A cost-effective ac-ac voltage sag protector with a fast dynamic response using a new RMS averaging method

Voltage sags has been identified as the largest negative impact on industrial productivity due to a sensitivity of electrical loads, and several voltage sag immunity standards such as SEMI F47, CEBMA Curve and IEC 61000-4-11, -34 were founded to improve equipment reliability, uptime and to reduce service costs. In this paper, a novel voltage sags controller along with a new RMS averaging method, which achieves not only a fast response but also a simple implementation, is proposed for the voltage sag protector employing a single-phase ac-ac voltage converter with an autotransformer. Simple and easy implementation of the converter due to no requirement of energy storage device and synchronization of voltage phase makes hardware cost-effective. A slow detection of a conventional RMS averaging method, which have been identified as a major problem, is improved by new scheme, where all stored voltage data within a queue is tuned up by new coming voltage data, is adopted for the new RMS averaging method. Experimental results are presented to verify the fast dynamics of the proposed voltage sag controller.