Brushless Motor Current Detection Using Dual Filters
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Higher-power and higher-efficiency brushless motors in electric power tools require distinct current protection for batteries and switching devices, as existing protection methods cannot differentiate between average and instantaneous currents, leading to potential overcurrent risks.
Innovation Solution
A motor current detection apparatus using a current detection unit and two filters with different passbands to extract average and instantaneous current signals, allowing for appropriate protection of the battery and switching devices based on these signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single current detection method is used for both battery and FET protection, then the device complexity is reduced, but the measurement precision for distinguishing average and instantaneous currents deteriorates
Solution Approach 1:
The patent segments the current detection function by using two separate detection circuits: one for detecting average current (for battery protection) and another for detecting instantaneous current (for FET protection). This segmentation allows each circuit to be optimized for its specific detection purpose, thereby achieving precise current type differentiation while maintaining reasonable device complexity through functional specialization.
2Power
If higher-power and higher-efficiency brushless motors are used, then the power and efficiency are improved, but the overcurrent risk to battery and FET increases
Solution Approach 1:
The patent implements feedback mechanisms by continuously monitoring both average and instantaneous currents and comparing them against predetermined thresholds. When the instantaneous current exceeds the FET rated current or when the average current exceeds the battery rated current, the system provides feedback to restrict current conduction, thereby protecting the motor system from overcurrent damage while maintaining high power output.
3Measurement precision
If complex circuit configuration is employed for current detection, then the measurement precision is improved, but the power consumption and device complexity increase
Solution Approach 1:
The patent applies local quality by designing detection circuits with different levels of complexity suited to their specific functions. The instantaneous current detection circuit uses a simpler configuration optimized for high-speed response to protect FETs, while the average current detection circuit employs integration mechanisms optimized for accurate averaging. This localized optimization achieves precise current detection for both purposes while minimizing overall power consumption and device complexity.
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
Enables effective detection and protection of both average and instantaneous currents, preventing overcurrent conditions in batteries and switching devices, while maintaining a simple and power-efficient configuration.
Implementation Method 1
a first filter which extracts a first current signal which is included in the conduction current signal outputted from the current detection unit and is a signal component in a frequency band equal to or lower than a predetermined first cutoff frequency
Implementation Method 2
a second filter which extracts a second current signal which is included in the conduction current signal outputted from the current detection unit and is a signal component in a predetermined frequency band within a frequency band equal to or lower than a predetermined second cutoff frequency higher than the first cutoff frequency
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A motor current detection apparatus in the present invention includes: a current detection unit (R0), a first filter (42, 73, 92), and a second filter (43, 74). The detection unit (R0) detects a conduction current flowing from a battery (19) to a brushless motor (30) and outputs a conduction current signal corresponding to the detected conduction current. The first filter (42, 73, 92) extracts a first current signal which is included in the conduction current signal outputted from the detection unit (R0) and is a signal component in a frequency band equal to or lower than a predetermined first cutoff frequency. The second filter (43, 74) extracts a second current signal which is included in the conduction current signal outputted from the detection unit (R0) and is a signal component in a predetermined frequency band within a frequency band equal to or lower than a predetermined second cutoff frequency higher than the first cutoff frequency and having the second cutoff frequency as a maximum value.