A Novel Two-Dimensional Random Switching Frequency PWM Method for Variable Frequency Drives

In this paper, a new two-dimensional random switching frequency pulse-width-modulation (2D-RSF-PWM) method is proposed for variable frequency drives (VFDs). The proposed 2D-RSF-PWM method is based on two newly defined parameters which are spread factor and number of repetitions. Hence, random switching frequency pattern with limited variation band of switching frequency is achieved by selecting the proper values of these two parameters. Accordingly, applying the proposed 2D-RSF-PWM method results in improved conductive EMI performance at high frequencies, enhanced switching noise reduction at low frequencies, and better total harmonic distortion (THD) in comparison to the conventional SPWM and RSF-PWM methods. Moreover, the input EMI filters are designed for both cases of applying the proposed 2D-RSF-PWM and the traditional SPWM methods to meet the IEC 61800-3 standard Category C2 requirements. Comparison between two designed input EMI filters to meet IEC 61800-3 standard demonstrates that the required values of CM and DM inductors of the input EMI filter are decreased by factor of 3 by applying the proposed 2D-RSF-PWM method in comparison to those values by applying the conventional SPWM method. The presented results and theoretical analysis verify the performance of the proposed 2D-RSF-PWM method.