Archive for the ‘Distribuited Generation’ Category

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.

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.


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

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

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.

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

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.

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

Other example of microgrid con cell fuel wind turbine PV microturbine battery bank and loads

This microgrid have different elements: wind turbine, photovoltaics, fuel cell, battery bank, microturbine and interconection with main grifd. The level power is little but it is a interesting microgrid for study. It is a typical AC microgrid with load distribuited in many locations into microgrid. Main grind is a sub-transmission network in 20 kV.

Image Source:
Aris L. Dimeas, Nikos D. Natziargyriou “Operation of Multiagent System for Microgrid Control” IEEE Transactions on Power Systems, Vol. 20, No. 3, August 2005.

Actions sequence for the market operation in the time domain and Powerflows and bids in the microgrid

The overall procedure is the following:

1. The Market Operator (MO) announces the prices for selling (SP) or buying (BP) energy to the Microgrid. Normally it is SP>BP.
2. The local loads announce their demands for the next 15 minutes and an initial price (DP) for the kWh. It is DP>BPand DP<SP.
3. The production units accept or decline the load offer according to an Auction Price (AP).
4. The negotiation continues for a specific time (5 min).
5. After the end of the negotiation time, all the units have adjusted their set points. If there is no production unit within the Microgrid to satisfy the load demand, the power is bought from the grid. In addition, the grid can be considered as a load too, so the production or storage units can sell energy to the grid.

Aris L. Dimeas, Nikos D. Natziargyriou “Operation of Multiagent System for Microgrid Control” IEEE Transactions on Power Systems, Vol. 20, No. 3, August 2005.

Control levels of the microgrid environment

The DNO’s responsible for the technical operation in a medium and low voltage area, in which more than one Microgrids may exist. In addition, one or more MO’s are responsible for the Market Operation of this area. These two entities do not belong to the Microgrid, but they are the delegates of the grid. The DNO
refers to the operational functions of the system and the MO to the Market functions. It should be noted that, despite the autonomous operation of the Microgrid, it should ideally appear as a controlled, intelligent unit in coordination with the DNO.

The MGCC is the main responsible for the optimization of the Microgrid operation, or alternatively, it simply coordinates the local controllers, which assume the main responsibility for this optimization.

The LC’s control the Distributed Energy Resources (DER), production and storage units, and some of the local loads. Depending on themode of operation, they have certain level of intelligence, in order to take decisions locally. Of course, in any type of operation there are certain decisions that can be taken only locally.

Aris L. Dimeas, Nikos D. Natziargyriou “Operation of Multiagent System for Microgrid Control” IEEE Transactions on Power Systems, Vol. 20, No. 3, August 2005.

distribution demand between micosourses electrical network external and storage in a microgrid DC

Sun –> energy provided from photovoltaic energy plant.
Wind –> similar from wind turbine(s)
Batt –> similar from battery bank
ene –> similar injected from electrical network external or utility electric network

In other image in red is the total suministed for this sources and red line is the demand. Other images is cost, evoluction of energy supply from each source and more details. It is made for me (Jorge Mírez) in Matlabb/Simulink and I utilized concept of linear programming. Image is from my destokp laptop.

Example of General hybrid power system model

A simple block diagram of a hybrid power system is shown in Figure. The sources of electric power in this hybrid system consist of a diesel generator, a battery bank, a PV array, and a wind generator. The diesel generator is the main source of power around the world. The output of the diesel generator is regulated ac voltage, which supplies the load directly through the main distribution transformer. The battery bank, the PV array, and the wind turbine are interlinked through a dc bus. The RTU (Remote Terminal Unit) regulates the flow of power to and from the different units, depending on the load. The integration of a RTU into a hybrid power system is important to enhance the performance of the system. The overall purpose of the RTU is to give knowledgeable personnel the ability to monitor and control the hybrid system from an external control center. Since the hybrid systems of interest in this research are located in remote areas, the ability for external monitoring and control is of utmost importance. The RTU is interfaced with a variety of sensors and control devices located at key locations within the hybrid system. The RTU processes the data from these sensors and transmits it to a control center. In addition, the RTU is also capable of receiving control signals and adjusting parameters within the system without the physical presence of the operating personnel.

Richard W. Wies, Ron A. Johnson, Ashish N. Agrawal and Tyler J. Chubb “Simulink Model for Economic Analysis and Environmental Impacts of a PV With Diesel-Battery System for Remote Villages” IEEE Transactions on Power Systems, Vol. 20, No. 2, May 2005

Example de AC Microgrid with Diesels CHPs PVs Boilers and conextion with Main Grid

This a example of a AC microgrid with differents equipment from usually photovoltaic solar plant (PV), CHPs, boilers and diesel generators. Many electric lines and loads placed on a characteristic topology of new tendence in market electrical

In-Su Bae and Jin-O Kim “Phasor Discrete Particle Swarm Optimization Algorithm to Configure Micro-grids” Journal of Electrical Engineering & Technology, Vol. 7, No.1, pp. 9 -16, 2012

Single-phase HFAC microgrid with active filters and DIEMS

The proposed DIEMS (distributed intelligent energy management system) allow instantaneous optimization of alternative and renewable power sources. The use of storage requires an optimization scheme that considers the time-integral part of the load flow. So, the energy management has to perform energy scheduling a single day or multiple days ahead. An intelligent energy management system in thus required which enables short-term energy allocation scheduling at minimun costs based on power generation and load demand. The function of the DIEMS is to generate set points for all the sources and storages in such a way that economically optimized power dispatch will be maintained to fulfill certain load demand. Generation forescast as well as some fast online algorithms are used to define the energy availability and, finally, to define the optimized power dispatch signals to the loads, as well as to the grid using UPLC (universal active power line conditioner). This energy management system, consists of prediction modulo, optimization module, and online control module, is shown in Figure.

Sudipta Chakraborty, Manoja D. Weiss and M. Godoy Simöes “Distributed Intelligent Energy Management System for a Single-Phase High-Frequency AC Microgrid” IEEE Transactions on Industrial Electronics. Vol. 54, No. 1, February 2007.

A block diagram of grid interconnection unit

There is a significative difference storage system and electric power system interconnection unit. The microgrid usually has as high power from grid point of view that it is connected to medium voltage fine, typically 15 kV in Poland. Although the power system interconnection unit has almost the structure as storage system, its primary voltage is in range of kilovolts and is sinusoidal. So, it requires different power electronic converter. It is assumed in Poland that all devices connected to 15 kV lines have to be joined using 50 Hz transformer. Hence, the grid interconnection unit can have a structure shown in Figure.

Piotr Biczel. “Power Electronic Converters in DC Microgrid”. IEEE 5th International Conference – Workshop, Compatibility in Power Electronics, CPE 2007. Poland.

General block diagram of the DC microgrid power plant

El block diagram structure of a microgrid is shown in Figure. The main task of the power plant’s power electronic converter is to fit primary energy converter’s output voltage to the microgrid power line voltage, and source operating point control as well as low and high level microgrid’s control. The converter’s structure depends on a type of primary energy converter. A common feature of the converters concerns their output current. It should be permanent and low ripple.

Piotr Biczel. “Power Electronic Converters in DC Microgrid”. IEEE 5th International Conference – Workshop, Compatibility in Power Electronics, CPE 2007. Poland.

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.

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.

John Stevens “CERTS Microgrid System Test”. IEEExplore

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.

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.

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.

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

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.

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.