l1-i VEL SINGLE-PHASE ZCS-PWM HIGH POWER FACTOR BOOST RECTIFIER IVO Barbi Carlos A. Canesin

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1 VEL SINGLE-PHASE ZCS-PWM HIGH POWER FACTOR BOOST RECTIFIER Carlos A. Canesin Paulista State University UNESP - FEIS - DEE - P.O. box 31 Fax: (+55) canesin@feis.unesp.br Ilha Solteira (SP) BRAZIL Abstract - This paper presents a novel single-phase high power factor PWM boost rectifier, featuring soft commutation of the active switches at zero-current (ZCS). It incorporates the most desirable properties of the conventional PWM and the softswitching resonant techniques. The input current shaping is achieved with average current mode control, and continuous inductor current mode. This new PWM converter provides ZCS burn-on and turn-off of the active switches, and it is suitable for high power applications employing IGBTs. Principle of operation, theoretical analysis, a design example, and experimental results from a laboratory prototype rated at 1600W with 400Vdc output voltage are presented. The measured efficiency and power factor were 96.2% and 0.99 respectively, with an input current THD equal to 3.94%, for an input voltage THD equal to 3.8%, at rated load. I. INTRODUCTION In the last years there have been increasing demands for high power factor and reduced harmonic distortion in the current drawn from the utility, specially when the forthcoming harmonic standards, such as IEC-555-2, must be satisfied. Therefore, in these applications, ACDC converters featuring almost unity power factor have been required. A variety of circuit topologies are available for powerfactor correction, and among the usually employed in singlephase power supplies are the boost derived topologies. The constant switching frequency average current control is the most recommended control technique to achieve high input power factor [l]. On the other hand, soft-commutation techniques have been of great interest for power quality in switching power supply applications. However, with few exceptions, circulating reactive energy that causes large conduction losses, and frequency modulation are two well known drawbacks [2 and 31. The zero-voltage switching (ZVS), and zero-voltage transition (ZVT) techniques are naturally recommended for MOSFETs. However, for high power applications (above 1kW) IGBTs are preferred when compared with power MOSFETs, which present much higher conduction losses than IGBTs. Furthermore, the turn-off losses are still a major part of the total switching losses in IGBTs, and zero-current switching (ZCS), or zero-current transition (ZCT) operation are most effective for IGBTs [4 and 51. IVO Barbi Federal University of Santa Catarina UFSC - INEP - P.O. BOX FAX: (+55) inep.ufsc.br Florian6polis (SC) BRAZIL In order to improve the efficiency even more and reduce the heat sink size, this paper presents a new principle to achieve zero-current switching at constant frequency in a power factor correction rectifier with average current control, using IGBTs. 11. THE NOVEL TOPOLOGY AND PRINCIPLE OF OPERATION Figure 1 shows the new single-phase ZCS-PWM high power factor boost rectifier. The commutation cell of this new boost rectifier is formed by two switches Sp (main switch) and Sa (auxiliary switch), two diodes Dl and 02, two small resonant inductors Lrl and Lr2, and one resonant capacitor Cr [6]. Vin I1 I l1-i II I I corn Current ensat,, PWM control Voka e 3854 compensator voltage reference Fig, 1 - The novel single-phase ZCS-PWM HPF boost rectifier. t vo Rload In order to explain the operation of this new converter and quantify their behavior, the following conditions are assumed: - all components are ideal; - the converter is operating in steady-state at a fixed switching frequency (f.7);- the input voltage (Vin) is a sine-wave, and the output voltage (V,) is constant; - the switching frequency is much higher than the AC line frequency (fun,), and the input filter (L) is large enough to be approximated by a current source (Ilin I), during a generic switching period (r). Figure 2.a shows the nine topological stages of the commutation for the simplified ZCS-PWM HPF boost rectifier, and Figure 2.b shows the main ideal waveforms, during a generic switching period /97/$10.00 Q 1997 IEEE 110

2 As can be seen in Figure 2, the main switch Sp starts conducting at t = to, and the auxiliary switch Sa at t = t2, both in zero-current switching (ZCS). Both switches turn off simultaneously during the time interval At6 = t6 - t5, in zerocurrent (ZCS) and zero-voltage (ZVS) switching. It should be noticed that the diodes DI and 0 2 are also softly commutated under zero-voltage switching, and from Figure 2, it can be seen that only during the switching intervals the: zero-current switching transition takes place, and the ZCS time interval AT is a small fraction of the switching period. The time interval AT depends on the resonant parameters, and it is independent of the output power ANALYSIS OF COMMUTATION In order to achieve soft-commutation at zero-current switching for both active switches (Sp and Sa), for the described operation mode, the following inequalities sbould be satisfied. Zi, =I Peak input current value; Pout == Nominal output power; q = Minimum value of efficiency, and Vjnf rms,min = Minimum rms input voltage value. The time interval AtoR to turn off the switches Sp and Sa simultaneously, is governed by equation (05). So, the time interval AT for the control of the auxiliary switch is defined by equation (06). Thus, r.- and, Where: liin I1 id Fig. 2 - (a)topological stages, and (b)main ideal waveforms, for the simplified ZCS-PWIM HPF boost rectifier, during a generic switching period. 111

3 IV. DESIGN PROCEDURE AND EXAMPLE W Step 5: The boost input inductance (L), and output filter The design procedure and example of the new ZCS-PWM capacitance (CO). HPF boost rectifier, is described as follows: With the parameters shown in the above steps, the boost H SteD 1: Input and output data specifications. inductance value L, and the output filter capacitance value C, vi,(m, = 220~ (nominal rms input voltage); to achieve the output ripple voltage less than 2%, are specified as follows: Vin( rm jmin = 187V V, = 400V ; Pout = 1600W ; L = 1mH, and C, = 680pF. 7 = 0.95(minimum value of efficiency), and f, = 20kHz. Figure 3 shows the implemented circuit of the new single- H Step 2: Peak input currente ( Zin,). The peak input current value (I,,,) is given by equation phase ZCS-PWM HPF boost rectifier. V. EXPERIMENTAL RESULTS (04). With the parameters shown in Step 1, we obtain: Figure 4 shows the photograph of the test unit for the new Zinp =12.7A. single-phase ZCS-PWM HPF boost rectifier. Step 3: Calculation of the resonant parameters. Figures 5.a and 5.b show the commutation of the main In order to minimize the influence of the resonant switch SP, near Vin( t )= 0, and near vin( t )= Vp respectively, parameters, and to satisfy the constraints for this operation at full load. Figures 5.c and 5.d show the ~m"mtation of the mode, equations (01) and (03), we selected: auxiliary switch Sa, near Vi,( t )= 0, and near Vi,( t )= Vp fs p = 0.6 ; amuz = 0.55, and - = 0.2. f0l 001 Where: f0l =z (10) Therefore, with these parameters and equations (Ol), (03), and (lo), we can obtain the resonant parameters. Thus, Lr,=46.6pH; Lr2=28pH,and Cr=94nF. H Step 4: Time interval (AT). The time interval for the control of the auxiliary switch (AT) is given by equation (07). Thus, AT = 7. 7 ~ ~ respectively, at full load. Figures 6.a and 6.b show the voltages and currents through diodes D1 and 02, also at full load. It can be seen that the results shown in Figures 5 and 6 are in agreement with the theoretical analysis. Furthermore, the results shown in Figures 5 and 6 demonstrate that zero-current switching is achieved at constant frequency for both active switches (Sp and Sa), and the diodes Dl and 02 were also softly commutated, under zero-voltage switching. Figure 6 demonstrates that recovery problems do not exist due to diodes Dl and 02. Therefore, the switching energy losses for this new ZCS-PWM boost rectifier are practically zero. Fig. 3 - Implemented circuit of the new single-phase ZCS-PWM HPF boost rectifier. 112

4 f Fig (c)near V,,( t)= 0 (d)near VLn( t ) = Vp voltage: IOOV/div, current: SMdiv, time scale. IOuddiv Voltage across Sp and current through Lrl, (a)nearv,,( t )= 0, and (b)near Vi,( t )= Vp; Voltage across Sa and current through Lr2, (c)nearv,,( t ) = 0, and (d)n (a) (bj voltage. IOO'V/div; Current: SMdiv, time scale: IOu.ddiv. Fig. 6 - (a)voltage and current through DI, (b) Voltage and current through 02, at full load. 113

5 E f i C 1 oc i e n c 95 Y I I I 9C Output Power (Wp600 (a (b) Fig. 7 - (a)lput voltage and current (voltage: IOOV/div; current: loa/div, time scale: 2ms/div), and (b)experimental efficiency. The input voltage and input current for the prototype operating at 1600W are presented in Figure 7.a. This result demonstrates that the power-factor is practically near of the unity (0.99) for full load, and the input current THD is equal to 3.94% for an input voltage THD equal to 3.8%. Figure 7.b shows the efficiency measurement of the new ZCS-PWM high-power factor boost rectifier as function of the output power, and it is equal to 96.2% for rated load. Therefore, the new ZCS-PWM technique significantly improves the circuit efficiency, providing a great reduction in the heat sinks size used. VI. CONCLUSION This paper has presented a novel single-phase ZCS-PWM high-power factor boost rectifier, rated at 1600W. Theoretical studies and experimental results for this new ZCS-PWM boost rectifier, allow us to draw the following conclusions: High-power factor is achieved through average current control for a wide load and wide input voltage range. The total harmonic distortion of the input current is very low, and it is in agreement with IEC-555-2; Soft-commutation (ZCS) is achieved for the active switches, from non-load up to full load; The passive switches (01 and 02) were also softly commutated (ZVS); w The converter is regulated by the conventional PWM technique, at constant frequency; Latching of IGBTs due to turn-off never occurs, this relieves it s RBSOA stresses; Low conduction losses are verified in the devices, in spite of an additional diode in series with the load; The converter is able to provide efficiency above 96% for a wide load. Thus, providing a great reduction in the heat sinks size. Therefore, this new ZCS-PWM HPF boost rectifier combines the advantages of the PWM and ZCS techniques, without additional current and voltage stresses, in comparison with the conventional hard-switching method, improving the converter performance, and maintaining high efficiency. ACKNOWLEDGMENTS C. A. Canesin would like to thank to INEP-UFSC, FEIS- UNESP, and CNPQ for supporting this work. REFERENCES [ 11 C. Silva, Power factor correction with the UC3854, Application note U-125, Unitrode Corporation, April-1990, pp [2] I. Barbi and S. A. 0. da Silva, Sinusoidal line current rectification at unity power factor with boost quasi-resonant converters, IEEE APEC Records, 1990, pp [3] G. Hua and F. C. Lee, Soft-switching techniques in PWM converters, IEEE IECON Records, 1993, pp [4] K. Wang, G. Hua and F. C. Lee, Analysis, design and experimental results of ZCS-PWM boost converters, IEEJ IPEC Records, 1995, pp [5] C. A. Canesin and I. Barbi, Comparison of experimental losses among six different topologies for a 1.6kW boost converter, using IGBTs, IEEE PESC Records, 1995, pp [6] C. A. Canesin and I. Barbi, Novel zero-current-switching PWM converters, IEEE Transactions on Industrial Electronics, in press. 114