Down-Sampled Repetitive Controller for Grid-Connected Ćuk CCM Inverter

The Ćuk inverter operating in the continuous conduction mode (CCM) is susceptible to grid disturbances, and its transfer function has two right-half-plane zeros (RHPZs), which causes a large phase lag. To improve the output-tracking precision in the grid-connected environment, a repetitive controller (RC) with linear phase-lead compensation has been developed for the Ćuk inverter. However, this controller requires a heavy computational burden and memory space; these problems become more severe as the converter operates at a higher switching frequency. This article proposes to use a down-sampled repetitive controller (DRC) for the Ćuk CCM inverter to alleviate these problems. The down-sampling technique itself can significantly reduce the computational burden and memory space of RC. On the contrary, its control accuracy becomes very low, particularly for the Ćuk CCM inverter. Unlike conventional module integrated inverters (MIIs), the Ćuk CCM inverter must adopt a fractional-order phase-lead compensation algorithm to compensate for the effect of the large phase lag in the down-sampled environment. To clarify the inevitable usage of DRC with a fractional-order phase-lead compensation for Ćuk CCM inverter, the DRC is classified into four types; this article provides its detailed design guideline based on stability analysis of the overall control system and also presents design examples for representative MIIs. Experiments using a 300-W prototype Ćuk inverter validate that the proposed control approach achieves acceptable output-tracking accuracy. The total computation time and memory space with the DRC decrease by 76.0% and 80.0% compared to those with the conventional RC, while the output-tracking accuracy with the DRC decreases by 0.42%.