Exploring the LCL Characteristics in GaN-Based Single-L Quasi-Z-Source Grid-Tied Inverters

As more widebandgap (WBG) devices are becoming commercially available, it is beneficial to use WBG device to increase the switching frequency in order to reduce the passive components. For quasi-Z-Source (qZS) grid-tied inverters, the reduction of passive components raises stability concerns as the coupling effect between the dc side and ac side of qZS inverter will increase. In this paper, the coupling effect between qZS impedance network and the output filter is analyzed by modeling both dc and ac sides. Analysis reveals the resonant characteristic of the qZS inverter. Controller parameter boundaries are derived, and a design method to improve stability is then proposed. Case studies for a 2.5-kW 10-kHz Si-based qZS inverter and a 1-kW 100-kHz GaN-based qZS inverter are presented. Circuit simulations and experimental verifications results are provided to assess analysis and the control design.