INDUCTOR VOLTAGE CONTROL OF PWM AC-DC BUCK-TYPE CONVERTER

Abstract

A novel Inductor Voltage Control method capable of achieving any input power factor including unity is being proposed for both the single and three phase buck type ac-dc PWM converters. In this method, the input inductor voltage is kept within a hysteresis band about a sinusoidal template by appropriately operating the switches, thus ensuring sinusoidal input current. The existing delta modulation control achieves sinusoidal input current with fast dynamics. However, the proposed Inductor Voltage Control is less sensitive to parameter and control signal changes than the existing delta modulation technique. The sensitivity problem with the delta modulation was identified and verified through simulations. Detailed analysis has been performed for a single phase converter using both the average circuit model and the switched circuit model. This analysis is applicable to both Inductor Voltage Control and Delta Modulation Control. Simulation and experimental results verify the theoretical results.

A modification was done to the inductor voltage control of the single phase converter which resulted in a reduction of switching frequency. This contributed to a possible reduction in the switching losses thus increasing the efficiency of the converter. This modification in the switching logic was theoretically studied and the theoretical results were compared with the simulation results. A new switching logic scheme is proposed which enables the Inductor Voltage Control (and Delta Modulation Control) to be extended to a three phase converter also. For the case of Inductor Voltage Control for the three phase converters, simulation and experimental results have been provided. The proposed inductor voltage control method for both the single phase and three phase converters has potential in applications such as de motor drives and ac-dc rectifier with current limiting.