Axially Movable Ferromagnetic Component for PM Machine Field Weakening
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Solution Overview
Problem
Permanent magnet machines face challenges in extending their constant power range and managing high-speed operations, where field weakening reduces efficiency and can lead to hazardous voltage levels due to increased back electromotive force (emf).
Innovation Solution
The implementation of axially movable ferromagnetic components that can be pressurized to weaken the rotor magnetic field, either through hydraulic fluid or centrifugal force, allowing for external field weakening without applying negative flux current, thereby controlling the magnetic flux and reducing high-speed losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If field weakening current is applied to extend constant power range, then speed range is extended, but efficiency is reduced
Solution Approach 1:
The invention extracts the field weakening function from the electrical domain (stator windings) to the mechanical domain (rotor-side ferromagnetic component). By placing the field weakening mechanism on the rotor and actuating it axially, the system achieves field weakening without requiring negative flux current from the stator, thereby eliminating the associated energy losses and efficiency reduction.
Solution Approach 2:
The invention introduces an intermediary ferromagnetic component between the rotor magnets and the air gap. This intermediate component, when actuated axially toward the rotor, modifies the magnetic flux distribution and achieves field weakening. The intermediary component serves as a mechanical mediator that replaces the need for electrical field weakening current.
2Duration of action of moving object
If field weakening current is applied to extend constant power range, then constant power range is extended, but torque is reduced
Solution Approach 1:
The invention extracts the field weakening function from the stator windings to a dedicated rotor-side mechanism. By using an axially actuated ferromagnetic component on the rotor, the system achieves field weakening independently of the torque-producing current, allowing constant power extension without the torque penalty associated with electrical field weakening current.
Solution Approach 2:
The invention segments the magnetic circuit by introducing a separate field weakening component distinct from the torque-producing stator windings. This segmentation allows independent control of field strength and torque production, enabling the system to extend constant power range while maintaining torque through separate control of the field weakening component and stator current.
3Power
If high speed operation is performed, then power output is increased, but hazardous voltages are created
Solution Approach 1:
The invention applies preliminary field weakening by actuating the ferromagnetic component axially before hazardous over-voltage conditions occur. This preliminary action reduces the back EMF and line-to-line voltages at high speed, preventing the inverter from operating as a rectifier and avoiding dangerous DC link voltage escalation.
Solution Approach 2:
The invention converts the potentially harmful high-speed operation that generates hazardous voltages into a beneficial condition by using the high-speed operation itself to drive the field weakening mechanism. The centrifugal force or hydraulic pressure generated during high-speed operation is utilized to actuate the ferromagnetic component, which then reduces the voltages that would otherwise become hazardous.
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 the efficiency of permanent magnet machines by increasing torque and extending the speed range while preventing hazardous voltage conditions by shorting rotor magnet fluxes with magnetic rings, thus improving operational efficiency and safety.
Implementation Method 1
The ferromagnetic component is configured for actuating axially toward the rotor to weaken a magnetic field of the rotor
Implementation Method 2
A permanent magnet machine includes a stator, a rotor inside the stator and a ferromagnetic component fixed axially movably to the rotor
Implementation Method 3
the axially fixed support and the axially movable ferromagnetic plate define a cavity axially therebetween, the cavity being configured such that an increase in pressure therein forces the ferromagnetic component toward the rotor
Implementation Method 4
an increase in pressure therein forces the ferromagnetic component toward the rotor
Implementation Method 5
at least one elastic element applying a preloading force to the movable ferromagnetic plate to hold the movable ferromagnetic plate axially away from the rotor carrier
Data Source
AI summary
The permanent magnet machine includes a stator, a rotor inside the stator and a ferromagnetic component fixed axially movably to the rotor. The ferromagnetic component is configured for actuating axially toward the rotor to weaken a magnetic field of the rotor. The method of constructing a permanent magnet machine includes providing a stator and a rotor inside the stator; and axially movably fixing a ferromagnetic component to the rotor such that the ferromagnetic component is configured for actuating axially toward the rotor to weaken a magnetic field of the rotor.