Research On Islanding Detection For Three-Phase Grid-connected Inverters

In the distributed power generation system, the solar energy, wind energy, nuclear energy are incorporated into the grid through the power electronics.Islanding is a condition in which a portion of the utility system that contains both load and distributed resources remains energized while isolated from the remainder of utility system. When the islanding occurs, distributed power generation device and local electrical equipment may be damaged because of the frequency and voltage out of control and also can endange the lives of maintenance personnel. Hence, it is necessary to detect islanding condition quickly and stop inverter.Firstly, the principles of islanding detection on three-phase inverter are dicussed.Some methods of islanding detection including passive and active methods are instroduced in this paper. Passive methods have on impact on power quality, because no disturbance is impressed on the system, but have a lager nondetection zone(NDZ). Active methods add the disturbance to inverter ouput and reduce or eliminate NDZ, but degrade power quality. So passive and active methods are combined to achieve efficient islanding detection.Besides, islanding detection of active current disturbances were studied, adding the appropriate active current disturbance will trigger islanding detection of under/over voltage protection(OVP/UVP) of the point of common coupling(PCC)voltage.There is NDZ in constant current disturbance when the load does not match, and the active current is continuously injected, which will affect the life or efficiency of the inverter; But for periodic current disturbance, there is no NDZ when load does not match and current disturbance is excessive. For the first two current disturbance problems, adaptive active current disturbance is analyzed in this paper, it can adaptively add current disturbance according to the actual load, making the OVP/UVP of the PCC voltage triggered.Compared with the periodic perturbation, the disturbance quantity and the disturbance time are reduced, and there is no DNZ. The simulation results verify the feasibility and effectiveness of the three islanding detection methods.Finally, a three phase grid-connected inverter is developed with TMS320F2812 DSP controller. All islanding detection methods are implented on the platform and experimental results verify that the adaptive current disturbance can be adaptively added to the disturbation according to the PCC point voltage with no NDZ, and the time of disturbance is reduced.