Current Harmonic Analysis of Multisampled LCLType Grid-connected Inverter

Multisampling control provides an attractive way to reduce the control delays in LCL-type grid-connected inverters, and thereby the bandwidth and stability margin will be improved. However, high frequency switching harmonics is introduced in the control loop when the inverter current is selected as a feedback. In order to investigate the effect of high frequency switching harmonics, the internal relationship between double-update pulse width modulation (PWM) and four-update PWM is deduced through the geometric analysis. Compared with the double-update PWM, a sampling instant is shifted a quarter of the switching period during each switching period. Hence the non-average value is sampled and low-order aliased harmonics will appear in the grid current. Finally, the theoretical analysis is verified through the simulation and experimental results.