Torque Demand Limiter for Electric Motor Battery Protection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electric motor control systems face challenges in managing high current demands from electric motors in vehicles, which can lead to battery depletion, especially during high assistance torque requirements, as they lack effective mechanisms to limit current draw and prevent battery overloading.
Innovation Solution
The proposed solution involves a torque demand limiter that generates a torque demand limit signal based on a motor and drive stage model, limiting the torque demand to prevent battery current from exceeding predefined limits, allowing for efficient current management and preventing battery depletion by integrating a torque demand generator and a drive stage that adjusts PWM signals to meet the demanded torque while adhering to current limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high current demand is allowed to meet high assistance torque requirements, then motor performance is improved, but battery depletion occurs
Solution Approach 1:
The torque demand limiter proactively limits the torque demand signal before it is processed by the current controller, preventing excessive current demand from being generated in the first place. This preliminary limitation ensures that the motor current remains within safe operating limits that the battery and alternator can sustain, avoiding battery depletion while still allowing the motor to deliver its maximum safe power output.
2Reliability
If torque demand is limited to prevent battery overloading, then battery safety is improved, but motor performance deteriorates
Solution Approach 1:
The torque demand limiter dynamically adjusts the torque demand signal based on real-time operating conditions including battery voltage, motor speed, and temperature. By continuously adapting the torque limit to current system conditions, the limiter ensures battery safety while maximizing motor performance within safe operating boundaries. The dynamic nature of the limitation allows the motor to deliver full power when conditions permit and reduces power demand only when necessary to protect the battery.
3Device complexity
If existing current controllers are used without modification, then device complexity is reduced, but current management capability is insufficient
Solution Approach 1:
The torque demand limiter acts as an intermediary component between the torque demand generator and the existing current controller. It processes the torque demand signal and outputs a limited torque signal that the current controller can handle without modification. This intermediary layer provides enhanced current management capability while allowing the existing current controller to continue operating as designed, thus improving reliability without increasing overall system complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively limits the current drawn by the motor, preventing battery overloading and ensuring the alternator can meet the power requirements, thereby maintaining a healthy vehicle electrical system without the need for modifying existing current controllers, and allows for dynamic adjustment of torque limits based on battery voltage and motor parameters.
Implementation Method 1
each phase being connected to upper and lower drive stage switches connected to the battery supply and an earth respectively. In a PWM strategy each phase is driven with a cyclic PWM drive signal having a first state and a second state and a duty ratio indicative of the ratio of the time spent in each state in a cycle.
Data Source
AI summary
An apparatus for controlling an electric motor having a controller, a torque demand limit generator, and a drive stage. The controller may be arranged to receive as an input a torque demand signal indicative of the amount of torque demanded from the motor and to produce as an output a set of motor current demand signals. The drive stage may receive the motor current demand signals and is arranged to cause currents to flow in each phase of the motor as required to meet the demanded torque. The torque demand limit generator may be arranged to output a torque demand limit signal indicative of a torque demand limit above which the battery current would exceed one or more limits.