Motor Control Device for Electric Power Steering with Sensor Failure Recovery
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Solution Overview
Problem
Conventional motor control devices for electric power steering systems fail to accurately drive and control multi-phase electric motors when a position sensor failure occurs, leading to difficulties in maintaining steering assist functions.
Innovation Solution
A motor control device that includes a motor electric angle initial value estimation unit to estimate the motor electric angle based on the response output of the multi-phase electric motor after a system restart, and a motor drive control unit that drives the motor using the estimated angle when the detection unit is abnormal, ensuring continued operation of the steering assist function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a position sensor is used to detect rotor rotation position, then the motor can be controlled under normal conditions, but the system becomes vulnerable to sensor failure and cannot accurately drive the motor after failure
Solution Approach 1:
The patent introduces an intermediary estimation mechanism that mediates between the failed position sensor and the motor control system. When the position sensor fails, the initial value estimation unit and estimation unit act as intermediaries to provide alternative motor electric angle information through mathematical modeling and observation of motor responses, rather than directly controlling the motor without angle information.
Solution Approach 2:
The patent implements beforehand cushioning by preparing alternative estimation methods in advance for when sensor failure occurs. The system pre-establishes the initial value estimation unit and estimation unit that can compensate for sensor failure, cushioning the impact of failure on system operation and maintaining continuous motor control capability.
2Measurement precision
If the system relies on position sensor detection, then normal operation is achieved, but accuracy is lost when sensor failure occurs
Solution Approach 1:
The patent creates a copy of the position sensor's function through software-based estimation units. Instead of relying solely on the physical sensor, the system generates estimation copies of the motor electric angle through the initial value estimation unit and estimation unit, which can replace sensor output when the sensor fails, maintaining measurement precision through alternative means.
Solution Approach 2:
The patent changes the parameter source for motor electric angle detection. Instead of always using the position sensor's direct measurement, the system switches to estimated parameters generated by the estimation units when sensor reliability is compromised, dynamically changing the detection parameter source to maintain precision under different operating conditions.
3Reliability
If no estimation mechanism is provided, then the system structure remains simple, but the steering assist function cannot be maintained after sensor failure
Solution Approach 1:
The patent segments the angle detection function into multiple independent components: the position sensor for normal operation, the initial value estimation unit for failure recovery, and the estimation unit for continuous operation. This segmentation allows the system to maintain steering assist reliability through distributed functionality while managing complexity through modular design where each segment has a specific, limited role.
Data Source
AI summary
An electric motor can be accurately drive-controlled even when a failure occurs in a motor electric angle detection unit. When at least one of a resolver and an angle computation unit is diagnosed as abnormal in an initial diagnosis after a system restart, a motor electric angle initial value is estimated on a basis of a response output of a three-phase electric motor in response to input of a motor drive signal to the three-phase electric motor, a motor electric angle estimation value is calculated on a basis of an output shaft rotation angle detection value detected by an output-side rotation angle sensor and a relative offset amount estimated on a basis of the estimated motor electric angle initial value, and the three-phase electric motor is drive-controlled on a basis of the calculated motor electric angle estimation value.