Bidirectional CLLC Resonant Converter Design for Photovoltaic Microinverters with Li-Ion Batteries

The integration of storage into solar photovoltaic systems helps address the increasing electricity demands and the intermittent nature of renewable energy sources. Since photovoltaics (PV) are easily affected by environmental conditions, PV microinverters with integrated batteries are one solution to achieve a more reliable power output to the grid. However, this results in a more complex microinverter system design which requires an additional dc-dc converter to charge and discharge the battery. In this system, proper power balancing control is needed to transfer energy to and from the battery while ensuring the dc link voltage stays within an acceptable voltage to properly provide power to the grid. This research proposes a system control method of a bidirectional CLLC resonant converter to provide a rapid transition between the batteries’ discharging and charging modes in the integrated microinverter. Also, the voltage gain of the resonant tank of the symmetric bidirectional CLLC converter using first harmonic approximation analysis is discussed. Simulation results in PSIM simulation software verify the validity of the proposed control method.