Minimizing Demagnetization in Rotor Magnets via Current Trajectory Control
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Solution Overview
Problem
Electric motors in hybrid and electric vehicles face challenges in minimizing demagnetization of permanent magnets over time due to temperature, age, and other factors, which affects performance and torque demands.
Innovation Solution
A propulsion system with a controller that determines a demagnetization line in a stator current graph, selects a starting point on the trajectory, and adjusts the stator current to maintain a predetermined voltage limit, generating a demagnetized torque capability while optimizing torque contribution from both the electric motor and secondary sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the electric motor operates at high torque demand, then the torque contribution is improved, but the permanent magnets experience demagnetization
Solution Approach 1:
The controller proactively determines a demagnetization line and establishes a stator current trajectory that prevents demagnetization before it occurs. By calculating the demagnetization line based on motor parameters and pre-planning the current trajectory, the system avoids conditions that would cause magnet degradation while still meeting torque demands.
Solution Approach 2:
The system dynamically adjusts the stator current trajectory in real-time based on operating conditions. The controller continuously monitors and modifies the d-axis and q-axis current components to keep the operating point within safe boundaries, allowing maximum torque generation without causing demagnetization under varying load and speed conditions.
2Force
If the stator current is increased to meet torque demand, then the torque output is improved, but the voltage limit is exceeded
Solution Approach 1:
The controller transforms the torque generation problem by changing the parameter representation from direct current magnitude to a trajectory in the d-q current plane. By working with current components and their relationships rather than total current magnitude alone, the system optimizes torque production while respecting voltage constraints through parameter transformation and coordinate system changes.
3Speed
If the d-axis stator current is increased, then the flux weakening is improved, but the permanent magnets are exposed to demagnetization risk
Solution Approach 1:
The system implements feedback control by continuously monitoring the operating point relative to the demagnetization line. The controller adjusts the d-axis current based on the position of the operating point, ensuring that flux weakening is achieved without crossing into the demagnetization zone. This closed-loop approach allows optimal speed control while protecting the permanent magnets.
Data Source
AI summary
A propulsion system for a device includes an electric motor configured to generate torque to propel the device. The electric motor includes a stator and a rotor with one or more permanent magnets. A controller is in communication with the electric motor and has recorded instructions for a method for minimizing demagnetization in the one or more permanent magnets. The controller is adapted to select a starting point and an intermediate point on a current trajectory in a stator current graph. The controller is adapted to obtain a final point on the stator current trajectory based on a comparison of the intermediate point and a predetermined voltage limit. A demagnetized torque capability is generated based on the final point on the current trajectory.