Compensation of Reactive Power and Sag Voltage Using Superconducting Magnetic Energy Storage System

Abstract

Technological developments such as Flexible AC Transmission Systems (FACTS) can improve the power quality of the power system and can respond to the ever-increasing demand for electrical energy. Superconducting magnetic energy storage (SMES) is a FACTS device that has been used for several years at utility and industrial sites throughout the United States, Japan, Europe, and South Africa to provide both transmission voltage support and power quality to customers who are vulnerable to fluctuating power quality [1]-[3]. SMES systems are classified into two groups: voltage source inverter (VSI) and current source inverter (CSI) SMES. The VSI SMES has many advantages when compared with the CSI SMES; for example, in the VSI SMES, the power rating of power electronic devices that are used in the inverter is much less than that of the CSI SMES, resulting in fewer switching and power losses. Also, the VSI SMES can be used as a Static synchronous Compensator (STATCOM) when its chopper is out of service. Moreover, for the same condition, the VSI SMES can store more energy than the CSI SMES; these advantages encouraged the authors to study VSI SMES. This type of SMES is composed of a magnetic energy storage coil with various structures and power conditioning systems that are also composed of different parts, such as AC-DC filters, a multi-level chopper, a capacitor bank, and a multi-level converter (i.e. an inverter or rectifier). These power conditioning systems are also used in many different sustainable energy systems, such as bio fuels, solar power, wind power, wave power, geothermal power, and tidal power. The converter is an interface between the power network and the capacitor bank and controls the electrical energy exchange between the two. Likewise, the chopper is also an interface between the magnetic energy storage coil and the capacitor bank, and controls electrical energy exchange between them. To store the electrical energy in the capacitor bank and the magnetic energy storage coil in the range of mega joules, it is necessary to employ high power-rating converters; to overcome the limitations of the current and voltage range of the semiconductors, multi-level converters are used. The advantages of using such converters include reducing voltage on the switches, harmonic order correction, decreasing or eliminating lateral equipment, decreasing switching frequency, decreasing total harmonic distortion (THD), decreasing switching losses, and decreasing the output current ripple.