A multivariable adaptive nonlinear controller for a five-level diode clamped active power filter

This paper presents a novel control system for a five-level diode clamped converter based active power filter. The converter has an auxiliary circuit connected to its DC bus. A model based approach is adopted to design the control system. First, the converter state space model is obtained. Next, a multivariable controller is proposed to stabilize the DC bus capacitor voltages and a backstepping method is utilized to design the controller that compensates the load current harmonics. The filter parameters that represent the power losses are assumed unknown during the design. The controller is therefore provided with adaptation laws that automatically retune the controller parameters when power losses change. The main characteristic of the proposed multivariable adaptive control design method is that it follows the input-output linearization method and uses the internal dynamic variables to stabilize the closed loop system. The performances of the filter are evaluated in simulation. The results demonstrate that load current harmonics are very well compensated. The converter DC-bus voltage is maintained at its reference value and capacitor voltages remain equal when the filter operating conditions change.