Aliasing Suppression of Multisampled Current-Controlled LCL-Filtered Inverters

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) is introduced in the control loop when the inverter-side current is sampled. In order to investigate the effect of multisampled high frequency SHs, the relationship between the double-update pulse width modulation (PWM) and multi-update PWM is deduced through geometric deduction. It is shown that the multi-update PWM is equivalent to double-update PWM with sampling instant shift, and the equivalent Nyquist frequency is equal to the switching frequency. Moreover, the non-averaged value of current is sampled within one switching period and aliased low-order harmonics will appear in the grid-side current. Hence, filtering the multi-sampled SHs is necessary, and an improved repetitive filter is proposed to remove all the sampled SHs and keep the advantage of phase boost by 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.