Power Tool Brushless Motor sFOC With Inline Shunt Current Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional brushless direct current (DC) motors in power tools rely on multiple sensors and complex control algorithms to generate magnetic fields, 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 high-side DC bus current sensors for robust protection, 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 generate magnetic fields, then the motor can achieve basic control functionality, but the device complexity increases and dynamic performance deteriorates
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 indirectly through current sensing and back-EMF detection, removing the physical sensors while maintaining control functionality through algorithmic compensation.
Solution Approach 2:
The patent replaces the mechanical sensor-based position detection system with an electronic control system that uses current measurements and mathematical algorithms to determine rotor position and speed, substituting physical sensing with computational methods.
2Productivity
If conventional control algorithms are used in brushless DC motors, then the motor can operate, but the dynamic and steady-state performance deteriorates
Solution Approach 1:
The patent implements a dynamic control algorithm that continuously adapts to changing motor operating conditions. The controller adjusts control parameters in real-time based on measured current and position information, enabling optimal performance across varying speed and load conditions rather than relying on fixed control parameters.
Solution Approach 2:
The patent employs closed-loop feedback control where the controller continuously monitors phase currents and rotor position, compares actual performance with desired performance, and adjusts control signals accordingly to maintain optimal dynamic and steady-state performance.
3Measurement precision
If low-side shunts are used to measure DC bus or motor line currents, then current measurement is possible, but measurement precision deteriorates due to PWM noise and limited sampling options
Solution Approach 1:
The patent introduces an intermediary measurement approach by using high-side DC bus current sensors that measure current at a point isolated from the PWM switching noise. This intermediary measurement point provides a clean signal that can be used to infer motor phase currents without direct exposure to switching disturbances.
Solution Approach 2:
The patent performs preliminary current measurement at the DC bus level before the current enters the PWM switching stage, capturing current information in a clean electrical environment. This preliminary measurement allows for accurate current sensing without the interference that would occur during PWM switching.
4Ease of operation
If classic block commutation control topologies are used in power tools, then the motor can be controlled, but the dynamic and steady-state performance and controllability deteriorates
Solution Approach 1:
The patent replaces static block commutation with dynamic field-oriented control that continuously adjusts control parameters based on real-time rotor position and speed. This dynamic approach optimizes torque production and efficiency across the entire operating range rather than using fixed commutation patterns.
Solution Approach 2:
The patent implements continuous adjustment of control parameters including current magnitude, frequency, and phase angle based on operating conditions. This parameter optimization enables superior dynamic response and steady-state efficiency compared to fixed block commutation schemes.
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 sinusoidal stator currents with low harmonic content, improved controllability, and robust protection against overcurrent and short-circuit conditions.
Implementation Method 1
one or more position sensors configured to generate output signals corresponding to a rotational position of the brushless motor
Implementation Method 2
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
Data Source
Figure 1
Figure 2
Figure 3
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.