Power Tool Braking Circuit With Battery Feedback Current Limiting
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Solution Overview
Problem
Existing power tools face issues with excessive braking force causing damage to the battery pack and safety hazards due to large feedback currents during the braking process, particularly in large-inertia sawing tools.
Innovation Solution
A control circuit with a driver circuit and controller adjusts the duty cycle of the control signal to manage the feedback current, switching between brake and freewheeling modes to limit the feedback current within a safe threshold, using a PI controller to monitor and adjust the duty cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If soft braking using feedback current is used, then braking force is improved, but battery pack damage risk increases
Solution Approach 1:
The patent applies dynamics by making the braking mode switchable between soft braking and regenerative braking based on real-time conditions. The control circuit dynamically adjusts the braking strategy: using soft braking when immediate stopping is needed, and regenerative braking when energy recovery is prioritized and battery conditions permit, thus optimizing both braking force and battery protection
Solution Approach 2:
The patent changes the parameter of feedback current magnitude by introducing a current threshold parameter. When the feedback current exceeds this threshold, the system automatically switches from soft braking to regenerative braking mode, effectively limiting the maximum feedback current to protect the battery pack while maintaining effective braking capability
2Productivity
If feedback current is increased for better braking, then braking performance is improved, but battery pack service life decreases
Solution Approach 1:
The patent implements feedback control by continuously monitoring the feedback current during braking and comparing it against a predetermined threshold. When the current exceeds the threshold, the system switches to regenerative braking mode, creating a closed-loop control mechanism that prevents excessive current from damaging the battery pack while maintaining optimal braking performance
Solution Approach 2:
The control circuit acts as an intermediary between the motor braking system and the battery pack. It introduces a current threshold as an intermediate parameter that mediates the interaction, allowing the system to recover energy through regenerative braking without subjecting the battery to damaging current levels, thus extending battery service life
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
Prevents battery pack damage while ensuring successful braking by maintaining the feedback current below a safe level, thereby extending the battery life and enhancing safety.
Implementation Method 1
During the braking process, the power tool usually brakes by short-circuiting the three phases of windings of the motor... In response to a brake signal, the driver circuit is controlled to operate in an energy feedback state and the duty cycle of the control signal is adjusted to adjust the magnitude of the feedback current
Data Source
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AI summary
A power tool includes a motor including a rotor and multiple phases of stator windings; a battery pack supplying power to at least the motor; and a control circuit for controlling the motor to rotate or brake. The control circuit includes a driver circuit including multiple high-side switching elements and multiple low-side switching elements; and a controller electrically connected to at least the driver circuit and outputting a control signal to control the states of the multiple high-side switching elements and the multiple low-side switching elements. The controller is configured to: in response to a brake signal, control the driver circuit to operate in an energy feedback state and adjust the duty cycle of the control signal to adjust the magnitude of the feedback current in the energy feedback state. The energy feedback state includes a brake mode and a freewheeling mode; and the feedback current generated in the freewheeling mode is fed back to the battery pack.