An evaluation of mitigation techniques for bearing currents, EMI and overvoltages in ASD applications

With the increased application of adjustable-speed drives (ASD's) for efficient speed control of ac motors, here has been a growing number of costly motor-drive-related process failures, The popular ASD's consist of a pulsewidth modulated inverter switching insulated gate bipolar transistors at 2-20 kHz, with rates of voltage rise (dv/dt) of 6000 V/mu s. The high dv/dt has adverse effects on the motor insulation due to motor terminal overvoltages (exacerbated by longer cable lengths) and contributes to EMI and damaging bearing and leakage currents caused by common-mode voltages. In response to these problems, a variety of mitigation techniques have emerged. However, oftentimes the industrial user searching the literature for an immediate solution faces difficulties determining which mitigation technique is best for his/her application. Using laboratory measurements, this paper evaluates and compares various suggested mitigation techniques for bearing currents, EMI, and motor terminal overvoltages in terms of their effectiveness and losses and provides practical application assessments for users.