionalFPMTS when test PI platform theregulator motor (Figure accel-when 11).the Figureeratedmotor 12a fromaccelerated shows 1000 current rpm from to 2000 1000responses rpmrpm with to controll 2000 an 800rpmed Nm with by load. a an traditional As800 shown Nm load. inPI Figure regulatorAs shown 12a, there whenin Figure the motorwere12a, accelerated markedthere were oscillations from marked 1000 inoscillations rpm the current to 2000 in responses. rpmthe current with Figure an responses. 800 12 Nmb shows load. Figure motor As 12b shown current shows in re- Figuremotor 12a,sponsecurrent there waveforms wereresponse marked inwaveforms the oscillations 2DOF regulatorin the in 2DOFth whene current theregulator motor responses. operatedwhen the Figure in motor the same 12b operated condition.shows inmotor the currentAssame shown response condition. in Figure waveforms As 12 shownb, there in was Figurethe no 2DOF oscillation 12b, regulatorthere and was the whenno current oscillation the response motor and signiﬁcantlyoperated the current in there- sameimproved.sponse condition. significantly As shown improved. in Figure 12b, there was no oscillation and the current response significantly improved.

FigureFigure 11. 11.The The FPMTS FPMTS test test platform. platform.

Figure 13 shows the experimental results of the restart process on the FPMTS test Figure 11. The FPMTS test platform. platform. The serious fault occurred at 0.1 s. Then the MCU block PWM and the DC contactor was de-energized. As the auxiliary loads on the vehicle continued to consume electric energy, the DC link voltage dropped. The system restarted at 0.4 s, and then the electric brake torque was generated, which was controlled by the voltage loop to maintain the DC link voltage at 600 V and establish the demagnetization current for the traction motor. The DC contactor was energized at 1.4 s, so the voltage rose to 750 V, and the voltage loop automatically exited. Then, the program responded to the torque command and entered the driving state. The experimental results showed that the system designed in

Electronics 2021, 10, 173 15 of 18

Electronics 2021, 10, x FOR PEER REVIEW 16 of 19 this project could quickly respond to failures and had a good restart performance without the system stopping.

(a)

(b)

FigureFigure 12. Motor 12. Motor curre current:nt: (a)( aadopting) adopting traditional traditional PI PI regulator and and (b ()b adopting) adopting the the 2DOF 2DOF regulator. regulator. The proposed control strategy of the FPMTS was implemented on the new type ofFigure shunting 13 locomotive. shows the Figureexperimental 14 shows results the test of run the photo restart of theprocess shunting on locomotivethe FPMTS test platform.dragging The eight serious vehicles. fault occurred at 0.1 s. Then the MCU block PWM and the DC contactor was de-energized. As the auxiliary loads on the vehicle continued to consume electric energy, the DC link voltage dropped. The system restarted at 0.4 s, and then the electric brake torque was generated, which was controlled by the voltage loop to maintain the DC link voltage at 600 V and establish the demagnetization current for the traction motor. The DC contactor was energized at 1.4 s, so the voltage rose to 750 V, and the voltage loop automatically exited. Then, the program responded to the torque command and entered the driving state. The experimental results showed that the system designed in this project could quickly respond to failures and had a good restart performance without the system stopping.

Electronics 2021, 10, x FOR PEER REVIEW 17 of 19

ElectronicsElectronics 20212021, ,1010, ,x 173 FOR PEER REVIEW 1716 of of 19 18

Figure 13. Responses in the restart process on the FPMTS test platform.

The proposed control strategy of the FPMTS was implemented on the new type of shunting locomotive. Figure 14 shows the test run photo of the shunting locomotive Figure 13. Responses in the restart process on the FPMTS test platform. Figuredragging 13. Responses eight invehicles. the restart process on the FPMTS test platform.

The proposed control strategy of the FPMTS was implemented on the new type of shunting locomotive. Figure 14 shows the test run photo of the shunting locomotive dragging eight vehicles.

FigureFigure 14. 14.Test Test run run of of the the diesel diesel shunting shunting locomotive locomotive equipped equipped with with FPMTS. FPMTS.

6.6. Conclusions Conclusions

ThisThis paper paper researched researched and and analyzed analyzed the the permanent permanent magnet magnet transmission transmission system system con- Figure 14. Test run of the diesel shunting locomotive equipped with FPMTS. trolcontrol of diesel of diesel railway railway vehicles. vehicles. Herein, Herein, we proposed we proposed that the that FPMTS the takeFPMTS the take PMSM the as PMSM both itsas generatorboth its generator and traction and motortraction and motor it was and constructed it was constructed as a coordinated as a coordinated control strategy control 6. Conclusions betweenstrategy thebetween diesel andthe diesel permanent and permanent magnet traction magnet motor. traction To further motor. improve To further the FPMTSimprove performance,theThis FPMTS paper performance, the researched design and theand implementationdesign analyzed and implemthe permanent of theentation 2DOF magnetof regulator the 2DOF transmission and regulator the standard system and the controlunitstandard current of diesel unit maximum currentrailway torquemaximumvehicles. control Herein, torque strategy wecontro proposed werel strategy investigated. that were the FPMTSinvestigated. In addition, take theIn the addition,PMSM wheel asslipthe both protectionwheel its generator slip controlprotection and and traction control fault protectionmotor and faultand strategy itprotection was constructed were strategy proposed. as were a coordinated The proposed. simulation controlThe andsim- strategyexperimentalulation between and experimental results the validateddiesel resuand thatlts permanent validated the FPMTS magnetthat and the control tractionFPMTS strategy andmotor. control obtainedTo further strategy a satisfyingimprove obtained theperformance.a FPMTSsatisfying performance, performance. The operation the The ofdesign shunting operation and machineimplem of shuntingentation showed machine of that the the 2DOF showed permanent regulator that magnet the and perma- the sys- standardtemnent was magnet unit an important current system maximum solutionwas an toimportant torque improve contro soluti the performancel onstrategy to improve were of diesel investigated. the performance railway vehicles,In addition, of diesel and thetherailway wheel study vehicles,slip of FPMTS protection and has the laidcontrol study the foundationand of FPMTSfault protection for ha thes laid subsequent strategythe foundation were application proposed. for the of permanent subsequentThe sim- ulationmagnetapplication and motors experimental of in permanent high-power resu ltsmagnet diesel validated locomotives motors that thein and FPMTShigh-power high-speed and control diesel diesel strategy multi-units.locomotives obtained and a high-speedsatisfyingIn the future,performance. diesel researchmulti-units. The should operation focus onof improvingshunting machine the energy showed utilization that efﬁciencythe perma- of nentrailway magnet vehicles. system Hence, was inan our important follow-up soluti work,on weto improve will try tothe add performance energy recycling of diesel and railwaystorage vehicles, devices to and the the FPMTS study in orderof FPMTS to optimize has laid the the system foundation control for strategy. the subsequent application of permanent magnet motors in high-power diesel locomotives and high-speed diesel multi-units.

Electronics 2021, 10, 173 17 of 18

Author Contributions: Conceptualization, L.K. and C.X; methodology, L.K.; software, C.X.; validation, L.K., Y.X., and K.S.; formal analysis, L.K.; investigation, L.K.; writing—original draft preparation, L.K.; writing—review and editing, C.X.; visualization, C.X.; supervision, C.X.; project administration, D.J. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by CRRC Tangshan Co., Ltd., grant number R91510. Data Availability Statement: The data presented in this study are available on request from the corresponding author. Acknowledgments: The authors would like to thank the anonymous reviewers for their reviews and comments. Conﬂicts of Interest: The authors declare no conﬂict of interest.

References 1. van der Meulen, D.; Möller, F. Sustainable heavy haul traction energy: A review of systemic issues. Proc. Inst. Mech. Eng. Part F J. Rail Rapid Transit 2014, 228, 687–694. [CrossRef] 2. Shiraki, N.; Satou, H.; Arai, S. A hybrid system for diesel railcar series Ki-Ha E200. In Proceedings of the 2010 International Power Electronics Conference (IPEC 2010), Sapporo, Japan, 21–24 June 2010; pp. 2853–2858. 3. Schmid, S.; Ebrahimi, K.; Pezouvanis, A.; Commerell, W. Model-based comparison of hybrid propulsion systems for railway diesel multiple units. Int. J. Rail Transp. 2018, 6, 16–37. [CrossRef] 4. International Union of Railways; International Energy Agency. Railway Handbook 2017; International Energy Agency: Paris, France, 2017. 5. Shamardina, V.N.; Anishchenko, M.V.; Lemeshko, S.M.; Kanunnikov, R.V. Functional efﬁciency enhancement of diesel-electric locomotive traction system. In Proceedings of the 2017 International Conference on Modern Electrical and Energy Systems (MEES 2017), Kremenchuk, Ukraine, 15–17 November 2017; pp. 20–23. 6. Germishuizen, J.; Jockei, A.; Hoffmann, T.; Teichmann, M.; Lowenstein, L.; Wangelin, F.V. SyntegraTM—Next generation traction drive system, total integration of traction, bogie and braking technology. In Proceedings of the 2006 International Symposium on Power Electronics, Electrical Drives, Automation and Motion(SPEEDAM 2006), Taormina, Italy, 23–26 May 2006; pp. 1073–1077. 7. Binder, A.; Koch, T. Permanent magnet gearless traction drive for German high speed train ICE 3. In Proceedings of the 2001 International Conference on Power Electronics (ICPE 2001), Seoul, Korea, 30 May–3 June 2011; pp. 756–760. 8. Shikata, K.; Kawai, H.; Nomura, H.; Aoki, H.; Fukasawa, S.; Tasaka, Y. PMSM propulsion system for Tokyo Metro. In Proceedings of the 2012 Electrical Systems for Aircraft, Railway and Ship Propulsion (ESARS 2012), Bologna, Italy, 16–18 October 2012. 9. Jianghua, F. Development Overview and Application Challenges of Permanent Magnet Synchronous Traction System for Rail Transit. High Power Convert. Technol. 2012, 3, 1–7. 10. Matsuoka, K. Development trend of the permanent magnet synchronous motor for railway traction. IEEJ Trans. Electr. Electron. Eng. 2007, 2, 154–161. [CrossRef] 11. Ito, T.; Inaba, H.; Kishine, K.; Nakai, M.; Ishikura, K. Method controlling four sets of permanent magnet synchronous motor by one inverter on a railway vehicle. In Proceedings of the 2014 17th International Conference on Electrical Machines and Systems (ICEMS 2014), Hangzhou, China, 22–25 October 2014; pp. 245–249. 12. Roumani, K.; Schmuelling, B. Topology selection for low voltage PMSM for in-wheel direct-drive application. In Proceedings of the 2017 19th International Conference on Electrical Drives and Power Electronics (EDPE 2017), Dubrovnik, Croatia, 4–6 October 2017; pp. 235–241. 13. Sheng, Y.; Zhou, W.; Hong, Z.; Yu, S. Field weakening operation control of permanent magnet synchronous motor for railway vehicles based on maximum electromagnetic torque at full speed. In Proceedings of the 29th Chinese Control Conference, Beijing, China, 29–31 July 2010; pp. 1608–1613. 14. Calleja, C.; López-de-Heredia, A.; Gaztañaga, H.; Aldasoro, L.; Nieva, T. Validation of a modiﬁed direct-self-control strategy for PMSM in railway-traction applications. IEEE Trans. Ind. Electron. 2016, 63, 5143–5155. [CrossRef] 15. Zhao, K.; She, J.; Zhang, C.; He, J.; Huang, G.; Liu, J. Robust Closed-loop Torque Control for PMSM of Railway Traction Considering Demagnetization. In Proceedings of the IECON 2019-45th Annual Conference of the IEEE Industrial Electronics Society, Lisbon, Portugal, 14–17 October 2019; pp. 6916–6921. 16. Taniguchi, S.; Yasui, K.; Yuki, K.; Nakazawa, Y.; Onda, S. A Restart Control Method for Position Sensorless PMSM Drive Systems Without Potential Transformer for Railway Vehicle Traction. Electr. Eng. Jpn. 2015, 193, 44–53. [CrossRef] 17. Zhao, S.; Huang, X.; Fang, Y.; Li, J. A control scheme for a High Speed Railway traction system based on high power PMSM. In Proceedings of the 2015 6th International Conference on Power Electronics Systems and Applications (PESA 2015), Hong Kong, China, 15–17 December 2015; pp. 1–8. 18. Zhang, Z.; Ge, X.; Tian, Z.; Zhang, X.; Tang, Q.; Feng, X. A pwm for minimum current harmonic distortion in metro traction pmsm with saliency ratio and load angle constrains. IEEE Trans. Power Electron. 2017, 33, 4498–4511. [CrossRef] 19. Jahns, T.M.; Kliman, G.B.; Neumann, T.W. Interior permanent-magnet synchronous motors for adjustable-speed drives. IEEE Trans. Ind. Appl. 1986, 738–747. [CrossRef] Electronics 2021, 10, 173 18 of 18

20. Kim, H.; Hartwig, J.; Lorenz, R.D. Using on-line parameter estimation to improve efficiency of IPM machine drives. In Proceedings of the 2002 IEEE 33rd Annual IEEE Power Electronics Specialists Conference, Cairns, Australia, 23–27 June 2002; pp. 815–820. 21. Nguyen, Q.K.; Petrich, M.; Roth-Stielow, J. Implementation of the MTPA and MTPV control with online parameter identification for a high speed IPMSM used as traction drive. In Proceedings of the 2014 International Power Electronics Conference (IPEC 2014), Hiroshima, Japan, 18–21 May 2014; pp. 318–323. 22. Li, F.; Xia, C. Inductance Identification Algorithm and Variable-Parameters MTPA Control Strategy for IPMSM Considering Magnetic Circuit Saturation. Diangong Jishu Xuebao/Trans. China Electrotech. Soc. 2017, 32, 136–144.