BLDC Motor Control Scheme for Power Tool Output
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Solution Overview
Problem
Existing power tools with brushless direct current (BLDC) motors lack the ability to incrementally increase power output beyond a maximum setting, and their control systems do not efficiently manage power delivery in response to varying battery voltage and user input, leading to suboptimal performance and efficiency.
Innovation Solution
A power tool system featuring a BLDC motor with a controller that generates pulse-width modulated (PWM) signals to control motor switches, allowing for incremental power adjustments by varying the conduction band and advance angle based on user input and battery voltage, enabling power output to be increased beyond initial maximum settings and optimizing performance across different battery conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the trigger is fully activated to achieve maximum power output, then the power output reaches its maximum value, but the power output cannot be increased beyond this maximum value
Solution Approach 1:
The patent applies dynamics by making the conduction band and advance angle adjustable rather than fixed. The controller dynamically modifies these parameters based on the trigger position, allowing the motor to operate efficiently across a wider power range. Specifically, the conduction band is varied from a first value at low power to a second value at high power, and the advance angle is adjusted accordingly, enabling continuous optimization of power delivery beyond traditional maximum limits
Solution Approach 2:
The patent employs parameter changes by modifying the conduction band width and advance angle of the motor phases. These parameters are changed in response to trigger position: at low trigger positions, a narrower conduction band and smaller advance angle are used, while at high trigger positions, a wider conduction band and larger advance angle are applied. This parameter variation enables extended power output beyond the traditional maximum setting
2Productivity
If conventional control systems are used to manage power delivery, then the system structure remains simple, but the performance and efficiency are suboptimal
Solution Approach 1:
The control system is segmented into distinct functional components: a controller that processes trigger position signals, a conduction band control module that adjusts switching durations, and an advance angle control module that adjusts phase timing. This segmentation allows each component to be optimized independently while working together to achieve superior performance. The controller generates specific control signals for each motor phase based on segmented processing of input signals
Solution Approach 2:
The control system implements dynamics through real-time adjustment of conduction band width and advance angle based on trigger position. The controller continuously monitors the trigger signal and dynamically modifies the motor phase switching characteristics. This dynamic control enables the system to adapt to varying load conditions and maximize efficiency across the entire operating range, transforming a static control system into an adaptive one
3Use of energy by moving object
If the conduction band and advance angle are kept at predetermined values, then the control system is simple to implement, but the motor efficiency is not optimized across varying battery voltages
Solution Approach 1:
The patent applies parameter changes by adjusting the conduction band width and advance angle as functions of battery voltage and trigger position. When battery voltage decreases, the controller increases the conduction band width to maintain current flow and torque production. The advance angle is simultaneously adjusted to optimize the timing of current application relative to rotor position. These parameter modifications compensate for voltage drop and maintain motor efficiency throughout battery discharge
Solution Approach 2:
The control system implements feedback by continuously monitoring battery voltage and using this information to adjust conduction band and advance angle parameters. The controller receives voltage information (either directly or through load characteristics) and modifies the motor control parameters in response. This closed-loop approach ensures the motor operates efficiently despite varying battery conditions, automatically adapting to maintain optimal performance
Data Source
Figure 1
Figure 2A
Figure 2B~3
AI summary
A power tool includes a multi-phase BLDC motor, a plurality of switches, an input unit, and a controller. For each phase, the controller operates to vary power output to the motor between a first power and a second power by varying a duty cycle of a PWM signal from 0 % to 100 % while keeping a conduction band (CB) of corresponding motor switches and/or an advance angle (AA) at a predetermined value when the input unit moves between a first position and a predetermined position between the first and a second position. For each phase, the controller operates to increase the power output by the motor to greater than the second power by increasing the CB/AA to greater than the predetermined value while keeping the duty cycle of the PWM signal at 100 % when the input unit moves between the predetermined position and the second position.