Optimal Reactive Power Allocation in Large-Scale Grid-Connected Photovoltaic Systems

In this paper, an optimal strategy is proposed for the reactive power allocation in large-scale grid-connected photovoltaic systems. Grid-connected photovoltaic systems with direct current to alternating current inverters are able to supply active power to the utility grid as well as reactive power. The active power, extracted by the direct current to alternating current inverters, is usually controlled to be around the maximum power point of the photovoltaic array attached to it. For large-scale grid-connected photovoltaic systems with multiple direct current to alternating current inverters, due to the limited apparent power transfer capability of each inverter, the reactive power needs to be allocated among the direct current to alternating current inverters in a proper way. The proposed method achieves the maximum reactive power transfer capability of the entire system by applying classic Lagrange multiplier method. The sufficient conditions of the optimal reactive power allocation strategy are provided and mathematically proved. The proposed optimal reactive power allocation strategy is then tested in a case study against a sample large-scale grid-connected photovoltaic system.