What is the microgrid? The concept and technical characteristics of the microgrid
Micro-Grid, also known as micro-grid, refers to a small-scale power distribution system consisting of distributed power sources, energy storage devices, energy conversion devices, loads, monitoring and protection devices.
The microgrid is an autonomous system that can realize self-control, protection and management. As a complete power system, it relies on its own control and management energy supply to achieve power balance control, system operation optimization, fault detection and protection, and power quality management. The function.
The proposed microgrid aims to realize the flexible and efficient application of distributed power sources and solve the problem of large-scale and diverse distributed power supply interconnection. The development and extension of the microgrid can fully promote the large-scale access of distributed power and renewable energy, and achieve high-reliability supply of multiple energy sources. It is an effective way to realize active distribution network, making the traditional power grid Smart grid transition.
The power sources in the microgrid are mostly distributed power sources with small capacity, that is, small units containing power electronic interfaces, including micro gas turbines, fuel cells, photovoltaic cells, small wind turbines, and energy storage devices such as supercapacitors, flywheels, and batteries. They are connected to the user side and have the characteristics of low cost, low voltage and low pollution.
The dual pressures of environmental protection and energy depletion have forced us to develop clean renewable energy. The development potential and profit space of the highly efficient distributed energy industry (cogeneration) is huge. The need to improve power supply reliability and power quality, as well as the constraints imposed by long-distance transmission, are driving the establishment of appropriate power sources close to the load center. Through the microgrid controller, centralized control of the entire power grid can be realized, and a distributed local controller is not required, but only a conventional measuring device is used, and a fast communication channel is adopted between the measuring device and the local controller. Micro-grid transient control is realized by local controller with distributed power supply and load, and the micro-grid centralized energy management system realizes steady-state safety and economic operation analysis. The microgrid centralized energy management system uses a weak communication connection with the local controller.
Microgrid features
Microgrid system structure diagram
Microgrid system is a large-scale, non-linear, multi-constrained and multi-time multi-dimensional complex system with a large number of distributed power sources with various characteristics. It is complex, nonlinear, adaptable and open. Complex system characteristics such as spatial hierarchy, organization and self-organization, dynamic evolution, etc. belong to a special complex giant system with many variables, complex operation mechanism and significant uncertainty factors. Therefore, the research and development and application of microgrid technology should firstly have a comprehensive understanding and mastery of its typical characteristics.
The construction concept of the microgrid is to configure the distributed power supply close to the user side for power supply. The transmission distance is relatively short. The load characteristics, the layout of the distributed power supply and the power quality requirements determine the capacity scale and voltage level of the microgrid. The main aspects such as structural mode and control mode are different from those of traditional power systems:
1. Capacity and voltage level: The capacity of the microgrid is relatively small, and its voltage level is often low or medium voltage;
2. Structural mode: According to the power supply system, the microgrid can be divided into three different structures: AC, DC and AC/DC. The technology is the most mature, and the most widely used is the AC microgrid structure.
3. Control mode: The micro-grid mainly has two kinds of peer-to-peer control modes and master-slave control modes. The master-slave control mode is still the mainstream of micro-grid experimental systems and demonstration projects at home and abroad.
Microgrid and large power grid relationship diagram
Due to the large number of distributed power sources with various characteristics and different characteristics, the microgrid has very complicated dynamic operation characteristics and energy management problems, which leads to the complicated operation and control mechanism of the microgrid system. In order to effectively coordinate and control the distributed power sources to achieve and ensure the safe, stable, economical and reliable operation objectives of the system, the planning and design of the microgrid, the operation control of the microgrid, the protection of the microgrid and the economy of the microgrid need to be viewed from a system perspective. Research on key technologies such as operation.
Key technologies of microgrid
1. Planning and design of microgrid: It is the first phase of research and development of microgrid system, and it is an important basis for ensuring safe, stable and economical operation of the system. The purpose is to meet the stable operation of the system and the load requirements under the jurisdiction. By optimizing the selection of system structure and power supply configuration, the realization and satisfaction of the safe and stable operation of the microgrid system during planning and the minimum system investment cost goal are met. The microgrid planning and design mainly covers multiple hybrid distributed power combinations with energy complementary characteristics. Key content of type, distributed power supply selection, operation mode, optimization objectives, operation strategies and constraints, optimization algorithms, and system network structure design.
2. Operation control of microgrid: It is the key technology to realize and ensure the safe, stable and economical operation of the microgrid system. It is to realize coordinated coordination and optimization between two levels of distributed power control at the unit level and micro-grid control at the system level. . The operation control technology of the microgrid mainly includes the operation control mode of the microgrid, the operation control strategy, the control methods of each distributed power supply (including the inverter control), and the coordinated control methods of multiple distributed power sources.
3. Protection of microgrid: It refers to a key technology that can quickly identify, locate and remove faults and restore the safe and stable operation of the system when the microgrid fails. The faults in the grid-connected operation mode are mainly reflected in the external faults and internal faults of the microgrid, and the faults are eliminated according to the corresponding fault protection strategies selected by different fault locations. The fault of the off-grid operation mode is mainly reflected in the power failure and the feeder fault, and then the power protection or the feeder protection method is used to eliminate the fault.
4. Economic operation of microgrid: It is the third phase of key technology to realize and guarantee the economic and environmental benefits of microgrid system. It is also the final embodiment of testing the pros and cons of microgrid planning and design and control scheme. The economic operation optimization problem of microgrid should fully consider the important factors such as microgrid operation mode, optimization scheduling objectives, economic benefits and environmental benefits, optimization algorithms, optimized scheduling strategies and operational constraints, and then meet the load power quality and power supply reliability. On the basis of realizing the maximum use of renewable energy, reducing greenhouse gas emissions and reducing system power costs.
to sum up
The microgrid is a new type of autonomous power system that realizes large-scale application of distributed generation technology and effectively improves the reliability of system power supply. It can be seen from the above analysis:
1. The microgrid belongs to a complex system with nonlinear, multi-constraint, multi-time scale and multi-dimensional. The characteristics and key technologies of the micro-grid should be deeply understood from a system perspective, so that the micro-grid can be scientifically researched and developed.
2. In order to achieve the safety, stability, reliability and economic operation objectives of the micro-grid system, the key technologies of the micro-grid should be reasonably selected on the basis of comprehensive consideration of the typical characteristics of the micro-grid, following the design principles of adapting to local conditions and adapting to the time.
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