Power Tool DC Link Control for Low Torque Ripple
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Solution Overview
Problem
Existing power tools face challenges in achieving a good power factor with low ohmic power loss, particularly when using a small DC link that results in high harmonic content and torque ripple due to induced back EMF exceeding the DC link voltage.
Innovation Solution
A power tool design with a small DC link capacitor that follows the rectified mains voltage, generating voltage half-waves, and a control unit that provides corresponding torque half-waves with a flattened waveform to match the voltage half-waves, reducing ohmic power loss and torque ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the DC link is dimensioned large to maintain constant voltage, then the torque curve becomes nearly constant, but the power factor deteriorates and harmonic content increases
Solution Approach 1:
The patent applies periodic action by intentionally allowing the DC link voltage to follow a periodic pattern (voltage half-waves) rather than maintaining constant voltage. The control unit synchronizes torque half-waves with these voltage half-waves, creating a periodic operation mode that reduces harmonic content while maintaining acceptable torque delivery. This resolves the contradiction by replacing constant voltage stability with controlled periodic voltage variation.
2Object-generated harmful factors
If the DC link is dimensioned small to follow mains voltage, then the power factor improves, but ohmic power loss increases and torque ripple occurs
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the torque half-wave parameters (amplitude, duration, shape) to match the varying DC link voltage conditions. The control unit modifies torque delivery parameters in response to voltage half-wave characteristics, optimizing the balance between power factor and ohmic losses. This resolves the contradiction by adapting torque parameters to voltage conditions rather than maintaining fixed parameters.
Solution Approach 2:
The patent applies dynamics by transitioning from static DC link voltage to dynamic voltage half-waves that follow the mains voltage envelope. The control system dynamically adjusts torque half-waves to synchronize with these voltage variations, creating a dynamic operating mode that improves power factor while managing ohmic losses through real-time adaptation.
3Adaptability or versatility
If the DC link voltage follows rectified mains voltage with small capacitance, then voltage half-waves are generated, but induced back EMF exceeds DC link voltage preventing current flow
Solution Approach 1:
The patent applies preliminary action by proactively shaping torque half-waves before current flow issues occur. The control unit anticipates voltage half-wave conditions and pre-adjusts torque delivery timing and magnitude to ensure current can flow reliably. This resolves the contradiction by preventing back EMF conflicts through advance torque waveform planning rather than reactive correction.
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 with reduced ohmic power loss and minimizes torque ripple, allowing for a smaller electric motor and improved efficiency.
Implementation Method 1
a rectifier arrangement with an intermediate circuit for providing an intermediate circuit voltage based on a mains voltage
Implementation Method 2
The DC link, for example a capacitor, is dimensioned so small that the DC link voltage follows the rectified mains voltage
Implementation Method 3
an electric motor for driving the tool and a control unit for controlling the electric motor
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
The invention relates to an electric tool (1), in particular a hand-held electric tool, e.g. a polisher (1A), a grinder and/or a saw (1B), comprising a tool (2), an electric motor (3) for driving the tool (2), and a control unit (4) for controlling the electric motor (3), the electric tool (1) being designed to be connected to a mains voltage (V1) and comprising a rectifier assembly (12) with a DC link (15) for supplying a DC link voltage (V2) on the basis of the mains voltage (V1), wherein the DC link voltage (V2) includes a plurality of successive voltage half-waves (16), and the control unit (4) is configured to provide, for each voltage half-wave (16), a torque half-wave (36) for controlling the electric motor (3), the shape of the torque half-wave (36) being flatter than the shape of the voltage half-wave (16).