Steep-fronted transients in inverter fed motors

摘要

The application of variable-speed drives inrnindustrial processes is increasing day to day. In therncase of a.c. motors the solution is a variable-frequencyrnsupply. These pulse width modulated (PWM)rnwaveforms achieved by modern solid state switchesrnconsist of steep-fronted pulses having rise times asrnshort as 20ns in some Insulated Gate Bipolarrntransistors (IGBT’s). The corresponding du/dt valuesrncan reach MV/ms values and propagate as travellingrnwaves along stator windings. When these waveformsrnreach the terminals of the motor they are partiallyrnreflected, and partially transmitted into the windings,rncausing overvoltages at the first coils. As the voltagernpulse propagates within the winding, there can bernsome resonances and local peaks that are prone tornproduce electrical stress well above the maximumrnacceptable values for the insulating materials.rnThis paper presents a distributed parameterrnmodel that allows voltage distribution prediction inrnwindings of low-voltage motors.