Status,Trends and Prospects of the Fractional Frequency Transmission System
The fractional frequency transmission system(FFTS),also known as low-frequency ac transmission,utilizes a relatively low frequency,e.g.,50/3 Hz,to alleviate the negative effects of the line capacitance and inductance on the power transmission,and therefore,increases the transmission capacity and distance.The FFTS makes good tradeoff between technical performance and engineering economy of the power transmission project,emerging as a prominent topic with the growth of renewable energy.China's"14th Five-Year Plan"outlines a commitment to vigorously develop scaled renewable energy bases in deserts,gobi and wasteland in its vast west,as well as offshore wind power in deep-water and far-shore areas along its eastern coastal lines.However,the western energy bases and load centers are inversely distributed,and the available integration points for offshore wind power are limited.Therefore,efficient power transmission methods are necessary to support the large-scale comprehensive utilization of these renewable energy.The FFTS has experienced a tremendous advance in both academic research and engineering practice in recent years.This paper summarizes the research results of the author's team and other scientific research institutions,and systematically organizes the development status and main achievements of the FFTS from four perspectives:basic principles and system construction methods,key power equipment,high-voltage and bulky-power inverters and the control technology,system safety and stability analysis and protection.Then,the future development trends and prospects are discussed.
fractional frequency transmission systemlow-frequency ac transmissionsystem constructionferromagnetic frequency triplermodular multilevel matrix converterpower system relaying protection
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