COMPARATIVE ANALYSIS OF CONTROL STRATEGIES FOR AC to DC CONVERTERS

Abstract

AC-to-DC converters have been dominated by uncontrolled rectifiers or line commutated phase controlled rectifiers followed by a bulk capacitor. These rectifiers are inexpensive, highly reliable. Passive filters are often used to filter the low order harmonics as they have a simple circuit configuration. Pulse width modulated (PWM) AC-to-DC voltage source converters or current controlled rectifiers (CCR's) have the merits of nearly sinusoidal- input current, good power factor and regeneration ability. A significant improvement in converter behavior has been achieved by means of closed loop control techniques. This thesis aims at the comparative analysis of various PWM control strategies for AC-to DC converters some of which include Hysteresis Current Control, Sinusoidal Pulse Width Modulation, Space Vector modulation, Indirect Current Control, Average Predictive Current Control for four wire rectifiers etc. Simulation models are developed in MATLAB for different control strategies to compare the results and obtain a performance evaluation. The performance of an AC-to-DC converter controlled by each control strategy has been evaluated under various conditions by varying the load, switching frequency, changing the operating mode from generative to regenerative. The performance parameters are calculated for all the converters and then compared with each other. A tabulation of all the performance measures is made.