Application Note: Sensorless Brushless DC Motor Control ...

AN035303-1015MultiMotor

SeriesMultiMotor

Series

Abstract

This MultiMotor Series application note investigates the closed-loop control of a 3-phase brushless direct current (BLDC) motor using a Z16FMC MCU. Zilog’s Z16FMC family of microcontrollers is designed specifically for motor control applications and, with this MultiMotor Series, features an on-chip integrated array of application-specific analog and digital modules using the MultiMotor Development Kit. The result is fast and precise fault control, high system efficiency, on-the-fly speed/torque and direction control, as well as ease of firmware development for customized applications.

This document further discusses ways in which to implement a sensorless feedback con-trol system using a Phase-Locked Loop with back-EMF sensing. Test results are based on using a MultiMotor Development kit equipped with a Z16FMC MCU module and a 3-phase, 24VDC, 30W, 3200RPM BLDC motor.

The source code file associated with this application note, AN0353-SC01, was tested with version 5.0.1 of ZDS II for ZNEO MCUs. Subsequent releases of ZDS II may require you to modify the code supplied with this application.

FeaturesThe power-saving features of this MultiMotor Series application include:

• Smooth S-curve motor start-up with reduced starting current

• Sensorless (back-EMF) control using Phase-Locked Loop feedback

• Microcontroller-based overcurrent protection

• Selectable speed or torque setting

• Selectable speed or torque control

• Selectable control of motor direction

• UART Interface for PC control

• LED to indicate motor operation

• LED to indicate UART control

• LED to indicate a fault condition

Discussion

Z16FMC Series Flash microcontrollers are based on Zilog’s advanced 16-bit ZNEO CPU core. These Z16FMC devices set a standard of performance and efficiency with up to 20

Note:

AN035303-1015

Application Note

Sensorless Brushless DC Motor Control with the Z16FMC MCU

of 20

http://www.zilog.com/docs/appnotes/an0353-sc01.zip

Sensorless Brushless DC Motor Control with the Z16FMC MCUMultiMotor Series Application Note

MIPS performance at 20 MHz. The Z16FMC MCU supports 16-bit internal bus widths and provides near-single-cycle instruction execution.

Up to 128 kilobytes of internal Flash memory are accessible by the ZNEO CPU, 16 bits at a time, to improve processor throughput. Up to 4 KB of internal RAM provides storage of data, variables and stack operations.

Figure 1 displays a block diagram of the Z16FMC MCU architecture.

In each of the Z16FMC products, the novel device architecture allows for realization of a number of enhanced control features:

• Time Stamp for Speed Control

Figure 1. The Z16FMC MCU Architecture

WDT withRC Oscillator

POR/VBO& Reset Control

Internal PrecisionOscillator

ZNEO20 MHz CPU

ADC 10-bit12-Channel

Comparator

OperationalAmplifier

3 x Timer

I C

ESPI

2 x LIN-UARTwith IrDA

DMAController

InterruptController

FlashController

RAMController

A B C D E F G H

128 KB

4 KB

Multi-ChannelPWM Timers

2

Ports

8 8 8 8 8 1 1 4 Number of pins available

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• Integrated Operational Amplifier

• Multi-Channel PWM Timer

Time Stamp for Speed Control

Most microcontrollers use at least one dedicated comparator to detect the zero crossing of the input AC voltage signal so that the output driving pulses can be synchronized and adjusted to properly regulate motor speed. An alternative approach based on the Z16FMC MCU eliminates the requirement for this comparator by instead employing an analog-to-digital converter (ADC) in conjunction with a timer. In such a scenario, the ADC samples the AC line voltage, with the timer running in the background.

When the ADC samples the line voltage’s zero crossing, it reads the timer count and writes the result to a register. As a result, the timers are cued for the output Pulse Width Modulation (PWM) pulses to efficiently regulate the speed of the motor. This time stamp approach results in a very simple and cost-effective solution for smooth operation of the motor in a steady state.

Integrated Operational Amplifier

Appliance controllers almost invariably monitor motor speed by sensing the current through the windings, using sensor and sensorless techniques in conjunction with the ADC. Ordinarily, sampling instances by the ADC are synchronized by the MCU. With this process, an external operational amplifier is often used to convert the current signal to a voltage signal; the ADC next samples the voltage signal and outputs the result to the pro-cessor. The processor then synthesizes the PWM outputs to control motor speed.

In the case of the Z16FMC MCU, an on-chip integrated operational amplifier eliminates the requirement for an external component, thereby reducing overall system cost.

Multi-Channel PWM Timer

The Z16FMC MCU features a flexible PWM module with three complementary pairs – or six independent PWM outputs – supporting deadband operation and fault protection trip input. These features provide multiphase control capability for a variety of motor types and conduct safe operation of the motor by ensuring immediate shutdown of the PWM pins during a fault condition.

Theory of OperationIn a brushless DC motor, the rotor is comprised of permanent magnets, while the stator windings are similar to those in poly-phase motors. For a detailed discussion of BLDC motor fundamentals, as well as closed-loop control using sensorless techniques, refer to the Motor Control Electronics Handbook by Richard Valentine, McGraw-Hill, NY, 1998.

In sensor-based control applications, the Hall elements are integrated, and are used to detect the position of the rotor for drive synchronization. In contrast, sensorless control employs the detection of back-EMF signals, which are generated (induced) by specific phase windings to synchronize the timing of the control loop.

A block diagram of the BLDC motor control system based on the Z16FMC MCU is shown in Figure 2. At any given instance in a 3-phase commutation arrangement, only two phases are energized. The back-EMF voltage is, in turn, generated in the unenergized

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phase winding, and the zero crossing of this induced voltage is detected for synchroniza-tion of the subsequent closed-loop control events. As discussed earlier, the innovative time stamp feature of the Z16FMC MCU provides for robust, efficient implementation of this critical sensing function without the requirement for an additional comparator.

The algorithm for back-EMF sensing is based on an implementation of a Phase-Locked Loop (PLL), which is described in Appendix C. Back-EMF Sensing Phase-Locked Loop on page 16. This algorithm is especially advantageous during startup, resulting in a very smooth increase in the motor speed, as well as a nearly-instantaneous reversal of direction of the rotation on command, as outlined below.

With a conventional approach during the start-up sequence, power is applied to the wind-ings to place the rotor in a known starting position, followed by commutation and the start of back-EMF sensing and control. In contrast to the traditional approach, the PLL-based approach implemented with this application makes it possible to lock the back-EMF signal from the onset of the start-up phase without the requirement for initial placement of the

Figure 2. . A 3-Phase BLDC Motor Control System

AN035303-1015 of 20


rotor in a specific position. Moreover, this approach significantly reduces any erratic movement of the motor during startup, or even a reversal of direction.

During normal operation following the start-up period, phase torque/current mode control is achieved with a sensing of the voltage generated across a sense resistor in the motor drive circuit. This voltage is routed to the on-chip integrated ADC, after which data pro-cessing by the CPU, based on a predefined computational algorithm, results in the regula-tion of the PWM commutation signal period(s).

As discussed earlier, another key feature of the Z16FMC MCU is the direct coupling of the on-chip integrated comparator to the PWM module to enable fast, cycle-by-cycle shut-down during an overcurrent fault event. Oscilloscope-generated waveforms representing this sequence of events are shown in Figure 3.

In conjunction with the integrated on-chip hardware blocks, the 3-phase BLDC motor control software developed for this application allows for ease of programming to achieve the desired closed-loop control characteristics. The routines that enable the sensing of the motor’s back-EMF and current are all interrupt-driven. It is critical that the highest inter-rupt priority is assigned to the back-EMF sensing event for subsequent synchronization of the commutation events. In this case, Timer 0 is used for the Time Stamp function, as well as for updating the commutation period, if necessary.

Figure 3. Cycle-By-Cycle Shutdown

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Testing

This section describes how to run the code and demonstrate this sensorless brushless motor application including its setup, implementation and configuration, and the results of testing.

Equipment UsedThe following equipment is used for the setup; the first four items are contained in the MultiMotor Development Kit (ZMULTIMC100ZCOG).

• MultiMotor Development Board (99C1358-0001G)

• 24 V AC/DC power supply

• LINIX 3-phase 24 VDC, 30W, 3200RPM BLDC motor (45ZWN24-30)

• Opto-Isolated UART-to-USB adapter (99C1359-001G)

• Z16FMC MultiMotor MCU Module (99C1357-001G) – Order separately

• Opto-Isolated USB SmartCable (99C0968) – Order separately

• Digital Oscilloscope or Logic Analyzer

Hardware SetupFigure 4 shows the application hardware connections.

Figure 4. The MultiMotor Development Kit with Z16FMC MCU Module and SmartCable

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Figure 5 displays the proper port settings in the terminal emulation program.

ProcedureObserve the following procedure to test the 3-Phase Sensorless BLDC Motor Control demo program on the Z16FMC MultiMotor MCU Module.

1. Install the ZDS II – ZNEO version 5.0.1 (or newer) software on your PC.

2. Connect the Opto-Isolated USB SmartCable to the PC.

– To install the driver of the Opto-Isolated USB SmartCable, refer to the installation guide for the Opto-Isolated USB SmartCable that is included in your MultiMotor Development Kit.

3. Connect the hardware as shown in Figure 4 on the previous page.

4. Power up the MultiMotor Development Board using the 24 VDC adapter included in the kit.

5. Open the AN0353-SC01 project in ZDS II for ZNEO.

Figure 5. Example: Terminal Display Settings

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6. From the main.c source file, choose the following mode for the Motor Control application:

#define LOOP_SELECT_VALUE 1u // 0u = torque loop, 1u = speed loop

7. Compile the application and download the code to the Z16FMC MultiMotor MCU Module.

8. In ZDS II, stop the Debug Mode. Unplug the power supply from the MultiMotor Development Board, then disconnect the Opto-Isolated USB Smart Cable.

9. Ensure that the RUN/STOP switch on the MultiMotor MCU Module is in the STOP position.

10. Connect the 24 V DC supply source to the MultiMotor Development Board.

11. Set the RUN/STOP switch on the MultiMotor MCU Module to RUN.

12. Additionally, observe the following points:

– If Speed Mode is selected, the speed of the motor can be varied by adjusting the potentiometer on the MultiMotor Development Board.

– If Torque Mode is selected, the motor speed is decreased with application of force on the shaft of the motor.

– The direction of rotation of the motor is set by changing the position of the direction switch on the MultiMotor Development Board.

You can now add your application software to the main program to experiment with addi-tional functions.

While debugging your code, ensure that the Opto-Isolated USB SmartCable controls the reset pin of the MCU. After debugging and running your code, detach the Opto-Isolated USB SmartCable from J14 of the MultiMotor MCU Module to free the Reset pin and apply a power cycle to reset the MCU from Debug Mode.

ResultsThis three-phase, sensorless, brushless motor control application was tested with a 3-phase BLDC motor connected to Zilog's MultiMotor Development Board. Testing of the Z16FMC MultiMotor MCU Modules confirms a seamless start-up of the motor from an idle mode to full operational speed, a safe on-the-fly reversal of the direction of rotation, an extremely fast fault-detection cycle, and a lower total solution cost.

• Maximum motor speed: 3200 RPM

• Two methods of controlling the motor:

– Manually using the Stop/Run & Direction switches and the speed pot on the MCU Module.

– Using menu-driven commands on a PC terminal emulator connected to the MultiMotor MCU Module through the UART connections

Note:

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• The Green LED illuminates when the motor is running

• The Yellow LED illuminates when under UART control

• The Red LED flashes when the motor is stopped or a fault is detected

Summary

This application note describes the closed-loop control of a sensorless BLDC motor using the advanced on-chip integrated features of the Z16FMC MCU. The software algorithm implemented in this application demonstrates how a three-phase BLDC motor is operated with a minimum set of peripherals using the ADC module for BEMF detection and a Phase Lock Loop for PI speed control. With this implementation, the need for an open loop start-up ramp was eliminated without sacrificing smooth motor start.

The results of this application confirm why the Z16FMC MCU is ideally suited for sensor-less brushless motor control applications. The Z16FMC MCU’s features, along with the powerful ZNEO CPU core and some of the best development tools available in the indus-try, result in less complex board designs and reduced design cycle time.

References

The following documents are associated with the Z16FMC Series of Motor Control MCUs; each is available for download on www.zilog.com.

• Z16FMC Series Motor Control MCU Product Specification (PS0287)

• MultiMotor Series Development Kit Quick Start Guide (QS0091)

• MultiMotor Series Development Kit User Manual (UM0262)

• Zilog Developer Studio II – ZNEO User Manual (UM0171)

• ZNEO CPU Core User Manual (UM0188)

• Space Vector Modulation of a 3-Phase AC Induction Motor with the Z16FMC MCU (AN0354)

• BLDC Motor Control on the Z16FMC MCU Using Sensored Sinusoidal PWM Modu-lation (AN0355)

• Three-Phase Hall Sensor BLDC Driver Using The Z16FMC MCU (AN0356)

• Implementing a Data Logger with Spansion SPI Flash (AN0360)

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http://www.zilog.com/docs/appnotes/AN0354.pdf

http://www.zilog.com/docs/zneo/UM0188.pdf

http://www.zilog.com

http://www.zilog.com/docs/appnotes/AN0360.pdf

http://www.zilog.com/docs/appnotes/an0355.pdf

http://www.zilog.com/docs/devtools/um0171.pdf

http://www.zilog.com/docs/appnotes/an0356.pdf

http://www.zilog.com/docs/ps0287.pdf


http://www.zilog.com/docs/devtools/qs0091.pdf


AN0353 of 20

r Control with the Z16FMC MCUltiMotor Series Application Note

Appe

UTING ALLOWS.

PB3

PH3

PC0

PC1

PH2

CS2-

CS2+

CS1-

CS1+

PC7_PWML0PC6_PWMH0

PD0_PWMH1ANA0 BEMF A

ANA1 BEMF BPD1_PWML1

ANA4PD2_PWMH2

HSB PD4HSC PD5

PD7_PWML2ANA2 BEMF C

HSA PD3

PD6

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PC7_PWML0A_LPC6_PWMH0A_H

B_H PD0_PWMH1BEMF_A ANA0

BEMF_B ANA1PD1_PWML1B_L

PD2_PWMH2C_HC_L PD7_PWML2

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CS1-CS2+CS2-TEMP

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PC0_T1IN_CINN

PC1_TOUT_COMPOUT

ANA6 CS1+

ANA7 CS1-

CS2+

CS2-

TEMPPH2_ANA10

PH3_ANA11_CPINP

PB3_ANA3_OPOUT

VCC_3v3

Buckeye Driveitas, CA 95035-457-9000 Website: www.zilog.com

Multi Motor Control Kit MCU Module. Z16FMC MCU

MCU



MCU



MCU

R3 0 ohm

J41

J2

HDR/PIN 2x15

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8642

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J51

J61

J81

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J111

J91

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R6

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J3

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J121

03-1015

Sensorless Brushless DC MotoMu

ndix A. Schematic Diagrams

Figures 6 and 7 show the schematics for the Z16FMC MCU Module.

Figure 6. Z16FMC MultiMotor MCU Module, #1 of 2

DBGINTERFACE

-RESET

IF VCC_3v3 is usedremove R8 andinstall R10 = 3.3K

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FAULT0

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PC7_PWML0

PC1_TOUT_COMPOUTDBG

PC6_PWMH0

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7_O

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7

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3_A

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3_O

PO

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3_A

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11_C

PIN

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PD2_PWMH2

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GND

VREF

GND

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C28

22pF

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6/A

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9

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03-1015


Figure 7. Z16FMC MultiMotor MCU Module, #2 of 2

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21

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FOR USE WITH AC MOTOR

Phase_C

HSAHSBHSC

H

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Phase_APhase_BPhase_C

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GC_H

VCC_12V

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Title

1590 Buckeye DriveMilpitas, CA 95035408-457-9000 Website: www.zilog.com

PageMulti Motor Control Kit. Main Board

Mosfets, gate drivers, MCU interface

Title




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03-1015


Figures 8 and 9 show the schematics for the MultiMotor Main Board.

Figure 8. MultiMotor Development Board, #1 of 2

J16 SETTINGS:1-2 AC MOTOR2-3 BLDC MOTOR

GA_H

GA_L

Phase_B

Phase_A

GA_H

GA_L

GB_L

GB_H

GC_L

GC_H

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B_L

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B_HPD0_PWMH1BEMF_A

BEMF_BB_LPD1_PWML1

C_HPD2_PWMH2C_LPD7_PWML2

CS1+BEMF_C

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GB_L

GB_HA_H

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PD4HSB

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R2910K

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R15 10K

C4

0.1uF

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R4150K

R7 2.2 ohm

+ C3220uF, 50V

R24150K

R28100 ohm

C9

0.1uF

R5150K

R2710K

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HI5

LI6

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1

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R16 22.1 ohm

R3010K

J4

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0.1uF, 50V

R180.100 ohm, 2W

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R322.1 ohm

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1

23

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C1

HB2

HO3

HS4

HI5

LI6

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R25150K

J6

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D1

BAV19WS

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AN0353 of 20


5V

SHU1-22-3

USE HEATSINK

VCC_5VM

VBUS_B

C17

0.1uF

-220

U5

MIC29150-5

OUT3

GN

D2

IN

+ C1510uF

12

J12

123

2V

3

03-1015


Figure 9. MultiMotor Development Board, #2 of 2

24VDC

GND

GND

12V

EXTERNAL VBUSUP TO 48VDC

holderNT POSITION EXTERNAL VBUS INTERNAL VBUS

NEED to change C25 to 50V Tantalum

50V

VBUS

VCC_24VVCC_12V

VCC_12V

VBUS

ENABLE

D51N4007-T

21

HS2

TO

11

22

33

J13

123

J8

123

1

+ C1410uF

12

+ C1310uF

12

J11

123

SH2

shunt

R33

2K

F1

FUSE/250V/2A

U4

MIC29150-12

OUT3

GN

D2

IN1

J10

123

J7

2 POS

12

FH1

250V/5x20

1 2

Q8MMBT3904

3

1

2

P1

PJ-003A

1

23

RL1

JS1A-1

1

52

D6BAS16

13

2

J14

123

HS1

TO-220

11

22

33

C16

0.1uF

J9

HDR/PIN 1x3

123


Appendix B. Flowcharts

This appendix displays flow charts that diagram the Main Function and the Read and Write APIs.

Figure 10 shows the main control loop.

The back-EMF sensing loop is shown in Figure 11.

Figure 10. Initialization and Application Code Space

Figure 11. Initialization and Application Code Space

Start

Peripheral Initialization

Enable Interrupts

Main Loop(Application Code)

t0_intrp (Back EMF ISR every Timer0time out forms Phase Locked Loop

Commutation Update(every other interrupt)

Back EMF Sensing and PLL Filter(opposite interrupt from Com Update)

Return

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A flow chart of the PWM loop is shown in Figure 12. This PWM loop can also be used for specific application code, such as communications or additional user interfaces.

Figure 12. Current Loop and Timed Housekeeping

pwm_timer_isr(Main Loop ISR every

PWM reload, 50μs)

Current Loop, PWM duty cycle control(500μs update)

LED Status (50μs update)and Blink (0.4 sec update)

Torque (current command from ADC2ms update, filtered)

Return

Direction Switch(7.5ms update, filtered)

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Appendix C. Back-EMF Sensing Phase-Locked Loop

The Phase-Locked Loop back-EMF algorithm, implemented to provide a smooth start-up of the motor, is shown in Figures 13 and 14. Additional details about the specific formulas in these figures are shown in Table 1; a description of these calculations follows.

Figure 13. Back-EMF Sensing Using the Phase-Locked Loop Algorithm

Figure 14. Proportional Integral (PI) Filter Representation for Back-EMF Sensing

Θrotor +

(radians)

Θerror VΘ

Back EMF Neutral(volts/radian)

Back EMF Divider(unitless)

ADC(counts/volt)

PI Filter(unitless)

speed

(sec) (radians/cycle/sec) (rev/cycle) (unitless) (radians/Hertz)Integrator

Frequency toAngular Frequency

ConversionRevolutions

per cycle

Electrical cyclesper Commutation

cycles

Commutationcycles per

Timer cycles

mec ƒmec ƒelect ƒcom ƒtimer

h h (cycles/sec) (cycles/sec)(rev/sec)(rev/sec)

(cycles/sec)

(radians) (volts) (volts) (counts) (counts)

kc + ѕτ21

TimerPrescale

R1 ADCcounts

Vcounts

ƒclock

Speed_countSpeed_constant

ѕτ2R1π

2π

+ R2

ѕ1

6

1

2

1

N

2

÷

Θ1(ѕ)

–

+ Θe(ѕ) Ud(s) = KdΘe(ѕ) Uƒ(s) = Ud(ѕ)F(ѕ)

VCO

FilterPhase Detector

Kd F(ѕ)

ѕKo

Θ2(ѕ)

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We begin with the transfer function of the Proportional Integral (PI) Filter in the s-plane:

Table 1. Back-EMF Sensing Phase-Locked Loop

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Next, by using the bilinear transform identity:

where T = the sampling period, yields the following equation.

When multiplying by:

the calculations that follow are:

where:

and:

Collecting terms and dividing by z yields the following result:

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When writing this computation as a computer program, it takes the form of a recursive fil-ter, with the coefficients A0 and A1:

where:

• Y0 = Current output

• Y1 = Output at the last sample period

• R0 = Current ADC sample of back-EMF (phase voltage – VBUS / 2)

• R1 = Most recent sample of back-EMF from ADC

• A0 = a0

• A1 = –a1

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This publication is subject to replacement by a later edition. To determine whether a later edition exists, please visit the Zilog website at http://www.zilog.com.

DO NOT USE THIS PRODUCT IN LIFE SUPPORT SYSTEMS.

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ZILOG’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS PRIOR WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF ZILOG CORPORATION.

As used herein

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©2015 Zilog, Inc. All rights reserved. Information in this publication concerning the devices, applications, or technology described is intended to suggest possible uses and may be superseded. ZILOG, INC. DOES NOT ASSUME LIABILITY FOR OR PROVIDE A REPRESENTATION OF ACCURACY OF THE INFORMATION, DEVICES, OR TECHNOLOGY DESCRIBED IN THIS DOCUMENT. ZILOG ALSO DOES NOT ASSUME LIABILITY FOR INTELLECTUAL PROPERTY INFRINGEMENT RELATED IN ANY MANNER TO USE OF INFORMATION, DEVICES, OR TECHNOLOGY DESCRIBED HEREIN OR OTHERWISE. The information contained within this document has been verified according to the general principles of electrical and mechanical engineering.

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