Improved Reactive Power Sharing Among Customers’ Inverters Using Online Thévenin Estimates

A growing number of inverter interfaced rooftop photovoltaic and battery systems are changing suburban distribution systems. The potential of reactive power support from this equipment is attracting attention as a way of addressing the systems' voltage magnitude problems. However, if the voltage is controlled by a conventional droop-based strategy, common radial configuration at suburban feeders can cause an uneven allocation of the reactive power compensation among the inverters. A droop control strategy is developed in this paper using two parameters of the steady-state Thévenin equivalent model of the system seen by each inverter. The Thévenin based droop control permits even allocation of the reactive power compensation. A sufficiently invisible low-level probing is utilized by each inverter to robustly identify Thévenin reactance and Thévenin source in steady state. The inverter's output power is adjusted by the two identified parameters. Demand changes are addressed. Interference by the neighbor inverters' simultaneous probing and compensation is also considered. Simulations results on the IEEE 33-bus and a large-scale system show the efficacy of the proposed strategy.