Variable R-T-B Magnet for Motor Efficiency
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Solution Overview
Problem
Permanent magnet synchronous motors face efficiency deterioration due to field-weakening effects when operated in intermediate/high speed regions or under low load, as they require a variable magnetic flux to counterbalance the magnetic flux generated by the armature current, which is not effectively achieved with existing R-T-B based permanent magnets.
Innovation Solution
A variable magnet with a composition of (R1-xYx)2T14B, where R is a rare earth element and x ranges from 0.2 to 0.7, providing a high residual magnetic flux density of 1.1 T or more and low coercivity of 400 kA/m or less, allowing for magnetization control by a small external magnetic field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a permanent magnet synchronous motor uses a stationary magnet with fixed magnetic flux, then the motor structure is simple, but the efficiency deteriorates in intermediate/high speed regions or under low load due to field-weakening effects
Solution Approach 1:
The patent applies the dynamics principle by replacing the stationary magnet with a variable magnet whose magnetic flux can be dynamically adjusted. The variable magnet's magnetization state changes in response to external magnetic fields, allowing the motor to adapt its magnetic flux to operating conditions. This enables efficient operation across a wide speed range by reducing magnetic flux in intermediate/high speed regions or low load conditions, thereby eliminating the need for field-weakening control and improving overall motor efficiency.
2Power
If a variable magnet with high residual magnetic flux density is used, then the motor output and efficiency improve, but the coercivity increases making magnetization control difficult with small external magnetic fields
Solution Approach 1:
The patent applies parameter changes by optimizing the composition parameters of the variable magnet. Specifically, it uses an R-T-B based permanent magnet with carefully controlled rare earth element composition (where R includes Nd, Pr, Dy, Ho, and/or Tb) to achieve a balanced set of magnetic parameters. This composition optimization enables the variable magnet to simultaneously possess high residual magnetic flux density (1.15-1.35 T) for high motor output and low coercivity (400-800 kA/m) for easy magnetization control with small external magnetic fields.
3Ease of operation
If Ce is used as a necessary rare earth element in R-T-B based permanent magnet to control coercivity, then the coercivity decreases to preferred low level, but the residual magnetic flux density drops to 0.80-1.25 T which is lower than the stationary magnet
Solution Approach 1:
The patent applies composite materials by creating a multi-element rare earth composition for the variable magnet. Instead of using a single rare earth element or simple Ce-based composition, it employs a composite rare earth system including Nd, Pr, Dy, Ho, and/or Tb in specific proportions. This composite composition synergistically combines the low coercivity contribution from Ce with the high residual magnetic flux density contributions from other rare earth elements, achieving both coercivity below 800 kA/m and residual magnetic flux density between 1.15-1.35 T.
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
The R-T-B based permanent magnet with high residual magnetic flux density and low coercivity maintains high efficiency across a wide rotational speed range, suitable for use in variable magnetic flux motors, enabling efficient operation in consumer, industrial, and transportation equipment.
Implementation Method 1
The R-T-B based magnet with the rare earth element(s) R composed of Nd, Pr, Dy, Ho and/or Tb has a large magnetic anisotropy field Ha
Implementation Method 2
the magnetic force changes reversibly via an action of an external magnetic field
Data Source
AI summary
An R-T-B based permanent containing main phase grains with a composition of (R1-xYx)2T14B (R is rare earth element(s) composed of one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, T is one or more transition metal elements including Fe or a combination of Fe and Co as essential elements, and 0.2≤x≤0.7), wherein the residual magnetic flux density Br is 1.1 T or more, the coercivity HcJ is 400 kA/m or less, and the ratio Hex/HcJ of the external magnetic field Hex required for obtaining a residual magnetic flux density Br of 0 to the coercivity HcJ is 1.10 or less.