Fault Diagnosis For Inverter Circuit Based On Hybrid System Theory

With the development of the automation in the industrial and agricultural production in recent years, more and more inverter-fed motor are used to drive mechanical equipment, but the inverter circuit is the weakest link in the motor drive system, the power switch open or short circuit fault often occurred in the inverter due to working conditions, these faults may cause system breakdown and huge losses. Therefore, the fault detection and isolation of inverter circuit has important significance. Inverter circuit is a hybrid system that the discrete switch singnal drive the continuous state variables over the time. Either the conventional fault diagnosis methods only considering the change of discrete control system ignored the change of continuous system state, or only considering the change of continuous system state ignored discrete control change, it is very easy to cause the loss of important fault information, and result in poor performance of fault diagnosis. Considering the discrete control system changes and continuous state changes at the same time, the hybrid system provides a new fault diagnosis method for inverter circuit.Considering the motor drive system being a typical hybrid system, this thesis put forwards a new fault diagnosis for inverter circuit with open circuit faults based on the theory of the hybrid system. Firstly, this thesis analyzed the hybrid characteristics of motor drive system, and introduced the hybrid system theory and mathematical basis and general form of mixed logic dynamic(MLD) model. Secondly, on analyzing motor drive system operation model, the MLD model is applied to establish a mixed logic dynamic model for motor drive system. Then on the basis of hybrid MLD, a state estimator is constructed for the inverter-fed motor drive system, and the state residual equation is established by using output of the real system and state estimator. On analyzing state residual, the residual Park vector method is put forward based on MLD model of the current state residual by using average current Park method. By using Clarke transformation, the three phase current residual is transformed into two phase current residual vector, any switch open circuit fault occurred in the inverter-fed motor drive system can be detected and isolated based on phase angle of two phase current residual vector. In the end, the MLD model simulation model for forming state residual is built based on MATLAB/SIMULINK, fault simulation are performed using residual Park vector method for inverter circuit, the simulation results are consistent with theoretical analysis, this verified the residual Park vector method presented in the thesis based on residual MLD model is effective, and it can detect and isolate the switch open circuit faults occurred in the inverter-fed motor drive system rapidly, effectively and accurately.