Power Tool Power Limiting Control for Battery Impedance Variation
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Solution Overview
Problem
Power tools with a common interface format face challenges in maintaining consistent power output due to variations in battery pack impedance, which can result from different cell chemistries and degradation over time.
Innovation Solution
The implementation of an electronic controller in power tools that monitors current and voltage values between the battery pack and the electric motor, computes a power value, and dynamically reduces the input power to the motor when the computed power exceeds a threshold, ensuring optimal operating parameters across different battery packs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a common interface format is used to accept various battery packs, then interoperability and flexibility are improved, but power output consistency deteriorates due to impedance variations
Solution Approach 1:
The patent implements dynamic power limiting control that continuously monitors battery pack impedance and adjusts motor input power in real-time. The controller dynamically modifies PWM duty cycle based on measured impedance values, transforming the static power delivery system into a dynamic one that adapts to different battery packs while maintaining consistent motor output power.
Solution Approach 2:
The system changes the electrical parameters (voltage, current, PWM duty cycle) based on the detected battery pack impedance characteristics. By measuring actual impedance and adjusting operating parameters accordingly, the system compensates for impedance variations across different battery packs, ensuring consistent power delivery to the motor despite using a common interface format.
2Adaptability or versatility
If battery packs with different cell chemistries are used, then versatility is improved, but impedance variation increases affecting power delivery
Solution Approach 1:
The patent employs a feedback control mechanism where the controller continuously monitors the actual current drawn from the battery pack and the voltage across the motor. Based on this feedback, the system calculates actual power delivery and compares it to target values, then adjusts PWM duty cycle to compensate for impedance variations caused by different cell chemistries, ensuring consistent motor performance across diverse battery packs.
Solution Approach 2:
The controller acts as an intermediary between the battery pack and motor, mediating the power transfer by adjusting PWM duty cycle based on detected impedance characteristics. This intermediary function allows the system to accommodate different battery chemistries (Li-ion, NiCd, NiMH) with their varying impedance profiles while maintaining consistent motor operation.
3Duration of action of stationary object
If battery packs are allowed to degrade naturally over time, then practical usability is maintained, but impedance increases reducing power delivery
Solution Approach 1:
The system performs preliminary measurement of battery pack impedance during initial operation or charging cycles. By detecting impedance characteristics early in the battery pack's life or upon connection, the controller pre-adjusts power delivery parameters to account for the battery's current state, ensuring optimal performance throughout its service life and compensating for progressive degradation.
Solution Approach 2:
The power delivery system transitions from a static design to a dynamic one that continuously adapts to the battery pack's aging state. As impedance increases with degradation, the controller dynamically adjusts PWM duty cycle and current limits to maintain consistent motor power output, extending the usable life of degraded battery packs.
Data Source
AI summary
Power tools described herein include an electric motor, an interface configured to receive a battery pack, and an electronic controller. The electronic controller is configured to monitor a current value between the battery pack and the electric motor, monitor a voltage value between the battery pack and the electric motor, compute a power value based on the current value and the voltage value, and reduce an input power of the electric motor in response to the power value exceeding a threshold.