Research On Islanding Detection For Distributed Generation Based On The Characteristics Harmonic Measurement At PCC

In recent years, energy problem increases seriously, so dose the requirement of power supply quality, the safety and reliability of system’s operation.The distributed power generation system can save more money and reduce energy consumption, improve the energy efficiency of electric power system and operation flexibility when compared with traditional energy using ways, which have a badly pollution problem and huge damage to entironment,it’s the development direction of electric power industry in the 21st century. However, when a large number of new energy power generation devices are accessed to the power grid in the form of distributed generation (DG), the power quality problems and operational planning problems occur at the same time. Islanding is one of major problems.The Definition of islanding is that:when the power grid disconnects to the system because of grid fault, stops the power supply, meanwhile, the system fails in detection, then a self powered island is formed by the distribution of power station and the local load. It would be a threat to the electricity equipments and workers, also could affect the stability and reliability of the system’s operation. The research of islanding detection method plays an important role in the development of distributed generation.Islanding detection method is divided into two kinds, passive islanding detection and active island detection. Passive islanding detection methods determine whether islanding or not through the change of the voltage, frequency or phase, but they have large none detection zone if distributed generation output power match the load power, the normal fluctuations of power grid also may causes misjudgment. Active island detection methods introduce some disturbance to the grid, then detect the change of the voltage, frequency or phase to test islanding. But they will affect the power quality because of the additional disturbance. This paper puts forward a kind of passive islanding detection method to the system with grid-connected inverter, based on the test of characteristic harmonic at point of common coupling (PCC).The method can solve problems caused by traditional islanding detection methods. This paper analyses the harmonic spectrum characteristic of grid-connected inverter, gets the result of harmonic transmission rule and the change of characteristic harmonic voltage at PCC, then explains the principle and concrete implementation steps of this method in detail. Finally, the simulation results and real projects show that the proposed islanding detection method is effective and practical.