Brushless Power Tool Field Weakening With Current-Based Control

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Solution Overview

Problem

Existing power tools face inefficiencies in increasing speed and energy output without increasing voltage, and existing field weakening techniques require significant processing power.

Innovation Solution

Implementing a current-based field weakening control that adjusts conduction angle and duty cycle of the brushless DC motor to optimize torque and efficiency, reducing processing requirements compared to field-oriented control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If field-oriented control is used to control the brushless DC motor, then the motor control precision is improved, but the processing power requirement increases significantly

Engineering Contradiction:

Improvemotor control precisionVSAvoidprocessing power requirement

Core Design Contradiction:

Measurement precisionVSPower

Solution Approach 1:

The patent extracts and eliminates the complex field-oriented control algorithm, retaining only the essential current-based control mechanism. This removes the computationally intensive components while preserving the core motor control functionality, thereby reducing processing power requirements while maintaining adequate control precision for power tool applications.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent employs a simpler, less computationally demanding control algorithm that requires minimal processing resources. This approach accepts slightly reduced theoretical precision compared to field-oriented control but achieves sufficient performance for practical power tool applications with dramatically lower processing requirements.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Productivity

If voltage is increased to increase speed and energy output, then the motor performance is improved, but the power consumption and energy loss increase

Engineering Contradiction:

Improvespeed and energy outputVSAvoidpower consumption and energy loss

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent changes the control parameter from voltage-based control to current-based control with field weakening capability. By controlling motor current and adjusting the conduction angle, the system achieves variable speed and energy output adjustment without proportionally increasing voltage, thereby reducing I²R losses and improving overall energy efficiency while maintaining productivity.

Inventive Principle:

Principle #35Parameter changes

3Power

If the duty cycle of PWM signal is increased to increase motor current, then the motor power output is improved, but the voltage drop across the motor increases

Engineering Contradiction:

Improvemotor power outputVSAvoidvoltage drop across motor

Core Design Contradiction:

PowerVSStress or pressure

Solution Approach 1:

The patent implements dynamic field weakening control that adjusts the conduction angle based on operating conditions. This dynamic adjustment optimizes the balance between motor current, voltage drop, and power output in real-time, allowing the system to operate efficiently across varying loads without excessive voltage drops even at high power output levels.

Inventive Principle:

Principle #15Dynamics

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

The current-based field weakening enhances torque production and efficiency by optimizing power tool performance across varying power sources and mechanical characteristics, reducing processing demands while maintaining efficient operation.

Implementation Method 1

a brushless direct current ("DC") motor. The power switching circuit provides a supply of power from a battery pack to the brushless DC motor

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

The current sensor senses a current of the brushless DC motor

Methodology Applied

Scientific EffectElectromagnetic sensing: Electromagnetic Induction

Implementation Method 3

The electronic controller is further configured to supply a pulse-width modulated ("PWM") signal having a duty cycle to the brushless DC motor to increase the current of the brushless DC motor

Methodology Applied

Scientific EffectPulse-width modulation:

Data Source

PatentUS20260019023A1Power tool including current-based field weakening

Publication Date: 2026.01.15 MILWAUKEE ELECTRIC TOOL CORP

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.