Voltage Sag Ride-Through of AC Drives: Control and Analysis

This thesis focuses on controller design and analysis for induction motor (IM) drives, flux control for electrically excited synchronous motors with damper windings (EESMs), and to enhance voltage sag ride-through ability and analysis for a wind turbine application with a full-power grid-connected active rectifier. The goal is to be able to use the existing equipment, without altering the hardware. Further, design and analysis of the stabilization of DC-link voltage oscillations for DC systems and inverter drives is studied, for example traction drives with voltage sags in focus. The proposed IM controller is based on the field-weakening controller of Kim and Sul [31], which is further developed. Applying the proposed controller to voltage sag ride-through gives a cheap and simple ride-through system. The EESM controller is based on setpoint adjustment for the field current controller. The analysis also concerns stability for the proposed flux controller. The DC-link stabilization algorithm is designed following Mosskull [38], where a component is added to the current controller. The algorithm is further developed. Analysis is the main focus, and concerns the impact of the different parameters involved. Proper parameter selection for the controller, switching frequency, and DC-link capacitor is given. The impact of voltage sags is investigated for a power-grid-connected rectifier. Here, we analyze the impact of different types of voltage sags and phaseangle jumps. The analysis gives design rules for the DC-link capacitor and the switching frequency. Experimental results and simulations verify the theoretical results.