Simulation of Soft-Switched Three-Phase Inverter for RL and Induction Motor Load

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2 imulation of oft-witched Three-Phase Inverter for RL and Induction Motor Load Pratibha Thakur PG cholar epartment of Electrical Enineerin amrat Ashok Technoloical Institute Vidisha, (M.P) India anjeev Gupta Associate Professor epartment of Electrical Enineerin amrat Ashok Technoloical Institute Vidisha, (M.P) India Abstract In this paper a new Quasi-Resonant topoloy is proposed for soft-switchin of all threephase inverter switches for both positive and neative C link current. This soft-switched three-phase inverter is proposed for a frequency of 400 Hz. The topoloy consists of four switches, two resonant inductors, and a capacitor. It will provide zero voltae switchin condition for obtainin softswitchin in all inverter switches when the switchin frequency is exceedin the limit. The soft-switchin operation of inverter is explained in terms of modes for both positive and neative C link current. A simulation model of soft-switched three-phase inverter for RL and induction motor load is developed usin MATLAB software. Keywords: MATLAB, ZV, oft-witchin, Threephase, Inverter, MOFET 1. Introduction Inverter is a device which convert C power into AC power at desired output voltae and frequency by usin power electronic devices. When the power switches of conventional pulse width modulated (PWM) inverter operate in switch mode so that due to hard switchin durin turn on and turn off process, the power electronic device has to withstand hih current and voltae simultaneously resultin hih stress and switchin power losses, These switchin losses is proportional to switchin frequency of PWM inverter, thus limitin the switchin frequency of conventional PWM inverter. When switchin power losses are increases the efficiency of inverter is reduce and also lare amount of heat produce inside the inverter, which forces to use larer heat sink for industrial personnel which causes volume and weiht of the system is increased and also system suffer from EMI. Today soft-switchin technique is very important in modern technoloy. In this technique zero voltae and zero current switchin were used which improved the performance as compared to hard-switched PWM Inverter [1]. oft switchin technique developed from load resonant to quasi resonant reported in [2-5]. In quasi-resonant technique resonant network is activated durin resonant interval to enable soft-switchin [5]. Quasiresonant C link for voltae source inverter have been reported in [5-10]. A two switch resonant link inverter is reported for operates with unity power factor load [5]. A two switch quasi-resonant topoloy havin displacement factor equal to 0.88 lein can be handle passive load [7]. A resonant snubber based topoloy in [8] is proposed for active and passive load. The modify topoloy of quasi-resonant technique [9], this modify topoloy has a limitation which restrict hih power factor load operation. A current controlled soft-switchin inverter which provides ood sinusoidal waveform of current for induction machine in [10]. All above reported topoloy of the quasiresonant link inverter have some limitation so that in this paper presented a new versatile quasi-resonant topoloy which provide soft-switchin of all threephase inverter switches for both positive C link current and neative C link current and also overcome the limitation of the above discussed topoloies. This topoloy can handle low as well as hih power factor active and passive load. The complete quasi-resonant soft-switched three phase inverter for RL and Induction motor load is simulated usin a MATLAB simulator. Typical simulation result of RL load and Induction motor load is presented in this paper. 2408

3 2. Proposed Topoloy The proposed quasi-resonant topoloy for three phase inverter of 400 Hz or 50 Hz is shown in Fi.1 which provides soft switchin at the hih rane switchin frequency. The resonant tank as shown in Fi.1 consist of main switch (W M ), auxiliary switch (W A ), two shunt switch ((W 1 - H ) and (W 2 - H )), two resonant inductor (Lr and L H ) and resonant capacitor C r. o this resonant network is activated durin resonant interval to enable soft-switchin transition. This soft-switchin transition is implemented by usin zero-voltae transition. The circulatin enery associated with soft-switchin transition due to resonance is quite small. The resonant components which are used in this topoloy involved with load current only durin the resonant interval and out of operation durin non-resonant interval. The C link voltae is always clamped to the source voltae in this topoloy. ince the resonant component are involved only durin a small interval of switchin cycle. The size and VA ratin of these resonant components become quite small. This topoloy provide soft-switchin operation when the link current is positive it means C link current flow from resonant tank to inverter and also provide soft switchin operation when the C link current is neative it means C link current flow from inverter to resonant tank. In this topoloy the C link current is denoted by l Link. In a switchin cycle this C link current is assumed to be ripple free. so that there are two operation one in which C link current is positive (i.e. resonant tank to inverter) and other operation where C link current is neative (i.e. inverter to resonant tank). Fiure 2. Initial condition under positive C link current Fiure 3. witchin waveform under positive C link current Fiure 1. Proposed Quasi-Resonant softswitched three phase inverter 3. Operatin principal Paper proposed quasi-resonant topoloy which provide soft-switchin of all three phase inverter switches and also provide soft-switchin operation in independent direction of C link current 2.1 Case I: The C Link Current is Positive The C link current is positive it means that link current flow from resonant tank to inverter and load. Fi.2 shows the initial condition under positive link current at this condition resonant capacitor clamped to source voltae and only main switch was conduct. For obtainin soft-switchin of three-phase inverter switches the circuit oes throuh various modes of operation, shows in Fi. 3 various modes of operation switchin waveform. MOE I (t o -t 1 ) This mode is started when the ate sinal to main switch W M is withdrawal at to. urin small interval of this mode resonant capacitor dischares to zero, because of zero-voltae diode which is antiparallel across the inverter switches et forwardbiased. At the instant of ZV, switchin status of inverter is chaned. End of this mode at t 1 ate pulse to auxiliary switch is released. The circuit topoloy of this mode is shown in Fi. 4(a). 2409

4 MOE II (t 1 - t 2 ) At startin of this mode auxiliary switch is turn-on. Current increases linearly from zero when flowin throuh the resonant inductor Lr, while the current which is flowin throuh diode in the inverter decreasin. At the end of this mode resonant inductor current is equal to link current and also the current becomes zero which is flowin throuh the antiparallel diodes of inverter switches. The circuit topoloy of this mode is shown in Fi. 4(b). MOE III (t 2 - t 3 ) This mode starts at t 2 with charin capacitor C r because resonance of L r and C r and the. Voltae across the C link / resonant capacitor C r radually increases from zero to source voltae V C.The resonant inductor current is equal to the sum of the link current and charin current of capacitor C r. ue to resonance of L r and C r link voltae is further increases causes diode p to be forward-biased. End of this mode at t 3 main switch is turned on and auxiliary switch is turned off. The circuit topoloy of this mode is shown in Fi. 4(c). MOE IV (t 3 - t 4 ) This mode starts at t 3 with turned on with main switch and turned off with auxiliary switch. When current in the resonant inductor rater then the C link current, the excess current which is more than the link current is flowin throuh the diode p. At the end of this mode at t 4 current in the resonant inductor is equal to load current. The circuit topoloy of this mode is shown in fi. 4(d). (a) MOE I (b) MOE II MOE V (t 4 - t 5 ) This mode starts at t 4 with turned off of diode p and main switch W M at the same time stats conductin. Now current in the Link is a some of the main switch current and current in the resonant inductor Lr. End of this mode at t 5 main switch W M conducts total link current and enery which is stored in resonant inductor is recovered. The circuit topoloy of this mode is shown in Fi. 4(e) which is chanes in to initial state and same mode is repeated. (c) MOE III 2410

5 (d) MOE IV Fiure 5. witchin waveform under neative C link current (e) MOE V Fiure 4. Modes under positive C link current (a) Mode I (b) Mode II (c) Mode III (d) Mode IV (e) Mode V 3.1 Case II: The C Link Current is Neative When the C link current is neative under these condition link current is flowin from inverter to resonant tank (i.e. neative). For neative C link current durin soft-switchin of inverter switches circuit oes throuh various modes of operation. The switchin waveform of ate pulse to shunt switches, resonant capacitor voltae and shunt inductor current are shown in the Fi. 5. The circuit topoloy of initial condition under neative link current is shown in fi 6. Initially due to conduction of diode p C link voltae is clamped to source voltae and all the switchin devices are off state in the resonant tank. Fiure 6. Initial condition under neative C link current Now explain each mode which shows how switchin status of inverter devices is chaned when C link current is neative. MOE I (t 0 - t 1 ) This mode starts at t 0 with release of ate pulse to shunt switches ( W 1-H, W 2-H ). In this mode dc-link voltae is clamped to the source voltae. hunt inductor current i Lsh linearly starts increasin from zero. In this mode C Link is the sum of current in shunt inductor i Lsh and current in diode p. At the end of this mode shunt inductor current equal to load current and diode p turn-off. The circuit topoloy of this mode is shown in Fi. 7(a). 2411

6 MOE II (t 1 - t 2 ) This mode starts at t 1 with turn off of diode p and discharin of resonant capacitor C r. current in the shunt inductor is sum of the discharin capacitor current and dc-link current. At the end of this mode t 2 the resonant capacitor C r dischares to zero voltae. The circuit topoloy of this mode is shown in Fi. 7(b). MOE III (t 2 - t 3 ) This mode starts at t 2 with discharin of resonant capacitor to zero voltae, at this instant switchin status of inverter devices is chaned under ZV and diode 1H et forward-biased throuh W I-H because of enery in the shunt inductor L sh. The current which is flowin throuh diode 1-H is the difference between dc link current and shunt inductor current. hunt inductor current i Lsh is conducted by the switch W 2-H. End of this mode at t 3 ate pulse from shunt switch is released W 1-H and W 2-H is released. The circuit topoloy of this mode is shown in Fi. 7(c). MOE IV (t 3 - t 4 ) This mode starts at t 3 with withdrawal of ate pulse from the shunt switches W 1-H, W 2-H. hunt inductor enery recovered to source throuh diode 1-H and 2-H so that conduction of diode 1-H and 2-H.The shunt inductor current decay to zero simultaneously resonant capacitor chared with dc link current. End of the mode at t4 resonant capacitor voltae equal to source voltae. The circuit topoloy of this mode is shown in Fi. 7(d). iode p conduct full C link current when becomes forward biased. (a) MOE I (c) MOE III (b) MOE II (d) MOE IV Fiure 7. Modes under neative dc link current (a) Mode I (b) Mode II (c) Mode III (d) Mode IV 2412

7 4. imulation Result The Proposed soft-switched three phase inverter has been simulated for RL and induction motor load usin MATLAB. Fundamental frequency of 400 Hz, switchin frequency of link is 40 KHz and modulation index of 0.9 are used. In Quasi-Resonant topoloy resonant parameters of small size and weiht are used L r = 1µH, L sh = 0.5µH, C r = 50nF. The source voltae is 150 V C. ue to hih frequency and low power operatin capability MOFET is selected as power switch in proposed soft-switched inverter. Gate pulse for main and auxiliary switch is iven from two pulse enerator and these pulses are iven such that when main switch is on auxiliary switch is off. Gate pulse for two shunt switches are iven from one pulse enerator because these two shunt switches are on at same time. Gate pulse for three-phase inverter switches is iven from discrete PWM enerator. Voltae across the resonant capacitor providin zero voltae switchin, when zero voltae condition is obtained across resonant capacitor switchin status of inverter device is chaned. Fiure 8. Voltae across the resonant capacitor The proposed quasi-resonant topoloy provide zero-voltae switchin condition across the resonant capacitor for obtainin soft-switchin in all inverter switches so now shown in Fi.8 zero voltae switchin waveform across the resonant capacitor C r. 4.1 For RL load For RL load R=5Ω, L= 5mH and source voltae of 150V C is taken. Fundamental frequency, switchin frequency, and modulation index were 400 Hz, 40 KHz and 0.9 taken respectively. Fi 9 shown simulation model of softswitched three-phase inverter for RL load and threephase current and voltae wave form shown in Fi.10 when RL load is used. 2413

8 A B C A B C imulation circuit witechin Voltae iscrete, Ts = 1.5e-005 s pow erui [M] m main switch [H] [A] auxilary switch shunt switch v Vin [H] + v - A B C Vabc Iabc a b Three-Phase V-I Measurement Three-Phase eries RL Branch c shunt switch2 [M] [H] NOT [A] Main switch Pulse [M] [A] hunt switch Pulse [H] Auxilary switch Pulse Loical Operator Unit elay 1 z Pulses iscrete PWM 6 pulses Fiure 9. imulation model of soft-switched three-phase inverter for RL load imulation result for RL load Fiure 10. Three phase current and voltae waveform for RL load 2414

9 4.2 For Induction motor load For Induction motor load source voltae of 150V C is taken. Fundamental frequency (400Hz) and switchin frequency (40 Khz) at modulation index 0.9 are considered. Fi11 showed simulation model of soft-switched three phase inverter for imulation circuit induction motor load and three phases current and voltae waveform in Fi.12 when Induction motor load is used. The current waveform is found sinusoidal. iscrete, Ts = 1.5e-005 s pow erui [M] m main switch [H] [A] auxilary switch shunt switch v Vabc A Iabc B a b C c 1 Constant Tm A B m + - v Vin [H] C shunt switch2 [M] [H] NOT [A] Main switch Pulse hunt switch Pulse Auxilary switch Pulse [M] [A] [H] Loical Operator 1 Pulses z iscrete PWM 6 pulses Fiure 11. imulation model of soft-switched three-phase inverter for induction motor load imulation result for Induction motor load Fiure 12. Three phase current and voltae waveform for Induction motor load 2415

10 5. Conclusion In this paper a soft-switched three-phase inverter is simulated in MATLAB for RL and Induction motor loads. The switchin sequence of various switches in the resonant link is allowed softswitchin of switches in the three-phase inverter. This soft-switchin is ensured independent of C link current direction by the quasi-resonant topoloy and its control stratey. The proposed quasi-resonant topoloy is attractive over other topoloy as it can work for both RL and induction motor loads.these soft-switched three-phase inverter is operated at hih frequency and resonant component of small size and weiht are used which is attractive for airborne power supplies. 6. References [1]. M. ivan, A resonant dc-link convertera new concept in static power conversion ", IEEE Trans. Ind. Appl., 1989, 25, (2), pp [2] Mohan, N., T. Undeland, and W. Robbins, Power electronics converters, applications and desin (John Wiley and sons, inapore. 1995). [3] M.. Bellar, T. Wu, A. Tchamdjou, J. Madhabi, and M Ehsani, A review of softswitched dc-ac converters, IEEE Trans. Ind. Appl.,1998, 34, (4), pp [4] V. V. eshpande and. R. oradla, A new topoloy for parallel resonant dc-link with reduced peak voltae, IEEE Trans. Ind. Appl., 1996, 32, (2), pp [5] K. Wan, Y. Jian.. ubovsky, G. Hua.. Boroyevich, and F. C. Lee, Novel dc-rail soft-switched three-phase voltae source inverters, IEEE Trans.Ind. Appl.,1997, 33, (2), pp [6] J. un and K. Nam, A simple dc-rail softswitched voltae source Inverter, IEEE PEC Conf Rec.,1998, pp [7] B. J. C Filho and T. A. Lipo, pace-vector analysis and modulation issues of passively clamped quasi-resonant inverters, IEEE Trans. Ind. Appl., 1998, 34, (4), pp [8] J.. Lai, Resonant snubber-based softswitchin inverters for electric propulsion drives, IEEE Trans. Ind. Appl., , (1) pp [9]. Behera,.P. as, and. R. oradla, esin, simulation and Implementation of a quasi-resonant dc-ac converter with improved performance. IEEE PE Conf Rec, 2001, pp [10]. Andrade, R. M. F Neto, L. C. Freitas, J. B. Vieira, and V. J. Farias, A soft-switched current-controlled converter for induction machine drives, IEEE Trans. Power Electron., 2001, 16, (1), pp