A Control Strategy of Hybrid Energy Storage System in Bipolar-type DC Micro-grid

This paper proposes a coordinated control strategy for the hybrid energy storage system (HESS) to stabilize the DC bus voltages in bipolar-type DC micro-grid. The hybrid energy storage system consists of the lithium battery and the super capacitor for their complementary performances of high energy density and high power density. And voltage balancer is also used to coordinate with hybrid energy storage to balance the power on two DC buses. In order to smooth the working current of the lithium battery and avoid the high-frequency harmonic interaction between two DC buses from voltage balancer, the super capacitor is adopted as an energy buffer to compensate the ripple power. The output power of the lithium battery and working state of voltage balancer are controlled separately by measuring the relationship between two sets of super capacitors. Meanwhile, the response of the lithium battery and voltage balancer to the super capacitor is correctly implemented by adjusting voltage reference values of DC buses. In the end, simulation