Motor drive system EMI reduction by asymmetric interleaving

Parallel operation of PWM rectifiers and inverters has been used in UPS, motor drives, telecom power supply, and other applications to reduce system development cost and to provide easy power scalability as well as redundancy. Conventional symmetric interleaving can eliminate certain harmonics and their sideband components but is not necessarily optimal for EMI filter design if the filter attenuation requirements are determined by one of the remaining harmonics. This paper demonstrates the application of asymmetric interleaving in modular three-phase motor drives to minimize their output EMI filter size. Experimental measurements show that compared to symmetric interleaving, optimized asymmetric interleaving can reduce EMI attenuation requirements by an additional 6-8 dB, resulting in significant reduction in both CM and DM filter size and weight.