Author: Zhai, Yueting
Title: Study of secondary control strategies of microgrids with high voltage quality
Advisors: Chan, K. W. (EE)
Degree: M.Sc.
Year: 2020
Subject: Microgrids (Smart power grids) -- Automatic control
Electric power systems -- Control
Hong Kong Polytechnic University -- Dissertations
Department: Department of Electrical Engineering
Pages: viii, 50 pages : color illustrations
Language: English
Abstract: In recent years, renewable energy power generation system, represented by solar photovoltaic power generation, storage battery and wind power generation, has developed rapidly. In this trend, microgrid and distributed energy have received great attention.
According to the current research, renewable energy will affect the operation of distribution network after grid connected operation. This dissertation introduces the characteristics of microgrid technology and analyzes the uneasiness of operation and control of microgrid caused by the randomness of distributed power supply and its adverse effect on the electrical energy quality.
The particularity of the electrical power quality of the microgrid is determined by the operation and control approaches of the microgrid. The power quality control strategies of microgrid has the following requirements: (1) reactive voltage control, (2) frequency stability, (3) unbalanced control, (4) harmonic suppression. Therefore, this thesis proposes a hierarchical control method of microgrid to study and improve the power quality of microgrid.
The manifestations of the above microgrid power quality issues are different, but the solutions depend on the balanced control of energy. The hierarchical control strategy is an important way to realize the energy balance and make sure the stable operation of the microgrid.
The deviation of voltage and frequency in microgrid are two important indexes of power quality. The traditional droop control method of distributed power inverters will cause the voltage and frequency deviation. In primary control of microgrid, most of the distributed power supplies use power electronic interface, and the load and network structure are variable, which increases the difficulty in stability control of voltage and frequency of microgrid.
How to ensure the microgrid to satisfy the voltage and frequency stability indexes in the island operation mode is the key to reliable operation of the grid. To compensate for the influence of voltage and frequency deviation of microgrid, the control strategy of microgrid based on secondary control is established. This control approach uses the primary control signal to regulate the output voltage amplitude and frequency of the inverter again to make the voltage and frequency deviation at PCC within a certain range. In addition, the smooth synchronization progress between microgrid and main grid can be achieved by adopting the grid-connected control method of the microgrid based on the secondary control. Finally, realizing smooth switching from the island mode to the grid-connected mode and avoiding the issue of impulse current occurring in grid-connection process.
Rights: All rights reserved
Access: restricted access

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