Variable Skew Rotor Assembly for Electric Motor Field Weakening
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Solution Overview
Problem
Existing electric motor field weakening techniques result in reduced system efficiency, particularly at high speeds, which is undesirable for electric vehicles requiring efficient propulsion systems.
Innovation Solution
The implementation of a rotor assembly with multiple rotatable parts that can be controlled to adjust their skew angle relative to each other, allowing for field weakening while maintaining efficiency by optimizing skew angles based on torque and speed conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If field weakening is performed using conventional power electronics control to manage magnet back EMF at high motor speeds, then the motor can operate at high speeds, but system efficiency is reduced
Solution Approach 1:
The rotor parts are made dynamically adjustable in their angular positions relative to each other. The controller can vary the skew angle between rotor parts based on operating conditions (speed, torque requirements), transitioning from fixed alignment to dynamic misalignment as needed for field weakening at high speeds while maintaining efficiency
Solution Approach 2:
The invention changes the geometric parameter (skew angle) of the rotor assembly to control magnetic field characteristics. By adjusting the angular offset between rotor parts, the system modifies the effective magnetic path and back EMF generation, enabling efficient field weakening without conventional power electronics losses
2Ease of manufacture
If the rotor parts are kept aligned with zero skew angle, then manufacturing and control are simplified, but field weakening capability is limited
Solution Approach 1:
The rotor is divided into multiple independently controllable rotor parts that can be positioned at different angular offsets. This segmentation enables the system to achieve field weakening capability while maintaining a simple baseline configuration (zero skew) for ease of manufacture, and only introducing angular offsets when field weakening is required
Solution Approach 2:
The rotor assembly transitions from a static aligned configuration to a dynamic misaligned configuration based on operational needs. The controller adjusts the skew angle between rotor parts only when field weakening is required, maintaining manufacturing simplicity while providing adaptability when needed
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces system power loss and back EMF, enhancing motor efficiency and reliability at high speeds, and supports higher gear ratios, thereby reducing motor size and improving overall performance.
Implementation Method 1
field weakening is performed by a power electronics control system to manage magnet back electromotive force (emf)
Data Source
AI summary
An electric machine assembly includes a rotor assembly that includes a plurality of rotor parts including a reference rotor part and a first control rotor part. Each rotor part is rotatable about a longitudinal axis and mechanically separated from another rotor part along the longitudinal axis. The first control rotor part is controllable to rotate while aligned with the reference rotor part with a zero or near zero skew angle relative to the reference rotor part. The first control rotor part is also controllable to rotate while unaligned with the reference rotor part with a non-zero skew angle relative to the reference rotor part. The electric machine assembly further includes a rotor controller that is configured to control the degree of skew angle between the control rotor part and the reference rotor part.