A Novel Control for Four-quadrant Operation of ITER VS Converter

This paper describes a novel control algorithm of four-quadrant operation of the ITER superconducting coil power supply for VS converter. The vertical stabilization of the plasma current is mainly engaged to the VS converter and the four-quadrant operation must be capable without zero-current discontinuous section. It is difficult to perform a reliable control for four-quadrant operation because of the complexity of each mode for current control according to the existing published papers and reports. And the pattern of circulating current is not constant because the control algorithm for circulating current to remove the zero-current discontinuous section is different. In this paper, the control scheme is divided into five operating modes depending on the load current and a simple algorithm for the circulating current control is proposed for stable control without the zero-current discontinuous section. The control algorithm of output voltage is also proposed according to the voltage command. The unbalanced current of the parallel converter is suppressed to set the rated limiter of control angle and the voltage response operates within 20 ms at the same time. The VS converter model is simulated by PSIM to verify the proposed four-quadrant control methods.