Archivo para febrero, 2016


difference of time connected beetwen condensers of a bank condensers

This is my simulation made on Matlab/Simulink about difference time of conextion in bank condensers. The reactive power change in the time and it is aleatory. In this context, the mathematical models have that made the emulation of this performance.

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Simulation of the changes in supply of reactive power in Condenser Bank

Any Condenser Bank have many condensers of equal or different capacity. Its is connected in function to the need of reactive power in the distributed network or microsource connected. The change time in the real world is aleatory and stochastic. This figure is a emulation by this problem. Maximum time change of 5 minutes (8.333 in this vertical scale). Horizontal scale is the progressive number times of realization change


CERTS Microgrid test bed

The CERTS Microgrid program has developed control methods to allow the installation of distributed generators (DGs) in commercial and industrial electric power systems in a “plug and play” manner. These control methods allow the generators to be electrically distributed, rather than be installed on the same electrical bus, and do not require intergenerator communications in order to maintain appropriate voltage and frequency at each generator. Note in figure that there is a communication link with the DGs that is labeled “Energy Manager”. This is a conventional  energy manager that is used for power dispatch purposes, not  for frequency or voltage control. This energy manager can  use relatively slow communications links, such as telephone  or internet, since it has no bearing on system stability.

Source:
John Stevens “CERTS Microgrid System Test”. IEEExplore


A example of DC microgrid

Many examples there is in this blog about DC microgrids (see last post or search in blog). This blog is for share information of actual tendence in electricity. It is part of my research as doctoral student in physics in National University of Engineering in Lima, Perú; and actually I am writing in english. For last post, the blog have a traductor box option. Near to 1000 post about diferents topic in renewable energy focused in microgrid, smartgrid and its modelling ans simulation witn Matlab/Simulink. I know this software and its very good, practical for science and engineering. In May or June is possible I will expose mi thesys doctoral, previus days or weeks I posted the exact time for all people see in live or via internet. This figure is other DC microgrid scheme with different technologies interconnected at a some bus DC for transfered electric power. Jorge Mírez (please visit and link my fanpage http://www.facebook.com/jorgemirezperu  )

Source of Figure:
N. R. Rahmanov, N. M. Tabatabaei, K. Dursun, O. Z. Kerimov. “Combined AC-DC Microgrids: Case Study – Network Development and Simulation” International Journal on Technical and Physical Problems of Engineering. September 2012, Issue 12, Volume 4, Number 3, Pages 157 – 161.


Example of power supply for office building using DC bus

In the office there are many electronic equipment, it for the general, to use DC voltage. There is certain paradigme about the data center made more for market that for technical reasons… ups, many companies it not like. Ok, the figure shown the special configuration (a example) of electrical supply to equipment office. Very good, it is a representative used of potential DC microgrids.

Source of Figure:
N. R. Rahmanov, N. M. Tabatabaei, K. Dursun, O. Z. Kerimov. “Combined AC-DC Microgrids: Case Study – Network Development and Simulation” International Journal on Technical and Physical Problems of Engineering. September 2012, Issue 12, Volume 4, Number 3, Pages 157 – 161.


 

Example of a hybrid microgrid

This a typical scheme of a microgrid AC/DC. It maybe contain many technologies as micro-source, storage, loads and monitoring and control. Un Microgrid Bus linked the different components.

Source:
N. R. Rahmanov, N. M. Tabatabaei, K. Dursun, O. Z. Kerimov. “Combined AC-DC Microgrids: Case Study – Network Development and Simulation” International Journal on Technical and Physical Problems of Engineering. September 2012, Issue 12, Volume 4, Number 3, Pages 157 – 161.


DC grid unipolar and bipolar

DC grid of a Microgrid DC may be unipolar with ground as return path or bipolar with positive and negative terminal. The figure (a) and (b) depicts unipolar and bipolar grid respectively.  If load connected to DC bus is DC such as TV, computers, fluorescent lamps; DC bus requires less power conversion stages. Since power conversion stages are less, losses in conversion also gets reduced.

Source:
Ganesh Patil, M. F. A. R. Satarkar, Gorakshanath Abande “New Scheme for Protection of DC Micro grid” International Journal of Innovative Reseach in Science, Engineering and Technology. Volume 3, Special Issue 3, March 2014.


Microgrid operation of islanded operation

The figure illustrates the concept of the power management method in the islanded mode. When a DC micro-grid must be separated from the ac grid and switch to the islanded mode, the grid-tied converter released control of the DC grid voltage and one of the converters in the micro-grid must take over that control. Since each converter of DGs is used for optimal control of each source, only the converters of the energy storage elements are free to regulate the DC grid voltage. During the islanded mode, the battery plays a main role in regulating the DC grid voltage and the super-capacitor plays a secondary role in responding to the sudden power requirement as an auxiliary converter.

Source:
Ji-Heon Lee, Hyun-Jun Kim, Byung-Moon Han, Yu-Seok Jeong, Hyo-Sik Yang and Han-Ju Cha “DC Micro-Grid Operational Analysis with a Detailed Simulation Model for Distributed Generation” Journal of Power Electronics, Vol. 11, No. 3, May 2011


Microgrid operation of grid-tied mode

The figure illustrates the concept of the power management method in the grid-tied mode and the bolded curve represents a load demand curve during a day. If the output sum of the DGs is sufficient to charge the storage elements, any excessive power is supplied to ac grid. If the sum of the power of the DGs and the storage elements is deficient with respect to the load demand, the required power is supplied from the ac grid. In the grid-tied mode, power management is performed in a complementary manner between storage elements and as a result the DC micro-grid can operate safely and efficiently

Source:
Ji-Heon Lee, Hyun-Jun Kim, Byung-Moon Han, Yu-Seok Jeong, Hyo-Sik Yang and Han-Ju Cha “DC Micro-Grid Operational Analysis with a Detailed Simulation Model for Distributed Generation” Journal of Power Electronics, Vol. 11, No. 3, May 2011


Example of configuration of DC micro-grid

As shown in Figure, the proposed DC micro-grid consists of uncontrolled DGs such as wind power, photovoltaic generation and controlled fuel-cell sources as well as energy storage elements such as super capacitors and batteries, DC loads and grid-tied converters. The wind power system consists of a 2kW PMSG (permanent magnet synchronous generator) which operates under a wide range of wind-speeds without a gear box, and a three-phase PWM converter which converts variable voltage, variable frequency AC voltage to fixed DC voltage with MPPT (maximum power point tracking) capability. The PV (Photo-Voltaic) array converter is a 1.5kW transformer-less boost converter which operates with the MPPT method under varying levels of irradiation and temperature. Since a 1.2 kW PEM (proton exchange membrane) type fuel cell stack generates a low varying DC voltage that is around 26V and is strongly influenced by ripple current, a three-phase isolated DC-DC converter with an active clamp is employed to limit the ripple current into the fuel cells and to increase efficiency. Bidirectional two-phase interleaved converters are used to charge or discharge into the elements. Energy storage elements such as super-capacitors and batteries play an important role for the power management of DC microgrids. They ensure a secure grid network and provide high quality power. A grid-tied three-phase converter, which is a conventional three-phase PWM converter, maintains a constant common DC grid voltage and regulates both the reactive power and the harmonic components in PCC. The DC load is simplified as a variable resistor.

Source:
Ji-Heon Lee, Hyun-Jun Kim, Byung-Moon Han, Yu-Seok Jeong, Hyo-Sik Yang and Han-Ju Cha “DC Micro-Grid Operational Analysis with a Detailed Simulation Model for Distributed Generation” Journal of Power Electronics, Vol. 11, No. 3, May 2011


DC distribution system

The figure shows the simplified distribution system of the DC microgrid system. The wire sizing has to comply with the South Africa National Standard (SANS) on the wiring of premises 6 mm2 for the generation and storage side, and 2.5 mm2 for the distribution side will allow an acceptable tolerance of voltage drop for this low voltage system, refer to SANS 10142

Source:
Gilbert M Bokanga, Atanda Raji, Mohammed TE Kahn. “Design of a low voltage DC microgrid system for rural electrification in South Africa”. Journal of Energy in Southern Africa • Vol 25 No 2 • May 2014.


Model design of the DC microgrid system

Hybrid renewable energy systems have been accepted as possible means of electrifying rural outlying areas where it is too expensive to extend the grid to supply them. As stipulated in the introduction, the system is intended to power households, and it must be cost effective; therefore, only solar energy system is retained. Figure 1 shows the overview of the low voltage DC microgrid system

Source:
Gilbert M Bokanga, Atanda Raji, Mohammed TE Kahn. “Design of a low voltage DC microgrid system for rural electrification in South Africa”. Journal of Energy in Southern Africa • Vol 25 No 2 • May 2014.


Path to the Perfect Power System

The basic philosophy in developing the perfect power system is first to increase the independence, flexibility, and intelligence for optimization of energy use and energy management at the local level; and then to integrate local systems as necessary or justified for deliveringperfect power supply and services.

This path started with the notion that increasingly consumers expect perfection in the end-use devices and appliances they have. Not only does portability enable a highly mobile digital society; but also once perfection in portability is defined, it provides elements of perfection that enable, in turn, a localize perfect system. Localized perfect systems can also accommodate increasing consumer demands for independence, convenience, appearance, environmentally friendly service and cost control.

Local systems can in turn be integrated into distributed perfect systems. Distributed perfect systems can, in turn be interconnected and integrated with technologies that ultimately enable a fully integrated perfect power system. The figure summarizes each of these system configuration stages.

Each of these configurations can essentially be considered a possible structure for the perfect power system in its own right, but each stage logically evolves to the next stage based on the efficiencies, and quality or service value improvements to be attained. In effect, these potential system configuration stages build on each other starting from a portable power system connected to other portable power systems which then can evolve into a building integrated power system, a distributed power system and eventually to a fully integrated power system.

Source:
Clark W. Gellings.The Smart Grid. CRC Press. 2009. ISBN-10 0-88173-623-6


Transformer Efficiency with Amorphous Metal Core Compared with Conventional Steel Core

Transformer losses consist of two types: core (or “no-load”) losses and winding losses (also called “coil” or “load” losses). Core losses result from the magnetizing and de-magnetizing of the transformer core during normal operation; they do not vary with load, but occur whenever the core is energized. Amorphous core transformers can reduce these core losses by as much as 80% compared with conventional materials (see Figure).

Winding losses occur when supplying power to a connected load. Winding loss is a function of the resistance of the winding material—copper or aluminum—and varies with the load. Conventional transformers use aluminum winding and are designed to operate at temperatures up to 150°C/270°F above ambient. Newer high-efficiency transformers use copper winding, reducing the size of the core, the associated core losses, and the operating temperatures to 80°C or 115°C (145°F to 207°F) above ambient. Hence, overall transformer efficiency is lowest under light load, and highest at rated load, regardless of which core material is used

Source:
Metglas & Clark W. Gellings.The Smart Grid. CRC Press. 2009. ISBN-10 0-88173-623-6


Smart Grid Concept EPRI IntelliGrid Program

A consortium was created by EPRI to help the energy industry pave the way to IntelliGridSM —the architecture of the smart grid of the future. Partners are utilities, manufactures and representatives of the public sector. They fund and manage research and development (R&D) dedicated to implementing the concepts of the IntelliGridSM.

The objective: The convergence of greater consumer choice and rapid advances in the communications, computing and electronics industries is influencing a similar change in the power industry. The growing knowledge-based economy requires a digital power delivery system that links information technology with energy delivery.


Summary of Potential Smart Grid Benefits

A smart grid has the potential to benefit the environment, consumers, utilities and the nation as a whole in numerous ways, as summarized in Figure. The benefits include the mechanisms for enhanced reliability and power quality as well as energy savings and carbon emission reductions, plus other dividends

Source:
EPRI Report 1016905, “The Green Grid,” June 2008


Illustration of the wind on the rotor area of a wind turbine

Wind turbines produce a complex and continuously fluctuating power. A large part of  the complexity resides on the input: the wind.The main source of power variation on  conventional wind turbines is the wind speed variation.  The wind is complex and the blades crossing the wind field modify the power fluctuations. The main objective of this chapter is to present a dynamic wind model for power quality assessment of a three bladed up-wind horizontal axis wind turbine type. The wind speed model includes the turbulence and tower shadowin the rotor area.  The figure illustrates an example of the wind field acting on the rotor area of a wind turbine.

Reference:
Pedro Rosas.”Dynamic Influences of Wind Power on the Power System”. PhD Thesys. DTU. 2003.


simulation of deficit and surplus of two microgrids interconnected in Matlab

This is a part of my results about interconnected of two microgrids. It have flow power in function a its capacities, but probably a deficit and/or surplus in supply or demand in both microgrids is present. Negative is deficit in microgrid to import from other source different to other microgrid. Positivo is surplus in microgrid by export to other demand different at other microgrid. The figure is a simple example for to show that it is possible using mathematical modelling and simulations on Matlab of MathWork Inc.


simulation of power flow between two microgrids interconnected in Matlab

This is part of my results in Matlab about power flow between two microgrids interconected. In different color shown the direction of power flow (from Microgrid 1 to Microgrid 2, and from Microgrid 2 to Microgrid 1). The figure is a simple example for to show that it is possible using mathematical modelling and simulations on Matlab of MathWork Inc.


when you exceed the nominal capacity of condensers bank

Sometimes, the reactive power in a electric system exceed the nominal capacity of condensers bank, therefore, all units capacitores is connected to give the maximum reactive power compensation possible. The figure is one of my simulations on Matlab and complement past post. Matlab is from MathWork Inc. The figure is the results of mathematical model of condensers bank operation (control and optimization).