9.1 Drives and Filters – Overview
Nowadays drives with induction motors and voltage type inverters are commonly used as adjustable speed drives (ASD) in industrial systems .
The inverters are built with insulated gate bipolar transistors (IGBT), whose dynamic parameters are very high, i.e. the on- and off-switch times are extremely short. Fast switching of power devices 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 adverse effects in the drives systems [2,3]. The main negative effects are faster motor bearings degradation, over-voltages on motor terminals, failure or degradation of motor winding insulation due to partial discharges, increase of motor losses, and higher electromagnetic interference levels. Other negative effects are increased by the long cables used to connect the inverter and motor.
The prevention or limitation of the negative effects of dv/dt is possible if proper passive or active filers are installed in the drive. In particular, passive filters are preferable for industrial applications (Figure 9.1).
Passive filters used in induction motor drivers are called inerter output filters or motor filters. Depending on filter structures and their parameters, the following filters are specified [4,5]: