- Microgrid operation control and protection technology
Compared with the conventional power system, the capacity of the microgrid is generally not large, and most of the connected power is the inverter power supply using power electronic devices, lacking a certain rotating reserve capacity. How to ensure the stability of the voltage and frequency of the system in different operating modes The key to the coordinated operation and control of distributed power sources in the microgrid. The smooth switching of the microgrid between the two modes is the difficulty in the operation of the microgrid, and the coordinated and optimized operation of the microgrid and the large power grid is realized and the support for the safety and stability of the large power grid is realized. , is an important technical feature that distinguishes the microgrid from the general distributed power supply.
In addition, the automatic disconnection technology of microgrid based on internal and external fault information and the self-synchronization technology of microgrid reconnection are also the key to realize flexible switching of microgrid operation mode. Due to the variety of devices in the microgrid, different control methods and different operating characteristics, the operation control and protection of the microgrid is very complicated.
At present, three modes are mainly proposed for the control architecture of microgrid in China and abroad: peer-to-peer control mode, master-slave control mode and multi-Agent-based hierarchical control mode. Existing inverter products and related technologies are not enough to meet the requirements of reliable and flexible operation of microgrids. So far, the multi-functional inverter control technology and device suitable for microgrid is still blank in China.
The microgrid central integrated monitoring system can comprehensively monitor the operation information of the microgrid, realize the integration of protection and monitoring of the microgrid, and implement optimal scheduling of distributed power sources. However, in the research and development of comprehensive monitoring platform, there is a lack of standardized function definitions and research on software and hardware architecture systems outside China. In the completed microgrid demonstration projects and laboratories, most of them use monitoring platforms similar to traditional power grids, such as distributed monitoring systems (DCS) for power plants and integrated automation systems for substations. It can realize functions such as conventional data collection and real-time operation data display, but it is difficult to meet the requirements of microgrid for stronger real-time requirements, more flexible operation, and higher degree of intelligence. It has become particularly important to carry out research on the design of the software and hardware structure of the microgrid integrated monitoring system and related implementation technologies.
- Microgrid operation control and protection technology
In the microgrid system, the frequent start and stop of the intermittent power supply and the change of power output will bring power quality problems such as voltage fluctuation and flicker to users; the power supply in the microgrid often adopts power electronic technology, which will cause harmonic pollution ; The existence of single-phase distributed power supply and single-phase load increases the three-phase unbalance level of the system. The United States, the European Union, Japan and other developed countries (regions) have taken the lead in conducting in-depth research on the power quality control and governance of microgrids. certain results.
At present, the technologies used to manage the power quality of microgrids include passive filters, static var compensation (SVC), etc. With the emergence of high-performance power electronic components and the development of microprocessing technology, information technology, and control technology, scholars The concept of custom power is presented. Customized power technology is a power supply technology that applies modern power electronics and control technology to achieve power quality control and provide users with specific needs. It is still in the research stage.
Research on microgrids in China mainly focuses on operation control and energy management, and there are few studies on power quality. In the microgrid demonstration projects that have been built in China, the power quality problem has not been paid enough attention. The power quality monitoring and analysis, power quality evaluation index and evaluation system of the microgrid, and the integrated control and governance technology of the power quality of the microgrid based on the inverter distributed generation, still need to be further studied.
- Microgrid energy optimization management technology
Because the microgrid integrates multiple energy inputs (solar energy, wind energy, conventional fossil fuels, biomass energy, etc.), multiple product outputs (cold, heat, electricity, etc.), multiple energy conversion units (fuel cells, micro gas turbines, Internal combustion engine, energy storage system, etc.), is a heterogeneous complex system with mutually coupled behaviors such as chemistry, thermodynamics, and electrodynamics. The uncertainty and time-varying energy in the microgrid are stronger, and the energy management and distributed power optimization of the microgrid system The dispatch method will be very different from the optimal dispatch of the main grid.
When the microgrid contains a variety of distributed power sources, various control and adjustment methods are fully utilized to realize the optimal operation of the microgrid and improve the overall operation efficiency of the microgrid through the energy management and economic dispatch of the distributed power sources in the microgrid. It is a subject that needs to be deeply studied from the aspects of modeling methods and solving techniques.
At present, the energy management system of microgrid mainly has two modes: centralized dispatching and decentralized control. The centralized scheduling mode consists of the upper-level central energy management system and the underlying distributed power supply, load and other local equipment controllers, and two-way communication is required between the two layers. The upper-level central energy management system can also realize information exchange with the regional power grid dispatching system. Based on market price information, output forecast of intermittent distributed power sources in the microgrid, and load forecast results of the microgrid, the system can operate according to different optimization objectives and constraints. At the same time, it integrates the functions of demand-side response and auxiliary services, formulates the optimal operation and scheduling strategy of the microgrid in real time, and issues control instructions to the underlying equipment controller.
When the decentralized control mode is adopted, the task of energy optimization in the microgrid is mainly completed by the decentralized device layer controllers. The main function of each device layer controller is not to maximize the use efficiency of the device, but to cooperate with other devices in the microgrid. Devices work together to improve the efficiency of the entire microgrid. The centralized scheduling mode is relatively mature in technology and is widely used at present. China’s existing demonstration projects are basically equipped with energy management systems, but most of them can only complete basic dispatching functions, and have not yet been able to achieve optimal dispatching of multiple energy sources. In addition, there is still room for further expansion and autonomy of the system. Research.