Motor Control Device for Electric Power Steering with Angle Offset Estimation
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Solution Overview
Problem
Conventional motor control apparatuses for electric power steering systems face challenges in accurately controlling multi-phase electric motors when a failure occurs in the motor electric angle detecting unit, leading to difficulties in maintaining steering assist functionality.
Innovation Solution
A motor control apparatus that includes an offset amount estimating unit, a motor electric angle estimating unit, and a motor driving control unit, which estimates the relative offset amount between the steering angle and the motor electric angle, allowing for continued control of the multi-phase electric motor even when the motor electric angle detecting unit is abnormal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a position sensor such as a resolver is used to detect the rotor rotation position, then the motor control accuracy is improved, but the system reliability deteriorates when the sensor fails
Solution Approach 1:
The patent introduces a steering angle detecting unit as an intermediary device to detect the rotor rotation position indirectly through the steering angle, rather than directly detecting the motor shaft position. This intermediary detection method provides a backup pathway for obtaining position information when the original position sensor fails, thereby resolving the contradiction between measurement precision and reliability under sensor failure conditions
Solution Approach 2:
The patent creates a duplicate detection pathway by introducing a steering angle detecting unit that copies the position detection function. When the original position sensor fails, the system can switch to using the steering angle detection results to calculate command voltages, ensuring continuous operation and maintaining system reliability
2Measurement precision
If the motor control system uses direct position sensor detection, then the control precision is improved, but the system becomes vulnerable to sensor failures
Solution Approach 1:
The patent implements a dynamic control strategy where the control method can switch between direct position sensor detection and steering angle-based detection depending on the operational state and sensor status. The controller dynamically selects the appropriate detection method, improving the system's adaptability to sensor failures while maintaining control precision through the most reliable detection pathway available
Solution Approach 2:
The patent changes the detection parameter from direct motor shaft position to steering angle when sensor failure occurs. By transforming the control parameter from θ (rotor position) to θs (steering angle) and using the relationship θ = nθs to calculate command voltages, the system maintains control precision while adapting to sensor failure conditions
Data Source
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AI summary
There are provided a motor control apparatus, an electric power steering apparatus, and a vehicle, capable of controlling the driving of an electric motor accurately even when a failure occurs in a motor electric angle detecting unit that detects a motor electric angle. The motor control apparatus includes: a relative offset amount estimating unit (62) that estimates a relative offset amount (θoff) between a reference value (θosr) of an output shaft rotational angle detection value (θos) of a steering shaft (12), detected by an output-side rotational angle sensor (13c), and a motor electric angle original point (θmd) of a three-phase electric motor (22); and a motor electric angle estimating unit (63) that calculates a motor electric angle estimate (θme) based on the output shaft rotational angle (θos) and the relative offset amount (θoff), wherein when at least either one of a resolver (23a) and an angle computing unit (60) is abnormal, the driving of the three-phase electric motor (22) is controlled based on the motor electric angle estimate (θme) estimated by the motor electric angle estimating unit (63).