Decoupling Current Control via Direct Plant Modification in Electric Power Steering
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Solution Overview
Problem
Electric Power Steering (EPS) systems using Permanent Magnet Synchronous Motors (PMSMs) face challenges in maintaining consistent torque control due to variations in operating parameters and limited supply voltage, requiring a control system that operates stably and predictably across the motor's velocity range while minimizing voltage transients.
Innovation Solution
A control system that generates a voltage command by determining a first set of gain factors to reduce the influence of motor operating parameter variations and a second set of gain factors based on the difference between feedback and desired current, allowing the motor to produce output current with reduced sensitivity to parameter changes and achieving specific order responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If closed-loop current control is applied to EPS systems with PMSM, then torque tracking capability is improved, but the system becomes sensitive to parameter variations and supply voltage limitations
Solution Approach 1:
The patent applies parameter changes by transforming the control approach from direct current control to voltage control with modified plant parameters. The control system changes the effective electrical time constant and resistance parameters through the plant modification block, allowing the system to maintain stability and predictability across varying operating conditions while achieving desired torque tracking performance.
2Use of energy by moving object
If the motor is sized efficiently for steady state power requirements, then power efficiency is improved, but transient voltage becomes smaller near peak power point requiring precise control
Solution Approach 1:
The plant modification approach enables the system to self-adjust its effective parameters based on operating conditions. The modified plant automatically compensates for voltage limitations near peak power points by adjusting its effective time constant and resistance, reducing the need for complex control algorithms while maintaining efficient motor sizing for steady-state operations.
3Stability of the object's composition
If direct plant modification is used for decoupling current control, then control stability is improved, but the control structure becomes more complex
Solution Approach 1:
The patent introduces an intermediary plant modification block that sits between the voltage controller and the motor. This intermediary transforms the control problem by modifying the plant's effective parameters, thereby decoupling the current control loops and improving stability without requiring complex multi-variable control algorithms. The intermediary absorbs the complexity of parameter coupling while presenting a simplified control interface.
Data Source
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AI summary
A method of controlling an electric motor that generates an output current from an input voltage command that includes a sum of a first voltage command and a second voltage command is provided. The method receives the output current from the motor as a feedback. The method determines a first set of gain factors to generate the first voltage command based on the feedback such that the input voltage command causes the motor to generate the output current with reduced influence of variations of a set of operating parameters of the motor. The method determines a difference between the feedback and a desired current. The method determines a second set of gain factors to generate the second voltage command based on the difference such that the input voltage command causes the motor to generate the output current as a first, second or higher order response.