Large-displacement stability of ac microgrids

Lee J Rashkin, Purdue University

Abstract

In ac power systems, it is important to regulate the amplitude and frequency of voltages throughout the system. Historically, this has been accomplished by ensuring sucient spinning reserve and controlling frequency through scheduling of the generators. Control strategies for emerging microgrids are being patterned after the classic grid. However, there are major dierences between the classic grid and a typical microgrid. In the classic grid, all generators have similar and well-known dynamic characteristics since there are only a small number of manufacturers worldwide and since the technology is similar between manufacturers (e.g. wound-eld synchronous machines). On the other hand, in a typical microgrid, there are numerous power sources with diverse characteristics (photovoltaic arrays, wind turbines, diesel-engine-driven generators), approaches of power conversion (converter and inverter circuits), and associated control strategies, leading to a wide range of dynamic characteristics among the constituent components. Mindful of these dierences, it is desirable to develop robust control methodologies that will ensure stability. In this thesis, a new control paradigm is set forth based upon an energy storage unit that regulates microgrid voltage/frequency, and a centralized clock that synchronizes all sources and loads within the microgrid. A computer study is used to illustrate the feasibility of the proposed approach and establish an inverter design that ensures large-disturbance stability. To quantify the stability region, the notion of stability in PQ space is introduced. The impact of the energy storage unit's physical constraints (e.g., magnitude and rate limits) on the region of stability in PQ space are established.

Degree

Ph.D.

Advisors

Wasynczuk, Purdue University.

Subject Area

Electrical engineering|Energy

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