Electric Motor Assembly with Phased Rotor Segments to Reduce Back EMF
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Solution Overview
Problem
At high rotor speeds, permanent magnet motors experience significant back electromotive force (EMF) that limits efficiency due to the need for field-weakening currents, which reduce the torque-producing current in stator windings.
Innovation Solution
The rotor of a radial-flux motor is divided into axial segments with offset permanent magnets that can be skewed relative to each other, reducing the amplitude of the magnetic field and back EMF through a phaser actuator and gear mechanism, allowing for reduced or eliminated field-weakening currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If field-weakening current is applied to suppress back EMF at high rotor speeds, then current can flow through stator windings, but motor efficiency decreases due to non-torque-producing current
Solution Approach 1:
The rotor is divided into multiple axially-spaced segments, each with its own set of permanent magnets. This segmentation allows independent control of magnetic field phases from different segments, enabling the superposition of sinusoidal back EMF waves to reduce total back EMF amplitude while maintaining torque-producing current flow at high speeds
Solution Approach 2:
The invention changes the phase parameter of the magnetic field by skewing different rotor segments by different angles relative to the stator. This parameter change transforms the back EMF characteristics, reducing its amplitude through destructive interference of sinusoidal waves from multiple segments, thereby eliminating the need for field-weakening current and improving efficiency
2Loss of energy
If rotor segments are skewed to reduce back EMF amplitude, then field-weakening current is eliminated, but device complexity increases due to phaser mechanism
Solution Approach 1:
The phaser mechanism dynamically adjusts the relative angular positions of rotor segments based on operating conditions. At high speeds, it creates optimal skew angles to minimize back EMF; at low speeds, it allows segments to align for maximum torque. This dynamic adjustment optimizes performance across the operating range while managing the added complexity through conditional adaptation
Solution Approach 2:
The system uses the motor's own operational parameters (speed, load) to automatically control the phaser mechanism, which in turn automatically adjusts rotor segment positions. This self-regulating system eliminates the need for external complex control systems, allowing the motor to self-optimize its back EMF reduction while managing the complexity internally
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 enhances motor efficiency by minimizing back EMF, ensuring that all currents in the stator windings contribute to torque production without the need for field-weakening, thereby improving performance at high speeds.
Implementation Method 1
The phaser actuator has a phaser rotor and a phaser stator surrounding the phaser rotor. The phaser stator has a second set of electrical windings and causes a change in an angular position of the phaser rotor when the second set of electrical windings is powered
Implementation Method 2
the rotating magnetic fields of the permanent magnets generate a 'back electromotive force' (EMF) in the windings. The magnetic field strength and back electromotive force acting on each phase of the stator winding varies sinusoidally with the rotational position of the rotor
Data Source
AI summary
An electric motor assembly includes a stator having a first set of electrical windings. The motor assembly includes a rotor assembly rotatable about an axis of rotation and that has a rotor with first and second rotor segments. Each of the rotor segments has a respective set of magnets spaced therearound. The motor assembly has a phaser that includes a phaser actuator and a phaser gear mechanism. The phaser gear mechanism has a plurality of members. The phaser actuator and the first and second rotor segments are each operatively connected to a different respective one of the members. The phaser actuator is activatable to change an angular position of the member to which the phaser actuator is operatively connected, moving one of the rotor segments about the axis of rotation relative to the other of the rotor segments to reduce back electromotive force in the first set of stator windings.