Archivo para enero 18th, 2016


Roadmap for microgrid development

Currently, an increasing number of microgrid pilot sites can be observed in many parts of the world. It is true, however, that up to now,cost, policy and technology barriers have largely restrained the wide deployment of microgrids in distribution networks owing to their limited commercial appeal or social recognition. However, these three barriers are currently undergoing considerable changes – they are very likely to turn into key enablers in the future, eventually leading to a widespread microgrid adoption worldwide.

Firstly, the cost factor might prove to be the most effective driving force for microgrids in the very near future. This might happen not only because of the reduction of microsource costs, but also because of the relative changes of external opportunity costs due to economic (fluctuating market prices), technical (aging of network infrastructure) and environmental (emission trading) factors.

When microsource penetration at a LV grid becomes significant, participants in the electricity retail business will consider the aggregated power from small generators as a new market opportunity. Unlike in the case of VPP, microgrid stakeholders will eventually recognize a unique feature of aggregated microsource units, namely locality: the microsource units can potentially sell directly to end consumers in an “over-the-grid” manner. In order to turn this potential into reality, however, the second factor – appropriate policy and regulatory environment – is needed to enable the operation of a local market within a microgrid.

Finally, the adoption of favorable selling prices in local retail markets will attract even more microsource units, allowing the microgrid to operate islanded, if beneficial. With the help of smart metering, control and communication technologies, the microgrid operator will eventually be able to coordinate a large consortium of intermittent and controllable microsource units, as well as central and distributed storage devices, to achieve multiple objectives and, at the same time, to cater for the interests of different stakeholders.

Source:
MICROGRIDS: Architectures and Control
Nikos Hatziargynou

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Microgrid operation strategies

Currently available DG technologies provide a wide variety of different active and reactive power generation options. The final configuration and operation schemes of a microgrid depend on potentially conflicting interests among different stakeholders involved in electricity supply, such as system/network operators, DG owners, DG operators, energy suppliers, customers and regulatory bodies. Therefore, optimal operation scheduling in microgrids can have economic, technical and environmental objectives

Depending on the stakeholders involved in the planning or operation process, four different microgrid operational objectives can be identified: economic option, technical option, environmental option and combined objective option.

In the economic option, the objective function is to minimize total costs regardless of network impact/performance. This option may be envisaged by DG owners or operators. DGs are operated without concern for grid or emission obligations. The main limitations come from the physical constraints of DG.

The technical option optimizes network operation (minimizing power losses, voltage variation and device loading), without consideration of DG production costs and revenues. This option might be preferred by system operators.

The environmental option dispatches DG units with lower specific emission levels with higher priority, disregarding financial or technical aspects. This is preferred for meeting environmental targets, currently mainly supported by regulatory schemes. DG dispatch is solely determined by emission quota; only DG physical limitations are considered.

The combined objective option solves a multi-objective DG optimal dispatch problem, taking into account all economic, technical and environmental factors. It converts technical and environmental criteria into economic equivalents, considering constraints from both network and DG physical limits. This approach could be relevant, for instance, to actors that participate not only in classical energy markets, but also in other potential markets for provision of network services and emission certificates

Source:
MICROGRIDS: Architectures and Control
Nikos Hatziargynou


FACTS devices can enhance the power flow on existing power lines. For the transmission line shown in figure, the sending end voltage isVS∠δS, the receiving end voltage is VR∠δR and the equivalent impedance of parallel connected lines isX. The power transfer through the lines is given by:

FACTS equation

the figure also shows how FACTS devices act on the power transfer equation. The TCSC can change the impedance of the line, the STATCOM can control the voltage magnitude at

FACTS applications for increased power transfer

the terminal to which it is connected by injecting or absorbing reactive power and the UPFC can alter the phase angle of the sending end voltage, thus power flow through a line can be controlled in a number of ways.

Source:
SMART GRID
TECHNOLOGY AND APPLICATIONS
Janaka Ekanayake
Cardiff University, UK
Kithsiri Liyanage
University of Peradeniya, Sri Lanka
Jianzhong Wu
Cardiff University, UK
Akihiko Yokoyama
University of Tokyo, Japan
Nick Jenkins
Cardiff University, UK
A John Wiley & Sons, Ltd., Publication

 


Evolution of electricity metering

Electricity meters are used to measure the quantity of electricity supplied to customers as well as to calculate energy and transportation charges for electricity retailers and network operators. The most common type of meter is an accumulation meter, which records energy consumption over time. Accumulation meters in consumer premises are read manually to assess how much energy has been used within a billing period. In recent years, industrial and commercial consumers with large loads have increasingly been using more advanced meters, for example, interval meters which record energy use over short intervals, typically every half hour. This allows the energy suppliers to design tariffs and charging structures that reflect wholesale prices and helps the customers understand and manage their pattern of electricity demand. Smart meters are even more sophisticated as they have two-way communications and provide a real-time display of energy use and pricing information, dynamic tariffs and facilitate the automatic control of electrical appliances

Source:
SMART GRID
TECHNOLOGY AND APPLICATIONS
Janaka Ekanayake
Cardiff University, UK
Kithsiri Liyanage
University of Peradeniya, Sri Lanka
Jianzhong Wu
Cardiff University, UK
Akihiko Yokoyama
University of Tokyo, Japan
Nick Jenkins
Cardiff University, UK
A John Wiley & Sons, Ltd., Publication


Possible communication infrastructure for the Smart Grid

The communication infrastructure of a power system typically consists of SCADA systems with dedicated communication channels to and from the System Control Centre and a Wide Area Network (WAN). Some long-established power utilities may have private telephone networks and other legacy communication systems. The SCADA systems connect all the major power system operational facilities, that is, the central generating stations, the transmission grid substations and the primary distribution substations to the System Control Centre. The WAN is used for corporate business and market operations. These form the core communication networks of the traditional power system. However, in the Smart Grid,it is expected that these two elements of communication infrastructure will merge into a Utility WAN.
An essential development of the Smart Grid (see figure ) is to extend communication throughout the distribution system and to establish two-way communications with customers through Neighbourhood Area Networks (NANs) covering the areas served by distribution substations. Customers’ premises will have Home Area Networks (HANs). The interface of the Home and Neighbourhood Area Networks will be through a smart meter or smart interfacing device.

Source:
SMART GRID
TECHNOLOGY AND APPLICATIONS
Janaka Ekanayake
Cardiff University, UK
Kithsiri Liyanage
University of Peradeniya, Sri Lanka
Jianzhong Wu
Cardiff University, UK
Akihiko Yokoyama
University of Tokyo, Japan
Nick Jenkins
Cardiff University, UK
A John Wiley & Sons, Ltd., Publication


Architecture of a DMSC

 

The figure shows the DMSC controller building blocks that assess operating conditions and find the control settings for devices connected to the network. The key functions of the DMSC are state estimation, bad data detection and the calculation of optimal control settings. The DMSC receives a limited number of real-time measurements at set intervals from the network nodes. The measurements are normally voltage, load injections and power flow measurements from the primary substation and other secondary substations. These measurements are used to calculate the network operating conditions. In addition to these real-time measurements, the DMSC uses load models to forecast load injections at each node on the network for a given period that coincides with the real-time measurements. The network topology and impedances are also supplied to the DMSC.
The state estimator uses this data to assess the network conditions in terms of node voltage magnitudes, line power flows and network injections. Bad measurements coming to the system will be filtered using bad data detection and identification methods.

Source:
SMART GRID
TECHNOLOGY AND APPLICATIONS
Janaka Ekanayake
Cardiff University, UK
Kithsiri Liyanage
University of Peradeniya, Sri Lanka
Jianzhong Wu
Cardiff University, UK
Akihiko Yokoyama
University of Tokyo, Japan
Nick Jenkins
Cardiff University, UK
A John Wiley & Sons, Ltd., Publication


Distribution network active management scheme

The Figure is a schematic of a simple distribution network with distributed generation (DG).There are many characteristics of this network that differ from a typical passive distribution network. First, the power flow is not unidirectional. The direction of power flows and the voltage magnitudes on the network depend on both the demand and the injected generation. Second, the distributed generators give rise to a wide range of fault currents and hence complex protection and coordination settings are required to protect the network. Third, the reactive power flow on the network can be independent of the active power flows. Fourth, many types of DGs are interfaced through power electronics and may inject harmonics into the network. The Figure also shows a control scheme suitable for achieving the functions of active control. In this scheme a Distribution Management System Controller (DMSC) assesses the network conditions and takes action to control the network voltages and flows. The DMSC obtains measurements from the network and sends signals to the devices under its control. Control actions may be a transformer tap operation, altering the DG output and injection/absorption
of reactive power.

Source:
SMART GRID
TECHNOLOGY AND APPLICATIONS
Janaka Ekanayake
Cardiff University, UK
Kithsiri Liyanage
University of Peradeniya, Sri Lanka
Jianzhong Wu
Cardiff University, UK
Akihiko Yokoyama
University of Tokyo, Japan
Nick Jenkins
Cardiff University, UK
A John Wiley & Sons, Ltd., Publication