Full ZVS Achievement for DCM Grid-Tied Inverter With Improved Average Current Model and Considering Nonlinear Parasitic Capacitance

This article proposes an improved current model for discontinuous current mode (DCM) grid-tied inverters operated with an off-time discrete control to improve its zero-voltage switching (ZVS) performance. The off-time discrete control can achieve ZVS by discretely adjusting the oscillation caused by the parasitic capacitance of semiconductor devices and the filter inductor during the zero current period of the DCM operation. However, the control method exhibits some errors, such as non-ZVS operation due to the nonlinearity of the parasitic capacitance. This article aims to provide a detailed modeling for inductor current and device voltage to improve the control accuracy and the ZVS performance of the off-time discrete control. The impact of the voltage-dependent parasitic capacitance on the resonance is analyzed in detail, and a calculation method for the oscillation period is proposed. A comparative study of the conventional and the proposed improved models is performed using the LTspice simulation. It confirms that the inductor current behavior can accurately be predicted by using the improved model and it significantly improves the control accuracy with the realization of ZVS. The feasibility of the control using the proposed improved average current model under various conditions was verified by the comparative experiments with a 1-MHz operated converter, which consists of gallium nitride high-electron-mobility transistor (GaN-HEMT) devices.