Method and system for diagnosing open-circuit fault of power switching device of three-phase three-level rectifier

A system for diagnosing an open-circuit fault of a power switching device of a three-phase three-level rectifier, comprising:

• a diagnosis variable determination module, configured to select an expected value of a phase-to-phase voltage between an X-phase and a Y-phase of the rectifier at a current time and an actual value of the phase-to-phase voltage, and use a deviation between the two is as a diagnosis variable;
• a diagnosis variable calculation module, configured to obtain voltage current information required for diagnosis from a control system of the rectifier, and calculate the diagnosis variable by adopting a screening technique;
• a diagnosis threshold determination module, configured to classify fault sections according to fault characteristics of faulty switches at different times, and update a diagnosis threshold at the current time for a current fault section;
• a polarity determination module, configured to judge whether the diagnosis variable exceeds a threshold range and a polarity thereof according to the diagnosis variable and the diagnosis threshold;
• a diagnosis module, configured to identify and locate a fault of an internal switching transistor according to the judgment result;
• a correction module, configured to check a diagnosis result of the fault to verify whether the diagnosis result is correct, and correct the diagnosis result of a fault of an external switching transistor that is misdiagnosed as the fault of the internal switching transistor to implement identification and location of an external switching fault, wherein the fault of the internal switching transistor is determined based on the diagnosis result is correct, and the fault of the external switching transistor is determined based on the diagnosis result is wrong,
• wherein alternating current side three-phase voltages, three-phase currents and a direct current side voltage obtained by the three-phase three-level rectifier through sampling are sent to the control system, and, according to the alternating current side three-phase voltages, the three-phase currents, the direct current side voltage, an alternating current side inductance and an alternating current side equivalent resistance, the control system obtains three-phase switching control signals of each power switching device of the three-phase three-level rectifier through calculation and sends the three-phase switching control signals to the three-phase three-level rectifier.