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

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