STABILITY ANALYSIS AND OPTIMAL CONTROL DESIGN FOR AC-DC POWER SYSTEM WITH CONSTANT POWER LOAD

摘要

This thesis studies the stability properties of an AC-DC system - a three-phase controlledudrectifi�er - with constant power load (CPL) and proposes an optimal design for the systemudcontrol. CPLs have been widely seen in power electronic applications. For example, motoruddrives and DC/AC inverters in advanced automotive systems may behave as CPLs. Due toudtheir negative impedances, CPLs often impact the power quality and stability of an AC/DCudsystem. This thesis considers a typical AC/DC system with constant power load, whereudthe three-phase rectifi�er is originally controlled by two PI controllers. It is demonstratedudthat the PI control strategy obtains narrow stability margin. To overcome the limitationudof PI control, a linear quadratic regulator with full state feedback is used to determine theudoptimal structure of the controller and tune the parameters of the controller and DC �filter.udThis method is shown to improve the stability margin of the AC-DC system tremendously.