Research On Open-Circuit Fault Diagnosis For Three-Level Diode-Clamped Active Power Filter

Active power filter(APF)has the ability to dynamically compensate the harmonics of the power grid for the purpose of improving power quality,and has been increasingly researched and applied in recent years.In order to improve the reliability of APF equipment operation,this dissertation researches on diode-clamped three-level APF as the research object,and conducts a detailed study on the fault diagnosis of IGBT open circuit of its power switching device.The hybrid logic dynamic modeling theory of hybrid theory is introduced into the analysis of APF system operation mode.The auxiliary logic variables are used to integrate the control transition and condition transition into the continuous state equation of the system,and the APF hybrid logic dynamic model considering IGBT open circuit fault is established.On this basis,the running track and output characteristics of IGBT open circuit fault in different positions of the system are described and analyzed.According to the output characteristics of the system,the fault model is divided into several fault sub models,and the switching conditions of the fault sub models are determined,which provides the basis for the open circuit fault diagnosis method.On the basis of fault modeling and analysis,two open circuit fault diagnosis methods for APF system are proposed.The first method of open circuit fault diagnosis based on current residual and O-switch injection uses hybrid logic dynamic model to construct system state current residual equation,extracts state residual information in ?-? coordinate system,locate fault phase and fault bridge arm firstly,and further uses different current residual characteristics of IGBT open circuit fault on the outside and inside of fault bridge arm in O-switch state locate the fault accurately.The second open circuit fault diagnosis method based on the standardization of line voltage error uses the standardized line voltage error value generated by the system in the fault sub mode operation state as the fault diagnosis variable to diagnose and locate the fault,eliminate the interference of common mode voltage,and make the algorithm independent of DC bus voltage;adopt the double standards of threshold comparison and time length to eliminate the estimation error and open Misdiagnosis caused by off delay,etc.The two fault diagnosis algorithms proposed in this paper make full use of the amount of electrical sampling needed by APF system in normal operation without additional hardware.At the same time,the stability of the proposed fault diagnosis algorithm under voltage distortion disturbance and load transient mutation is analyzed and verified,and the performance evaluation indexes of the proposed algorithm and the similar algorithm are compared,highlighting the advantages of the proposed algorithm.While conducting open-circuit fault diagnosis research on the three-level APF,the control strategy of the APF is also studied,and the control strategy adopted and the fault diagnosis method proposed are simulated and experimentally verified.The paper has 46 figures,18 tables and 90 references.