Brushless Power Tool Current Control Using Field-Weakening Angles
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Solution Overview
Problem
Existing power tools face inefficiencies in controlling motor current and torque, particularly in adapting to varying battery states and loads, which affects performance and energy efficiency.
Innovation Solution
Implementing a current-based field weakening control algorithm that adjusts the conduction angle and pulse-width modulation (PWM) duty cycle to optimize torque and current output, using a brushless DC motor with an electronic controller that senses current and voltage to dynamically adjust power delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If traditional motor control methods are used, then the system is simple to implement, but energy efficiency deteriorates due to inability to adapt to varying battery states and loads
Solution Approach 1:
The control system dynamically adjusts the conduction angle based on real-time current sensing and battery state detection. The controller modifies the conduction angle throughout the commutation cycle to optimize torque production at different speeds and loads, enabling the system to adapt to varying operating conditions and maximize energy efficiency
Solution Approach 2:
The invention changes the conduction angle parameter as a function of motor speed, current, and battery state. By varying this electrical parameter dynamically rather than keeping it fixed, the system optimizes the balance between torque production and energy consumption across different operating conditions
2Power
If PWM duty cycle is increased to maximize torque output, then power output is improved, but current consumption increases reducing energy efficiency
Solution Approach 1:
The controller applies partial conduction angle modulation rather than full PWM cycling. By conducting current for only a portion of the commutation cycle (the optimized conduction angle) rather than the entire cycle, the system produces sufficient torque while reducing overall current consumption and improving energy efficiency
Solution Approach 2:
The conduction angle modulation is applied periodically throughout the motor commutation cycles. The controller continuously adjusts the conduction angle in sync with the motor's rotational phases, creating a periodic control pattern that optimizes torque delivery while managing current consumption
3Adaptability or versatility
If the control algorithm continuously adjusts PWM and conduction angle, then adaptability to varying conditions is improved, but processing requirements increase
Solution Approach 1:
The control algorithm focuses adjustments on specific local parameters (conduction angle and PWM duty cycle) rather than redesigning the entire control system. By making targeted local modifications to the control strategy, the system achieves adaptability to varying battery states and loads without requiring complex global system changes
Solution Approach 2:
The system uses current sensing feedback to detect motor load and battery state, then uses this feedback to dynamically adjust the conduction angle. This closed-loop feedback mechanism enables the controller to adapt to varying conditions in real-time while keeping processing requirements manageable through straightforward sensing and response logic
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
This approach enhances energy efficiency by maximizing torque at the lowest possible current, automatically adjusting to changes in the power source and mechanical characteristics, reducing processing requirements, and improving power tool performance across varying conditions.
Implementation Method 1
a brushless direct current (DC) motor within the housing
Implementation Method 2
a current sensor configured to sense a current of the brushless DC motor
Implementation Method 3
supply a pulse-width modulated ('PWM') signal having a duty cycle to the brushless DC motor to control the current of the brushless DC motor
Data Source
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AI summary
A power tool that includes a brushless motor, a power switching circuit, a current sensor, and an electronic controller. The power switching circuit provides a supply of power to the brushless motor. The current sensor is configured to sense a current of the brushless motor. The electronic controller is configured to receive a first signal indicative of current of the brushless motor, generate a current command, set a conduction angle of the brushless motor based on the current command, supply a PWM signal having a duty cycle to the brushless motor to increase current of the brushless motor, determine whether duty cycle equals a first threshold, maintain the duty cycle at the first threshold, modify the conduction angle to increase the current of the brushless DC motor, determine whether current equals a second threshold, and control the second conduction angle to maintain current at the second threshold.