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.
