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The thesis reports on the modeling and simulation of PV systems with grid-connection. The research carried out assesses the impact of key parameters of Photovoltaic systems on power generation and power quality. It also examines a utilization of Battery energy storage system (BESS) which serves the purpose to support the active power production by charging and discharging the surplus and reduced power generation from PV. The use of renewable energy systems, such as Photovoltaic (PV), is becoming highly popular in modern power systems. However, the random and fluctuating nature of the solar resource increases the possibility of power mismatches between power generation and power demand in the grid. A large penetration of such a fluctuating energy resource can degrade the reliability of supply, the stability of system operation and introduce adverse power quality phenomena. Battery Energy Storage Systems (BESS) are recognized to be a viable solution to overcome the fluctuations present in PV systems. Hence, the integration of BESS with grid-connected PV systems will greatly enhance the reliability of the overall power grid. In this thesis, the modeling and simulation of PV-BESS is carried out using the MATLAB/Simulink environment. A test system comprising a 100 KW PV panel is connected through a DC-DC converter in tandem with a DC-AC inverter to a Point of Common Coupling (PCC) of an equivalent power grid. The effects of changes in solar irradiance and temperature, on the output power of the PV system, are assessed in the first part of the thesis. The integration of a BESS model in parallel with a PV system model is carried out in the second part of the thesis, where the overall intermittent behavior of the combined system is assessed. It should be stressed that the key purpose of integrating a BESS and a PV system is to provide constant power supply to the load system under varying environmental conditions. The outcome of this investigation shows that the integration of the BESS into the PV system yields very encouraging results in counteracting the fluctuation of the PV installation, helping to ensure a constant power supply to the load.

The power distribution systems are continuously expanding due to the rise in world population and its migration to urban areas. But consuming the non-renewable resources to generate the electric power, the carbon emissions have made a serious call to global warming so, during the last decade, the electric power systems have seen the penetration of renewable energy resources. This phenomenon has given flexibility to the power grid but also its complexity has increased. In order to successfully integrate the distribution generation of the renewable energy resources, the power grid demands modern power electronic equipment and state-of-the-art techniques, control approach and simulation tools to assess the practical like conditions of the systems. In this continuous struggle to modernize and advance state-of-the-art power grid, this master research thesis investigates the two-stage converter topology for the grid-connected photovoltaic generator using the Newton Raphson iterative method in MATLAB programming. The reason to choose the photovoltaic generator is the rapid growth of such systems and the Newton Raphson method has the advantage of being fast in convergence and robust. The analytical tool for this research thesis is MATLAB coding. The maximum power point tracking of the photovoltaic generator was applied in MATLAB coding to always extract the maximum power from the photovoltaic panels. Later on the admittance matrix, nodal voltages, linearized system of equations of the dc converter are constructed. Then this system of equations is incorporated into the linearized system of equations of the voltage source converter. To implement this scenario in power flows the dc converter implementation in power flows is also represented. The results of different test cases indicate that the two-stage converter topology, involving dc/dc and voltage source converter, for the distribution generation improves the voltage profile significantly at each bus of the system and inject the active power into the nodes generated by the DG units.

This thesis focuses on static reactive power compensators in utility applications. The objectives for the thesis are to disclose the benefits of the Main Reactor based Static VAr compensator (SVC) compared to the conventional SVC, to find out the most important factors affecting the feasibility of different compensator technologies and to perform a case study, which illustrates the benefits of the Main Reactor concept. Static compensators, like SVC and Static synchronous compensator (STATCOM), are used in utility applications to provide voltage control and power oscillation damping and to increase capacity and stability of the network. Reactive power compensating has a major role in controlling the voltage of the transmission system, especially during fault and transient situations. Additionally, reactive power compensation can be used to reduce losses in the transmission system in a steady state. Due to STATCOMs modularity and good tolerance for varying network conditions, its competitiveness has improved, compared to SVC. Sometimes conditions in the power system are so harsh that the performance of the traditional SVC is not sufficient enough to meet all the requirements. Main Reactor concept improves the performance of SVC and provides a cost-effective, competitive alternative for STATCOM based solutions. This thesis outlines the technical background for the improved performance of Main Reactor SVC. Characteristics of the Main Reactor SVC are discussed from the most important aspects for the designing process. The case study presented in this thesis revealed the competitiveness of the Main Reactor SVC under challenging network conditions.

This thesis reports on an investigation of the impact of static var compensators (SVC) and static compensators (STATCOM) on the voltage and frequency stability of practical transmission system. It also explores an application of a battery energy storage system (BESS) which serves the purpose of stabilizing an otherwise unstable power transmission network. A mismatch of energy production and consumption at a given area results in power exports over long distances, sometimes across borders. Power exporting and system stability are some of the major concerns in the transport of electrical energy. It has been acknowledged that FACTS devices are a possible way forward to ensure high throughputs of power with enhanced stability. FACTS equipment has lived up-to its promise in cases where system stability has been a concern. BESS application in power transmission is a new area of study which is just commencing to be explored. The thesis assesses the impact of the SVC and STATCOM on Siirtoverkkomalli and Nordic-32 in an equivalent form. It includes a comparative study of both FACTS devices under unstable network conditions. Preliminary assessments have indicated that, BESS are very effective means for providing frequency and voltage support during load variations. In this thesis, BESS is applied in Siirtoverkkomalli to assess whether or not BESS can be effective to stabilize an otherwise unstable network. It has been found that using both the SVC and STATCOM in a transmission system significantly improves stability. The comparison shows that the STATCOM is very effective, outperforming the better known SVC. On the other hand, when a BESS is applied in Siirtoverkkomalli, it shows that it has great potential in stabilizing an otherwise unstable system. Hence, a BESS can perform multiple functions, it provides stability support, similar to the SVC or STATCOM, but it can provide frequency support during load changing periods.

This thesis investigates the application of three-phase State Estimation in Micro-Grids with distributed PV generators. In particular, it explores the use of three-phase Power Flows and State Estimation together with VSC modeling. The VSC may be used to provide voltage regulation at selected nodes of the micro-grid in which case it acts as a STATCOM or it may be used to provide the interface between the DC PV generator and the AC side of the micro-grid. Small renewable energy plants are increasing their share of the overall energy resource. They are installed at the low-voltage end of the grid and this is blurring the otherwise classical concept of producers and consumers of electrical energy. More and more, consumers are able to produce electrical energy by installing PV cells at their premises and so they are becoming prosumers. This has resulted in the appearance of energy plants distributed all over the power grid. Hence, power flows might not be as straightforward to determine as previously, when producers and consumers were very clearly separated. In order to ensure an effective control of the operation of the grid it is of paramount importance to have an effective knowledge of the actual state of the power network. Single-phase state estimators for power grids represent a classical concept in electric power systems theory but this is limited to positive-sequence representations of the power grid, i.e., three-phase power networks which exhibit a perfect balance. Needless to say that a major limitation of the positive-sequence network representation is its inapplicability to cases when the network unbalances are significant and cannot be ignored. In real life the load is not always equally spread between the three phases; no matter how hard engineers try to achieve a reasonable balance, there is always a degree of unbalance which ought to be studied because it may impair the operation of the grid and increase its power losses. This can only be assessed by representing the three-phase power grid on its natural coordinate system, which is the abc frame-of-reference. This thesis presents a three-phase modeling approach to power flows and state estimation of balanced and unbalanced power networks. A second contribution is the modeling of a three-phase VSC that has been derived from an existing single-phase VSC. The model is then extended to incorporate the model of PV generator. Because of the flexibility with which the code has been developed, the incorporation of multiple STATCOMs and PV generators may be simulated to be a realistic part of the power grid, enabling the distributed concept and the micro-grid concept to be brought together.

This thesis reports on the evaluation of the impact of a battery energy storage system (BESS) on the voltage and frequency stability of a power transmission system. With the increased penetration of renewable energy sources, particularly wind power, into the power system network new challenges regarding the two major concerns in the transportation and distribution of electrical energy, i.e. power quality and system stability, are being experienced. One way to reduce these concerns is the application of MW-level Battery Energy Storage Systems (BESSs). Despite a long-standing interest in the BESS technology, its application in the transmission system had not been seriously considered until relatively recently. Since the main focus for this study is frequency stability, a comprehensive discussion on frequency control, including primary and secondary frequency controls is included. This provides the opening for the evaluation of the impact of the BESS on system frequency. In addition, this thesis outlines several BESS installations from early 1980s to today’s state of the art technology. The thesis conducts research using modeling and simulation in PSCAD and PowerWorld environments to carry out a comprehensive assessment of the impact of the BESS technology to ameliorate the frequency excursions that follow a power load increase in a high-voltage transmission system and providing effective voltage support. In brief, the findings of this thesis indicate the positive influence of the BESS on the power transmission system stability.

A photovoltaic system transforms solar radiation into electrical energy using so-called PV panels. A key component of this system is the power electronics subsystem which enables maximum power extraction from the available solar irradiation, as well as con-nection to the AC power grid. However, the current and voltage waveforms at the point of common coupling (PCC) with the power grid contain a degree of harmonic distortion which, in some instances, may surpass that recommended by existing standards. The presence of high harmonic distortion in an electrical installation significantly decreases power quality and the renewable energy sources’ power electronics carries the potential to yield high harmonic distortion. This thesis reports on an investigation of some of the factors that impact adversely the quality of the current and voltage waveforms in an electrical power distribution network with distributed photovoltaic systems. These factors include irradiance levels, imperfect conditions of the filtering system, resonant conditions, load imbalances and selection of the inverter’s switching frequency. To quantify current and voltage harmonic injections, a two-stage model of a photovoltaic array was designed in Simulink in order to show the impact of a single photovoltaic system. The basic PV system model is then applied to a model of an electrical power distribution grid, with several distributed PV units. The study indicates that irradiance is the primary factor influencing THD and that at low PV power outputs, harmonic emissions may exceed the recommended harmonic distortion limits, particularly when resonant conditions exist at the output of connection of the PV plant. Different MPP control methods employed in the DC-DC conversion stage were also investigated and it is observed that they do not seem to have much impact on THD. This applies in the absence of partial shading, an issue which was not considered as part of this research project. As expected, the use of well-designed filters is the key to keeping harmonics emissions low. Nevertheless, perfect filtering does not exist in actual installations and the study also investigates the impact of imperfect filtering parameters and filter branch failure, on the voltage and current waveforms at PCC.

Aiming at reducing the rather high percentage of CO2 emissions attributed to the electrical energy production industry, a new generation of power plants has been introduced which produce electricity by using primary energy resources which are said to be renewable, such as wind, solar, geothermal and biomass. This has had not only the benefit of reducing CO2 emissions into the atmosphere to a trickle, by the new power plants but to also encourage a great deal of technological advance in both the manufacturing sector and in research institutions. Wind power is arguably the most advanced form of renewable energy generation today, from the bulk energy production and economic vantages. This doctoral thesis rigorously deals with the analysis, assessment and description of the impact of double-fed variable speed wind turbine on the dynamic behaviour of both, the wind farm itself and its interconnection with the conventional power generation system. Analytical analysis of the results published in the open literature is used as a tool to gain a solid understanding of the dynamic behaviour of power systems with wind generation. The influence of the characteristics of the electrical system and wind turbines or external parameters on stability is assessed using modal analysis. Studies conducted have focused on the analysis of transient stability and small signal stability for the damping of oscillations in power systems and its enhancement. Analysis of small signal stability and transient stability analysis are carried out using modal analysis and dynamic simulations in the time domain. This thesis proposes the implementation of sliding mode control techniques for the DFIG WT converters, both the Machine-Side Converter (MSC) and the Grid-Side Converter (GSC). The proposed control system is assessed on conventional dynamic power systems with wind power generation under different test case scenarios. The newly developed SMC control scheme demonstrates the importance of employing non-linear control algorithms since they yield good operational performances and network support. This is of the utmost important since in power systems with wind power generation is critically important to ensure the robust operation of the whole system with no interaction of controllers. Sliding Mode Control shows to be more robust and exible than the classical controller, opening the door for a more widespread future participation of DFIG-WECS in the damping of power system oscillations., Con el objetivo de reducir el elevado porcentaje de las emisiones de CO2 atribuidas al sector de la generación de energía eléctrica, se ha introducido una nueva generación de centrales eléctricas cuya fuente primaria de energía es de naturaleza renovable como las eólicas, solares, geotérmicas y de biomasa. Esto no sólo beneficia la reducción de las emisiones de CO2 a la atmósfera sino que también estimula e impulsa el avance tecnológico, tanto en el sector manufacturero como en los centros de investigación. En la actualidad la energía eólica es probablemente la fuente de energía renovable más avanzada, desde la producción de energía hasta las ventajas económicas. La presente Tesis Doctoral se ha centrado en analizar, evaluar y describir rigurosamente el impacto de los aerogeneradores de velocidad variable doblemente alimentados en el comportamiento dinámico tanto del propio sistema eólico como de su interconexión con el sistema síncrono convencional de generación de energía eléctrica. El análisis analítico de los resultados publicados en la literatura es utilizado como herramienta para una mejor comprensión del comportamiento dinámico de los sistemas de potencia con generación eólica. La influencia de las características del sistema eléctrico y de los aerogeneradores o parámetros externos sobre la estabilidad es evaluada empleando análisis modal. Los estudios realizados se han enfocado en el análisis de estabilidad transitoria y de pequeña señal para la evaluación de la amortiguación de oscilaciones en las redes eléctricas de potencia. Análisis de estabilidad de pequeña señal y análisis de estabilidad transitoria son llevados a cabo usando análisis modal y simulaciones dinámicas en el dominio del tiempo. En esta tesis se propone la aplicación de técnicas de control en modo deslizante en los convertidores de los aerogeneradores doblemente alimentados, tanto en el convertidor de la máquina como en el convertidor de la red. El sistema de control propuesto es evaluado en redes dinámicas de generación convencional con generación eólica, considerando diferentes escenarios. El recientemente desarrollado sistema de control CMD demuestra la importancia de implementar algoritmos de control no lineales, ya que producen un buen rendimiento y dan soporte a la red. Esto es sumamente importante ya que en los sistemas de potencia con generación de energía eólica es vital asegurar el funcionamiento eficiente de todo el sistema sin interacción de los controladores. El Control en modo deslizante demuestra ser más robusto y flexible que el controlador cl asico, abriendo la puerta a un futuro con una mayor participación de generación eólica en la amortiguación de las oscilaciones de potencia.

This thesis reports on an investigation of the impact of battery energy storage systems (BESS) on the voltage and frequency stability of a transmission system. It also explores an application of a BESS into an active distribution system which delves the realm of smart grids. Power quality and system stability are two major concerns in the transportation and distribution of electrical energy. It has long been recognised that energy storage is a possible way forward to improve on these parameters; but the battery technology and the ancillary power electronics had not been developed sufficiently, until quite recently; to meet such expectations. Current battery energy storage challenges the paradigm of instantaneous usage of electrical energy. Intermittent renewable energy production has the potential to improve the quality and efficiency of energy production. The thesis gives an explanation of the battery working principles and includes a com-parative study of battery technologies and the main advantages and disadvantages of batteries in comparison to other electrochemical energy storage technologies. Besides, the thesis addresses the all-important issue of power electronic converters. Battery con-verters are responsible for controlling the power exchange between the grid and the BESS. The link between the battery and the DC bus, i.e., DC-DC converter, and the link between the DC bus and the grid, i.e., DC-AC converter, are covered in depth. It has been found that using a BESS in a transmission system significantly improves frequency stability. The damping of oscillations following a transient event is much improved. The BESS can be seen as additional spinning reserve in the system. On the other hand, when a BESS is applied in an active distribution system, the power, deliv-ered by an intermittent energy source is of much higher quality. In particular, it is shown that the BESS has the potential for turning a part of the distribution system with intermittent generation, self-reliable from the energy perspective In brief, the outcome of this thesis shows the positive influence of the BESS in electrical powers grid. Further research is required to develop a more detailed model of the battery which would include battery ageing and temperature dependency.

Aiming at reducing the rather high percentage of CO2 emissions attributed to the electrical energy production industry, a new generation of power plants has been introduced which produce electricity by using primary energy resources which are said to be renewable, such as wind, solar, geothermal and biomass. This has had not only the benefit of reducing CO2 emissions into the atmosphere to a trickle, by the new power plants but to also encourage a great deal of technological advance in both the manufacturing sector and in research institutions. Wind power is arguably the most advanced form of renewable energy generation today, from the bulk energy production and economic vantages. This doctoral thesis rigorously deals with the analysis, assessment and description of the impact of double-fed variable speed wind turbine on the dynamic behaviour of both, the wind farm itself and its interconnection with the conventional power generation system. Analytical analysis of the results published in the open literature is used as a tool to gain a solid understanding of the dynamic behaviour of power systems with wind generation. The influence of the characteristics of the electrical system and wind turbines or external parameters on stability is assessed using modal analysis. Studies conducted have focused on the analysis of transient stability and small signal stability for the damping of oscillations in power systems and its enhancement. Analysis of small signal stability and transient stability analysis are carried out using modal analysis and dynamic simulations in the time domain. This thesis proposes the implementation of sliding mode control techniques for the DFIG WT converters, both the Machine-Side Converter (MSC) and the Grid-Side Converter (GSC). The proposed control system is assessed on conventional dynamic power systems with wind power generation under different test case scenarios. The newly developed SMC control scheme demonstrates the importance of employing non-linear control algorithms since they yield good operational performances and network support. This is of the utmost important since in power systems with wind power generation is critically important to ensure the robust operation of the whole system with no interaction of controllers. Sliding Mode Control shows to be more robust and exible than the classical controller, opening the door for a more widespread future participation of DFIG-WECS in the damping of power system oscillations. ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Con el objetivo de reducir el elevado porcentaje de las emisiones de CO2 atribuidas al sector de la generación de energía eléctrica, se ha introducido una nueva generación de centrales eléctricas cuya fuente primaria de energía es de naturaleza renovable como las eólicas, solares, geotérmicas y de biomasa. Esto no sólo beneficia la reducción de las emisiones de CO2 a la atmósfera sino que también estimula e impulsa el avance tecnológico, tanto en el sector manufacturero como en los centros de investigación. En la actualidad la energía eólica es probablemente la fuente de energía renovable más avanzada, desde la producción de energía hasta las ventajas económicas. La presente Tesis Doctoral se ha centrado en analizar, evaluar y describir rigurosamente el impacto de los aerogeneradores de velocidad variable doblemente alimentados en el comportamiento dinámico tanto del propio sistema eólico como de su interconexión con el sistema síncrono convencional de generación de energía eléctrica. El análisis analítico de los resultados publicados en la literatura es utilizado como herramienta para una mejor comprensión del comportamiento dinámico de los sistemas de potencia con generación eólica. La influencia de las características del sistema eléctrico y de los aerogeneradores o parámetros externos sobre la estabilidad es evaluada empleando análisis modal. Los estudios realizados se han enfocado en el análisis de estabilidad transitoria y de pequeña señal para la evaluación de la amortiguación de oscilaciones en las redes eléctricas de potencia. Análisis de estabilidad de pequeña señal y análisis de estabilidad transitoria son llevados a cabo usando análisis modal y simulaciones dinámicas en el dominio del tiempo. En esta tesis se propone la aplicación de técnicas de control en modo deslizante en los convertidores de los aerogeneradores doblemente alimentados, tanto en el convertidor de la máquina como en el convertidor de la red. El sistema de control propuesto es evaluado en redes dinámicas de generación convencional con generación eólica, considerando diferentes escenarios. El recientemente desarrollado sistema de control CMD demuestra la importancia de implementar algoritmos de control no lineales, ya que producen un buen rendimiento y dan soporte a la red. Esto es sumamente importante ya que en los sistemas de potencia con generación de energía eólica es vital asegurar el funcionamiento eficiente de todo el sistema sin interacción de los controladores. El Control en modo deslizante demuestra ser más robusto y flexible que el controlador cl asico, abriendo la puerta a un futuro con una mayor participación de generación eólica en la amortiguación de las oscilaciones de potencia.