Brushless DC Motor Speed Control via Dynamic Hall Sensor Sampling
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Solution Overview
Problem
Existing motor control devices for brushless DC motors face inaccuracies in rotation speed calculation at high speeds due to reduced magnetic field detection cycles, leading to irregular motor rotation and hunting issues, especially when transitioning from low-speed to high-speed regions.
Innovation Solution
A motor control device that detects magnetic fields using a magnetic field detection section and calculates rotation speed based on the time between edges in a signal, adjusting the electrical angle incrementally as the rotation speed increases, allowing accurate speed calculation from low-speed to high-speed regions by counting time between edges at progressively larger electrical angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic field detection is performed per 60° electrical angle during low-speed rotation, then rotation speed calculation accuracy is improved, but at high-speed rotation the detection cycles are reduced in time causing inaccuracies
Solution Approach 1:
The patent dynamically adjusts the electrical angle interval for magnetic field detection based on the current rotation speed. During low-speed rotation, detection is performed per 60° electrical angle to ensure accurate speed calculation. During high-speed rotation, the detection interval is increased to per 360° electrical angle to maintain adequate detection cycles and prevent inaccuracies. This dynamic adaptation resolves the contradiction between measurement precision and speed.
2Productivity
If PI control is performed using inaccurately calculated rotation speed, then control response is maintained, but hunting occurs and motor rotation becomes irregular
Solution Approach 1:
The patent implements a feedback mechanism that continuously monitors rotation speed and adjusts the magnetic field detection interval accordingly. The control section receives feedback about the current rotation speed and automatically switches between 60° and 360° detection intervals. This feedback loop ensures that accurate rotation speed data is always provided to the PI controller, preventing hunting and maintaining stable motor rotation while preserving control response.
3Reliability
If magnetic field detection errors occur due to hall sensor assembly errors, then detection reliability deteriorates, but the influence on rotation speed calculation becomes larger as rotor rotation speed increases
Solution Approach 1:
The patent changes the detection parameter (electrical angle interval) based on rotation speed conditions. By switching from 60° interval at low speeds to 360° interval at high speeds, the system adapts to the changing impact of sensor assembly errors. At high speeds where detection cycles are naturally reduced, the larger 360° interval compensates for potential errors by providing more robust sampling, thereby maintaining both reliability and measurement precision across the full speed range.
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
Enables accurate rotation speed calculation across a wide range of speeds, preventing hunting and ensuring smooth motor rotation control from low-speed to high-speed regions by adapting the sampling frequency based on increasing rotation speed.
Implementation Method 1
a magnetic field detection section that detects a magnetic field of a permanent magnet rotating together with an output shaft of a motor
Data Source
AI summary
A motor control device is provided that enables smooth rotation control from a low-speed region to a high-speed region. A microcomputer of the motor control device calculates the rotation speed of a rotor from the time between edges that appear per 60° electrical angle at the time of starting the motor, from a signal that is output when a the hall sensor detects the magnetic field of a rotating rotor and, in conjunction with an increase in the rotation speed of the rotor, calculates the rotation speed of a rotor from the time between edges that appear at electrical angles that are larger than the electrical angle 60° in the signal, per 180° electrical angle, per 360° electrical angle, per 900° electrical angle, and per 1800° electrical angle.