High Frequency Single Phase AC Chopper

Transcription

1 olume, Issue, October-December, 03, pp. 7-76, IASTER 03 Online: , Print: ABSTRACT High Frequency Single Phase AC Chopper M. Sujith, C. Sivapragash, 3 A. Raja Senior Assistant Professor, Department of Electrical and Electronics Engineering, IFET College of Engineering, illupuram, Associate Professor, Department of Electrical and Electronics Engineering, ivekanandha College of Technology for Women, Namakkal, 3 Associate Professor, Department of Electrical and Electronics Engineering, SSM College of Engineering, Komarapalayam, The aim of this paper is To Simulate and design the ac chopper and improve the efficiency of the ac chopper, to minimize the switching losses and total harmonic distortion present in the system. The ac voltage regulator is the one of important equipment used in day-to-day life for obtaining fixed ac voltage from a fluctuating source. The single-phase ac chopper is designed by a minimum number of switches and configured to convert the constant AC voltage source from the time variant quasi sinusoidal input voltage. The traditional methods of controlling the thyristors are phase angle, integral cycle control are employed. The harmonics introduced in to system due to the presence of hard switching. Due to the firing angle retardation of thyristors, switching loss is exists in the system to be maximum. The Proposed system model is designed to be soft switching in nature and verified using Matlab / Simulation. Keywords: Harmonics, Resonant switching, Sinusoidal Amplitude, EMI. INTRODUCTION. Hard Switching Due to the hard switching the maximum stress occurs on the switches, which causes damage to the switch. During on and off process, the switches need to withstand for maximum voltage and current simultaneously, which results in switching loss.. Problems of Hard-Switching: Switching losses EMI due to high current stress and voltage stress across the devices Energy loss in inductance and capacitance.3 Soft Switching Zero voltage switches can be turn-on; the voltage across the device is reduced to zero before the current increase. Zero current switches can be turn-off the current flowing through the device is reduced to zero before the voltage increase.. SINGLE PHASE AC CHOPPER The proposed single phase AC Chopper consists of four switches S, S, S3, S4 are bidirectional in nature with series inductance and parallel capacitances shown in Fig.. During a positive half cycle mode the switch S & S3 is switched on with respect to S, S4 is switched off and negative 7

2 olume-, Issue-, October-December, 03, (O) (P) half cycle S & S4 switched on with respect to S, S3 is switched off. Ideally Switch S3 is on state for purpose of high frequency resonant switching []. At the time of switching period the proposed system tends to reduce the switching losses and presence of harmonics to be minimized. Due to the high frequency switching, losses occurred in inductance and capacitance to be neglected [3]. The main advantage of Proposed AC chopper is tends to operates in both continuous and discontinuous mode [4]. Fig.Circuit topology for Proposed System The proposed converter converts the varying input voltage to constant AC voltage source with the help of Controller circuit [4]. The voltage sensor present in this circuit tends to sense the error signal from the output and passes them to oscillator present in the controller block shown in Fig.. The controller block compares the reference signal with the error signal and changed the gating pulses applied to the Switches. Fig.Block diagram of Proposed System 3. OPERATING MODES Fig. represents the circuit topology of the proposed system. In this circuit, the switch consists of anti parallel diodes and the resonant operation is classified in to positive half cycle [Mode ] and negative half cycle mode [Mode ] operation for converting quasi sinusoidal input voltage to constant output AC voltage. Mode In this mode the switch S & S3 is switched on, then the current flowing through the inductance linearly increase passing through S, S anti parallel diodes which is naturally turned off, S3 & S4 anti parallel diode. The Switch S & S4 act as a freewheeling diode and provide the conduction path to the inductance L and Capacitance C. The resonant operation starts from in,l r, S & S3, C r. 7

3 olume-, Issue-, October-December, 03, (O) (P) Due to the resonant frequency switching the current flowing through the L r is increasing at the time of peak voltage arrives, after that the current value starts to decrease and then drops to zero. The output state of positive cycle ends here. Then the mathematical expression for resonant frequency is given by ω () r L C r r The voltage stress at the capacitance C r is to maximum given by C r = * input voltage () The resonant current through inductance in positive half cycle is given by Input oltage I I (3) Lr L Z o The output impedance (Z 0 ) is given by L r Z 0 (4) Cr Therefore the output voltage measured across the capacitance is given as cr = * input voltage ( in ) (5) Mode The decreased resonant current reaches to zero in mode due to decrease in resonant voltage. Then the Switch S3 is switched off, the resonant current starts to increase in negative half cycle. After the peak value of voltage arrives, again the resonant current starts to decrease. Same process is continued sequentially. The mathematical expression for resonant through the inductor is given by Input oltage I I (6) Lr L Zo After that the resonant current through the inductor i Lr drops the value to zero, the stored energy in capacitance starts to discharges to the load. Then the condition for achieving the switching frequency at the switches is given as ω r f (7) π s 4. PROPOSED MATLAB MODEL The proposed model is modelled in Matlab/Simulink. In this system we considered the input varying sinusoidal input voltage with respect to the time. The model regulates varying input to the constant output voltage with help of resonant switching frequency The model consists of switches and anti parallel diodes to perform freewheeling operations under positive and negative half cycle mode. 73

4 olume-, Issue-, October-December, 03, (O) (P) The Mathematical derivation of the switching frequency (F s ) given as F Initial frequency Sensitivit y * Error oltage (8) s The controller block compares the error signal from the voltage sensor with reference signal and generates the pulse with respect to constant on time with variation of off time.the proposed system in order to reduce the harmonic level. In general THD THD n HarmonicsPower Fundamental power 3... Then the transfer function of the filter L & C is given by X ωl X L c ωc j j C C j L G jω () The resonant frequency is calculated by ω or (3) LC P LC s Where C p & C s is parallel and series capacitance in the circuit. 5. MATLAB SIMULATION The proposed matlab system parameters are given below L, L r =. mh, C,C r =0μF, R=7Ω, L=00mH (9) (0) () Fig.3. Proposed High Frequency Resonant AC Chopper 74

5 Efficiency% International Journal of Research in Electrical & Electronics Engineering olume-, Issue-, October-December, 03, (O) (P) Fig.4. Input Sinusoidal Quasi Waveform Fig.5. Pulse Generator for the proposed model Fig.6. Proposed Model -Output Waveform The proposed system shown in fig.3-6 converts the variable input quasi sinusoidal to constant sinusoidal output. From that we observe the switching losses is less; conversion efficiency of the proposed system is 9 %. The efficiency comparison for conventional, soft & hard switching shown in Fig.7 Output Power(W) Fig.7.Comparison between Conventional, Soft Switching and Hard Switching AC oltage Regulator 75

6 olume-, Issue-, October-December, 03, (O) (P) CONCLUSION A high frequency resonant AC Chopper is designed in Matlab with simple and flexible for all fluctuating input AC input voltage. Additional Switch is not required for the proposed converter. The advantages of proposed single phase high frequency resonant AC Chopper is operated in the manner of soft switching, so the switching losses is minimized. The proposed model achieved overall efficiency of 9% and minimum THD value of 0.0 with output power 600W. REFERENCES [] B.W.Williams, Asymmetrically modulated AC choppers, IEEE Trans. Ind. Electron., vol. IE-9, no. 3, pp. 8 85, Aug. 98. [] G. Roy, P. Poitevin, and G. Olivier, A comparative study of single phase modulated AC choppers, IEEE Trans. Ind. Appl., vol. IA-0, no. 6, pp , Nov./Dec [3] G.H.Choe,A.K.Wallace, andm.h. Park, An improved PWMtechnique for AC choppers, IEEE Trans. Power Electron., vol. 4, no. 4, pp , Oct [4] D. H. Jang and G. H. Choe, Improvement of input power factor in AC choppers using asymmetrical PWM technique, IEEE Trans. Ind. Electron., vol. 4, no., pp , Apr [5] N. A. Ahmed, K. Amei, and M. Sakui, A new configuration of singlephase symmetrical PWM AC chopper voltage controller, IEEE Trans. Ind. Electron., vol. 46, no. 5, pp , Oct [6] L. Wang and Q. Liu, A there-level AC chopper with clock-interleaved constant frequency integration control, in Proc. IPEMC 009, pp [7] L. Wang and Q. Liu, One-cycle controlled single phase ac chopper, in Proc. IPEMC 009, pp [8] J. Zhang, Y. Zou, W. Yu, L. Lin, and F. Li, Research on AC chopper power module with module parallel control, in Proc. IEEE APEC 008, pp