Electric Motor Torque Control Near the Controllability Limit
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Solution Overview
Problem
Existing electric motor control systems in vehicles face uncontrollable conditions when driver requests exceed the motor's controllability zone, leading to undesirable operation.
Innovation Solution
A control process and apparatus that utilizes a control unit to determine the motor's controllability limit based on torque and supply voltage, predicts output speed, and adjusts torque delivery to maintain controllability by applying a correction to the driver's torque request.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the driver requests torque exceeding the motor's controllability zone, then the driver's torque demand is met, but the motor operates in an uncontrollable manner
Solution Approach 1:
The control system performs preliminary action by predicting the motor's output speed before the uncontrollable condition occurs. The prediction is based on the current torque and supply voltage, allowing the system to anticipate when the motor will exit the controllability zone and take preventive corrective action.
Solution Approach 2:
The system implements feedback by continuously monitoring the difference between the predicted output speed and the controllability limit speed. This feedback loop enables the control unit to determine when corrective action is needed and to adjust the torque delivery accordingly, ensuring the motor remains within controllable limits.
2Reliability
If the control system limits torque delivery to maintain controllability, then motor stability is maintained, but the driver's torque request cannot be fully satisfied
Solution Approach 1:
The control system applies preliminary anti-action by correcting the torque delivery before the motor actually exits the controllability zone. The correction is based on the predicted output speed and the difference from the controllability limit, allowing the system to prevent uncontrollable operation while minimizing the impact on torque delivery.
3Reliability
If the system uses real-time speed measurement to prevent uncontrollable operation, then motor stability is improved, but the system complexity increases
Solution Approach 1:
The system replaces direct mechanical speed measurement with a prediction-based approach. Instead of using complex sensors and measurement systems to detect speed in real-time, the control unit predicts the output speed based on torque and supply voltage data, which are already available in the control system.
Data Source
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AI summary
A process for controlling an electric motor (2) includes providing a functional relationship, which associates a first and a second quantity (T, Vdc), indicative of a torque delivered by the electric motor (2) and of the supply voltage respectively, with a speed parameter (ωlim) of the electric motor (2), determining a pair of values of the first and of the second quantity (T, Vdc), determining (101) a value of a third quantity (ω) indicative of an output speed of the electric motor (2), determining (102) a value of the speed parameter (ωlim) corresponding to the pair of values determined through the functional relationship, determining (103) a value of a fourth quantity (Δω) indicative of a difference between the value of the speed parameter (ωlim) and the value of the third quantity (ω), determining (104) a target value (Ttgt) for the first quantity (T) as a function of the value of the fourth quantity (Δω), and controlling the electric motor (2) according to the determined target value (Ttgt).