Wind Turbine and Battery Energy Storage System: Connection ...

UNIVERSIDAD DE LOS ANDES

Wind Turbine and Battery Energy Storage

System: Connection Impact Analysis

Natalia Avendaño Prieto

Submitted in fullment of the requirements for the Degree of

Electrical Engineer

Engineering Faculty

Department of Electrical and Electronic Engineering

June 18, 2016

http://www.uniandes.edu.co/

mailto:[email protected]

https://ingenieria.uniandes.edu.co/

https://iee.uniandes.edu.co/

Author's Declaration

1. I am aware that any fraud in this thesis is considered a serious oense in college. By signing,

deliver and present this proposal Thesis Or Graduation Project, I express testimony that this

proposal was developed in accordance with standards established by the University. Similarly,

assure you that I did not participate in any kind Of fraud and at work concepts or ideas that

are taken from other sources are properly expressed.

2. I am aware that the work that I perform include ideas and concepts Of the author and the

Advisor and may include course materials or previous work in the University and therefore,

give proper credit and I will use this material in accordance with human rights standards

copyright. Likewise, I will not publications, reports, articles and presentations at conferences,

seminars or conferences without review or authorization of the Counsel who represent in this

case the University.

Signature:

Name: Natalia Avendaño Prieto

Student Number ID: 201112745

C.C.: 1.020.788.232

Date: June 24, 2016

i


Abstract

Engineering Faculty


This document describes the analysis connection between a wind farm with 21 MW capacity and

an energy storage system with the electrical grid. It is explained and analyzed the voltage drop

test in a wind farm according to IEC 61400-21 standard. Moreover, it is specied the battery sizing

and model that it is used in the project; likewise, the converters model and control to charge and

discharge the battery correctly. Finally, there is a power quality analysis between the connection of

the design battery and the grid.





Abstract

Engineering Faculty


Este documento describe el análisis de la conexión entre un parque eólico con capacidad de 21 MW y

almacenamiento de energía con la red eléctrica. Se explica y analiza la caída de voltaje en el parque

eólico de acuerdo al estándar IEC 61400-21. Adicionalmente, se especica la capacidad y el modelo

de la batería que se utiliza en el proyecto. Asimismo, el modelo y control de los conversores para

cargar y descargar la batería correctamente. Finalmente, se da un análisis de calidad de potencia

entre la conexión de la batería diseñada y la red.




Acknowledgements

I thank my family for all the support and lessons they have given me throughout my life. To my

parents, Carlos Alfonso Avendaño Cruz y Martha Ligia Prieto Casella, I am grateful for all the

eort and work they did to contribute to my studies, future, help me to reach my goals and to

teach me to be persistent and ght for my dreams. My sister Catalina, for being my role model

and give the passion about traveling and extreme sports. My brother Carlos Jose, who doesn't get

tired to see me as his role model, action that give me courage to go forward, facing any adversity,

also for giving me his trust and the moments that he cheers me up. Furthermore, I want to thank

my uncle Raul Avendaño, my aunt Luz Marina Ovalle and my cousin Carolina Avendaño, who were

an unconditional support during my student life and promote my research internship at Cornell

University; which was one of the greatest and rewarding experiences that I would ever have in my

personal and academic life

My adviser, professor Gustavo Ramos, who has managed to guide me patiently. David Felipe Celeita

and Miguel Hernandez, who were patients and helped me to solve any worry and problem that I

had during the project, and without them this project would not be the same.

iv

Contents

Author's Declaration i

Abstract ii

Acknowledgements iv

List of Figures vii

List of Tables ix

Abbreviations x

1 Introduction 1

2 Problem Context 2

2.1 General Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.2 Specic Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.3 Description of the solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3 State of Art 4

3.1 Wind turbine connection to the grid . . . . . . . . . . . . . . . . . . . . . . . . . . . 43.1.1 Standard IEC-61400-21- Measurement and assessment of power quality char-

acteristics of grid connected wind turbines . . . . . . . . . . . . . . . . . . . . 53.1.1.1 Response to voltage drops . . . . . . . . . . . . . . . . . . . . . . . . 5

3.2 Energy Storage System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.2.1 Energy Storage System Applications . . . . . . . . . . . . . . . . . . . . . . . 73.2.2 Energy Storage Systems Technologies . . . . . . . . . . . . . . . . . . . . . . . 7

4 Methodology 11

5 System Design 13

5.1 IEC 61400-21 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

v

Contents vi

5.1.1 Short circuit analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135.1.1.1 Positive Sequence Analysis . . . . . . . . . . . . . . . . . . . . . . . 155.1.1.2 Negative Sequence Analysis . . . . . . . . . . . . . . . . . . . . . . . 175.1.1.3 Zero Sequence Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 17

5.1.2 Three Phase Fault Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205.1.3 Two Phase Fault to Ground Analysis . . . . . . . . . . . . . . . . . . . . . . . 21

5.2 Case Study System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225.2.1 Bidirectional Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225.2.2 DC/AC Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

6 Simulation Results 25

6.1 Voltage Drop Validation Test - IEC 61400-21 Standard . . . . . . . . . . . . . . . . . 256.1.1 Three Phase Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256.1.2 Two Phase Fault to Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

6.2 Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306.2.1 Battery Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306.2.2 Wind Farm and Battery connection to the grid . . . . . . . . . . . . . . . . . 31

7 Discussion and Conclusion 34

7.1 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347.2 Conclusion y Further Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

A Appendix 36

A.1 IEC 61400-21 Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36A.1.1 Three Phase Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36A.1.2 Two Phase Fault to Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

A.2 Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

List of Figures

3.1 System with short circuit emulator for testing wind turbine response to temporaryvoltage drop [1] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.2 Positioning of ESS technologies [2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.1 Input and output variables for the project . . . . . . . . . . . . . . . . . . . . . . . . 114.2 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5.1 System Design to test voltage drop in the wind farm . . . . . . . . . . . . . . . . . . 145.2 Line conductors distance [3] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145.3 Positive sequence short circuit system diagram and thevenin's equivalent. [4] . . . . . 165.4 Negative sequence short circuit system diagram and thevenin's equivalent . . . . . . 185.5 Zero sequence short circuit system diagram and thevenin's equivalent . . . . . . . . . 195.6 Three phase fault equivalent circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205.7 Two phase fault to ground equivalent circuit . . . . . . . . . . . . . . . . . . . . . . . 215.8 Case Study Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225.9 Bidirectional Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235.10 DC/AC Converter topology: (a) Rectier (b) PWM Inverter . . . . . . . . . . . . . 24

6.1 Wind Farm System on Matlab/Simulink-Three phase fault . . . . . . . . . . . . . . . 256.2 Pn = 90%, VDrop = 0.9pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 266.3 Pn = 90%, VDrop = 0.5pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 266.4 Pn = 90%, VDrop = 0.2pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 276.5 Wind Farm System on Matlab/Simulink-Two phase fault to ground . . . . . . . . . . 286.6 Pn = 90%, VDrop = 0.9pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 286.7 Pn = 90%, VDrop = 0.5pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 296.8 Pn = 90%, VDrop = 0.2pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 296.9 (a) Battery Percentage State of Charge (b) Bidirectional Converter Voltage Output . 316.10 Case Study Diagram on Matlab/Simulink . . . . . . . . . . . . . . . . . . . . . . . . 32

A.1 Pn = 30%, VDrop = 0.9pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 36A.2 Pn = 10%, VDrop = 0.9pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 37A.3 Pn = 30%, VDrop = 0.5pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 37A.4 Pn = 10%, VDrop = 0.5pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 38A.5 Pn = 30%, VDrop = 0.2pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 38A.6 Pn = 10%, VDrop = 0.2pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 39

vii

List of Figures viii

A.7 Pn = 30%, VDrop = 0.9pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 39A.8 Pn = 10%, VDrop = 0.9pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 40A.9 Pn = 30%, VDrop = 0.5pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 40A.10 Pn = 10%, VDrop = 0.5pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 41A.11 Pn = 30%, VDrop = 0.2pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 41A.12 Pn = 10%, VDrop = 0.2pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals 42A.13 Battery output voltage signal and %THD (a) without 5th,7th, 11th and 13th order

harmonic lter, (b)with 5th,7th, 11th and 13th order harmonic lter . . . . . . . . . 42A.14 Battery output current signal and %THD (a) without 5th,7th, 11th and 13th order

harmonic lter, (b)with 5th,7th, 11th and 13th order harmonic lter . . . . . . . . . 43A.15 Battery Disconnected from Grid. Voltage pu in (a) Wind Farm Terminals and (c) Load. 43A.16 Battery Disconnected from Grid. Active and Reactive Power in (a) Network Equiva-

lent (b) Wind Farm Terminals (c) Load . . . . . . . . . . . . . . . . . . . . . . . . . 44A.17 Battery Connected to Grid. Voltage pu in (a) Wind Farm Terminals (b) Load and

(c) Battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45A.18 Battery Connected to Grid. Active and Reactive Power in (a) Network Equivalent

(b) Wind Farm Terminals (c) Load and (d) Battery . . . . . . . . . . . . . . . . . . . 46

List of Tables

3.1 Specication of voltage drops test [1] . . . . . . . . . . . . . . . . . . . . . . . . . . . 63.2 Dention of Energy Storage Applications [2] . . . . . . . . . . . . . . . . . . . . . . . 83.3 ESS Applications [2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.4 ESS technologies characteristics [2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5.1 Conductor Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145.2 Line Impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145.3 System Sequence Impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205.4 Three phase fault impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205.5 Three phase fault impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215.6 Bidirectional Converter and Battery Parameters . . . . . . . . . . . . . . . . . . . . . 235.7 PWM inverter-LC lter parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

6.1 Three Phase Fault-Voltage Drop at Wind Farm Terminals with Dierent Rated ActivePower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

6.2 Two Phase Fault to Ground-Voltage Drop at Wind Farm Terminals with dierentrated active power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

6.3 Battery State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316.4 Voltage in the system without and with battery connection to grid . . . . . . . . . . 336.5 Active power in the system without and with battery connection to grid . . . . . . . 33

ix

Abbreviations

C&I Commercial and Industrial

DCR DC and Resistance

DFIG Doubly-fed and Electric Machine

ESR Equivalent and Series Resistance

ESS Energy Storage System

UPME Unidad de Planeación Minero Energética

THD Total Harmonic Distortion

TOU Time of Use

T&D Transmission and Distribution

WF Wind Farm

x

Chapter 1

Introduction

During the past 10 years, there have been a high interest about the development and implementation

of renewable and clean energies, such as photo-voltaic, wind, hydraulic, geothermic and biomass

energy. However, some of these energy sources are highly uctuating through the power generation,

such as wind and solar energy systems [5]. In relation to wind energy, a cause of it is intermittent,

indeterminate and unpredictable, it is dicult the integration between wind turbines and the electric

grid; likewise, the wind farms have limitation to supply electrical power to the grid. Therefore, in

order to compensate the intermittency generated by wind turbines and increase the stability in the

system, it is necessary to include energy storage systems or batteries to wind farms [6].

By controlling the power in the grid using ESS or batteries technologies, it is a way to create

stability in the system. The batteries are devices that dynamically can adjust active and reactive

power. They can control power oscillations with low frequency and can improve the system stability

[7]. Moreover, including ESS to a wind farm, it is possible to mitigate the generation volatility

and improve the physical availability aligning the peak generation at peak loads. Furthermore,

it is possible to reduce the imbalance caused by programming errors, reducing the congestion in

transmission system reliability.

1

Chapter 2

Problem Context

A consequence of the risk of conventional energy generation and environmental awareness, the de-

velopment of renewable resources have increased in the past 10 years. The wind energy is renewable

resource that generates electrical energy through wind turbines. In 2010, the overall wind turbine

capacity in China has exceeded 40000 MW, and expect to generate 150000 MW in 2020 when 7

large wind farms projects of 10000 MW is completed [8]. In the Colombian case, in 2015 UPME

sign three wind power generation projects, where those projects contribute 474 MW to the grid [9].

The high volatility and intermittency of wind power systems creates a great uncertainty in the

reliability of this type of generation system. Moreover, it is dicult to developed large scale wind

farms, because its impact over the grid on power dispatch, power quality and system stability increase

with the penetration level [8].

2.1 General Purpose

Given the above scenario, the objective of this graduation project is analyze the connection impact

between an energy storage system with a wind farm during a system voltage drop.

2

Chapter 2. Problem Context 3

2.2 Specic Objectives

1. Research and analyze the state of art from the dierent energy storage systems technologies.

2. Asses the connection performance between the wind turbine and the grid.

3. Asses the connection performance between the battery and the grid.

4. Make a power quality analysis about the battery connection to the grid.

5. Validate the developed system in a computational software.

2.3 Description of the solution

In a wind farm the ESS is used to keep constant the active power since the variations from the

wind power. The extra power generated can be stored in the batteries at hours of low demand. The

combination between batteries and wind power synthesized the output wave when there is reactive

power consumption or injection, allowing the active power ow required by the load [8].

It is dicult to store large quantities of electrical energy; thus, its production and consumption

must be balanced in real time. During the past years, the large quantity of electrical energy stored

have been solve through large-scale energy storage system technologies. Hence, large-scale ESS is

considered as a potential technology to improve the exibility and receptivity of power grid and

solving the coordination problem of intermittent energy of wind power [8].

Chapter 3

State of Art

3.1 Wind turbine connection to the grid

I. Voltage Fluctuation on grid: The wind variations generates power uctuation at the wind

turbines. The uctuations generate sag and swell voltages on the grid; where the amplitude

depends on grid strength, network impedance and power factor. Nowadays, the power quality

assessment and measurement on grid connected to wind turbine is dene by IEC 61400-21

standard. In this standard is stated that 10 minute average of voltage uctuation should be

within +/- 5% of nominal value [10].

The start up of wind turbines causes a swell voltage on the grid, where in most cases a reduction

of 3% is acceptable. In IEC 61400-3-7 standard are dened the assessment of emission limit

for uctuation load [10].

On the other hand, the behavior of wind farms in presence of voltage drops in the electrical

network is a problem to be aware. The voltages drops are caused by faults in the network,

which are characterized by their amplitudes and duration. Those voltage dips creates doubts

about the wind power generation capacity to remain connected during and after the fault [11].

II. Reactive Power: The traditional wind turbine works with induction generator. Thus, the

generator requires reactive power from the grid to operate correctly. On this type of wind

turbines are used xed capacitor to compensate the reactive power. As a result, the risk of

4

Chapter 3. State of Art 5

self excitation may occur during o grid operation. In this manner, sensitive equipment may

be subjected to over/under voltage and frequency operation [10].

III. Harmonics The harmonic emission is an important issue for the connection between wind

turbines and the grid. The harmonics can cause overheating in the generator and other prob-

lems because it may result in voltage distortion and torque pulsations [12].

The wind turbines emit low-order harmonics and interharmonics, which are non-integer har-

monics. Low-order harmonics are ltered with self commuted converters, that are used in the

modern turbines. Nevertheless, those converters emit high-order harmonics to the grid. In

the IEC 61000-4-7 and IEC 61400-21 are dened the requirements for the measurement of

harmonics, interharmonics and higher current components [12].

3.1.1 Standard IEC-61400-21- Measurement and assessment of power quality

characteristics of grid connected wind turbines

The IEC 61400-21 standard is the reference normative for the certication of power quality of

wind turbines. The procedures and methodology for the measurement and assessment of power

quality characteristics of grid-connected turbines are determined by this standard. According to

this standard, the measurements should be performed during normal and switching operations for

voltage drops, harmonic content, icker, and active and reactive power [11].

Since this graduation project focus on voltage drops on wind turbines, this section will explained

the response to voltage drops on wind turbines according to IEC-61400-21 Standard [1].

3.1.1.1 Response to voltage drops

According to item I. the voltage drops are a main problem for wind farms connection to the grid.

Hence, the IEC 61400-21 standard gives a methodology to check the wind farms behavior in case of

voltage drops.

The test must be apply at the wind turbine terminals when it is disconnected from the grid. The

wind turbines response to voltage drops shall be stated at two dierent situations: the rst one a)


between 10% and 30% of Pn (Rated active power) and the second b) above 90% Pn. On table 3.1

are specied the voltage drops magnitudes and duration that have to be tested at the wind turbine

terminals [1].

Table 3.1: Specication of voltage drops test [1]

CaseMagnitude of voltagephase to phase (pu)

Magnitude of positivesequence voltage (pu)

Duration(s)

V D11 0.9 ± 0.05 0.9 ± 0.05 0.5 ± 0.02V D21 0.5 ± 0.05 0.5 ± 0.05 0.5 ± 0.02V D31 0.2 ± 0.05 0.2 ± 0.05 0.5 ± 0.02V D42 0.9 ± 0.05 0.95 ± 0.05 0.5 ± 0.02V D52 0.5 ± 0.05 0.75 ± 0.05 0.5 ± 0.02V D62 0.2 ± 0.05 0.60 ± 0.05 0.5 ± 0.021 Symmetrical three-phase voltage drop.2 Symmetrical two-phase voltage drop.

The wind turbine response to the temporary drops specied in table 3.1 shall include time-series of

active power, reactive power, active current, reactive current and voltage at wind turbine terminals

for the time shortly prior to the voltage drop and until the eect of the voltage drop has extinguished.

The test can be carried out using the the set-up illustrated in gure 3.1; where the voltage drops

are created by a short-circuit emulator that connects the three or two phases to ground through an

impedance [11].

𝑍1

𝑍2

𝑆

𝑊𝑇

Figure 3.1: System with short circuit emulator for testing wind turbine response to temporaryvoltage drop [1]


The voltage drop is created by connecting the impedance Z2 by the switch S, which must be able to

control the time between connection and disconnection of Z2. The impedance of Z2 should be adjust

to get the voltage magnitudes specied in table 3.1 at the wind turbine terminals. The impedance

of Z1 is for limiting the eect of the short circuit on the upstream grid. The value of this impedance

should be selected with the purpose that the voltage drop testing won't have a signicantly eect

at the upstream grid and the transient response of the wind turbine [11].

3.2 Energy Storage System

3.2.1 Energy Storage System Applications

The energy storage systems (ESS) are applied on photo-voltaic and wind energy connection to the

grid. The ESS stored energy near the loads, support the transmission and distribution systems,

connection of electrical vehicles, and have commercial, industrial and residential applications [2].

The ESS help to voltage and frequency regulation, enhancement of power quality, peak-shaving,

load leveling, reserve capacity, and so on to improve the renewable resources integration to the

grid,[13]. On table 3.2 there are 9 energy storage systems applications.

3.2.2 Energy Storage Systems Technologies

There are dierent ESS technologies for various applications. On table 3.4, there is the application

(describe on table 3.3) for each technology and their respective capacity, power, duration, and e-

ciency. Moreover, on gure 3.2 is graphically explained the characteristics of various ESS technology

options in terms of system power rating (X-axis) and duration of discharge time at rated power

(Y-axis) [2].


Table 3.2: Dention of Energy Storage Applications [2]

Aplication Description Size

Generation and

System Level

Applications

Wholesale EnergyServices

Utility-scale storage systemsfor bidding into energy, capacityand ancillary services markets

1-300 MW

RenewablesIntegration

Utility-scale storage providingrenewables time shifting, loadand ancillary services for grid

integration

1-10 MWdistributed100-400 MWcentralized

T&D Systems

Applications

Stationary Storagefor T&D Support

Systems for T&D system support,improving T&D system utilizationfactor, and T&D capital deferral

10-100 MW

Transportable Storagefor T&D systems

Transportable storage systems forT&D system suppor tand T&D

deferral at multiple sites as needed1-10 MW

Distributed energystorage systems

Centrally managed modular systemsproviding increased customer

reliability, grid T&D support andpotentially ancillary services

1-phase:25-200 kW3-phase:25-75 kW

End-User

Applications

C&I Power Qualityand Reliability

Systems to provide power qualityand reliability to commercialand industrial customers

50-1000 kW

C&I EnergyManagement

Systems to reduce TOU energycharges and demand charges

for C&I customers50-1000 kW

Home EnergyManagement

Systems to shift retail loadto reduce TOU energy and

demand charges2-5 kW

Home BackSystems for backup powerfor home oces with high

reliability value2-5 kW


Table 3.3: ESS Applications [2]

Applications

1- Wholesale Energy Services- Large wind farm and renewable integration- Ancillary Services

2- Utility Frequency Regulation- Power Quality- Renewable energy

3- Utility T&D Substation Grid Support- Peak Shaving; CapEx Deferral, Reliability- Dual Mode-Frequency Regulation/RTO Market Participation

4- Commercial and Industrial Energy Management- Power Quality, energy management; reliability

5

- Distributed Energy Storage at Pad-Mounted Transformer- Peak Shaving- Reliability- Dual-Mode Frequency Regulation

6- Residential- Home Energy Management, Back-up Power, Reliability- Home Photovoltaic Time Shifting

Figure 3.2: Positioning of ESS technologies [2]


Table 3.4: ESS technologies characteristics [2]

ESSTechnology

ApplicationCapacity(MWh)

Power(MW)

Duration(hrs)

%Eciency(total cycles)

PumpedHydro

11680-5300 280-530 6-10 80-82

(>13000)5400-14000 900-1400 6-10

CAES1

1080135

8(>13000)

2700 203 250 50 5 (>10000)

CT-CAES 1 1440-3600 1808

(>13000)20

SodiumSulfur

1 300 50 675

(4500)3

7.2 1 7.24

AdvancedLead-Acid

1200 50 5

85-90(2200)

250 20-50 4 85-90(4500)400 100 5

2 0.25-50 1-100 0.25-175-90

(>100000)3 3.2-48 1-12 3.2-4 75-90

(4500)4 0.1-10 0.2-1 4-10

5 0.1-0.25 0.025-0.05 2-585-90(4500)

Lead-Acid 60.01

0.0052 85-90

(1500-5000)0.02 4

VanadiumRedox

1 250 50 565-75

(>10000)

3 4-40 1-10 560-65

(>10000)

4 0.6-0.4 0.2-1.2 3.3-3.565-75

(>10000)

Flywheel 2 5 20 0.2585-87

(>100000)

Li-on

2 0.25-5 1-100 0.25-187-92

(>100000)

3 4.24 1-10 2-490-94(4500)

4 0.1-0.8 0.05-0.2 2-480-93(4500)

5 0.025-0.05 0.025-0.05 1-480-93(5000)

6 0.007-0.04 0.001-0.01 1-775-92(5000)

Chapter 4

Methodology

Figure 4.2 illustrates the methodology to accomplish this graduation project. Figure 4.1 shows the

input and output variables for this project. The input variables are the wind farm and battery

parameters; and the output variable is the voltage drop analysis. For the wind farm is necessary

to know the generator, converter and turbine variables and the control parameters for each turbine.

To correctly size the battery is signicant its application, duty cycle, room temperature, depth of

charge and discharge and energy loss.

Wind Farm

GridPWind PGrid

PB

atte

ry

AC

DC

Generator parametersConverter parameters

Turbine parametersControl parameter

Battery parameters since its application

Voltage Drop Analysis

Figure 4.1: Input and output variables for the project

11

Chapter 4. Methodology 12

Start

Search for ESS technologies and

application

Search for ESS models

Search for wind farms models

Make voltage drop analysis between the connection of the

wind farm with the grid-according IEC 61400-21

Make voltage drop analysis between the

battery and grid connection

Validate the system with a Study Case in

Matlab/SimulinkEnd

Search for impact of wind farms

connected to the grid

Size ESS

Size and control DC/DC bidirectional

converter

Control DC/AC converter, and size

LC filter

Figure 4.2: Methodology

Chapter 5

System Design

5.1 IEC 61400-21

As it was mentioned before, it is used the model showed in gure 3.1 to test the voltage drops at the

wind turbines. Therefore, it is necessary to make the system short circuit analysis to calculate the

impedance Z2. This impedance is calculated to get the table 3.1 voltage magnitudes at the wind

turbines terminals.

5.1.1 Short circuit analysis

For a symmetrical three-phase voltage drop is just necessary the positive sequence short circuit

analysis. Whereas, for a symmetrical two-phase voltage drop it is necessary the three sequences

short circuit analysis.

Figure 5.1 represents the system design and its main parameters, which are used to test the wind

farm voltage drops.

The line impedance (see table 5.2) is calculated with ATP draw software [14], where the distances

between the conductors are specied in gure 5.2.

13

Chapter 5. System Design 14

CA

Fault

100 km

T1

230 kV/34.5 kV

Network Equivalent

X0/X1=42500 MVA

Wind Farm-21 MW (14 Turbines-1.5 MW)

Yg

Figure 5.1: System Design to test voltage drop in the wind farm

7.62 m 7.62 m

14.6304 m

24.384 m

9.144 m

Figure 5.2: Line conductors distance [3]

Table 5.1: Conductor Parameters

Conductor Parameters[15]

Phase Conductor ACSR FINCH 54/19

Guard Cable ACSR LEGHORN 12/7

Table 5.2: Line Impedance

Line Impedance

Sequence R [Ω/km] X [Ω/km] B [S/km]

0 0.692294 1.05921 2.78379e-6

1 0.361258 0.545528 3.09785e-6


5.1.1.1 Positive Sequence Analysis

Figure 5.3 illustrates the positive sequence short circuit system diagram. In gure 5.3(a), the second

transformer (Transformer 2) does not appear in the gure 5.1 because it is the wind turbines internal

transformer.

The capacitor impedance from the line and the magnetization impedance from each transformer are

insignicant for the positive sequence impedance calculation because they are pretty large. On the

other hand, the magnetization impedance from the wind turbines is signicant to solve the system.

As a consequence, to start to simplify the circuit, the rotor voltage source (VR) is transformed to a

current source, as it is showed at gure 5.3(b), where:

IR =VR

RR + LR(5.1)

The gure 5.3(c), represent the equivalent circuit with the transformation from the current source

to a voltage source, the new values are obtained with equations 5.2 and 5.3.

ZR||M =ZR × ZM

ZR + ZM(5.2)

VRNEW= IR × ZR||M (5.3)

The the equivalent circuit is showed in gure 5.3(d), where

Req1 = R1 +RL (5.4)

Leq1 = L1 + LL (5.5)

Req2 = RT1prim +RT1sec +RT2prim +RT2sec +RS +RR||M (5.6)

Leq2 = LT1prim + LT1sec + LT2prim + LT2sec + LS +RR||M (5.7)

To solve the system thevenin's equivalent it is necessary to transform both voltage sources into

current sources as shown in gure 5.3(e), where:


I1 =VR1

Req1 + Leq1

IRNEW=

VRNEW

Req2 + Leq2

(5.8)

CA CA𝑉1

𝑅1 𝐿1 𝑅𝑇1𝑝𝑟𝑖𝑚

𝐶𝐿 𝐶𝐿

𝑅𝐿 𝐿𝐿 𝐿𝑇1𝑝𝑟𝑖𝑚

𝑅𝑇1𝑀 𝐿𝑇1𝑀

𝑅𝑇1𝑠𝑒𝑐 𝐿𝑇1𝑠𝑒𝑐 𝑅𝑆 𝐿𝑆

𝐿𝑀

𝑅𝑅 𝐿𝑅

𝑉𝑅

𝑅𝑇2𝑝𝑟𝑖𝑚 𝐿𝑇2𝑝𝑟𝑖𝑚


𝑅𝑇2𝑠𝑒𝑐 𝐿𝑇2𝑠𝑒𝑐

Network Equivalent Line Transformer 1 Transformer 2 Wind Generator

𝐹𝑎𝑢𝑙𝑡

(a)

CA CA𝑉1

𝑅1 𝐿1 𝑅𝑇1𝑝𝑟𝑖𝑚 𝑅𝐿 𝐿𝐿 𝐿𝑇1𝑝𝑟𝑖𝑚 𝑅𝑇1𝑠𝑒𝑐

𝐿𝑇1𝑠𝑒𝑐 𝑅𝑆 𝐿𝑆

𝐿𝑀

𝑅𝑅

𝐿𝑅

𝐼𝑅

𝑅𝑇2𝑝𝑟𝑖𝑚 𝐿𝑇2𝑝𝑟𝑖𝑚 𝑅𝑇2𝑠𝑒𝑐

𝐿𝑇2𝑠𝑒𝑐


(b)

CA𝑉1

𝑅1 𝐿1 𝑅𝑇1𝑝𝑟𝑖𝑚 𝑅𝐿 𝐿𝐿 𝐿𝑇1𝑝𝑟𝑖𝑚 𝑅𝑇1𝑠𝑒𝑐

𝐿𝑇1𝑠𝑒𝑐 𝑅𝑆 𝐿𝑆

𝑉𝑅𝑁𝐸𝑊

𝑅𝑇2𝑝𝑟𝑖𝑚 𝐿𝑇2𝑝𝑟𝑖𝑚 𝑅𝑇2𝑠𝑒𝑐

𝐿𝑇2𝑠𝑒𝑐

𝐹𝑎𝑢𝑙𝑡 CA

𝐿𝑅||𝑀 𝑅𝑅||𝑀

(c)

CA𝑉1

𝑅𝑒𝑞1 𝐿𝑒𝑞1

𝑉𝑅𝑁𝐸𝑊 𝐹𝑎𝑢𝑙𝑡 CA


(d)

CA𝐼1

𝑅𝑒𝑞1

𝐿𝑒𝑞1

𝐼𝑅𝑁𝐸𝑊 𝐹𝑎𝑢𝑙𝑡 CA

𝑅𝑒𝑞2

𝐿𝑒𝑞2

(e)

CA

𝑅𝑒𝑞𝑠𝑒𝑞 1 𝐿𝑒𝑞𝑠𝑒𝑞 1

𝑉𝑒𝑞𝑠𝑒𝑞 1

(f)

Figure 5.3: Positive sequence short circuit system diagram and thevenin's equivalent. [4]

Then, both current sources sum up to have a total current source, and solved parallel impedance to

have an equivalent impedance in parallel to the fault impedance. Afterwards, to solve the simplied

circuit as seen in gure 5.3(f), the current source with the parallel impedance is transformed to a


voltage source with a series impedance. The equations 5.9 and 5.10 explained how to obtain the

nal values for the thevenin's equivalent.

Ieqseq1 = I1 + IRNEW

Zeqseq1 =Zeq1 × Zeq2

Zeq1 + Zeq2

(5.9)

Veqseq1 = Ieqseq1 × Zeqseq1 (5.10)

5.1.1.2 Negative Sequence Analysis

Figure 5.4 illustrates the negative sequence short circuit system diagram; where Transformer 2 in

gure 5.4(a) corresponds to wind turbines internal transformer.

Alike the positive sequence analysis, the capacitor impedance from the line and the magnetization

impedance from each transformer are insignicant, and the magnetization impedance from the wind

turbines is signicant to solve the system.

To simplify the circuit, rst it is solved the parallel impedance between the rotor and the magneti-

zation impedance, using equation 5.2. The simplied circuit can be seen in gure 5.4(b).

Then, to get the equivalent circuit seen in gure 5.4(c), the equations 5.4 - 5.7 are used. Finally, to

get the equivalent negative sequence impedance (gure 5.4(d)), it is used the equation 5.11.


Zeq1 + Zeq2

(5.11)

5.1.1.3 Zero Sequence Analysis

Figure 5.5 illustrates the zero sequence short circuit system diagram; where the transformer in gure

5.5(a) corresponds to wind turbines internal transformer.

For this analysis, the generators impedance are disconnected from the circuit because their ground-

ing are solid. Regarding the transformers, since the rst transformer (Transformer 1) conguration



𝐶𝐿 𝐶𝐿




𝐿𝑀

𝑅𝑅 𝐿𝑅 𝑅𝑇2𝑝𝑟𝑖𝑚 𝐿𝑇2𝑝𝑟𝑖𝑚





(a)

𝑅1 𝐿1 𝑅𝑇1𝑝𝑟𝑖𝑚 𝑅𝐿 𝐿𝐿 𝐿𝑇1𝑝𝑟𝑖𝑚


𝑅𝑆 𝐿𝑆 𝑅𝑅||𝑀 𝐿𝑅||𝑀 𝑅𝑇2𝑝𝑟𝑖𝑚 𝐿𝑇2𝑝𝑟𝑖𝑚



(b)




(c)

𝑅𝑒𝑞𝑠𝑒𝑞 2

𝐿𝑒𝑞𝑠𝑒𝑞 2

(d)

Figure 5.4: Negative sequence short circuit system diagram and thevenin's equivalent

is wye-delta (see gure 5.1), the primary side impedance is connected to the circuit while the sec-

ondary side impedance is connected to ground. On the other hand, the wind turbines transformer

(Transformer 2) conguration is delta-wye, then the primary side impedance is connected to ground

and the secondary side is connected to the circuit next to it, as it can be seen in gure 5.5(a).

Alike the positive and negative sequence analysis, the capacitor impedance from the line and the

magnetization impedance from each transformer are insignicant to solve the system. After the last

description, gure 5.5(b) shows the equivalent circuit system to solve. Then, to get the equivalent

circuit seen in gure 5.5(c) it is used the equations 5.12 - 5.7. Finally, to get the equivalent zero

sequence impedance (gure 5.4(d)) it is used the equation 5.9.

Req1 = RL (5.12)


Leq1 = LL (5.13)

Req2 = RT1prim +RT1sec (5.14)

Leq2 = LT1prim + LT1sec (5.15)


Zeq1 + Zeq2

(5.16)


𝐶𝐿 𝐶𝐿




𝐿𝑀

𝑅𝑅 𝐿𝑅 𝑅𝑇2𝑝𝑟𝑖𝑚 𝐿𝑇2𝑝𝑟𝑖𝑚





(a)

𝑅𝑇1𝑝𝑟𝑖𝑚 𝑅𝐿 𝐿𝐿 𝐿𝑇1𝑝𝑟𝑖𝑚



(b)




(c)

𝑅𝑒𝑞𝑠𝑒𝑞 0

𝐿𝑒𝑞𝑠𝑒𝑞 0

(d)

Figure 5.5: Zero sequence short circuit system diagram and thevenin's equivalent

Since the last explanation, the calculated positive, negative and zero sequence impedance are shown

on table 5.3.


Table 5.3: System Sequence Impedance

SequenceImpedance [Ω]Reqseq XLeqseq

0 12.0587 44.54791 12.4603 45.28192 12.4603 45.2819

5.1.2 Three Phase Fault Analysis

In a three phase fault analysis is only used the positive sequence. Figure 5.6 represent the three

phase fault equivalent circuit. To nd the three phase impedance fault value, for the three cases of

voltage drop (table 3.1), it is used equation 5.17 for each case.

Zfault =Vfault × Zeqseq1

Veqseq1 − Vfault(5.17)

CA

𝑅𝑒𝑞𝑠𝑒𝑞 1 𝐿𝑒𝑞𝑠𝑒𝑞 1

𝑅𝑓𝑎𝑢

𝑙𝑡

𝐿𝑓𝑎𝑢

𝑙𝑡

𝑉𝑒𝑞𝑠𝑒𝑞 1 𝑉𝑓𝑎𝑢𝑙𝑡

+

−

Figure 5.6: Three phase fault equivalent circuit

Table 5.4 shows the three phase fault impedance for gure 5.1 system, to get a voltage drop at wind

turbine terminals of 0.9, 0.5 and 0.2 p.u.

Table 5.4: Three phase fault impedance

Fault Voltage [p.u]Fault Impedance [Ω]Rfault XLfault

0.9 112.14223 407.53700.5 12.4603 67.90140.2 3.1151 15.0904


5.1.3 Two Phase Fault to Ground Analysis

In a two phase fault to ground analysis is used the positive, negative and zero sequence. Figure 5.7

represent the two phase fault to ground equivalent circuit. To nd the two phase impedance fault

value, for the three cases of voltage drop (table 3.1), it is used equation 5.19 for each case.

ZT =Vfaultseq1

Vfaultseq1

Zeqseq2+

Vfaultseq1+Veqseq1

Zeqseq1

(5.18)

Zfault = −ZT + Zeqseq0

3(5.19)

Table 5.5 shows the two phase fault impedance for gure 5.1 system, to get a voltage drop at wind

turbine terminals of 0.9, 0.5 and 0.2 p.u.

Table 5.5: Three phase fault impedance

Fault Voltage [p.u] Fault Impedance [Ω]

0.9 300.6590.5 60.773530.2 0.002039

CA

𝑅𝑒𝑞𝑠𝑒𝑞1

𝐿𝑒𝑞𝑠𝑒𝑞1

𝑉𝑒𝑞𝑠𝑒𝑞 1 𝑅𝑒𝑞𝑠𝑒𝑞2

𝐿𝑒𝑞𝑠𝑒𝑞2

𝑅𝑒𝑞𝑠𝑒𝑞

0

𝐿𝑒𝑞𝑠𝑒𝑞

0 +

−

3×𝑅𝑓𝑎𝑢𝑙𝑡

3×𝐿𝑓𝑎𝑢𝑙𝑡

𝑉𝑓𝑎𝑢𝑙 𝑡𝑠𝑒𝑞 1

+

−

Figure 5.7: Two phase fault to ground equivalent circuit


5.2 Case Study System Design

Figure 5.8 illustrates the case study diagram to analyze the impact connection between batteries

and the grid with a wind farm. The impedance line parameters are shown in table 5.2. The battery

bank is connected next to the wind farm, through a bidirectional converter, DC/AC converter and

a transformer in that order. In this section it is explained the model of the bidirectional converter

and DC/AC converter that it is used in the system. The wind farm has 14 DFIG wind turbines,

and it is used the Simulink DFIG wind turbine model.

CA

40 km

230 kV/34.5 kV

Network Equivalent

X0/X1=42500 MVA

Wind Farm-21 MW (14 Turbines-1.5 MW)

Battery Bank

Yg

Yg480

V/3

4.5

kV

T1

T2Load

20 MW2.2 MVar

AC

DC

DC

DC

Figure 5.8: Case Study Diagram

5.2.1 Bidirectional Converter

The model of the bidirectional converter is based on [16]. Figure 5.9 show the bidirectional converter

diagram, where Q1 and Q2 are the power switches. Table 5.6 shows the denition and value of each

variable from the converter. A cause of the case study is a transmission system and the battery

purpose is voltage regulation in the grid, it is used a lithium battery with a size of 500 Ah.


Battery Voltage 𝑉𝑜𝑢𝑡

+

−

𝑉𝐵

𝑅𝐵

𝑅𝐶𝑖

𝐶𝑖

𝑅𝐿 𝐿

𝑄1

𝑄2

𝑅𝐶𝑜

𝐶𝑜

PWM2

PW

M1

Figure 5.9: Bidirectional Converter

Table 5.6: Bidirectional Converter and Battery Parameters

Variable Denition Value

VB Battery Voltage 600 V

RB Battery Resistance 0.03 Ω

IBAhBattery Rated Capacity 500 Ah

Ci Input Capacitance 2.5 mF

RCiInput capacitor ESR 74e mΩ

L Inductance 70 µH

RL DCR of Inductance 9.6 mΩ

Co Output Capacitance 40 mF

RCo Output capacitor ESR 5 mΩ

Vout Output Voltage 679 V

5.2.2 DC/AC Converter

The DC/AC converter is necessary to transform DC battery voltage and current into AC; conse-

quently it is possible to connect the batteries to the grid. It is used two power converters: a rectier

to charge the battery and a PWM inverter to discharge the battery [17]. Figure 5.10 illustrates the

basic topology of the rectier 5.10(a) and PWM inverter 5.10(b).

As it is illustrated in gure 5.10(b), the inverter has a LC lter to mitigate harmonics. Table 5.7

shows the LC lter parameters. Furthermore, due to the converters generate in the voltage and


current signal 5th, 7th, 11th, and 13th order harmonics, after the DC/AC converter there is a lter

to mitigate those harmonics.

𝑉𝐷𝐶

+

−

n

- +

- +

- +

a

b

c

D1 D3

D6D4

D5

D2

(a)

VDC

D1 D3 D5

D4 D6 D2

Q1 Q3 Q5

Q4 Q6 Q2

LA

LB

LC

CA CB CC

(b)

Figure 5.10: DC/AC Converter topology: (a) Rectier (b) PWM Inverter

Table 5.7: PWM inverter-LC lter parameters

LC Filter parameters

Variable Value

fc 500 Hz

L 10 mH

C 10.1321 mF

Chapter 6

Simulation Results

6.1 Voltage Drop Validation Test - IEC 61400-21 Standard

6.1.1 Three Phase Fault

Figure 6.1 represents the circuit system developed in Matlab/Simulink [18], which corresponds to

diagram of gure 5.1. In this section it is explained the three phase fault results, according to IEC

61400-21 standard parameters.

Figure 6.1: Wind Farm System on Matlab/Simulink-Three phase fault

25

Chapter 6. Simulation Results 26

In this section there are the results of the wind farm behavior before, during and after a three phase

fault. The impedance fault for each case are in table 5.4. The length fault is 0.5 s, from 0.4 s to 0.9

s.

Figure 6.2,6.3, and 6.4 represents the voltage magnitude at the fault node and wind farm terminals,

when the wind farm has 90% of the rated active power and a 0.9, 0.5 and 0.2 pu voltage drop

respectively.

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8138Y: 0.8616

Time (s)

V_f

ault

(pu)

Voltage Magnitude at Fault Node(0.9 Pn)

X: 1.07Y: 1.033

Phase APhase BPhase C

(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8307Y: 0.8748

Time (s)

V_W

F (

pu)

Voltage Magnitude at Wind Farm Node(0.9 Pn)

X: 1.072Y: 1.046


(b)

Figure 6.2: Pn = 90%, VDrop = 0.9pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Terminals

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.794Y: 0.4635

Time (s)

V_f

ault

(pu)


X: 1.031Y: 1.033


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8445Y: 0.4772

Time (s)

V_W

F (

pu)


X: 1.059Y: 1.05


(b)



0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.824Y: 0.1556

Time (s)

V_f

ault

(pu)


X: 1.298Y: 1.037


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8304Y: 0.1599

Time (s)

V_W

F (

pu)


X: 1.382Y: 1.053


(b)


Table 6.1 resume the three voltage drop magnitude cases at the wind farm terminal with the dierent

active rated power. It is visible that during dierent wind farm active power percentage, the voltage

drop is insignicant.

Table 6.1: Three Phase Fault-Voltage Drop at Wind Farm Terminals with Dierent Rated ActivePower

Case Voltage DropPn

90% 30% 10%

1 0.9 0.8748 0.9321 0.9329

2 0.5 0.4772 0.5318 0.5442

3 0.2 0.1599 0.2063 0.2403

For each case, in Appendix A section A.1.1 are the graphs of the voltage magnitude at the fault

node and wind farm terminals, when the wind farm has 30% and 10% of the rated active power

6.1.2 Two Phase Fault to Ground

Figure 6.5 represents the circuit system developed in Matlab/Simulink, which corresponds to diagram

of gure 5.1. In this section it is explained the two phase fault to ground results, according to IEC

61400-21 standard parameters.


Figure 6.5: Wind Farm System on Matlab/Simulink-Two phase fault to ground

In this section there is the results of the wind farm behavior before, during and after a two phase

fault. The impedance fault for each case are in table 5.5. The length fault is 0.5 s, from 0.4 s to 0.9

s.

Figure 6.6,6.7, and 6.8 represents the voltage magnitude at the fault node and wind farm terminals,

when the wind farm has 90% of the rated active power and a 0.9, 0.5 and 0.2 pu voltage drop

respectively.

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.7817Y: 0.8982

Time (s)

V_f

ault

(pu)


X: 0.7935Y: 1.015

X: 1.142Y: 1.032


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8233Y: 0.884

Time (s)

V_W

F (

pu)


X: 0.8691Y: 0.9787

X: 0.8036Y: 0.9903

X: 1.19Y: 1.042


(b)


In gure 6.6,6.7 and 6.8, it is visible that when it is apply a two phase fault to ground at the system,

in the wind turbine terminals is view like one phase fault. This happens because the transformer 1

conguration (see gure 5.1) which is wye-delta.


0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.6655Y: 0.8631

Time (s)

V_f

ault

(pu)


X: 0.6552Y: 0.6028

X: 0.648Y: 0.5146

X: 1.222Y: 1.032


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.7735Y: 0.4798

Time (s)

V_W

F (

pu)


X: 0.7765Y: 0.7162

X: 0.7706Y: 0.8141

X: 1.232Y: 1.041


(b)


0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8295Y: 0.6025

Time (s)

V_f

ault

(pu)


X: 1.19Y: 1.034


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.7526Y: 0.3923

Time (s)

V_W

F (

pu)


X: 0.7483Y: 0.2402

X: 0.7584Y: 0.6235

X: 1.332Y: 1.047


(b)


It is notable that when it is analyzing the system for the third case (voltage drop=0.2 pu), it is not

well computed. In Matlab/Simulink software a two phase fault to ground impedance below 40 Ω

is not well simulated. For this reason, in gures 6.8(a), A.11(a) and A.12(a), instead of phases B

and C have a voltage drop to 0.2 pu, the phase A and C drops to 0.6025, 0.6174 pu and 0.6229 pu

respectively and phase B drops to 0 pu.


Table 6.2 resume the three voltage drop magnitude cases at the wind farm terminal with the dierent

active rated power. It is visible that during dierent wind farm active power percentage, the voltage

drop is insignicant.

Table 6.2: Two Phase Fault to Ground-Voltage Drop at Wind Farm Terminals with dierent ratedactive power

Case Voltage Drop

Pn

90% 30% 10%

Phase Phase Phase

A B C A B C A B C

1 0.9 0.9903 0.9787 0.884 1.04 1.033 0.9284 1.041 1.041 0.9272

2 0.5 0.8141 0.7162 0.4798 0.8376 0.743 0.5162 0.8639 0.7787 0.5157

3 0.2 0.6235 0.3923 0.2402 0.6925 0.4219 0.2922 0.7312 0.4254 0.3399

For each case, in Appendix A section A.1.2 are the graphs of the voltage magnitude at the fault

node and wind farm terminals, when the wind farm has 30% and 10% of the rated active power.

6.2 Case Study

6.2.1 Battery Validation

Figure 6.9 illustrates the battery behavior when the voltage at the grid is during, under and above

of 1 pu. The battery state (charge, discharge, idling) is controlled by the voltage that is after the

DC/AC converter; and also depends of the battery state of charge percentage (%SOC). In table 6.3

is explained the battery state according to the voltage measured after the DC/AC converter and the

%SOC.


Table 6.3: Battery State

Battery State Voltage after DC/AC converter [pu] %SOC [%]

Idling 0.97 ≤ V ≤ 1.03 100,≤ 20

Charging V > 1.03 < 100

Discharging V < 0.97 > 20

Figure 6.9 represents the battery state of charge and the bidirectional converter voltage output. At

the beginning, the battery is arriving to its stable state and meanwhile the battery state is idling.

Then at 0.5 s the voltage increase therefore the battery starts to charge. Finally, at 1 s the voltage

decrease, so the battery starts to discharge to supply power to the grid.

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.689.95

90

90.05

90.1

90.15

90.2

90.25

90.3

90.35

90.4

90.45

Time [s]

SO

C [%

]

(a)

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60

100

200

300

400

500

600

700

800

Time [s]

Con

vert

er o

utpu

t Vol

tage

[V]

(b)

Figure 6.9: (a) Battery Percentage State of Charge (b) Bidirectional Converter Voltage Output

6.2.2 Wind Farm and Battery connection to the grid

Figure 6.10 represents the circuit system developed in Matlab/Simulink, which corresponds to dia-

gram of gure 5.8.


Figure 6.10: Case Study Diagram on Matlab/Simulink

On this case, at the beginning (from 0 to 0.5 s) the wind farm, the equivalent network and the

battery are connected to the load, and after 0.5 s the equivalent network is disconnected from the

grid. Figures A.15 and A.16 represents the battery, wind farm, and load voltage, active and reactive

power respectively when the battery is not connected to the grid. On the other hand, gures A.17

and A.18 illustrates the battery, wind farm, and load voltage, active and reactive power respectively

when the battery is connected to the grid. The battery voltage is measured in the secondary side of

transformer T2 (34.5 kV side).

A cause of the DC/DC and DC/AC converter, the battery generates harmonics in the voltage and

current signal. Figure A.13 and A.14 represents the battery output voltage and current signal

respectively with and without an harmonic lter. For this reason, it is connected a 5th,7th, 11th

and 13th order harmonic lter to the system to decrease the total harmonic distortion in the voltage

and current signal.

In gure A.13(a), it is visible that without the harmonic lter the THD in the voltage signal is 3.87%,

3.94% and 3.64% in phase A, B, and C respectively. In contrast, in gure A.13(b) the THD in the

signal decreases to 0.76%, 0.70% and 0.68% in phase A, B, and C respectively. In gure A.14(a),

it is visible that without the harmonic lter the THD in the current signal is 51.55%, 52.03% and


51.67% in phase A, B, and C respectively. On the other hand, in gure A.14(b) the THD in the

signal decreases to 8.40%, 8.16% and 6.26% in phase A, B, and C respectively.

Table 6.4 and 6.5 shows the voltage and active power in dierent parts of the system respectively,

when the network equivalent is disconnected from the grid. It is notable that when the battery is

not connected, the voltage drops to 0.9096 and 0.9002 pu at the wind farm and load respectively,

and the active power in the system decrease from 20 MW to 15.98 MW. On the contrary, when the

battery is connected to the grid, it compensates the voltage drop in the grid because the voltage

at the wind farm and the load increase to 0.9667 and 0.9556 pu respectively; as a result, the active

power in the wind farm and load increase to 18.21 MW and 19.16 MW respectively. Therefore, with

battery there are less losses in the system.

Table 6.4: Voltage in the system without and with battery connection to grid

Voltage [pu]

Battery Disconnected Battery Connected

Wind Farm 0.9096 0.9667

Battery - 0.9669

Load 0.9002 0.9556

Table 6.5: Active power in the system without and with battery connection to grid

Active Power [MW ]

Battery Disconnected Battery Connected

Wind Farm 15.98 18.21

Battery - 1.074

Load 15.98 19.16

Chapter 7

Discussion and Conclusion

7.1 Discussion

This graduation project was able to asses the connection performance between the wind turbine and

the grid. According to the IEC 61400-21 standard, it was able to test the voltage drops in a wind

farm with 14 wind turbines, through a three fault and a two phase fault to ground. The three phase

fault test was correctly compute. On the other hand, the two phase fault to ground test is necessary

to repeat it on another software because it was not able to have a correct voltage measurement in

the case of 0.2 pu voltage drop.

Moreover, it was able to model and control a DC/DC and DC/AC converter to charge and discharge

the battery. Therefore, it was able to asses the connection performance between the battery and

the grid. Furthermore, it was possible to analyze the voltage drop in the system with and without

battery.

7.2 Conclusion y Further Work

With this graduation project it was possible to validate IEC 61400-21 standard for a three and two

phase voltage drop simulation test in a wind farm with 14 DFIG wind turbines, where each turbine

generates 1.5 MW

34

Chapter 7. Discussion and Conclusion 35

It is able to charge and discharge the batteries under certain conditions, since the correct sizing,

model and control of the batteries and converters. Thus, it is possible to analyze the performance

connection between the batteries and the grid.

The designed batteries bank can support and compensate a voltage drop in the grid in a range of

0-0.5 pu. On the other hand, the battery converters generate harmonics in the voltage and current

signal. With an harmonic lter it was possible to decrease the %THD in the voltage and current

signal from 4% to 0.7% and 51.75% to 7.6067% respectively.

For further work, it is necessary to test the two phase fault to ground scenarios with other software,

cause the results computed by Matlab/Simulink did not agree with the mathematical results. More-

over, improve the converter control to decrease the harmonics in the system. Furthermore, it would

be better to make a full harmonic analysis in the system to mitigate the harmonics generated by

the battery. Finally, apply the model application in Opal-RT.

Appendix A

Appendix

A.1 IEC 61400-21 Standard

A.1.1 Three Phase Fault

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8174Y: 0.8711

Time (s)

V_f

ault

(pu)


X: 1.111Y: 1.042


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8335Y: 0.9321

Time (s)

V_W

F (

pu)


X: 1.087Y: 1.1


(b)

Figure A.1: Pn = 30%, VDrop = 0.9pu; Voltage Magnitude: (a) Fault Bus (b) Wind Farm Termi-nals

36

Appendix. Appendix A 37

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 1.135Y: 1.041

Time (s)

V_f

ault

(pu)


X: 0.8171Y: 0.8698


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8329Y: 0.9329

Time (s)

V_W

F (

pu)


X: 1.125Y: 1.1


(b)


0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8243Y: 0.4719

Time (s)

V_f

ault

(pu)


X: 1.152Y: 1.042


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8033Y: 0.5318

Time (s)

V_W

F (

pu)


X: 1.167Y: 1.098


(b)



0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 1.077Y: 1.042

Time (s)

V_f

ault

(pu)


X: 0.8175Y: 0.4728


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 1.256Y: 1.1

Time (s)

V_W

F (

pu)


X: 0.846Y: 0.5442


(b)


0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 1.215Y: 1.042

Time (s)

V_f

ault

(pu)


X: 0.8138Y: 0.1592


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 1.281Y: 1.097

Time (s)

V_W

F (

pu)


X: 0.8393Y: 0.2063


(b)



0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8416Y: 0.1611

Time (s)

V_f

ault

(pu)


X: 1.167Y: 1.041


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8552Y: 0.2403

Time (s)

V_W

F (

pu)


X: 1.325Y: 1.099


(b)


A.1.2 Two Phase Fault to Ground

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8026Y: 1.021

Time (s)

V_f

ault

(pu)


X: 0.8113Y: 0.9026

X: 1.118Y: 1.042


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8085Y: 0.9284

Time (s)

V_W

F (

pu)


X: 0.8111Y: 1.04

X: 0.858Y: 1.033

X: 1.135Y: 1.098


(b)



0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.7966Y: 0.9001

Time (s)

V_f

ault

(pu)


X: 0.7933Y: 1.019

X: 1.161Y: 1.041


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8189Y: 1.041

Time (s)

V_W

F (

pu)


X: 0.8161Y: 0.9272

X: 1.136Y: 1.099


(b)


0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.8444Y: 0.8611

Time (s)

V_f

ault

(pu)


X: 0.8313Y: 0.611

X: 0.8312Y: 0.5168

X: 1.156Y: 1.041


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.7043Y: 0.8376

Time (s)

V_W

F (

pu)


X: 0.6946Y: 0.743

X: 0.6913Y: 0.5162

X: 1.149Y: 1.086


(b)



0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.7901Y: 0.8611

Time (s)

V_f

ault

(pu)


X: 0.8001Y: 0.6051

X: 0.8071Y: 0.5103

X: 1.099Y: 1.04


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.7829Y: 0.8639

Time (s)

V_W

F (

pu)


X: 0.7938Y: 0.7787

X: 0.786Y: 0.5157

X: 1.159Y: 1.097


(b)

Figure A.10: Pn = 10%, VDrop = 0.5pu; Voltage Magnitude: (a) Fault Bus (b) Wind FarmTerminals

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.7482Y: 0.6174

Time (s)

V_f

ault

(pu)


X: 1.207Y: 1.042


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.7706Y: 0.2922

Time (s)

V_W

F (

pu)


X: 0.7638Y: 0.4219

X: 0.7724Y: 0.6925

X: 1.263Y: 1.097


(b)



0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.7758Y: 0.6229

Time (s)

V_f

ault

(pu)


X: 1.205Y: 1.041


(a)

0 0.5 1 1.50

0.2

0.4

0.6

0.8

1

X: 0.7893Y: 0.3399

Time (s)

V_W

F (

pu)


X: 0.7515Y: 0.4254

X: 0.7417Y: 0.7312

X: 1.243Y: 1.101


(b)


A.2 Case Study

0.65 0.66 0.67 0.68 0.69 0.7 0.71 0.72 0.73 0.74 0.75

−1

−0.8

−0.6

−0.4

−0.2

0

0.2

0.4

0.6

0.8

1

Battery Output Voltage

tiempo (s)

Vol

tage

(p.

u)

Phase A: THD=3.87% Phase B: THD=3.94% Phase C:THD=3.64%

(a)

0.65 0.66 0.67 0.68 0.69 0.7 0.71 0.72 0.73 0.74 0.75

−1

−0.8

−0.6

−0.4

−0.2

0

0.2

0.4

0.6

0.8

1

Battery Output Voltage

tiempo (s)

Vol

tage

(p.

u)


(b)

Figure A.13: Battery output voltage signal and %THD (a) without 5th,7th, 11th and 13th orderharmonic lter, (b)with 5th,7th, 11th and 13th order harmonic lter


0.65 0.66 0.67 0.68 0.69 0.7 0.71 0.72 0.73 0.74 0.75−3000

−2000

−1000

0

1000

2000

3000Battery Output Current

tiempo (s)

Cur

rent

(A

)


(a)

0.65 0.66 0.67 0.68 0.69 0.7 0.71 0.72 0.73 0.74 0.75−3000

−2000

−1000

0

1000

2000

3000Battery Output Current

tiempo (s)

Cur

rent

(A

)


(b)

Figure A.14: Battery output current signal and %THD (a) without 5th,7th, 11th and 13th orderharmonic lter, (b)with 5th,7th, 11th and 13th order harmonic lter

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.4

0.5

0.6

0.7

0.8

0.9

1

1.1

X: 0.7474Y: 0.9096

Wind Farm Voltage

tiempo (s)

Vol

tage

(p.

u)


(a)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.4

0.5

0.6

0.7

0.8

0.9

1

1.1

X: 0.7474Y: 0.9002

Load Voltage

tiempo (s)

Vol

tage

(p.

u)


(b)

Figure A.15: Battery Disconnected from Grid. Voltage pu in (a) Wind Farm Terminals and (c)Load.


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1−1

0

1

2

3x 10

6

X: 0.3065Y: 1.733e+06

Grid Equivalent Active Power

tiempo (s)

Act

ive

Pow

er (

W) Active Power

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

1

2

3

x 106 Grid Equivalent Reactive Power

tiempo (s)

Rea

ctiv

e P

ower

(V

ar)

Reactive Power

(a)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.5

1

1.5

2

x 107

X: 0.6878Y: 1.598e+07

Wind Farm Active Power

tiempo (s)

Act

ive

Pow

er (

W)

X: 0.3055Y: 1.823e+07

Active Power

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

1

2

3

4

5x 10

6 Wind Farm Reactive Power

tiempo (s)

Rea

ctiv

e P

ower

(V

ar)

Reactive Power

(b)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.5

1

1.5

2

x 107

X: 0.6875Y: 1.598e+07

Load Active Power

tiempo (s)

Act

ive

Pow

er (

W)

X: 0.3066Y: 2.018e+07

Active Power

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.5

1

1.5

2

x 106 Load Reactive Power

tiempo (s)

Rea

ctiv

e P

ower

(V

ar)

Reactive Power

(c)

Figure A.16: Battery Disconnected from Grid. Active and Reactive Power in (a) Network Equiv-alent (b) Wind Farm Terminals (c) Load


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.4

0.5

0.6

0.7

0.8

0.9

1

1.1

X: 0.7398Y: 0.9667

Wind Farm Voltage

tiempo (s)

Vol

tage

(p.

u)


(a)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.4

0.5

0.6

0.7

0.8

0.9

1

1.1

X: 0.7458Y: 0.9556

Load Voltage

tiempo (s)

Vol

tage

(p.

u)


(b)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.4

0.5

0.6

0.7

0.8

0.9

1

1.1

X: 0.7327Y: 0.9669

Battery Voltage

tiempo (s)

Vol

tage

(p.

u)


(c)

Figure A.17: Battery Connected to Grid. Voltage pu in (a) Wind Farm Terminals (b) Load and(c) Battery


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1−1

0

1

2

3x 10

6

X: 0.3062Y: 1.551e+06

Grid Equivalent Active Power

tiempo (s)

Act

ive

Pow

er (

W) Active Power

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

1

2

3

x 106 Grid Equivalent Reactive Power

tiempo (s)

Rea

ctiv

e P

ower

(V

ar)

Reactive Power

(a)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.5

1

1.5

2

x 107

X: 0.6875Y: 1.821e+07

Wind Farm Active Power

tiempo (s)

Act

ive

Pow

er (

W)

X: 0.3061Y: 1.824e+07

Active Power

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

1

2

3

4

5x 10

6 Wind Farm Reactive Power

tiempo (s)

Rea

ctiv

e P

ower

(V

ar)

Reactive Power

(b)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.5

1

1.5

2

x 107

X: 0.6875Y: 1.916e+07

Load Active Power

tiempo (s)

Act

ive

Pow

er (

W)

X: 0.3066Y: 2.02e+07

Active Power

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.5

1

1.5

2

x 106 Load Reactive Power

tiempo (s)

Rea

ctiv

e P

ower

(V

ar)

Reactive Power

(c)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0

5

10

15

20x 10

5

X: 0.6874Y: 1.074e+06

Battery Active Power

tiempo (s)

Act

ive

Pow

er (

W) Active Power

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

−2

0

2

4

x 106 Battery Reactive Power

tiempo (s)

Rea

ctiv

e P

ower

(V

ar)

Reactive Power

(d)

Figure A.18: Battery Connected to Grid. Active and Reactive Power in (a) Network Equivalent(b) Wind Farm Terminals (c) Load and (d) Battery

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