Apply High-Power-Density AFPM Machines to EV Traction

Apply High-Power-Density AFPM Machines to EV Traction

This short article is element of the Electric power Management Series: Delving Into Electrical power Density

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What you will discover:

  • What is an axial-flux long-lasting-magnet motor?
  • Types of AFPM motors.
  • Gains of in-wheel traction motors.

All motors can alter their inherent vitality into mechanical power. The simple functionality of a motor is its coil and magnet, which are based on the theory of an electromagnetic interaction of the magnetic discipline generated by the coil and magnet contained in the construction by itself.

In this post, we will go over the added benefits of the axial-flux everlasting-magnet (AFPM) motor that provides superb, significant electricity density.

The AFPM Equipment

The really 1st motor, invented by Michael Faraday in 1821, was an axial-flux style. Later on, in 1834, Davenport invented the radial-flux motor, which was acknowledged as the basic motor. Let’s compare these two forms of motors.

The axial-flux motor has an air gap that is planar. Because that air-gap magnetic-discipline distribution is together the axial route, the air-gap magnetic subject is fundamentally perpendicular to the air-gap plane. In today’s motor enhancement, the trend is superior velocity, very low fat, and superior efficiency—all qualities of the axial-flux motor.

The positive aspects of these motors are:

  • Large electric power density
  • Significant torque density
  • Little quantity
  • Reduced weight
  • Compact framework, in individual for short axial dimensions
  • Small conclusion-winding
  • Pretty fantastic cooling effectiveness

Axial-Flux Motor Purposes

Substantial electrical power density does not only count on higher speed, but also on the impact of torque density. Higher pace leads to small service time and better noise even so, the main of the substantial-pace motor is the enhancement of torque density. The axial flux motor provides these rewards to such programs as motor bikes, aircraft, and automotive (including racing autos).

Sorts of AFPM Motors

One particular key use of the AFPM motors is for electrical-auto (EV) in-wheel traction programs. AFPM motors have to have to fulfill two major needs for this application: high power density and fault tolerance. The pursuing are some types of AFPMs:

Yokeless Stator AFPM with FSCW

AFPM motors that have a fractional slot concentrated winding (FSCW), with a yokeless and segmented armature (YASA), have lately been a option of designers for their high-electricity density and opportunity manufacturability. Which is owing to their concentrated winding and modular stator core configuration.

A person issue with FSCW machines is significant rotor decline induced by armature reaction harmonics, which can existing troubles with rotor heat dissipation. This is in particular evident in higher-pace use for EV traction programs.

An additional Selection

Working with dispersed winding is normally used in superior-pace radial-flux long term-magnet (PM) motors. This choice permits reduced armature harmonics, thus encouraging to make improvements to rotor heat dissipation.

AFPM Windings

A comparative review was finished for yokeless stator AFPM traction motors with integer-slot dispersed-winding (ISDW) and FSCW configurations in EV applications.1 Let us get a glance at an exceptional mixture of stator and rotor configurations that are amongst four feasible topologies (Fig. 1).

The ISDW configuration, a 48-slot 8-pole framework with double layer, is a person of the most typically utilized configurations for EV traction in vehicles this kind of as the Toyota Prius. For the FSCW configuration, a 12-slot 10-pole composition with double-layer is viewed as a very good decision between several solutions for a a lot more sinusoidal back-EMF, superior winding component, and lessen torque ripple (Fig. 2).

In-Wheel Traction Motors

The rewards of in-wheel traction motors (Fig. 3) are bigger effectiveness owing to driving the wheels straight and bypassing the need for standard electricity-transmission mechanisms. This technique of substantial electrical power and torque density together with light-weight qualities also will empower lighter and a lot more compact types. Independent management of the wheels will guide to the chance of even further increasing electronic balance handle (ESC) and traction manage systems (TCS) (Fig. 3).


Everlasting-magnet synchronous motors (PMSM), driven sinusoidally, permit the special functions required for traction motors to be used in EVs. Between these, AFPM synchronous motors are an fantastic fit for in-wheel programs. Electrical motors used in this kind of application have to fulfill two main specifications: superior ability density and fault tolerance.

Go through more content in the Electric power Administration Series: Delving Into Electricity Density


1. Comparative Study of Yokeless Stator Axial-Flux PM Machines Possessing Fractional Slot Concentrated and Integral Slot Dispersed Windings for Electrical Automobile Traction Programs, IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 70, NO. 1, JANUARY 2023

2. Optimal Design of a A few-Period AFPM for In-Wheel Electrical Traction, IEEE 2014

3. In-Wheel Motor for Electric Cars, Superior Science Information, Martin Grolms, 2019