Selected Problems of Induction Motor Drives with Voltage Inverter and Inverter Output Filters

. Fast switching of power devices in an inverter causes high dv/dt at the rising and falling edges of the inverter output waveform. . High dv/dt in modern inverters is the source of numerous disadvantageous effects i.e. faster motor bearings degradation, over-voltages on motor terminals, failure or degradation of the motor winding insulation due to partial discharges, increase of motor losses, and a higher electromagnetic interference level. . The prevention or limiting of the negative effects of dv/dt is possible if proper passive or active filters are installed in the drive. Particularly passive filters are preferable for industrial application . Passive filters used in induction motor drives are called inerter output filters or motor filters. Depending on filter structures and their arameters, the following filters are specified . Differential mode filters also known as sinusoidal filters or LC filters, and the motor supply voltage is smoothed to almost a sinusoidal shape contrary to the inverter output voltage (filter’s input), which is composed of series of short rectangular pulses. . Common mode filters are used mainly to limit the motor leakage currents, which flow through motor parasitic capacitances. . dv/dt filters are used to eliminate the wave reflection effect in long cables, in order to avoid over-voltages on the motor terminal as well as to secure the motor windings insulation from failure.