BLDC Motor Commutation Control for Heat Distribution
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Solution Overview
Problem
Conventional power tools using direct current motors with brushes face wear issues and limitations, while brushless motors are underutilized due to design considerations related to motor control, despite offering advantages like improved motor life and electronic commutation.
Innovation Solution
Implementing a brushless direct current (BLDC) motor with a controller that selectively uses pulse-width modulation (PWM) commutation and centerline commutation schemes, transitioning between them based on motor speed and conditions, and distributing heat generation among switching array components to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If brushes are used for motor commutation in power tools, then the motor can achieve reliable commutation and operation, but the brushes will wear down over time and adversely affect operation
Solution Approach 1:
The patent replaces the mechanical brush-commutator system with an electronic commutation system using power transistors and control circuits. This substitution eliminates the mechanical contact and wear associated with brushes while maintaining reliable motor commutation through electronic switching of current phases based on rotor position feedback.
2Duration of action of stationary object
If brushless motors are implemented in power tools, then motor life is improved and electronic commutation is achieved, but design considerations and control complexity increase
Solution Approach 1:
The control system uses feedback from rotor position sensors to automatically determine when to switch current phases, enabling the motor to self-regulate its commutation timing without complex external control logic. The system monitors its own operational state and adjusts switching accordingly.
Solution Approach 2:
The patent incorporates rotor position sensing that provides feedback to the control circuit, which then adjusts the timing of current switching in the stator windings. This feedback mechanism simplifies the control logic by using actual motor state information to drive commutation decisions rather than relying on complex pre-programmed sequences.
3Speed
If PWM commutation is used to drive the motor, then precise speed control is achieved, but heat generation increases in the switching array
Solution Approach 1:
The patent implements periodic switching of the power transistors in a pulse-width modulation pattern, where the duty cycle is varied to control average power delivery. This periodic action enables precise speed control while the switching is distributed over time, allowing heat to be managed through the natural thermal cycles of the switching components.
Solution Approach 2:
The control system dynamically adjusts the PWM duty cycle parameter to regulate motor speed. By changing this single parameter, precise speed control is achieved without requiring complex mechanical adjustments or additional heating elements, and the switching frequency remains constant to manage thermal characteristics.
Data Source
AI summary
Brushless direct-current (“BLDC”) motor and control for a power tool. A BLDC motor of a power tool is controlled in either a pulse-width modulation (“PWM”) commutation mode or a centerline commutation mode. When the motor is rotating slowly, the motor is operated using PWM commutation. When the motor is rotating at a speed greater than a threshold speed value, the operation of the motor is transitioned to the centerline commutation mode. When operating in the centerline commutation mode, the high-side field-effect transistors (“FETs”) and low-side FETs can each be used for motor speed control. By switching between speed control using the high-side FETs and speed control using the low-side FETs, the heat generated by freewheeling currents can be approximately evenly distributed among the high-side and low-side FETs.