Performance Investigation of Three-Phase Three-Switch Direct PWM AC/AC Voltage Converters

Abstract

Reducing the number of active switches is substantial for obtaining a simple, reliable, high-efficiency, and cost-effective AC/AC voltage converter. In this paper, two topologies of three-phase direct PWM AC/AC voltage converter are proposed. The first is for the buck converter and the other is for the boost one. Each converter has no DC energy storage elements and employs only three IGBTs. The proposed converters do not use lossy snubber circuits and have not commutation problems. A simple, reliable, and cost-effective control strategy, which employs only one voltage sensor, is also proposed. Using a closed-loop voltage control technique, two complementary PWM gate signals are generated to drive the three active switches of each converter. Adjusting the duty ratio of PWM gate signals regulates the output voltage of the AC/AC converters. Operating principle and mathematical analysis of the converters are presented. Voltage stresses across active and passive semiconductor switches of the proposed converters are derived. Small signal analysis based on complex DQ transformed equivalent circuits of the converter is introduced. Voltage controller design using frequency response analysis is provided. The converters are simulated using MATLAB/SIMULINK and laboratory prototypes are implemented in real-time using DSP-DS1104 control board. The converters are tested under different operating conditions and their performances are investigated and compared. The symmetry of the output voltage/current is examined by the theory of symmetrical components. The simulation and experimental results are in a close agreement. This confirms the validity of the theoretical analysis, the effectiveness of the control strategy, and the feasibility of the proposed converters.