Zhao Dongyuan: A brief discussion on the development of power quality under the flexible power trading of energy internet

China Energy Storage Network: With the development of energy internet, the emergence of large-scale distributed source storage, electric vehicles and charging facilities, the field of power quality faces new challenges of complicated disturbance problems. The 3,500 power sales companies that emerged after the deepening of power system reform directly changed the main players in the power trading market, and flexible power trading has become a trend. Energy storage power quality devices based on energy discretization and Internetization are not only new devices to solve power supply quality, but also new means to achieve flexible power trading. At the same time, it is the future direction to establish an open power quality information system based on the Internet cloud platform with transparent information sharing, terminal compatible access, distributed storage computing, and support for friendly interaction.

1.What is Energy Internet?

According to Academician Zhou Xiaoxin's "Discussion on Development Trends and Research Directions of Future Power Systems", the Global Energy Internet is a strong smart grid with UHV power grid as the backbone and globally interconnected, and its characteristics are "UHV power grid + smart grid + clean energy".

According to the "Notice of the National Energy Administration on Organizing and Implementing the Internet + Smart Energy (Energy Internet) Demonstration Project", various types of renewable energy, smart grids, electric vehicles and charging and discharging facilities are integrated to build a low-carbon city. A demonstration area energy Internet security data sharing platform and energy trading platform are built to support the construction of smart cities. Its characteristics are "low carbon, Internet +, new business forms".

At the same time, the energy internet demonstration park based on clean energy hubs (such as natural gas combined cooling, heating and power, photovoltaics, wind power, etc.) realizes multi-energy flow coordinated energy management, explores flexible trading and demand response modes for various energy forms, and improves clean energy utilization and terminal energy efficiency. Its characteristics are "distributed source storage, Internet +, flexible trading".

Energy Internet is a new form of energy industry development that deeply integrates the Internet with energy production, transmission, storage, consumption and energy market. It has the main characteristics of intelligent equipment, multi-energy collaboration, information symmetry, decentralized supply and demand, flat system and open transactions. In simple terms, Energy Internet has the following "1-2-3-4" characteristics:

1. A multi-network integrated energy chain: It relies on a highly reliable and secure main grid, has flexible and scalable capabilities, and supports plug-and-play of distributed energy (production, storage, and consumption).

2 important features: clean energy and "Internet +"

3 levels:

Physical foundation (equipment layer): distributed power sources, energy storage, electric vehicles and charging facilities

Data communication layer: integration of energy information-physical systems, plug-and-play energy network cards, and smart hardware

Value mining (application layer): innovative energy operation model, new electricity sales, photovoltaic assets, energy Internet finance

Four characteristics of the Internet:

Free multilateralism, broad participation, information symmetry, user experience

At present, the energy Internet projects that have been built in China are based on the integration of "trigeneration + distributed photovoltaic + energy storage". There are also several problems: Can the seamless switching of the grid-connected/off-grid conversion process be achieved? What is the interconnection protocol between multiple devices? What is the decision-making basis for multi-energy complementary coordinated control? Furthermore, does the decision-making basis of energy operation management support the long-term business model of the park?

The virtual power plants built in the United States, Germany and other countries reflect the multi-party participation and Internet + business model, which has certain reference significance. For example, when users purchase kW-level energy storage equipment for photovoltaic supporting, Ampard (Ampard Energy Manager) uses their energy management system to manage the user's energy storage equipment and provide primary frequency control backup and other services in the form of virtual power plants. Fenecon guarantees that it will provide users with €400 in income each year for 4 years, and Fenecon claims that it may also provide users with an additional income of €400-500 each year.

2. New requirements for power quality under the energy internet

Power quality disturbances are complicated by:

1 Distributed Power Generation

Positive impact: Distributed power sources and energy storage can achieve local energy balance, improve the load-bearing capacity of the distribution network and system stability, and provide more solutions.

Negative impact: Due to the natural randomness, volatility and undispatchability (under existing technical means) of photovoltaic and wind power generation, the access of distributed power sources is prone to cause power quality problems such as voltage sag, fluctuation and flicker, harmonic pollution, and voltage over-limit.

2 Energy storage - providing support for power and energy

3 Electric Vehicles - Is it a Vehicle or a Battery? Is it a Load or a Power Source?

Negative impact: disordered charging, power shock fluctuation, harmonics, power quality

Positive impact: Flexible and dispatchable energy storage

Power quality data is diversified. With the in-depth construction of the energy internet, various energy types such as chemical energy and thermal energy, with electricity as the core, have increasingly participated in and affected the relationship between power supply and consumption. Power quality data formats are diverse, including electricity data, event data, graphic data, geographic information data, climate data, etc. And the data is widely distributed. Therefore, power quality data is diversified and heterogeneous.

Strict power quality. Modern automated production lines are completely dependent on digital information and are extremely sensitive to various electromagnetic interferences. Small voltage fluctuations that originally had no effect on the motor load may affect the normal operation of the electronic control system and even cause tripping or production suspension, which in serious cases will cause great economic losses.

Electricity trading is flexible and diversified. The diversification of electricity trading is reflected in the changes in market entities and trading models. The original electricity supply was only between power grid companies and electricity users. Now, with the deepening of power system reform, a large number of new power sales companies have emerged, which directly changed the market entities of electricity trading. The development of energy Internet technology and related policies have also clearly proposed new models and new formats such as point-to-point Internet transactions, Internet operations of electric vehicles and energy storage, demand-side response and auxiliary services, which will change the traditional electricity trading model. The above new power sales companies and trading models require the development of power quality monitoring technology.

3. Development trend of power quality under energy internet

Energy Internet aims to increase the proportion of renewable energy, promote the clean and efficient use of fossil energy, improve the overall energy efficiency, and promote the opening of the energy market and industrial upgrading. The physical layer mainly includes distributed power sources (photovoltaic power generation, wind power generation, etc.), distributed energy storage, electric vehicles and charging facilities, and adjustable loads. The data layer is mainly based on high-speed information networks, integrating physical information systems such as smart terminals and energy routers. The application layer is mainly based on cloud platforms and big data technologies to carry out clean energy efficient consumption, smart energy use and value-added services, and user-side responsive interactive Internet transactions and services. The above technical connotations of Energy Internet have promoted the new development of power quality.

Technical system of energy internet based on distributed source storage:

In the above technical systems, domestic photovoltaic power generation, inverters, and charging systems have achieved major breakthroughs in industry and technology. However, several issues (in red font) are bottlenecks that need to be broken through and are also important research hotspots.

In view of the above issues, this research center has started the following research:

3.1 Research on key technologies of energy virtualization

Taking battery energy storage as a breakthrough, a networked battery management and control system will be established, which is different from the existing fixed battery grouping route.

Its important technical focuses include: dynamically reconfigurable structure, accurate SOC estimation of single cells and battery groups, fast calculation of complex networks based on fuzzy measurement, implementation of battery networking communication protocol, and cloud management and control of battery energy.

Based on the above technologies, Internet energy management and control demonstration applications are being carried out: Internet dispatch of energy storage devices based on retired batteries in microgrids; energy response, frequency and peak regulation, and power quality applications of distributed energy storage in active distribution networks; energy storage-type power quality devices, etc.