A Method for Improving Power Factor in Inverter-Fed Induction Motors by the Use of Rotor Convex Copper Bars

Copper bars are often utilized in the rotor of a high power induction motor in order to reduce joule loss and improve overall efficiency. In this article, a kind of rotor convex copper bar is introduced instead of the conventional rectangle copper bar in the case of inverter-fed induction motors. The difference in the leakage reactance between the convex and the rectangle copper bar is analyzed. The use of convex copper bars can reduce the leakage reactance to some extent as the frequency rises. The decrease of the leakage reactance can contribute to restraining the ascending trend of the rotor reactive current. Finite-element method is taken to carry out the simulation, and a 550 kW prototype is produced to validate the proposed method. Experimental results indicate that the application of convex copper bars can help to lower the rotor reactive current and improve the power factor when the motor works near the end of the constant power area.