Electric Power Steering Motor Control via Speed-Dependent Harmonic Injection

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Solution Overview

Problem

Existing electric power steering devices using multiphase AC motors face challenges in maintaining high output and steering resolution without increasing steering wheel torque, particularly at varying vehicle speeds, which affects the steering feel for drivers.

Innovation Solution

The electric power steering device incorporates a control system that adds a harmonic component to the fundamental drive voltage, making the modulation wave variable with vehicle speed, allowing for increased motor output at low speeds and high-resolution steering at high speeds without increasing torque, using a PWM inverter for efficient control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a three-phase sine-wave command voltage is used for PWM control, then the steering control is simple, but the voltage utilization rate is low and motor output is limited

Engineering Contradiction:

Improvecontrol simplicityVSAvoidmotor output

Core Design Contradiction:

Ease of manufactureVSPower

Solution Approach 1:

The patent changes the waveform parameter of the command voltage from a standard sine wave to a sine wave with added third-order harmonic components. This parameter modification increases the voltage utilization rate and motor output while maintaining the fundamental sine-wave characteristic for simple control implementation

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite voltage waveform by combining the fundamental sine-wave command voltage with third-order harmonic voltage components. This composite approach achieves both high voltage utilization and simple control by overlaying harmonic corrections on the basic sine wave

Inventive Principle:

Principle #40Composite materials

2Power

If the amplitude ratio of command voltage is increased to improve voltage utilization, then motor output increases, but torque ripple increases and steering feeling deteriorates

Engineering Contradiction:

Improvemotor outputVSAvoidtorque ripple

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful effect of voltage utilization limitations into a benefit by intentionally adding third-order harmonic components. These harmonics, which would normally be considered distortions, actually improve voltage utilization and motor output while the control system manages torque ripple through coordinated harmonic application

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Ease of manufacture

If a fixed modulation wave is used, then control is simple, but the system cannot adapt to different vehicle speeds, affecting steering resolution and feeling

Engineering Contradiction:

Improvecontrol simplicityVSAvoidvehicle speed adaptability

Core Design Contradiction:

Ease of manufactureVSAdaptability or versatility

Solution Approach 1:

The patent makes the modulation wave dynamic by varying the third-order harmonic components based on vehicle speed. At different speeds, different harmonic amplitudes are applied, allowing the system to adapt to varying steering requirements while maintaining a relatively simple control structure based on speed-dependent parameter adjustment

Inventive Principle:

Principle #15Dynamics

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This configuration enhances voltage utilization and motor output at low speeds while maintaining high-resolution steering at high speeds without affecting the steering feel, reducing torque ripple and operational losses.

Implementation Method 1

PWM control by a triangular-wave comparison technique is for comparing a three-phase sine-wave command voltage with a reference triangular-wave voltage and for generating a PWM-control signal voltage

Methodology Applied

Scientific EffectPWM control:

Implementation Method 2

An electric power steering device causes an electric motor to generate auxiliary torque in accordance with steering wheel torque by a steering operation by a driver and reduces the steering wheel torque

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS8354810B2Electric power steering device

Publication Date: 2013.01.15 HONDA MOTOR CO LTD

AI summary

An electric motor is driven with high output at the time of low-speed running, and a steering at a high resolution is enabled at the time of fast-speed running. An electric power steering device causes the electric motor to generate auxiliary torque in accordance with the largeness of steering wheel torque by the steering operation of a wheel made by a driver and reduces the steering wheel torque to the driver. A control device drives, based on a vehicle-speed signal (Vs) from a speed sensor, the electric motor with high output at the time of low-speed running, and enables steering at a high resolution at the time of fast-speed running without increasing an electric-motor output.