Unbalance and voltage maintenance control with BESS: laboratory investigations for low-voltage grids

Laboratory tests investigate controls using one to three single-phase inverters of battery energy storage systems (BESSs) for unbalance reduction and voltage maintenance to keep VUF, kU0and voltage within the limits of DIN EN 50160. The laboratory setup includes a grid simulator, line impedance, BESS units, unbalanced loads, and measuring systems. The control mechanisms were tested with varied scenarios and loads. The control decouples active and reactive power to influence voltage amplitude and phase angle separately. This controls can operate at any grid connection point independently. The system proved fundamentally stable, reducing unbalance and maintaining voltage, though exceptions occurred with low BESS power. Scenarios include varied unbalance loads, grid voltage and varied power and connection of one to three single-phase BESS. Best results involved all three BESSs or matching BESS phase conductors with unbalanced loads. In one case, three active BESSs reduced VUF from 2.55% to 1.49%. The tests provided technical insights into BESS design, implementation, and potential for dynamic unbalance reduction and voltage maintenance in low-voltage grids.