Dual Permanent Magnet Rotor for Variable-Speed Electrical Machine
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Solution Overview
Problem
Conventional permanent-magnet-type rotating electrical machines face challenges in achieving variable-speed operation over a wide range, particularly at high speeds, due to limitations in torque production, efficiency, and material usage, especially with AlNiCo magnets which are prone to demagnetization and have insufficient output.
Innovation Solution
The implementation of a rotor with first and second permanent magnets of different magnetic characteristics, where the first magnet has a coercive force of 100 kA/m to 300 kA/m and a remanent flux density of 0.6 T or more, and the second magnet has a higher coercive force, allowing for reversible and irreversible flux adjustments using armature coil currents to optimize linkage flux and torque production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If AlNiCo permanent magnets are used to generate flux, then the rotating electrical machine can operate, but the magnets are demagnetized by load current which decreases torque output
Solution Approach 1:
The invention uses a composite magnet structure combining AlNiCo permanent magnets (first permanent magnets) with ferrite magnets (second permanent magnets). The AlNiCo magnets provide high permeability for easy magnetization control, while the ferrite magnets provide high coercive force for stable flux generation. This composite approach allows the machine to achieve both high torque output and magnet stability, resolving the contradiction between torque production and magnet demagnetization.
Solution Approach 2:
The invention changes the magnetic parameters of the rotor by using two types of permanent magnets with different characteristics. The AlNiCo magnets have high permeability allowing their flux to be easily controlled by armature reaction, while ferrite magnets have high coercive force making them resistant to demagnetization. By adjusting the proportion and arrangement of these two magnet types, the system can optimize both torque output and flux stability under different operating conditions.
2Power
If the flux amount of permanent magnets is increased to generate sufficient torque, then torque production improves, but the voltage induced by permanent magnets becomes very high at high rotation speed which exceeds withstand voltage of electronic parts
Solution Approach 1:
The invention changes the magnetic parameter characteristics by using AlNiCo magnets with high permeability instead of relying solely on increasing flux amount. The high permeability allows the armature reaction to effectively control the flux, enabling sufficient torque production without requiring excessively high flux amounts that would induce dangerous voltages at high speeds.
Solution Approach 2:
The invention makes the flux amount dynamic by using AlNiCo magnets whose flux can be irreversibly changed by armature reaction. The flux amount is no longer fixed but can be adjusted based on operating conditions, allowing the system to optimize torque production at low speeds while limiting induced voltage at high speeds.
3Power
If a very large current is passed to magnetize thick AlNiCo magnets, then the magnets can be magnetized, but the permanent magnets are hardly magnetized and the flux amount becomes unchangeable
Solution Approach 1:
The invention uses a composite magnet structure where AlNiCo magnets (with high permeability) are combined with ferrite magnets. This composite approach allows the AlNiCo magnets to be easily magnetized by armature reaction without requiring very large currents, while the ferrite magnets provide stable flux generation. The combination resolves the contradiction between magnetization capability and flux controllability.
4Object-affected harmful factors
If flux-weakening control is applied to suppress induced voltage, then voltage control improves, but a demagnetizing field is applied to permanent magnets which may cause irreversible demagnetization
Solution Approach 1:
The invention uses a composite magnet structure where ferrite magnets (with high coercive force) are combined with AlNiCo magnets. The ferrite magnets are resistant to demagnetization by the demagnetizing field used in flux-weakening control, allowing voltage suppression without risking irreversible demagnetization. This resolves the contradiction between voltage control and magnet integrity.
Solution Approach 2:
The invention changes the coercive force parameter of the permanent magnets by using ferrite magnets with high coercive force. This high coercive force allows the magnets to withstand the demagnetizing field applied during flux-weakening control without irreversible demagnetization, enabling effective voltage control while maintaining magnet integrity.
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 enables high torque at low speeds and high output at middle to high speeds, improves efficiency, reduces material usage, and extends the variable-speed operating range while minimizing harmonic losses and demagnetization risks.
Implementation Method 1
a coercive force of 100 kA/m to 300 kA/m, a remanent flux density of 0.6 T or over, and a knickpoint of 0.6 T or over, the knickpoint being a point on a hysteresis curve where a reversible magnetizing range shifts to an irreversible magnetizing range
Implementation Method 2
a magnetic field created by a current of the armature coil at a magnetic pole magnetizes the first permanent magnet so as to irreversibly change a flux amount of the first permanent magnet
Implementation Method 3
the permanent magnets always generate constant linkage flux to increase a voltage induced by the permanent magnets in proportion to a rotation speed
Data Source
AI summary
A permanent-magnet-type rotating electrical machine capable of realizing variable-speed operation in a wide range from low speed to high speed at high output and improving, in a wide operating range, efficiency, reliability, and productivity. The rotating electrical machine includes a first permanent magnet whose product of coercive force and magnetizing direction thickness is small and a second permanent magnet whose product of coercive force and magnetizing direction thickness is large, to form a magnetic pole. The product of coercive force and magnetizing direction thickness of the first permanent magnet is equal to or larger than the product of magnetic field strength and magnetizing direction thickness of the second permanent magnet at a no-load operating point. At the magnetic pole, a magnetic field created by a current of an armature coil magnetizes the first permanent magnet, irreversibly changing a flux amount of the first permanent magnet.