Article Inductive Power Transfer Subsystem for Integrated Motor Drive
Zbigniew Kaczmarczyk 1, Marcin Kasprzak 1, Adam Ruszczyk 2, Kacper Sowa 2 , Piotr Zimoch 1,* , Krzysztof Przybyła 1 and Kamil Kierepka 1
1 Department of Power Electronics, Electrical Drive and Robotics, Silesian University of Technology, 44100 Gliwice, Poland; [email protected] (Z.K.); [email protected] (M.K.); [email protected] (K.P.); [email protected] (K.K.) 2 ABB Corporate Technology Center, 31038 Cracow, Poland; [email protected] (A.R.); [email protected] (K.S.) * Correspondence: [email protected]; Tel.: +48-32-237-12-47
Abstract: An inductive power transfer subsystem for an integrated motor drive is presented in this paper. First, the concept of an integrated motor drive system is overviewed, and its main components are described. Next, the paper is focused on its inductive power transfer subsystem, which includes a magnetically coupled resonant circuit and two-stage energy conversion with an appropriate control method. Simplified complex domain analysis of the magnetically coupled resonant circuit is provided and the applied procedure for its component selection is explained. Furthermore, the prototype of the integrated motor drive system with its control is described. Finally, the prototype based on the gallium nitride field effect transistors (GaN FET) inductive power transfer subsystem is experimentally tested, confirming the feasibility of the concept.
Keywords: motor drives; wireless power transfer (WPT); inductive power transfer (IPT); coupled circuits; resonant converters Citation: Kaczmarczyk, Z.; Kasprzak, M.; Ruszczyk, A.; Sowa, K.; Zimoch, P.; Przybyła, K.; Kierepka, K. Inductive Power Transfer Subsystem 1. Introduction for Integrated Motor Drive. Energies Wireless power transfer (WPT) has been an object of increased interest of researchers 2021, 14, 1412. https://doi.org/ in recent years. Contactless energy transmission eliminates cables and connectors, thus 10.3390/en14051412 increasing reliability. The technology is also naturally safe by providing electrical insulation. Inductive power transfer (IPT), which usually employs two magnetically coupled coils Academic Editor: Alon Kuperman (forming a loosely coupled transformer) and compensation capacitors, is one of multiple technologies used for WPT [1–3]. IPT systems allow to achieve relatively long transmission Received: 19 January 2021 distances with relatively high efficiencies. Their efficiencies depend heavily on the coupling Accepted: 1 March 2021 Published: 4 March 2021 coefficient between primary and secondary coils and their quality factors [4,5]. They can also supply multiple receivers [6]. IPT technology is a very popular solution for a wide
Publisher’s Note: MDPI stays neutral range of applications [7–9], e.g., contactless charging of electric vehicles [10,11] and mobile with regard to jurisdictional claims in devices [5], powering biomedical implants [4], flexible induction heating [12], or fluorescent published maps and institutional affil- lighting [13]. Recent advances in this regard relate to the structures of IPT systems [14–16], iations. compensation circuits [15,17] and coil designs [5,18,19]. So far, little attention has been paid to the possibility of using IPT technology for motor drive systems. For example, [20] proposes a wireless in-wheel motor drive for electric vehicles to solve the problems with power cables and signal wires exposed to harsh environments. This system applies an additional controller and power converter Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. at the motor side. In turn, in [21] a wireless bidirectional servo motor drive is described This article is an open access article and [22] presents a wireless switched reluctance motor drive. In both cases the principles distributed under the terms and of the so-called “energy encryption” [23] and selective wireless power transfer [24] are conditions of the Creative Commons applied. The reluctance motor drive in [22] is switched by using receiver coils of different Attribution (CC BY) license (https:// resonant frequencies, while the servo motor drive in [21] is based on the same method creativecommons.org/licenses/by/ for bidirectional motion. In [21] and [22], neither a controller nor a power converter at 4.0/). the secondary-side of the IPT system is used. In contrast to these studies, the solution
Energies 2021, 14, 1412. https://doi.org/10.3390/en14051412 https://www.mdpi.com/journal/energies Energies 2021, 14, 1412 2 of 14
presented in this paper provides a fully functional electric motor drive system, which is integrated with motor housing. Importantly, the system is powered via a contactless plug which makes it suitable for specific applications. It can easily be adapted to all types of electric motors [25]. The developed system is composed of an electric motor connected to a dedicated drive, powered wirelessly by transmitter and receiver modules—a substitute for a regular plug. Therefore, the system is fully hermetic and dedicated to harsh environments, e.g., the food and beverage (F&B) industry. The average lifetime of motors in the F&B industry is about one month [26]. The main failure reasons are bearings or windings of the motors. Motors that have been in operation for more than a month are often replaced by new ones as part of preventive maintenance [27,28]. The most popular motors are rated in the range of 1 to 2 kW and are used in pumps, conveyors, compressors, and others. The F&B industry (similarly to the chemical industry) has very high requirements for clean and reliable operation due to the continuous production process. Any unpredicted stops and delays may damage semi-products used in production and increase operating costs. The system modularity is a valuable advantage, allowing for simple installation and quick replacement of a damaged module (drive with motor). Due to the complexity of the whole system, this paper is mainly focused on presenting the general concept of the developed system and in more detail on its IPT subsystem. This IPT subsystem has a fully load-independent voltage gain. Similar solutions are analyzed in [29–31], but the design method of the IPT subsystem given in this paper is simplified and appropriately adapted. At the same time, additional feedback is applied to ensure the required fully load-independent voltage gain. Section2 provides an overview of the integrated motor drive system and its structure. The selection of magnetically coupled resonant circuit components is given in Section3 . Section4 describes the prototype of the integrated motor drive system, presenting the applied IPT subsystem and its control in detail. The results of experimental tests of the prototype are shown in Section5. Finally, the conclusions are drawn in Section6.
2. Concept of IPT-IMD System The proposed IPT-IMD system includes the IPT subsystem powering the integrated motor drive (IMD), which consists of a variable-frequency drive (VFD) with an electric motor (M). First, it should be clarified that the IPT and IMD subsystems can be considered individually. The IPT subsystem provides the required power to the IMD subsystem under a variable load, and its DC output voltage aligned with to the DC input voltage contains the information about the set angular velocity of the motor. On the other hand, the IMD subsystem based on this voltage is responsible for obtaining the desired angular velocity. A 3D visualization of the system is presented in Figure1 and its schematic is depicted in Figure2. The applied magnetically coupled coils are designed to be identical and to fit within the plastic casings. They are single-layer and spiral, wound with litz-wire. Additionally, the coils are shielded with 3F3 ferrite and aluminum plates. The casings are built to have the same dimensions as the motor housing. The IPT-IMD system can be divided into the following sections: the input (IN) consisting of the DC supply UI with capacitor bank CI, the primary-side GaN FET inverter (INV), the magnetically coupled resonant circuit (MCR circuit), the secondary-side bridge rectifier (REC) and the output load (OUT/IMD) consisting of a DC link with capacitor bank CO and the VFD with the electric motor (M). The equivalent components for the MCR circuit are also shown on the schematic. Namely, the AC sinusoidal source u1 on the primary-side, and the AC load resistance ROAC equivalent to the DC load resistance RODC on the secondary-side. Energies 2021, 14, x FOR PEER REVIEW 3 of 14 Energies 2021, 14, 1412 3 of 14 Energies 2021, 14, x FOR PEER REVIEW 3 of 14
electric motor secondary primary electric motor secondary casingsecondary casing primary VFD magnets primary secondarycoil casing casing coilprimary VFD magnets coil coil
rectifier optical link inverter rectifier magnetic shields optical link inverter aluminummagnetic plates shields (a) aluminum plates (a)
(b) (b) FigureFigure 1. Visualization 1. Visualization of IPT-IMD of IPT-IMD system: system: (a) (disassembled,a) disassembled, (b) ( bassembled.) assembled. Figure 1. Visualization of IPT-IMD system: (a) disassembled, (b) assembled. control loop of IPT subsystem control loop of IMD II control loop of IPT subsystem control loop of IMD IO II T1 T3 C1 R R i1 p1 p2 i2 IO T1 T3 C1 R R D1 D3 i1 p1M p2 i2 CO C D1 D3 I M CO UI UO CI u1 L1 L2 u2 M T2 T4 R ~ UI ROAC ODCUO ~ u1 L1 L2 u2 ~ M T2 T4 D2 D4 R ~ ROAC ODC ~ D2 D4 INV MCR circuit REC VFD M IN INV IPT MCRsubsystem circuit REC OUTVFD / IMD M IN IPT subsystem OUT / IMD Figure 2. Schematic of the IPT-IMD system. Figure 2. SchematicSchematic of of the the IPT-IMD IPT-IMD system. The applied magnetically coupled coils are designed to be identical and to fit within the plasticTheThe casings.applied angular Theymagnetically velocity are single-layer of the coupled motor ancoils isd controlledspiral, are de woundsigned by the towith be VFD, identicallitz-wire. proportionally andAdditionally, to fit within to the thetheoutput coils plastic are voltage shieldedcasings.UO ,Theywith which 3F3are varies ferritesingle-layer with and theal anuminum inputd spiral, voltage plates. wound UTheI .with Incasings turn, litz-wire. theare built IPT Additionally, subsystem to have thetheis same controlled coils dimensions are shielded to ensure as withthe the motor 3F3 equality ferrite housing. of andUI Thealanduminum IPT-IMDUO despite plates. system load The can variation.casings be divided are Therefore, built into to thehave the followingtheMCR same circuit sections: dimensions is designed the input as the accordingly, (IN) motor consisting housing. to make of The the the IPT-IMDDC output supply voltage system UI with stable can capacitor be in divided a wide bank rangeinto C Ithe, of thefollowingload primary-side conditions sections: andGaN the to FET beinput approximately inverter (IN) consisting (INV), 10% the of higher themagnetically DC than supply the inputcoupled UI with voltage resonantcapacitor in case circuitbank of open- C I, (MCRtheloop primary-sidecircuit), operation. the secondary-side Additionally, GaN FET inverter an bridge optical (INV), rectifier link the is (REC) used magnetically asand feedback the output coupled information load resonant (OUT/IMD) about circuit the consisting(MCRoutput circuit), voltage of a DC theU linkO secondary-sidefor with the IPTcapacitor subsystem bridge bank re controlCctifierO and in (REC)the case VFD ofand closed-loopwith the theoutput electric operation. load motor (OUT/IMD) Further (M). Theconsistingconsiderations equivalent of componentsa DC are link made with underfor capacitorthe theMCR assumption circuibank tC areO and thatalso the theshown VFD primary-side onwith the the schematic. electric inverter motorNamely, switching (M). theThefrequency AC equivalent sinusoidal is 150 components source kHz and u1 on the for the inputthe primary-side, MCR and circui output tand are voltages thealso AC shown shouldload on resistance the change schematic. R inOAC the equiva- Namely, range of lentthe100 to AC tothe 300sinusoidal DC V, load which resistance source relates u1 R toonODCthe the on fullprimary-side, the range secondary-side. of angular and the velocity AC load of resistance the considered ROAC equiva- motor lent(motorThe to angularthe parameters DC load velocity resistance are of given the motorR inODC Section on is thecontro 4.3 secondary-side.).lled The by selected the VFD, switching proportionally frequency to the ensures out- putfeasibility voltageThe angular U andO, which acceptable velocity varies powerof with the motorthe losses input is of contro the voltage IPT-IMDlled U byI. In system.the turn, VFD, the It propor has IPT a subsystem directtionally impact to is the con- on out- the trolledputparameters voltage to ensure U ofO , the thewhich magneticallyequality varies of with U coupledI andthe input UO coils, despite voltage which load UI should. Invariation. turn, be the flat Therefore, IPT and subsystem properly the MCR is fill con- the trolled to ensure the equality of UI and UO despite load variation. Therefore, the MCR
Energies 2021, 14, x FOR PEER REVIEW 4 of 14
circuit is designed accordingly, to make the output voltage stable in a wide range of load conditions and to be approximately 10% higher than the input voltage in case of open- loop operation. Additionally, an optical link is used as feedback information about the output voltage UO for the IPT subsystem control in case of closed-loop operation. Further considerations are made under the assumption that the primary-side inverter switching Energies 2021, 14, 1412 4 of 14 frequency is 150 kHz and the input and output voltages should change in the range of 100 to 300 V, which relates to the full range of angular velocity of the considered motor (motor parameters are given in Section 4.3). The selected switching frequency ensures feasibility andplastic acceptable casings. power Hence, losses their of relatively the IPT-IMD high sy qualitystem. factorsIt has a anddirect strong impact magnetic on the couplingparam- etersare obtained.of the magnetically coupled coils, which should be flat and properly fill the plastic casings.An Hence, additional their componentrelatively high of thequality system factors is a setand of strong magnets magnetic placed coupling in the corners are ob- of tained.both casings. In the event of a failure on either side of the system, it can be quickly plugged or unpluggedAn additional without component having of to the use system any wires. is a set of magnets placed in the corners of both casings. In the event of a failure on either side of the system, it can be quickly plugged or3. unplugged MCR Circuit without Component having to Selection use any wires. A schematic of the MCR circuit is shown in Figure3. It is assumed that passive 3.components MCR Circuit of Component the circuit areSelection linear, invariant in time and ideal, except for the parasitic resistancesA schematic of the of coils. the MCR Overall, circuit two is series–series shown in Figure compensation 3. It is assumed capacitors that arepassive included com- in ponentsthe circuit. of the The circuit analysis are islinear, carried invariant out using in fundamentaltime and ideal, harmonic except approximationfor the parasitic in re- the sistancescomplex of domain—sinusoidal the coils. Overall, two voltages series–ser and currents.ies compensation The primary-side capacitors inverter are included is replaced in theby circuit. a voltage The source analysisU 1is(1), carried while out the usin rectifierg fundamental is substituted harmonic by an approximation equivalent resistance in the complexROAC (2)—Figure domain—sinusoidal2. voltages and currents.√ The primary-side inverter is replaced U U 2 2 by a voltage source U1 (1), while the rectifier1 = 2 is= substituted by an equivalent resistance(1) π ROAC (2)—Figure 2. UI UO
-jXC1 -jXC2 I1 Rp1 Rp2 I2 jXM
U1 jXL1 jXL2 ROAC U2
FigureFigure 3. 3.SchematicSchematic of ofMCR MCR circuit. circuit.
U1 and U2 stand for root mean square (RMS) values of the input and output voltages. 𝑈 𝑈 2√2 = = (1) 𝑈R 𝑈 8π OAC = 2 (2) U1 and U2 stand for root mean squareRODC (RMS) valuπ es of the input and output voltages.
The MCR circuit is described by the𝑅 following8 equations: = (2) 𝑅 π √ U = I Rp1 + j(XL1 − XC1) − jkI XL1XL2 The MCR circuit is 1described1 √ by the following equations:2 U2 = jkI1 XL1XL2 − I2 Rp2 + j(XL2 − XC2) , (3) U = R I 2𝑈 =𝐼 OAC 𝑅 2+ 𝑗 𝑋 −𝑋 −𝑗𝑘𝐼 𝑋 𝑋 (3) where Rp1 and Rp2 are𝑈 the = parasitic𝑗𝑘𝐼 𝑋 resistances𝑋 −𝐼 𝑅 of+ the𝑗 𝑋 coils. −𝑋 The , mutual reactance XM is expressed by the coils’𝑈 self-reactance =𝑅 𝐼 values XL1, XL2 and the coupling coefficient k. Previous works [29–31] show that in the analyzed series-series compensated circuit where Rp1 and Rp2 are the parasitic resistances of the coils. The mutual reactance XM is it is possible to obtain the output voltage U2, which is nearly invariant with changes in expressed by the coils’ self-reactance values XL1, XL2 and the coupling coefficient k. the load resistance ROAC and proportional to the input voltage U1. Complete invariance Previous works [29–31] show that in the analyzed series-series compensated circuit can only be obtained if the circuit is lossless (Rp1 = Rp2 = 0). If the coils’ quality factors Q1 it is possible to obtain the output voltage U2, which is nearly invariant with changes in the and Q2 (4) are high, the output voltage does not change much. Additionally, if the coils are loadstrongly resistance coupled ROAC (k and> 0.8—[ proportional32]) the efficiency to the input is also voltage high. U1. Complete invariance can
XL1 XL2 Q1 = , Q2 = (4) Rp1 Rp2
Further analysis is done for the special case of the IPT subsystem—the output voltage UO should be approximately 10% higher than the input voltage UI in open-loop operation and the coils should be roughly similar. Initially, the analysis is simplified by assuming the Energies 2021, 14, x FOR PEER REVIEW 5 of 14
only be obtained if the circuit is lossless (Rp1 = Rp2 = 0). If the coils’ quality factors Q1 and Q2 (4) are high, the output voltage does not change much. Additionally, if the coils are strongly coupled (k > 0.8—[32]) the efficiency is also high.
𝑋 𝑋 𝑄 = ,𝑄 = (4) 𝑅 𝑅 Energies 2021, 14, 1412 Further analysis is done for the special case of the IPT subsystem—the output voltage5 of 14 UO should be approximately 10% higher than the input voltage UI in open-loop operation and the coils should be roughly similar. Initially, the analysis is simplified by assuming the circuit to be lossless (Rp1 = Rp2 = 0). By applying Thevenin’s theorem to the MCR circuit, circuit to be lossless (Rp1 = Rp2 = 0). By applying Thevenin’s theorem to the MCR circuit, thethe equivalent equivalent schematic schematic shown shown in inFigure Figure 4 4is is obtained. obtained.
ZE I2
E ROAC U2
FigureFigure 4. Thevenin’s 4. Thevenin’s equivalent equivalent of ofMCR MCR circuit. circuit.
TheThe equivalent equivalent circuit circuit is isdescri describedbed by by the the following following equations: equations: √ U𝑈 𝑘k 𝑋X L1𝑋X L2 E𝐸== 1 , ,(5) (5) 𝑋X L1−𝑋− X C1 𝑘k2𝑋X 𝑋X 𝑍 = 𝑗 𝑋 −𝑋 − 𝑗 L1 L2. (6) ZE = j(XL2 − XC2) − j𝑋 −𝑋 . (6) X L1 − X C1
It isIt obvious is obvious that that the the output output voltage voltage U2 isU independent2 is independent of the of load the loadresistance resistance ROAC R(UOAC2 = E(U) when:2 = E) when: ZE = 0. (7) 𝑍 =0. (7) Condition (7) is met, among others, for: Condition (7) is met, among others, for: X = X 1 − k 2 , 𝑋C1 =𝑋 L11−𝑘 , (8) = (8) X𝑋C2 =0.0.
TheThe output output to toinput input voltage voltage ratio ratio UUO/OU/I UisI equalis equal to tothe the ratio ratio of ofU2U to2 toU1U (1).1 (1). By By using using EquationsEquations (5), (5), (7), (7), and and (8), (8), it is it isobtained: obtained: s 𝑈 𝑈 𝐸 1 𝑋 UO =U2 = E = 1 X. L2 (9) 𝑈 = 𝑈 = 𝑈 =𝑘 𝑋 . (9) UI U1 U 1 k XL1
Therefore,Therefore, if ifthe the coupling coupling coefficient coefficient kk isis in thethe orderorderof of 0.9 0.9 and and the the coils’ coils’ self-reactance self-reac- tance XL1 and XL2 are similar, the output voltage will be approximately 10% higher than XL1 and XL2 are similar, the output voltage will be approximately 10% higher than the theinput input voltage. voltage. EquationEquation (8) (8) will will be beused used for for the the design design process process of ofthe the MCR MCR circuit. circuit. In Inthis this case case the the inputinput impedance impedance of ofthe the circuit circuit is: is: 𝑈 𝑅 𝑘 𝑋 𝑋 𝑅 𝑘 𝑋 𝑍 =U = R k2X X + 𝑗 R2 k2X (10) = 𝐼1 = 𝑅OAC +𝑋L1 L2 +𝑅 OAC+𝑋 L1 Z1 2 2 j 2 2 (10) I1 ROAC + XL2 ROAC + XL2 and remains inductive for any resistance value. This is beneficial due to the use of a reso- nantand voltage remains source inductive inverter for (Figure any resistance 2). Considering value. the This non-zero is beneficial parasitic due resistances to the use of a theresonant coils, the voltage efficiency source of the inverter MCR (Figurecircuit 2can). Considering be estimated the using non-zero the following parasitic equation: resistances of the coils, the efficiency of the MCR circuit can be estimated using the following equation:
2 2 2 2 ∆P Rp1 I + Rp2 I Rp2 Rp1 R + X η = 1 − = 1 − 1 2 = 1 − − OAC L2 (11) P Re[U I∗] R R k2X X 1AC 1 1 OAC OAC L1 L2 Energies 2021, 14, x FOR PEER REVIEW 6 of 14