A utility scale battery energy storage system for intermittency mitigation in multilevel medium voltage photovoltaic system

A battery energy storage system (BESS) for a utility scale photovoltaic (PV) power plant is proposed. PV systems suffer from intermittency and partial shading problems, which could lead to power fluctuations and reduce grid stability. Utilities' inability to service the contracted load might lead to hefty penalties by the regulators. To reduce the effects of intermittency on PV output, a utility scale BESS is proposed for a multilevel inverter with medium frequency transformer link. This also enables PV plants to participate in short-term energy markets. The BESS power is rated at 10% of the PV plant rating. The battery is interfaced to the PV system dc bus through a bidirectional 3-level boost-buck dc-dc converter, which is controlled to regulate power flow. Analysis shows that a 10% BESS rating is capable of providing real power support to mitigate insolation intermittencies by 80%. The operation for battery charging and discharging modes are discussed in this paper. A design example for a 125 kW BESS is provided and simulation results validate grid support capability. Experimental results from a scaled-down laboratory prototype are also presented in this paper.