Optimal Local Reactive Power Control by PV Inverters

The high penetration of photovoltaic (PV) generators leads to a voltage rise in the distribution network. To comply with grid standards, distribution system operators need to limit this voltage rise. Reactive power control is one of the most proposed remedies. A popular form of reactive power control is an active power dependent characteristic to define the reactive power control of a PV generator. This standard Q(P) characteristic is a simple curve, which is not adapted to the specific situation in the grid. Therefore, this work proposes a method to define the optimal Q(P) curve. The optimal Q(P) curve is represented as a piecewise constant or a piecewise linear function. The parameters are optimized based on historical smart meter information, to obtain a Q(P) curve that keeps the voltage within limits throughout the whole year, with a minimal amount of reactive power. An easy to solve convex optimization problem defines the parameters. The method is applied to unbalanced three-phase four-wire systems. Several simulations with realistic data are performed on an existing distribution network to compare the optimal Q(P) curve with standard Q(P) and Q(V) curves.