Key Technical Issues and Position Signal Detection Methods for Wheel Hub Motors

Wheel hub motor technology, also known as in-wheel motor technology, is characterized by the integration of power, transmission and braking systems inside the wheel hub, which greatly simplifies the mechanical components of electric vehicles.

Key technical issues in the research of wheel hub motor systems

• The integration of driving, braking, and bearing functions in electric wheel hub motor systems makes optimization design difficult.

• The limited space inside the wheel requires high motor power density performance, leading to design difficulties.

• The integration of the motor and wheel results in a large unsprung mass, which worsens suspension shock absorption performance and affects vehicle handling and safety on uneven road conditions. At the same time, wheel hub motors are subject to large road impact loads, placing high demands on motor shock resistance.

• Wheel hub motors are prone to overheating and burning when vehicles climb long hills at low speeds under heavy loads, so motor cooling and forced cooling must be taken seriously.

• Water and dirt can accumulate easily on the wheel, causing corrosion and damage to the motor, and affecting its reliability and service life.

• Fluctuations in the running torque of wheel hub motors may cause vibrations and noise in the vehicle's tires, suspension, and steering system, as well as other overall vehicle noise and vibration issues.

Position signal detection methods for wheel hub motors without position sensors

Back-EMF method

The basic principle of this method, which is the most mature, effective, and common method, is to delay the detected back-EMF signal when it crosses zero by 30° electrical angle, yielding the switch signal of the power pipe. As there is no or weak back-EMF signal when the motor is stationary or rotating at low speed, the back-EMF method is generally used in conjunction with "three-stage" starting technology.

Freewheeling diode method

This method of wheel hub motors determines the rotor position by detecting the conduction state of the freewheeling diode on the anti-parallel and inverter bridge power switches.

Inductance method

This method observes changes in winding inductance with rotor position, and calculates the rotor position signal through certain calculations.

State observer method

This method of wheel hub motors estimates the rotor position of the motor by using the motor's three-phase voltage and current as coordinates based on the Park equation. As the coordinate transformation only considers the fundamental component, this method is mainly used for PMBLDCM with sine-wave back-EMF.