Investigation of Power Losses by Various Brushless Motor Modulation Methods in Motor Mode

The paper presents a comparative analysis of different modulation techniques for BLDC motor control in terms of several types of losses in the system inverter – BLDC motor in motor mode. The experimental investigated modulation strategies are: unipolar modulation of upper (PWM-TOP or UT) transistors, a bipolar PWM-ON modulation (PWM-ON-BIP), a symmetrical modulation (PWM-PWM), a vector control and non-modulation mode. A simple equivalent circuit for the BLDC motor is used to calculate different losses and the system efficiency. On the basis of the equivalent circuit for the different modulation techniques, simple design procedures are discussed for the determination the eddy current and mechanical viscous loss, the copper loss, the hysteresis and mechanical friction loss, the voltage-drop loss of the inverter transistor and diode. Loss distribution experimental data for the brushless DT4260 motor when operating with different modulations and load torque are presented. On the basis of the obtained values for the efficiency of the studied modulations, references for use in battery powered devices such as electric vehicles, electric scooters and more are made.