| With the growth of global energy demand and the aggravation of environmental pollution,photovoltaic power generation has become the main way of new energy utilization.As the key link between photovoltaic array and the power grid,the stability and reliability of photovoltaic grid-connected inverters can directly affect the efficiency of photovoltaic generation and the safe operation of the grid.Because of harsh and complex working conditions and frequent on-off switching,the power devices in the main circuit of photovoltaic inverters become the part with high failure rate.When the circuit works abnormally,it is of great significance to judge the fault location in time according to the fault information and start the protection and fault-tolerant operation mechanism for improving system efficiency and reducing economic losses.This research takes three-phase photovoltaic grid-connected inverter as the object.The vector control strategy based on grid voltage orientation is analyzed and the parameters of the controller and LCL filter are designed according to the principle of engineering application.Based on the principle analysis of SVPWM and the mathematical model derivation of normal operation inverter,the simulation model and experimental platform of three-phase photovoltaic grid-connected inverter system are built.Test results show that the output of the inverter meets the grid-connected requirements,which provides reliable support for the follow-up study of fault identification and fault-tolerant technology.According to the number and location of fault switches,22 open-circuit fault modes of IGBT in the main circuit of photovoltaic inverter are classified and coded.The operation characteristics of the inverter under various open-circuit fault modes are analyzed through theory,simulation and experiment,then the output three-phase current of the inverter is determined as the basis of fault identification.The effects of open-circuit fault on inverter output voltage and non-fault IGBT junction temperature are studied and the necessity of fault identification and fault-tolerant control is proved.Based on the fault current data samples under various photovoltaic conditions,the millisecond fault detection is realized by using the rotation angle feature of the current vector.From the perspective of frequency domain characteristics of inverter output current,an open-circuit fault identification and location method for inverters based on wavelet packet transform and BP neural network optimized by bat algorithm(BA-BP)is proposed.The validity of the method is tested by simulation and experiment.From the perspective of time domain characteristics of inverter output current,an open-circuit fault identification and location method for inverters based on time-domain parameters and extreme learning machine optimized by grey wolf optimization algorithm(GWO-ELM)is proposed.Simulation and experiment results show that the fault identification effect of GWO-ELM is better than that of BA-BP.The traditional phase redundancy fault-tolerant topology is improved and simulation results show the improved topology can realize fault-tolerant control of all kinds of single-switch and two-switch open-circuit faults,which can effectively enhance the reliability of the inverters. |
