PMSM Electric Tool Control for High Speed Without Torque Loss
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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 employs a Permanent Magnet Synchronous Motor (PMSM) with a control unit that performs vector control, including field weakening control, to independently manage flux-weakening and torque currents, allowing for increased rotation number by generating a magnetic flux opposite to the permanent magnet's flux, and switching between field weakening and regular control based on torque demands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If field weakening control is applied to increase rotation number, then the rotation number increases, but torque performance deteriorates
Solution Approach 1:
The control unit dynamically switches between field weakening control and regular control based on real-time torque requirements. When high rotation number is needed and torque demand is low, field weakening control is applied. When torque demand increases, the system transitions to regular control to maintain torque performance while operating at reduced speed.
Solution Approach 2:
The system changes the control mode parameter based on operating conditions. By monitoring torque requirements and rotation number demands, the control unit adjusts the control strategy between field weakening (which weakens magnetic flux to enable higher speeds) and regular control (which maintains optimal flux for torque production).
2Speed
If brushless DC motor is used with conventional control, then结构简单性 is maintained, but rotation number increase capability is limited
Solution Approach 1:
The patent applies field weakening control by injecting d-axis current to weaken the magnetic flux, enabling the motor to operate beyond its base speed. This parameter change in the control strategy allows significant rotation number increase while utilizing the existing brushless DC motor structure.
Solution Approach 2:
The control unit is designed to perform multiple functions: it can operate in field weakening control mode for high-speed applications and switch to regular control mode for high-torque applications. This multi-functionality allows a single control system to handle diverse operating conditions without requiring separate control circuits.
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 solution enhances the rotation number of the AC motor, reducing operation time for tasks like screw tightening and maintaining torque performance, while minimizing distortion and correcting performance variations due to electromotive voltage and battery voltage fluctuations.
Implementation Method 1
Electromagnetic interaction between the coil 141 and the permanent magnet 131 rotates the rotor 13 with respect to the stator 14
Implementation Method 2
The flux-weakening current generates, in the coil 141, a magnetic flux that weakens the magnetic flux of the permanent magnet 131 (weakening flux)
Data Source
Figure 1
Figure 2
Figure 3
AI summary
It is an object of the present disclosure to provide an electric tool configured to increase the rotation number of an electric motor. An electric tool (1) includes an AC motor (15) (an electric motor) and a control unit (4). The AC motor (15) includes a permanent magnet (131) and a coil (141). The control unit (4) is configured to perform control on operation of the AC motor (15). The control performed by the control unit (4) includes field weakening control. In the field weakening control, the control unit (4) causes a flux-weakening current to flow through the coil (141). The flux-weakening current is a current that generates, in the coil (141), a magnetic flux that weakens a magnetic flux of the permanent magnet (131).