AC motors &modelingmechatronic systemsKON-C2004 Mechatronics BasicsRaine Viitala 5.11.2020

Feedback – Thank you!!• First round: 10h (2018 8h, 2019 9h)

• - 14 h of work is alot in the end, but hey its nothing new to be overworked• I warned you ☺

• Fairly easy and also very good reminder of the topics

• Ottakaa nyt herranjestas koko kurssille desimaalipiste -pilkun tilalle.

• Sorry, this is a property of MyCourses!

• The lectures were excellent! I would hope for a few more attempts in the exercises

because it's harder to get help during the exercise sessions than normally.• Number of trials here vs. in industry, in working life? What could be good ratio?

• Number of trials here vs. in traditional written exercises vs. in exam?

• Points partly from exercises vs. grading 100% from exam?

• The lectures were good especially the interactions on teams and the complementary

videos. I wish that question 11 in the mechanics section was a bit more clear. Overall

very satisfied. Thank you!

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Applications

Electric motors

DC- Brushed

- Brushless

AC- Synchronous

• Permanent magnet motor

• Field excitation

• Reluctance

- Asynchronous (Induction)

• Squirrel cage

• Wound rotor

Speed range

From a couple hundred rpm

to hundreds of

thousandsof rpmhttp://www.ebikes.ca/learn/hub-motors.html

http://www.celeroton.com/en/products/motors.html

Power range

From some watts

to millions of watts

Brushless DC motor (BLDC)

Permanent magnet rotor

Stator with windings

External commutation- integrated position sensosr,

usually hall sensors

Almost service free

Withstands well short term overloading- heat is transported effectively from the stator into the environment

More complex control system

BLDC commutation

BLDC commutation

http://www.mpoweruk.com/motorsbrushless.htm

AC motor

Two categories- Asynchronous

- Synchronous

Input usually three phase sinusoidal AC voltage

Only bearings need service

Control with variable frequency drive

http://www.pump-zone.com/topics/motors/ac-motors-part-two-three-phase-operation/page/0/1

AC field generation

Three field coils (per pole)- 120 °phase difference

http://tdflashzone.net23.net/1_6_Physics-Flashes.html

Synchronous AC: Permanent magnet

Permanent magnet AC motor is almost the same as BLDC.

Synchronous AC: Permanent magnet

https://www.ecnmag.com/article/2009/10/comparing-motor-control-techniques

Asynchronous AC: Induction

Stator field induces current in the bars which causes torque- Requires slip to create induced currents

Types- Squirrel cage

• Rotor made of conducting short circuited bars in steel frame

- Wound rotor

http://www.nidec.com/en-IN/technology/motor/basic/00026/?prt=1

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AC field generation

Three field coils (per pole)- 120 °phase difference

http://tdflashzone.net23.net/1_6_Physics-Flashes.html

Speed

For a 50 Hz three phase supply:

2 poles or 1 pair of poles =

3,000 RPM (minus the slip speed

= about 2,750 RPM or 6 -7% n)

n = 60 ∗ 0.93 ∗𝑓

𝑝

Asynchronous AC: Induction

http://people.ece.umn.edu/users/riaz/animations/sqmovies.html

Field weakening

Field weakening

http://ecomodder.com/forum/showthread.php/bsfc-chart-thread-post-em-if-you-got-1466-26.html

Losses for some PM motor

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http://www.ansys.com/de-de/products/electronics/electric-motors

Efficiency

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https://www.slideshare.net/mcburwell/techno-frontier-2013-m-burwell-ica-

ev-traction-motor-comparison-v18-eng

AC motor control

Rotational speed is determined

by the frequency of the input voltage

Frequency is controlled with variable frequency drive/inverter

(taajuusmuuttaja in Finnish)

- Rectification of the three phase voltage to DC voltage

- The rectified DC voltage is converted e.g. with pulse width modulation (PWM) to AC voltage with the needed frequency

- The AC voltage is fed to one of the three coils of the stator according to the sensors of the control system.

Variable frequency drive DC back to AC

Output AC is the average of pulse width modulated DC voltage

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Rated values of an induction motor

Rated values are for continuous duty- Rated voltage – winding insulation

- Rated current – ohmic resistive losses

- Rated field – magnetic saturation of the material

- Rated power = T*omega

For a dimensioning a motor for a variable load, it is possible to

calculate an equivalent constant load or simulate the system

Summary

Electric motors can be found anywhere and for any power rating

They have excellent efficiency at proper loading conditions- Usually this means a large enough rpm

Output power usually limited by temperature- Can be overloaded for a short while

Maximum rotating speed limited by back emf / supply voltage

Modeling

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Model

A simplified representation of a - System

- Physical object

- Process

- Thing

Theories are models of reality

Is used to- Estimate

- Predict

- Explain

- Describe

- Design

Better understanding leads to better results

Several areas to be modeled

Control code- Logic

- Control algorithms

Electronics- Input circuits – amplifiers, filters

- Output circuits – power electronics

Mechanics- Multi-body systems, kinematics, stresses, loads

- Fluid dynamics

Mechatronic system- Interaction between each area and their combined behaviour

Concept sketching

asd

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Topology models

Functional structure- Abstract

- Describes process

• No concrete implementation

- Helps in thinking different ways of doing the same

Analytical equations

Easy for static analysis

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Solve this by hand? ☺

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Mechanical design elements 1

Mechanical design elements 2

Hydraulical design elements

Electrical design elements

Physical analogies

Intensity Flow Inertor Capacitor Resistor Transformer Gyrator

Electricity Voltage Current Coil Capacitor Resistor Transformer Electrical

motor

Mechanics –

translation

Force Speed Mass Spring Friction Lever arm -

Mechanics –

rotation

Torque Angular

speed

Moment of

inertia

Torsional bar Friction Gears -

Fluid power Pressure Flow Tube Pressure

accumulator

Flow

restriction

Pressure

transformer

Hydrodynamic

s

Numerical Models - Simulations

Usually differential equations- Not all formulas can be analytically solved!

Adding more complexity makes it nearly impossible

to solve analytically -> use numerical methods to approximate

Numerical solvers have their own difficulties- Convergence

- Time stepping

- Numerical errors

Dynamic model of the system

Simulink

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Multibody simulation

Interaction of rigid or elastic bodies- Kinematic coinstraints such as joints

- Force elements such as springs and dampers

Shape of part not relevant- Only with collision detection

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CAE model

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Finite element method

1. Discretize the volume to

tiny cells

2. Solve basic equations for

each small cell- Fluid flow

- Electric and magnetic fields

- Mechanical stresses

- Heat flow

- Optics

- Everything

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Finite element model of solenoid’smagnetic circuitComsol Multiphysics

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Rapid prototyping

To get a feel of the real part

Can be used for

(limited?) testing- Depending on the material strength

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HIL simulation

Hardware In the Loop- The system is partly hardware partly software model

Including hard-to-model systems- For example rubber is surprisingly difficult to model

Testing controller against a model of a system- Motor controller controls simulated motor etc.

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Model verification with experiments

Solenoid actuator prototype

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-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9-2

0

2

4

6

8

10

12

14

16

Time [ms]

Cu

rre

nt [A

]

Simulation, 12L14, 3 mm coil height

Simulation, 12L14, 6 mm coil height

Simulation, Somaloy, 3 mm coil height

Simulation, Somaloy, 6 mm coil height

Measurement, Somaloy, 6 mm coil height

Measurement, 12L14, 6 mm coil height

Measurement, Somaloy, 3 mm coil height

Measurement, 12L14, 3 mm coil height

-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Time [ms]

Po

sitio

n [m

m]

Simulation, Permendur, 80 turns

Simulation, Permendur, 80 turns

Simulation, Permendur, 140 turns

Simulation, Permendur, 140 turns

Measurement, Permendur, 80 turns

Measurement, Permendur, 80 turns

Measurement, Permendur, 140 turns

Measurement, Permendur, 140 turns

Genetic solenoid optimization

Matlab

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Computational Fluid Dynamics

Ansys Fluent

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Improvement with CFD and 3D printing

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Resulting 16-valve manifold

Modeling electronics

KiCAD

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Electric circuit simulation

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SPICE = Simulation Program with Integrated Circuit Emphasis- Analog electronic circuit simulation

LTspice

Result

Microcontroller based 16-channel power electronics for a digital

valve system.

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Resulting prototype

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Modeling involved- Manual sketching

- Lots of analytical equations

- CAD

- Finite element

• Magnetic fields

o Genetic optimization

• Mechanical stresses

- Modeling of dynamics

• Simulink

- Computational Fluid Dynamics

- Electrical circuit

• Topological, physical

• Transient simulation

Modeling accuracy

Understand how your model and the program running it works- Or at least know its limits

• Is something relevant neglected?

Accuracy vs. computational cost- Time step, mesh refinement, turbulence model etc…

- 2D vs 3D model, using symmetries

- Desktop pc vs. computing clusters

Sanity check with simple simulation cases

Verification against experimental tests

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Simulation tools available to youGeneral

- Matlab – Simulink (via Aalto) (check also SimScape toolboxes)

- OpenModelica (open source)

Electronic circuits- Design: KiCAD (open source)

- Simulation: LTspice (free) – one of many SPICE-based programs

Finite element- Comsol Multiphysics (via Aalto)

- OpenFOAM (open source)

- Finite Element Method Magnetics (FEMM) (open source)

CAD- Creo, NX, Solid Edge (via Aalto) – contain also FEM solvers

- SketchUp, FreeCAD (free)

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