Copyright © 2018 Authors. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. International Journal of Engineering & Technology, 7 (3.1) (2018) 178-182 International Journal of Engineering & Technology Website: www.sciencepubco.com/index.php/IJET Research paper Voltage Regulation Using STATCOM with PI and Adaptive PI Controls S. Felix Stephen 1 , Dr. I. Jacob Raglend 2 1 Assistant Professor, Department of Electronics and Instrumentation Engineering, Noorul Islam Centre for Higher Education, Kumaracoil, India 2 Professor, Vellore Institute of Technology, Vellore, India *Corresponding author E-mail : felixstephensfs@ymail.com Abstract In power systems, voltage instability problems occur due to its continuous demand in heavily loaded networks. So it is essential to stabi- lize the voltage levels in power systems. The stabilization of power systems can be improved by Flexible Alternating Current Transmis- sion System (FACTS) devices. One of the FACTS devices named Static Synchronous Compensator (STATCOM) injects the compensat- ing current in phase quadrature with line voltage and replicate as inductive reactance to produce capacitive power for the AC grid or as capacitive reactance to draw inductive power from the AC grid for controlling power flow in the line. This paper proposes Adaptive PI control over conventional PI that normally self-adjusts the controller gains under disturbances and helps in improving the performance and attaining a preferred response, irrespective of the change of working conditions. The work is implemented under MATLAB/SIMULINK environment. This method performs more efficient than the original PI with fixed control gains and also im- proves the system response speed consistently. Keywords: Adaptive control; Proportional Integral (PI) control; Reactive Power; STATCOM; Voltage stability 1. Introduction The stable operation of power system has become a significant problem for a secured system operation. Power system instability may occur due to large number of interconnections; more power transmissions through long transmission lines; new technologies; increased power consumption in heavy load areas; use of more number of induction machines and local uncoordinated controls. The stability of power system is that for a given early operational condition, it is the capability to use a state of operating steadiness when open to any physical distraction, with maximum of the sys- tem parameters controlled so that nearly the whole system rests unspoiled. Voltage stability is a dangerous stability problem in refining the security and consistency of power systems. Voltage stability is the ability in upholding stable voltages at every buses in the system and also maintaining or restoring balance between demand and source of load from its specified early working cir- cumstances under disturbances. Another problematic, Voltage collapse highly complex voltage insecurity is the sequence by which the assembly of voltage instability leads to an unusual con- dition of small voltages blackout or blackout in important parts of a power system. Such voltage collapse has some symptoms like heavy reactive power flows; low voltage; heavily loaded systems and inadequate reactive support. Generally, sufficient reserves will be available those settle to a steady voltage level [1]. Though, system instability may occur because of the combined effect of system conditions and events that the deficiency of added reactive power that leads to voltage downfall. Thus the system meets a partial or total collapse. Figure 1 shows the voltage stability phenomenon. In power sys- tems, voltage steadiness is worried with load regions and load features and basically it is load constancy. Voltage stability is of four types as, Large disruption Small disruption Transient Longer term Figure 1. A voltage stability phenomenon 1.1. Causes of Voltage uncertainty • Surge in load demand • Failure to meet reactive power request • Disorders such as system errors, circuit constraints or small per- turbations • Critical load components • Complex loads in transmission lines • Too distant voltage sources from the load centres • Very low generation • ULTC action during low voltage conditions • Uncoordinated control and protective systems • Deficient load reactive compensation.