REVIEW OF TRANSFORMERLESS UPFC DEVICE FOR POWER QUALITY ENHANCEMENT IN POWER SYSTEM

Abstract

In this paper, a modulation and control method for the new transformer-less unified power flow controller
(UPFC) is presented. As is well known, the conventional UPFC that consists of two back-to-back inverters requires bulky
and often complicated zigzag transformers for isolation and reaching high power rating with desired voltage waveforms.
To overcome this problem, a completely transformer-less UPFC based on an innovative configuration of two cascade
multilevel inverters (CMIs) has been proposed. The new UPFC offers several advantages over the traditional technology,
such as transformer-less, light weight, high efficiency, low cost and fast dynamic response. This paper focuses on the
modulation and control for this new transformer-less UPFC, including optimized fundamental frequency modulation
(FFM) for low total harmonic distortion (THD) and high efficiency, independent active and reactive power control over
the transmission line, dc-link voltage balance control, etc.