Coordinated control strategy for grid-connected PV systems with hybrid energy storage to enhance transient support capability

Abstract

In grid- connected applications featuring a large share of renewable generation, the output fluctuations of photovoltaic (PV) generation deteriorate the power quality of grid-connected systems, and the improper power allocation within the hybrid energy storage system (HESS) further degrades the operational performance. With these concerns in mind, this study develops a grid-connected PV configuration that incorporates a battery–supercapacitor HESS. In terms of energy storage converter control, an improved voltage–current dual closed-loop strategy based on Model Predictive Control (MPC) is proposed for the bidirectional DC/DC converter, in which the outer PI loop stabilizes the DC bus voltage while the inner MPC loop achieves accurate tracking of the inductor current. Compared with the conventional PI-based dual closed-loop control, the maximum voltage deviation is reduced by 2.1 V, and the recovery time is shortened by up to 0.32 s. With respect to power sharing, considering that the conventional low-pass filter (LPF) approach suffers from difficulties in determining the time constant and ignores the state of charge (SoC) of the storage units, an alternative scheme governed by the supercapacitor SoC is proposed, in which the battery compensation coefficient is varied adaptively in accordance with the SoC. The simulation results demonstrate that the proposed strategy markedly reduces the count of charging and discharging cycles of the battery, and effectively prevents the supercapacitor from entering over-charged or overdischarged conditions, thereby ensuring the safe operation of the storage devices.