Summary of Micro-Grid Control Technology

Abstract:

The inherent drawbacks of the traditional power grid and distributed energy resources are increasingly restricting the development of power systems. The micro-grid integrating of a variety of new green energy and having perfect self-control can meet the load demand and achieve sustainable development of environment at the same time. The basic definitions, system structure, the control strategy and the last research of micro-grid through a comprehensive literature review are presented. The literature analyzes the power supply control, power quality control and overall control and points out the characteristics and deficiencies of each control mode. Finally, some prospects of micro-grid on research findings in China were proposed.

• Periodical: Advanced Materials Research (Volumes 1070-1072)
• Pages: 1326-1334
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.1070-1072.1326
• Online since: December 2014
• Authors: Jun Jie Jiang, Rong Ju
• Keywords: Control Strategy, Micro-Grid, Overall Control, Power Quality Control, Power Supply Control

References

[14] The method generally have a distributed power or energy storage devices when the system is in islanding operation to use the VF to provides a reference voltage and frequency and other micro power output stability power with PQ control. ② Peer control mode. This approach is based on power electronic technology and equal thought to control all the micro-power by Droop control.

DOI: 10.1049/pbpo217e_ch12

[15] ③ Hierarchical control. The multi agent technology of traditional power system is applied to the micro-grid. By using the autonomous system, agent, reaction ability and spontaneous behavior and other characteristics meet the requirements of the control of the micro-grid. 3. 3. 1 Master-slave control mode Master slave control is commonly employed in isolated island operation. When the system is in the isolated island operation, a distributed power or energy storage device called the main controller will take the VF control to maintain the frequency and voltage of whole system and other distributed power took the PQ control call the following controller. The distributed energy or storage device that can be used as the main controller requires certain conditions. It not only requires the large system capacity, but also needs enough speed to follow the load fluctuation. Under this control, when the system is in grid connected operation, all distributed power take the PQ control and energy storage device is in a storage state; when it comes to the isolated island operation, distributed power or energy storage need to become the main control should be quickly to take VF control. The common main control methods are the following: ① The energy storage device as the main control module. The energy storage device can absorb excess power when the output power is abundant and balance the load fluctuation by discharge when the system is in isolated operation. But the capacity of energy storage device is limited. If the device has been in a discharge state for a long time, it cannot be able to maintain the voltage and frequency of micro grid stability. ② The distributed power as the main control module. Because the wind turbine and photovoltaic power generation output varies greatly, they are not suitable as a main controller. Distributed energy like gas turbine is very suitable, because its output can be adjusted flexibly in a certain range and power supply is stable and easy to control. 3. 3. 2 Peer control mode The so-called peer-to-peer control mode is to make all the distributed sources and energy storage devices in the same position and do not distinguish between the principal and subordinate relationship. Both in the grid connected and islanded operation, each micro power will take the droop control strategy. According to the actual load fluctuation, the system will automatically assign the active and inactive power output between each micro power, and maintain the voltage and frequency stability. Compared with the master-slave control, Peer control can automatically adjust the voltage and frequency and communication system is saved that can reduce the cost of the system. Then both in grid connected and isolated island operation, the micro power take peer control can achieve seamless handoff easily. At present, the Belgian Katholiekewe micro-grid laboratory, Spain's Catalunyada university laboratory micro -rid are studied are researching the peer control. 3. 3. 3 The hierarchical control mode The hierarchical control mode generally has two layers. The first layer is the central control system, It will accept lower measurement feedback signal, and give control signal to other distributed power control by computers. The second layer has the micro power module, relay protect module, communication module and load. As shown in Figure 5, the center control system preset operation plan. Then according to the collected voltage, frequency and power signal from sub layer, the control core will control each micro power, protection device and switch the start and stop of load to ensure the micro grid voltage and frequency stability. Depended on the reliable work of communication device, the hierarchical control increased the cost of whole system. The present study for hierarchical control concentrated upon the coordination of market transactions and power quality management and has not yet entered the study of power, voltage and frequency control. Conclusion As the concentrated grid system, micro-grid, involves many aspects. This paper mainly introduces the basic definition, structure, and control method of micro-grid technology, but the study included other aspects relay protection operation and market transactions. As our research of micro-grid is late than foreign countries, but many domestic research institutes, such as Tientsin University, Xi`an Jiaotong University, Hefei University have made many achievements in the research of the micro-grid. I believe that as long as technology continues to improve and the policy support, the micro-grid technology and new energy industry will cause the electric power industry revolution, and benefit of all mankind in the future . Reference documentation.

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