Archivo para marzo, 2016


Conceptual diagram of a dc-bus microgrid system

The dc-bus microgrid link the diferent component of the microgrid both loads as sources. The figure is a general representation with conextion to AC-grid, wind turbine, PV solar plant, DC and AC loads, Batteries, fluwheel, micro turbine, AC/DC converser, DC/AC converser and DC/DC converser.

Source:
S. Vimalraj, P. Somasundaram, “Fault Detection, Isolation and Identification of Fault Location in Low-Voltage DC Ring Bus Microgrid System,” Int. J. Advanced Res. in Electrical, Electronics and Instr. Eng. vol. 3, special iss. 2, pp: 570-582, Apr. 2014

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The schematic diagram for the dc micro-grid proposal for Bangladesh

In this system, a PV-diesel hybrid concept with dc grid has been proposed where the PV panel is not placed in any central location but distributively placed on roof tops at conventional locations. The number of solar PVs placed on a roof is such that they can be connected directly to the grid. The diesel generator is needed to give support to the system during bad weather and reduce the battery storage for the system. Diesel generator is placed at a convenient location and in case of higher demand; several diesel generators could be installed at the same place as per increased load demand. Diesel generators would be connected to the grid via ac-dc converters. A battery may be placed to store the power generated from diesel generator. Each consumer is connected to the grid and is metered for the energy consumed. Schematic diagram of a dc micro grid and a typical setup inside the consumer premises is shown in Figure. A consumer will have a dc-dc converter to convert the high grid voltage to nominal 12 V and charge a battery set up individually at the premises to store energy. It may be mentioned here that the charge controller to protect the battery is built inside the converter. During the day time, solar panels will produce output to be stored in the batteries of the individual customers. The size of the batteries will be deduced as per their energy demand. The customer has two options so far the household loads are connected-he/she can use all dc loads or can use an inverter (similar to an IPS) to have 240 Vac load in his house. This option will be useful when the actual power consumption by some of the consumers (well off consumers) are high and rich enough to use household gadgets like fridge, TV etc.

Source:
Syed Enam Reza, Mou Mahmood, A. S. M Kalkobad, Ehasanul Kabir, Nahid-ur-Rahman Chowdhury, “A Novel Load Distribution Technique of DC Micro-Grid Scheme on PV-Diesel Hybrid System for Remote Areas of Bangladesh,” Int. J. Scient. & Tech. Res., vol 2, issue 1, pp: 133-137, Jan. 2013


A schematic of dc microgrid

A schematic of the dc microgrid with the conventions employed for power is given in Figure. The dc bus connects wind energy conversion system (WECS), PV panels, multilevel energy storage comprising battery energy storage system (BESS) and supercapacitor, EV smart charging points, EV fast charging station, and grid interface. The WECS is connected to the dc bus via an ac–dc converter. PV panels are connected to the dc bus via a dc–dc converter. The BESS can be realized through flow battery technology connected to the dc bus via a dc–dc converter. The supercapacitor has much less energy capacity than the BESS. Rather, it is aimed at compensating for fast fluctuations of power and so provides cache control.

Source:
Kai Strunz, Ehsan Abbasi and Duc Nguyen Huu “DC Microgrid for Wind and Solar Power Integration” IEEE Journal of Emerging and Selected Topics in Power Electronics, Vol. 2, No. 1, March 2014.


Control of active and reactive power in a wind turbine with multipole PMSG

Another example for the control structure used for full-scale converter-based wind turbine concept is shown in Figure. An advantage of this turbine system is that the dc link performs some kinds of control decoupling between the turbine and the grid. The dc link will also give an option for the wind turbines to be connected with energy storage units, which can better manage the active power flow into the grid system—this feature will further improve the grid supporting abilities of the wind turbines. The generated active power of the WTS is controlled by the generator side converter, whereas the reactive power is controlled by the grid side converter. It is noted that a dc chopper is normally introduced to prevent overvoltage of dc link in case of grid faults, when the extra turbine power needs to be dissipated as the sudden drop of grid voltage

Source:
Frede Blaabjerg and Ke Ma “Future on Power Electronics for Wind Turbine Systems” IEEE Journal of Emerging and Selected Topics in Power Electronics, Vol. 1, No. 3, September 2013


Control of a wind turbine with DFIG

The control methods for a DFIG-based WTS are shown in Figure. Below maximum power production, the wind turbine will typically vary the rotational speed proportional with the wind speed and keep the pitch angleθ fixed. At very low wind speed, the rotational speed will be fixed at the maximum allowable slip to prevent over voltage of generator output. A pitch angle controller is used to limit the power when the turbine output is above the nominal power. The total electrical power of the WTS is regulated by controlling the DFIG through the rotor side converter. The control strategy of the grid side converter is simply just to keep the dc-link voltage fixed. It is noted that a trend is to use a crowbar connected to the rotor of DFIG to improve the control performance under grid faults.

Source:
Frede Blaabjerg and Ke Ma “Future on Power Electronics for Wind Turbine Systems” IEEE Journal of Emerging and Selected Topics in Power Electronics, Vol. 1, No. 3, September 2013


Variable-speed wind turbine with full-scale power converter

The second important concept that is popular for the newly developed and installed wind turbines is shown in Figure. It introduces a full-scale power converter to interconnect the power grid and stator windings of the generator, thus all the generated power from the wind turbine can be regulated. The asynchronous generator, wound rotor SG (WRSG) or permanent magnet SG (PMSG) have been reported as solutions to be used. The elimination of slip rings, simpler or even eliminated gearbox, full power and speed controllability as well as better grid support ability are the main advantages compared with the DFIG-based concept. The more stressed and expensive power electronic components as well as the higher power losses in the converter are, however, the main drawbacks for this concept.

Source:
Frede Blaabjerg and Ke Ma “Future on Power Electronics for Wind Turbine Systems” IEEE Journal of Emerging and Selected Topics in Power Electronics, Vol. 1, No. 3, September 2013


Variable-speed wind turbine with partial-scale power converter and a DFIG

This wind turbine concept is the most adopted solution nowadays and it has been used extensively since 2000s. As shown in Figure, a PEC is adopted in conjunction with the DFIG. The stator windings of DFIG are directly connected to the power grid, whereas the rotor windings are connected to the power grid by the converter with normally 30% capacity of the wind turbine. In this concept, the frequency and the current in the rotor can be flexibly regulated and thus the variable speed range can be extended to a satisfactory level. The smaller converter capacity makes this concept attractive seen from a cost point of view. Its main drawbacks are however, the use of slip rings and the challenging power controllability in the case of grid faults—these disadvantages may comprise the reliability and may be difficult to completely satisfy the future grid requirements

Source:
Frede Blaabjerg and Ke Ma “Future on Power Electronics for Wind Turbine Systems” IEEE Journal of Emerging and Selected Topics in Power Electronics, Vol. 1, No. 3, September 2013


Evolution of wind turbine size and the power electronics seen from 1980 to 2018

The size of individual wind turbine is also increasing dramatically to obtain a reduced price per generated kilowatt hour. In 2012, the average turbine size delivered to the market was 1.8 MW, among which the average offshore turbine has achieved a size of 4-MW. The growing trends of emerging turbine size between 1980 and 2018 are shown in Figure, where the development of power electronics in the WTS (rating coverage and function role) is also shown. It is noted that the cutting-edge 8-MW wind turbines with a diameter of 164 m have already shown up in 2012. Right now most of the turbine manufacturers are developing products in the power range 4.5–8 MW, and it is expected that more and more large wind turbines with multimegawatt power level, (even up to 10-MW will appear in 2018), will be present in the next decade—driven mainly by the considerations to lower down the cost of energy.

Source:
Frede Blaabjerg and Ke Ma “Future on Power Electronics for Wind Turbine Systems” IEEE Journal of Emerging and Selected Topics in Power Electronics, Vol. 1, No. 3, September 2013


Distribution of wind turbine market share by the manufacturers in 2012

Regarding the markets and manufacturers, the U.S. became the largest markets with over 13.1 GW capacity installed in 2012, together with China (13 GW) and the EU (11.9 GW) sharing around 87% of the global market. The Danish company Vestas first gives out the top position among the largest manufacturers since 2000, while GE catches up to the first because of the strong U.S. market in 2012. Figure summarizes the worldwide top suppliers of wind turbines in 2012. It is seen that there are four Chinese companies in the top 10 manufacturers with a total market share of 16.6%, which is a significant drop compared with the 26% in 2011.

Source:
Frede Blaabjerg and Ke Ma “Future on Power Electronics for Wind Turbine Systems” IEEE Journal of Emerging and Selected Topics in Power Electronics, Vol. 1, No. 3, September 2013


Global cumulative installed wind power capacity from 1999 to 2020

The cumulative wind power capacity from 1999 to 2020 is shown in Figure, and it can be seen that the wind power has grown fast to a capacity of 283 GW with ∼45 GW installed only in 2012, and this number is expected to achieve 760 GW in 2020 on moderate scenario [9]. The wind power grows more significant than any other renewable energy sources and is becoming really an important player in the modern energy supply system. As an extreme example Denmark has a high penetration by wind power and today > 30% of the electric power consumption is covered by wind. This country has even the ambition to achieve 100% nonfossil-based power generation system by 2050.

Source:
Frede Blaabjerg and Ke Ma “Future on Power Electronics for Wind Turbine Systems” IEEE Journal of Emerging and Selected Topics in Power Electronics, Vol. 1, No. 3, September 2013


Wind PV BESS hybrid power generation system with large-scale battery energy storage station

The Figure shown an example of Wind PV BESS hybrid power generation system with large-scale battery energy storage station (it is in BESS – Battery Energy Storage Station). It is used for compensation of aleatory energy production from wind turbine or PV plant. This BESS have orden of MW’s both for charge/discharge process.

Source:
Xiangjun Li, Dong Hui and Xiaokang Lai “Battery Energy Storage Station (BESS) – Based Smoothing Control of Photovoltaic (PV) and Wind Power Generation Fluctuations”. IEEE Transactions on Sustainable Energy, Vol. 4, No. 2, April 2013.


System topology for the smart grid in transition

In the not too distant future, the smart grid will emerge as a system of organically integrated smart microgrids with pervasive visibility and command-and-control functions distributed across all levels. The topology of the emerging grid will therefore resemble a hybrid solution, the core intelligence of which grows as a function of its maturity and extent. Figure shows the topology of the smart grid in transition.

Source:
Hassan Farhangi “The Path of the Smart Grid” IEEE Power & Energy Mazagine. January/February 2010. Pag 18 -28.


The smart grid of the future

As Figure shows, the smart grid is therefore expected to emerge as a well-planned plug-and-play integration of  smart microgrids that will be interconnected through dedicated highways for command, data, and power exchange.  The emergence of these smart microgrids and the degree  of their interplay and integration will be a function of rapidly escalating smart grid capabilities and requirements. It is also expected that not all microgrids will be created equal. Depending on their diversity of load, the mix of primary energy sources, and the geography and economics at work in particular areas, among other factors, microgrids will be built with different capabilities, assets, and structures.

Source:
Hassan Farhangi “The Path of the Smart Grid” IEEE Power & Energy Mazagine. January/February 2010. Pag 18 -28.


The existing grid

As Figure demonstrates, the existing electricity grid is  a strictly hierarchical system in which power plants at the top of the chain ensure power delivery to customers’ loads  at the bottom of the chain. The system is essentially a oneway pipeline where the source has no real-time information about the service parameters of the termination points. The grid is therefore overengineered to withstand maximum anticipated peak demand across its aggregated load. And since this peak demand is an infrequent occurrence, the system is inherently inefficient. Moreover, an unprecedented rise in demand for electrical power, coupled with lagging investments in the electrical power infrastructure, has decreased system stability. With the safe margins exhausted, any unforeseen surge in demand or anomalies across the distribution network causing component failures can trigger catastrophic blackouts.

Source:
Hassan Farhangi “The Path of the Smart Grid” IEEE Power & Energy Mazagine. January/February 2010. Pag 18 -28.


Basic Smart Grid ingredients

As Figure depicts, the convergence of communication technology and information technology with power system engineering, assisted by an array of new approaches,  technologies and applications, allows the existing grid to traverse the complex yet staged trajectory of architecture, protocols, and standards towards the smart grid.

Source:
Hassan Farhangi “The Path of the Smart Grid” IEEE Power & Energy Mazagine. January/February 2010. Pag 18 -28.


The smart grid compared with the existing grid

The smart grid needs to provide the utility companies with full visibility and pervasive control over their assets and services. The smart grid is required to be self-healing and resilient to system anomalies. And last but not least, the smart grid needs to  empower its stakeholders to define and realize new ways of engaging with each other and performing energy transactions across the system. To allow pervasive control and monitoring, the smart grid is emerging as a convergence of information technology and communication technology with power system engineering. Figure depicts the salient features of the smart grid in comparison with the existing grid.

Source:
Hassan Farhangi “The Path of the Smart Grid” IEEE Power & Energy Mazagine. January/February 2010. Pag 18 -28.


Typical compensation system for renewable energy applications based on flywheel energy storage

There are two broad classes of flywheel-energy-storage technologies. One is a technology based on low-speed flywheels (up to 6000 r/min) with steel rotors and conventional bearings. The other one involves modern high-speed flywheel systems (up to 60 000 r/min) that are just becoming commercial and make use of advanced composite wheels that have much higher energy and power density than steel wheels. This technology requires ultralow friction bearing assemblies, such as magnetic bearings, and stimulates a research trend. Most applications of flywheels in the area of renewable energy delivery are based on a typical configuration where an electrical machine (i.e., high-speed synchronous machine or induction machine) drives a flywheel, and its electrical part is connected to the grid via a back-to-back converter, as shown in Figure. Such configuration requires an adequate control strategy to improve power smoothing. The basic operation could be summarized as follows. When there is excess in the generated power with respect to the demanded power, the difference is stored in the flywheel that is driven by the electrical machine operating as a motor. On the other hand, when a perturbation or a fluctuation in delivered power is detected in the loads, the electrical machine is driven by the flywheel and operates as a generator supplying needed extra energy. A typical control algorithm is a direct vector control with rotor-flux orientation and sensorless control using a model-reference-adaptive-system (MRAS) observer.

Source:
Juan Manuel Carrasco, Leopoldo García Franquelo, Jan T. Bialasiewicz, Eduardo Galván, Ramón C. Portillo Guisado, Ángeles Martín Prats, José Ignacio León and Narciso Moreno-Alfonso “Power-Electronic Systems for the Grid integration of Renewable Energy Sources: A Survey”. IEEE Transactions on Industrial Electronics, Vol. 53, No. 4, August 2006


Variable-speed wind turbine with a hydrogen storage system and a fuel-cell system that reconverts hydrogen to electrical grid

As the wind penetration increases, the hydrogen options become most economical. Also, sales of hydrogen as a vehicle fuel are more lucrative than reconverting the hydrogen back into electricity. Industry is developing low-maintenance electrolysers to produce hydrogen fuel. Because these electrolysers require a constant minimum load, wind turbines must be integrated with grid or energy systems to provide power in the absence of wind.

Electrical energy could be produced and delivered to the grid from hydrogen by a fuel cell or a hydrogen combustion generator. The fuel cell produces power through a chemical reaction, and energy is released from the hydrogen when it reacts with the oxygen in the air. Also, wind electrolysis promises to establish new synergies in energy networks. It will be possible to gradually supply domestic-natural-gas infrastructures, as reserves diminish, by feeding hydrogen from grid-remote wind farms into natural-gas pipelines. The Figure shows a variable-speed wind turbine with a hydrogen storage system and a fuel cell system to reconvert the hydrogen to the electrical grid…

Source:
Juan Manuel Carrasco, Leopoldo García Franquelo, Jan T. Bialasiewicz, Eduardo Galván, Ramón C. Portillo Guisado, Ángeles Martín Prats, José Ignacio León and Narciso Moreno-Alfonso “Power-Electronic Systems for the Grid integration of Renewable Energy Sources: A Survey”. IEEE Transactions on Industrial Electronics, Vol. 53, No. 4, August 2006


Five-level cascaded multilevel converter connected to a multipole low-speed wind-turbine generator

The use of low-speed permanent-magnet generators that have a large number of poles allows obtaining the dc sources from the multiple wounds of this electrical machine, as can be seen in Figure. In this case, the power-electronic building block (PEBB) can be composed of a rectifier, a dc link, and an H-bridge. Another possibility is to replace the rectifier by an additional H-bridge. The continuous reduction of the cost per kilowatt of PEBBs is making the multilevel cascaded topologies to be the most commonly used by the industrial solutions. This as one alternative to multinivel conversors.

Source:
Juan Manuel Carrasco, Leopoldo García Franquelo, Jan T. Bialasiewicz, Eduardo Galván, Ramón C. Portillo Guisado, Ángeles Martín Prats, José Ignacio León and Narciso Moreno-Alfonso “Power-Electronic Systems for the Grid integration of Renewable Energy Sources: A Survey”. IEEE Transactions on Industrial Electronics, Vol. 53, No. 4, August 2006


Two HVDC transmission solutions_Classical LCC-based system with STATCOM and VSC-based system

Classical HVDC transmission systems [as shown in Figure (a)] are based on the current source converters with naturally commutated thyristors, which are the so-called linecommutated converters (LCCs). This name originates from the fact that the applied thyristors need an ac voltage source in order to commutate and thus only can transfer power between two active ac networks. They are, therefore, less useful in connection with the wind farms as the offshore ac grid needs to be powered up prior to a possible startup. A further disadvantage of LCC-based HVDC transmission systems is the lack of the possibility to provide an independent control of the active and reactive powers. Furthermore, they produce large amounts of harmonics, which make the use of large filters inevitable. Voltage-source converter (VSC)-based HVDC transmission systems are gaining more and more attention not only for the grid connection of large offshore wind farms. Figure (b) shows the schematic of a VSC-based HVDC transmission system

Source:
Juan Manuel Carrasco, Leopoldo García Franquelo, Jan T. Bialasiewicz, Eduardo Galván, Ramón C. Portillo Guisado, Ángeles Martín Prats, José Ignacio León and Narciso Moreno-Alfonso “Power-Electronic Systems for the Grid integration of Renewable Energy Sources: A Survey”. IEEE Transactions on Industrial Electronics, Vol. 53, No. 4, August 2006