Sensorless BLDC Motor Restart Using Back-EMF Rotor Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing sensorless control schemes for brushless direct-current (BLDC) motors in power tools face challenges in providing high efficiency and accurate rotor angle resolution, particularly at varying speed ranges, leading to torque ripple and limited power input.
Innovation Solution
Implementing a controller that applies vector-space pulse-width modulation (VSPWM) for field-orientated control, combined with high-frequency injection (HFI) and sliding-mode observer (SMO) techniques to detect the angular position of the rotor, enabling precise commutation and efficient power delivery across different speed ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If trapezoidal control scheme is used for BLDC motor, then high speed efficiency is improved, but torque ripple occurs at low speeds and total power input is limited
Solution Approach 1:
The patent transitions from trapezoidal control to sinusoidal control, changing the current waveform parameter from rectangular to sinusoidal. This parameter change eliminates torque ripple at low speeds while maintaining efficiency across the full speed range, directly resolving the contradiction between high-speed efficiency and low-speed torque ripple.
2Measurement precision
If conventional sensorless control with back-EMF monitoring is used, then rotor position detection is achieved, but rotor angle resolution is limited to 60-degree intervals
Solution Approach 1:
The patent replaces the conventional back-EMF monitoring method with magnetic field sensing using Hall sensors or magnetoresistive sensors. This substitution provides continuous rotor angle measurement with high resolution, eliminating the 60-degree interval limitation while maintaining sensorless operation and avoiding complex control schemes.
3Device complexity
If BLDC motor is provided without position sensors to reduce complexity, then device complexity is reduced, but accurate rotor position detection becomes difficult
Solution Approach 1:
The patent introduces magnetic field sensors (Hall sensors or magnetoresistive sensors) as intermediaries that detect the rotor's magnetic field position without requiring direct mechanical coupling or complex sensor assemblies. These sensors provide accurate rotor position feedback while keeping the overall system simple and sensorless in operation.
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 solution provides high-resolution rotor angle detection and efficient motor commutation, ensuring maximum power input and reduced torque ripple across varying speeds, enhancing the performance of BLDC motors in power tools.
Implementation Method 1
monitoring the motor induced voltage generated by the back-electromotive force (back-EMF) of the motor in the motor windings to detect a rotational position of the motor
Data Source
AI summary
An apparatus comprises a housing; a brushless motor including a rotor; a power switch circuit; a switch disposed on the housing; and a controller. The controller executes the steps of: receiving a power-ON signal from the switch; estimating an angular position of the rotor based on at least one electrical signal associated with a back electromotive force of the brushless motor; operating a switching of the power switch circuit to control a commutation of the brushless motor based on the angular position of the rotor upon receiving the power-ON signal from the switch if a rotational speed of the brushless motor associated with the angular position of the rotor is greater than a predetermined speed threshold; and braking the motor if the rotational speed of the brushless motor less than or equal to the predetermined speed threshold.