Efficient Motor Commutation through Advanced Position Sensing - The Trend towards Brushless DC Motors

Confidential © ams AG 2014

Efficient Motor Commutation through

Advanced Position Sensing:

The Trend towards Brushless DC

Motors

Heinz Oyrer, Senior Manager Global Marketing

Sensors Expo and Conference , June 24-26, 2014


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EFFICIENT MOTOR COMMUTATION THROUGH

ADVANCED POSITION SENSING The Trend towards Brushless DC Motors

EFFICIENCY OF ELECTRICAL MOTORS

BRUSHLESS DC MOTORS

MOTOR POSITION SENSOR

INTEGRATED POSITION SENSING IN EPS


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• Electric motors are the single biggest

consumer of electricity.

• They account for about 2/3 of industrial

power consumption and, about 45% of global

power consumption, according to a new

analysis by the International Energy Agency

Source: CleanTechnica, abb.com/energyefficiency

Electric Motors Use Majority of Global Electricity


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• Thousands of words and column inches are

devoted to topics such as nuclear power,

renewable energy, and electric vehicles

• Rarely discussed is the fact that the majority

of electric motors are inefficient,

oversized, or running when they don’t

need to be running.


Majority of Electric Motors are Inefficient


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Opportunities for Efficiency

• Addressing the efficiency of electric motors is

an important topic that needs to be tackled.



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An electric motor system comprises three layers of

equipment :

1. Electric motor: a fully functioning electric

motor runs from the electric grid.

2. Core motor system. The core motor

system controls torque and speed. It

consists of the electric motor, its driven

piece of mechanical equipment along with

the necessary interconnection and a

variable‐speed drive (VSD) system between

the grid and the motor.

3. The total motor system consists of the

core motor system plus the eventual

application of power and the electric

equipment between the grid and the motor.

Energy‐efficiency for Electric Motor‐driven Systems

Source: International Energy Agency,

Energy-Efficiency Policy Opportunities

for Electric Motor-Driven Systems 2011


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BRUSHLESS DC MOTORS




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Motor Types Key Parameters

Stepper Motor AC Induction Brushless / Servo Universal


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• Brushless Direct Current (BLDC) motors are rapidly gaining popularity.

• BLDC motors are used in appliance, automotive, aerospace, consumer,

medical, industrial automation equipment and instrumentation

applications.

• BLDC motors do not use brushes for commutation; instead, they are

electronically commutated.

• BLDC motors offer many advantages over brushed DC motors and

induction motors, including:

Being more reliable: no brushes

Better speed versus torque characteristics

High dynamic response

High efficiency

Long operating life

Noiseless operation

Higher speed ranges, acceleration rates and torque/size ratio

Better EMC performance

• In addition, the ratio of torque delivered to the size of the motor is

higher, making ideally suited for applications where space and weight

are critical.

Introduction to Brushless DC Motors


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Brushless Direct Current (BLDC) motors are rapidly gaining popularity

• "Sales volumes of brushless DC motors are forecast to grow much

faster than that of either brushed DC motors or stepper motors. Major

advantages of brushless DC motors include higher efficiency at

converting electricity into mechanical power, reduced noise, longer

lifetime and higher reliability.“, Michael Liu, IMS Research

• E-Motor market is growing 40% from 2012 to 2017

Government regulations worldwide

• Require the industry to implement new efficiency classes IE1, IE2,

IE3, … (IE = International Efficiency to reduce CO2 (higher efficiency

means better motor control)

Key requirements in Automotive market

• Reducing CO2-emissions by saving weight and reducing fuel

consumption

• Improve passenger safety and anti-collision systems and electric

stability program

• Improve passenger comfort to reduce noise and improve handling

The Trend Towards Brushless Motors


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• Today: Cost of brushed > Cost of BLDC but < Cost of BLDC +

electronics

• Near future: Cost of brushed = Cost of BLDC + PCB

• Future: Cost of brushed > Cost of BLDC + electronics all

brushed motors will be replaced by BLDC

• Most brushed motors do not have electronics but all BLDC need it.

(Cost of brushed – Cost of BLDC) = available amount for

electronics, however also cost pressure for electronics

• Reduce the number of gearboxes by increasing the torque of the

motor - no gearbox means lower motor speed – direct drive

Cost Pressure for Brushless Motors


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• BLDC motors consist of a rotating permanent

magnet (rotor) and (min) 3 equally spaced

fixed windings (stator).

• By controlling the currents in the stator, a

magnetic field of arbitrary direction and

magnitude can be produced.

• Torque is produced by the attraction and

repulsion between the rotor and stator field

• In the case of a brushed DC motor, feedback

is implemented using a mechanical

commutator and brushes. In a BLDC motor, it

is achieved using multiple feedback sensors.

• The most commonly used sensors are hall

sensors and optical encoders.

Brushless Motor Basics


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In order to apply the most efficient stator field, the position of the rotor must be known. There are several methods to detect the rotor position:

• Sensor-less

By measuring back-EMF and/or stator coil currents

• Optical switches

Using a coded disc

• Resolvers

Flanged onto the rotor shaft

• Hall switches

Embedded into the stator, actuated by the rotor magnet. Based on the combination of these three Hall sensor signals, the exact sequence of commutation can be determined.

• Integrated Hall sensors = Position Sensor

A Hall effect magnetic position sensor is a transducer that varies its output voltage in response to a magnetic field.

Mounted at the end of the shaft

Rotor Position Feedback


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Motor Application Requirements

Requirement Sensor - Types Sensorless

Speed control • Magnetic Position Sensor

• Optical Encoder

Sensorless is possible with back

EMF and FOC at speed > 300rpm*

Commutation

• 3 discrete Hall switches

• Magnetic Position Sensor

• Optical Encoder

Sensorless is possible with back

EMF and FOC at speed > 300rpm*

Position Control

Torque Control

• Optical Encoder

• Magnetic Position Sensor

• Inductive (Resolver)

Sensorless not possible

Sensor always needed

EMF … electro magnetic force

FOC … field oriented control

* Lower rpm possible but very complex algorithms


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BRUSHLESS DC MOTORS




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• One single Hall sensor can reduce component cost, the cost for

precision mounting is saved

• It can output the rotor position by one single sensor and deliver the

absolute angle position of the rotor during start

• Electric brake and hold

• Increase efficiency by software

• Applicable for small motor designs

• The sensor does not need to reside on specific positions inside the

motor which results in more design freedom for the motor designer

• Power efficient (no power dissipation like with sensor-less/shunt)

• Easy integration

• High temperature environment

• High start-up torque, low torque ripple, low audible noise

• High accuracy, excellent reliability and high safety levels

(automotive)

When Do Customers Need a Position Sensor?


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Efficient motor commutation

• Needs fast and accurate position measurement

Key enablers

• Measurement quantization (resolution)

• INL (integral-non-linearity)

• Noise

• System propagation delay

Benchmark

• INL (8mm Magnet + displacement) = 1.2deg

• Noise = 0.05deg

• System propagation delay = 1.9µs

• Core resolution = 14bit

• Maximum Speed = 28.000 rpm

• Flexible choice of interfaces

• Immunity to external stray field

Position Sensing for Efficient Motor Commutation


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Angle accuracy: ideal slope


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Angle accuracy: system propagation delay


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Integrated Dynamic Angle*) Error Compensation

Dynamic Angle Error

Hardware Compensation integrated!

No Software needed!

External HW + SW compensation needed

Ma

gne

tic P

ositio

n S

en

sor

Syste

m

*) DAEC™ - patent pending


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BRUSHLESS DC MOTORS




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• Magnetic position sensing is now becoming the

leading solution for automobile EPS systems that

have greater operational effectiveness.

• Sophisticated sensor devices with multiple

sensing elements on a single die enable faster

and more accurate acquisition of information

required by the EPS system.

• Precise position of the automobile's steering

wheel, improved performance of its EPS system

while keeping costs and required space to a

minimum.

Stability over temperature

Robustness against tolerances

Robustness against interfering field

Up to 7 pole pairs

Up to 28.000 rpm (depending on application)

Angle error <1° deg

ISO26262-compliance (depending on OEM

specification)

Integrated Position Sensing in EPS

BLDC

Rotor Position Sensor

Electric Power Steering dominates the steering market,

EPS outperforms other markets in growth.

The motor position

sensor controls the

commutation of a

brushless DC motor

employed in the

system.


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Summary

• Improving the efficiency of electric motors has become an important topic at a global level

• The core motor system offers a great potential for savings

Controlling torque and speed as well costs

BLDC motors as a key enabler

• BLDC motors offer many advantages over brushed DC motors and induction motors.

Better speed versus torque characteristics, high dynamic response, high efficiency, long

operating life, noiseless operation, higher speed ranges, rugged construction and so on.

Torque delivered to the motor size is higher, making it ideal for applications where space and

weight are critical factors.

BLDC motors find wide spread adoption in applications such as automotive, appliance,

aerospace, consumer, medical, instrumentation and automation

• Magnetic position sensing as a monolithic integrated function is becoming the leading

technology for motor control applications that demand:

Higher accuracy & broader speed specifications

Integrated chip design (no SW/HW compensation in ECU)

Reduced system & component costs

More design freedom for motor designers


Thank you

Please contact me at [email protected]

and/or visit our website www.ams.com

mailto:[email protected]

http://www.ams.com/


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APPENDIX


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1.) Higher efficiency (government – rules) … to reduce the CO2 ww

Motor market trends


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When Do Customers Need a Position Sensor?

Motor-Types Benefits for the customer Resolution [PPR]

Stepper Motor

- Count the steps and monitor the position

- Reduce power consumption

- Reduce motor size

- Reduce total weight

- Reduce system costs

- Safety

200, 256 (10-bit)

300

400

500, 512 (11-bit)

BLDC Motor

EC Motor

- Remove 3 discrete Hall switches (cost down)

- Get also the absolute angle position of the rotor during start

- Increase efficiency by software

- Small motor designs possible

90 (8.5-bit)

360 (10.5-bit)

720 (11.5-bit)

PMSM Motor

AC Servomotor

- Reduce system cost

- Replace Optical Encoders - expensive (~15 – 50.- EUR)

- Replace Resolvers - very expansive (> 50.- EUR)

- Higher reliability compare to optical

- Smaller motor design possible

500, 512 (11-bit)

1000, 1024 (12-bit)

2000 (13-bit)

2500 (~14-bit)

BLDC … Brushless DC Motor

EC … Electric commutated

PMSM … Permanent Magnet Synchron Motor


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Standard Interfaces

Interface

name

Output for

what?

Number

of wires Function

ABI

(quadrature

interface)

Incremental 3 - Speed & direction control

- Position control

- Standardized

- For high speed

(up to 30.000 rpm)

UVW Motor

commutation 3

- Motor control (provide same

output as 3 discrete Halls) - Standardized on BLDC

PWM (pulse

width

modulation)

Absolute

angle

information

1 - Absolute rotor position

information for start

- One wire only

- Slow interface

SPI, I2C,

SSI (digital

interfaces)

Absolute

angle

information

2, 3, 4

- Absolute rotor position for start

- Speed & direction control

- Position control

- Direct motor control

- Good for

System Integrator

- No standard for

Motor Controller

Analog

Absolute

angle

information

1 Absolute rotor position

information for start

- One wire only

- Slow interface


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• Position sensors measure the distance a body has moved from its

reference and the resulting output is given as a feedback to the

control system.

• Motion of a body can be rectilinear or curvilinear; accordingly,

position sensors are called linear position sensors or angular

position sensors.

• Position sensors use different sensing principles to sense the

displacement of a body. Depending on these different sensing

principles they can be classified contacting or non-contacting

position sensors.

• Contacting sensors measure linear or angular position through a

mechanical connection whereas non-contacting position sensors

measure the linear or angular position of an object without any

physical contact.

What are position sensors?


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• Non-contacting position sensors are highly reliable and offer a

long functional life due to the absence of mechanical parts and

physical contact.

• Magnetic sensors use:

The Hall effect to determine position, angle, or displacement

The anisotropic magneto resistive effect or a magnetically

actuated reed switch to detect magnetic fields generated by a

reference magnet.

• Hall Effect based Magnetic Position Sensors - A Hall effect

sensor is a transducer that varies its output voltage in response to a

magnetic field. Hall effect sensors are used for sensing proximity

switching, positioning, speed detection and current.

What are position sensors?


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• Emergence of contactless and integrated

magnetic position sensors

• Traditional sensors are replaced by

contactless sensors that handle complex

and highly integrated electronics –

delivering higher sensitivity, smaller form

factors and increased flexibility

• Strong trend is going from simple angle and

distance sensors towards robust, intelligent

sensor systems and applications with

multiple simultaneous measurement axes

• Tackling the shortcomings of optical,

magneto resistive, inductive and linear Hall

sensors and switches

• No wear, insensitive to humidity, dust, dirt

and harsh environments

• Solutions offer enhanced precision,

repeatability, and robustness in addition to

stray field immunity.

Why hall-based magnetic position sensing?

Efficient Motor Commutation through Advanced Position Sensing - The Trend towards Brushless DC Motors

Technology

efficiency of electric

electric motor system

induction motors

electric motordriven

electric equipment

electric grid

brushed dc motors

efficient motor commutation