Accurate, robust, and reliable control systems are inevitable for proper operations of Flexible AC Transmission Systems (FACTS) devices. Digital control systems based on up-to-date advanced digital signal processors (DSP) and field-programmable gate arrays (FPGA) are used in combination with a hierarchical (Master-Slave) structure for FACTS devices, where the high number of switching devices and dc link stages make necessary the use of parallel processing techniques in the control loops. Generally, the calculations are carried out by DSP (Master), and the synchronous switching operations of semiconductor switches are achieved by FPGA (Slave) upon orders taken from DSP.

The fiber optic technology is used between DSP/FPGA and FPGA/semiconductor switches as connection bridges by which EMI/EMC problems are eliminated, and time delays resulting from cable transmission are decreased. Furthermore, auxiliary systems like High Voltage (HV) and Medium Voltage (MV) switchgears, water cooling systems, fire and temperature alarm systems, air conditioners, etc. are controlled by Programmable Logic Controllers (PLC).