Study on Modulating Carrier Frequency Twice in SPWM Single-Phase Inverter

The electromagnetic interference (EMI) of the inverter output, which is controlled through a sinusoidal pulse width modulation method, is mainly generated at the carrier frequency and its harmonics. The peaks of the interference can be reduced effectively by using carrier-frequency modulation (CFM). The spectrum of the output differential-mode voltage in a SPWM inverter with periodic CFM is analyzed theoretically in this paper. Through changing the maximum frequency deviation, periodic signal´s frequency and waveform of CFM, the suppression effects of interference peaks are discussed. A new scheme, in which the carrier frequency is modulated twice, is presented. In this scheme, the frequencies and waveforms of periodic signals are optimized and selected under the condition of the same maximum frequency deviation, and the synthetic modulation signal which has the best suppression effect of the maximum interference peak is obtained. The feasibility and validity of the scheme are proved by simulation and experiment results in a single-phase inverter.