Permanent Magnet Motor Field Weakening via DC Injection
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Solution Overview
Problem
Existing AC permanent magnet electric motors face challenges in accurately controlling torque and extending speed range due to limitations in voltage and current management, particularly in field weakening control, where the counter-EMF exceeds the drive voltage, leading to reduced torque and limited speed ratios.
Innovation Solution
The method involves a permanent magnet AC motor with a stator and rotor, where a direct current is injected in the opposite direction of the magnetic flux to weaken the magnetic field, allowing for increased speed up to a higher speed ratio by modifying the air gap and winding arrangements, thereby reducing the required voltage and extending the speed range without needing additional components like gearboxes or reconfigurable winding sets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If field weakening control is used to extend speed range, then maximum speed increases, but torque decreases
Solution Approach 1:
The patent changes the magnetic field strength parameter by injecting DC current in the opposite direction of the permanent magnet flux. This parameter change allows the motor to operate at higher speeds by reducing the counter-EMF, thereby extending the speed range while maintaining controllable torque through the adjusted magnetic field configuration.
2Speed
If counter-EMF is reduced to enable higher speeds, then speed ratio increases, but voltage requirements change
Solution Approach 1:
The patent modifies the magnetic flux parameter by injecting opposing DC current, which directly changes the counter-EMF voltage characteristics. This parameter change enables the motor to achieve higher speed ratios while managing voltage stress through the adjusted magnetic field configuration, allowing operation beyond traditional voltage limits.
3Speed
If traditional field weakening is used, then speed control is achieved, but device complexity increases with additional components
Solution Approach 1:
The patent extracts the need for additional components like gearboxes and reconfigurable winding sets by implementing field weakening control through DC current injection into the existing stator windings. This approach achieves extended speed control within the motor itself, eliminating the need for external mechanical complexity.
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 approach enables a higher speed ratio of 2:1 to 20:1, reducing the need for gearboxes and multiple winding sets, resulting in a more efficient, cost-effective, and safer motor operation with improved torque control and extended speed range, even in adverse conditions.
Implementation Method 1
The counter-EMF is created by, in a permanent magnet motor, the current induced in the motor windings by the rotating magnetic fields of the permanent magnets
Implementation Method 2
injecting a direct current in the opposite direction of a magnetic flux created by the permanent magnet and weakening the magnetic field of the permanent magnet
Data Source
AI summary
A permanent magnet motor having a high speed ratio may remove the need for a gearbox or multiple windings in the permanent magnet motor. A gearbox or a multiple-winding configuration stator may thus be omitted.