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.