Charge Control of Critical Conduction Mode Grid-Tied Inverters to Enhance Dynamics and Robustness

Critical conduction mode (CRM) operation stands as a highly effective strategy for grid-tied inverters to achieve zero-voltage switching, thereby minimizing switching losses and circumventing the switching frequency limitation. To eliminate the additional hardware cost and complexity associated with conventional zero-crossing detection circuits, fully digital control implementations for CRM have attracted much research interest. This article introduces a novel charge control methodology. The core principle involves precisely regulating the total charge transferred through the inverter-side inductor within each well-defined control cycle. Crucially, this approach directly establishes and leverages a deterministic regulatory relationship between the commanded charge quantity and the required turn-on time of the switches. Beyond enabling reliable CRM-based zero-voltage-switching operation, the proposed charge control inherently reduces the system order compared to traditional average current control schemes, facilitates faster dynamic response due to its the direct charge-to-time mapping mechanism and demonstrates enhanced robustness against grid impedance variations. Experimental validation conducted on a 1-kW prototype inverter operating under typical grid conditions verifies the effectiveness of the proposed control strategy in achieving these advantages.