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A new PWM pattern generation method for a PWM converter applied to a superconducting magnet

This paper presents a new algorithm for pulse-width modulation (PWM) pattern generation for three-phase current-source converters. Since switching devices of the converters require a minimum conducting duration to ensure current commutation, it is difficult to keep stably their output voltage close to zero for the converters using the conventional methods of PWM pattern generation. We propose a new PWM pattern generation method that can realize the zero output voltage perfectly without any restrictions on the conducting duration of the switching devices by optimizing the arrangement of the pulse patterns. The performance of this new algorithm is demonstrated by the numerical simulation using PSCAD/EMTDC. This method is applicable to a PWM converter of the superconducting magnet power supply, because it can maintain the coil current constant stably by keeping the output voltage zero and change its operation mode between rectification and inversion without additional complicated controls.