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.
A photovoltaic (PV) system has a variable power output that depends on solar irradiance level and ambient temperature. This will be an issue when there is a massive penetration of PV in the future. Therefore, an energy storage system is indispensable to compensate the problem of PV output fluctuations. Battery energy storage system (BESS) employing power electronic converters can be used for compensating the fluctuating PV power. This paper proposes a 2-kW full-bridge bidirectional isolated dc-dc converter that is employed in a BESS with PWM converter for PV output power leveling. This paper also presents a current controller using the DQ synchronous reference frame for regulating voltage at the high-voltage dc side, and a bidirectional power flow control for controlling the output power of the BESS to ensure that the power that is injected to the point of common coupling (PCC) is leveled at 2 kW. The performance of the system is confirmed with PSCAD simulation.Keywords-Bidirectional isolated dc-dc converters, energy storage systems, photovoltaic (PV) output power leveling, battery energy storage system (BESS), point of common coupling (PCC).
This paper presents the experimental verification of a 2 kW battery energy storage system (BESS). The BESS comprises a full-bridge bidirectional isolated dc-dc converter and a PWM converter that is intended for integration with a photovoltaic (PV) generator, resulting in leveling of the intermittent output power from the PV generator at the utility side. A phase-shift controller is also employed to manage the charging and discharging operations of the BESS based on PV output power and battery voltage. Moreover, a current controller that uses the -synchronous reference frame is proposed to regulate the dc voltage at the high-voltage side (HVS) to ensure that the voltage ratio of the HVS with low-voltage side (LVS) is equivalent to the transformer turns ratio. The proposed controllers allow fast response to changes in real power requirements and results in unity power factor current injection at the utility side. In addition, the efficient active power injection is achieved as the switching losses are minimized. The peak efficiency of the bidirectional isolated dc-dc converter is measured up to 95.4% during battery charging and 95.1% for battery discharging.
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