Variable Stabilizing Compensator for Electric Power Steering
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Solution Overview
Problem
Conventional electric power steering devices face a trade-off between responsiveness and stability due to a fixed characteristic stabilizing compensator, which results in insufficient responsiveness at low base assist gain and insufficient stability at high gain, leading to response delays and viscosity feelings for drivers.
Innovation Solution
A control device and method using a stabilizing compensator with a second-order or higher transfer function, where the frequency characteristic is variable based on base assist gain, incorporating responsiveness and damping parameters to generate stabilizing compensation torque and current command values for motor control, distinguishing frequency domains for responsiveness and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a fixed characteristic stabilizing compensator is used, then stability is improved, but responsiveness deteriorates at low base assist gain
Solution Approach 1:
The patent applies dynamics by making the stabilizing compensator's frequency characteristic variable rather than fixed. The compensator dynamically adjusts its parameters based on the base assist gain value, allowing it to adapt to different operating conditions. This resolves the contradiction by enabling the system to switch between stability-optimized and responsiveness-optimized characteristics depending on the current base assist gain level.
Solution Approach 2:
The patent changes the parameters of the stabilizing compensator based on the base assist gain. Specifically, the frequency characteristic parameters (such as cutoff frequency or damping ratio) are adjusted according to the base assist gain value. This parameter adaptation allows the system to maintain both stability and responsiveness across different operating conditions.
2Speed
If base assist gain is increased to improve responsiveness, then responsiveness is improved, but stability deteriorates
Solution Approach 1:
The stabilizing compensator dynamically adapts its frequency characteristic to the current base assist gain level. When base assist gain is high, the compensator adjusts to maintain stability; when base assist gain is low, it adjusts to enhance responsiveness. This dynamic adaptation resolves the trade-off by allowing both high responsiveness and high stability at different operating points.
Solution Approach 2:
The frequency characteristic parameters of the stabilizing compensator are changed according to the base assist gain value. This parameter modulation enables the system to optimize both responsiveness and stability across the full range of base assist gain values, eliminating the need to choose between the two opposing requirements.
3Stability of the object's composition
If a second-order or higher transfer function with variable frequency characteristic is used, then both responsiveness and stability are improved, but device complexity increases
Solution Approach 1:
The patent uses a second-order or higher transfer function for the stabilizing compensator with parameters that are changed based on the base assist gain. While this increases control algorithm complexity, it significantly improves both stability and responsiveness. The complexity is justified by the substantial performance improvement in the power assist control system.
Data Source
AI summary
Both responsiveness and stability of a power assist control system are satisfied. A processor executes, in accordance with a program, determining base assist gain based on steering torque and base assist torque, generating stabilizing compensation torque based on the base assist torque, with use of a stabilizing compensator that has a second-order or higher transfer function in which a frequency characteristic is variable in accordance with the base assist gain and which is expressed using a responsiveness parameter ω and a damping parameter ζ, and generating a current command value for use in control of the motor based on the stabilizing compensation torque.