SAFE STARTUP METHOD FOR ZERO-VOLTAGE- SWITCHING MOSFET GRID INVERTER

Abstract

Zero-voltage-switching (ZVS) MOSFET grid inverter has distinct advantages such as higher efficiency and higher power density. However, the ZVS inverter may lose zero-voltage-switching condition during startup stage if it does not start properly. It may increase the voltage stress on MOSFETs and even destroy the power semiconductor device. In order to achieve the zero-voltage-switching condition for ZVS inverter during the startup stage, this project proposes a safe startup method with an auxiliary clamping capacitor pre-charging circuit and designed ZVS pre-charging pulse sequence. The pre-charging circuit is enabled only at startup stage. Theoretical analysis shows that the proposed method is capable of reducing the voltage stress during the startup stage for the ZVS inverter. Finally, the proposed safe startup method is verified on a 3kW Grid inverter.

Existing System

The startup procedure of the grid-connected inverter is composed of two steps: the first step is charging the voltage of the DC side capacitor and another step is starting PWM modulator and giving the drive signal to the inverter.

Proposed System

The ZVS MOSFET grid-connected inverter is better to start with three steps. The first step is pre-charging the voltage of the DC side capacitor, the second step is pre-charging the voltage of the auxiliary clamping capacitor by the additional pre-charging circuit or by designed pre-charging pulse sequence, and the third step is starting the modulator and giving the ZVS PWM signal of normal operation to the inverter. In order to solve the high voltage stress problem during the startup stage for the ZVS MOSFET inverter, the ZVS condition should be realized for the single-phase grid-connected inverter during the startup stage and satisfy the practical application. This project proposes a safe startup method to solve the startup problem for single-phase ZVS inverter. It based on the idea of adding a pre-charging stage during the conventional startup procedure and designing the ZVS pre-charging pulse sequence for the ZVS inverter in the pre-charging stage.

Architecture

Proposed Pre-charging scheme with additional circuit