Parabolic PWM for Current Control of Voltage-Source Converters (VSCs)

A novel parabolic carrier pulsewidth modulation (PWM) method is proposed in this paper for direct current control in a voltage-source converter (VSC). This method employs a pair of parabolic PWM carriers (a positive one and a negative one) to determine the switching states of the two switches in a converter phase leg while limiting the current tracking error within a nonlinear hysteresis band. Similar to the hysteresis PWM method, the proposed parabolic PWM can regulate both dc current and ac current with excellent and accurate dynamic response. Furthermore, as a carrier-based PWM method, the proposed parabolic PWM can maintain a constant switching frequency by the automatic peak current error adjustment through the PWM process. In this paper, the basic operation principle of the proposed PWM method is discussed, and its implementation scheme is presented. Simulation and experimental results based on a single-phase VSC with bipolar PWM implementation are provided.