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A Single-phase Bidirectional Rectifier With Power Factor Correction Bor-Ren Lin Member IEEE and Zong-Liang Hung Abstract- A single-phase rectifier based on the conventional two-level full-bridge rectifier and one AC power switch is proposed. The voltage stress of the full-bridge rectifier is equal to the DC bus voltage, but AC power switch has a voltage rating of half DC-link voltage. The control signals of the rectifier switches are derived , from the voltage balance compensator, current controller and detected operation region of mains voltage. A novel PWM control scheme is proposed to draw a clean sinusoidal line current with high power factor. Three-level P W M pattern is generated on the AC terminal of the adopted rectifier converter by using the proposed control scheme. To verifi the proposed operation strategy, performance characteristics are provided by the computer simulations. Index Terms-Power of power factor correction and reversible power flow. The pulsewidth modulation (PWM) control scheme is proposed to generate a multilevel voltage waveform on the AC side of adopted rectifier and draw a sinusoidal line current. To control the AC source current, the hysteresis current controller is adopted in the inner loop control. A voltage balance compensator is added to the line current command so as to maintain the neutral point voltage in the desired reference voltage. A proportional integral controller is employed in the outer loop control to maintain the constant DC-link voltage. To verify the validity of the proposed control strategy, the computer simulations are provided and discussed. factor correction, PWM rectifier. L INTRODUCTION 0 wing to power converters widely used in the industry products, serious power pollution is produced in the distributionnetwork. High current harmonics, low power factor (0.5-0.9) and high pulsating current generated from the diode rectifiers (nonlinear loads) are the main power pollution. One of the most important issues of the power electronic designer is the reduction of current or voltage harmonics created by the converters. Passive filter is often used to improve the power quality for its simple circuit configuration. Main drawbacks of this configuration are bulk passive elements, fixed compensation characteristics and series or parallel resonance. Active single-phase [ 1-41and three-phase [5-101 rectifiers have been proposed to draw a nearly sinusoidal line current. For high voltage or high current applications, power semiconductors with high voltage or high current stress are generallyrequired in the conventional two-level rectifiers. The series or parallel connections of power semiconductors can achieve high voltage or high current applications. Multilevel scheme provides a greater number of advantages over the conventional schemes especially for high power or medium voltage applications [l l-151. The advantages of multilevel converters over the two-level convertersare improved voltage waveform on the AC side, smaller filter size, lower switching loss, lower electromagnetic interferenceand lower acousticnoise. However, this scheme can be easily applied to medium and low power applications. This paper presents a single-phase rectifier with the function Bor-Ren Lin and Zong-Liaug Hung are with the Electrical En&eering Department,National Yunlin Univmity of Science and Technology,Yunlin 640, Taiwan, ROC (e-mail:linbr@pine.yuntech.edu.tw) IEEE Catalogue No. 01CH37239 0-7803-71 01- I / 01 / $1 0.00 0 2001 IEEE. @) Fig. 1 Conventionalfull-bridge rectifier (a) circuit configuration (b) PWM waveform on the AC side. II. SYSTEM DESCRIPTION Fig. 1 shows a conventional two-level full-bridge rectifier and its PWM waveform. Power switches are controlled to generate a two-level voltage waveform on the AC side in each half cycle of line frequency. In the positive mains voltage, voltage levels v, and 0 are generated. On the other hand, voltage levels -v, and 0 are achieved in the negative half cycle. Because the multilevel voltage approaches the sinusoidal signal closer than the two-level voltage waveform. A three-level PWM rectifier as shown in Fig. 2 is employed to achieve power factor correction. The power circuit of the adopted rectifier is constructed by adding an AC power switch to the conventional 111-bridge rectifier. The AC power switch is built with two unidirectional power switches connected in series. The neutral point voltage on the DC-link is controlledby AC power switch S to adjust the neutral point current io. If the average neutral point current io,m in one line frequency is zero, then the neutral point voltage is equal to half DC-link voltage, i.e. vl=vz=vJ2. By the appropriate control, five different voltage levels, v,, vJ2, 0, 601 Authorized licensed use limited to: UNIVERSITY OF NOTTINGHAM. Downloaded on March 07,2022 at 08:27:55 UTC from IEEE Xplore. Restrictions apply. 4 2 , -vo, are generated on the AC terminal of the adopted rectifier. Power switches TI-T4 have a voltage rating of v, and AC power switchShave a voltage rating of vd2 which is a lower cost device than switches TI-T4. L L The voltage vab generated by the rectifier can be expressed as (7) vab = vao -vbo . Substituting( 5 ) and (6) into (7), voltage v d is given as L L L L Table 1 Valid switching states and the corresponding voltage vab. (b) Fig. 2 Proposed three-level PWM rectifier (a) circuit configuration(b) PWM waveform on the AC side. - Fig. 3 Simplified circuit of the adopted rectifier. III. OPERATION PRINCIPLE To achieve a clean sinusoidal line current with low current distortion and low total harmonic distortion (THD) of P W M waveform, power devices of the adopted rectifier are switched on or offaccordingto the line currenterror and the sign of mains voltage. The voltage v d generated by the rectifier depends on the switching states of the power switches. Some constraints of power switches are defined so as to avoid the power switches in each rectifier leg conducting at the same time TI +T2 +S=I, (1) T3+ T4=1, (2) where Ti (or S) =1 if switch Ti (or S) is on, or Ti (or S)=O if switch Ti (or S) is off, i=l, 2, 3, 4. The equivalent switching functionin each rectifier leg is shown in Fig. 3 and defined as 1 if T1 (or 01)is turned on 1={ if Sisturnedon , - 1 if T 2 (or 0 2 ) is turned on fa= 0 1 if T3 (or 0 3 ) is turned on fb - 1 if T 4 (or 0 4 )is turned on (3) (4) The relationshipsbetween the equivalent switching functionsf, and& and the voltages v, and vb, are given as If capacitor voltages V I and vz are equal, i.e. AFO, then there are five different voltage levels, v,, vd2,0, -vd2, -vo, on the voltage vd as shown in Table 1. The valid switching states of power switches and the corresponding voltages on the AC side of rectifier are shown in Table 1. There are six valid switching states in the adopted rectifier. Two switching states of power switches generate voltage vab=o. By the combinations of power switches, five different voltage levels are generated by the rectifier. The switching states of the rectifier and the corresponding equivalent circuits are shown in Fig. 4. In the first operation mode, power switches TI and T4 are turned on to achieve voltage vo on the ac side. Positive line current charges both capacitorvoltages vI and v3 Line currentis decreasedbecause the boost inductor voltage is negative. Power switches S and T4 are turned on to generate voltage level vz on the AC side in the second operation mode. Capacitor voltage v2 is charged by the positive line current. Line current is linearly increasing or decreasing if the mains voltage is greater or less than capacitor voltage v2. In modes 3 and 4, voltage vd equals zero. The boost inductor voltage is equal to v,. The line current is increasing or decreasing according to the sign of mains voltage. In mode 3, power switches T2 and T4 are turned on. In mode 4, power switches TI and T3 are turned on. The dc load current discharges two capacitor voltages. Voltage vd equals -vI in operation mode 5. The boost inductor voltage is equal to vs+vl. Capacitor voltage V I is charged by the negative line current. The line current is increasing (or decreasing)if the mains voltage greater (or less) than -vl. In the last mode, power switches T2 and T3 are turned on to achieve voltage -v, on the ac side. Negative line current will charge both capacitor voltages vI and vz. Line current is controlled to increasing because the boost inductor voltage is positive. In the positive half cycle of mains voltage, the power switch T4 is turned on and the voltage vb, is equal to -vz (=-vd2).TO 602 Authorized licensed use limited to: UNIVERSITY OF NOTTINGHAM. Downloaded on March 07,2022 at 08:27:55 UTC from IEEE Xplore. Restrictions apply. generate voltage level vI+vz (mode l), power switch TI is tumed on and line current is decreasing. In this case, the line current charges both DC-link capacitors. Power switches S and T4 are turned on to generate vd=vz (mode 2) The line current will compensate voltage vz in this switching state. The line current is increasingor decreasing if the mains voltage is greater or less than capacitor voltage vz. If power switches T2=T4=1, the voltage vab is shorted and line current is linearly increasing. In this positive half cycle, three voltage levels v,, vJ2 and 0 are generated. During the negative half cycle of mains voltage, the rectifier generates another three voltage levels 0, -vJ2 and -vo on the AC side. The switch T3 is turned on in this half cycle and voltage vh=vl (=vJ2). The power switch TI, S or T2 is tumed on to achieve voltage vd=O, -vJ2 or -vo respectively (assumed vl=vz=vJ2).In the proposed operation principle, the switching frequency of switches T3 and T4 is equal to the line frequency. The Kirchhoff law applied on the AC side of rectifier can obtain di, v, = r i , + L - + v * . (9) dt The instantaneous power at the ac and dc sides of the rectifier is equal. 4tl= c u t (12) v*i, = vlil - v2i2. (13) According to (8), the currents il and iz on the DC side based on (13) can be given as L L The neutral point current io can be expressed in terms of the switching functionsf, and&. io = -il - i2 = -<f; - f; )is = (1 - f a2 )is (16) wheref,=l, 0 or -1, andfb=l or -1. The DC side currents can also be expressed as the function of load current amd two capacitor voltages. dvl vl +v2 il = C - + dt R ' d. 2 VI +v? i2 = -C--dt R Substituting(17) and (18) into (16), the neutral point current is expressed as This equation gives . L,r f. (4 (f) Fig. 4 Operation mode of the adopted rectifier (a) mode 1 (b) mode 2 (c) mode 3 (d) mode 4 (e) mode 5 ( f ) mode 6. According to (8), (9) can be derived as dis 1 . +K . (20) C This means that a DC component in the neutral point current io can be used to balance the dc side voltages. AV = (VI fa-fb vo + f2-f; vs=ris+L-+dt 2 2 If the capacitor voltages on the DC side are balanced, ( 1 0) can be rewritten as v, =ri, + L -dis + - f a -f b ( 1 1) dt 2 If the power switches are considered idea. There is no power loss and energy storage during the instantaneous commutation. " ' -vZ) = --Jlodt T3 I T4 I 1 Fig. 5 Operation region and the corresponding switch gating signals. IV. CONTROL STRATEGY Two operation regions of mains voltage during one cycle of the input line frequency are defined to generate a three-level voltage pattern. These operation regions and the corresponding PWM voltage waveforms are shown in Fig. 5 and Table 2. There is one high voltage level and one low voltage level in each operation region. In the positive half cycle of mains 603 Authorized licensed use limited to: UNIVERSITY OF NOTTINGHAM. Downloaded on March 07,2022 at 08:27:55 UTC from IEEE Xplore. Restrictions apply. voltage,power switch T4 is turned on and power switches TI (or T2) is turned off in the first (or second) region. Mode 1 and mode 2 are employed in the second region, and mode 2 and mode 3 are used in the first region. Three voltage levels v,, vd2 and 0 are generated on the AC side voltage vd. For the negative mains voltage, switch T3 is turned on and power switches T2 is tsuned off in the first region and switch TI is turned off in the second region. Similarlyvoltage levels 0, -vd2 and -v, are given on the voltage vd. T 4 = -fb(h-1) 2 ' (28) S = l - f,". (29) If capacitor voltages v1 and v2 are equal, then there are five voltage levels (v,, vd2,0, -vd2, -vo)on the voltage v ~ . Table 3 Control strategy of the adopted three-level PWM Table 2 Operation regions and the correspondingvoltage level - vo Low Level The goals of control strategy for the three-level PWM rectifier are sinusoidal line current with unity power factor, constant DC-link voltage and balance capacitor voltages. Generally the time-shift or voltage-shift triangle waves and the modulating wave are compared to generate properly multilevel P W M waveforms. Fig. 6 shows the control blocks of the adopted rectifier. A proportional-integral(PI) voltage controller is employed in the outer loop control to maintain the constant DC link voltage. The line current command is derived from the output of PI controller and the phase-locked loop circuit. The reference mains current is i: = (k,Av, + kiJ Av,dt) .%, v, switch Gating Signals T4 SI I v2 Fig. 6 Control block diagram of the adopted rectifier. (21) where V , is the amplitude of the mains voltage. The phase-locked loop generates a unit sinusoidal wave in phase with mains voltage. The phase shifter, phase detector, counter and digital-to-analog converter are used in the phase-locked circuit. To balance the DC link voltage, the voltage gap v1-v~is added to the line current command. A current controller is adopted in the inner loop control to track the line current command. Many PWM schemes for multilevel convertershave been proposed [16]. In the proposed control scheme, three control signals dI-d3 are employed to generate a three-level voltage waveform on the AC terminal of the rectifier. These control signals are d l =0, if v,>O; or I, if vs<O, (22) d2=0, if o<lvsl<vJ2;or I, if lvsl>v,J2, (23) d3=0, if Ai,>h; or I, if Ai, <-h. (24) According to three control signals, the switching functions are generated based on the look-up table (Table3). For example, if the (dl, d2, d3)=(0, 1, 0), i.e. positive mains voltage, second operation region and line current error Ai?h, then voltage Vab-2 is generate to increase the line current. Similarly switching functions can be achieved if the control signals are given. The actual switching signals of power switches TI-T4 are expressed as followings T1= f a (fa + 1) 2 ' f a (fa - 1) T2 = 2 ' TI R T3 V. SIMULATIONRESULTS To verify the proposed control algorithm of the adopted three-level rectifier, computer simulations are performed. The capacitance of two capacitors is 2200pF. The mains voltage is 220V- and source fkequency is 60Hz. The boost inductance is 2mH. The DC-link voltage of the proposed rectifier is 400V. The current hysteresis band is 0.5A. Fig. 7 shows the simulated waveforms of line voltage, line current and dc side voltage v d operated in the rectificationmode. There is a three-level voltage pattern on the voltage v&. The simulated line current is nearly sinusoidal wave with unity power factor. Fig. 8 shows the simulated waveforms of the adopted rectifier operated in the inversion mode. Based on the simulated results by using the discrete fourier transform, the input power factor is close to unity and total harmonic distortion of the line current is close to 5%. To investigatethe voltage variation between two capacitor voltages on the dc-link, the simulated capacitor voltages are shown in Fig. 9. Two capacitor voltages are almost balanced from the simulated results. The voltage difference between two capacitors is about 5V under the simulatedresult. W. CONCLUSION This paper presents a simple control algorithm for the three-level PWM rectifier. The proposed control scheme is based on a look-up table instead of the conventional complex control algorithm. The high power factor, low current distortion, 604 Authorized licensed use limited to: UNIVERSITY OF NOTTINGHAM. Downloaded on March 07,2022 at 08:27:55 UTC from IEEE Xplore. Restrictions apply. and stable capacitor voltages are implemented fiom the simulationresults. The advantages of the proposed three-level active rectifier instead of two-level rectifier are implementing high voltage application by using low voltage devices and reducing the voltage harmonic contents. an w QP om n3 aa w aa w a, , , , , , , , , , a(w ,an om ’ LWS J ea M REFERENCES [l] J. T. Boys, and A. W. Green, “Current-Forced Single-phase Reversible Rectifief‘, IEE F’roceedings-B, vol. 136, pp. 205-211,1989. [2] B. R. Lin,and T. S.Huang, “Single Phase Rectifier with High Power Factor in Discontinuous Conduction Mode”, IEEE International Symposium on Industrial Electronics, pp. 421426,1995. [3] S.Manias, “Novel Full Bridge Semicontrolled Switch Mode Rectifier”, IEE Proceedings-B, vol. 138, pp. 252-256, 1991. [4] R Martinez, and P. N. Enjeti, “A High-Perfomce Single-Phase Rectifier with Input Power Factor Correction”, IEEE Trans. on Power Electronics, vol. 11, pp. 311-317, 1996. [5] C. Cuadros, D. Borojevic, S. Gataric, V. Vlatkovic, H. Mao, and F. C. Lee, “Space Vector Modulated, Zero-Voltage Transition Three-phase to DC Bidirectional Converter”, IEEE Power Electronics Specialist Conference Record, pp. 16-23,1994. [6] M. S. Dawande, V. R. Kanetkar, and G. K Dubey, ‘Three-Phase Switch Mode Rectifier with Hysteresis Current Control”, IEEE Trans.on Power Electronics, vol. 11, pp. 466-471, 1996. [7] Y. F. Lue, and P. C. Sen, Large-Signal Modeling of Hysterestic Current-F’rogmmnedConverters”, IEEE Trans. on Power Electxunics, vol. 11, pp. 423430,1996. [8] B. R Lin,and D. P. Wu, ‘kplementation of Three-phase Power Factor Correction Circuit with Less Power Switches and Current Sensors”,IEEE Trans. on Aerospace and Electronic Systems, vol. 34, pp. 664-670,1998. [9] B. T. Ooi, “A Three-phase Controlled-Current PWM Converter with Leading Power Factor”, IEEE Trans. on Industry Applications, voL 23, pp. 78-84, 1987. [lo] B. R. Lin, and D. P. Wu,“High Power Factor Correction Circuits with Space Vector and Hysteresis Control Methods”, Journal of Electric Power Systems Research, 43, pp. 207-214,1997. [ll] C. Hochgraf, R Lasseter, D. Divan, and T. A. Lipo, ‘‘Comparison of Multilevel Inverters for Static Var Compensation”, IEEE Industrial Applications Society Annual Meeting, pp. 921-928,1994. [12] G. Sinha, and T. A. Lipo, “A Four-Level Rectifier-Inverter System for Drive Applications”, IEEE Industry Applications Magnazine, pp.66-74, 1998. [13] B. S. Suh, and D. S. Hyun, “A New N-Level High Voltage Inversion System”, IEEE Trans. on Industrial Applications, vol. 44,pp. 107-115, 1997. [14] J. R. Pinheiro, D. L. Vidor, and H. A. Grundling, “Dual Output Three-Level Boost Power Factor Correction Converter with Unbalanced Loads”, IEEE Power Electronics Specialists Conference Record, pp. 133-739,1996. [151 J. S.Lai,and F. Z. Peng, “Multilevel Converters -A New Breed of Power Converters”,IEEE Trans. on Industrial Applications, vol. 32, pp. 509-55 1, 1996. [16] G. Carrara, and S. Gardella et al, “A New Multilevel PWM Method A TheoreticalAnalysis”, IEEE Trans. on Power Electronics, vol. 7, no. 3, pp. 497-505,1992. ’ w ’ am ’ ” w ’ am ’ am I a4 Fig. 7 Simulated waveforms of the adopted rectifier under the rectificationmode. 4” a7 P a7 sm, so01 a7 ” ’ an an an , 4 ” a74 1 am t ” 0.76 an a z an a74 am 0.78 , , , , , , ’ ’ ’ an an an ’ a74 ” an am L $ 0.m b ’ ae < L an am am ae , , _ , I _ ’ ’ ’ ’ 1 am a x an am am ae J (=) Fig. 8 Simulated waveforms of the adopted rectifier under the inversion mode. 605 Authorized licensed use limited to: UNIVERSITY OF NOTTINGHAM. 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