Electric Power Steering Torque Control for High-Frequency Ripple Suppression

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Solution Overview

Problem

Conventional torque control methods in electric power steering devices are susceptible to high-frequency disturbances and cannot effectively suppress high-frequency torque fluctuations, making it difficult to meet stringent market demands for noise, vibration, and harshness (NVH) comfort.

Innovation Solution

A control device for an electric power steering device that includes a torque controller and a model following controller. The model following controller uses a high-pass filter to remove low-frequency components from the correction torque, applies friction compensation to estimate mechanical friction torque, and adds this to the filtered correction torque to generate a second correction torque, which is fed back to the motor control target.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional torque control is used, then the steering system can provide basic assist torque, but it cannot suppress high-frequency torque fluctuations and is susceptible to high-frequency disturbances

Engineering Contradiction:

Improvesuppression of high-frequency torque fluctuationsVSAvoidhigh-frequency disturbances

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent segments the correction torque into different frequency components using a high-pass filter. The filter separates high-frequency components from low-frequency components, allowing independent processing of each frequency range to address specific disturbance characteristics effectively.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a high-pass filter as an intermediary element between the disturbance observer and the torque controller. This filter acts as a mediator that selectively passes high-frequency disturbance components while blocking low-frequency components, enabling targeted suppression of high-frequency torque fluctuations.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If friction compensation control is applied using a friction model as a function of angular velocity, then friction can be compensated, but chattering occurs because the sign of friction torque is rapidly inverted around zero angular velocity

Engineering Contradiction:

Improvefriction compensation accuracyVSAvoidchattering

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent extracts the friction compensation function from the conventional angular velocity-based model and relocates it to the high-frequency correction torque path. By taking out the friction compensation from the main control loop and applying it only to high-frequency components, the system achieves accurate friction compensation without causing chattering at zero crossing points.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent creates a separate friction compensation path that operates independently from the conventional angular velocity-based friction model. This copied friction compensation mechanism processes only high-frequency components, avoiding the chattering problem while maintaining friction compensation effectiveness.

Inventive Principle:

Principle #26Copying

3Stability of the object's composition

If a robust controller is used to reduce the influence of disturbance and parameter variation, then steering control stability improves, but high-frequency torque fluctuations cannot be suppressed

Engineering Contradiction:

Improvesteering control stabilityVSAvoidsuppression of high-frequency torque fluctuations

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The patent introduces dynamic frequency-selective processing by implementing a high-pass filter in the feedback path. This dynamic element allows the system to adaptively differentiate between low-frequency steering commands and high-frequency disturbances, suppressing only the harmful high-frequency components while maintaining overall steering control stability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent enhances the feedback mechanism by processing the correction torque through a high-pass filter before applying friction compensation. This modified feedback path selectively feeds back high-frequency disturbance components, enabling the robust controller to focus on suppressing high-frequency torque fluctuations while maintaining stability for low-frequency steering operations.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS12202554B2Motor control device, motor control method, motor module, and electric power steering device

Publication Date: 2025.01.21 NIDEC CORP(JP)

AI summary

A motor control device includes a torque controller to operate based on a steering torque and to give an input to a control target that is a motor, and a model following controller to generate a first correction torque based on an output from the control target. A model following controller includes a high-pass filter to remove a low frequency component from a first correction torque, a friction compensation calculator that is coupled in parallel to the high-pass filter to apply friction compensation to the first correction torque to calculate an estimated value of a mechanical friction torque, and an adder to add the estimated value of the friction torque to the first correction torque from which the low frequency component is removed by the high-pass filter to generate a second correction torque and feed back the second correction torque to an input to the control target.