The Research on the 3L-Neural Point Clamp Isolation Bidirectional DC/DC Converter

Isolated bidirectional DC-DC converters-IBDCs, with the two-way power flow ability and the high frequency transformer isolation, are the critical units to connect the different kind power such as battery, generator and supercapacitors etc. The three level neural point clamp-3L-NPC IBDC can realize high voltage converting with the lower rated power switches and expand the power grade, and improve the electromagnetic compatibility as well. In this paper a two ports 3L-NPC IBDC was proposed and the control strategies of the 3L-NPC IBDC was invested in detail and the operation were divided into two modes according to relationship between the duty cycle of the inner bridge and the phase shift ratio of the two bridges. The leakage inductance current, the output voltage and the transfer power characteristics are analyzed and the analytical expressions were given according the two operation modes respectively. The average current of the neural point must be kept at zero to ensure the two clamp capacitors have the approximately equal voltage in one period in the both operation modes. The results show that the 3L-NPC IBDCs are feasible and have a good prospect application in the high power conversion.