Abstract— Theoretical background included in part 1 of this

work has shown the wide variety that the wind energy industry is

offering in terms of electrical/electronic components and

configurations. Though the first part of the course provides the

student with an updated knowledge of the current technological

status of the wind energy conversion systems (WECS), from the

educational point of view the lectures are mainly teacher-centered

and some relevant skills for electrical engineers are not excited. In

spite of the breaking activities (videos, tests, challenging

questions, etc), the role of the student keeps being somewhat

passive. Aiming to overcome this shortcoming, this second part of

the course places the student in the center of the teaching-

learning process through hands-on work. The teacher becomes a

consultant and the student has to build a wind energy system

using simulation tools. Results of the experience prove that not

only the motivation of the students is increased, but also the

performance and acquisition of adequate competences.

Index Terms— Wind energy conversion systems, power

electronics, electrical machines, simulation tools.

I. INTRODUCTION

he type of competences that the wind energy industry

requires from electrical engineers is usually far from what

the graduated engineers have acquired throughout the degree.

The multidisciplinary nature of the WECS challenges the

engineer to have a proper training for this emerging

application [1]-[3]. Showing the student the technological

status of the currently manufactured WECS and all the

knowledge associated to these systems (electrical machines,

power converters, control theory, etc) is the first step to

prepare the student to be a proficient engineer in this area.

Nevertheless, it is well-known that teacher-centered

methodologies with a passive role of the student do not

provide the student with adequate competences [4].

The long-life learning can only be achieved by means of a

methodology that involves the student in the learning process

and challenges his mind to fully understand all related

concepts. On the other hand, simulation skills are more and

more considered at industries with a constant need for

research, development and innovation [5]-[7]. For these

reasons, the second part of the course proposes a problem-

based approach [8] through the use of simulations, letting the

students build their own wind energy system simulators. Since

the background of the students regarding simulation tools is

moderate, the students are guided in the simulation activities.

This second part of the course reinforces the theoretical

background of the first part but also provides the student with

basic knowledge about simulations. Assessment of this course

has been conducted both measuring the students’ satisfaction

and their performance, showing that a proper combination of

lectures and hands-on work can result in a complete

methodology that satisfies the student and promotes a wide

range of competences.

The second part of the paper is structured so that the

description of the simulation activities is included in section II

and the assessment of the whole course is discussed in section

III. The main conclusions are finally summarized in section

IV.

II. SIMULATION OF WIND ENERGY CONVERSION SYSTEMS

The second part of the course consists of the simulation of a

WECS, aiming to reinforce the concepts related to wind

energy and to develop simulation skills on the students. The

first step is the selection of a specific topology from the wide

variety shown in the first part of the course. The choice is

made on the basis of promoting simplicity and industrial

interest. Although the horse of the wind energy industry has

been the DFIG in partial power topologies [9], new

developments (e.g. Gamesa G-10) are selecting PMSGs and

using multiphase machines [10]-[13]. Since the mathematical

model of such generators is simpler, PMSG was therefore

selected for the simulation. Low voltage ride through

requirements [14]-[15] are also pushing wind energy industry

to full-power topologies and the most widely used type of

converter in WECS is the 2-level VSC. Based on that

Wind Energy Conversion System Course for

Electrical Engineers. Part 2: Simulation

activities

Mario J. Durán, Federico Barrero, Hugo Guzmán, Francisco Guzmán, Ana Pozo

T

978-1-4673-2486-1/12/$31.00 ©2012 IEEE 154

premises, the final topology selected to challenge the students

is shown in Fig. 1. Although the gearbox is optional depending

on the number of poles of the PMSG, it is included in the

simulation for the sake of completeness. The generator-side

analysis has been included in the lab sessions. Simulation of

the PWM and voltage oriented control (VOC) of the grid-side

converter (theoretically explained in Part 1) is somewhat

similar to PWM and FOC of the generator side, which

simplifies the teaching practice.

The content of this second part of the course is organized

following an inclusive strategy. Each element of the WECS

shown in Fig. 1 is simulated as an input/output box which is

connected to the previous elements in the simulation. During

the different stages of the course the student simultaneously

develops simulation skills and enhances WECS understanding.

The simulation of the different elements (table I of part 1) is

briefly described below:

1. Matlab/Simulink intro: .m files are executed from

Simulink using Matlab and S-function blocks and .mdl files

send simulation data to Matlab using to file and to workspace

blocks. Bidirectional connection Simulink-Matlab and Matlab-

simulink is thus exemplified to introduce the software. Later

on in the course the students can understand the benefits of this

procedure, which include running cascade simulations in loops

and easy and flexible representations of the results.

2. Wind Simulation: since the course is oriented to

electric/electronics engineering students, the simulation of the

wind is built from the empiric relations of (1) that provide the

wind power and low-speed shaft torque. The use of functions

is reinforced by simulating (1) through Matlab functions. At

the end of the simulation, the students are asked to obtain the

power/torque curves as in Fig. 2. Tip speed ratio, maximum

power point tracking (MPPT) and pitch control, explained in

part 1, are reviewed and discussed.

),(2

1 3 λβρ pwsam CVAP =

w

tt

w

t

V

R

V

V ωλ ==

1

4.18

14.2

1

2.13002.058.0151

73.0),(λββ

λλβ

−

−−−= eCp

(1)

0 1 2 3 4 5 6 7 8 90

1

2

3

4

5

6

7

8

9

10x 10

5 WIND TORQUE CURVE

λ

Tw

(N

m)

β = 0

β = 3

β = 6

β = 9

MPPT

Fig. 2. Wind torque as a function of the tip speed ratio and

pitch.

3. Gearbox simulation: the gearbox is considered to be

lossless for the sake of simplicity. The rotational speed of the

low-speed shaft in the blades is transformed to provide the

high-speed at the generator shaft using (2). High speed,

medium speed and low speed (gearless) concepts are reviewed

and Matlab plotting options are further explored.

blades

gb

turbinek

ωω1

= blades

gbturbine T

kT

1= (2)

4. Mechanical system simulation: the rotational equation of

the wind generator (3) is implemented next. The students

implement a differential equation in Simulink for the first time,

writing the equation in state-space form to avoid derivative

blocks that are known to cause simulation divergence. The

inertia shown in (3) collects the whole power train but it is

intentionally lowered for simulation purposes.

( )eturbine

turbine TTJdt

d−=

1ω (3)

Fig. 1. Full-power WECS simulated in the second part of the course.

155

5. PMSG model and control: although the design of the

simulation has been made step-by-step to help the students’

implementation, the permanent magnet generator model and

control are both included in the same stage because the

generator without control easily leads to simulation

divergence. The PMSG is implemented in Simulink using (4),

where P is the number of pairs of poles, Ld is the direct

inductance, Lq is the quadrature inductance, R is the stator

resistance, λm is the PM flux and ωelec is the electrical speed of

the generator.

The students are asked to implement the state-space

equations of (4) in Simulink using the parameter of a 2MW

PMSG well-defined in [16].

( )

( )

( )( )qdqdqme

melecqddelecq

q

q

dqqelecd

d

d

iiLLiPT

RiiLuLdt

di

RiiLuLdt

di

−−=

−−−=

−+=

λ

λωω

ω

2

3

1

1

(4)

The field oriented control (FOC), previously reviewed in

part 1, is also implemented in Simulink using equation (5),

which includes the PI controllers (for outer speed and inner

current control loops) and the decoupling terms (ed and eq) that

are added as feedforward signals. The zero d-current (ZDC)

criterion is applied for convenience. The inverter is considered

as ideal (vd=vd* and vq=vq

*) until the next stage.

( ) ( )( )∫ −⋅+−⋅= tintpnq nnknnkitt

***

[ ] ( )[ ]dddifddpfd eiikiikv +−⋅+−⋅= ∫ ***

[ ] ( )[ ]qqitqptq eiikiikv

qq+−⋅+−⋅= ∫ *** (5)

elecqqd iLe ω−= elecddelecmq iLe ωωλ +=

Implementation of (4) and (5), together with the Clarke and

Park transformations, allows the simulation of the wind

generator in a controlled manner. At this stage, the students are

asked to:

� Start the wind generator.

� Simulate sudden wind gusts (Fig. 3).

� Include noise in the current measurements and

evaluate the impact on the control performance.

� Modify the pitch angle during the simulation.

� Make multiple simulations in cascade (from .m file)

and plot 3D figures (Fig. 4).

6. VSC model and PWM design: at this stage the students

include the real stator voltages provided by the voltage source

converter (VSC) and implement a carrier-based pulse width

modulation (PWM) scheme. The inverter is considered ideal

and the stator phase voltages are calculated from the switching

functions Si and the value of the DC link voltage using (6).

( )

( )

( ) dcbacc

dccabb

dccbaa

VSSSv

VSSSv

VSSSv

−−=

−−=

−−=

23

1

23

1

23

1

(6)

The applied PWM scheme is carrier-based method with a

triangular carrier signal at 1 kHz. The students are then asked

to:

� Test the WECS with PWM supply (Fig 5).

� Modify the DC link voltage to review the modulation

index explanation.

� Modify the switching frequency to evaluate its

impact on the system performance.

� Calculate the total harmonic distortion (THD) and

the spectrum of the generated stator currents, using

the PowerGui from the SimPowerSystems toolbox

(Fig. 6).

7. Creative simulation time: students are asked to propose

their own simulation features and WECS performance, aiming

to promote deep understanding [17]. The course reserves some

time to promote creative thinking within the lab time, arising

the teacher a secondary role in the educational process. This

role is devoted with suggesting actions from time to time to

guide students’ proposals, overtaking any lack of initiative.

0 2 4 6 8 10 12 14 16 18 200

10

20

nt* ,

nt (

rpm

)

nt*

nt

0 2 4 6 8 10 12 14 16 18 20-2000

-1000

0

1000

i q*,

i q (

A)

iq*

iq

0 2 4 6 8 10 12 14 16 18 20-1

0

1

i d*,

i d (

A)

id*

id

0 2 4 6 8 10 12 14 16 18 20-1000

0

1000

v a,

v b,

v c (

V)

va

vb

vc

0 2 4 6 8 10 12 14 16 18 20-2000

0

2000

Time(s)

i a,

i b,

i c (

A)

ia

ib

ic

Fig. 3. PMSG acceleration, wind gust at t =7.8 s and pitch

angle moved to 9º at t = 13 s.

156

0

2000

4000

6000

8000

10000

6

7

8

9

10

14.9

15

15.1

15.2

15.3

15.4

15.5

15.6

kpn

PMSG transient after a wind gust

Time (s)

PM

SG

sp

ee

d (

rpm

)

15

15.1

15.2

15.3

15.4

15.5

15.6

15.7

15.8

Fig. 4. Transient of the PMSG after a wind gust using different

values of the PI speed loop controller defined in (5).

1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2-1000

0

1000

v a,

v b,

v c (

V)

va

vb

vc

0 2 4 6 8 10 12 14 16 18 20

-2000

-1000

0

i q*,

i q (

A)

iq*

iq

0 2 4 6 8 10 12 14 16 18 20-100

0

100

i d*,

i d (

A)

id*

id

Fig. 5. Stator voltage and d-q currents with PWM supply.

At the end of these seven steps the students have successfully

implemented the generator-side control. The grid side is not

considered due to its similarity. Each stage includes an

input/output box and all boxes are finally connected in the

complete system (see Fig. 7). Then, the main features of part 2

can be summarized as follows:

� The whole simulator is built step by step by students,

starting from the scratch to promote simulation skills.

� The selected WECS is as simple as possible,

approaching the student to industry standards (e.g.

FOC, PWM).

� The full-power WECS configuration has a wide

technological variety and includes useful concepts for

electric/electronic engineers (e.g. modulation index,

THD, inner and outer control loops, transients, noise,

etc.).

� The simulation is directly connected and reinforces

the concepts included in the theoretical part of the

course (part 1).

� Implementation has a low cost for the School of

Engineering.

� Simulation skills are increased, which offer a

multidisciplinary background to the students because

the whole simulation block/part has been

implemented from the grounds of the state-space

equations using generic Simulink blocks and simple

Matlab code.

At the end of the course the students are asked to complete

the WECS by simulating the grid-side control using voltage

oriented control (VOC) to regulate the DC link voltage and the

reactive power injected in the network. A voltage dip is

suggested to be analyzed and reported showing the behavior of

both generator and grid-side performance.

III. RESULTS

The teaching experience has been evaluated using a survey

of 43 items [18] that contains redundancy in different

questions to evaluate the same dimension. It has been

anonymously answered by the students both before and after

the course to verify the satisfaction of the learners and to

improve the teaching methodology. Before the course, the

students were asked to answer the survey with their general

expectations of a course in the present context (engineering

degrees at the University of Malaga). After the course, the

same students were also asked to fill the same survey to detect

the weakness and strengths of the course, comparing with the

context.

13 13.05 13.1 13.15 13.2 13.25 13.3 13.35 13.4

-500

0

500

FFT window: 4 of 195 cycles of selected signal

Time (s)

0 500 1000 1500 2000 2500 3000 3500 40000

20

40

60

80

100

Frequency (Hz)

Fundamental (9.75Hz) = 535.8 , THD= 35.73%

Mag (

% o

f F

undam

enta

l)

Fig. 6. Waveform, spectrum and THD of the PWM supply

using PowerGui.

157

----------------------------- WIND EQUATIONS ----------------------- ----------------------------- GEARBOX -----------------------

-------------------------------- MECHANICAL SYSTEM ------------------------------

--------------------------- ELECTRICAL GENERATOR --------------------------

------------------------------------------------------------- PERMANENT MAGNET SYNCHORONOUS GENERATOR ----------------------------------------------------------

SPEED LOOP Q-CURRENT LOOP D-CURRENT LOOP

CHAPTER 7: SIMULATION OF THE POWER CONVERTER MODULATION (Example 7_1)

------------------ VOLTAGE SOURCE INVERTER -------------

WIND SPEED

TURBINE SPEED

WIND TORQUE

WIND POWER

-------------- VOLTAGE MONITORING --------

id *

0

WIND POWER

Vw (m/s)

SPEED

REFERENCE

PWM MODULATED VSI

Vphar

Vphbr

Vphcr

vpha

vphb

vphc

PITCH

PID

PID

PID

PHASE CURRENTS

Manual Switch

MECHANICAL SYSTEM

[welec ]

[id ]

[Te ]

[iq ]

[nt_ref][id_ref ]

[wt ]

[vd_ref ]

[vq_ref ][iq_ref ]

[w]

[T ][va ]

[Tw]

[vc ]

[vb ][Pm]

[Vw]

-1

GEARBOX

[vb _r]

[idm ]

[iq _ref]

[iqm ]

[wt ]

[Tw]

[nt ]

[va _r]

[ed ]

[Te ]

[eq ]

[welec ]

[vq ]

[vd ]

[vc _r]

[T ]

[w]

ELECTRICAL GENERATOR

vd

vq

welec

id

iq

Te

Fig. 7. Scheme of the different subsystems simulated by students to build the generator-side control of the WECS.

The results of the different dimensions (understanding,

motivation, etc) for the pre and post evaluation are reported in

Table I and Fig. 8. It is considered the feedback from the

different editions of the course with 52 students on average.

The mean values of the scores are included in the form

before/after.

Since the two parts of the course are quite of a different

nature, the survey was also answered at the end of each part to

verify the students’ perception of the lectures and simulation

tasks (Fig. 8).

TABLE I

SURVEY TO VERIFY STUDENTS’ SATISFACTION

Dimension Pre/post

score

Dimension Pre/post

score

Course assessment 2.9 / 4.5 Satisfaction 3.3 / 4.5

Lecturer

Assessment

2.9 / 4.6 Motivation 2.5 / 4.5

Content 2.8 / 4.1 Material 3 / 4.2

Interactivity 2.6 / 3.8 Methodology 3 / 4.4

Understanding 2.8 / 4.1 Application 2.7 / 4.4

Results show that all dimensions have been improved, being

especially remarkable the increase of the motivation (80%)

and application sense (63%). The general course assessment

also shows a clear improvement (55%). In relation to the

partial scores, differences in the survey answers are small, and

both parts of the course are satisfactory for the students.

An objective assessment of the first part of the course was

also conducted using a test with 72 multiple-choice questions

[18] asking for general concepts of the different chapters

previously listed in Table I of part 1. Results of Fig. 9 show

that the test was correctly answered in a percentage higher than

80% on average for all chapters of the course, showing that the

main concepts were correctly understood.

In the second part of the course, all students were able to

build the complete simulation although some of them required

more help depending on the previous background. It is also

noticeable that optional subjects on electrical machines (EM)

and power electronics (PE) at the University of Málaga have

increased the number of students by 33 and 50% respectively

in the course 2011/2012.

158

0 1 2 3 4 5

Course

Lecturer

Content

Interactivity

Understand

Satisfaction

Motivation

Material

Method.

Application

Before the course After the course

0 1 2 3 4 5

Course Part 1 Course Part 2

0 1 2 3 4 5

Course

Lecturer

Content

Interactivity

Understand

Satisfaction

Motivation

Material

Method.

Application

Before the course After the course

0 1 2 3 4 5

Course Part 1 Course Part 2

Fig. 8. Satisfaction of the students attending the course.

0 20 40 60 80 100

WE situation

FAQS

EM & PE

Topologies

Regulation

Partial-Power

Full-Power

Trends

Fig. 9. Objective assessment through multiple choice tests

(Part 1).

IV. CONCLUSIONS

After initial skepticism and problems, principally due to the

power grid stability, renewable energies are now widely seen

as a real alternative to conventional energy sources. Wind

energy systems are nowadays the most popular choice among

all renewable energies. A high diversity of electrical machines,

power converters, control strategies and topologies are

involved into a modern wind generator. In this paper, a wind

generator has been placed into the centre of interest of a course

about electrical machines and power converters to increase

motivation of the students with a high industry-oriented end-

application. An educational methodology that combines

valuable state-of-the-art information about the technology and

hands-on simulation work is proposed. The experience has

been tested comparing with the contextual educational

environment (engineering degrees at the University of Malaga,

Spain). Obtained results prove that the proposed pedagogical

scheme satisfies the students and promotes a wide variety of

competences. The proposal can be easily extended thanks to its

flexible and low-cost procedures.

ACKNOWLEDGEMENT

The authors gratefully acknowledge the Spanish

Government and the European Union (FEDER funds) for the

economical support provided within the National Research,

Development and Innovation Plan, DPI2011-25396.

REFERENCES

[1] N. Mohan, A.K. Jain, P. Jose, R. Ayyanar, “Teaching utility applications of power electronics in a first course on power systems,” IEEE Transactions on Education, vol. 19, no. 1, pp. 40–47, 2004.

[2] J.J. Rodriguez-Andina, L. Gomes, S. Bogosyan, “Current Trends in Industrial Electronics Education,” IEEE Transactions on Education, vol. 57, no. 10, pp. 3245–3252, 2010.

[3] M. Chunting, Z.J. Shen, T. Ceccarelli, “Continuing education in power electronics,” IEEE Transactions on Education, vol. 48, no. 1, pp. 183–190, 2005.

[4] S.L. Toral, F. Barrero, M.R. Martinez-Torres, S. Gallardo, M. Duran, “Modeling Learner Satisfaction in an Electronic Instrumentation and Measurement Course Using Structural Equation Models,” IEEE Transactions on Education, vol. 52, no. 1, pp. 190–199, 2009.

[5] M.J. Durán, S. Gallardo, S.L. Toral, M.R. Martínez-Torres, F. Barrero, “A learning methodology using Matlab/Simulink for undergraduate electrical engineering courses attending to learner satisfaction outcomes,” International Journal of Technology and Design Education, Vol. 17, no. 1, pp. 55-73, 2007.

[6] L. Shuhui, R. Challoo, “Restructuring an electric Machinery course with an integrative approach and computer-assisted teaching methodology,” IEEE Transactions on Education, vol. 49, no. 1, pp. 16–28, 2006.

[7] J.R. Arribas, C. Veganzaones, F. Blázquez, C.A. Platero, D. Ramirez, S. Martínez, J.A. Sánchez, N.H. Martínez “Computer-based simulation and scaled laboratory bench for teaching and training of engineers on the control of doubly-fed induction generators,” IEEE Transactions on Power Systems, vol. 26, no. 3, pp. 1534–1543, 2011.

[8] D. Santos-Martin, J. Alonso-Martínez, J. E. Carrasco, S. Arnaltes, “Problem-based learning in wind energy using virtual and real stups,” IEEE Transactions on Education, in press, 2012.

[9] B. Andresen, J. Birk, “A high power density converter system for the Gamesa G10x 4,5 MW wind turbine,” in Proc. EPE, pp. 1-8, 2007.

[10] M.J. Duran, S. Kouro, B. Wu, E. Levi, F. Barrero, S. Alepuz, “Six-phase PMSG wind energy conversion system based on medium-voltage multilevel converter,” in Proc. EPE, pp. 1-10, 2011.

[11] M.J. Duran, F. Salas, M.R. Arahal, “Bifurcation analysis of five–phase

induction motor drives with third harmonic injection,” IEEE Trans. on

Industrial Electronics, vol. 55, no. 5, pp. 2006−2014, 2008. [12] M.J. Durán, J. Prieto, F. Barrero, S. Toral, “Predictive Current Control

of Dual Three–phase Drives using Restrained Search Techniques,” IEEE Trans. on Industrial Electronics, vol. 58, no. 8, pp. 3253–3263, 2011.

[13] M.J. Durán, J. Prieto, F. Barrero, S. Toral, “Reduction of Common-Mode Voltage in Five–phase Induction Motor Drives Using Predictive Control Techniques,” IEEE Trans. on Industry Applications, (accepted for publication), 2012.

[14] C. Jauch, J. Matevosyan, T. Ackerman, S. Bolik, “International comparison of requirements for connection of wind turbines to power systems,” Wind Energy, vol. 8, no. 3, pp. 295-306, 2005.

[15] Red Eléctrica de España. P.O. 12.3: Requisitos de Respuesta frente a Huecos de Tensión de las Instalaciones de Producción en Régimen Especial [Online]. Available: http://www.ree.es/operacion/pdf/po/ PO_resol_12.3_Respuesta_huecos_eolica.pdf.

[16] B. Wu, Y. Lang, N. Zargari, S. Kouro, “Power conversion and control of wind energy systems,” Wiley, 2011.

[17] J. Biggs and C. Tang, Teaching for Quality Learning at University, 3rd ed. Maidenhead, U.K.: Open Univ. Press, 2007.

[18] http://epropias.cv.uma.es/course/view.php?id=551&edit=off&sesskey=J5y18Avsrz

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