Abstract: To smooth the random fluctuation of the active power in the stand-alone photovoltaic generation system, this paper proposes a coordination control strategy for the charge or discharge power allocation between different energy storage medium in the hybrid energy storage system. Based on the real-time state of charge （SOC） and the maximum possible charge or discharge time, this strategy commands the super capacitors to charge or discharge firstly, when reaching the limit of the SOC, and then controls the batteries to work. According to the theory of life cycle cost and the constraints of the real time SOC, the loss of power supply probability and the system independent operation ability, we establish the capacity allocation optimization model for hybrid energy storage system. Then, we use an improved particle swarm optimization algorithm to solve the given example, and verify the effectiveness of the energy coordination control strategy and the validity of the capacity allocation optimization model by comparing with the single-battery energy storage system.

Key words: stand-alone photovoltaic, hybrid energy storage, energy coordination control, capacity allocation