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Abstract

Content

Introduction

The last decades were characterized by fast development of technology, economy and society in which there are fundamental changes (high technology, population growth, global climate change, etc.) which affects energy balance, and applies new demands to it.

Among the most significant changes in the development of the energy sector, foreign scientists and researchers include the following [1]:

– the insufficiency of electric energy;

– ever-increasing demands for reliability and quality of electricity by consumers;

– constant increase in the cost of electrical energy throughout the world;

– requirements of environmental and industrial safety of energy facilities;

– system-wide cost reduction.

These changes require the development of a new concept of innovative development of electric power. This concept on the one hand must correspond to modern ideas, goals and values of social development, being created and expected needs of people and society, in general. And on the other - the highest consideration to the basic trends and scientific, technological progress in all sectors, spheres of life of society [2].

1. Theme urgency

Nowadays, the electrical systems in Ukraine are based on the outdated design of mid-20th century. This is one of the main reasons of complexity of the enlargement of the network infrastructure for satisfaction of permanently growing energy needs. In the next decade it is expected that the demand for electricity will increase by 19%, and the existing network infrastructure has the ability to increase their productivity by only 6% [ 1 ]. For these reasons, disconnect and power interruptions are the problems for the majority of electrical networks.

Continuous growth of energy resources cost, which are based on the fossil hydrocarbons (oil, gas, coal, etc.), and the increasing complexity of their production are deterrents to the development of traditional energy infrastructure. Processing of hydrocarbonic fuel resources has a negative impact on the environment. Therefore, it is very actual the application of renewable energy in the large and in small power systems [ 3 ].

Renewable energy is based on solar, wind, water and other nonpolluting resources. In the future it will be able to compete with traditional power energy. According to forecasts of the European Council on Renewable Energy, the share of renewable energy sources (RES) in global primary energy production in 2020 will be 23.6%, in 2030 – 34.7%, in 2040 – 47.7% [ 4 ]. The main disadvantage of renewable energy – unstable graph generation, which depends on the geographic location, season, time of day, weather conditions and other factors [ 3 ]. Therefore, by using renewable energy demand special, so-called "intelligent" systems that can use optimal the various distributed power sources. One of the types of the smart energy system is microgrid system. This is low-voltage intelligent distribution network containing various distributed energy sources, energy storage, controlled load and other elements (Fig. 1).

Building in the microgrid system

Figure 1 – Building in the microgrid system

The marked features do actual creation of a uniform technique of development and research of the distributed power supply systems with the considerable share of generation from renewable energy sources.

2. Goal and tasks of the research

The purpose of the master's work is the research of electrical systems of smart buildings with the usage of distributed renewable energy.

The tasks of the master's work include:

  1. Analysis of the electrical loads of the building, the division according to their priorities.
  2. Binding to different rates for the electric power.
  3. Analysis of distributed energy sources for smart buildings (public power supply, small solar power station, small wind power station, etc.).
  4. Analysis of the energy storage system (battery).
  5. Development of mathematical model loads, energy sources, energy storage for smart building.
  6. Developing an algorithm management of distributed energy sources, energy storage and energy consumers for intelligent buildings.
  7. Evaluation of the control algorithm and its effectiveness.

Review of literature, research and development

The research of microgrid systems , motives and reasons for its use are given in [5-11], where the core values of new energy are viewed :

– Accessibility – providing consumers with electricity without restriction depending on when and where it is needed, and depending on its quality, paid by consumers;

– reliability – the ability to confront the physical and informational negative impacts without total shutdown or high costs for the restoration work, the most rapid recovery (self-healing) of efficiency;

– efficiency – optimization of electricity tariffs for consumers and system-wide cost reduction;

– effectiveness – to maximize the effectiveness of the usage of all types of resources, technologies and equipment in the production, transmission, distribution and consumption of electricity;

– the organic interaction with the environment – the maximum possible reduction of negative environmental impacts;

– security – preventing situations in the power, dangerous to humans and the environment.

– flexibility in terms of response to changing needs.

The main components of the power distribution system – Distribution Networks substation and associated electrical equipment and controls are described in [12] Commercially available technologies for distributed generation based on wind turbines, internal combustion engines, micro-and mini-gas turbines, fuel cells, photovoltaic system, low-head hydroelectric and geothermal systems are viewed. The sequence of automation, including fault detection, localization, isolation and recovery load is also described.

In the agent framework, each energy resource and load in the microgrid is represented as an autonomous agent that provides a common communication interface for all the different components in the system. The control strategy for the represented energy resource or load is completely incorporated in the software port of the agent, so it is also called “control agent”. With each control agent running on a separate computer, the energy system is distributed.The agent-based approach facilitates self-organization. Since each agent is independent, once it joins the system, the logic enables it to interface itself to the other existing agents. One common method for the interface is through a directory service whereby agents register themselves to a common directory and then self-organize their activities. The ability for agents to be self-organized contributes to the scalability and robustness of the microgrids. Since the system is self-organizing, there could be no limit to how many agents can join the microgrid at one time and no restrictions on when an agent should/can join.he proposed agent-based distributed energy resources microgrid is shown in Fig. 1.

Agent-based control framework for DER microgrid

Fig. 2. Agent-based control framework for DER microgrid.

1. Energy source unit: The energy source unit provides electricity or heat to the microgrid. Examples of typical distributed energy sources are fuel cells, microturbines, photovoltaic cells, wind turbines, geothermal plants, and micro-hydro plants.

2. Energy storage unit: The energy storage unit stores energy when the energy supply within the microgrid is sufficient and supplies energy back to the microgrid when excess energy is demanded. Examples of energy storage units may include hydrogen storage systems (electrolyzer, hydrogen storage, and fuel cell systems), supercapacitors, batteries, flywheels, and superconductive magnetic energy storage (SMES) systems.

3. Load: The load on the microgrid represents the electricity or heat demand of a specified area.

4. Energy source agent: The energy source agent manages the represented energy source based on the local measured information and the communications with other agents. The agent will determine how much energy will be supplied and direct the corresponding energy source to do so. The control strategies for different types of energy sources may be different than each other, depending upon the characteristics of the fuels.

5. Energy storage agent: The energy storage agent manages the represented energy storage unit based on the local measured information and the communications with other energy source agents and load agents. The energy storage agent will determine how much energy will be stored or supplied at any time.

6. Load agent: The load agent is to manage the load to make it a controllable energy resource. In an agent-based microgrid, the load also participates in the competition.

7. HMI: The human-machine interface (HMI) is for the operators to monitor and observe the status of the system.

Fig. 3 shows the process of electricity in microgrid. Smart system selects which source of electricity use at the moment to supply the load. Either it will be centralized network, or alternative sources of energy, and sometimes it will be the source of the storage element (battery) charged earlier.

The process of electricity loads in microgrid

Figure 3 – The process of electricity loads in microgrid
(animation: number of frames:4, number of cycles:4, size: 48 кB)

Conclusion

Microgrid system allows to provide consumers the required energy at the lowest cost for its production, transfer and accumulation . The energy arrives to consumers of such networks from centralized power grid, as well as from distributed renewable energy. Renewable energy can be obtained from the sun, wind, water and other "green" sources. The energy consumption from local electricity network within microgrid system should be minimal, which is determined by economic and environmental requirements.

The data given above, can differ from information and the received results given in the text of the performed master's work, which will be complete by January, 2015.

References

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