Synthesis of a robust control system for an unstable plant using QFT

The paper aims to synthesize by Quantitative Feedback Theory (QFT) a robust controller represented as a transfer function containing two left zeros and two left poles to stabilize a model of a plasma unstable vertical position in the T-15MD tokamak (Kurchatov Institute, Moscow, Russia). Due to the relatively large overshoot and oscillations of a transient response, the two-cascade robust control system of the plasma position with PID controllers was designed by the QFT. An inner cascade controls a current in a horizontal field coil and an outer cascade stabilizes the plasma vertical position. An actuator is a model of a 6-pulse multiphase thyristor rectifier.