Power Tool Sensorless Motor Control Using Load-Point Switching

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Solution Overview

Problem

The use of rotor position sensors in BLDC motors for power tools increases cost, size, and inefficiencies, necessitating the development of sensorless motor control methods for efficient operation without external sensors.

Innovation Solution

Implementing a motor controller that determines load points and corresponding control techniques based on user inputs and operating parameters, using high-frequency injection signals to detect rotor position while maintaining lower switch frequencies on the inverter bridge, allowing for sensorless operation of the motor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If rotor position sensors (Hall sensors or encoders) are used to detect rotor position in BLDC motors, then motor control precision is improved, but device complexity and cost increase

Engineering Contradiction:

Improverotor position detection precisionVSAvoiddevice complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The motor controller uses the motor's own back-EMF signals and current measurements to determine rotor position, eliminating the need for external sensors. The system serves itself by utilizing existing operational parameters (phase currents, voltage signals) to achieve position detection without adding separate sensing components.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent replaces mechanical/electrical sensor systems with an electronic control-based detection method. Instead of using physical Hall sensors or encoders to detect rotor position, the system uses electronic analysis of motor operating parameters (current, voltage, frequency) to infer rotor position through computational algorithms in the motor controller.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Manufacturing precision

If rotor position sensors are included in BLDC motors, then motor control accuracy is improved, but manufacturing cost increases

Engineering Contradiction:

Improvemotor control accuracyVSAvoidmanufacturing cost

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent employs software-based control algorithms and standard microcontroller components rather than expensive specialized sensor hardware. By using readily available electronic components and computational methods, the system achieves sensor-level functionality at a fraction of the cost of actual rotor position sensors.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Measurement precision

If high-frequency injection signals are used to detect rotor position, then rotor position detection capability is improved, but energy consumption increases

Engineering Contradiction:

Improve rotor position detection capabilityVSAvoidenergy consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The motor controller performs high-frequency signal injection only during specific operational phases (such as startup or low-speed operation) when sensorless detection is most beneficial, rather than continuously. This periodic injection approach maintains position detection capability while minimizing energy consumption by activating the high-frequency signals only when necessary.

Inventive Principle:

Principle #19Periodic action

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 reduces costs and complexities by eliminating the need for sensors, enhancing motor efficiency and reliability by automatically controlling the motor based on detected rotor position and load conditions.

Implementation Method 1

coupling, using a coupling circuit, a high-frequency injection signal to the motor and detecting, using the motor controller, a motor response to the high-frequency injection signal

Methodology Applied

Scientific EffectHigh-frequency injection:

Implementation Method 2

A controller of the power tool controls the power switching elements, for example, using pulse-width modulated (PWM) drive signals to operate the motor. The duty cycle of the PWM signals can be varied to vary the speed of rotation of the motor.

Methodology Applied

Scientific EffectPulse-width modulation:

Data Source

PatentUS11833655B2Sensorless motor control for a power tool

Publication Date: 2023.12.05 MILWAUKEE ELECTRIC TOOL CORP

AI summary

Methods and power tools for sensorless motor control. One embodiment provides a method for automatic control switching for driving a sensorless motor (150) of a power tool (100). The method includes determining, using a motor controller (224), a first load point based on user inputs (232) and determining, using the motor controller (224), a first motor control technique corresponding to the first load point. The method also includes driving the motor (150) based on the first motor control technique. The method further includes determining, using the motor controller (224), a change from the first load point to a second load point and determining, using the motor controller (224), a second motor control technique corresponding to the second load point. The method includes driving the motor (150) based on the second motor control technique.