Digitally controlled output filters for improvement of temperature behavior of machine tool main spindle drives

Variable speed main spindle drives of machine tools are usually fed by three-phase two-level inverters. Because of the switching operating mode of these inverters, the motor voltages and currents contain harmonics which do not contribute to torque formation but solely to an undesirable warming of motor spindle elements. This warming results in thermal elongation of the spindle shaft and therefore to a deviation in dimensional accuracy. The increased wear of the spindle bearings through high temperature differences between the inner and outer rings of the bearings is another drawback. This paper proposes a novel high-performance control system of an interior permanent magnet synchronous motor (IPMSM) using an inverter with an LC output filter. The combination of inverter and filter reduces the motor losses by compensating the switching ripples and therefore leads to an evident improvement of the temperature behavior of the main spindle drive.