PWM-based control strategy for forced commutated cycloconverters

Abstract

This paper presents a new control method for three-phase to single-phase cycloconverters based on pulse width modulation (PWM) technique. Due to the proposed control method, the desired output voltage can be generated even with unbalanced input voltages. The proposed control method can easily be extend to three-phase to n-phase cycloconverters. The theoretical analysis based on the proposed method is given for both of the conventional topologies of three-phase to single-phase cycloconverters. Using the proposed control method, the maximum output/input voltage transfer ratios for balanced operation are 0.5 and 1.5 for cycloconverters that consist of three and six bidirectional switches, respectively. It is important to note that the low voltage transfer ratio is an intrinsic limitation of the conventional control methods. This method has no limitation on frequency conversion and is independent of the load. In other words, using the proposed control method, the three-phase to single-phase cycloconverter can operate as a step-up voltage and frequency. The other advantage of this method is no low order harmonics in the input and output quantities. Therefore, the size of required filters is decreased. The operation and performance of the proposed control method has been verified by simulation and experimental results of a three-phase to single-phase cycloconverter.