Research On Fault Diagnosis For Three Phase Photovoltaic Inverter

Three-phase grid-connected inverter is the bridge which connected the photovoltaic panels with the distribution system. So the reliability of the inverter is related to the operation stability of the photovoltaic systems. But the grid-connected inverter is vulnerable to the short-circuit and open-circuit of the IGBT, capacitor, inductors and other components, therefore, determining the fault type for the voltage and current output under different fault types accurately is important for the fault location, equipment maintenance and protection formulation.In this paper, using the fault characteristics of three-phase photovoltaic grid connected inverter with constant power control as the research object, the fault characteristics of AC side output current and DC side input current are analyzed. Then an inverter fault diagnosis method based on AC side current detection and an IGBT open circuit fault diagnosis method based on DC side current detection are presented.Firstly, the main topology and control mode of three-phase photovoltaic grid-connected inverter are introduced, and the model of the typical PV system and various device failures are built based on PSCAD/EMTDC simulation platform. At the same time, the research on the protection of the inverter is carried out, and the fault diagnosis of the device is carried out on the basis of considering all kinds of inverter protection.Secondly, the main failure mechanisms of four kinds of devices, such as DC side capacitor, IGBT, fly-wheel diode and inductor, and the fault characteristics of AC side output current and DC side input current (or voltage) after short circuit, open circuit fault occurs of the devices are summarized.Thirdly, the inverter fault diagnosis method based on AC side current detection is proposed. Using the ac output current waveform characteristics, and total harmonic distortion rate of three phase current and of positive and negative half wave current as two supplements, four kinds of fault diagnosis of IGBT open circuit, fly-wheel diode open circuit, inductor open circuit and inductor short circuit are realized.Finally, based on the principle of reducing the number of sensors, the IGBT open circuit fault diagnosis method based on DC side current detection is proposed. The method of Fourier decomposition is used for harmonic analysis and feature extraction of the DC current under normal operation and fault condition. Then use support vector machine (S VM) method to classify the operation of the inverter. The simulation results show that with dc component and second harmonic ratio of dc side current can effectively realize the inverter switching device fault diagnosis.