The Research Of The PV Power System Islanding Detection Methods

At present how to solve the problem of energy crisis is becoming more and more serious all over the world, the sustainable development of the electric power industry has gradually directed to new energy resources. Solar photovoltaic power generation as a promising green energy occupies an important position. But one of the key problems encountered in the promotion of photovoltaic grid connected power generation technology is the islanding effect, so the islanding detection technology is mainly studied in this paper.Islanding detection methods mainly consist two categories: active detection method and passive detection method. The detection principle of passive detection method achieves the purpose by detecting the parameters of point of common coupling such as voltage, frequency, phase, harmonic. When it comes to active detection method, the algorithm is based on the system with different disturbance and then detecting whether the parameters of public point beyond the normal work scope. The following contents are studied in this paper based on these detection principles:1?The present development situation and the characteristic of current domestic and international PV market is introduced. Even though the technical level and innovation ability of it is being limitation, but the space for future development is huge, therefore various countries have introduced relevant policies to support and encourage the photovoltaic industry, and the situation is gratifying. Then the entire structure of the photovoltaic power generation system and related links is sorted out, and the working principle, classification, and technical requirement of inverter is emphatically introduced.2?The concept of islanding effect is expounded, and the mathematical model is established. Further more the harm and the serious consequences caused by the islanding effect on the system is analyzed, and the international standards of the islanding detection is introduced. Taking a panoramic view of the research status at home and abroad of the islanding detection technology, then a detailed comparative analysis of the basic principles of the passive and active islanding detection methods is made, including its application. For the non-detection zone of islanding detection method, the effectiveness evaluation method's advantages, disadvantages and application of the islanding detection based on four coordinate systems are summarized.3?The four representative kinds of active detection methods' principle, flow chart are given respectively, including AFD, AFDPF, current amplitude perturbation method, and SMS method. The simulation model is establish through the simulation software Matlab/simulink, and relevant system parameters are set. The validity analysis and verify of the non-detection zone of the above methods are presented, finally the simulation results directly reflect the characteristics of various methods' detection time, non-detection zone and the power quality influence.4?An improved detection strategy based on dq transform and positive feedback is proposed in this paper. Due to the addition of voltage feedback mechanism, the active current increases, increasing the power mismatch degree of inverter and the local load. Considering the requirements of all aspects of the relevant indicators of islanding effect, so the comprehensive evaluation index is high. Extraction of transient component of the active power and reactive power signal, the algorithm control precision of system is relevant higher. The harmonic injection is lower, the harmonic pollution is reduced accordingly. Simulation results of the algorithm are not affected by the load properties, so the non-detection zone can be effectively reduced. With the length of determine time, the optimized algorithm can effectively prevent false islanding caused by system fluctuation.