Instability of Wind Turbine Converters During Current Injection to Low Voltage Grid Faults and PLL Frequency Based Stability Solution

• Published in: IEEE transactions on power systems Vol. 29; no. 4; pp. 1683 - 1691
• Main Authors: Goksu, Omer, Teodorescu, Remus, Bak, Claus Leth, Iov, Florin, Kjaer, Philip Carne
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.07.2014; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Converters; current control; Electric potential; Faults; Impedance; Instability; Phase locked loops; power system faults; Power system stability; Stability; Stability analysis; Voltage control; Voltage drop; Wind power; Wind power generation; Wind turbines
• ISSN: 0885-8950; 1558-0679
• DOI: 10.1109/TPWRS.2013.2295261

In recent grid codes for wind power integration, wind turbines are required to stay connected during grid faults even when the grid voltage drops down to zero; and also to inject reactive current in proportion to the voltage drop. However, a physical fact, instability of grid-connected converters during current injection to very low (close to zero) voltage faults, has been omitted, i.e., failed to be noticed in the previous wind power studies and grid code revisions. In this paper, the instability of grid side converters of wind turbines defined as loss of synchronism (LOS), where the wind turbines lose synchronism with the grid fundamental frequency (e.g., 50 Hz) during very deep voltage sags, is explored with its theory, analyzed and a novel stability solution based on PLL frequency is proposed; and both are verified with power system simulations and by experiments on a grid-connected converter setup.