Local reactive power droop control modification for distributed generators

A reactive power control modification is proposed for the reactive power control methods defined by the South African Renewable Power Plant Grid code is explained in this paper. Initially constant reactive power and droop control are compared. Droop control is shown to provide reduced voltage variations on a test feeder and requires less reactive power. The improved voltage control comes at the cost of relying more heavily on generators, connected to remote parts of the network, for reactive power support. This paper proposes a method of combining droop control and constant power factor control. The droop setpoint is adjusted using the average network voltage for a 30 minutes cycle. The adjustable setpoint allowed the droop controller to be more effective over a wider range of voltages. It was found that the improved control reduced the voltage variations, tap operations and reactive power demand of the network.