Aliasing Suppression of Multisampled Current-Controlled LCL-Filtered Inverters

Abstract

Multisampling control provides an attractive way to reduce the control delays in LCL-filtered grid-connected inverters. Thereby, the bandwidth and stability margin will be improved. However, high-frequency switching harmonics (SHs) are introduced in the control loop when the inverter-side current is sampled. To investigate the effect of multisampled high-frequency SHs, the relationship between the double-update pulsewidth modulation (PWM) and multiupdate PWM is deduced through geometric deduction. It is shown that the multiupdate PWM is equivalent to double-update PWM with sampling instant shift, and the equivalent Nyquist frequency is equal to the switching frequency. Moreover, the nonaveraged value of current is sampled within one switching period and aliased low-order harmonics will appear in the grid-side current. Hence, filtering the multisampled SHs is necessary, and an improved repetitive filter (IRF) is proposed to remove all the sampled SHs and keep the advantage of phase boost using the multisampling control. The method is evaluated with a single-loop inverter-side current control, and its effectiveness is verified through the simulation and experiment.