Limitations of dq-Transformation for Modeling Healthy and Faulty Modes of Multiphase Electric Drives

At present, the most widely used methods for modeling electromagnetic processes occurring in multiphase inverter-fed AC electric drives (MACD) are methods based on the use of dq-transformation. The authors of this paper analyzed the errors of this method in relation to the steady-state failure-free and failure modes of operation of the MACD. This paper proves that, in the indicated operation modes with the overwhelming majority of the values of the MACD phase number, the use of dq-transformation causes the loss of a certain share of information about phase voltages and currents, electromagnetic torque of the AC motor, and current at the input circuit of the frequency converter. This is due to the fact that the application of the basic operations of dq-transformation leads to mutual compensation of some harmonic components of phase voltages (and, therefore, phase currents).