IJSTE - International Journal of Science Technology & Engineering | Volume 2 | Issue 06 | December 2015 ISSN (online): 2349-784X
Implementation of DSP Based Sinusoidal Pulse Width Modulation for Three Thase Inverter Krupa M Assistant Professor Department of Electrical and Electronics GSSS Institute of Engineering and Technology for Women, Mysuru
Abstract This paper presents the implementation of sinusoidal pulse width modulation for a three phase Bridge inverter. Basically three sinusoidal reference signals which are phase shifted by120 degree apart from each other and compliment of these three sinusoidal signals are compared with the carrier signal to generate six different PWM signals for six switches of three phase inverter.LC filter is employed to reduce higher order harmonics in the three phase inverter output voltage. Closed loop operation is carried out. Hardware is implemented for open loop system where the SPWM algorithm is implemented in DSPIC30F2010. The efficiency of the inverter is high and offers less harmonic distortion. The proposed technique is simulated using MATLABSimulink model and THD is measured. Keywords: Sinusoidal Pulse Width Modulation, Total Harmonic Distortion, DSPIC30F2010 ________________________________________________________________________________________________________
I. INTRODUCTION Sinusoidal pulse width modulation technique is applied to three phase inverter to obtain necessary output sinusoidal voltage without much harmonics. This is possible if the sampling frequency is much higher than the fundamental output frequency of the inverter. This method is characterized by constant amplitude pulses with various duty cycles in each period [1]. Most popular application of sinusoidal pulse width modulation is the motor control and inverters. This paper presents the implementation of sinusoidal pulse width modulation for three phase inverter to obtain output voltage with reduced harmonics. Output of the inverter is filtered using a second order passive filter in order to obtain a sine wave output [2]. Total harmonic distortion of the output voltage of the inverter with filter and without filter are measured.THD of the output voltage of inverter with filter is less compared to the THD of the output voltage of inverter without filter. Closed loop operation is carried out using PI controller to obtain constant inverter output.
II. THREE PHASE SPWM INVERTER Basic block diagram of SPWM implemented three phase inverter is shown in figure 1. It can be divided into two parts. Power circuit and control circuit. Power circuit includes three phase inverter, DC supply, star connected load and LC filter. Control part includes PI controller and a sensing circuit. Power circuit includes semiconductor devices which have non linear characteristics. This non linearity will generate dominant harmonics in the inverter output. Hence LC filter is employed to filter major harmonics from the inverter output. Trigger pulses for the inverter is generated using sinusoidal pulse width modulation technique.
Fig. 1: Block Diagram
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