Permanent Magnet Rotor Segmentation for Variable-Speed Electrical Machines
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Solution Overview
Problem
Permanent-magnet-type rotating electrical machines face challenges in achieving wide-range variable-speed operation from low to high speeds while maintaining high torque and efficiency, as existing flux-weakening control methods lead to increased iron loss and harmonic flux issues, limiting their operational range and efficiency.
Innovation Solution
The use of a rotor with both low-coercive-force and high-coercive-force permanent magnets, where the low-coercive-force magnets can be magnetized by a d-axis current to adjust flux density and the high-coercive-force magnets maintain their flux, allowing for adjustable linkage flux and reduced voltage, enabling high-output variable-speed operation without continuous field-weakening currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If flux-weakening control is applied to expand variable-speed range to high speeds, then voltage margin is created and speed range is expanded, but d-axis current must be continuously applied causing increased iron loss and efficiency deterioration
Solution Approach 1:
The rotor is segmented into two distinct permanent magnet types: low-coercive-force magnets (first permanent magnets) and high-coercive-force magnets (second permanent magnets). This segmentation allows independent control of flux from each magnet type, enabling flux adjustment without continuous d-axis current while maintaining high-speed operation capability.
Solution Approach 2:
The invention changes the magnetic parameter (coercive force) of different permanent magnets to create distinct behavioral characteristics. The low-coercive-force magnets respond to d-axis current for flux adjustment, while high-coercive-force magnets maintain stable flux, allowing dynamic flux control without continuous energization and reducing iron loss.
2Power
If d-axis current is applied for flux-weakening control, then voltage reduction is achieved for high-speed operation, but harmonic flux is generated causing voltage increase and limiting speed expansion
Solution Approach 1:
By segmenting the permanent magnets into low-coercive-force and high-coercive-force types positioned at different radial locations, the invention creates distinct flux control zones. The low-coercive-force magnets near the stator respond to d-axis current for voltage control, while high-coercive-force magnets deeper in the rotor provide stable flux, reducing harmonic generation.
Solution Approach 2:
The low-coercive-force permanent magnets act as intermediaries between the d-axis current control system and the main flux production. They translate control currents into flux adjustments without requiring high continuous currents, thereby reducing harmonic flux generation while maintaining voltage control capability.
3Reliability
If high-coercive-force permanent magnets are used to prevent demagnetization, then reliability is improved, but flux adjustment capability for wide-speed operation is reduced
Solution Approach 1:
The rotor is divided into two permanent magnet segments with different coercive force characteristics. High-coercive-force magnets provide reliable, stable flux foundation resistant to demagnetization, while low-coercive-force magnets provide adjustable flux component responsive to control currents, achieving both reliability and adaptability.
Solution Approach 2:
Different regions of the rotor are assigned different magnetic material properties: low-coercive-force magnets in regions requiring flux adjustment (near stator) and high-coercive-force magnets in regions requiring stability (deeper in rotor). This local differentiation of material quality enables simultaneous flux control and demagnetization resistance.
4Power
If continuous d-axis current is applied for field-weakening control, then voltage margin is maintained for high-speed operation, but output current is reduced due to increased losses
Solution Approach 1:
The rotor is pre-configured with low-coercive-force permanent magnets that can be magnetized by control currents. This preliminary magnetic design allows flux adjustment through brief magnetizing actions rather than continuous current application, maintaining voltage margin while preserving output current capability.
Solution Approach 2:
The low-coercive-force permanent magnets serve themselves by maintaining adjusted flux states without requiring continuous external energization. Once magnetized by control currents, they self-maintain the flux level, eliminating the need for continuous d-axis current and preserving output current for productivity.
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 configuration allows for high torque at low speeds, high output at middle and high speeds, and improved efficiency by reducing iron loss and harmonic flux, enabling operation up to five times the base speed with minimized voltage and increased reliability.
Implementation Method 1
a low-coercive-force permanent magnet whose coercive force is of such a level that a magnetic field created by a current of the stator coil may irreversibly change the flux density of the magnet
Implementation Method 2
A permanent-magnet-type rotating electrical machine always generates constant linkage flux from permanent magnets, to increase a voltage induced by the permanent magnets in proportion to rotation speed
Data Source
AI summary
An object of the present invention is to provide a permanent-magnet-type rotating electrical machine capable of realizing a variable-speed operation at high output in a wide range from low speed to high speed and improving efficiency and reliability. The permanent-magnet-type rotating electrical machine of the present invention includes a stator provided with a coil and a rotor in which there are arranged a low-coercive-force permanent magnet whose coercive force is of such a level that a magnetic field created by a current of the stator coil may irreversibly change the flux density of the magnet and a high-coercive-force permanent magnet whose coercive force is equal to or larger than twice that of the low-coercive-force permanent magnet. At the time of high-speed rotation with a voltage of the permanent-magnet-type rotating electrical machine being around or over a power source maximum voltage, the low-coercive-force permanent magnet is magnetized with a magnetic field created by a current in such a way as to decrease total linkage flux of the low- and high-coercive-force permanent magnets, thereby adjusting a total linkage flux amount.