External Use

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An Overview of the Resolver

Interface for Motor Control

Applications

FTF-AUT-F0234

A P R . 2 0 1 4

Leos CHALUPA | Automotive MCU Product Group

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External Use 1

Session Introduction

• This session will explain cost-effective solutions to interface the

resolver position sensor directly to Freescale's automotive MCU.

• We will discuss basic operation, benefits of saving an external IC,

run time diagnostics and flexible selection of the “limp” mode.

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Session Objectives

• By the end of this session you will:

− Be more familiar with resolver-based position sensing

− Understand the run-time diagnostic principles

− Describe how to use Freescale microcontrollers to save an external

IC for Resolver interfacing

− Name the advantages of the presented solution

− Know where to look for support, documentation and examples

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Agenda

• Resolver basics

− Brief history

− Resolver types, constructions and operation principles

• Angle position sensing

− Principle of resolver position extraction

− Sources of position sensing errors

• Direct MCU-resolver interface

• Freescale support, examples, documentation and

more

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Resolver Basics

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Brief Resolver History

• Developed in 1940s at MIT (Supported by the U.S. military)

• Resolvers have been part of electromechanical servo and shaft angle positioning systems for over 50 years

• Resolver position sensor constructions evolved over time − 1970s: Brushless resolver

− 1980s: Hollow shaft brushless resolver

− 1990s: Variable reluctance resolver

• Resolver position conversion methods evolved from phase analog techniques to tracking observer-based digital techniques with run-time diagnostic

• Since 2000, the Freescale Motor Control team has investigated different approaches of the resolver-to-digital conversion using available MCUs/DSCs. The first application was the SMT pick and place machine where fast dynamics and high precision is a key for overall cost effectiveness. Until today, the method was continuously improved and ported to practically all el. motor control MCUs, including special CPU autonomous version based on the eTPU to target ramping EV and HEV markets

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Resolvers: Electro-magnetic Induction Angle Sensors

Rotor is put directly on the drive’s shaft

Stator is fixed on drive’s shield

Simple assembly and maintenance

No bearings – “unlimited” durability

Resist well against distortion, vibration, deviation of operating temperature and dust

Worldwide consumption is millions of pieces at present time

Widely used in precise positioning applications

The number of generated sine and cosine cycles per one mechanical revolution depends on the number of resolver pole-pairs (usually 1-3 cycles)

Basic parameters:

− Electrical Error – +/-10’, Transformation Ratio – 0.5, Phase Shift – +/-10°

− Input Voltage – 4-30V, Input Current – 20-100 mA, Input Frequency – 400 Hz – 40 kHz

Uref

Usin

Rotor shaft

Ucos

Uref

Usin

Rotor shaft

Ucos

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External Use 7

Resolver Types

θ [°] stator

rotor

sin

cos

HF

excitation

Secondary Side

Primary side

θ [°] stator

sin

cos

HF

excitation

Secondary side

Primary side

rotor

θ [°]

sin

cos

HF

excitation

Secondary side

Primary side Rotary coupling

transformers

Traditional Brushless

With variable air-gap

Brushless Variable Reluctance

With solid rotor

Rotating magnetic coupling transfers HF

energy from the stator (primary) to the rotor

(secondary), connected directly to the resolver

primary. This generates an AC magnetic field

with a sinusoidal distribution, hence causing HF

voltages in the stator windings (secondary side)

with amplitudes dependent (sine/cosine) on the

rotational angle of the rotor.

The VR solid rotor resolver has primary

and secondary windings in the stator,

therefore it does not need a rotating

magnetic coupling. The rotor contains a

diagonal section of highly permeable

material that varies the magnetic field

across the stator as the rotor turns.

Thus, the induced voltage amplitudes

correspond to the sine and cosine of

the rotor angle.

The VR variable air-gap resolver has

primary and secondary windings in the

stator, therefore it does not need a

rotating magnetic coupling. The contour

of rotor is made as the permeance

of air-gap between the stator and rotor

is varied in sinusoid oscillation. Thus,

the induced voltage amplitudes

correspond to the sine and cosine of

the rotor angle.

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Traditional Brushless Resolver

Source: Artus, www.psartus.com Source: Tamagawa Seiki co., www.tamagawa-seiki.com

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Brushless VR Resolver

Source: Tamagawa Seiki co., www.tamagawa-seiki.com Source: Admotec Inc., machinedesign.com

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Basic Resolver Terms

• Excitation – The winding powered by high frequency (e.g. 10 kHz) sine

wave

• Number of multiples/poles – The multiplied speed ratio of the output

angle signal is indicated. The number of poles is twice that of shaft angle

multiplication

• Transformation ratio – Ratio of output voltage amplitude to the excitation

voltage amplitude

• Phase shift – Phase difference between the excitation voltage and output

voltage

• Electrical error – The difference between electrical angle (presented by

the ratio of resolver outputs) and theoretical angle value

• Input impedance – The impedance of the excitation side

• Output impedance – The impedance of the output windings

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Resolver Angle Position Sensing

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External Use 12

Resolver Based Angular Sensing Methods

• Phase Analog Technique

− The two stator windings are excited by signals that are in phase quadrature to each

other. This induces a voltage in the rotor winding with an amplitude and frequency that

are fixed and a time-phase that varies with shaft angle. This has been the most widely

used technique because it can easily be converted to produce a digital signal by

measuring the change in phase shift with respect to the reference signal.

• Angle Tracking Resolver to Digital Conversion (RDC)

− A tracking converter contains a phase demodulator. Therefore, frequency variation and

incoherent noise do not affect accuracy. Tracking converters can operate with any

reference excitation, sine or square wave, with only minor accuracy variations.

− This technique is implemented by most of the RDC ICs.

− More will be discussed further in this presentation.

RDC IC Ext. circuitry

Analogue demodulation,

PLL RC

Network

Amplifier Resolver

excitation

Angle

Sensor

Δ sin

Δ cos

VCO Counter

Sine

Cosine

Run Time Diagnostic

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Angle Tracking Observer Principle

Pos. Error

Comparator Regulator

Angle Tracking

e() Envelope

Extractor

LP

Filter

est

est

Sine

Cosine

Generator

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External Use 14

+ +K1

1s

1s

K2

- +

sin ( )

cos( )

sin( )

cos( )

(s) + +K1

1s1s

1s

K2

1s1s

K2

- +

sin ( )

cos( )

sin( )

cos( )

(s)

e( -)

Angle Tracking Observer Basics

Features:

• Non-sensitivity to disturbance and harmonic distortion of the carrier

• Non-sensitivity to voltage and frequency changes

• High accuracy of the angle extraction

( )

121

2

21

KsKKs

sK1K

Θ(s)

(s)Θ̂F(s)

Implementation Basics:

Transfer function:

Angular error evaluation:

( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( )

7Θ̂-Θfor Θ̂-ΘΘ̂-ΘsinΘ̂-Θe

Θ̂-ΘsinΘ̂sinΘcosΘ̂cosΘsinΘ̂-Θe

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400600

8001000

12001400

0.51

1.52

0

5

10

15

20

25

30

35

Damping factor [-]Natural frequency [rad/s]

Pe

ak o

ve

rsh

oo

t [%

]

400600

8001000

12001400

0.51

1.52

0

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

Damping factor [-]Natural frequency [rad/s]

Se

ttlin

g t

ime

[s]

Transfer function of the General Second Order System:

BASICS OF ANGLE EXTRACTION 5/6 TUNNING THE ANGLE TRACKING OBSERVER

Transient responses:

Overs

hoot

±2%

Settling time

Tuning the Angle Tracking Observer

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Direct MCU R-D Conversion

There are two basic approaches to performing resolver-to-digital conversion using on-chip resources

• Case 1) – Based on the synchronous “rectification” of the high frequency carrier of the feedback signals:

− This requires synchronized triggering of the ADC S&H circuit with respect to the resolver excitation signal

− This is mostly approached by using RSD ADC + triggering timer channels + angle tracking software algorithm

• Case 2) – “Demodulation” of the oversampled feedback signals:

− This does not require synchronized triggering, however it requires fast ADC capable to over-sample two high-frequency feedback signals

− This is mostly approached by using Sigma-Delta ADC + high-frequency digital demodulation + angle tracking software algorithm (with phase-delay compensation)

− Improves dynamics

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Case 1: Sin/Cos Envelope Extractor

Timer OC

ADC Trigger

ADC

sampling

ADC

sampling

Resolver excitation

signal at 10 kHz

Resolver feedback

“sin” signal

Resolver feedback

“cos” signal

“sin” envelope

“cos” envelope

Detail view

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Case 2: Over-sampling of Resolver Signals

Timer OC

SDADC sampling

Resolver excitation

signal at 10 kHz

Resolver feedback

“sin” signal

Resolver feedback

“cos” signal

“sin” envelope

“cos” envelope

Detail view

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Direct MCU-Resolver Interface

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Direct MCU R-D Conversion vs. RDC IC

Peripherals CPU Ext. circuitry

∑∆A/D Demodulation ATO PD RC

Network

Output

H/W layer eTIMER

Angle

Sensor

Δ sin

Δ cos

Application

s/w SW RDC

MPCxxxxX

Sync.

RDC IC

Run Time Diagnostic

RDC IC MCU Ext. circuitry

Analogue demodulation,

PLL RC

Network

Amplifier

SWG -

Resolver

excitation

Angle

Sensor

Δ sin

Δ cos

Application

s/w

Run Time Diagnostic

VCO Counter

Sine

Cosine

Run Time Diagnostic

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MPCxxxxX

Direct MCU R-D Conversion: Application Example

Resolver

S1 S3

S2

S4

R2 R1

Cosine

Sine

Excitation

Amplifier

LP Filter,

DC

Common

Mode

Shift

Detection

SDADC 2+3 2xch. s. ended mode

SDADC 0+1 2xch. s. ended mode

SDADC 4+5 2xch s. ended mode;

optional excitation

monitoring

PWM (eTPU)

2nd order

LP Filter

CPU

12 V

Angle Tracking

Observer

ATO Angular position

Angular speed

INIT values

Diagnostic

sin

, co

s

Tra

ckin

g e

rr.

Fault diagnostic

Angular speed

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Resolver Differential Excitation Stage

Excitation Amplifier ≈ existing solution

Low-pass filter

MPCxxxxX

PWM (eTPU)

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Resolver Input Stage (Phy. Layer)

MPCxxxxX

SDADC 0+1 2xch. s. ended mode

SDADC 2+3 2xch. s. ended mode

SDADC 4+5 2xch s. ended mode;

optional excitation

monitoring

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External Use 24

• Position accuracy ±0.13 deg. 12bit ±2LSB

• External hardware

‒ Excitation amplifier

‒ LP Filter, DC Common Mode Shift Detection

• True 12-bit resolution without noise

• Repeatability ±0.07 deg.

Evaluation Results

RDC IC

• Position accuracy ±0.09 deg. 12bit ±1LSB

• External hardware

‒ Excitation amplifier

‒ Hardware tuned for given resolver

‒ Differential measurement

‒ Phase difference, offset, gain error uncompensated

‒ LP Filter, DC Common Mode Shift Detection

• Noise, repeatability ±0.033 deg.

‒ Higher CPU* & ADC load

MPC5746M SW RDC

-0,1

-0,05

0

0,05

0,1

0,15

-180 -135 -90 -45 0 45 90 135 180

reso

lve

r e

rro

r [m

ech

. d

eg[

reference position [mech. deg]

angleErr

Po

sitio

n a

ccu

racy

Nois

e

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Diagnostics: Calibratable Fault Thresholds

• Fault diagnostic thresholds are implemented in software, therefore

can be easily calibrated.

SIN_POS

COS_POS

SIN_ZERO

COS_ZERO

SIN_NEG

COS_POS

SIN_AMPLS

COS_AMPL

SIN_AMPLS

COS_AMPL

UNIT_CIRCLE_MAX

UNIT_CIRCLE_MIN

OBSERVER

_ERROR

OBSERVER

_ERROR

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Fault Example: SIN Short to GND

Sin Cos Means Unit Circle ATO

Calculated Angle

SIN_ZERO

SIN_POS

SIN_NEG

SIN_AMPL

COS_ZERO

COS_POS

COS_NEG

COS_AMPL

SIN_MEAN_POS

SIN_MEAN_NEG

COS_MEAN_POS

COS_MEAN_NEG

UNIT_CIRCLE_MIN

UNIT_CIRCLE_MAX

OBSERVER_ERROR

1.2b SIN Wire(or pin) short to GND ? ? ? 1 ? ? ? ? 1 0 ? ? 1 1 ? +/- 35deg

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Fault Example: REFSIN Open

Sin Cos Means Unit Circle ATO

Calculated Angle

SIN_ZERO

SIN_POS

SIN_NEG

SIN_AMPL

COS_ZERO

COS_POS

COS_NEG

COS_AMPL

SIN_MEAN_POS

SIN_MEAN_NEG

COS_MEAN_POS

COS_MEAN_NEG

UNIT_CIRCLE_MIN

UNIT_CIRCLE_MAX

OBSERVER_ERROR

1.3a REFSIN Wire(or pin) open ? 0 1 0 ? ? ? ? 0 1 ? ? 1 1 ? wrong

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Fault Example: Shortcut REZ_GEN and REFSIN

Sin Cos Means Unit Circle ATO

Calculated Angle

SIN_ZERO

SIN_POS

SIN_NEG

SIN_AMPL

COS_ZERO

COS_POS

COS_NEG

COS_AMPL

SIN_MEAN_POS

SIN_MEAN_NEG

COS_MEAN_POS

COS_MEAN_NEG

UNIT_CIRCLE_MIN

UNIT_CIRCLE_MAX

OBSERVER_ERROR

2.2 Short between REZ_GEN and REFSIN ? 1 0 1 ? ? ? ? 1 0 ? ? 1 1 ? wrong

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Resolver + R/D IC Comments

• Advantages

− Position information during MCU initialization stage

− High resolution: 12-bit

− Simple SPI interface between MCU and RDC IC

• Disadvantages

− Only simple diagnostic possible (raw signal data not accessible)

− No limp operation modes

− RDC IC may require up to 30 pins

− Larger board area

− Higher system cost

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Resolver + SW Observer Comments

• Advantages

− High resolution: 10-12 bit (dependent on the resolution of A/D converter)

− Simple hardware

− Lower cost than resolver + ASIC

− Intelligent diagnostics possible with complex conditioning for fault source

detection

− Limp mode operation modes possible

• Disadvantages

− Intensive calculation needs, higher CPU load easily managed by

Freescale 32-bit Qorivva microcontrollers

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Freescale Support, Examples,

Documentation

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External Use 32

Motor Control Development Kit: Composition

MCU

Controller Board

MC33937A

3-phase

Low Voltage

Power Stage

PMSM with

Resolver/Encoder or

BLDC with

Hall/No Sensor

FET DRIVER

MC33937A

FET 3-phase

Power Stage

3-phase Current

Shunts

Resolver/Sin-Cos

Interface

Incremental

Encoder Interface

Qorivva

MPC5643L MCU

Switches and Pushbuttons

ON/OFF, Up/Down, Reset

SBC

MC33905

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Sensor: Position and Speed Measurement

Functional properties:

• Sine-wave excitation signal generation

• Position measurement

• Speed measurement

• Revolution measurement

Key features:

• Adjustable magnitude of excitation signal

• Adjustable frequency of excitation signal

• Sensor fault state detection

ADC measurement

Uref

Usin

Rotor shaft

Ucos

Uref

Usin

Rotor shaft

Ucos

Resolver

Encoder

Incremental Encoder Pulses

Source: Heidenhain

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Motor Control Development Kit Series: Content

• Out-of-the-box experience offers:

− Complete schematics of the development kit hardware

− Complete source code of the development kit software application

− Math and Motor Control libraries (MCLib) in object code

− FreeMASTER & MCAT interface to easy application visualization / control

− Extensive documentation including User Guide, Quick Start Guide and Fact Sheet

FreeMASTER HTML-based Control Page FreeMASTER Scope

www.freescale.com/AutoMCDevKits

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External Use 35

MLIB

• Trigonometric Functions

• GFLIB_Sin, GFLIB_Cos,

GFLIB_Tan

• GFLIB_Asin, GFLIB_Acos,

GFLIB_Atan, GFLIB_AtanYX

• Limitation Functions

• GFLIB_Limit,

GFLIB_VectorLimit

• GFLIB_LowerLimit,

GFLIB_UpperLimit

• PI Controller Functions

• GFLIB_ControllerPIr,

GFLIB_ControllerPIrAW

• GFLIB_ControllerPIp,

GFLIB_ControllerPIpAW

• Interpolation

• GFLIB_Lut1D, GFLIB_Lut2D

• Hysteresis Function

• GFLIB_Hyst

• Signal Integration

Function

• GFLIB_IntegratorTR

• Sign Function

• GFLIB_Sign

• Signal Ramp Function

• GFLIB_Ramp

• Square Root Function

• GFLIB_Sqrt

GFLIB

• Finite Impulse Filter

• GDFLIB_FilterFIR

• Moving Average Filter

• GDFLIB_FilterMA

• 1st Order Infinite Impulse

Filter

• GDFLIB_FilterIIR1init

• GDFLIB_FilterIIR1

• 2nd Order Infinite Impulse

Filter

• GDFLIB_FilterIIR2init

• GDFLIB_FilterIIR2

GDFLIB

• Clark Transformation

• GMCLIB_Clark

• GMCLIB_ClarkInv

• Park Transformation

• GMCLIB_Park

• GMCLIB_ParkInv

• Duty Cycle Calculation

• GMCLIB_SvmStd

• Elimination of DC Ripples

• GMCLIB_ElimDcBusRip

• Decoupling of PMSM

Motors

• GMCLIB_DecouplingPMSM

GMCLIB

• Absolute Value, Negative

Value

• MLIB_Abs, MLIB_AbsSat

• MLIB_Neg, MLIB_NegSat

• Add/Subtract Functions

• MLIB_Add, MLIB_AddSat

• MLIB_Sub, MLIB_SubSat

• Multiply/Divide/Add-

multiply Functions

• MLIB_Mul, MLIB_MulSat

• MLIB_Div, MLIB_DivSat

• MLIB_Mac, MLIB_MacSat

• MLIB_VMac

• Shifting

• MLIB_ShL, MLIB_ShLSat

• MLIB_ShR

• MLIB_ShBi, MLIB_ShBiSat

• Normalisation, Round

Functions

• MLIB_Norm, MLIB_Round

• Conversion Functions

• MLIB_ConvertPU,

MLIB_Convert

ACLIB/AMCLIB

• Angle Tracking Observer

• Tracking Observer

• PMSM BEMF Observer in

Alpha/Beta

• PMSM BEMF Observer in

D/Q

• Content To Be Defined

Target Platform GreenHills Multi WindRiver Diab Cosmic

Qorivva MCU RTM Rev 1.0 RTM Rev 1.0

S12ZVM RTM Rev 1.0

Auto Math and Motor Control Library Set

ω ωfbck wRotElRes

GetPositionElRes()

GetSpeedElRes()

GDFLIB_FilterMA

GFLIB_ControllerPIrA

W GFLIB_IntegratorTr

θerr θfbck

- thRotElRes

GFLIB_Sin

GFLIB_Cos

si

n

cos

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MC Development Kits: Web Page Summary

Motor Control Development Kits

Math & Motor Control Library Set

Motor Control Application Tuning Tool (MCAT)

FreeMASTER

www.freescale.com/MCAT

www.freescale.com/freemaster

www.freescale.com/automclib

www.freescale.com/AutoMCDevKits

See short promotional video on Freescale’s YouTube channel

See short promotional video on Freescale’s YouTube channel

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© 2014 Freescale Semiconductor, Inc. | External Use

www.Freescale.com