Robust Fault Reconstruction Of Modular Multilevel Converter Based On Sliding Mode Observer

The modular multilevel converter(MMC)is a new type of flexible transmission form in flexible DC transmission system,which is widely used in flexible DC transmission engineering and other medium and high voltage technical field s.MMC is formed by cascad ing a large number of sub-modules.Once a failure occurs,it will seriously threaten the operation and equipment safety of the MMC system,so it is particularly important to monitor the status of the MMC system in real time.The fault reconstruction technology can not only detect and separate faults,but also realize fault estimation.Therefore,it is very meaningful to apply fault reconstruction research to MMC systems.This thesis studies the robust fault reconstruction of modular multilevel converter based on sliding mode observer,the main work is summarized as follows:Firstly,according to the operating principle of the single-phase MMC equivalent circuit,the voltage-current relationship equation obtained by Kirchhoff's law,a state space system model based on sensor fault reconstruction and a state space system model based on simultaneous fault reconstruction of actuator and sensor are established respectively.Next,aiming at uncertain systems such as sensor fault and interference in MMC,a robust fault reconstruction method based on sliding mode observer is proposed.By introducing filters to transform sensor faults into actuator state-enhanced state-space systems,according to the design conditions of the sliding mode observer of the augmented system and Lyapunov stability analysis,the idea of equivalent output control to maintain the sliding mode motion is used for sensor failures.The reconstruction method is designed,combined with the linear matrix inequality method t o design the observer gain and optimize the solution.The simulation results verify the effectiveness of the robust fault reconstruction method of the sensor.Finally,aiming at the uncertain system in which actuator fault,sensor fault and interference occur simultaneously in MMC,the robust fault reconstruction based on sliding mode observer is studied.Through coordinate transformation and introducing filter,the sensor fault in the original system is transformed into the extended actuator fault state space form.Considering the conditions that the design of sliding mode observer satisfies for the extended system fault reconstruction,the actuator and sensor fault form are designed with the idea of maintaining sliding mode motion by equivalent output control,and the observer gain and other parameters are designed with LMI method Convex optimization solution,the feasibility of this method is verified by simulation results.