Research On Islanding Detection Based On Interharmonic Impedance

The problem of environmental pollution caused by non-renewable energy is becoming more and more serious in recent years.Renewable energy generation based on solar energy,hydraulic power,wind energy and fuel cells has been universally recognized worldwide and its development is becoming more and more rapid.Distributed generation has the characteristics of zero emission,low loss and low pollution.It can improve the flexibility and reliability of power system.However,the application of distributed generation technology brings many problems to the power system,among which islanding effect is one of them.Detecting the islanding timely is very important for ensuring the safe and stable operation of the power system.The grid-connected inverter is an important component in the renewable energy power generation system.This paper analyzes the control method of the grid-connected inverter and sets up the MATLAB simulation model.Through mathematical calculations,the parameters of each component in the SPWM inverter circuit are set.At the same time,the mechanism of the interharmonics generated by the SPWM inverter and the interharmonic content generated by the SPWM inverter at different carrier frequencies are analyzed.The feasibility of detecting the islanding effect by interharmonic injection into the grid through SPWM inverter was verified.This paper proposes an islanding detection method based on interharmonic impedance for distributed generation systems with photovoltaic power supply.The related modeling calculations and simulations were performed,and the specific setting methods of the interharmonic voltage range and the conditions for the islanding determination were given.Through simulation,the interharmonic content generated by the grid-connected inverter under the model is analyzed to ensure that it can meet the standards for harmonic content limits between power systems.Simulation analysis was performed for distributed power generation systems with different load capacities,and analysis was performed to verify the effect of islanding detection on load capacity changes.In this paper,the method is also applied to a system with a rectified load,and the islanding detection method is proved to be affected by the nonlinear load very little and the anti-jamming capability is strong.According to the characteristics of the system with the AC-DC-AC converter in the load,a new method of islanding detection using the characteristic interharmonic of the AC-DC-AC converter is proposed.This method broadens the scope of the interharmonic impedance method applied to island detection,greatly reduces the cost of the detection device by using the low-frequency interharmonic,and has good economic benefits.For the distributed power generation system with multiple inverters,modeling and simulation were performed.The advantages of the interharmonic impedance method over the traditional impedance method for islanding detection in a multi-grid inverter system were analyzed and compared.It is verified that this method has good adaptability to multi-inverter system.Each inverter chooses different frequency interharmonics,so it will not have dilution effect,and it has the characteristics of fast islanding detection speed.