Battery Systems for VAR support in Distribution Substations

Battery Energy Storage Systems (BESS) can the integration of Distributed Energy Resources (DER) and create a more reliable power grid. This paper will investigate the use of BESS smart inverters to provide VAR support, assess the impact of reactive power compensation on the lifetime of a BESS and determine how these adverse effects (if any) can be mitigated/eliminated. Initial analysis showed that filter design on the DC side plays a crucial role in reducing current flow in the battery (which impacts the State of Charge). As a remedial measure, an inductor filter has been tested on both the DC side (between the battery and inverter) and AC side (between the inverter and grid) to reduce the battery current and keep the total harmonic distortion of the system within acceptable limits. The results show that during the intervals when there is no real power flowing to/ from the BESS and only reactive power is being inject/absorb, the battery current is zero. This demonstrates that with proper filtering BESS can provide VAR support without impacting its lifetime. Additional use cases were simulated to reflect real grid components at the substation. Most notable is the assessment of VARs from the BESS in parallel with capacitor banks and shunt reactors at the substation.