BLDC Motor Speed Control Using Reverse Electromotive Force
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Solution Overview
Problem
Existing BLDC motor drivers face challenges in rapidly decreasing the rotation speed of BLDC motors due to rotor inertia, requiring complex physical speed decreasing devices and incurring additional costs, while also being susceptible to noise and vibrations.
Innovation Solution
A method and apparatus that utilize reverse electromotive force to rapidly decrease the rotation speed of BLDC motors by dividing the rotation phase angle into speed decreasing and zero crossing point detecting regions, calculating speed decreasing times based on current rotation speed, and electrically connecting all terminals to a power supply or ground, allowing for repeated calculations and detections to achieve the required speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If only the duty ratio of the PWM signal is controlled to decrease the rotation speed, then the control method is simple, but a large time is required to decrease the rotation speed to a required speed due to rotor inertia
Solution Approach 1:
Instead of applying forward electromagnetic force to drive the motor, the invention applies reverse electromotive force by connecting motor terminals to power supply terminals during deceleration. This inverts the normal operation mode to create a braking effect that rapidly decreases speed without requiring complex physical braking devices.
Solution Approach 2:
The invention replaces physical mechanical speed decreasing devices (such as mechanical brakes) with an electrical control method using reverse electromotive force. This substitution eliminates mechanical complexity while achieving rapid speed decrease through electrical connection of motor terminals to power supply terminals.
2Speed
If a physical speed decreasing device is used to rapidly decrease the rotation speed, then the speed decreasing performance is improved, but the physical configuration becomes very complicated and additional cost is required
Solution Approach 1:
The existing motor terminals and power supply terminals are made multi-functional. During normal operation, terminals receive power to drive the motor; during deceleration, the same terminals are connected in reverse to apply braking force. This eliminates the need for separate speed decreasing devices while maintaining rapid deceleration capability.
Solution Approach 2:
The invention merges the driving and speed decreasing functions into a single control system. By controlling the connection between motor terminals and power supply terminals, both acceleration (through PWM duty ratio control) and deceleration (through reverse electromotive force) are achieved using the same electrical components, simplifying the overall system configuration.
3Speed
If a physical speed decreasing device is used, then the speed control performance is improved, but noise and vibrations cannot be avoided
Solution Approach 1:
The invention replaces mechanical speed decreasing devices that generate noise and vibrations with an electrical control method. By using reverse electromotive force through terminal connections, speed control is achieved without mechanical contact or physical braking, thereby eliminating noise and vibration issues.
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 enables rapid and efficient reduction of BLDC motor speed without the need for separate physical speed decreasing devices, reducing noise and vibration issues and improving speed control accuracy.
Implementation Method 1
a rotation speed of a BLDC motor is rapidly decreased to a required speed using a reverse electromotive force generated in the case in which a BLDC motor is rotated
Data Source
AI summary
Disclosed herein is an apparatus of a sensorless brush less direct current (BLDC) motor capable of rapidly driving the BLDC motor at a decreased speed. The apparatus includes: a switching unit configured to switch a direct current (DC) power depending on a plurality of pulse width modulation (PWM) signals to generate a three-phase alternating current (AC) power and apply the generated three-phase AC power to the BLDC motor to drive the BDLC motor; a plurality of voltage dividers configured to divide voltages of reverse electromotive forces generated in the BLDC motor; and a controlling unit configured to calculate a current rotation speed of the BLDC motor using output signals of the plurality of voltage dividers, generate the plurality of PWM signals depending on the calculated current rotation speed and a command rotation speed and output the plurality of PWM signals to the switching unit, divide a rotation phase angle of the BLDC motor into a speed decreasing region and a zero crossing point (ZCP) detecting region in the case of decreasing a rotation speed of the BLDC motor, decrease the rotation speed of the BLDC motor in the case in which the rotation phase angle of the BLDC motor is in the speed decreasing region, and detect ZCPs of the reverse electromotive forces in the case in which the rotation phase angle of the BLDC motor is in the ZCP detecting region. The apparatus may very rapidly decrease a speed of the BLDC motor to a required speed.