Power Tool Motor Control Using Voltage-to-Torque Half-Waves
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Solution Overview
Problem
Existing power tools face challenges in efficiently managing torque ripple and power factor issues due to varying intermediate circuit designs, especially when using distorted AC supply voltages, leading to potential torque ripple and increased ohmic losses.
Innovation Solution
A control unit that samples each voltage half-wave to convert it value-for-value into a respective torque half-wave, aligning the phase of the torque half-wave with the voltage half-wave without detecting phase position, thereby reducing susceptibility to errors in distorted supply voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the intermediate circuit is dimensioned large to provide constant intermediate circuit voltage, then the torque curve of the electric motor becomes almost constant, but the power factor deteriorates and harmonic components in the pick-up current increase
Solution Approach 1:
The patent applies dynamics by making the intermediate circuit voltage time-dependent through controlled discharge. Instead of maintaining constant voltage, the system dynamically adjusts the voltage profile by controlling the discharge current from the intermediate circuit capacitor, creating a voltage waveform that compensates for rectifier voltage drops and maintains stable motor torque while reducing harmonic components.
2Device complexity
If the intermediate circuit is dimensioned small to follow the AC supply voltage, then the device complexity is reduced, but torque ripple with twice the mains frequency occurs and ohmic power loss in the motor windings increases
Solution Approach 1:
The patent applies parameter changes by modifying the intermediate circuit voltage profile through controlled discharge. The system changes the voltage parameter over time to compensate for rectifier voltage drops, ensuring that the voltage supplied to the motor bridge remains sufficient throughout the mains half-wave, thereby eliminating torque ripple and reducing ohmic losses without requiring a larger capacitor.
3Device complexity
If conventional control is used with a small intermediate circuit, then the device complexity is reduced, but areas occur where the induced counter voltage of the electric motor is greater than or equal to the intermediate circuit voltage and no current can flow into the motor
Solution Approach 1:
The patent applies preliminary action by pre-charging the intermediate circuit capacitor to a voltage higher than the peak motor counter voltage before the motor bridge conducts. This preliminary voltage buildup ensures that when the motor bridge becomes conductive, current can immediately flow without interruption, preventing gaps in current supply and eliminating torque ripple caused by voltage mismatches.
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 ensures consistent torque delivery and reduced susceptibility to errors in distorted AC supply voltages, improving power tool performance and efficiency.
Implementation Method 1
a rectifier arrangement with an intermediate circuit for providing an intermediate circuit voltage on the basis of the AC supply voltage
Implementation Method 2
The intermediate circuit is, for example, a capacitor, which is used in particular to smooth the rectified AC supply voltage
Implementation Method 3
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, a sawing device and/or a router, with a tool, an electric motor for driving the tool and a control unit for controlling the electric motor, in which the power tool is designed for connection to an AC supply voltage and includes a rectifier arrangement with an intermediate circuit for providing an intermediate circuit voltage on the basis of the AC supply voltage. The intermediate circuit voltage has a plurality of successive voltage half-waves, and in which the control unit is configured to calculate, for each voltage half-wave, a respective torque half-wave for controlling the electric motor, the control unit being configured to sample each voltage half-wave in order to obtain a plurality of voltage half-wave values, and to convert each voltage half-wave value into a respective torque half-wave value in order to calculate the respective torque half-wave.