Research On The Islanding Detection Methods Of Photovoltaic Grid-Connected Inverter

As a new power supply mode,the distributed generation brings a range of issues.The islanding is a basic problem in DG.After the islanding occurs,the safety of the workers and the equipment will be damaged.So islanding detection is a necessary protection function of distributed generation device.Therefore,the researches of this paper focus on the islanding detection methods of grid connected inverter based DG systems,the specific contents are as follows.(1) Researched on some basic contents related to the paper of islanding detection technology is based on grid-connected inverter.The islanding detection method based on grid connected inverter are described, and analyzed the advantage and disadavantage of the active frequency drift methods.Analyzed the Qf0×Cnorm description method,and given the calculating methods of NDZ’s boundary for AFD and AFDPF.(2) Selected the active frequency drift methods to study.In the Qf0×Cnormframe, deduced the position and size of non-detection zone of the active frequency drift method, and verified the AFD and AFDPF’s non-detection zones consistency with the formula derivation.Then,proposed the adaptive algorithm parameters islanding detection method based on the relationship between islanding detection algorithm and the NDZ. Simulation shows that the method has the characteristics of high probability of successful detection.(3) Analyzed and simulated the distortion on inverter current when using AFD and AFDPF.The results show that the THD increases as cf increases,and the THD under different cf value is very similar with the theoretical analysis.Then,proposed the less distortion methods based on the relationship between the islanding detection algorithm parameters and the harmonic.Simulation shows that the method has less THD.(4) At present,the research on active frequency drift type multi-grid inverter islanding detection method are mainly based on Qf0×Cnorm frame.But there are some disadvantages of Qf0×Cnorm frame,such as:it can not reflect the relationship between the load parameters and the NDZ directly because of coordinate coupled to each other.HoweverQf0×Cnorm frame can not only solve this problem, but also retains the advantages of frame on it can describe the frequency algorithm NDZ on a plan.So,analyzed and simulated the performance of active frequency drift type multi grid connected inverter islanding detection method are mainly based on Qf0×Cnorm frame in the paper. Simulation shows that the correctness of theoretical analysis.And,simulated and compared the islanding detection performance under the condition of one inverter and multi-grid inverter.The result shows that there are interference between each inverters when the multi grid connected inverter using different islanding detection methods,and the interference factor is form the output power of other inverters.