MDPS Motor Control via Torque Ripple Fault Detection
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Solution Overview
Problem
Conventional motor-driven power steering (MDPS) systems fail to control the motor operation when faults occur in hall sensors or encoders, leading to impaired steering assistance and potential accidents.
Innovation Solution
A control apparatus for the MDPS system that includes a torque sensor, hall sensor fault determination unit, encoder fault determination unit, and motor control unit, which estimate the motor rotor position and control the motor based on determination results to ensure safe operation even with faults in hall sensors or encoders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the MDPS system uses hall sensors or encoders to sense motor rotor position, then the motor control precision is improved, but the system reliability deteriorates when faults occur in these sensors
Solution Approach 1:
The system changes the operating parameters by injecting test currents at specific frequencies (d-axis and q-axis currents) to excite the motor and observe torque ripple characteristics. By monitoring changes in torque signal parameters under controlled current conditions, the system can detect sensor faults while maintaining normal operation, thus resolving the contradiction between precise position sensing and system reliability during faults
Solution Approach 2:
The system implements continuous feedback by monitoring torque sensor signals and comparing them against expected values during motor operation. The torque signal processing unit continuously analyzes torque ripple and compares it with reference values to detect hall sensor or encoder faults in real-time, allowing the system to maintain reliability even when position sensors fail by detecting faults through torque feedback
2Reliability
If the MDPS system adds fault determination units for hall sensors and encoders, then the system safety is improved, but the device complexity increases
Solution Approach 1:
The torque sensor and torque signal processing unit serve multiple functions: they not only provide normal steering torque feedback for motor control but also act as fault detection sensors for hall sensors and encoders. By analyzing torque ripple characteristics during motor operation, the same torque sensing system detects position sensor faults, eliminating the need for separate fault detection hardware and reducing overall system complexity while maintaining safety
Solution Approach 2:
The system uses its own operational parameters (torque signals, current signals, and motor rotation information) to perform self-diagnosis of position sensor faults. The torque signal processing unit analyzes the motor's own torque ripple during normal operation to detect hall sensor or encoder failures, allowing the system to monitor its own health without external monitoring equipment, thus improving safety without adding significant complexity
3Reliability
If the MDPS system continuously monitors torque signals for fault detection, then the fault detection capability is improved, but the energy consumption increases
Solution Approach 1:
The system performs fault detection by analyzing torque signals during periodic motor operation cycles. The torque signal processing unit processes torque information at regular intervals during motor rotation, rather than continuously computing fault metrics. By leveraging the periodic nature of motor operation and torque ripple, the system maintains effective fault detection while reducing computational load and energy consumption compared to continuous real-time analysis
Data Source
AI summary
A control apparatus of an MDPS system may include: a current supply unit configured to drive a motor by injecting a preset frequency and magnitude of current to the motor; a torque sensor configured to sense a torque of a steering shaft; a hall sensor fault determination unit configured to determine whether a fault has occurred in a hall sensor; a torque signal processing unit configured to process a signal outputted from the torque sensor and calculate the magnitude of a torque signal; an encoder fault determination unit configured to determine whether a fault has occurred in an encoder, using the torque signal outputted from the torque signal processing unit; and a motor control unit configured to acquire a position of a motor rotor according to the determination results of the hall sensor fault determination unit and the encoder fault determination unit, and control the operation of the motor.