Electric Motor Torque Control Under Low Battery State of Charge
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Solution Overview
Problem
Conventional electric motor power control systems in hybrid electric or fully electric propulsion systems face issues where battery voltage becomes sensitive to electrical load as the state of charge decreases, leading to system shutdowns due to high torque demands, even if energy is available, reducing operational time.
Innovation Solution
A control system that determines if a battery can supply a commanded power or torque based on its state of charge, outputting either the commanded or available maximum power/torque to prevent shutdowns by adjusting power output according to the battery's capability, using a comparison module, battery model module, and flight mode counter to manage power delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the motor controller allows high torque demand at low battery state of charge, then the motor can deliver required power, but the battery voltage drops below the minimum operating level causing system shutdown
Solution Approach 1:
The control system proactively limits the torque command before the battery voltage can drop below the minimum operating threshold. By calculating the available power based on battery state of charge and voltage characteristics, the system prevents the harmful voltage drop from occurring in the first place, rather than reacting after shutdown occurs
Solution Approach 2:
The control system continuously monitors battery state of charge and voltage levels, using this feedback to dynamically adjust the maximum allowable torque command. The power limitation is adjusted in real-time based on battery conditions, ensuring the voltage remains within the safe operating range while maximizing available power
2Reliability
If the motor controller limits power output at low battery state of charge, then battery voltage remains above minimum level, but the motor cannot deliver required torque and system operational time is reduced
Solution Approach 1:
The control system dynamically adjusts the power limitation based on real-time battery state of charge and voltage characteristics. Rather than applying a fixed power cap, the system continuously adapts the maximum allowable torque to match the battery's instantaneous capability, optimizing the balance between reliability and power delivery throughout the discharge cycle
3Power
If the motor controller operates without power limitation at low battery state of charge, then maximum power is available, but the battery voltage becomes too sensitive to load causing system shutdown
Solution Approach 1:
The control system changes the operating parameters by adjusting the maximum allowable torque command based on battery state of charge. As the battery depletes and voltage sensitivity increases, the system modifies the power demand parameter to keep the voltage within the stable operating range, preventing shutdown while maximizing available power at each state
Data Source
AI summary
A control system for an electric motor powered by a battery can be configured to receive an input power or torque command corresponding to a commanded power or torque. The control system can be configured to determine if the battery is capable of supplying the commanded power or torque over a time period based on a state of charge of the battery. The control system can be configured such that if the battery is capable of supplying the commanded power or torque over the time period, the control system outputs the input power or torque command, and if the battery is not capable of supplying the commanded power or torque over the time period, the control system outputs an available maximum power or torque command corresponding to an available maximum power or torque over the time period that is less than the commanded power or torque.