Variable Coercivity Rotor for Wide-Speed Electric Machine Operation
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Solution Overview
Problem
Permanent magnet type rotary electric machines face challenges in achieving efficient variable-speed drive due to high induced voltage at high speeds, leading to electronic component breakdowns and reduced output at low speeds, and struggle to effectively utilize interlinkage flux for maximum torque, especially when rotating in both forward and reverse directions.
Innovation Solution
The design incorporates a rotor core with alternating first and second permanent magnets of different coercive forces, where the fixed magnetic force magnet maintains high coercive force and the variable magnetic force magnet has lower coercive force, allowing for adjustable interlinkage flux and optimized torque by varying the magnetization state with axis d current, enabling efficient variable-speed operation and reduced losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the amount of interlinkage flux of permanent magnet is increased to improve output and efficiency at low speed, then the induced voltage becomes very high at high speed rotation, but this causes electronic components to breakdown
Solution Approach 1:
The rotor is divided into two types of permanent magnets: fixed magnetic force magnets (high coercive force) and variable magnetic force magnets (low coercive force). This segmentation allows different regions to serve different functions - the fixed magnets provide stable baseline flux while the variable magnets can be dynamically adjusted to control total interlinkage flux, preventing excessive induced voltage at high speeds while maintaining sufficient flux at low speeds for optimal output and efficiency.
Solution Approach 2:
The variable magnetic force magnets can change their magnetic flux density irreversibly in response to magnetic fields generated by stator winding current. This dynamic characteristic enables the system to adapt the total interlinkage flux according to operating conditions - reducing flux at high speeds to limit induced voltage and protecting electronic components, while maintaining higher flux at low speeds to maximize output and efficiency.
2Reliability
If the amount of interlinkage flux is reduced to protect electronic components at high speed, then the output and efficiency decrease in low speed area
Solution Approach 1:
By segmenting the permanent magnets into fixed and variable types, the system can independently control the baseline flux (from fixed magnets) and the adjustable flux (from variable magnets). This allows the variable magnets to reduce their flux contribution at high speeds to protect electronics, while the fixed magnets maintain sufficient baseline flux to ensure adequate output and efficiency at low speeds.
Solution Approach 2:
The magnetic flux density of the variable magnetic force magnets can be changed as a controllable parameter based on operating conditions. At low speeds, the variable magnets maintain high flux density to maximize output and efficiency. At high speeds, the flux density is reduced to limit induced voltage and protect electronic components, while the fixed magnets continue to provide stable baseline flux.
3Power
If variable magnetic force magnet is increased in magnetic force to reduce magnetization current requirement, then a large-sized inverter is still required due to great magnetization current needed to increase magnetic force
Solution Approach 1:
The rotor is segmented into fixed magnetic force magnets and variable magnetic force magnets with different coercive forces. The variable magnets are designed with lower coercive force to enable easier magnetization control, reducing the magnetization current requirement compared to using only high-coercive-force magnets. This segmentation allows the system to achieve the required magnetic force with more manageable current levels, avoiding the need for excessively large inverters.
Solution Approach 2:
The system utilizes parameter changes in the magnetic flux density of variable force magnets through controlled magnetization and demagnetization processes. By adjusting the magnetization state of variable magnets rather than constantly maintaining maximum magnetic force, the required magnetization current is reduced, allowing for more compact inverter design while still achieving the necessary power output when needed.
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 a wide range of variable-speed operation from low to high speeds while minimizing losses and improving efficiency by effectively managing interlinkage flux and torque, preventing electronic component overload and enhancing rotary electric machine performance.
Implementation Method 1
interlinkage flux of a permanent magnet is produced constantly with a certain strength, an induced voltage (back electromotive voltage) by the permanent magnet becomes higher in proportion with a rotation speed
Implementation Method 2
a magnetic flux density changes irreversibly by a magnetic field formed by current of a stator winding
Data Source
AI summary
According to one embodiment, a rotor includes a rotor core including magnetic poles arranged in a circumferential direction, a cavity formed on an axis q and extending toward a central axis, and a flux barrier band formed in the magnetic pole between a pair of the cavities to cross an axis d and including a first bridge part facing one cavity, a second bridge part facing the other cavity, and a magnet embedding hole formed between the first and the second bridge parts, a first permanent magnet formed of a fixed magnetic force magnet and disposed in the magnet embedding hole to be adjacent to the first bridge part, and a second permanent magnet formed of a variable magnetic force magnet and disposed in the magnet embedding hole to be adjacent to the second bridge part.