EPS Motor Control via Virtual Resistance Decoupling
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Solution Overview
Problem
Current electric power steering (EPS) systems using permanent magnet synchronous motors (PMSMs) face challenges in maintaining consistent torque response and robustness due to limited supply voltage, motor parameter inaccuracies, and noise transmission characteristics, especially near the peak power point of operation.
Innovation Solution
The implementation of a motor control system with a first module generating a voltage command based on virtual resistance and targeted frequency characteristics, and a second module using estimated inductance and resistance values to decouple the d-axis and q-axis responses, combined with a feedback compensator to enhance plant dynamics and improve robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If closed-loop current control is applied to EPS systems with limited supply voltage, then torque tracking capability is improved, but voltage command transients become larger near peak power point
Solution Approach 1:
The control system dynamically adjusts control parameters including virtual resistance values and frequency response characteristics based on operating conditions. The virtual resistance is modified as a function of motor velocity and operating point, allowing the system to maintain stable current control with reduced voltage transients across the entire operating range including near peak power point
Solution Approach 2:
The control system implements adaptive dynamics by continuously adjusting the virtual resistance and frequency response characteristics based on real-time motor velocity and operating conditions. This dynamic adaptation allows the system to optimize torque tracking while minimizing voltage command transients under varying load and speed conditions
2Use of energy by moving object
If motor is sized efficiently for steady state power requirements, then power efficiency is improved, but transient voltage available becomes smaller near peak power point
Solution Approach 1:
The system modifies control parameters including virtual resistance and current limits as a function of motor velocity and operating point. This allows efficient utilization of the motor's steady-state capabilities while adapting to reduced transient voltage availability near peak power operations
Solution Approach 2:
The control system proactively adjusts current limits and virtual resistance before reaching peak power conditions. By anticipating the reduced transient voltage availability and pre-adjusting control parameters, the system prevents excessive voltage commands while maintaining efficient operation
3Device complexity
If d-axis and q-axis currents are coupled in traditional control, then control simplicity is maintained, but torque response behavior and disturbance rejection are compromised
Solution Approach 1:
The control system segments the current control into independent d-axis and q-axis loops with decoupled control. Each axis has its own virtual resistance and frequency response characteristics, allowing independent optimization of torque production (q-axis) and flux control (d-axis) while improving disturbance rejection and torque response behavior
Solution Approach 2:
The control system introduces virtual resistance as an intermediary element that decouples the d-axis and q-axis current loops. This virtual resistance acts as a mediator that allows independent control of each axis while maintaining overall system stability and improving torque response characteristics
Data Source
AI summary
A system includes a first module that: receives the output current from the electric motor as a feedback, the output current including a direct axis component and a quadrature axis component; and generates a first voltage command based on a virtual resistance value, the feedback, and a targeted frequency characteristic of the motor control system. The system includes: a second module that: receives a difference between the feedback and a commanded current; and generates a second voltage command based on an estimated inductance value, an estimated resistance value of an electric motor, the virtual resistance value, a targeted frequency response characteristic of the motor control system, and the response of the d-axis component of the output current being decoupled from the response of the q-axis component. The system includes an addition module that generates an input voltage command for the electric motor by adding the first and second voltage commands.