A Variable Switching Frequency PWM Method for Indirect Matrix Converters

A variable switching frequency PWM technique (VSF-PWM) for indirect marix converter(IMC) is proposed in this paper. The maximum peak-to-peak value of the three-phase current ripples in each switching cycle can be calculated by analyzing the output current-error vector trajectory of IMC on a-b-c plane and projecting it onto the three-phase coordinate axis. Then the switching frequency is adjusted in real-time according to change of the maximun peak-to-peak value of the current ripples. Compared with the constant switching frequency PWM method (CSF-PWM), the proposed method can reduce the average switching frequency and the swithing loss. Meanwhile, the switching sequence of the traditional SVPWM is modified, which can achieve zero current commutation in rectifier of IMC, and makes the commutation frequency controllable. Simulation results prove that with the proposed method, the distribution range of output current harmonic spectrum is expended and the spikes in the spectrum are eliminated, which will be effective in suppressing the EMI of the converter output and noise of the load.