A Novel Control Technique for Islanding Detection of Photo-voltaic Systems using A Reactive Power Droop

Abstract

Unplanned islanding of grid-connected photo-voltaic (PV) generation sources is a situation that must be avoided. Passive and active approaches were developed to detect islanding incidents with each approach having its own merits and disadvantages. Passive islanding techniques suffer from non-detection zones (NDZ) when the generated power closely matches the consumption of almost purely resistive loads. This paper proposes a passive islanding detection method through modifying the control interface of PV systems to provide an anti-islanding controller. The technique utilizes a reactive power\frequency (Q-f) droop in generating the 3-phase voltage in the inverter. As PV systems are not required to supply reactive power to the grid, this droop equation can be considered inactive in grid-connected mode as the frequency is imposed by the grid and the distributed generation (DG) is operated at unity power factor. In islanded mode, the droop equation results in a phase shift that reflects in an error in the reactive power computation in the controller which is based on measurements at the terminals of the DG. Several case studies validate the proposed technique in MATLAB/Simulink as shown in the simulation results. The method is shown to work for both single DG and multi-DG systems with no drawbacks during normal operation in grid-connected mode.