EV Controller Torque-Free Sensor Diagnosis
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Solution Overview
Problem
Electric vehicles equipped with three-phase alternating-current motors face challenges in identifying an unusable current sensor without generating unnecessary torque, which can cause driver discomfort, especially when a current sensor fails or its signal/power line breaks during vehicle travel.
Innovation Solution
The controller sets the d-axis voltage command to zero and the q-axis voltage command to a non-zero value, allowing current to flow to the motor without generating torque, and uses measurements from two usable sensors to estimate the current of the unusable sensor, employing Kirchhoff's law to identify and isolate the unusable sensor, thereby preventing unintended torque production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current is applied to identify unusable current sensor during vehicle travel, then the unusable sensor can be identified, but the motor may generate unnecessary torque causing driver discomfort
Solution Approach 1:
The controller changes the voltage command parameters by setting d-axis voltage to zero and q-axis voltage to non-zero value, creating a specific operating condition where current flows but torque is eliminated. This parameter change allows sensor identification without harmful torque output.
Solution Approach 2:
The controller preemptively eliminates torque generation by setting d-axis voltage to zero before applying current for sensor identification. This preliminary anti-action prevents the harmful effect of unnecessary torque from occurring during the identification process.
2Object-generated harmful factors
If d-axis voltage is set to zero and q-axis voltage to non-zero value, then current flows without torque generation, but this control mode is only effective above a predetermined angular speed
Solution Approach 1:
The controller dynamically adjusts the d-axis current based on motor speed conditions. At low speeds below the lower-limit angular speed, it sets d-axis current to a positive value to compensate for insufficient back-EMF, ensuring torque elimination remains effective across all operating speeds.
Solution Approach 2:
The controller modifies the d-axis current parameter based on speed conditions: zero d-axis current at high speeds where back-EMF is sufficient, and positive d-axis current at low speeds to maintain torque elimination effectiveness across the full speed range.
Data Source
AI summary
An electric vehicle includes a traction motor, an inverter that supplies the motor with an alternating current, three current sensors that respectively measure current of each phase of the alternating current output by the inverter, the alternating current being a three phase alternating current; and a controller that controls the motor through the inverter. The controller is configured to, when one of the current sensors becomes unusable, identify the unusable current sensor while controlling the motor with a d-axis voltage command value set to zero and a q-axis voltage command value set to a non-zero value.