Research On Fault Diagnosis And Fault Tolerant Control Of Three-level Active Power Filter

With the increasing complexity of power system loads,non-linear loads as a source of harmonics pose a serious threat to power quality and seriously affect the stability of power supply.Active power filters are widely used in the management of power quality in power systems due to their good dynamics and adaptability to harmonics of different orders.The traditional active power filter main circuit uses a two-level three-phase converter.As the voltage level and capacity increase in modern power systems,the active power filter main circuit using a two-level converter cannot meet the requirements of harmonics governance,the three-level converter as the main circuit of the active power filter realizes the requirement to increase the compensation capacity,but the number of switching devices of the three-level converter is double that of the two-level converter.The probability of failure of the switching device is greater,which affects the normal operation of the system.This article first analyzes the principle of the three-level active power filter and the working principle of the main circuit T-type three-level inverter.The control method of the three-level active power filter is studied,and the ip、iq method is applied of in the detecting harmonics method.For the tracking method of reference current,the traditional three-level hysteresis control and the hysteresis control based on space voltage vector are compared and analyzed.The hysteresis control based on space voltage vector selects the optimal voltage vector through area judgment.The current error is within the allowable range.This method can effectively eliminate the effect of phase-to-phase and ensure the accuracy of current tracking in a lower switching frequency condition.The comparative simulation analysis also verifies the superiority of the hysteresis control based on the space voltage vector.Aiming at the fault of the three-level T-type active power filter,the fault characteristics when open circuit fault of the power device occurred in different positions are studied,and the fault type of the power device is divided into the horizontal bridge arm fault and vertical bridge arm fault.The hybrid theory is introduced into the fault diagnosis of the converter,and a normal model and a fault model of open circuit faults of different power devices are established,and the faults are located according to the residuals generated by the model predicted output and actual output.The effectiveness of the method is verified through simulation.Based on the SVPWM control method,according to the change of the basic vector in the space voltage vector diagram after the power device at different positions,two fault-tolerant control methods are proposed.For the open-circuit fault of the power device in the vertical bridge arm,a fault-tolerant control method based on hardware topology reconstruction is applied.For the open circuit fault of the power device in the horizontal bridge arm,a fault tolerance method based on vector redundancy is adopted.The lost basic voltage vector can be replaced by the redundant voltage vector or can be equivalently synthesized by adjacent basic vectors.Finally,the fault-tolerant effects of these two methods are verified by simulation.