Abstract
The thesis introduces passive island detection methods and active island detection methods, and further derives their non-detection zone (NDZ). The advantage of passive island detection methods are convenient to perform; however, they have the larger NDZ. As for active island detection methods, it is usually performed by injecting different kinds of disturbance signals which can make harmonics distorted. Based on the positive feedback principle of the island detection, amplifying the offset of voltage and frequency when the islanding event happened so that the voltage and frequency of point of common point can be up to the detection condition and then enables the system to automatically switch from current control to voltage control. Noted that the disturbance signal would continuously inject to the system so that ill-designed positive gain easily makes the system switch accidentally. In contrast, if the positive gain is too small, the system can not switch at the proper timing since it would take much time to fulfill the detection. Therefore, in order to make the positive gain well designed, analyze the small signal model through the dynamic equation and then find out the boundary of the positive gain by root locus. At the end of the thesis, simulate respectively the system with island event happening with detection structure and without detection structure by Simulink under the situation that the converter delivers the whole power to the load. Analyze the boundary of the positive gain in real time and then compare with the boundary of the positive gain in frequency domain to verify the stability.