Fluctuating photovoltaic (PV) output power reduces the reliability in power system when there is a massive penetration of PV generators. Energy storage systems that are connected to the PV generators using bidirectional isolated dc-dc converter can be utilized for compensating the fluctuating PV power. This paper presents a grid connected energy storage system based on a 2？kW full-bridge bidirectional isolated dc-dc converter and a PWM converter for PV output power leveling. This paper proposes two controllers: a current controller using the d-q synchronous reference and a phase-shift controller. The main function of the current controller is to regulate the voltage at the high-side dc, so that the voltage ratio of the high-voltage side (HVS) with low-voltage side (LVS) is equal to the transformer turns ratio. The phase-shift controller is employed to manage the charging and discharging modes of the battery based on PV output power and battery voltage. With the proposed system, unity power factor and efficient active power injection are achieved. The feasibility of the proposed control system is investigated using PSCAD simulation. 1. Introduction Many countries are implementing PV solar panels as they are a clean and sustainable source to meet their power demands. However, the grid connected PV unit without energy storage unit can affect the utility grid in a negative manner due to the intermittent nature of PV. In order to solve this problem, integration of energy storage system to level the output power of PV is necessary [1–4]. There are many types of energy storage systems such as superconducting magnetic energy storage, flywheel, capacitor, battery, and pump hydrostorage. The battery energy storage device is modular, making it easy to be connected close to the point of load and the PV generators. Li-ion batteries have high energy density and are being increasingly used in battery connected PV systems [5]. However, as long as it is employed for PV application, an efficient bidirectional system is required to perform the charging and discharging of the batteries. Various configuration of a bidirectional isolated dc-dc converter has been investigated in [6]. Bidirectional dc-dc converter can be categorized as isolated and nonisolated topologies. Although an isolated converter is more complicated and expensive than a nonisolated converter, it benefits the system safety, reliability, and flexibility. In addition, the full-bridge topology has a high efficiency, while providing minimum switching loss, improved EMI, and galvanic isolation for energy
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