Small signal modeling and control of isolated three port DC-DC converter for PV-battery system

The inclusion of battery energy storage systems (BESSs) with PV is technically attractive and is capable of solving intermittency and voltage issues. From the economic perspective, it may allow a consumer to shift their PV generation to satisfy their household loads. The addition of a battery to a home solar system requires an additional power converter. The traditional method for interconnecting PV-battery systems uses at least two separate power converters which results in multistage power conversion for some power flows. This paper proposes an isolated dc-dc three port converter (TPC) based on a dual active bridge (DAB) configuration for the PV-battery system and presents small signal modeling and power flow control of the proposed TPC using a circuit averaging approach. The TPC will interface a PV, a rechargeable battery and a load. Two degrees of freedoms (DOFs) are required to control the instantaneous power of three ports simultaneously. As a result, two controllers are designed for port 2 and port 3 (i.e. PV and load) while port 1 (battery) is responsible for power balance. The phase shift modulation (PSM) technique is used to generate the phase shifted converter voltages to facilitate the power transfer between the ports. The simulation results show that the controllers are capable of independently regulating the instantaneous power flow between the three ports.