Stator Flux Control for Electric Motor Torque Stability
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Solution Overview
Problem
Existing electric vehicle torque control systems face challenges in maintaining peak torque performance while preventing instability, particularly at high speeds and during flux weakening, due to sensitivity to motor parameter changes and errors in flux estimation.
Innovation Solution
The implementation of a vehicle stability control system using stator flux-oriented control, which determines slip frequency or stator flux angle to adjust the q-axis current, thereby improving peak torque performance and mitigating instability by activating a slip or stator flux angle limiter to reduce current levels when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If traditional torque control systems are used to maintain peak torque performance, then the system can operate at high torque levels, but instability occurs particularly at high speeds and during flux weakening due to sensitivity to motor parameter changes and flux estimation errors
Solution Approach 1:
The patent changes the control parameter from flux-based control to stator current-based control with stator flux-oriented control. By using stator current commands (id*, iq*) as primary control variables instead of relying on flux estimation, the system maintains peak torque performance while becoming less sensitive to motor parameter changes and flux estimation errors, thereby improving stability at high speeds and during flux weakening operations
Solution Approach 2:
The patent implements feedback mechanisms by continuously monitoring stator current, rotor speed, and motor parameters, then adjusting the stator current commands (id*, iq*) in real-time. The controller uses feedback from current sensors and speed sensors to dynamically adjust control parameters, ensuring stable operation at peak torque conditions while compensating for parameter variations and preventing instability during flux weakening
2Reliability
If the system reduces q-axis current to prevent instability, then stability is improved, but peak torque performance is unnecessarily reduced
Solution Approach 1:
The patent implements dynamic control of q-axis current based on real-time operating conditions. Instead of statically reducing q-axis current to prevent instability, the system dynamically adjusts iq* based on rotor speed, load conditions, and flux weakening state. This allows the system to maintain maximum q-axis current (and thus peak torque) when stable operation is possible, while only reducing current when actually needed to prevent instability, optimizing both torque performance and stability
3Measurement precision
If the system is made sensitive to motor parameter changes to improve control precision, then control accuracy is improved, but the system becomes more susceptible to instability from parameter variations
Solution Approach 1:
The patent changes the control approach to be less dependent on precise motor parameters. By using stator flux-oriented control with stator current as the primary control variable instead of rotor flux-based control, the system maintains control accuracy while reducing sensitivity to parameter variations such as rotor resistance changes and flux estimation errors, thereby improving robustness without sacrificing control precision
Data Source
AI summary
Dynamic stability control for electric motors is provided. The system determines, for an electric motor of the electric vehicle, a slip frequency indicating a difference between a synchronous speed of a magnetic field of the electric motor and a rotating speed of a rotor of the electric motor. The system compares the slip frequency with a threshold. The system activates, responsive to the slip frequency greater than or equal to the threshold, a slip limiter to adjust a current command to generate an adjusted current command that causes a reduction in the slip frequency. The system deactivates, responsive to an external torque command less than a subsequent current command received subsequent to transmission of the adjusted current command, the slip limiter.