3-Phase AC Motor Control with Sensor Fault Transition
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Solution Overview
Problem
Existing motor-driven electric driving systems for environmentally friendly vehicles face operational challenges when current sensors used to control 3-phase brushless AC motors fail, leading to potential accidents due to inability to assist steering force, as they cannot perform normal driving control without functional current sensors.
Innovation Solution
The system transitions from vector control mode to voltage/frequency (V/F) control mode when current estimation errors exceed a threshold, using voltage equations and rotor speed to maintain normal operation of the 3-phase brushless AC motor even if current sensors are faulty, by calculating current command values and voltage commands based on torque and magnetic flux commands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If vector control mode is used for precise motor control, then control precision is improved, but system reliability deteriorates when current sensors fail
Solution Approach 1:
The system changes control parameters dynamically by switching between vector control mode (using current sensor feedback for precise current control) and V/F control mode (using voltage and frequency control without current sensors). When sensor failure is detected, the controller transitions to V/F control with adjusted voltage and frequency parameters to maintain motor operation, thus resolving the contradiction between control precision and reliability.
Solution Approach 2:
The control system implements dynamic adaptability by continuously monitoring sensor status and automatically switching control modes. The system transitions from static vector control to dynamic mode selection, allowing it to adapt to sensor failure conditions while maintaining operational reliability, thereby resolving the contradiction between precise control and system reliability.
2Measurement precision
If current sensors are used for monitoring motor operation, then measurement accuracy is improved, but device complexity increases due to additional sensors and control circuits
Solution Approach 1:
The system creates a virtual copy of current sensor functionality through mathematical models and calculations. Instead of relying solely on physical current sensors, the controller uses voltage commands, rotor speed, and motor parameters to calculate equivalent current values, thereby maintaining measurement accuracy while reducing dependence on additional physical sensors and associated complexity.
3Reliability
If the system switches from vector control to V/F control upon sensor failure, then reliability is improved, but control precision deteriorates
Solution Approach 1:
The system prepares compensatory measures in advance by implementing a dual-mode control architecture. Before sensor failure occurs, the system is already configured with V/F control parameters and switching logic ready. Upon sensor failure, the pre-prepared V/F control mode activates immediately, cushioning the impact on control precision while maintaining operational reliability.
Data Source
AI summary
A method for controlling a 3-phase AC motor may include; transforming a torque command signal of an upper control into a voltage command, generating a current measurement value for a current flowing in two phases of the 3-phase AC motor depending on the voltage command by using a current sensor, generating a current estimation value by using driving sensing information of the 3-phase AC motor depending on the voltage command, calculating a current estimation error by using the current measurement value and the current estimation value, comparing with a preset reference value by using the calculated current estimation error, and performing a state transition changing a driving control type of the 3-phase AC motor depending on the comparison result.