Design and analysis of a unity power factor buck-boost rectifier with sinusoidal input current

Abstract

With the increasing use of diode and lor thyristor rectifiers, the harmonic and lor reactive current generated by diode and thyristor rectifiers are becoming a troublesome problem in ac power lines. Low power electronic equipment, such as radio, TY etc is widely used in household, Switch mode power electronic equipment ( e.g. PC), and modem commercial buildings have 50% and upto 90% of the demand originated by nonlinear loads, which are composed mainly of rectifiers. These growing low power electronic equipment and nonlinear loads results in a variety of undesirable phenomena in the operation of power systems. The most important among these are harmonic contamination, increased reactive power demand and power system voltage fluctuations. Harmonic pollution has become a major concern for utility service provider due to its effects on sensitive loads and on the power distribution systems. Harmonic current components increase power system losses, can create significant interference with the communication lines. Methods to reduce this current distortion are recognized, but economic incentives are yet to be realized. Standardization is the most effective means to influence equipment design and to control distortion in power systems. A PWM rectifier is promising because it can draw almost sinusoidal ac currents with unity fundamental power factor from the ac power source. Basically there are two kinds of PWM rectifiers, a current source rectifier (CSR) and a voltage source rectifier (YSR). Theoretically, CSR can feed an adjustable dc output voltage which ranges from zero volts to Ym if the amplitude of the ac supply voltage is Ym while YSR can feed that which ranges from Ym to infinity. In the hysteresis current controlled boost rectifier and high frequency rectifiers, PWM output have been investigated by experimental test, and was found that the rectifier delivers near sinusoidal current waveforms at unity power factor requiring small filters. This thesis presents a study of a power circuit, control circuit and filter sections of a rectifier to achieve near sinusoidal input current and unity power factor. Cost effectiveness and power conversion efficiency has been taken as a main consideration when designing the rectifier.