The Research On Islanding Detection For Grid-connected Distributed Generation

Because of the rapidly increasing of power demand and more and more serious environment problem human facing, distributed generation technology develops fast in the world recent years, and will be an important development direction of the future power industry. Distributed generation technology not only can solve the energy and environment issues, but also can reduce costs and power losses and improve the stability and flexibility of power system. However, human will face a great technology challenge, while enjoying the benefits brought by distributed generation. There will be big change with the structure and operation of distributed generation itself and the whole power system,when distributed generation operates connected to grid. So how to ensure the safety and reliability of the new system will be important aspect of research on DG. Islanding detection and related technology is an important component of it.So many islanding detection methods have being presented, and they consist of long-range methods detecting from grid side and local methods detecting from distributed generation side. Long-range detection methods are not limited by the kind of distributed generation, and local detection methods are not completely the same in accordance to the types of distributed generation. Because it is difficult to realize the technology and the costs are so high, long-range methods are seldom used and local methods are always selected. Local detection methods can be divided into active and passive detection assay. Active methods have high detection sensitivity, but the stability and power quality of the system will effect. While, non-detection zone of existing passive methods is large.Aiming at the shortcomings of existing methods, a new method detecting islanding by monitoring the value of ?f ?V L is proposed based on analyzing the basic principle of passive islanding detection method. Disturbance of the system is identified by the change of amplitude or frequency of the voltage, then calculate the value ?f ?V L and compare it with the threshold. If the calculated value is larger than the threshold, we think islanding happen. Or, it is considered that other disturbance happen.Simulation experiments are done as grid-connected inverter distributed generation and low-power synchronous generator to example, based on considering the impacts of change of local load, voltage sag of grid, harmonic pollution and power mismatch on islanding detection. The results show that the new algorithm is simple and feasible, fast and reliable, and it has high sensitivity, good anti-interference ability, and very small"non-detection zone", and it is not limited by type of distributed generation.