real-time bldc motor control using the stellaris lm3s8962

7/28/2019 Real-time Bldc Motor Control Using the Stellaris Lm3s8962

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REAL-TIME BLDC MOTOR CONTROL USING THE STELLARIS LM3S8962

MICROCONTROLLER

Radu Duma1), Petru Dobra2), Dorin Petreus3), Ioan Valentin Sita4) and Radu Adrian Munteanu5)

1, 2, 4)

Automatic Control Department,

3)

Applied Electronics Department,

5)

Electrical Measurement DepartmentTechnical University of ClujNapocastr. Memorandumului nr. 28, 400114, Cluj-Napoca, Romania

phone: + 4 0264 401 433, fax: +4 0264 592 055, email:1)

[email protected],2)

[email protected],3)[email protected], 4)[email protected], 5)[email protected]

web: www.utcluj.ro

ABSTRACT

The paper presents a brushless direct current (BLDC)motor closed loop control application using the Texas

Instruments (TI) Stellaris LM3S8962 microcontroller. Themotor speed can be controlled and monitored in real-time

using the CAN module of the LM3S8962 microcontrollerand a graphical user interface (GUI) implemented inMatlab. The data transfer between the microcontroller andthe PC is done using a USB to CAN converter. Theapplication presented in this paper also allows the remotecontrol of the BLDC motor using the Ethernet controller of

the LM3S8962 microcontroller. For speed control a PIDcontroller with anti-windup is implemented on the StellarisLM3S8962 microcontroller.

1. INTRODUCTION

Brushless direct current (BLDC) motor are extensively used

in many industry fields due to their characteristics: betterspeed versus torque characteristics, high dynamic response,high efficiency, long operating life, noiseless operation,higher speed ranges.

For BLDC motor control there are analog solutions,integrated solution and digital control solutions. Mostintegrated circuits producers offer analog ICs for BLDCmotor control [1, 2]. There are also integrated controlsolutions [3, 4] which allow the customization of thecontrol algorithm from a PC, using a graphical user

interface. The highest flexibility can be achieved byimplementing the control algorithm on a microcontroller or

a Digital Signal Processor (DSP). Texas Instruments (TI)offers several digital control solutions for BLDC motorcontrol [5].

In this paper a closed loop control application for a BLDCmotor is implemented on a Stellaris LM3S8962microcontroller [6]. Most BLDC motor control evaluationkits implement a graphical user interface (GUI) whichallows the control of the BLDC motor, using the serialinterface for communication between the PC andmicrocontroller. The Stellaris BLDC motor control

reference design kit [7] implements a GUI whichcommunicates with the control board using Ethernet. In this

paper, for real-time data exchange the CAN bus of the

microcontroller and an USB to CAN converter are used. A

GUI, implemented in Matlab, allows data visualization andthe control of the speed of the motor. Using the Ethernetcontroller of the LM3S8962 microcontroller, also the

remote control of the BLDC motor is implemented. A PIDcontroller with anti-windup is used for closed loop BLDC

motor control.

2. HARDWARE ARCHITECTURE

In this paper the Stellaris LM3S8962 microcontroller,

member of the Stellaris LM3S8000 series, is used for theimplementation of a BLDC motor control algorithm. TheStellaris family of microcontrollers - the first ARM Cortex-M3 based controllers - brings high-performance 32-bitcomputing to cost-sensitive embedded microcontrollerapplications. The Stellaris LM3S8000 series combinesBosch Controller Area Network (CAN) technology with

both a 10/100 Ethernet Media Access Control (MAC) and

Physical (PHY) layer.The LM3S8962 microcontroller is targeted for industrial

applications, including remote monitoring, electronic point-of-sale machines, test and measurement equipment,

network appliances and switches, factory automation,HVAC and building control, gaming equipment, motioncontrol, medical instrumentation and fire and security. Inaddition, the LM3S8962 microcontroller offers theadvantages of ARM's widely available development tools,System-on-Chip infrastructure IP applications, and a large

user community.

Using the Stellaris microcontrollers a reduced time to

market can be obtained due to the following reasons:StellarisWare on ROM includes driver and peripherallibraries to ease development, C friendly IDE and compilers

from industry leaders, low cost development tools,application specific and advanced development kits,production-ready application modules. The Stellarismicrocontrollers are supported in several IDEs: KeilMicrocontroller Development Toolkit for ARM, IAREmbedded Workbench, Code Composer Studio, Code RedTechnologies' RedSuite, Code Sourcery SourceryG++. For

the application presented in this paper Code ComposerStudio is used.

The hardware test setup is presented in Fig. 1. A Stellaris

Proceedings of the 4th European DSP in Education and Research Conference

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Figure 1 Test setup.

LM3S8962 Ethernet+CAN evaluation kit, equipped with a

LM3S8962 microcontroller is used. The motor which iscontrolled is a Hurst-Emerson BLDC motor [8]. On theshaft of the motor an encoder is mounted.

The integrated power module IRAMS10UP60A, optimizedfor electronic motor control, is used as motor drive for theBLDC motor.

In order to communicate between the embedded processorand the PC, an USB to CAN converter produced by Systec-Electronic [9] is used

Unlike a brushed DC motor, the commutation of a BLDCmotor is controlled electronically. To rotate the BLDC

motor, the stator windings should be energized in a certainsequence. For each motor the producer defines thecommutation sequence.

There are various modulation techniques for controllinginverter drives: upper modulation, lower modulation,

rotating modulation, or balanced modulation. In this paperthe upper modulation is used. Using upper modulationtechnique, only the upper transistors of the three phasebridge are controlled using Pulse Width Modulation(PWM) signals while for the lower transistorsenable/disable signals are used.

In Fig. 2 is presented an example of the upper modulation

waveforms and the signature of the Hall sensors. In thisfigure, HW, HV, HU represent the signals from the Hallsensors, corresponding to the three phases of the motorU,

V, W respectively; UP, VP and WP represent the uppertransistors of the three phase bridge corresponding to the

three phases of the motor U, V, Wrespectively; while UN,VN and WNrepresent the lower transistors of the three phasebridge corresponding to the three phases of the motorU, V,Wrespectively. According to Fig. 2, when the signature ofthe HALL sensors is 3 (3 corresponds to binary value 11,that isHW= 0,HV= 1 andHU= 1) the VPand WN transistors

of the three phase inverter bridge have to be controlled.

Figure 2 - Upper modulation technique.

3. SOFTWARE ARCHITECTURE

The block diagram of a closed loop control system for

BLDC motor control with a LM3S8962 microcontroller ispresented in Fig. 3.

The controller must generate three PWM signals forcontrolling the upper arm transistors of the three phase

bridge, while three General Purpose Input Output (GPIO)pins are used to generate the enable/disable signals for thelower arm transistors of the three phase bridge.

The signals from the HALL sensors are applied on three

GPIOs which are configured to generate an interrupt on

both edges of the incoming signal. The speed of the motor

can be determined using the signals from the Hall sensors,

but for applications which require a high accuracy of the

measured speed an encoder must be used. The referencespeed of the motor can be set over CAN or Ethernet. Based

on the reference and measured speed, the PID controller

computes the duty cycle for the PWM control signals.

TI provides for the Stellaris LM3S8962 microcontroller alibrary for the drivers and the peripherals of the

microcontroller and well documented code examples,which ease the development process. In the followingsubsections some details of the software implementation arepresented.

Figure 3 - Closed loop control diagram with the LM3S8962microcontroller.

BLDC Motor LM3S8000 Evaluation Kit USB-CAN Converter Driver

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3.1 Control SignalsIn order to control the three-phase bridge using the uppermodulation technique, the microcontroller must generatethree PWM signals. The Stellaris PWM module provides agreat deal of flexibility. It can generate simple PWMsignals, such as those required by a simple charge pump. It

can also generate paired PWM signals with dead-banddelays, such as those required by a half-H bridge driver.

Three generator blocks can also generate the full sixchannels of gate controls required by a 3-phase inverterbridge. Using the functions from the driver library theLM3S8962 microcontroller is configured to generate threePWM signal.

The upper modulation technique also requires threeenable/disable signals which are generated using three

GPIO pins. Based on the commutation sequence of theBLDC motor, a certain PWM signal and a GPIO pin must

be used to control the three-phase bridge. The outputcontrol block of the PWM module allows the enable/disableof each PWM signal. This feature is used for the control ofthe three phase bridge.

3.2 Feedback SignalsThe BLDC motor must be commutated electronically, thusit is important to know the position of the rotor. BLDCmotors have HALL sensors embedded in the stator. The

signals from the HALL sensors have to be applied toexternal hardware interrupts pins, such that themicrocontroller can commutate the motor. Three GPIO pinsof the LM3S8962 microcontroller are configured as inputs.Also the GPIOs are configured to generate interrupts onboth rising and falling edges of the signals generated by theHall sensors.

For closed loop control the speed of the motor is measuredusing an encoder. The LM3S8962 microcontroller includestwo quadrature encoder interface (QEI) modules. Each QEI

module interprets the code produced by a quadratureencoder wheel to integrate position over time and determine

direction of rotation. In addition, it can capture a runningestimate of the velocity of the encoder wheel. For thepresented application, the QEI block is configured forcapturing the velocity by counting the number of edgesduring a fixed time period.

3.3 InterruptsAn embedded control system uses the interrupts of themicrocontroller for assuring real-time constraints. For

controlling a BLDC motor there are required anasynchronous interrupt for motor commutation and asynchronous interrupt for PID controller computation. TheNested Vectored Interrupt Controller (NVIC) of theLM3S8962 microcotroller prioritizes and handles allexceptions.

In the asynchronous interrupts generated by the Hallsensors the value of the three Hall sensors is read and the

corresponding transistors are energized based on the

commutation sequence. A timer of the microcontroller isused for the generation of a periodic interrupt. In thisinterrupt, based on the value from the encoder the speed of

the motor is computed. Using the reference speed and themeasured speed, the PID controller computes a new value

for the duty cycle of the PWM control signals. The new

value for the PWM duty cycle is applied on theasynchronous interrupts.

4. CLOSED LOOP CONTROL

In this section the structure of the implemented PIDcontroller is described and the closed loop results arepresented.

4.1 Controller implementationThe standard equation of a PID controller is presented

below:

t

d

i

pdt

tdTd

TtKtu

0

)()(

1)()(

where )()()( tytyt sp is the error signal, spy is the

set point and y is the output of the process.

Several modifications have been done to the standard PIDcontroller structure. A pure derivative gives a very largeamplification of measurement noise. The gain of the

derivative must thus be limited, by low-pass filtering thederivative term, resulting in a limited gain N at high

frequencies. A fraction of the command signal acts on theproportional part, while the derivative component acts onlyon the output of the process.

The structure of the PID controller with integrator anti-windup is shown in Fig. 4. Taking into consideration theabove remarks, the PID algorithm can be described by thefollowing equations [10]:

Figure 4 - The structure of the PID controller.

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real-time bldc motor control using the stellaris lm3s8962

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