DC Motor Current Limiting for EPS Voltage Source Protection
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Solution Overview
Problem
Existing DC machine control systems in electric power steering (EPS) systems face challenges in effectively limiting supply current to protect the voltage source, such as a car battery, while maintaining torque capability.
Innovation Solution
A control system comprising a current command module and a supply current limiting module that computes and enforces motor current limits based on a supply current limit, ensuring the system does not exceed the specified current draw, thereby protecting the voltage source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a voltage versus supply current limit is imposed to protect the voltage source, then the voltage source is protected, but the torque capability is reduced
Solution Approach 1:
The system dynamically adjusts the motor current command in real-time based on the calculated supply current limit, rather than using a fixed current limit. The supply current limiting module continuously monitors and modifies the current command to ensure the supply current does not exceed the limit while maximizing torque output within that constraint.
Solution Approach 2:
The system changes the current command parameter dynamically based on operating conditions and the supply current limit. By adjusting the current command as a variable parameter rather than a fixed value, the system can optimize torque production while staying within the supply current constraints to protect the voltage source.
2Reliability
If the motor current command is modified to ensure the system does not draw more current than specified, then the voltage source is protected, but the torque capability is reduced
Solution Approach 1:
The supply current limiting module uses feedback from the calculated supply current limit to continuously adjust the motor current command. The system monitors the relationship between motor current and supply current, and uses this feedback to modify the current command in a way that protects the voltage source while maintaining optimal torque production within the current constraints.
Solution Approach 2:
The control system automatically adjusts its own current command based on the supply current limit without requiring external intervention. The supply current limiting module self-regulates the motor current to ensure voltage source protection while maximizing torque output, making the system self-adjusting and autonomous in managing the current-torque trade-off.
Data Source
AI summary
An embodiment of a control system includes a current command module configured to receive a torque command and output a current command for controlling a direct current (DC) motor, and a supply current limiting module configured to receive a supply current limit as an input and actively compute a motor current limit based on the supply current limit, the supply current limiting module configured to limit the current command based on the motor current limit.