Capacitor-Less Bidirectional Synchronous Buck-Boost Converter for Vanadium Redox Flow Battery

The reliability of power electronic converters is crucial for battery-based energy storage systems. This reliability is mostly influenced by the dc-link capacitors, which are employed for reducing the voltage and current fluctuations. The voltage or current ripples affect the battery state-of-health for different solid-state reaction-based battery technologies, including lead-acid and lithium-ion batteries. However, unlike solid-state reaction-based conventional battery technologies, the vanadium redox flow battery (VRB) features solution-based charge-discharge reactions. Therefore, the VRB system possesses much higher mass transfer rates and may not be affected by the voltage or current ripples. Considering this characteristic of VRB, a capacitor-less bidirectional synchronous buck-boost dc-dc converter is proposed in this paper. The proposed converter is operated in current control mode to charge or discharge the VRB system up to a certain level of state-of-charge (SOC). The average charging or discharging current is controlled by a PI controller. The operating principle of the proposed converter is explained in detail, and the performances are verified by the simulation results.