Electric Power Steering Control Using Dual-Time-Scale Current Calculation
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Solution Overview
Problem
Conventional electric power steering control systems generate unpleasant noise due to motor current variations, which are difficult to suppress at high frequencies, and reducing these variations increases CPU calculation load and costs.
Innovation Solution
An electric power steering control apparatus with a calculation section that calculates a first target current at a 1 msec sampling period and a second target current at a shorter 0.125 msec control period, using moving average or low-pass filter processing to set the motor current command value, thereby shifting noise to higher frequencies and reducing CPU load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the sampling period is set to 1 msec to reduce CPU calculation load, then the control sound frequency becomes 1 kHz which is easily heard as unusual noise, but if the sampling period is shortened to reduce noise frequency, then the CPU calculation load increases
Solution Approach 1:
The patent divides the current control into two stages: a first target current calculation section that operates at a longer period (e.g., 1 msec) to reduce CPU load, and a second target current calculation section that operates at a shorter period (e.g., 0.1 msec) to reduce noise frequency. This segmentation allows each section to operate at optimal periods for their specific functions without increasing overall system complexity.
Solution Approach 2:
The patent introduces a dual-time-scale control architecture by adding another dimension of control period differentiation. Instead of using a single sampling period, the system employs multiple control periods (first control period for torque-based current calculation, second control period for noise reduction), effectively solving the contradiction by operating in different time dimensions.
2Object-affected harmful factors
If the motor current command value varies at 1 kHz frequency, then the control sound is generated at a frequency easily heard as unusual noise, but suppressing this variation reduces the responsiveness of the steering assist
Solution Approach 1:
The patent applies different control qualities to different parts of the control system. The first target current calculation section maintains high responsiveness by calculating based on torque sensor feedback at appropriate intervals, while the second target current calculation section applies smoothing processing specifically targeted at reducing high-frequency noise components. This local differentiation of control quality allows responsiveness and noise reduction to coexist.
Solution Approach 2:
The patent implements dynamic control by adjusting the control period based on the specific calculation stage. The system dynamically switches between a longer first control period for overall current target calculation and a shorter second control period for noise reduction processing, allowing the control characteristics to adapt dynamically to different operational requirements.
Data Source
AI summary
An electric power steering control includes a torque sensor for detecting steering torque as torque information, a motor for generating assist torque, a calculation section for calculating a motor current command value based on the torque information at each predetermined sampling period, and a motor current control section for driving and controlling the motor based on the motor current command value. The calculation section includes a first target current calculation section for calculating a first target current based on the torque information detected in a time series manner at a first control period corresponding to the sampling period, and a second target current calculation section for calculating a second target current based on the first target current at a second control period shorter than the first control period. The motor current control section controls the motor by using the second target current as the motor current command value.