EMI reduction in PWM inverters using adaptive frequency modulation carriers

In this paper, we propose deterministic carrier frequency modulation (FM) techniques instead of random carrier frequency modulation (RCFM) to reduce EMI of carrier harmonics in PWM inverters. In particular, we first propose a linear frequency modulation (LFM) method to spread the carrier harmonic energy out in a certain frequency range. Second, considering the characteristic of EMI propagation from the EMI source to the victim under test, we propose a nonlinear frequency modulation (NFM) method to adaptively modulate the carrier frequency based on the EMI spectrum received by the victim such that the influence of propagation path can be properly compensated. Consequently the EMI spectrum received by the victim is flattened and the carrier harmonic EMI level is reduced. Simulation and experimental results validate our EMI reduction scheme using deterministic carrier frequency modulations.