A simple and cast effective solution to reduce motor bearing currents in PWM inverter drives

High frequency PWM inverters increase the circulation of motor bearing currents due to a high frequency flux induced by common mode currents, which link the stator, rotor and bearing loop. These circulating currents damage the motor bearings, increasing the overall maintenance costs. This paper analyzes the influence of motor design parameters in motor bearing currents amplitude and proposes different alternatives to eliminate them. Among the alternatives proposed in this paper, different types of shunt passive filters, and link reactors are analyzed, and also the influence of the resistance of the rotor bars are studied. Experimental results obtained in a laboratory prototype prove the viability of the theoretical analysis and the effectiveness of the proposed compensating alternatives.