Protecting control panels against voltage sags using square-wave series voltage compensators

Voltage sag is one of the most important power quality problems affecting sensitive industrial equipment. Control panels consist of one or several units of Programmable Logic Controllers (PLC), Contactors and Adjustable Speed Drives. These devices are all sensitive to voltage sags. When a voltage sag occurs, a contactor could trip or a PLC could reset while the controlled process would still work, eventually tripping the process protection and leading to an unplanned process shutdown. This paper discusses the use of a square-wave series voltage compensator in the protection of control panels against voltage sags. PLCs and contactors are modeled. Simulation results of a protected control panel by the square-wave series voltage compensator are presented, showing the effectiveness of this proposition.