Voltage control in a LV microgrid by means of an SVC

There is an increase of renewable sources supplying low voltage (LV) micro-grids, sometimes connected to a more powerful grid or sometimes working as isolated grids. In the last case there is a high degree of uncertainty on the availability of the sources, which causes problems of stability and of power quality (PQ) in some points of the grid. At a bigger scale, such kind of problems, are well known in medium voltage (MV) networks, where the proposed solutions to fix the stability and PQ problems are based on the control of reactive power flow in the grid. The equipment to perform such control function ranges from the simple capacitor banks driven by electromechanical contactors, through the Static Var Compensators (SVC) based on the combination of Thyristor Switched Capacitors (TSC) and Thyristor Controlled Reactors (TCR) or Active Power Filters (APF). This paper describes the design and implementation of a low voltage SVC prototype, of 180 kVAr (C) plus 60 kVAr (L) to compensate variations of the line voltage at the end of a long LV line, supplied by a transformer station. The compensation range is -15 V, + 5 V for a rated voltage of 400 V phase to phase.