Motor Control Device Abnormal Terminal Voltage Compensation
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Solution Overview
Problem
Existing motor control devices for DC motors in electric power steering systems lack robustness when terminal voltage is abnormal, leading to potential excess assist output and reduced responsiveness due to reliance on fixed steering angle speed and broad threshold settings.
Innovation Solution
A motor control device with an H-bridge circuit and inter-terminal voltage calculation unit that selects the inter-terminal voltage with the smallest absolute value, independent of abnormal state determination, to estimate steering angle speed and execute compensation control, thereby restricting excess assist and improving robustness and responsiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the steering angle speed is fixed based on abnormal state determination, then the compensation control can be executed, but the responsiveness is reduced and excess assist may be outputted
Solution Approach 1:
The system pre-calculates and stores multiple inter-terminal voltage calculation values (Vma_cal, Vmb_cal, Vmc_cal) from different detection value combinations before abnormal state determination is needed. When abnormal state determination is required, the system simply selects from pre-calculated values, avoiding delayed computation and maintaining responsiveness while ensuring robustness.
2Reliability
If the threshold value for abnormal state determination is broadened to cover dispersion, then the determination becomes more reliable, but the abnormal state may not be detected
Solution Approach 1:
Instead of using a single threshold value for abnormal state determination, the system segments the determination into multiple independent inter-terminal voltage calculation values. Each value is calculated from different detection value combinations, and the system selects the most appropriate value based on which combination shows the smallest dispersion, thereby maintaining both reliability and detection accuracy.
Solution Approach 2:
The system dynamically changes the selection criterion for inter-terminal voltage based on the dispersion characteristics of different detection value combinations. When one combination shows small dispersion, it is selected; when another shows smaller dispersion, that is selected. This parameter adaptation allows the system to maintain high determination reliability while preserving abnormal state detection accuracy.
3Device complexity
If only one inter-terminal voltage calculation is performed, then the device complexity is reduced, but the robustness against abnormal terminal voltage is insufficient
Solution Approach 1:
The system applies local quality by creating different inter-terminal voltage calculation values from different local combinations of detection values (M1a-M2a, M1b-M2b, M1c-M2c). Each calculation represents a different local measurement path, and the system selects the one with the smallest dispersion, thereby achieving robustness without requiring all calculations to be equally complex.
Data Source
AI summary
A terminal voltage detection circuit of a motor control device detects first detection values of a first terminal of a DC motor and second detection values of a second terminal of the DC motor. An inter-terminal voltage calculation unit calculates inter-terminal voltage calculation values from the first detection values and the second detection values. The inter-terminal voltage calculation unit outputs one of the calculation values having the smallest absolute value as an inter-terminal voltage selection value. A steering angle speed estimation unit estimates a steering angle speed based on the selection value and a motor current. A compensation control unit executes a compensation control based on the steering angle speed estimated by the steering angle speed estimation unit. Accordingly, robustness of the compensation control is improved and excess assist is restricted.