A Reactive Power Boosting Strategy for BESS-STATCOMs

The integration of conventional STATCOMs with a battery energy storage system (BESS-STATCOM) has been gaining popularity recently. A BESS-STATCOM is interfaced to the grid via a power conversion system (PCS). This PCS is often a single-stage dc-ac converter directly connected to the BESS without an intermediate dc-dc converter to reduce costs and size. In this configuration, BESS's voltage drops associated with a lower State of Charge (SoC) can reduce the capabilities of the BESS-STATCOM to inject reactive power. This paper introduces a control strategy to boost the reactive power capabilities of a BESS-STATCOM with a single-stage PCS. The proposed strategy disconnects the battery pack from the power conversion system (PCS) and charges the dc link capacitor to its full rated voltage from the grid. The transition into the boost mode and vice versa is seamlessly performed at zero battery pack's current, eliminating the need for a dc circuit breaker.The effectiveness of the proposed control strategy is validated through a Matlab/Simulink simulation using a 5 MVA BESS-STATCOM, followed by an experimental validation using a 32.5 kVA scaleddown PCS. The results show that when the battery pack's SoC is at 20%, the proposed strategy increases the reactive power capability approximately threefold compared to the scenario without the strategy.