Power Tool Torque Control for Small DC-Link Power Factor
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Solution Overview
Problem
Existing power tools face challenges in achieving a good power factor with low ohmic dissipation, leading to inefficiencies and increased harmonic components in the pickup current, especially when using a small intermediate circuit.
Innovation Solution
A power tool design with a small intermediate circuit that follows the rectified mains voltage, combined with a control unit that generates a flattened torque half-wave for each voltage half-wave, ensuring a uniform current flow to reduce ohmic power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the intermediate circuit is dimensioned small, then the intermediate circuit voltage follows the rectified mains voltage and a good power factor is achieved, but the electric motor must be designed larger
Solution Approach 1:
The control unit implements dynamic torque control that adapts to the small intermediate circuit's voltage variations. This dynamic adjustment allows the motor to operate efficiently with reduced current requirements, enabling a smaller motor design while maintaining the power factor benefits of a small intermediate circuit.
Solution Approach 2:
By changing the torque waveform parameters to optimize current utilization, the system reduces the overall current demand on the motor. This parameter optimization allows for a smaller motor design that can still achieve the desired power factor with a small intermediate circuit, avoiding the need for oversized motors.
2Loss of energy
If the intermediate circuit is dimensioned small, then a good power factor is achieved, but torque ripple with twice the mains frequency occurs
Solution Approach 1:
The control unit dynamically compensates for the torque ripple caused by the small intermediate circuit by adjusting the torque half-wave in real-time. This dynamic compensation counteracts the twice-mains-frequency torque variations, maintaining stable motor operation while preserving the power factor advantages of the small intermediate circuit design.
Solution Approach 2:
The control unit uses feedback from the intermediate circuit voltage and motor operation to detect and compensate for torque ripple. By continuously monitoring and adjusting the torque output based on detected variations, the system eliminates the destabilizing torque ripple while maintaining the power factor benefits of using a small intermediate circuit.
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 solution achieves a power factor of at least 0.70 or 0.75 while reducing ohmic power dissipation, allowing for a smaller electric motor design and improved efficiency.
Implementation Method 1
a rectifier arrangement with an intermediate circuit for providing an intermediate circuit voltage based on the mains voltage
Implementation Method 2
an electric motor for driving the tool
Data Source
AI summary
A power tool, in particular a hand-held power tool, for example a polishing device, a grinding device and/or a sawing device, with a tool, an electric motor for driving the tool and a control unit for controlling the electric motor. The power tool is designed for connection to a mains voltage and includes a rectifier arrangement with an intermediate circuit for providing an intermediate circuit voltage based on the mains voltage, the Intermediate circuit voltage having a plurality of successive voltage half-waves, and the control unit being configured to provide, for each voltage half-wave, a respective torque half-wave for driving the electric motor, the waveform of which torque half-wave is flattened with respect to the waveform of the voltage half-wave.