Top PDF Performance Analysis of a Grid connected Wind Energy system

Abstract: - This paper is concerned with the study of a small wind generation system used for battery charging. A topology that aims at the exploitation of maximum energy from the generator, generated at low speed is proposed. The characteristics of the wind turbine and the generator are discussed, providing the overview of the system modeling. Simulation tests of the system are obtained using MATLAB/SIMULINK. We adopt compact permanent magnet type synchronous generator, which doesn’t need exciting current, and step- up /down buck-boost chopper to wind power generating system of a few kW output with rotor speed sensor. In addition, we employ rectifier circuit using Diode Bridge instead of AC-DC converter with PWM method and a battery charging system. Using these methods we achieve a simple wind power generation system.

In recent years, wind resource is a kind of renewable energy and becomes more and more important in many countries.Wind power has its own characteristics, such as discreteness, randomness, and uncontrollability.With the increase of power capacity of future wind farms in power system, the study of how big integrated wind farms affect power system operation becomes quite important.For this reason, and in order to investigate the effects of wind farms on the grid, adequate models must be used.Voltage instability problems and collapse typically occur on power system that is not able to meet demand of reactive power, for considering heavy loads and fault conditions.When wind farms are connected to a weak network, the voltage stability is one of the most important factors that affect wind farm’s stable operation. The wind turbines have to be able to continue uninterrupted operation under transient voltage conditions to be in accordance with the grid codes. An induction generator connected with a wind turbine to generate electricity is sink of reactive power. Different solutions are found to support the transient behavior of squirrell cage induction generators in case of changes in the grid voltage. Mechanically switched capacitors, SVC, Synchronous Condensers and Voltage Source Static Var Compensator such as the STATCOM can be used to regulate voltage as shunt compensator to improve the grid interface of directly connected asynchronous wind generators. The voltage profile is main issue when considering stable operation of wind farm In order to maintain stable operation and avoid over-speed of the induction generators, some control strategies which use FACTS devices are presented to improve stability margin.

In the last few years, there was a huge grown of the number of photovoltaic systems installed all over the world. This happens thanks to the reduction of the PV modules fabrication cost and the policies adopted by most of the countries in the world that give some benefits and new fees to whom have those systems installed at home. However, this growth has not been accompanied by important improvements in the field of PV system diagnosis, supervision and fault detection [3] because it is a common belief that PV systems are maintenance free and monitoring PV systems represent an extra cost. Even if a PV panel shows a really low failure rate, it is important to keep in mind that PV systems are composed by other elements that may also have failures. Also, faults in PV systems do not only affect the performance of the system but may also lead to damage the equipment. Moreover, although PV systems generally operate without problems, when there are faults on the system they are hard to be observed by the operating personnel. In order to prevent faults and failures that lead to a decrease of the lifetime of a PV system, and to improve the system efficiency, monitoring and fault detection have to be practiced.

In the above system, the stator of the DFIG is directly connected to the grid, while two back to back PWM voltage source converters (VSCs) are inserted between the rotor and the grid to control the rotor and stator output power which is fed to the grid for the variable speed operation [6]. It is possible to control rotor current injection using VSCs to ensure effective operation in both sub and super synchronous modes. Decoupled control of active and reactive powers using the vector control is presented in [7] and current control methods for wind turbines using DFIG are presented in [8]. Both stator and rotor are able to supply the power, but the direction of active power flow through the rotor circuit is dependent on the wind speed and accordingly, the generator speed. Below the synchronous speed, the active power flows from the grid to the rotor side, and the RSC acts as a voltage source inverter while the GSC acts as a rectifier but above the synchronous speed, RSC acts as a rectifier and GSC acts as an inverter. The rotor VSC is controlled to limit the torque pulsation, and the grid VSC is controlled to limit the DC voltage ripple [9]. Two back to back voltage fed current regulated converters are connected to the rotor circuit. The firing pulses are given to the devices (IGBTs) using PWM techniques. The converters are linked to each other by means of DC-link capacitor. The main purpose of the GSC is to control the DC-link voltage and ensures the operation at unity power factor by making the reactive power drawn by the system from the utility grid equal to zero, while the RSC controls the active and reactive powers by controlling the d-q components of the rotor currents i dr and i qr .

HOMER is a micro power optimization software used in evaluating designs of both off-grid and grid- connected power systems for a variety of applications. The cost benefit analysis of a wind turbine-solar hybrid system was done using HOMER software and comparison was also made with the cost per kilowatt of central grid or utility supply. The hybrid system have a pay-back period of about thirty-three years and at current costs, central grid power is the least expensive option but may not be available to most rural households far from the grid. Hence it is necessary to supply these areas from isolated power sources. 1. INTRODUCTION

The proposed system presents power-control strategies of a grid-connected hybrid generation system with versatile power transfer. This hybrid system allows maximum utilization of freely available renewable energy sources like wind and photovoltaic energies. For this, an adaptive maximum power point tracking (MPPT) algorithm along with standard perturbs and observe method will be used for the system. The turbine rotor speed is the main determinant of mechanical output from wind energy and Solar cell operating voltage in the case of output power from solar energy. Permanent Magnet Synchronous Generator is coupled with wind turbine for attaining wind energy conversion system. This paper addresses dynamic modeling and control of a grid- connected wind–PV–battery hybrid system with versatile power transfer. The hybrid system, unlike conventional systems, considers the stability and dispatch-ability of its power injection into the grid. The hybrid system can operate in three different modes, which include normal operation without use of battery, dispatch operation, and averaging operation. This paper also indicates the merits of the proposed system.

Solutions based on asynchronous generators, the so called Doubly Fed Induction Generators (DFIG), with the stator windings directly connected to the grid and a partial scaled electronic converter between the rotor and the grid, allow a low to moderate variation of the rotor speed. Since the power converter is partially scaled, typically one third of the rated power of the system [11], this solution is somewhat cost effective but, on the other hand, there are limitations to control effectively the grid variables, which translates in a deficient quality power system [12]. It should be pointed out that this concept uses a geared drive train to match the low rotational speed promoted by wind velocities to the higher efficient rotational speed of this generator type.

ABSTRACT: The successful in the implementation of wind turbines depends on several factors, including: the wind resource at the installation site, the equipment used, project acquisition and operational costs. In this paper, the production of electricity from two small wind turbines was compared through simulation using the computer software HOMER - a national model of 6kW and an imported one of 5kW. The wind resources in three different cities were considered: Campinas (SP/BR), Cubatão (São Paulo/BR) and Roscoe (Texas/ USA). A wind power system connected to the grid and a wind isolated system - batteries were evaluated. The results showed that the energy cost ($/kWh) is strongly dependent on the windmill characteristics and local wind resource. Regarding the isolated wind system – batteries, the full supply guarantee to the simulated electrical load is only achieved with a battery bank with many units and high number of wind turbines, due to the intermittency of wind power.

It is clear that reactive power is supplied by the grid to the stator winding of the induction generator for development of the rotating magnetic field at the stator. The reactive power demand compensation at steady state is provided by the capacitor bank which is inserted across the terminals of wind turbines. 3LG fault occurs at 25KV network in the transmission line at 15 sec & is cleared after 200 ms i.e. fault is cleared at 15.2 sec. It is seen that during the fault, whole of WPP units trip and exit from the circuit as shown in Fig 9(a) & Fig 9(b). Tripping is because of grid unable to fulfill reactive power of WPP as shown in Fig 10 (a) & Fig 10 (b) .The voltage at bus B2 drops from unity as shown in Fig11 (a) & Fig 11 (b) and rotor of the wind turbines accelerates out of control as shown in Fig 12 (a) & Fig 12 (b) .This leads to instability conditions of the grid .When STATCOM or SSSC is connected reactive power is generated thereby fulfilling the reactive power requirement of WPP shown by Fig 10(a) & Fig 10 (b) , preventing their tripping as shown by Fig 9(a) & Fig 9 (b).Voltage at bus B2 is improved as shown in Fig 11 (a) & Fig 11 (b). Turbine rotor accelerates but is under control as shown in Fig 12 (a) & Fig 12 (b). PI controller of STATCOM and SSSC is replaced by NFC and system performance is improved as shown in Fig 9(a) & 9(b), Fig 10(a) & 10(b), Fig 11(a) & 11(b) and Fig 12 (a) & 12 (b). The settling time of the system has reduced making system relatively stable.

Wind energy has become one of the significant alternative renewable energy resources because of its abundance and the strong drive for its commercialization. Dynamic electric load variations and wind velocity excursions cause excessive changes in the prime mover kinetic energy and the corresponding electrical power injected into the AC grid utility system. In this paper, a scheme based on the low cost static switched filter compensator (SSFC) is presented for voltage sag/swell compensation, power factor improvement in distribution grid networks with the dispersed wind energy interface. The SSFC scheme is based on an intermittent switching process between two shunt capacitor banks to be one of them in parallel with the capacitor of a tuned arm filter. Two regulators based on a tri- loop dynamic error driven inter-coupled weighted modified proportional-integral- derivative (PID) controller which is used to modulate the PWM.

IV. S IMULATION WITH H OMER SOFTWARE Homer is an abbreviation of “Hybrid Optimization Model for Electric Renewables.” It is a micro power optimization model developed and regularly improved by the American National Renewable Energy Laboratory. This software helps to find the best electricity generation system configuration that is to say the appropriated technologies, the size and number of each component, also comparing costs and environmental impacts. It models both conventional and renewable energy technologies in particular solar photovoltaic and wind turbines which are the options envisaged for energy efficient technologies. Homer is able to evaluate economics and technical feasibility of the system. First, Homer simulates the working power system by calculating the hourly energy balance for a year. Hour by hour, Homer determines the electric demand of the site and the local electricity supplied by the system. Comparing these energy flows, Homer is able to estimate if the configuration is feasible that is to say if the system can satisfy the electricity requirements. Then, Homer optimizes the results. Among the possible configurations defined by the simulation, Homer retains the most cost-effective in a table ranked by Net Present Costs (NPC). Homer can realize a sensitivity analysis by modifying some inputs in a range defined by the user in order to compare different possible scenarios [11]

The conventional DFIG is connected to the grid and without any energy storage and normal operation is observed. The various quantities plots are observed with respect to time. The wind speed is varied from 8m/s to 12m/s. This paper describes the disadvantages of conventional DFIG scheme and suggests a new scheme with integrated energy storage (ES). The simulation results show the successful working of the modified new scheme with integrated storage system. The difference between battery and super-capacitor is that the battery can provide extra power for minutes to hours depending on the selected capacity, while the super-capacitor can provide extra energy for few seconds to minutes, only. It shows that super- capacitor is more suitable for voltage sag and swell, transient, fault ride through application or where the extra power demand is very low. But battery can be used for the support of large amount of power for a large time period.

The search for clean and renewable energy alternatives has been, in recent decades, a new worldwide trend. This is mainly due to the need for reducing the dependency of oil derivatives and pollutant emissions. Another determining factor in the search for alternative energy was the energy crisis that the world has suffered in the 70's of last century. The great dependence on fossil fuels awakened the interest in investing in the use of other energy sources, including the renewable, such as solar energy (PEREIRA, 2011). This energy can be directly converted into electric power by means of physical effects on certain materials, including photovoltaic, which is characterized by the interaction of the photons contained in sunlight with the atomic structure of matter. The French physicist Edmond Becquerel primarily observed this photovoltaic effect in 1839. In 1873, Willoughby Smith discovers the photoconductivity of selenium and, in 1876, Adms and Day realized that the junction of selenium and platinum develops photovoltaic effect when exposed to sunlight. Subsequently, in 1905, Albert Einstein (PINA, 2013) theoretically explained this phenomenon.

Abstract: This paper shows the topology of the hybrid grid-connected power system and the performances of the front-end three-phase power inverter. The renewable sources of the hybrid power system consist of a solid oxide fuel cell and a wind-turbine. This type of combination is the most efficient one. The proposed topology benefits of the one common DC-AC inverter which injects the generated power into the grid. The architecture diminishes the cost of the power conditioning system. Moreover, due to the power balance control of the entire power conditioning system the bulk dc link electrolytic capacitor is replaced with a small plastic film one. The final power conditioning system has the following advantages: independent control of the reactive power, minimize harmonic current distortion offering a nearly unity power factor operation (0,998) operation capability, dc link voltage regulation (up to 5% ripple in the dc-link voltage in any operated conditions), fast disturbance compensation capability, high reliability, and low cost. The experimental test has been performed and the performances of the grid power inverter are shown.

In the case of Syst. 6, one of the justifications for the excellent performance are due to the fact that this system was installed in the optimum conditions, that is, with azimuthal deviation from the geographic north, very close to zero, and the 22 ° inclination of the modules very close to the latitude value of the city of Curitiba (25 °), and the panel is in a shaded area. These factors contribute to the maximization of energy generation throughout the year. The Neoville (NV) system presents the best installation characteristics, panel tilt angle equal to the latitude of the city in which it was installed, zero azimuth deviation, and a totally free shading area. However, it did not present the best performance index due to the high disconnection rate of the utility grid, thus leaving the system inoperative for several hours during the day.

The first problem of a CGS with a conventional configuration is that the line heaters low thermal efficiency which causes them to burn too much fuel. The current thermal efficiency of conventional heaters have been reported to be in range of 0.35 to 0.5 (Arabkoohsar et al., 2014). In order to overcome this problem many proposals have already been presented previously. These proposals mainly include employing renewable energy source heating systems to support the line heater at the CGS and reduce its heating duty. In one of the first efforts in this regards, employing a direct solar heat system for a typical CGS station in Iran was proponed (Farzaneh-Gord et al., 2011). As the previous proposed system considered an ideal instantaneaously controllable line heater, in contrats with the real common available heaters in the market, the authors modified their previous work by considering an actual heater and adding a solar storage tank to store the collectoed solar heat and using it at nightly hours during which the heating demand of CGS is naturally higher than daily hours (Farzaneh-Gord et al., 2012). In another work, by the same token, employing a smart solar heating system equipped with a solar storage tank along with a controllable line heater in CGSs was proposed and a thorough exergy and energy analysis on such a CGS was carried out (Arabkoohsar et al., 2014). In another work, employing geothermal system in CGSs was evaluted and this system was economically compared to the previous systems proposed for the same objective (Farzaneh-Gord et al., 2015).

ABSTRACT: As we know India faces problem of Power blackout every year due to the overloading on the main electrical grid. To avoid the above problem, Microgrids are the best solution. Basically, Microgrids are the small version of electrical grid. They are independent power system. Microgrids can be connected with renewable energy sources such as solar and wind. The use of renewable energy introduces the need of various storing devices and supplies it whenever required. Microgrids can provide wide range of applications in buildings, military camps and corporate/academic campuses, etc. They can have efficient and effective provision of electricity to “off-grid” areas as well as “keep the lights on” in times of crisis for critical applications like hospital. Though, Microgrids being so advantageous it has several technical challenging issues to overcome i.e. voltage and frequency control, islanding and its protection in Microgrids. This paper discusses the overview of Microgrids and issue to overcome in it-its Protection.

Bangladesh has seven hundred kilometer coastal line, analysis of upper air data by Center for Wind Energy Technology (CWET) India show that wind energy resource of Bangladesh is not good enough for grid connected wind parks [11]. At present, several wind resource assessment program (WERM,SWERA, WRAP of BPDB) is ongoing in the country. From the previous studies it can be inferred that the small wind turbines can be installed in the coastal regions of the country [12]. The wind speed in some regions of Bangladesh is satisfactory for operation pumps and for generation of electricity. It was found that the wind speed in Chittagong is 2.57 m/sec or more for 4000 hours a year. At this available speed a wind plant can be operated both for generation of electricity and for driving pumps. Recently, several small wind generators have been installed by BRAC (11 small wind turbines in various coastal sites) and Grameen Shakti (two wind generators of 300 W and 1 KW at its Chakoria Shrimp Farm).

Due to its construction, the phase windings are exactly the same and the flux linkage between each other can be neglected. This fact allows the analysis of only one phase to determine the flux linkage (λ) and the electromagnetic torque (Te). The modular configuration of the TFPM enables the finite element method to be performed in only one pole pitch (Fig. 2). The saturation effect is taking into account considering the non-linear characteristic of the core material. The flux linkage in phase A can be determined by the finite element method applied to the mesh geometry shown in Fig. 3. In addition, the general electrical machine theory can be used to determine the induced voltage in each winding using the equation (1).

It is important to highlight that before the publication of ANEEL’s resolution n. 482 on the regulation of GCPVSs, Curitiba had already two systems installed. These systems are: (i) the GCPVS 2.1 kWp installed in the Green Office of the Technological Federal University of Paraná (UTFPR) in 2011, and (ii) the GCPVS 8.64 kWp of ELCO company, installed at the company's headquarters at the beginning of 2012. The ELCO’s system was the first GCPVS to be homologated by the Energetic Company of Paraná (COPEL) on October 2nd, 2013 9 .