Centrifugal Flux-Adjusting Rotor for High-Speed Back-EMF Control
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Solution Overview
Problem
Permanent magnet synchronous motors face inefficiencies in increasing speed due to back electromotive force (BEMF), which limits maximum speed as it opposes the applied voltage, and existing methods to counteract BEMF, such as injecting direct current, are inefficient.
Innovation Solution
The motor design includes radially outer and inner permanent magnets, where inner magnets are movable between two positions, biased by springs and with reduced friction, allowing them to move outward as rotor speed increases, thereby weakening the magnetic field and reducing BEMF at high speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If direct current is injected to counteract BEMF at higher speeds, then motor speed can be increased, but energy efficiency deteriorates
Solution Approach 1:
The patent makes the magnetic field strength dynamic by allowing inner permanent magnets to move radially between inner and outer positions. At higher speeds, the magnets move to the outer position to weaken the magnetic field, reducing BEMF and improving energy efficiency. This dynamic adjustment resolves the contradiction between maintaining high speed and preserving energy efficiency.
Solution Approach 2:
The patent changes the magnetic field parameter (strength) in response to operating conditions. By moving the inner permanent magnets radially, the magnetic field strength is adjusted: stronger at low speeds for maximum torque, weaker at high speeds to reduce BEMF. This parameter change enables the motor to maintain energy efficiency across different speed ranges.
2Force
If inner permanent magnets are moved closer to radially outer permanent magnets, then magnetic field strength increases for better low-speed torque, but friction increases requiring biasing members and surface treatment
Solution Approach 1:
The patent uses spring biasing members to counteract the harmful friction force. The springs apply a radial inward biasing force on the inner permanent magnets, counterbalancing the friction that occurs when magnets move close together. This allows the magnets to achieve close positioning for strong magnetic fields while the biasing members handle the frictional resistance.
Solution Approach 2:
The patent replaces dry friction contact with a biased mechanical system. Instead of relying on frictionless guides or complex mechanical systems, simple spring biasing members are used to manage the frictional forces, providing a practical and efficient solution to the friction problem.
3Use of energy by moving object
If radially inner permanent magnets are made movable to adjust magnetic field, then motor efficiency improves at high speeds, but device complexity increases
Solution Approach 1:
The patent segments the permanent magnets into two functional groups: radially outer permanent magnets that remain fixed and provide stable magnetic field, and radially inner permanent magnets that are movable and adjust the magnetic field strength. This segmentation allows the system to achieve variable magnetic field control while maintaining structural simplicity through functional differentiation.
Solution Approach 2:
The patent introduces simple intermediary elements (spring biasing members and radial guides) that mediate between the stationary rotor structure and the movable inner permanent magnets. These intermediaries enable the complex function of adjustable magnetic field while keeping the overall device structure relatively simple by providing straightforward mechanical support and movement constraints.
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 design reduces the current needed to counteract BEMF, enhancing motor efficiency by allowing higher speeds without the inefficiencies of traditional methods.
Implementation Method 1
Each of the inner permanent magnets can be supported in a radial slot of the rotor. Each of the inner permanent magnets can be biased towards the first radially inner position with a biasing member. The biasing member can include a spring.
Implementation Method 2
The radially inner permanent magnets are movable radially between a first radially inner position and a second radially outer position... allowing them to move outward as rotor speed increases
Implementation Method 3
At least one of a surface of the radially inner permanent magnets or a surface of the rotor can be polished. At least one of a surface of the radially inner permanent magnets or a surface of the rotor can include a coating for reducing friction.
Implementation Method 4
The motor operates through the interaction between the magnetic fields of the magnets of the rotor and electrical current in conductors of the windings to generate force in the form of torque
Implementation Method 5
Back EMF (BEMF), also referred to as counter-electromotive force, is a well-known phenomenon of electric motors. In a PMSM, back EMF increases linearly with the rate of rotation of the motor and acts against the applied voltage that is causing the motor to spin.
Implementation Method 6
The rotor can include a magnetic isolator adjacent the plurality of radially inner permanent magnets
Data Source
AI summary
An electric motor including a stator, and a rotor supported for rotation within the stator. The rotor includes a plurality of circumferentially spaced-apart radially outer permanent magnets fixed to the rotor and a plurality of circumferentially spaced-apart radially inner permanent magnets movably supported by the rotor. The radially inner permanent magnets are movable radially with respect to the rotor between a first radially inner position and a second radially outer position to weaken the magnetic field of the radially outer permanent magnets at higher speeds.