Improvement of Power Quality Using PWM Rectifiers

The paper presents the modeling, simulation and analysis of an AC-DC converter based PWM rectifier. It provides a suitable control algorithm for a pulse width modulation rectifier which reduces ripple from the DC output side as well as shapes the input current properly. The basic objective of a PWM rectifier is to regulate the DC output voltage and also ensure a sinusoidal input current and unity power factor operation. This is implemented by high speed IGBT switches connected in anti parallel mode across the rectifier diodes. The output voltage is controlled by switching these IGBTS and higher order ripples at the output can be easily eliminated with the help of passive filters. Lower order harmonics are eliminated using PWM technique. The control subsystem generates gating pulse to the universal bridge by passing the output voltage through a network consisting of comparator, discrete PI controller and discrete PWM generator. The output of this generator are the gating pulses to be applied to the universal bridge. By this control method, we have tried to reduce the input current harmonic distortion and bring the input current and voltage in same phase as well as make it sinusoidal. The control of modulation index(m) and phi has been shown in the closed loop system. This paper presents the state of the art in the field of regenerative rectifiers with reduced input harmonics and improved power factor. The influence of the discussed modulation methods on the line current distortion and the switching frequency has been examined. The simulation results of the presented techniques have been demonstrated and concluded for various load resistance.