Research Of H_∞ Control Theory In PWM Excitation System Of Synchronous Generator

The excitation system of synchronous generator is one of the most important measures which keep power system operation safe and stable. Since the 1950s' , many changes has happened in the control method and rectifier power unit of excitation system. H∞control theory is a kind of powerful tool analyzing and designing uncertain system, which can solve mainly control problems of control quality worsening due to the error of object modeling and model perturbation within a certain range. PWM rectifier is the key point that pays more attention to and needs more study in academe; it successfully applies chopper control to the latest power electronics unit which can be shut down and turn on at any moment. H∞control theory is used to synchronous generator PWM excitation system and solve many problems which result from traditional excitation systems in this paper.Mathematical model of synchronous generator PWM excitation rectifier system is proposed in two types of coordinates; on the other hand, mathematical model of synchronous generator is advanced in this paper. The topology of synchronous generator PWM excitation system is put forward, at the same time, it is given how to select and control the important power electronics unit of synchronous generator PWM excitation system in this paper.Double closed-loop control method is applied to achieve the control of synchronous generator PWM excitation system. PI controller is designed to control current interior loop. It assures the current on the side of rectifier AC input is sine wave and keeps its operation high power factor. H∞theory is used to design voltage external loop, integrated mathematical model of current interior loop and synchronous generator is put forward. A simple H∞controller is got by means of selecting the rational weighting function and finding the solution of Riccati equation. The excitation regular is satisfied after examining the performance of controller.The computer simulation result shows that the PWM excitation system which is designed by H∞control theory successfully solves such problems as the slow response, low power factor and high THD which result from the traditional phasic control rectifier, and improves the security of synchronous generator.