High-frequency Differential Mode Modeling of Universal Motor's Windings

Abstract

The universal motor is a rotating electrical machine that can operate on either direct current or single-phase alternating current, similar to a DC motor. It has been widely used in various small and inexpensive drives for a long time, mostly in home appliances and hand tools. The noise generated by a universal motor is believed to be closely associated with the electromagnetic torque fluctuations of the machine, which are caused by variations in the current supplied to the motor. The power electronics utilized for controlling the motor's speed are responsible for these current changes. Accurate high-frequency motor models are crucial for reliable electromagnetic interference simulations in motor drive power electronic systems. Research efforts have expanded to explore different realistic configurations that can be used to investigate the electromagnetic compatibility behavior of electrical machines. This study describes a method for predicting the differential mode impedance of universal motor. The behavior of each motor winding has been individually studied through impedance measurements, starting with the armature, followed by the series winding, and finally the inductive compensating winding. The prediction results over a wide frequency range up to 1 MHz are in good agreement with the measurements and enabled us to propose a model circuit for each motor winding.