| Abstract |
Power converters for motor drives with fast switching semiconductors and a high pulse frequency allow motors of almost ideal sinusoidal shape, but the voltage applied to the motor contains a lot of harmonics. Besides the resulting EMC problems it comes to an additional stress on the coil isolation due to the high du/dt of the motor voltage. There is an intensification of this effect, if the motor is connected to the inverter with an electrical long (e.g. 100 m.) power line, because the voltage blocks generated by the converter are reflected on both ends of the line. The result is an HF oscillation on the line after each switching activity of one of the power semiconductors, fading away in a slow balancing process. A second effect of the reflections are overvoltage peaks at the motor terminals of up to the double of the dc-link voltage. This paper deals with EMC filters to avoid the reflections at at least one end of the inverter motor power line. The filters work as a transmission line termination according to the HF-TEM theory, the aim is to transfer the voltage blocks to the motor with only a minimum of deformation, and to reduce the overvoltage at the motor terminals. |
