Key technologies and applications involved in smart grid

Abstract: This paper specifically describes the key technologies of smart grid, mainly in terms of measurement, communication, information management, dispatching, power electronics and distributed energy access. Finally, with the help of the research and application of smart grid in the United States, the functions realized by smart grid technology are summarized and commented.

1 Technical Overview of Smart Grid

Smart grid is to achieve energy substitution and compatible utilization. It needs to integrate the data in the system and optimize the operation and management of the power grid on the basis of creating an open system and establishing a shared information model. It mainly forms an instant network interaction between users and between users and power grid companies through terminal sensors, so as to achieve real-time, high-speed and two-way effects of data reading, and improve the overall efficiency of the power grid as a whole. It can use sensors to monitor and integrate the operating conditions of key equipment such as power generation, transmission, distribution and power supply in real time. When encountering the peak period of power supply, it can be dispatched in time between different regions to balance the power supply gap, so as to achieve the optimization management of the operation of the entire power system; at the same time, smart meters can also be used as Internet routers to promote the power sector to communicate, operate broadband services or transmit TV signals based on its end users.

From June 27 to 28, 2009, the first Smart Grid Research Forum was held at Tianjin University. The forum arranged 14 academic reports, which discussed the construction and development of China's smart grid from multiple perspectives, including the basic concepts, technical components, and equipment requirements of smart grids. Academician Yu Yixin of Tianjin University gave a report titled "The driving force, technical components, and implementation routes of smart grids." The report pointed out that safe and stable operation of the system, demand-side management, and distributed power sources are the driving forces for promoting the construction of smart grids. Smart grids are the integrated application of communications, advanced sensors, distributed computing, and other technologies to improve the safety, reliability, and efficiency of power transmission and distribution networks.

Academician Cheng Shijie of Huazhong University of Science and Technology pointed out in his report on "Energy Storage Technology and Its Application in Smart Grids" that in power systems with a large proportion of renewable energy generation, the application of energy storage technology is a feasible way to solve the problem of how to ensure the normal operation of the system. He also proposed the basic requirements of smart grids for energy storage systems, namely, sufficiently large energy storage capacity, sufficiently fast power response speed, sufficiently large exchange power, sufficiently high energy storage efficiency, sufficiently small discharge cycle, sufficiently long service life, and sufficiently small operating costs.

Professor Wang Chengshan, Dean of the School of Electrical and Automation Engineering of Tianjin University, gave a report on "Distributed Power Sources, Microgrids, and Intelligent Distribution Systems", introducing the key technologies, applications, and existing problems of distributed power sources, microgrids, and intelligent distribution systems, and analyzing the relationship between the three. Professor Xu Bingyin of Shandong University of Technology gave a report on "Distribution Automation Technology in Intelligent Distribution Networks", Luan Wenpeng of British Columbia Hydro, Canada, gave a report on "Advanced Measurement System", Chen Jianghua of the State Grid Demand Side Management Center gave a report on "The Practical Results and Prospects of Demand Side Management in China", and Liu Qianjin of ABB gave a report on "Smart Grid - Vision, Technology and Application", all of which analyzed and discussed the technical characteristics, implementation methods, and development prospects of smart grids from different perspectives.

2 Key Technologies of Smart Grids

China's digital power grid construction covers all aspects of power generation, dispatching, transmission and transformation, distribution, and users, including: information platform, dispatching automation system, stable control system, flexible AC transmission, substation automation system, microcomputer relay protection, distribution network automation system, power consumption management and collection system, etc. In fact, China's current digital power grid construction can be regarded as the prototype of smart grids.

2.1 Reference Measurement Technology

Parameter measurement technology is a basic component of smart grid. Advanced parameter measurement technology obtains data and converts it into digital information for use in various aspects of smart grid. They evaluate the health of grid equipment and the integrity of the grid, read meters, eliminate electricity bill estimates, prevent electricity theft, alleviate grid congestion, and communicate with users. The

future smart grid will eliminate all electromagnetic meters and their reading systems, and replace them with smart solid-state meters that enable two-way communication between power companies and users. Microprocessor-based smart meters will have more functions. In addition to measuring electricity usage and electricity costs at different times of the day, they will also store peak power price signals and electricity rates issued by power companies, and notify users of what rate policies to implement. More advanced functions include users compiling schedules based on rate policies and automatically controlling internal power usage strategies.

For power companies, parameter measurement technology provides more data support to power system operators and planners, including power factor, power quality, phase relationship (WAMS), equipment health and capacity, meter damage, fault location, transformer and line load, temperature of key components, power outage confirmation, power consumption and prediction. New software systems will collect, store, analyze and process this data for other business of power companies.

Future digital protection will be embedded with computer agents, greatly improving reliability. Computer agents are autonomous and interactive adaptive software modules. Wide area monitoring systems, protection and control solutions will integrate digital protection, advanced communication technologies and computer agents. In such an integrated and distributed protection system, protection elements can communicate with each other adaptively. Such flexibility and adaptability greatly improve reliability, because even if part of the system fails, other protection elements with computer agents can still protect the system.

2.2 Smart grid communication technology

Establishing a high-speed, two-way, real-time, integrated communication system is the basis for realizing smart grids. Without such a communication system, any smart grid features cannot be realized. Because data acquisition, protection and control of smart grids all require the support of such communication systems, establishing such communication systems is the first step towards smart grids. At the same time, the communication system should be as deep as the power grid, so that two closely connected networks are formed - the power grid and the communication network. Only in this way can the goals and main features of smart grids be achieved. High-speed, bidirectional, real-time, and integrated communication systems make smart grids a large-scale infrastructure for dynamic, real-time information and power exchange and interaction. When such a communication system is built, it can improve the power supply reliability and asset utilization of the power grid, prosper the power market, resist attacks on the power grid, and thus increase the value of the power grid. The

communication technology suitable for smart grids must have the following characteristics: First, it must have bidirectional, real-time, and reliable characteristics. For security reasons, it should theoretically be a power communication network isolated from the public network. Second, it must be technologically advanced and able to carry the existing business of smart grids and future expansion business. Third, it is best to have independent intellectual property rights and have the ability to customize development and business upgrades for power smart grid business.
As a subsidiary of State Grid Corporation of China engaged in the construction and operation management of backbone information and communication networks, State Grid Information and Communication Co., Ltd. attaches great importance to the construction of smart grids, actively carries out relevant preliminary research, and strives to promote the development of software and hardware products related to information and communication technology (ICT), and conducts research on the network model of the new generation of power information and communication (ICT), accelerating the industrialization of information and communication.

The power customer electricity consumption information collection system is an important part of the smart grid. The information and communication company actively participates in the research related to the information and communication profession and submits a communication-related technical report to the State Grid Corporation of China. At the same time, it actively promotes the industrialization process and further improves the power consumption information collection master station software platform, collectors based on power line broadband communication technology and other products.
Smart grid customer service is an important part of the smart grid electricity consumption link. It is an important means to achieve real-time interactive response between the power grid and customers, enhance the comprehensive service capabilities of the power grid, meet interactive marketing needs, and improve service levels. Xintong Company has set up smart grid customer service pilot projects in Beijing Lianxiangyuan Community and No. 95 Fucheng Road. Among them, the No. 95 Fucheng Road pilot project is characterized by fiber-to-the-home, and uses set-top boxes and TVs as display means to achieve a series of special services such as three-meter reading and query, property, distribution, and network value-added, reflecting good interactivity and intelligent features.

2.3 Information Management System

The information management system in the smart grid should mainly include five functions: collection and processing, analysis, integration, display, and information security. (1) Information collection and processing. It mainly includes detailed real-time data collection system, distributed data collection and processing services, dynamic sharing of intelligent electronic device (IED) resources, large-capacity high-speed access, redundant backup, and accurate data synchronization. (2) Information analysis. Business analysis of information after collection, processing and integration is an important auxiliary tool for conducting power grid-related business. Vertically, it includes the business analysis of the four-level industrial chain of "generation-transmission-distribution-demand side" and the information analysis of the four-level power grid of "national-regional-provincial-county". Horizontally, it includes the analysis of business modules such as power generation planning, power outage management, asset management, maintenance management, production optimization, risk management, market operation, load management, customer relationship management, financial management, and human resource management. (3) Information integration. The information system of the smart grid should realize the information integration of the industrial chain and power grid in the vertical direction, and the information integration of the internal business of power grid enterprises at all levels in the horizontal direction. (4) Information display. To provide personalized visual interfaces for various types of users, it is necessary to reasonably use video and audio technologies such as flat display, three-dimensional animation, voice recognition, touch screen, geographic information system (GIS), etc. (5) Information security. The smart grid must clarify the confidentiality and authority of each stakeholder and protect their data and economic interests. Therefore, it is necessary to study network survival, active real-time protection, secure storage, network virus prevention, malicious attack prevention, network trust system and new password technologies under complex large systems.

2.4 Intelligent Dispatching Technology

Intelligent dispatching is an important part of smart grid construction, and the smart grid dispatching technology support system is the core of intelligent dispatching research and construction. It is the technical basis for comprehensively improving the dispatching system's ability to control large power grids and optimize resource allocation, in-depth risk defense capabilities, scientific decision-making management capabilities, flexible and efficient regulation capabilities, and fair and friendly market allocation capabilities.
The existing dispatching automation system faces many problems, including non-automatic, messy information, unsafe control process, lack of centralized control methods, and difficulty in accident decision-making. In order to adapt to the construction, operation and management requirements of large power grids, ultra-high voltage and smart grids, and to achieve scientific decision-making in dispatching business, efficient management of power grid operation, and rapid response to power grid anomalies and accidents, it is necessary to analyze and study intelligent dispatching.

In order to accelerate the overall design of the smart grid dispatching technology support system and the preparation of application function specifications, the State Grid Electric Power Research Institute was entrusted by the National Electric Power Dispatching Center to undertake the overall design of the smart grid dispatching technology support system. From July 6 to 18, 2009, under the leadership of the National Dispatching Center, the State Grid Electric Power Research Institute working group successfully completed the overall design of the smart grid dispatching technical support system, and discussed and determined the functional specification system of the smart grid dispatching technical support system, providing guidance for the rapid and orderly construction of the integrated smart grid dispatching technical support system. The members of the State Grid Electric Power Research Institute working group participated in the overall design of the basic platform and four major applications of the smart grid dispatching technical support system, and undertook and successfully completed the functional process and overall design of the dispatching plan application, safety verification application and dispatching management application.

2.5 Advanced power electronics technology

Power electronics technology is a modern technology that uses power electronic devices to transform and control electric energy. The energy saving effect can reach 10% to 40%, which can reduce the volume of electromechanical equipment and achieve optimal working efficiency. At present, semiconductor power components are developing towards high voltage and large capacity. The power electronics industry has seen the emergence of flexible AC transmission technology represented by SVC, new ultra-high voltage transmission technology represented by high-voltage DC transmission, electrical drive technology represented by high-voltage frequency conversion, synchronous disconnection technology represented by intelligent switches, and user power technology represented by static VAR generators and dynamic voltage restorers.
Flexible AC transmission technology is one of the key technologies for large-scale access to the power grid system for new energy and clean energy. It combines power electronics technology with modern control technology, and through continuous adjustment and control of power system parameters, it greatly reduces transmission losses, improves the transmission capacity of transmission lines, and ensures the stability of the power system.

High-voltage DC transmission technology has unique advantages for long-distance transmission and high-voltage DC transmission. Among them, the light DC transmission system uses GTO, IGBT and other turn-off devices to form a converter, making medium-sized DC transmission projects competitive even at shorter transmission distances. In addition, the inverter composed of the shut-off device can also be used to supply power to isolated small systems such as offshore oil platforms and islands. In the future, it can also be used in urban power distribution systems to access distributed power sources such as fuel cells and photovoltaic power generation. Light DC transmission systems are more helpful in solving the problem of clean energy access stability.

The biggest advantage of high-voltage frequency conversion technology is that the power saving rate can generally reach about 30%, but the disadvantage is that the cost is high and high-order harmonics are generated to pollute the power grid. Synchronous breaking (intelligent switch) technology is to complete the opening or closing of the circuit at the specified phase of voltage or current. At present, most high-voltage switches are mechanical switches with long breaking time and large dispersion, making it difficult to achieve accurate phase-fixed breaking. The fundamental way to achieve synchronous breaking is to replace mechanical switches with electronic switches.

2.6 Distributed Energy Access Technology

The core of smart grid is to build an intelligent network system with intelligent judgment and adaptive adjustment capabilities for unified access and distributed management of multiple energy sources. It can monitor and collect power grid and user power consumption information in real time, and use the most economical and safest transmission and distribution methods to transmit electric energy to end users, so as to achieve the optimal configuration and utilization of electric energy and improve the reliability of grid operation and energy utilization efficiency.

There are many types of distributed power sources (DER), including small hydropower, wind power generation, photovoltaic power sources, fuel cells and energy storage devices (such as flywheels, supercapacitors, superconducting magnetic energy storage, flow batteries and sodium sulfur batteries). Generally speaking, their capacity ranges from 1kW to 10MW. DER in the distribution network is widely adopted because it is close to the load center, reducing the need for grid expansion and improving power supply reliability. In particular, distributed renewable energy, which helps to mitigate the greenhouse effect, has grown rapidly with the strong support of government policies in many countries. At present, in several Nordic countries, DER has a share of more than 30% of the power generation. In the United States, DER currently accounts for only 7% of the total capacity, but it is expected that this share will reach 25% by 2020.

A large number of distributed power sources are running on medium-voltage or low-voltage distribution networks, which completely changes the characteristics of the traditional one-way flow of distribution systems, requiring the system to use new protection schemes, voltage control and instruments to meet the needs of two-way flow. However, through advanced automation systems, these distributed power sources can be seamlessly integrated into the power grid and coordinated to operate, which will bring huge benefits. In addition to saving investment in the transmission network, it can improve the reliability and efficiency of the entire system, provide emergency power and peak load power support for the power grid, and other auxiliary service functions such as reactive power support and power quality improvement; at the same time, it also provides great flexibility for system operation. For example, in storms and snowy weather, when the large power grid is severely damaged, these distributed power sources can form islands or microgrids to provide emergency power supply to important users such as hospitals, transportation hubs, and radio and television.

3. Functional realization of smart grid

At present, the United States is the most mature country in smart grid research. Many states in the United States have begun to design smart grid systems. GE, IBM, Siemens, Google, Intel and other leading information industry companies have invested in smart grid business.

Maitin Schoenbauer of the U.S. Department of Energy's China Office attended the first Smart Grid Research Forum held at Tianjin University in June 2009 and introduced the relevant situation of the U.S. smart grid. Martin Schoenbauer introduced the "U.S. Department of Energy Smart Grid Business". The U.S. Department of Energy is initiating the establishment of a smart grid information sharing and exchange platform and information database, funding smart grid technology research and development projects, and pointed out that clean energy and smart grid will be important contents of Sino-U.S. energy cooperation.
Boulder, Colorado, is the first smart grid city in the United States. Every household is equipped with a smart meter, so people can intuitively understand the current electricity price, so as to arrange some things, such as washing and ironing, in the time period when the electricity price is low. The meter can also help people give priority to clean energy such as wind power and solar energy. At the same time, the substation can collect the electricity consumption of each household. Once a problem occurs, the power can be re-equipped.

In West Virginia, Allegheny Energy's "Super Circuit" project combines advanced monitoring, control and protection technologies to enhance the reliability and safety of power supply lines. The grid will integrate biodiesel power generation, energy storage, and advanced metering infrastructure (smart meters) and communications networks to quickly predict, identify and help solve network problems.

Fort Collins, Colorado, and the city-owned utility company support multiple clean energy initiatives. One involves combining nearly 30 renewable energy sources, including solar and wind, in five customer areas. The initiative, along with other distributed power systems, supports a zero-energy zone in the city called FortZED.

The University of Hawaii is developing a distribution management system platform that uses smart metering as a gateway station, integrating demand response, residential energy-saving automation, distributed generation optimization management, storage and load of distribution systems, and various control methods that allow distribution systems to coordinate with other systems in the main grid.

The "Perfect Power" project at the Illinois Institute of Technology uses advanced technology to build a prototype microgrid that can respond to changes in the main grid, enhance grid reliability, and reduce electricity demand.