Small-Signal Stability Analysis and Enhancement of Secondary Frequency Control in Islanded Microgrids

Shichao Liu
Thursday, May 17, 2018


Microgrids can greatly facilitate the high-level penetration of renewable-based distributed generations (DGs) and enhance the ability of the self-healing of smart grids.  These abilities of microgrids boost their rapid growth in the world-wide implementation. A microgrid can operate in the grid-connected mode and the islanded mode. The energy management of a microgrid follows a hierarchical control structure, including primary control, secondary control and tertiary control. The tertiary control is to optimally dispatch the power flow between the microgrid and the grid. The droop-based primary control sustains the fast stabilization of the dynamics of the active and reactive power caused by sudden load changes and disturbances. While the droop control can keep the microgrid stable, it results in voltage deviations. For the seamless reconnection and disconnection of a microgrid to the main grid, the voltage deviations have to be removed. To restore the frequency and amplitude of voltages, the secondary control is necessary and can be designed in either centralized or distributed structure. Both the centralized and distributed secondary control structures involve communications among controllers.

This presentation will discuss the small-signal stability analysis and enhancement of the secondary frequency control of islanded microgrids in terms of communication delays. Firstly, the effect of the communication delay on the stability of islanded microgrids is analyzed. A small-signal model based method is introduced for the microgrid to find delay margins below which the microgrid can maintain stable. By performing a series of trial studies, the relationships between secondary frequency control gains and delay margins are obtained. Then, a gain scheduling approach is also proposed to compensate the effect of the communication delay on the secondary frequency control. Moreover, results from an islanded microgrid with four inverter-based DGs will be shown to evaluate the impact of communication delays on the microgrid secondary frequency control and the performance of the proposed gain scheduling approach. In the end, the future work plan will be introduced, focusing on phasor measurement unit (PMU) based distributed frequency and voltage control of islanded microgrids.


Short Biography of Shichao Liu

Dr. Shichao Liu has been an Associate Professor in the School of Mechanical, Electronic and Control Engineering at Beijing Jiaotong University, Beijing, China, since November-2016. From September-2014 to October-2016, Shichao Liu was a postdoctoral fellow at Carleton University. Shichao Liu received his Ph.D. degree from the Carleton University, Ottawa, ON, Canada, in 2014. He was the winner for the 2010 Carleton President’s Doctoral Fellowship. In 2018, he was in the inventory list of the NSERC Visiting Fellowship.

Dr. Liu is currently an Associate Editor of IEEE Access. Dr. Liu was a Keynote Speaker in the International Conference on Mechanical, Material and Aerospace Engineering, May 12-14, 2017, Beijing, China. He is a member of the technical committee of IEEE SMC Interactive and Wearable Computing and Devices. He was the Publication Chair of 2016 IEEE 20th International Conference on Computer Supported Cooperative Work in Design, Nanchang, China.

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