A New Approach for Enhancement of Fault Current Interruption for the Power Quality Improvement
The dynamic voltage restorer (DVR) is a custom power device utilized to counteract voltage sags . It injects controlled three-phase ac voltages in series with the supply voltage, subsequent to a voltage sag, to enhance voltage quality by adjusting the voltage magnitude, wave shape, and phase angle . The main components of a DVR i.e., a series transformer, a voltage- source converter (VSC), a harmonic filter, a dc-side capacitor, and an energy storage device . The line-side harmonic filter consists of the leakage inductance of the series transformer and the filter capacitor.The DVR is conventionally bypassed during a downstream fault to prevent potential adverse impacts on the fault and to protect the DVR components against the fault current . A technically elaborate approach to more efficient utilization of the DVR is to equip it with additional controls and enable it also to limit or interrupt the downstream fault currents. A control approach to enable a DVR to serve as a fault current limiter is provided. The main drawback of this approach is that the dc-link voltage of the DVR increases due to real power absorption during fault current-limiting operation and necessitates overcome the aforementioned limitations, this paper proposes an augmented control strategy for the dvr that provides: 1) voltage-sag compensation under balanced and unbalanced conditions and 2) a fault current interruption (FCI) function.a switch to bypass the DVR when the protective relays, depending on the fault conditions, do not rapidly clear the fault. The adopted DVR converter is comprised of three independent H-bridge VSCs that are connected to a common dc-link capacitor. These VSCs are series connected to the supply grid, each through a single-phase transformer. The proposed FCI control system consists of three independent and identical controller’s one for each single-phase VSC of the DVR. This paper introduces an auxiliary control mechanism to enable the DVR to interrupt downstream fault currents in a radial distribution feeder. The current ripples can be reduced by using SVPWM technique. This control function is an addition to the voltage-sag compensation control of the DVR. The performance of the proposed controller, under different fault scenarios, including arcing fault conditions, is investigated based on time-domain simulation studies in the MATLAB/SIMULINK environment.
