A network model for inverter-fed induction-motor drives

A network model is presented for inverter-fed induction motors operated at steady state. The model is based on the transmission line matrix (TLM) method considering the cable impedance L, capacitance C, conductivity G and resistance R described by 3x3 matrices combined with a 3 phase (abc)-model for the induction machine. For steady-state operation, the induction-motor model is reduced to a 3x3 frequency-dependent matrix which can be described in a very simple way. The 3-phase cable is modelled using the Transmission-Line (TLM) Theory where cable impedance L, capacitance C, conductivity G and resistance R are described by 30 matrices. The induction-motor is represented by a 3-phase (abc)-approach. In the steady state case this approach is simplified to a 3x3 impedance matrix which can be coupled with the TLM-model. The result is a transfer function which couples the input voltage with the output voltage at the motor. To calculate the voltage at the motor, the voltages pulses from the inverter are transformed into the frequency domain via FFT. In the frequency domain the voltage at the motor is easy computed by multiplication with the transfer function. The simulation results are compared to measurements for the voltage output of a drive with an inverter, cable and induction motor for which the parameters are well known.