A simple and practical voltage balance method for a solid-state transformer using cascaded H-bridge converters

In this paper, a simple voltage balance method for a SST using cascaded H-bridge converters is proposed to reduce the voltage difference of H-bridge converters. The tolerance of DAB converter's passive components in each secondary stage causes the unbalance problem of output voltage in primary side H-bridge converter. In order to reduce the voltage difference of H-bridge converters, the additional voltage balance controller is merged in DAB converter's voltage controller. By using the proposed voltage balance controller, the modified phase shift angle is applied for each DAB converters. Due to the proposed control methods, the dc-link voltage through each H-bridge converters can be balanced. Compared to the conventional methods, the proposed balance method does not require the additional current sensors for voltage balance control. The design and performance of the proposed SST are verified by experimental results using a 5kW prototype.