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International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 6- Feb 2014 Performance Analysis of Z-Source Inverter for Various Pulse Width Modulation Techniques Gokarakonda Surya Nihanth1, Nerella Chaitanya Kumar2 , Balivada Jayanth3 , Charan Tej Yaadav4 1,2,3,4 Final Year B.Tech, EEE, KLUniversity, Vaddeswaram, Guntur Abstract -The voltage source inverter is a buck (step down) inverter for dc-to-ac power conversion and it is a boost (step-up) rectifier (or boost converter) for ac to-dc power conversion, i.e the voltage of VSI is limited below or exceeded above its dc-rail voltage this problem of voltage source inverter can be overcome by using a z source network between switching devices and dc-rail. In this paper various pulse width modulation techniques like sine pwm, third harmonic pwm, space vector pwm were applied to z-source inverter. The simulation is done using Simulink. Keywords: z-source inverter, sinepwm,space vector pwm, thirdharmonic pwm. I. INTRODUCTION The Z-Source inverter refers to an inverter which has the combined characteristics of both the voltage source inverter and the current source inverter to convert direct current feed to alternating current feed. Generally the problem associated with the voltage source inverter is that the ac output voltage is limited below and cannot exceed the dcrail voltage or the dc-rail voltage has to be greater than the ac input voltage. Therefore, the V-source inverter is a buck (step-down) inverter for dc-to-ac power conversion and it is a boost (step-up) rectifier (or boost converter) for ac-to-dc power conversion. For applications where over drive is desirable and the available dc voltage is limited, an additional dc-dc boost converter is needed to obtain a desired ac output. The problem relating to the current source inverter is the ac output voltage has to be greater than the original dc voltage that feeds the dc inductor or the dc voltage produced is always smaller than the ac input voltage. Therefore, the I source inverter is a boost inverter for dc-to-ac power conversion and the I-source converter is a buck rectifier (or buck converter) for ac-to dc power conversion. For applications where a wide voltage range is desirable, an additional dc–dc buck (or boost) converter is needed. So, to overcome these problems we use Z-source inverter where the crossover operation of two inductors (choke) and two capacitors (condenser) is used for both the step up (boost) operation and step down (buck) operation is possible to get the desired output. II. SINUSOIDAL PULSE WIDTH MODULATION In single-pulse and multiple pulse modulation techniques the width of all pulses are same but in sinusoidal pulse width modulation the width of each pulse is varied in proportion to the amplitude of a sine wave. In this technique the gate signals are generated by comparing a sinusoidal reference signal with a triangular carrier wave. The DF and LOH are reduced significantly. The output voltage is obtained from the mat lab results. The DF and LOH are measured by using FFT analysis. The gate signal for the inverter is obtained by taking the repeating sequence( triangular wave)as the control signal and comparing it with the reference wave(sinusoidal wave).In order to detect or eliminate the zero sequence currents we use zero hold circuit and by comparing the with the help of greater than or equal to blocks. Fig.1 sine pwm pulse generator Fig.2 three phase z-source inverter ISSN: 2231-5381 http://www.ijettjournal.org Page 324 International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 6- Feb 2014 III. THIRD INJECTION PWM In sinusoidal pwm the dc bus in not completely utilized as the peak of reference signal goes above the carrier signal peak i.e reaching over modulation region, in order to get the reference signal to modulation region third harmonic is injected into the fundamental signal and compared with carrier signal. Injection of third harmonic does not affect output because triplen harmonics are not present in output. Fig. 3 sine pwm three phase voltages Fig.5 third harmonic pulse generator Fig.6 third harmonic three phase voltages Fig. 4 Sine pwm output FFT Analysis ISSN: 2231-5381 http://www.ijettjournal.org Page 325 International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 6- Feb 2014 STEPS TO IMPLEMENT SVPWM, THE CONVENTIONAL METHOD: 1) The sector in which the tip of the reference sector is situated is to be determined from the instantaneous phase references Va *, Vb * and Vc* Va *, Vb *, Vc * vα,vβ Θ= tan-1(vβ/vα) α = Θ- k(600) ; k such that α < 600 Sector number = k + 1 2) Computation of T1 and T2; here lookup tables are needed to know the values of Sin (600- α) and Sin α 3) Determination of switching vectors. Using the corresponding sector information the actual switching time for each inverter leg is generated from the combination of effective times and zero sequence time. Equating volt-seconds along the α -axis: (ІVsrІcosα)* Ts = Vdc *T1 + (Vdccos600) * Ts Equating volt-seconds along the β -axis: (ІVsrІsinα) * Ts = (Vdcsin600) *T2 Solving the above two simultaneous equations, one gets: Fig.7 thirdharmonic pwm FFT analysis IV. SPACE VECTOR PULSE WIDTH MODULATION Space vector modulation is a PWM control algorithm for multi-phase AC generation, in which the reference signal is sampled regularly; after each sample, non-zero active switching vectors adjacent to the reference vector and one or more of the zero switching vectors are selected for the appropriate fraction of the sampling period in order to synthesize the reference signal as the average of the used vectors. The topology of a three-leg voltage source inverter is Because of the constraint that T1 | v sr | Ts sin( / 3 ) Vdc sin( / 3) T2 | v sr | Ts sin Vdc sin( / 3) |Vsr | represents the length of the reference Vector and is measured from the start of the vector. 4) Assert the appropriate control signals to affect the required switching action. the input lines must never be shorted and the output current must always be continuous a voltage source inverter can assume only eight distinct topologies. Six out of these eight topologies produce a nonzero output voltage and are known as non-zero switching states and the remaining two topologies produce zero output voltage and are known as zero switching states. ISSN: 2231-5381 http://www.ijettjournal.org Page 326 International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 6- Feb 2014 Fig.9 space vector pwm implementation Fig.8 Switching sequence TABLE I Sector no. 1 2 3 4 5 6 On-sequence 8-1-2-7 8-3-2-7 8-3-4-7 8-5-4-7 8-5-6-7 8-1-6-7 Off-sequence 7-2-1-8 7-2-3-8 7-4-3-8 7-4-5-8 7-6-5-8 7-6-1-8 The above mentioned algorithm is implemented in Simulink and is as shown Fig.10 space vector pwm three phase voltages ISSN: 2231-5381 http://www.ijettjournal.org Page 327 International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 6- Feb 2014 Phase Voltage Source Inverter” IJERT, Vol.2 Issue-5. [5]. Trzynadlowski, A.M. “An overview of modern PWM techniques for three-phase, voltagecontrolled, voltage-source inverters”. Industrial Electronics, 1996. ISIE '96., Proceedings of the IEEE International Symposium on (Volume:1 ) [6]. B. K. Bose, Power Electronics and Variable Frequency Drives:Technology and Applications. IEEE Press, 1997 Fig. 11 space vector pwm FFT Analysis V. CONCLUSION The pulse width modulation strategies like sinusoidal pwm, third harmonic pwm, space vector pwm are implemented by Simulink for z-source inverter. The output voltages are analysed , the dc-bus utilization improved for each modulation techniques. The total harmonic distortion got reduced to each technique. REFERENCES [1]. Mohan, Undeland, Riobbins, “Power electronic converters, applications and design” WILEY STUDENT EDITION. [2]. Muhammad H. Rashid, “Power electronic circuits,devices, and applications. Low price edition. [3]. Md. Shahinur Islam, Nazmul Islam Raju, Ahsan Uddin Ahmed “Sinusoidal PWM Signal Generation Technique for Three Phase Voltage Source Inverter with Analog Circuit & Simulation of PWM Inverter for Standalone Load & Microgrid System” IJRER, Vol.3 No.3 [4]. Prachi S. Dharmadhikari, Gaurav N. Goyal “Analysis & Hardware Implementation Of Three- ISSN: 2231-5381 http://www.ijettjournal.org Page 328