Fault Diagnosis Of Active Power Filter

Active Power Filter improves the power quality effectively with PWM technology and double closed-loop control strategy. However, APF not only has the weaknesses of power electronic devices, but also works long time under high frequency, high voltage and high temperature, so short circuit and open circuit fault can happen easily. According to surveys, the faults of IGBT and dc-linked capacitor account more than 50% of the total failure, which affects the reliability of the APF system greatly. It diagnoses and locates the faults of IGBT and dc-linked capacitor with modeling and system identification, which makes a contribution to high reliability fault-tolerant control for APF.Fault theories and types of IGBT is studied, especially the reasons and parameter electrical changes of short circuit and open circuit fault. It discusses open circuit diagnosis methods in aspects of the diagnostic time, algorithm complexity, location accuracy and reliability. From the inverter fault diagnosis field, it improves the tube voltage and average current method, then proposes the fault diagnosis scheme based on residual current in summarizing the voltage and current methods, and analyzes its diagnosis principle with mathematical model. A comprehensive evaluation system of power electronic fault diagnosis algorithm is proposed, and it evaluates the five kinds of typical open circuit fault diagnosis methods from six dimensions, and proves the superiority of the current residual method.It analyzes the internal structure and fault principle of dc-linked capacitor, and establishes the equivalent circuit and mathematical model. The judging basis is given based on the relationships between ESR, C and capacitors failure. Through theoretical analysis and mathematical deduction, residual life prediction model is established. It also propose an online detection method based on the non-power frequency sine excitation current, and designed a band-pass and band-stop filter, with studying the responses of the capacitance, it measured the capacitance value, which contributes to the life prediction model validation.A double closed-loop PI controller and a real-time simulation platform are designed based on MATLAB/Simulink. The simulation results show that fault solution based on the current residual is obvious better than tube voltage method and average current methods, it can disgnoses quicker, locates accuracy, costs less and is not affected by loads. The real-time online detection method based on the non-power frequency sine excitation has higher precision and smaller errors, which can meet the requirements of the residual life prediction.