DISTRIBUTED REACTIVE POWER COMPENSATION FOR RADIAL FEEDER

Abstract

Voltage regulation of distribution lines is a challenging problem, particularly when it is not economic to upgrade the entire feeder system. The distribution networks supplying rural areas are often quite weak because of the long distances involved and the high R/X ratio of the lines that are used. Hence, as demand increases on these networks, power quality issues such as poor voltage regulation and voltage sags often become a significant problem. Lumped compensation by power electronic converters is reported in literature to have the potential to improve supply quality and increase line utilisation in weak distribution networks. But widespread use of this technology has been limited due to costly power electronics processing for high power rating and reliability concerns. This thesis illustrates the concept of distributive approach for realizing the cost effective solution and more effective functionality of Power Electronics converters for proposed distributed solution. Low cost electronic devices, power electronics and communication technologies if distributedly applied, entire subtransmission and distribution network may be covered more effectively and cost effective power flow control can easily be done by Distributive Compensation. Often under such configurations the central control approach is quite complex and require large communication setup and coordination of sensors, and often the basic theme of simplicity of distributive compensation is lost. This thesis explores the use of Distributed Shunt compensators based on autonomous control to achieve stable steady state and dynamic compensation of the voltage profile along a radial distribution system under widely varying load conditions. The proposed scheme allows independent operation of each unit, such that each unit has to compensate the voltage drop of its preceding section of line by supplying the requisite reactive power. This autonomous control along the radial feeder with proposed autonomous distributed control technique is shown working effectively by improving voltage profile, operating at unity power factor and by compensation of load reactive power. A decentralized control strategy is also used under grid connected mode to compensate reactive demand of load under widely varying condition. Simulated results under MATLAB environment are presented to validate the effectiveness of the proposed control schemes for distributed compensation under load perturbations.