A multivariable adaptive nonlinear controller for a five-level diode clamped StatCom

This paper presents a novel control strategy for a five-level diode clamped converter that uses an auxiliary circuit to equalize its DC-bus capacitor voltages. This multilevel converter is used to design a Static Compensator (StatCom) that supplies a power grid. The paper also presents a method to find the state space model for a general N-level diode clamped converter. This model is utilized to find the controller equations. The power grid parameters and the converter parameters that represent the power losses are assumed unknown for the design. The controller includes an adaptation module that automatically adjusts its parameters when the grid parameter and the power losses change. A multivariable nonlinear control design scheme is adopted since the converter model is nonlinear and multivariable. The proposed control system and the StatCom are evaluated in simulation. The results show that the DC-bus capacitor voltages are perfectly equalized and the StatCom terminal voltage is maintained constant regardless of changes in the grid operating condition.