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 o f costly motor-drive-related process failures, The popular ASD's consi st 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) a nd 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 difficu lties determining which mitigation technique is best for his/her appli cation. Using laboratory measurements, this paper evaluates and compar es various suggested mitigation techniques for bearing currents, EMI, and motor terminal overvoltages in terms of their effectiveness and lo sses and provides practical application assessments for users.