Brushless Power Tool Overcurrent Control With Variable Drive Periods
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Solution Overview
Problem
Alternating current power tools, especially high-voltage brushless tools, are prone to overcurrent under heavy load, which can damage electronic components and affect user experience due to insufficient power supply capability.
Innovation Solution
A control method for power tools that includes a control module to detect phase current values in real time and adjust the operation of electronic switches within periodic time intervals, limiting current by turning off switches when thresholds are exceeded and turning them back on when necessary, with the period of the drive signal varying randomly or continuously to manage grid voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the power tool operates under heavy load with sufficient grid power supply capability, then the power tool can deliver high performance, but overcurrent occurs which damages electronic components and affects user experience
Solution Approach 1:
The patent implements dynamic current limiting by continuously monitoring phase current values and adjusting the drive signal duty cycle in real-time. When overcurrent is detected, the control module dynamically reduces the duty cycle to limit current, and when current returns to normal, it restores the duty cycle. This dynamic adjustment allows the system to deliver high power when needed while preventing component damage through real-time protection.
Solution Approach 2:
The patent employs feedback control by detecting phase current values through current detection modules and using this information to adjust the drive signal. The control module continuously monitors current status and adjusts the duty cycle of electronic switches based on feedback from the detection modules, creating a closed-loop control system that prevents overcurrent while maintaining optimal performance.
2Device complexity
If the drive signal period is fixed, then the control is simple, but it cannot effectively compensate for grid voltage fluctuations and reduce electromagnetic interference
Solution Approach 1:
The patent implements dynamic period adjustment by varying the period of the drive signal within a preset range based on grid voltage conditions. When grid voltage fluctuates, the control module adjusts the drive signal period to compensate, which helps reduce electromagnetic interference. This dynamic period variation adds complexity but significantly improves EMI reduction and voltage compensation capabilities.
Solution Approach 2:
The patent changes the period parameter of the drive signal to achieve different control objectives. By varying the period within a preset range, the system can adapt to different grid voltage conditions and reduce electromagnetic interference. This parameter change approach allows flexible adaptation without fundamentally changing the control structure.
Data Source
AI summary
A power tool includes a housing, an electric motor, a driver circuit, a control module, and a current detection module. The control module is configured to: acquire a phase current value of the electric motor in real time within periodic time intervals; and turn off an on-state electronic switch within remaining time of a present time interval when the acquired phase current value exceeds a preset current threshold, and turn on an electronic switch which is controlled by the control module at present to be on when a present period of the drive signal ends, where the duration of each time interval among the periodic time intervals is the same as a period corresponding to the drive signal at present, and a period of the drive signal varies randomly within a second preset period range.