Improvement on stability and islanding detection performances by advanced inverter control of DG

The islanding detection is one of the most important issues for grid-connection of the distributed generation (DG) systems. Several recent researches have developed two types of islanding detection methods (IDMs) with high-performance. One is the power and voltage (P-V) characteristic of load based IDM, and the other is the inverter's switching frequency based IDM. Although the above IDMs have no non-detection zone (NDZ) theoretically, their usefulness mainly depends on the control performance of the inverter in practice. In other words, the inverter must achieve the decoupled real and reactive control and successful operation of phase-locked loop (PLL). To deal with these problems, this paper describes the design of inverter controller to improve both system stability and islanding detection performance with the NDZ. The proposed controller uses the magnitude and phase of measured voltage directly instead of using the direct and quadrature axes voltages and currents. Additionally, it does not need an instant phase of point of common coupling (PCC) voltage, which is required in the conventional controller, and therefore makes it possible for the PLL independent control. Several case studies are carried out to verify that the proposed controller has better performance than the conventional controller.