Impacts of Discretization of the Capacitor-Current-Feedback Path Phase Lead Compensator on Digitally Controlled LCL- Type Grid-Connected Inverter Stability and Robustness

The inherent digital control delay in digitally controlled LCL-type grid-connected inverter has a negative impact on its capacitor-current-feedback (CCF) active damping performance and adding a first-order phase lead compensator in the CCF path is an effective way to enhance the robustness. Considering the complexity of designing the compensator directly in discrete domain, an easier common practice is to design the compensator and analyze the system in continuous domain firstly and then discretize it by a certain method. This paper proposes a set of first-order phase lead compensator design method consisting of an s-domain design guidance and an assorted prewarp Tustin method for discretization. System stabilities are analyzed and compared when Tustin, backward rectangular and prewarp Tustin methods are used respectively. Comparison studies shows that the highest robustness and the smallest difference between s-domain and z-domain system stability analyses can be achieved by using prewarp Tustin method to discretize the proposed compensator. Finally, the analytical results have been proved on a 1-kW prototype.