MODULAR MULTILEVEL CONVERTER WITH HARMONICS COMPENSATION FOR STATE-FEEDBACK CONTROLLER

The voltage variations among the sub-module (SM) capacitors result in harmonicssuperimposed unto the circulating current. The conventional control of the SM voltages usesa closed-loop proportional Integral (PI) controller based on carrier shifted pulse widthmodulation (CSPWM). The PI-controller provides a dc reference circulating current for thecontrol of the modular multilevel converter (MMC) measured circulating current. Todecrease the influence of the voltage variation and improve the voltage control of the SMcapacitors with harmonics elimination, this paper proposes a simple but an improvedcirculating current control within the MMC using a state-feedback controller. The proposedmethod employs state-feedback controller shaped by a linear quadratic regulator for a betterreference tracking. The voltage disturbance in the PI-control loop is considered anddisturbance rejection by feed forward compensation concepts is employed in the proposedscheme to produce an opposing compensation current to the circulating current reference.The feed forward current produced in the proposed method opposes and cancels the acharmonicsdue to the voltage disturbance/variations with simplicity and without the use ofany additional filters or harmonic controllers such as resonant controllers. The MMCperformance in the conventional method and proposed method is presented in a simulation.Finally, results from experiment are given to verify the simulation.