Software Phase Compensators for Electric Power Steering
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Solution Overview
Problem
Conventional electric power steering apparatuses face increased product costs due to hardware-based phase advance compensators, which also amplify high-frequency components and quantization errors, leading to deteriorated steering feel and merchantability issues when replaced with software-based compensators.
Innovation Solution
An electric power steering apparatus with software-based first, second, and third-stage phase compensators, configured to apply phase compensation using specific Laplace transformation equations, ensuring that the phase compensation frequencies coincide, reducing the impact of quantization errors and allowing for a more cost-effective solution without compromising stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hardware-based first-stage phase advance compensator is used, then the steering system stability is improved, but the product cost increases
Solution Approach 1:
The patent replaces the hardware-based first-stage phase advance compensator with a software-based compensator implemented on a microcomputer. This substitution eliminates the need for additional hardware components while maintaining the phase compensation function, thereby reducing product cost without sacrificing steering system stability.
Solution Approach 2:
The microcomputer in the patent serves multiple functions: it performs A/D conversion of the torque signal, implements the first-stage phase advance compensator, implements the second-stage phase advance compensator, and controls the motor. By consolidating these functions into a single software-based system, the patent reduces hardware requirements and product cost while maintaining all necessary control functions.
2Ease of manufacture
If a software-based phase advance compensator is used to reduce cost, then product cost decreases, but quantization errors and noise are amplified leading to deteriorated steering feel
Solution Approach 1:
The patent introduces a third-stage phase delay compensator as an intermediary element between the second-stage phase advance compensator and the motor control. This third-stage compensator is specifically designed to reduce the gain in the high-frequency band, thereby attenuating quantization errors and noise before they reach the motor, while the overall phase compensation maintains steering system stability.
Solution Approach 2:
The patent adjusts the frequency characteristics of the phase compensators by modifying their transfer function parameters. The third-stage phase delay compensator is designed with specific time constants (T5 and T6) to create a low-pass filter effect, changing the system's frequency response to reduce high-frequency gain and thereby suppress quantization errors and noise.
3Speed
If the torque signal is A/D-converted at high frequency (e.g., 1 kHz), then the responsiveness is improved, but quantization errors in the high-frequency band are amplified
Solution Approach 1:
The patent converts the harmful effect of high-frequency quantization errors into a beneficial outcome by using the third-stage phase delay compensator to intentionally reduce the gain in the high-frequency band. This compensator acts as a low-pass filter that attenuates quantization errors and noise while preserving the necessary phase compensation for steering stability, effectively turning the presence of quantization errors into an opportunity to demonstrate the effectiveness of frequency-selective compensation.
Data Source
AI summary
A first-stage phase compensator, a second-stage phase compensator, and a third-stage phase compensator are configured in such a way that a frequency at which a phase calculated through the transfer function of the first-stage phase compensator becomes maximal and a frequency at which a phase calculated through a transfer function of the first-stage phase compensator and the third-stage phase compensator becomes maximal coincide with each other; a motor for generating assist torque is controlled, based on a torque signal to which the first-stage phase compensator, the second-stage phase compensator, and the third-stage phase compensator have applied phase compensation.