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    ECE 480 Application Note

    Brushless DC MotorControl Algorithms

    and ApplicationsAbstract

    Brushless DC motors are high efficiency motors which are used

    across a wide variety of applications. These motors require more robustcontrol algorithms then their brushed DC counterpart. BLDC motors are

    synchronous motors that require a 3-phase C signal to drive them. This

    note will give a brief overview of BLDC motor control as well as give

    information and an e!ample of a basic control algorithm.


    BLDC" #-step commutation" rduino" motor controller" bac$ %&'" (all %ffect" )nverter"

    %lectric *ehicle"

    By: Matt Myers


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    Brushless DC &otor Control lgorithms and pplications 201


    Table of Contents




    )nverter Bridge----------------------------------------------+


    rduino )mplementation----------------------------------#Coding with the rduino----------------------------------

    Testing the code--------------------------------------------




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    Brushless DC &otor Control lgorithms and pplications 201




    Brushless DC motors are becoming more common in a variety of motor

    applications such as fans" pumps" appliances" automation" and automotive drive. Thereasons for their increased popularity are better speed versus torque characteristics" high

    efficiency" long operating life" and noiseless operation. )n addition to these advantages"the ratio of torque delivered to the si4e of the motor is higher" ma$ing it useful in

    applications where space and weight are critical factors.

    The stator of a BLDC motor is similar to that of an induction machine but the

    windings are distributed quite differently. The stator windings can be seen on the outsidering of figure . The two different common distributions of the windings are distributed

    and sinusoidal. distributed winding will have a trape4oidal bac$ %&' while a

    sinusoidal winding will have a sinusoidal bac$ %&'. 'or more information on bac$ %&'see this note.This application note will focus on BLDC motors with distributed stator

    windings. The rotor of a brushless DC motor is different in the fact that the rotor containspermanent magnets instead of additional windings. This is represented by the north andsouth poles in figure .

    5nli$e a brushed DC motor" the commutation of a BLDC motor in controlled

    electronically. To rotate the BLDC motor" the stator windings should be energi4ed in asequence. )n order to ma$e sure the motor controller is energi4ing coils in the correct

    sequence6 (all %ffect sensors must be used to detect the position of the rotor in the motor.

    7hen the rotor is spinning inside the motor either a 8orth or 9outh :ole will pass by the

    (all %ffect sensors which will cause the sensor to output which section of the rotor ispassed.

    Figure 1

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    Brushless DC &otor Control lgorithms and pplications 201




    This application note outlines the basic theory behind BLDC motor control

    algorithms and also will give an overview of how to implement basic versions of thesealgorithms on both the C1222 launch pad and an rduino microcontroller.

    Inverter Bridge

    %very C motor controller will have a high voltage bridge that feeds current into

    the separate phases. diagram of this system can be seen in figure 1. This bridge consists

    of si! &;9'%T switches that force current through two of the three phases of the motoras seen in figure three. The top three &;9'%T9 are attached to the positive side of the

    DC voltage while the bottom three &;9'%Ts are attached to the ground side of the DC

    supply. This allows the motor controller to create a negative voltage by changing thedirection the current travels through the inductor. 'igure 3 below" shows one of the si!

    possible positions the switches can be in. )n order to prevent shorts only a single

    &;9'%T on the top and bottom rows can be closed at one time.


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    Brushless DC &otor Control lgorithms and pplications 201



    Figure !


    Commutation is process of switching the state of the &;9'%T9 in the (-bridge

    in order to $eep the motor spinning. s mentioned previously there are si! possible statesthat can be used to drive a BLDC motor" the table below DC- 8C ?(" B?L

    2 2 DC> 8C DC- # ?(" C?L

    2 8C DC> DC- , B?(" C?L2 2 DC- DC> 8C + B?(" ?L

    2 DC- 8C DC> 3 C?(" ?L

    2 2 8C DC- DC> 1 C?(" B?LFigure "

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    Brushless DC &otor Control lgorithms and pplications 201



    Figure #

    The graphs above

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    Brushless DC &otor Control lgorithms and pplications 201


    32,3+,.docthe program visit the rduino site here.The main window of the software should loo$

    similar to the window pictured below in figure .

    Figure $

    Coding "it# t#e Arduino

    To start coding connect your rduino to the computer via the 59B connection.The 59B connection provides communication as well as power to the chip. )f you are

    unfamiliar with the rduino coding environment these tutorials onoutubeare helpful.

    8ow the chip is ready to be programmed. Below a simple e!ample will be e!plained toget your motor spinning.

    The code below shown in figure seen gives the basic variables that need to bedefined. These variables will store the hall effect sensor states and the current speed that

    is desired for the motor. 8e!t the pin modes must be set. %ach pin on the rduino haseither an output or an input mode. )8 figure below the pin setup is shown. The pin

    setup must be contained within your void

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    Brushless DC &otor Control lgorithms and pplications 201



    Figure %

    Figure & Figure '

    8e!t you must setup the :7& pins so that the frequency they operate is 31 $(4. Thiscan be accomplished in a few different ways and is outside the scope of this document.There is a great tutorial for accomplishing this tas$here.8ow that the pin modes"

    variables" and other settings are correct the main loop of the program can be constructed.

    )t is helpful to instantiate the serial communication available on the rduino6 this

    allows you to debug the program as it is running in real time. The code to start the serialcommunication is shown in figure 0. The code above will need to be uncommented in

    order to wor$ properly. 8e!t the program will need to read information from the user and

    the hall effect sensors from the motor.

    Figure 1(

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    Brushless DC &otor Control lgorithms and pplications 201


    32,3+,.doc'igure 2 shows the code necessary to set variables equal to the inputs on the

    microcontroller. The final step of programming is to implement the #-step commutation

    in code. The e!ample code for this step is given in e!ample 1 of the appendi!. This

    section of code is a state machine that switches state depending on the input from the halleffect sensors. These states will change the outputs of the microcontroller so that the

    :7& is applying the correct voltage to each phase in turn.

    $esting t#e Code

    s mentioned previously the serial monitor on the rduino is a great tool fortroubleshooting code that has been developed. There are several other ways that code can

    be tested for this proect. Before hoo$ing the microcontroller to the motor it is possible to

    test its output using a dummy hall effect input. This can be accomplished in software withthe rduino or with another microcontroller that can be interfaced with the rduino. )n

    e!ample one of the appendi!" code is given which will simulate the hall effect output of amotor. This code is written for the &9:+32 microcontroller and is essentially a statemachine with si! states that change based on a predetermined rotation. This code is

    written so that the hall effect sensors cycle at a frequency of + (4. The code can easily

    be modified to vary the frequency based on a voltage input. The code for the analog to

    digital conversion is given at the top of the e!ample code.


    This application note gives a rudimentary overview of BLDC motor control and a way to

    implement a simple BLDC motor controller. There is much more involved with anindustrial grade controller such as :)D control" over current protection" temperature

    sensing and other capabilities. )t is possible to use the rduino to implement some of

    these features but it is recommended to move to a more powerful microcontroller in orderto provide smooth operation and increased safety. ;ne option to loo$ at is T)s :iccolo

    microcontrollers which have far more capabilities then the rduino.


    )xa*ple 1+ Dummy (all %ffect 9ensor designed for &9:+32

    Auns at + (E Can easily be adapted to another microcontroller

    /include Fmsp+32g1,,3.hG

    int 8e!t?9tateH16

    int Current?9tateH6

    long delayH26

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    Brushless DC &otor Control lgorithms and pplications 201


    32,3+,.docint mainB)T1>B)T36

    Knalog to Digital 9et5:K

    DC2CTL H )8C(?+> C;89%M?16 KK%nable Continuous one channel read

    DC2%2HB)T+6 KKTurns on + which is on :.+

    KK9ets on *?ref to 1.,KK%nables Aeference" CD2 and

    KK9ets 9ample and (old time to + cycles

    KK%nable &C9

    DC2CTL2 H A%'1?,* > A%';8 > DC2;8 > DC29(T?2 > B)T>9A%'?6?delay?cycles DC29C6 KK%nables DC


    9et5pKDC;CTL H CLDC;?#&(E6 KK9ets DC; to # &(4

    BC9CTL H CLBC?#&(E6

    KK:)8 :.# ;utputs T2.:9%LHB)T26

    KK&C!H The timer repeatedly counts from 4ero up to the value of TCCA2 and bac$ down to 4ero.

    KK9&CLN is the cloc$ source

    T2CTLHT99%L?1>B)T,>B)T+6 KK5pKdown modeO the timer counts up to TCCA2 then down to 2222h.T2CCA2H2136 KKma! value to DC

    T2CCTLH;5T&;D?16 KK9et mode #

    T2CCAH1+,6 KK9ets the Duty Cycle



    case +O:;5THB)T16



    case ,O:;5THB)T>B)T16

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    Brushless DC &otor Control lgorithms and pplications 201



    case #O





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    Brushless DC &otor Control lgorithms and pplications 201


    32,3+,.doc case +O

    KK:;ATD H B22!!!226 KK Desired ;utput for pins 2-

    :;ATD @H B2226

    :;ATD JH B22222226 KK


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    Brushless DC &otor Control lgorithms and pplications 201




    Bac, )-F sitehttpOKKphysics.bu.eduKRduffyKsc,+,?notes2+Kbac$?emf.html

    B./C *otor control by *icroc0ip


    -ore B./C *otor control



    C0anging 2- Fre3uency on t0e Arduino


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