Control Method for Overvoltage Suppression Across the DC Capacitor in a Grid-Connection Converter Using Leg Short Circuit of Power mosfets during the Initial Charge

This paper proposes a control method for the initial charge of the dc-capacitor in voltage-source power converters. The proposed method is suitable for the power converter equipped with a small dc capacitor and is capable of removing the initial charge circuit. The proposed method makes a leg short circuit by using power devices employed in the power converter, discharges the dc capacitor, and suppresses its overvoltage due to the initial charge. The short-circuit operation only occurs for a short time and is used once in each leg to distribute the loss to each power device. The experimental verification using a 200-V, 5-kVA three-phase converter shows that the proposed method can reduce the peak voltage of the dc capacitor from 520 to 420 V. The experimental results exhibit a good capability of the proposed method to suppress the overvoltage due to initial charge without fatal damage to the power devices. As a result, the proposed method enables removal of the initial charge circuit, resulting in a reduction in the size and cost of power converters.