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无刷直流电机参考设计 AN208

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无刷直流电机参考设计 AN208

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无刷直流电机参考设计_AN208.pdf 2M

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AN208  
SENSORLESS BRUSHLESS DC MOTOR REFERENCE DESIGN  
1. Introduction  
This reference design provides a hardware and Most computer hard disc drives use a sensorless  
software solution for Sensorless Brushless dc motors. brushless dc motor. However, these small motor drives  
This document includes complete schematics, printed use a linear regulator to control the voltage applied to  
circuit board layout, and firmware. The Sensorless the motor. This works well for small motors, but is too  
Brushless dc motor reference design may be used as a inefficient to use for motors greater than a few watts.  
starting point for motor control system designers using Larger motors require PWM control for efficient  
Silicon Laboratories MCUs, significantly reducing the operation. Using PWM control makes the task of  
design time and time to market.  
measuring the back EMF of the motor more difficult, due  
to noise coupled from the active windings.  
Brushless dc motors consist of a permanent magnet  
rotor with a three-phase stator winding. Brushless dc Sensorless Brushless dc motors are well suited for fans  
motors evolved from conventional dc motors where the and rotary pumps from a few watts up to about 1 kW.  
function of the brushes is replaced by electronics. Fans and pumps’ loads are predictable and fairly well  
Brushless dc motors offer longer life and less behaved. Most Sensorless Brushless dc motors do not  
maintenance than conventional brushed dc motors.  
provide the same level of dynamic speed control  
available from Hall effect controlled BLDC motors or dc  
motors. While it is theoretically possible to achieve high-  
performance from a sensorless BLDC motor using  
sophisticated vector control, most practical sensorless  
BLDC implementations address the much simpler fan  
and pump applications. This reference design is  
targeted for simple fan applications.  
Most Brushless dc motor designs historically use Hall  
effect sensors to measure the position of the rotor. Hall  
effect sensors provide absolute position information  
required to commutate the motor. Using Hall effect  
sensors provides simple, robust commutation and  
performance roughly comparable to brushed dc motors.  
One of the major barriers limiting the market penetration  
of Brushless dc motors has been the cost of using Hall Sensorless BLDC motor drives often compete against  
effect sensors. The Hall effect sensors themselves are ac induction motors for certain applications. A system  
not particularly expensive. However, the Hall effect designer must consider the power level, efficiency  
assembly adds significant expense to the cost of requirements, and starting requirements when choosing  
manufacturing the motor. Hall effect sensors also between BLDC motors and ac induction motors. BLDC  
typically require 5 additional wires, adding to the motors are most often used for small motors ranging  
installation costs.  
from 1 watt to 1 kW. AC induction motors are readily  
available from 250 W to 10 kW or more. BLDC motors  
offer potentially higher efficiency than ac induction  
motors. This is due to the fact that ac motors have high  
rotor losses while BLDC motors do not waste energy in  
magnetizing the rotor. AC induction motors are much  
easier to start than sensorless BLDC motors. The  
complexity of starting a fully loaded BLDC motor often  
makes the ac induction motor a better choice,  
particularly for piston pumps and compressors.  
A “Sensorless” Brushless dc motor does not have Hall  
effect sensors. Sensorless Brushless dc motors employ  
more sophisticated electronics using some alternative  
scheme to control the commutation of the motor. The  
most common scheme involves measuring the back  
EMF of the motor and using this information to control  
the commutation of the motor.  
Rev. 0.2 9/06  
Copyright © 2006 by Silicon Laboratories  
AN208  

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