Power Tool Brushless Motor sFOC With Hall and Inline Shunt Feedback
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Solution Overview
Problem
Conventional brushless direct current (DC) motors in power tools rely on multiple sensors and complex control algorithms to align stator and rotor fluxes, which can lead to inefficiencies and limitations in dynamic and steady-state performance.
Innovation Solution
The implementation of sensored field-oriented control (sFOC) in power tools, which uses two inline shunts to accurately measure inverter/motor line currents and employs digital Hall effect sensors to estimate rotor speed and angle, allowing for independent control of motor speed and torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional brushless DC motors use multiple position sensors and complex control algorithms to align stator and rotor fluxes, then the motor can achieve proper magnetic field generation, but the device complexity and control difficulty increase
Solution Approach 1:
The patent extracts and eliminates the need for multiple position sensors by using sensorless control methodology. The control system determines rotor position and speed indirectly through current sensing and mathematical algorithms, removing the physical sensors while maintaining control accuracy.
Solution Approach 2:
The patent replaces the mechanical/sensor-based position detection system with an electronic/software-based solution. The microcontroller uses current measurements and field-oriented control algorithms to calculate rotor position and speed, substituting physical sensors with computational methods.
2Device complexity
If conventional control topologies are used in power tools, then the control system is simpler to implement, but the dynamic and steady-state performance deteriorates
Solution Approach 1:
The patent implements closed-loop feedback control through field-oriented control (FOC). The system continuously monitors motor current, calculates rotor position and speed, and adjusts stator current phases in real-time to maintain optimal magnetic field alignment, significantly improving dynamic response and steady-state performance.
Solution Approach 2:
The patent transforms the control approach by changing from simple commutation to field-oriented control with independent flux and torque current components. This parameter transformation allows separate control of magnetic flux and torque production, enabling superior performance in both dynamic and steady-state conditions.
3Device complexity
If low-side shunts are used to measure DC bus or motor line currents, then the measurement setup is simpler, but the measurement accuracy and PWM noise immunity deteriorate
Solution Approach 1:
The patent introduces an intermediary filtering and signal conditioning stage between the current shunts and the microcontroller. Low-pass filters and differential amplifiers are used to isolate the measurement circuit from PWM switching noise, providing accurate current measurements even in the high-noise power tool environment.
4Speed
If interrupt routines are used on the microcontroller for position sensor processing, then the control response is faster, but the computational overhead and system complexity increase
Solution Approach 1:
The patent implements continuous position and speed estimation algorithms that run in the main control loop without requiring interrupt routines. The field-oriented control mathematics continuously calculate rotor position and speed from current measurements, providing smooth and continuous control action without the discontinuities introduced by interrupts.
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
sFOC enhances the dynamic and steady-state performance of brushless DC motors in power tools by providing robust short-circuit and overcurrent protection, enabling actual overcurrent detection, and achieving sinusoidal stator currents with low harmonic content.
Implementation Method 1
Conventional brushless direct current ('DC') motors include a stator and a rotor configured to rotate with respect to the stator by a magnetic field generated in one or more phases of the stator
Implementation Method 2
The one or more position sensors are configured to generate output signals corresponding to a rotational position of the brushless motor
Data Source
AI summary
A power tool including a housing, a brushless motor, one or more position sensors, a power switching circuit, and an electronic controller. The one or more position sensors are configured to generate output signals corresponding to a rotational position of the brushless motor. The power switching circuit is configured to provide a supply of power from a power source to the brushless motor. The electronic controller is configured to implement field-oriented control (“FOC”) of the brushless motor. The electronic controller configured to receive the output signals from the one or more position sensors, determine a parameter of the brushless motor based on the output signals, determine drive parameters for the brushless motor based on the parameter of the brushless motor using FOC, generate drive commands based on the drive parameters, and drive the brushless motor based on the drive commands.