Power Steering PWM Phase Control for Magneto-Strictive Noise
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In electrically driven power steering systems, noisy magneto-strictive sounds are generated due to fluctuating voltage command values and detection errors, leading to complex phase switching and noise development when voltage command values between phases become close.
Innovation Solution
Implementing a pulse shift control mechanism that adjusts the PWM duty signal timings for the maximum, middle, and minimum phases, ensuring a predetermined difference between their on timings, and using hysteresis correction to stabilize phase determination, thereby reducing noise and improving detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PWM pulse phase correction is applied to detect phase currents, then current detection accuracy is improved, but voltage command values fluctuate and cause magneto-strictive noise
Solution Approach 1:
The patent applies preliminary anti-action by introducing a hysteresis mechanism before phase switching occurs. When the voltage command value difference between phases falls within a predetermined hysteresis range, the system maintains the current phase assignment rather than immediately switching phases. This prevents the fluctuation and complicated switching that generates magneto-strictive noise, while still allowing phase correction to improve current detection accuracy when conditions clearly warrant it.
2Reliability
If phase switching is performed when voltage command values are close, then current detection is maintained, but noisy sound develops due to complicated phase switching
Solution Approach 1:
The hysteresis mechanism serves as preliminary anti-action by preventing unnecessary phase switching when voltage command values are close. The system only switches phases when the difference exceeds the hysteresis threshold, thereby maintaining current detection reliability while avoiding the complicated switching that produces noisy sound.
3Loss of time
If PWM pulse phase correction is applied, then phase current detection time duration is secured, but detection error and voltage fluctuation occur
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the hysteresis threshold based on operating conditions. The predetermined value is set to balance the detection time requirement with the accuracy requirement, allowing sufficient detection time duration while minimizing voltage fluctuation and detection error through optimized parameter selection.
Data Source
AI summary
An electrically driven power steering system is capable of reducing development of a noisy magneto-strictive sound. A voltage corresponding to each PWM pulse achieving time corresponding to a hysteresis is added to one of the voltage command values of a large voltage phase from among three phase first voltage command values. The added voltage is subtracted from one of the remaining voltage command values, which is a voltage small phase, to derive virtual voltage command values, and the virtual voltage command values are mutually compared to carry out a voltage magnitude phase determination for a three-phase brushless motor of the power steering system.