Design Of Nonlinear Coordinated Sliding Mode Controllers For SVC And HVDC

High voltage and Direct Current Transmission (HVDC) system is controllable highly, and a set of control system is the core technology of HVDC. Whether or not HVDC system can run normally is relative closely with the basic controller. Moreover, the additional controller also is the important guarantee to improve the stability of running in HVDC/AC. The main contents have:Firstly, the paper introduces basic constitution of HVDC. And, based on a systematic mathematical model, the paper analyzes both the principle and performance of main control and accommodation mode for HVDC system.Secondly, the basic concept of the differential geometry theory is introduced. The exact linearization condition and the linearization process are analyzed on basis of SISO system and MIMO system, respectively. The basic principle of the sliding variable structure control is expounded. The design process and method is analyzed fully. A detail analysis on the vibration cause of the sliding variable structure control is made, and ways how to weaken vibration are discussed.Thirdly, A basic controller of HVDC is designed. This Paper adopts the constant reactive current control at the inverter, Which is different from the traditional control method. The constant reactive current control can adjust reactive Power consume at the inverter and improve the voltage stability. Based on feedback linearization in the nonlinear systems and Variable-Structure control theory in the linear system, new nonlinear basic controller and additional controller are designed in this paper. The effectiveness and superiorities of new controllers have been testified through simulation.Fourthly, Focusing on the contradiction between the consumed reactive Power of inverter and the voltage stability, the chapter adopted SVC to compensate reactive power of inverter so that it make the voltage at inverter side more stabile. After modeling a system equation of HVDC and SVC, on the basis of differential geometry, the generator nonlinear SVC and HVDC system is putted up by combining the differential geometry theory with the vector variable structure control theory. At last, the HVDC and SVC nonlinear cooperative controller is presented. And the simulation result shows that the transient performance of the system can be improved effectively, and the voltage performance is also further improved, reach a better control result.