Design of Low Order Robust Controllers for a VSC HVDC Power Plant Terminal

This paper describes the design of controllers for a Voltage Source Converter High Voltage Direct Current (VSC HVDC) power terminal, a MIMOpl ant that must operate over a wide range and that experiences disturbances due to Pulse Width Modulation (PWM) switching. The controllers are designed using two approaches: the Glover–McFarlane loop shaping procedure (LSDP), and a novel implementation of a multiple operating point version of the LSDP using the ellipsoidal set approach, in which low order controllers are obtained using an iterative sequence of LMI programs and a convexifying potential function formulation. The LSDP provides controllers that give robust performance in the neighborhood of the nominal plant but poorer behavior at distant operating points. The novel approach is demonstrated to be practical on a rigorous plant model including the switching behavior. Both full and low order controllers are designed whose overall behavior is better than that of the standard LSDP.