Browse Publications Technical Papers 2019-01-1400
2019-03-25

The Motor Current Sensor Fail-Operation Algorithms for the EPS System 2019-01-1400

Recently, steering systems for automobiles have been largely replaced by EPS (Electric Power Steering) in HPS (Hydraulic Power Steering). However, the EPS system that assists the steering by the power of the motor stops the steering assist because the motor can not be normally controlled when the current sensor of the motor fails. When the steering assist stops, the steering wheel becomes suddenly heavy, which can lead to a dangerous situation. Therefore, in this paper, we propose a method to maintain the EPS steering assist by continuously driving the motor even when the motor current sensor fails. The fail-operation method proposed in this paper is designed for a 3-phase PMSM (Permanent Magnet Synchronous Motor) motor and an EPS system using two current sensors to control it. To safely transition to the current sensor Fail-Operation mode, there should be no problems with other circuits for motor drive. However, the method based on the difference between the current command and the feedback value, which is generally used for detecting the fault of the current sensor, also detects the failure of the motor driving circuit. Therefore, in this paper, an algorithm to distinguish faults of only the current sensor is additionally designed so that the transition to the fail-operation mode can be made safely. In addition, we propose a new method to make an output table for motor control and refer to the table efficiently, so that the motor command current for steering assist can be continuously followed in Fail-Operation mode. In order to continue the fail-operation operation, the safety of the system should be guaranteed. However, it is difficult to diagnose the motor current control error in the fail-operation mode in which the current sensor fails. In this paper, we propose an algorithm that can calculate the feedback current, which should be calculated with 2-phase current value only by the 1-phase current value, so that fault diagnosis is possible in Fail-Operation mode. The proposed fail-operation algorithms are implemented in SW and verified their operation in the vehicle.

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