Research On Adaptive Distance Protection Of Distribution Network Accessed By Photovoltaic Power Supply

Photovoltaic power generation has the advantages of being cheap and renewable,clean and pollution-free,and inexhaustible.However,with the increase in the scale of photovoltaic grid-connected networks,distribution network grids have become complex topologies for multiple power supplies.At the same time,photovoltaic power generation is volatile.Intermittent and intermittent,its flexible grid-connected way causes the traditional distance protection to measure the impedance can't accurately reflect the location of the fault.It needs a dynamic setting impedance that can adapt to various environmental factors and operating modes to ensure sensitive and reliable movement.Therefore,It is necessary to study the adaptive distance protection of the distribution network for photovoltaic power access.Researched and analyzed the components and control principles of each part of the photovoltaic system,and established a photovoltaic grid-connected simulation model based on PSCAD/EMTDC,including a photovoltaic array model,a boosting chopper circuit model,an inverter model,an MPPT and an inverter control model,etc.The theoretical analysis and simulations verify the impact of the photovoltaic power supply on the traditional distance protection of the distribution network when it is connected to the busbars and feeders;the use of photovoltaic grid-connected for the sensitivity reduction and refusal of the distance protection II caused by the access of the photovoltaic power supply to the distribution network.The general equivalent model of each part of the system and Thevenin's theorem define the dynamic equivalent impedance of the PV power plant.According to the dynamic equivalent impedance,a new method of adaptive distance protection is proposed.The current conditions are calculated by using the parameters of the PV power plant and the dynamic parameters that can be monitored.The dynamic equivalent impedance and dynamic branching coefficient k_D of the PV power plant are obtained,and the dynamic set impedance of the adaptive distance protection II section is obtained.The adaptive distance protection based on the dynamic equivalent impedance of the photovoltaic power station is achieved by comparing the dynamic setting impedance and the measured impedance.Aiming at the distortion of the output characteristics of the photovoltaic array due to local shadow and affecting the dynamic tuning of the adaptive distance protection,the mathematical model of the photovoltaic array under local shadow is established by using the engineering equivalent model considering the influence of light intensity and temperature,and the open circuit voltage of the photovoltaic array under local shadow is defined.And the reduction degree of short-circuit currents ?_Uand ?_I,using ?_Uand ?_Ito analyze the changes of the dynamic equivalent impedance of photovoltaic power stations under local shadows,and thus propose an adaptive distance protection scheme that takes into account local shadows of photovoltaic arrays,calculated according to ?_Uand ?_I.The dynamic equivalent impedance ratio coefficientK_UII judges the current lighting condition of the PV array,selects the corresponding dynamic equivalent impedance model of the PV power plant,and calculates the dynamic setting impedance of the adaptive distance protection II section under the new condition,thereby realizing the self-concealment of the local shadow of the photovoltaic array.Adapt to distance protection.Using PSCAD simulation and MATLAB data processing,it is verified that this method is not affected by any lighting conditions,fault types and operating modes;solves the problem of sensitivity reduction and refusal of distance protection in segment II caused by photovoltaic power access to distribution network;The setting value has real-time and volatility for the amount of fault information,which can effectively improve the reliability and sensitivity of the protection.