Adaptive Observer for Capacitor Voltages in Multilevel STATCOMs

Abstract

AbstractControl of multilevel STATCOMs is complex mainly due to the internal converter control, where several capacitors are used as a fundamental component of multilevel converters. The capacitor voltage must be regulated to ensure the multilevel output voltage waveform, and to equally distribute the high input voltage among the power semiconductors. Regulation of the capacitor voltages needs the knowledge of the capacitor voltages. In this chapter, a nonlinear adaptive observer for DC capacitor voltages estimation is proposed for a class of multilevel converters. The observation scheme estimates simultaneously the state of the system and the system parameters, adding robustness and improving the state estimation when system parameters are uncertain. The observation scheme is developed using an instantaneous model of the system. The original system model is an n-dimensional system which is not observable. The original model is split into a suitable set of n-interconnected subsystems. This new representation allows overcoming the unobservable condition of the original system, which enables the design of an observation scheme for the capacitor voltages and system parameters. Hence, the observer for the whole system is approached by designing a separate exponential observer for each individual subsystem. As a result, the whole system state is reconstructed from the individual exponential observer designed for each subsystem. Thus, the interconnected system, which is constituted by the interconnected exponential observers, is an observer for the original system.KeywordsMultilevel convertersNonlinear estimationSTATCOM