A new concept of two-stage multi-element resonant-/cyclo-converter for two-phase IM/SM motor

POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 11 |NUMBER: 4 |2013 |SEPTEMBER A New Concept of Two-Stage Multi-Element Resonant-/Cyclo-Converter for Two-Phase IM/SM Motor Mahmud Ali Rzig ABDALMULA Department of Electrical and Electronic, Faculty of Engineering, Sabrata, University of Zawiya, P.O.Box 164 18 Zawiya, Libya [email protected] Abstract. The paper deals with a new concept of power electronic two-phase system with two-stage DC/AC/AC converter and two-phase IM/PMSM motor. The proposed system consisting of two-stage converter comprises: input resonant boost converter with AC output, two-phase half-bridge cyclo-converter commutated by HF AC input voltage, and induction or synchronous motor. Such a system with AC interlink, as a whole unit, has better properties as a 3phase reference VSI inverter: higher efficiency due to soft switching of both converter stages, higher switching frequency, smaller dimensions and weight with lesser number of power semiconductor switches and better price. In comparison with currently used conventional system configurations the proposed system features a good efficiency of electronic converters and also has a good torque overloading of two-phase AC induction or synchronous motors. Design of two-stage multielement resonant converter and results of simulation experiments are presented in the paper. Keywords Computer simulation, cyclo-converter, direct converter, frequency converter, resonant converter, two-phase AC motor, two-stage electronic converter. 1. Introduction To increase power density and energy efficiency a resonant converter topology with up to 5 resonant (accumulating) elements - LLCLC are currently being developed. Although this topology contains several resonant elements as in the case of LLC converter, the magnetic components can be integrated with small size and lower losses. The proposed system also deals with several resonant elements converter as in the case of the LLCLC converter, and deals with the investigation of one of new topologies – LC(T)LC converter. This type of resonant LC(T)LC converter with two resonant LC circuits, serial and parallel, tuned to the harmonic, comprises integrated HF transformer, whose elements are an integral part of the resonant LC circuit. Current tendencies in the field of power electronics require new power converter topologies and/or architectures with high power density, high efficiency and with low EMI/EMC influence. Fig. 1: Principle circuit scheme of: a) LLC and b) LLCLC converter with DC output [1], [2]. Typical architecture of power system utilized for distributed power system is shown in [1], [2] prototype of the module of a power resonant LCLCL converter, whose parameters are as follows: output power: 1 kW, switching frequency 1 MHz, power density 95 W/in3 (= 95 W ×2,543/cm3= 1556 W/cm3) and efficiency c 2013 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 244 POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 11 |NUMBER: 4 |2013 |SEPTEMBER 95,5 %. To achieve the mentioned parameters of the power converter, next techniques and technologies are being used: increase of power density and efficiency of high-frequency LLC converters with the use of resonant mode and synchronous rectification techniques. The designed AC/DC/DC system converters with AC interlink, as a whole unit, has better properties as 3phase reference VSI inverter [3]. The following topologies are being developed: LLC converter with Schottky rectifier (Fig. 1(a)); LLCLC converter with synchronous MOSFET rectifier (Fig. 1(b)); LC(T)LC converter (Fig. 2) with serialand parallel resonant circuits. The final parameters of such a multi-element converter reach the latest published values. Fig. 2: Principle circuit scheme of LCLC (LCTLC) converter with HF AC output [5]. 2. New Concept of Two-Stage Multi-Element Resonant-/Cyclo-Converter Based on the schemes of the resonant converters mentioned in Chapt. 1 one can choose the principle conception of two-stage multi-element resonant-/cycloconverter (TS-MERC) with HF interlink, Fig. 3. Fig. 3: Scheme of power circuits of 2-stage two-phase converter with HF interlink; Sa,b - bidirectional electronic switches. The TS-MERC converter consists of input DC/DC converter, LCL2C2resonant interlinks with HF output and two-phase half-bridge cycloor matrix converter, [4], [5]. Due to decreased phase voltage of halfbridge cyclo-converter we proposed a new converter connection with increasing autotransformer HF interlink, Fig. 4. Fig. 4: Possible scheme of power circuits of 2-stage two-phase converter with increasing autotransformer HF interlink. As bidirectional switches there can be used MOSFET transistors, IGBT transistors, reverse blocking RB IGBT transistors or SCR/GTO thyristors. The choice depends on power of application and used switching frequency, Fig. 5. Fig. 5: Possible connection of bidirectional switches with: a) MOSFET transistors, b) IGBT transistors, c) reverse blocking RB IGBT transistors or SCR/GTO thyristors. 2.1. The First Stage Design and Control of TS-MERC Converter 1) Design of LCL2C2Element As mentioned above, the first stage consists of the simple input DC/DC converter and the LCL2C2resonant interlink with HF output. The resonant frequency of L1C1and L2C2should be the same as basic fundamental frequency of the converter and is governed by load requirements. Thus, based on the Thomson relation ωres =r1 L1C1 =r1 L2C2 ,(1) or, respectively L1ωres =1 ωresC1 =L2ωres =1 ωresC2 ,(2) where ωres is equal to 2π×fundamental frequency of the converter. Values of storage LC components and c 2013 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 245 POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 11 |NUMBER: 4 |2013 |SEPTEMBER their parameters are important for properties of LCLC filter and/or LCTLC inverter, respectively. Theoretically, ωresL1and other values of (2) can be chosen from a wide range. For our first design approximation we suppose a simple resonant circuit with a resonant frequency equal to the input switching frequency (ωres =ωsw). The LC design process can be considered from three different points of view or criteria, [6], [7], [8]: •1st: nominal voltage and current stresses at steady-states, •2nd: minimum voltage and current stresses during transients, •3rd: required value of total harmonic distortion of the output voltage. In order to not exceed nominal voltages of the storage elements, we use the value of internal impedance of the storage element equal to the nominal load |ZN|: Lωres =1 ωresC=|ZN|=U2 1 P1 ,(3) where U1,P1are nominal output voltage or power, respectively (fundamental harmonic). Let’s define the nominal design factor qNfor LC components as qN=Lωres |ZN|=1 ωresC|ZN|.(4) The above equation is similar to the quality factor defined by q= (Lloadωres)/Rload, however qNdoes not depend on the actual value of load resistance Rload. From the Eq. (3) and Eq. (4) one can obtain the design formulas for LC storage elements of series chain L=U2 1 ω1P1 qN, C =P1 ω1U2 1 1 qN .(5) The voltage on storage elements at nominal steadystate is calculated as UL=LωresINqN=Lωres P1 U1 qN,(6) UC=1 ωresCINqN=1 ωresC P1 U1 qN.(7) That means that for qNequal to one, the voltages across the storage elements will be nominal values, and they depend proportionally on qNfactor. From the above derived relations we can design the resonant element of LCL2C2as follows L1=U2 1 ω1P1 qN, C1=P1 ω1U2 1 1 qN .(8) where U1,P1,ω1are nominal output voltage, power and frequency, respectively (fundamental harmonic). L2=U1 22 ω1 P1 2 1 qN , C2= P1 2 ω1U1 22qN.(9) 2) Control of LCL2C2Resonant Converter The control can be done by: •classical asymmetrical duty cycle control for regulation of output voltage magnitude (fundamental harmonic) [10], Fig. 6, •frequency control (by changing the switching frequency), •LF modulation using bipolar PWM control. Fig. 6: Asymmetrical duty cycle control [10] for 165/195◦el. asymmetry. Using the Fourier theory for waveform in Fig. 6 one can derive relation ([10]) for basic harmonic amplitude of output voltage of inverter U1M(β) U=2√2 πp1−cos(β/2),(10) where βis pulse-width of input rectangular voltage of LCL2C2. Using an asymmetrical control, the output voltage of inverter comprises all harmonic components, both odd and even ones of Fourier series as it in Fig. 7, [9]. So, the first two methods are not suitable for deep control of output voltage because harmonic content and non-linear transfer function of the LCL2C2circuit. c 2013 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 246 POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 11 |NUMBER: 4 |2013 |SEPTEMBER Fig. 7: Harmonic content of input voltage of the LCL2C2inverter under asymmetrical control 165/195◦el. [9]. 3) LF Modulation Using Bipolar PWM Control Principle of LF modulation is based on multiplication of carrier HF voltage with F control harmonic waveform, Fig. 6. The problem is that we have not HF carrier harmonic voltage to disposal. Fig. 8: Principle of LF modulation carrier HF voltage by LF control signal. Although the principle of modulation is easy, practical realization make some problems, because we cannot compare both waveforms as we have not any HF carrier harmonic voltage. Thues we have to calculate each switching time (i.e. duty cycle during each switching period). The obtained result is shown in Fig. 9, and details of the method of calculation are prepared for publishing together with my colleagues. Simulation of the LCL2C2stage operation is given in the chapter 3. Fig. 9: Principle of LF modulation carrier HF voltage by LF control signal. 2.2. The Second Stage Design and Control of TS-MERC Converter The second stage of TS-MERM converter consists of a half-bridge matrix converter for each phase of twophase induction/synchronous motor, Fig. 8. Fig. 10: Circuit scheme of two/phase half-bridge cycloconverter with IM-SM motors. Fig. 11: Output voltage of cycloconverter PWM modulated control of the first stage. The maximum voltage of each phase is one half of the entire input voltage of the second stage. So, the motor should be adapted for this voltage or the voltage should be increased by the first stage of TS-MERC converter. c 2013 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 247 POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 11 |NUMBER: 4 |2013 |SEPTEMBER Fig. 12: Power circuit scheme of TS-MERC converter with PWM modulation of each phase of IM-SM motors. There was chosen a two-phase application with IM/SM motor that is widely described in references [11], [12], [13], [14], [15]. Output voltage of cycloconverter can be controlled: •by the first stage as mentioned above, Fig. 6, Fig. 8, •or by a cycloconverter using phase control, Fig. 11. Because of two phase’s application each phase must be controlled separately - both phases cannot be controlled by the same PWM signal from the first stage, but they must be shifted by 90 degrees. The adequate power circuit connection is shown in Fig. 12. 2.3. Simulation Experiments In Fig. 13 and Fig. 14 there are shown output quantities of LCL2C2 stage in steady state (without control, duty cycle D= 0,5) and with PWM control. Fig. 13: Output quantities of LCL2C2stage in steady state without control (duty cycle D= 0,5). One can see clearly harmonic voltage of the first stage without (Fig. 12) and with PWM modulated control (Fig. 13). The time course of the output voltage of the second stage controlled by duty cycle control from the first stage is presented in Fig. 15. Fig. 14: LF modulation PWM control with modulation indexes ma=1, mf=20. Fig. 15: The output voltage of six-pulse cycloconverter and its fundamental harmonic. Fig. 16: Output quantities of cycloconverter under classical phase-shift control and RL load. During these experiments it was necessary to synchronize control system quantities (reference values) with output voltage of cycloconverter. c 2013 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 248 POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 11 |NUMBER: 4 |2013 |SEPTEMBER 3. Conclusion New concept of power electronic two-phase system with two-stage TS-MERC converter and two-phase IM/PMSM motor is presented in the paper. The system with the TS-MERC converter can be used in: •AC variable frequency motor application, •hardening the metal with AC currents of the frequency 5–40 kHz, also for demagnetization by production of bearings – without second stage, •power supply for the high frequency applications in the aerospace industry and cosmonautics and finally, •as a source of AC harmonic voltage (e.g. UPS - the uninterruptible power supply 50 Hz), working parallel to the system, as a cold or hot reserve - using an output rectifier instead of cyclo-converter. The real experimental verification is preparing to be done and will be published, too. Acknowledgment The author thanks the Faculty of Electrical Engineering of the University of Zilina for fruitful cooperation and possibility for publication the paper in the scientific journal. References [1] LEE, F. C., S. WANG, P. KONG, CH. WANG and D. FU. Power Architecture Design with Improved System Efficiency, EMI and Power Density. In: Power Electronics Specialists Conference, 2008. PESC 2008. Rhodes: IEEE, 2008, pp. 4131–4137, ISBN 978-1-4244-1668-4. DOI: 10.1109/PESC.2008.4592602 . [2] FU, D., F.C. LEE, Y. LIU and M. XUFOR. Novel Multi-Element Resonant Converters for Front-end DC/DC Converters. In: Power Electronics Specialists Conference, 2008. PESC 2008. Rhodes: IEEE, 2008, pp. 250–256, ISBN 978-1-4244-16684. DOI: 10.1109/PESC.2008.4591934. [3] GONTHIER, L., F. BERNOT, S.D. BOCUS, S. ELBAROUDI and A. BERTHON. HighEfficiency Soft-Commutated DC/AC/AC Converter for Electric Vehicles. ELECTROMOTION. 1998, vol. 5, no. 2, pp. 54–64. ISSN 1223-057X. [4] BALA, S. and G. VENKATARAMANAN. Matrix Converter BLDC Drive using ReverseBlocking IGBTs. In: Twenty-First Annual IEEE Applied Power Electronics Conference and Exposition, APEC ’06. Dallas: IEEE, 2006, pp. 660–666. ISBN 0-7803-9547-6. DOI: 10.1109/APEC.2006.1620609. [5] DOBRUCKY B., M. PRAZENICA, M. A. R. ABDALMULA. Two-stage electronic system with two-phase orthogonal output using matrix converters. In: EDPE 2009: 15th International Conference on ELECTRICAL DRIVES and POWER ELECTRONICS - 4th Joint Slovak-Croatian Conference. Dubrovnik: TU Kosice, 2009, pp. 415– 419. ISBN 978-953-6037-55-8. [6] DOBRUCKY B., M. BENOVA, M. A. R. ABDALMULA and S. KASCAK. Design analysis of LCTLC resonant inverter for two-stage 2-phase power electronic supply system. In: EDPE 2011: 17th International Conference on ELECTRICAL DRIVES and POWER ELECTRONICS - 5th Joint Slovak-Croatian Conference. Stara Lesna: TU Kosice, 2011, pp. 182–187. ISBN 978-80-5530734-3. [7] ABDALMULA M. A. R. and B. DOBRUCKY. State-Space Analysis of 2nd - and 4th Order Resonant Filter LC and LCLC under Transient Condition. Aplimat-Journal of Applied Mathematics. 2011, vol. 4, no. 2, pp. 333–340. ISSN 1337-6365. [8] BENOVA M., M. A. R. ABDALMULA and B. DOBRUCKY. Modelling of the 4th Order Resonant Filters LCLC Considering Non-Linearities. Aplimat-Journal of Applied Mathematics. 2011, vol. 4, no. 1, pp. 173–180. ISSN 1337-6365. [9] ZASKALICKA, M., P. ZASKALICKY, M. BENOVA, M. A. R. ABDALMULA and B. DOBRUCKY. Analysis of complex time function of converter output quantities using complex Fourier transform/series. Communications: Scientific Letters of the University of Zilina. 2010, vol. 12, no. 1, pp. 23–30, ISSN 1335-4205. [10] IMBERTSON, P. and N. MOHAN. Asymmetrical duty cycle permits zero switching loss in PWM circuits with no conduction loss penalty. IEEE Transactions on Industry Applications. 1993, vol. 29, iss. 1, pp. 121–125. ISSN 0093-9994. DOI: 10.1109/28.195897. [11] BLALOCK, T. J. and N. MOHAN. The first polyphase system a look back at two-phase power for AC distribution. IEEE Power and Energy Magazine. 2004, vol. 2, iss. 2, pp. 63–66. ISSN 1540-7977. DOI: 10.1109/MPAE.2004.1269626. c 2013 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 249 POWER ENGINEERING AND ELECTRICAL ENGINEERING VOLUME: 11 |NUMBER: 4 |2013 |SEPTEMBER [12] BLAABJERG, F., F. LUNGEANU, K. SKAUG and M. TONNES. Two-Phase Induction Motor Drives. IEEE Industry Applications Magazine. 2004, vol. 10, no. 4, pp. 24–32, ISSN 1077-2618. DOI: 10.1109/MIA.2004.1311160. [13] BLAABJERG, F., F. LUNGEANU, K. SKAUG and M. TONNES. Evaluation of low-cost topologies for two phase induction motor drives, in industrial applications. In: Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344). Pittsburgh: IEEE, 2002, vol. 4, pp. 2358–2365. ISBN 0-7803-7420-7. DOI: 10.1109/IAS.2002.1042775. [14] KASSA, J. and M. PRAZENICA. New Concept of Two-Stage Two-Phase Orthogonal Converter with Two-Phase Motor. In: EDPE 2011: 17th International Conference on ELECTRICAL DRIVES and POWER ELECTRONICS - 5th Joint SlovakCroatian Conference. Stara Lesna: TU Kosice, 2011, pp. 188–193, ISBN 978-80-553-0734-3. [15] PRAZENICA M., J. KASSA and J. SEDLAK. Investigation of Power Losses of Two-Stage TwoPhase Converter with Two-Phase Motor. Advances in Electrical and Electronic Engineering. 2011, vol. 9, no. 2, pp. 77–83, ISSN 1804-3119. About Authors Mahmud Ali Rzig ABDALMULA was born in Eljamel, Libya. He received his M.Sc. from University of Zilina, Slovakia in 1995. He received the Ph.D. degree in Electrical Engineering from the same university in 2004. His thesis is focused on Shaft Sensorless Position Control of PMSM with Focus on Position Estimation at Zero and Low Speed. He is now Associate Professor at Faculty of Engineering/Sabrata, University of Zawia. His research interests include power electronic systems, electrical machines, simulation and computer analysis. c 2013 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 250