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

Ivan Maradzhiev,Tsvetana Grigorova,Emil Dinkov

doi:10.13189/ujeee.2020.070203

Abstract

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.

Highlights

Brushless DC motors are a very good solution for the use in electric drive systems in the industry and transportation. Due to their simple design, reliability and efficiency, they are an alternative to induction and DC motors used in electric vehicles
The ability of MOSFET transistors to operate as synchronous rectification results in a smaller voltage drop and reduced inverter losses when the BLDC motor operates in the motor mode
With PWM-ON-BIP modulation, no negative current peaks are observed when the current is switched from one phase to another, which is a prerequisite for less electromagnetic noise and easier operation of the power source

Summary

Introduction

Brushless DC motors are a very good solution for the use in electric drive systems in the industry and transportation. In [1,2,6,7], studies are performed with different modulations: a unipolar modulation of upper (PWM-TOP or UT) or lower transistors (PWM-BOT or BT), modulations PWM-ON and ON-PWM, a bipolar PWM-ON modulation (PWM-ON-BIP) and symmetrical modulation (PWM-PWM). The ability of MOSFET transistors to operate as synchronous rectification results in a smaller voltage drop and reduced inverter losses when the BLDC motor operates in the motor mode. It is established in [2,8], that modulations that allow operation as synchronous rectification are PWM-PWM and PWM-ON-BIP. The other used modulations result in negative current peaks, which are especially large in PWM-PWM modulation

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Results

Conclusion