Study on a BLDC motor having higher winding inductance: A key to field weakening

Abstract

The study covers the design, analysis and experimental study of a 1 kW motor which is designed for a special in-wheel motor driven light electric vehicle. The main concern is to design a BLDC motor having a higher value direct-axis phase inductance which is providing high performance field weakening operation. A sub-fractional slot concentrated winding structure with unequal tooth widths is chosen. The design phase is including the motivation and the computer aided design works. A software package based on configurator approach is used to determine the motor parameters in a broad sense. Then the motor is modeled in a Finite Element Analysis (FEA) package for detailed analysis and, particularly the 2D and 3D field analyses are obtained to verify winding inductance value. The designed motor is manufactured precisely and an experimental study is held to verify the design work including the precise measurement efforts for the motor inductance. Also the field weakening operation of the motor is managed by using phase current advance method. Index Terms-Brushless DC motor, field weakening operation, winding inductance

On Field Weakening Performance of a Brushless Direct Current Motor with Higher Winding Inductance: Why Does Design Matter?

“…Due to the lack of a flux control parameter, SMPM motors can achieve higher speeds only by providing a negative inductance voltage that is contributing to the back-emf, and this slope depends on the d-axis inductance. The basic voltage equation of a BLDC motor regarding its equivalent circuit is given in Equation (1) [5].…”

“…The only way to provide a wider operation region for higher speeds is to make the characteristic current smaller, i.e., to make the d-axis inductance value higher [3,13]. However, the main bottleneck of the traditional SMPM motor design is the well-recognized low and non-changing winding inductance which leads to a higher characteristic current [5,16].…”

“…For most of the passenger cars, propulsion electric motor drive systems have 5:1 or higher CPSR values to provide both extreme operation modes in smaller electric motor structures, i.e., high torque at starting and high speed at flat road cruising [4]. Even for in-wheel applications, higher cruising speed is required to fulfill the driver requirements [5]. However, it is not possible to obtain higher torques at higher speeds for a certain power value without a dedicated control method [2,3].…”

Comparison of parallel BLDC FSPM machines with strong flux-weakening capability

“…The equivalent inductance of stator of conventional brushless DC motor is usually small and its energy storage capacity is relatively weak, which limits the capability to expand speed range [21][22][23][24][25][26]. Typically, a Brushless dc motor is driven by a three-phase inverter with, six-step commutation.…”

A parallel BLDC FSPM machines with wide fluxweakening capability

“…The equivalent inductance of stator of conventional brushless DC motor is usually small and its energy storage capacity is relatively weak, which limits the capability to expand speed range [21][22][23][24][25][26]. Typically, a Brushless dc motor is driven by a three-phase inverter with, what is called, six-step commutation.…”