Confined Band Variable Switching Frequency Pulse Width Modulation (CB-VSF PWM) for a Single-Phase Inverter With an LCL Filter

Variable switching frequency pulse width modulation (VSF PWM) has been proposed in the past to optimize the total harmonic distortion (THD) performance and switching losses of an inverter. Nevertheless, such VSF PWMs give rise to switching harmonics which vary across a wide frequency spectrum, where the lower frequencies could resonate with the filter while the upper frequency could exceed the maximum switching frequency. This complicates VSF PWM design, restricting their practical uses. In this paper, a confined band VSF PWM (CB-VSF PWM) for a single-phase inverter with an LCL filter is presented. By confining the switching frequencies within a practical band, the design of the filter becomes easier while maintaining low current THD with low switching losses. The choices of the upper and lower bands of the proposed VSF are defined and the design criterion is introduced. It is found that the proposed method allows reduction in switching losses as well as reduction in current THD when the effect of the LCL filter is taken into consideration. The performance analysis is validated through simulation and experimental results in a 1 kW inverter.