Motor Torque Control via Speed-Dependent Power Limiting
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Solution Overview
Problem
Existing electric vehicle control systems unnecessarily limit motor torque and induce vibrations by deriving power limits solely from battery strength, leading to performance restrictions, especially at low speeds and during battery voltage fluctuations.
Innovation Solution
Implementing a computing device with a processor and memory to calculate and limit power output based on motor speed, allowing torque adjustments as a function of speed to maintain performance and reduce vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If torque is limited solely as a function of battery strength, then power draw from the battery is limited, but motor performance is unnecessarily restricted especially at low speeds
Solution Approach 1:
The control system dynamically adjusts torque limits based on motor speed, transitioning from a static torque limit (function of battery strength only) to a dynamic torque limit that varies with operating conditions. At low speeds, higher torque is permitted while maintaining power constraints, and at high speeds, torque is reduced to prevent excessive power draw, optimizing both power management and motor performance across the entire operating range.
Solution Approach 2:
The system changes the controlling parameter from battery strength alone to a combination of battery strength and motor speed. By introducing speed as an additional parameter, the torque limit becomes a function of multiple variables rather than a single parameter, enabling more nuanced control that balances power constraints with performance requirements at different operating points.
2Power
If torque is limited to induce a restrictive drive shaft speed, then power is controlled, but torque available for braking or driving the load at low speeds is reduced
Solution Approach 1:
The torque limit is made dynamic by incorporating motor speed as a variable. At low speeds, the system permits higher torque output to maintain force availability for braking and load driving, while at high speeds, torque is reduced to control power output. This dynamic adjustment ensures that torque availability is optimized for each operating condition rather than being uniformly restricted.
3Power
If torque limiting is applied during battery voltage fluctuations, then power is controlled, but transient torque changes and drive shaft vibration are induced
Solution Approach 1:
The control system continuously monitors motor speed and uses this feedback to adjust torque limits in real-time. By incorporating speed feedback into the torque calculation, the system can smooth out transient torque changes that would otherwise occur during battery voltage fluctuations, maintaining more stable torque delivery and reducing drive shaft vibration.
4Device complexity
If a fixed torque limit is applied based on battery strength, then power management is simplified, but motor speed control flexibility is reduced
Solution Approach 1:
The system transitions from a fixed torque limit parameter to a dynamic parameter that incorporates motor speed. This allows the control system to adapt torque limits based on operating conditions, providing speed control flexibility while maintaining power management through a systematic approach that balances complexity and adaptability.
Data Source
AI summary
A method of assembling an electric drive system includes providing a power conversion assembly and coupling an electric power source and a motor to the power conversion assembly. The method also includes coupling a computing device that includes a processor and a memory device operatively coupled to the processor to the power conversion assembly. The method further includes configuring the computing device to record at least one measurement related to a speed of the motor. The method also includes configuring the computing device to calculate a power output limit of the power conversion assembly and limit the power output of the power conversion assembly by limiting torque induced by the motor as a function of the speed of the motor.