Brushless Power Tool Circuit Using Back-EMF for Power Factor Control
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Solution Overview
Problem
High-voltage brushless power tools experience a low power factor, affecting electromagnetic compatibility and efficiency in utilizing electrical energy.
Innovation Solution
A power tool with a control circuit that includes a driver circuit, power circuit with two operating states, and a controller to manage the power circuit based on bus voltage and back electromotive force, using a power switch and inductor to optimize energy utilization and suppress noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional power circuit is used in high-voltage brushless power tools, then the device can operate, but the power factor remains low affecting electromagnetic compatibility and energy utilization efficiency
Solution Approach 1:
The power circuit dynamically switches between two operating states (first state with power switch off, second state with power switch on at preset frequency) based on real-time comparison between bus voltage and back electromotive force, enabling adaptive optimization of power factor across varying operational conditions while maintaining electromagnetic compatibility
Solution Approach 2:
The controller changes the operating parameters of the power circuit by switching between different states depending on the voltage conditions. When bus voltage exceeds back EMF, the circuit operates in the first state; when bus voltage is less than or equal to back EMF, it switches to the second state, thereby optimizing energy utilization and power factor through parameter adjustment
2Use of energy by moving object
If the power switch is turned on continuously to maintain current flow, then energy utilization improves, but the inductor may become saturated and noise increases
Solution Approach 1:
The power switch operates through periodic on-off cycles at a preset frequency rather than continuously. This periodic action allows the inductor to charge and discharge in controlled intervals, preventing saturation while maintaining current flow through the motor, thereby reducing noise and improving electromagnetic compatibility without sacrificing energy utilization
Solution Approach 2:
The controller predicts and prevents inductor saturation by switching the power circuit to the second state at appropriate times based on voltage comparison. The periodic switching at preset frequency ensures the inductor remains in an unsaturated state by limiting the maximum current buildup, thereby preventing harmful effects before they occur
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
Enhances power factor and electromagnetic compatibility, ensuring efficient energy utilization and effective noise suppression across varying loads and operational states.
Implementation Method 1
the inductor is charged to an unsaturated state
Implementation Method 2
in the case where the bus voltage is less than or equal to the back electromotive force
Data Source
AI summary
A power tool includes: an electric motor including a rotor and a plurality of stator windings; a power interface having at least a positive electrode interface and a negative electrode interface and configured to be connected to a power supply; and a control circuit connected between the power interface and the electric motor and configured to control the electric motor to operate. The control circuit includes: a first power line connected to the positive electrode interface; a second power line connected to the negative electrode interface; and a plurality of noise suppression devices configured to suppress noise on a side of the electric motor. The plurality of noise suppression devices includes a first noise suppression device, a first terminal of the first noise suppression device is connected to the plurality of stator windings, and a second terminal of the first noise suppression device is connected to the first power line.