Modelling Photovoltaic Systems Using PSpice

371 Pages·2002·15.037 MB·English

by  Luis Castañer, Santiago Silvestre

Modelling Photovoltaic
Systems using PSpice@
Luis Castafier and Santiago Silvestre
Universidad Politecnica de Cataluiia, Barcelona, Spain
JOHN WILEY & SONS, LTD
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Library of Congress Cataloging-in-Publication Data
CastaAer, Luis.
Modelling photovoltaic systems using PSpice / Luis Castaiier, Santiago Silvestre.
p. cm.
Includes bibliographical references and index.
ISBN 0-470-84527-9 (alk. paper) - ISBN 0-470-84528-7 (pbk. : alk. paper)
1. Photovoltaic power systems-Mathematical models. 2. Photovoltatic power
systems-Computer simulation. 3. PSpice. I. Silvestre, Santiago. 11. Title.
TK1087 .C37 2002
62 1.3 1' 2446~12 200202741
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
ISBN 0-470-845279 (HB) 0-470-84528-7 (PB)
Preface
Photovoltaic engineering is a multidisciplinary speciality deeply rooted in
physics for solar cell theory and technology, and heavily relying on electrical and electpolrlli;c
engineering for system design and analysis.
The conception, design and analysis of photovoltaic systems are important tasks o h
requiring the help of computers to perform fast and accurate computations or simuhfim.
Today’s engineers and professionals working in the field and also students of dSa&
technical disciplines know how to use computers and are familiar with r~nning.r peckaliz&
software. Computer-aided technical work is of great help in photovoltaics became a#
the system components are described by nonlinear equations, and the node circuit quaions
that have to be solved to find the values of the currents and voltages, most often do II& have
analytical solutions. Moreover, the characteristics of solar cells and PV generators sarongly
depend on the intensity of the solar radiation and on the ambient temperature. As ka re
variable magnitudes with time, the system design stage will be more accurate if a4.1
estimation of the performance of the system in a long-term scenario with realistic tikm
series of radiation and temperature is carried out.
The main goal of this book is to help understand PV systems operation gathering
concepts, design criteria and conclusions, which are either defined or illustrated us&
computer software, namely PSpice.
The material contained in the book has been taught for more than 10 years as an
undergraduate semester course in the UPC (Universidad Politecnica de catahria) in
Barcelona, Spain and the contents refined by numerous interactions with the studats.
PSpice was introduced as a tool in the course back in 1992 to model a basic solar celI and
since then more elaborated models, not only for solar cells but also for PV gemerators,
battery, converters, inverters, have been developed with the help of MSc and PhD -dents.
The impression we have as instructors is that the students rapidly jump into the tool and am
ready to use and apply the models and procedures described in the book by themselves-
Interaction with the students is helped by the universal availability of Pspice or mze
advanced versions, which allow the assignments to be tailored to the development: of
the course and at the same time providing continuous feedback from the students on the
xvi PREFACE
difficulties they find. We think that a key characteristic of the teaching experience is that
quantitative results are readily available and data values of PV modules and batteries from
web pages may be fed into problems and exercises thereby translating a sensation of
proximity to the real world.
PSpice is the most popular standard for analog and mixed-signal simulation. Engineers
rely on PSpice for accurate and robust analysis of their designs. Universities and semi-
conductor manufacturers work with PSpice and also provide PSpice models for new devices.
PSpice is a powerful and robust simulation tool and also works with Orcad CaptureB,
Concept@ HDL, or PSpice schematics in an integrated environment where engineers create
designs, set up and run simulations, and analyse their simulation results. More details and
information about PSpice can be found at http://www.pspice.com/.
At the same web site a free PSpice, PSpice 9.1 student version, can be downloaded. A
request for a free Orcad Lite Edition CD is also available for PSpice evaluation from http://
www.pspice.com/download/default.asp.
PSpice manuals and other technical documents can also be obtained at the above web site
in PDF format. Although a small introduction about the use of PSpice is included in Chapter
1 of this book, we strongly encourage readers to consult these manuals for more detailed
information. An excellent list of books dedicated to PSpice users can also be found at http://
www.pspice.com/publications/books.asp.
All the models presented in this book, developed for PSpice simulation of solar cells and
PV systems behaviour, have been specially made to run with version 9 of PSpice. PSpice
offers a very good schematics environment, Orcad Capture for circuit designs that allow
PSpice simulation, despite this fact, all PSpice models in this book are presented as text files,
which can be used as input files. We think that this selection offers a more comprehensive
approach to the models, helps to understand how these models are implemented and allows a
quick adaptation of these models to different PV system architectures and design environ-
ments by making the necessary file modifications. A second reason for the selection of text
files is that they are transportable to other existing PSpice versions with little effort.
All models presented here for solar cells and the rest of the components of a PV system
can be found at www.esf.upc.es/esf/, where users can download all the files for simulation of
the examples and results presented in this book. A set of files corresponding to stimulus,
libraries etc. necessary to reproduce some of the simulations shown in this book can also be
found and downloaded at the above web site. The login, esf and password, esf, are required
to access this web site.
Contents
Foreword xiii
Preface xv
Acknowledgements xvii
1 Introduction to Photovoltaic Systems and PSpice 1
Summary 1
1.1 The photovoltaic system 1
1.2 Important definitions: irradiance and solar radiation 2
1.3 Learning some of PSpice basics 4
1.4 Using PSpice subcircuits to simplify portability 7
1.5 PSpice piecewise linear (PWL) sources and controlled voltage sources 9
1.6 Standard AM1.5G spectrum of the sun 10
1.7 Standard AM0 spectrum and comparison to black body radiation 12
1.8 Energy input to the PV system: solar radiation availability 15
1.9 Problems 17
1.10 References 18
2 Spectral Response and Short-Circuit Current 19
Summary 19
2.1 Introduction 19
2.1.1 Absorption coefficient a(X) 20
2.1.2 Reflectance R(X) 21
2.2 Analytical solar cell model 22
2.2.1 Short-circuit spectral current density 23
2.2.2 Spectral photon flux 24
2.2.3 Total short-circuit spectral current density and units 24
2.3 PSpice model for the short-circuit spectral current density 25
2.3.1 Absorption coefficient subcircuit 25
2.3.2 Short-circuit current subcircuit model 26
2.4 Short-circuit current 29
viii CONTENTS
2.5 Quantum efficiency (QE) 30
2.6 Spectral response (SR) 32
2.7 Dark current density 33
2.8 Effects of solar cell material 34
2.9 Superposition 35
2.10 DC sweep plots and I(V) solar cell characteristics 35
2.11 Failing to fit to the ideal circuit model: series and shunt resistances
and recombination terms 38
2.12 Problems 39
2.13 References 39
3 Electrical Characteristics of the Solar Cell 41
Summary 41
3.1 Ideal equivalent circuit 41
3.2 PSpice model of the ideal solar cell 42
3.3 Open circuit voltage 45
3.4 Maximum power point 47
3.5 Fill factor (FF) and power conversion efficiency (7) 49
3.6 Generalized model of a solar cell 51
3.7 Generalized PSpice model of a solar cell 53
3.8 Effects of the series resistance on the short-circuit current and the
open-circuit voltage 54
3.9 Effect of the series resistance on the fill factor 55
3.10 Effects of the shunt resistance 58
3.1 1 Effects of the recombination diode 59
3.12 Temperature effects 60
3.13 Effects of space radiation 64
3.14 Behavioural solar cell model 68
3.15 Use of the behavioural model and PWL sources to simulate the response
to a time series of irradiance and temperature 72
3.15.1 Time units 72
3.15.2 Variable units 72
3.16 Problems 75
3.17 References 75
4 Solar Cell Arrays, PV Modules and PV Generators 77
Summary 77
4.1 Introduction 77
4.2 Series connection of solar cells 78
4.2.1 Association of identical solar cells 78
4.2.2 Association of identical solar cells with different irradiance levels:
hot spot problem 79
4.2.3 Bypass diode in series strings of solar cells 81
4.3 Shunt connection of solar cells 82
4.3.1 Shadow effects 83
4.4 The terrestrial PV module 84
4.5 Conversion of the PV module standard characteristics to arbitrary irradiance
and temperature values 89
4.5.1 Transformation based in normalized variables (ISPRA method) 89
4.6 Behavioural PSpice model for a PV module 91
CONTENTS ix
4.7 Hot spot problem in a PV module and safe operation area (SOA) 95
4.8 Photovoltaic arrays 96
4.9 Scaling up photovoltaic generators and PV plants 98
4.10 Problems 100
4.1 1 References 101
5 Interfacing PV Modules to loads and Battery Modelling 103
Summary 103
5.1 DC loads directly connected to PV modules 103
5.2 Photovoltaic pump systems 104
5.2.1 DC series motor PSpice circuit 105
5.2.2 Centrifugal pump PSpice model 106
5.2.3 Parameter extraction 106
5.2.4 PSpice simulation of a PV array-series DC motor-centrifugal
pump system 112
5.3 PV modules connected to a battery and load 113
5.3.1 Lead-acid battery characteristics 114
5.3.2 Lead-Acid battery PSpice model 117
5.3.3 Adjusting the PSpice model to commercial batteries 123
5.3.4 Battery model behaviour under realistic PV system conditions 125
5.3.5 Simplified PSpice battery model 131
5.4 Problems 132
5.5 References 132
6 Power Conditioning and Inverter Modelling 133
Summary 133
6.1 Introduction 133
6.2 Blocking diodes 133
6.3 Charge regulation 135
6.3.1 Parallel regulation 135
6.3.2 Series regulation 139
6.4 Maximum power point trackers (MPPTs) 143
6.4.1 MPPT based on a DC-DC buck converter 144
6.4.2 MPPT based on a DC-DC boost converter 145
6.4.3 Behavioural MPPT PSpice model 147
6.5 Inverters 154
6.5.1 Inverter topological PSpice model 157
6.5.2 Behavioural PSpice inverter model for direct PV
generator-inverter connection 164
6.5.3 Behavioural PSpice inverter model for battery-inverter connection 169
6.6 Problems 175
6.7 References 177
7 Standalone PV Systems 179
Summary 179
7.1 Standalone photovoltaic systems 179
7.2 The concept of the equivalent peak solar hours (PSH) 180
7.3 Energy balance in a PV system: simplified PV array sizing procedure 184
7.4 Daily energy balance in a PV system 187
7.4.1 Instantaneous power mismatch 188
x CONTENTS
7.4.2 Night-time load 190
7.4.3 Day-time load 191
7.5 Seasonal energy balance in a PV system 192
7.6 Simplified sizing procedure for the battery in a Standalone PV system 194
7.7 Stochastic radiation time series 196
7.8 Loss of load probability (LLP) 198
7.9 Comparison of PSpice simulation and monitoring results 205
7.10 Long-term PSpice simulation of standalone PV systems: a case study 207
7.11 Long-term PSpice simulation of a water pumping PV system 212
7.12 Problems 214
7.13 References 214
8 Grid-connected PV Systems 215
summary 215
8.1 Introduction 215
8.2 General system description 216
8.3 Technical considerations 217
8.3.1 Islanding protection 218
8.3.2 Voltage disturbances 218
8.3.3 Frequency disturbances 218
8.3.4 Disconnection 219
8.3.5 Reconnection after grid failure 219
8.3.6 DC injection into the grid 219
8.3.7 Grounding 219
8.3.8 EM1 219
8.3.9 Power factor 220
8.4 PSpice modelling of inverters for grid-connected PV systems 220
8.5 AC modules PSpice model 225
8.6 Sizing and energy balance of grid-connected PV systems 229
8.7 Problems 242
8.8 References 242
9 Small Photovoltaics 245
Summary 245
9.1 Introduction 245
9.2 Small photovoltaic system constraints 245
9.3 Radiometric and photometric quantities 246
9.4 Luminous flux and illuminance 247
9.4.1 Distance square law 247
9.4.2 Relationship between luminance flux and illuminance 247
9.5 Solar cell short circuit current density produced by an artificial light 248
9.5.1 Effect of the illuminance 25 1
9.5.2 Effect of the quantum efficiency 251
9.6 I(V) Characteristics under artificial light 253
9.7 Illuminance equivalent of AM1.5G spectrum 253
9.8 Random Monte Carlo analysis 255
9.9 Case study: solar pocket calculator 258
9.10 Lighting using LEDs 260
9.1 1 Case study: Light alarm 262
9.1 1 .I PSpice generated random time series of radiation 264
9.11.2 Long-term simulation of a flash light system 267
9.12 Case study: a street lighting system 2.70
9.13 Problems nr
9.14 References 272
Annex 1 PSpice Files Used in Chapter 1 273
Annex 2 PSpice Files Used in Chapter 2 283
Annex 3 PSpice Files Used in Chapter 3 187
Annex 4 PSpice Files Used in Chapter 4 293
Annex 5 PSpice Files Used in Chapter 5 303
Annex 6 PSpice Files Used in Chapter 6 305
Annex 7 PSpice Files Used in Chapter 7 389
Annex 8 PSpice Files Used in Chapter 8 319
Annex 9 PSpice Files Used in Chapter 9 321
Annex 10 Summary of Solar Cell Basic Theory 333
Annex 11 Estimation of the Radiation in an
Arbitrarily Oriented Surface 339
Index 353
Introduction to Photovoltaic
Systems and PSpice
Summary
This chapter reviews some of the basic magnitudes of solar radiation and some of the basics of PSpice.
A brief description of a photovoltaic system is followed by definitions of spectral irradiance, irradiance
and solar radiation. Basic commands and syntax of the sentences most commonly used in this book
are shortly summarized and used to write PSpice files for the AM1 SG and AM0 sun spectra, which are
used to plot the values of the spectral irradiance as a function of the wavelength and compare them with
a black body radiation. Solar radiation availability at the earth’s surface is next addressed, and plots are
shown for the monthly and yearly radiation received in inclined surfaces. Important rules, useful for
system design, are described.
1.1 The Photovoltaic System
A photovoltaic (PV) system generates electricity by the direct conversion of the sun’s energy
into electricity. This simple principle involves sophisticated technology that is used to build
efficient devices, namely solar cells, which are the key components of a PV system
and require semiconductor processing techniques in order to be manufactured at low cost
and high efficiency. The understanding of how solar cells produce electricity from detailed
device equations is beyond the scope of this book, but the proper understanding of the
electrical output characteristics of solar cells is a basic foundation on which this book is
built.
A photovoltaic system is a modular system because it is built out of several pieces or
elements, which have to be scaled up to build larger systems or scaled down to build smaller
systems. Photovoltaic systems are found in the Megawatt range and in the milliwatt range
producing electricity for very different uses and applications: from a wristwatch to a
communication satellite or a PV terrestrial plant, grid connected. The operational principles
though remain the same, and only the conversion problems have specific constraints. Much
is gained if the reader takes early notice of this fact.