Electric Tool Motor Control With Field Weakening for Higher Speed
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Solution Overview
Problem
Existing electric tools with brushless DC motors face limitations in increasing the rotation number of the motor, particularly when high torque is required, leading to reduced efficiency and longer operation times.
Innovation Solution
The electric tool incorporates a Permanent Magnet Synchronous Motor (PMSM) with a control unit that performs field weakening control by generating a flux-weakening current, allowing the motor to operate at higher rotation numbers by weakening the magnetic flux of the permanent magnet, and switching to regular control for high-torque applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional brushless DC motor control is used, then the motor can operate with simple control structure, but the rotation number cannot be increased beyond a certain limit
Solution Approach 1:
The patent applies parameter changes by introducing field weakening control that modifies the magnetic flux parameter of the motor. By controlling the flux-weakening current to generate a magnetic flux that weakens the permanent magnet flux, the motor can operate at higher rotation numbers than conventional control allows, thus resolving the speed limitation without requiring fundamental structural changes.
2Speed
If field weakening control is applied to increase rotation number, then high-speed operation is achieved, but torque may be reduced
Solution Approach 1:
The patent employs dynamics by making the control mode adaptable based on operational requirements. The control unit dynamically switches between field weakening control for high-speed operation and regular control for high-torque applications, optimizing both speed and torque performance across different operating conditions without permanent compromise.
Solution Approach 2:
The control system dynamically adjusts the flux-weakening current parameter based on operational needs. By modulating this parameter, the system can weaken the magnetic flux to increase rotation number when needed, while maintaining full flux for maximum torque when high force is required, thus resolving the speed-torque trade-off.
3Productivity
If the motor operates at higher rotation numbers, then operation time is reduced, but control precision becomes more difficult to maintain
Solution Approach 1:
The patent implements feedback control where the control unit continuously monitors motor operation and adjusts the flux-weakening current accordingly. This feedback mechanism maintains control precision at high rotation numbers by compensating for variations in battery voltage and induced electromotive voltage, ensuring stable and precise motor control even during high-speed operation that reduces operation time.
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 enhances the rotation number of the motor, reducing operation time and maintaining torque performance, while also compensating for variations in battery voltage and induced electromotive voltage, thus improving overall tool efficiency and usability.
Implementation Method 1
The flux-weakening current is a current that generates, in the coil, a magnetic flux that weakens a magnetic flux of the permanent magnet
Data Source
AI summary
An electric tool includes an AC motor (an electric motor) and a control unit. The AC motor includes a permanent magnet and a coil. The control unit is configured to perform control on operation of the AC motor. The control performed by the control unit includes field weakening control. In the field weakening control, the control unit causes a flux-weakening current to flow through the coil. The flux-weakening current is a current that generates, in the coil, a magnetic flux that weakens a magnetic flux of the permanent magnet.