Improvement of input side currents of a three phase rectifier combining active and passive filters

Abstract

In order to reduce the Total Harmonic Distortion (THD) in a three phase boost rectifier, active switching and passive filters are incorporated in this work. A constant frequency switching is used for active filtering and pulse width modulation is used to regulate the output voltage. An input Electro Magnetic Interference (EM!) filter is used to suppress the high frequency component generated by the active switching. Moreover, a series LC filter resonating with the supply frequency is also used to suppress the low frequency component that may pass to the input. With addition of this series LC filter, the THD value could be made less than three percentages, which is a great improvement over the earlier rectifiers that have only EMI filter. In the earlier types of rectifiers, the THD value was as high as 17%. The efficiency of the module is also studied. As the output voltage has nonlinear relation with duty cycle, the efficiency is also nonlinear with output voltage variation. But up to certain range of duty cycle it could be made linear in nature with output voltage. The input LC series filter and the EMI filter design are discussed. The efficiency versus output voltage, THD versus duty cycle curve for the proposed rectifier circuit is given for clear understanding of the model. ORCAD 9.1 release Version, very powerful Electrical and Electronics design software is used to design the rectifier circuits. A lot of efforts had to be done to get the ultimate results by simulation.