Output Voltage Control Method for PWM-Controlled Cycloconverters Using Instantaneous Values of Input Line to Line Voltages

The forced commutated cycloconverters (PWM-controlled cycloconverters) have no energy storage components except for small ac filters for elimination of switching ripples. Therefore, the PWM-controlled cycloconverters can be made compact and highly reliable compared with the conventional rectifier-inverter systems. The PWM-controlled cycloconverters, however, directly connect the input terminals to the output terminals by the switching devices. Therefore, if the source voltages contain asymmetrical and/or harmonic components, the influences directly appear on the output terminals. This problem may be a major obstacle for the PWM-controlled cycloconverters to be used in place of the conventional converter-inverter systems. We have already reported a real time control method based on a coordinate transformation. The method realizes sinusoidal output voltages and sinusoidal input currents with controllable input displacement factors regardless of the load power factors. But the control functions of this control method need complex calculations to compensate the distortion of the input source voltages and are difficult to comprehend physically. In this paper, we propose a novel control method using a new control function with a clear physical meaning. By this control method, the compensation of the asymmetrical and harmonic components of the input source voltages is easily realized. Feasibility of the proposed control method is confirmed by simulations and experiments.