Online control of SVG for network unbalance suppression

Abstract

Conventional control strategies of static var generators (SVG) mostly focus on the compensation for concentrated unbalanced loads or unbalanced voltage at the PCC. With the size of networks increases, many distributed unbalanced loads appear, the total cost applying these unbalance control methods may increase significantly. Therefore, the SVG control strategy for network unbalance suppression has become an essential problem. To solve the problem, this paper proposes an unbalance control system which contains an SVG, power quality measuring equipments and a central controller. Firstly, the network parameters are acquired by inserting a small disturbance current with the SVG and collecting information from the measuring equipments. Secondly, these parameters will be employed by the central controller to calculate the optimal current reference online, during which two objectives are considered, i.e. to minimize the summation of square of negative sequence voltage at each node and to keep unbalance factor of voltage at each node within limit. Finally, the current reference will be transmitted to the SVG. With the proposed strategy, single SVG can compensate for the power system unbalance online intelligently without predetermined system information. A 7-node network in PSCAD is employed to validate the effectiveness of these analyses.