Fractional Order PID Control Strategy for Modular Multilevel Converters

In order to simplify the control of the modular multilevel converter and reduce the harmonic component in the circulation, I propose a fractional order PID control method. And I build a state equation of the single-phase equivalent circuit of the modular multilevel converter. Then According to the analysis of the state equation, we need to adjust the total voltage of the input by a fractional-order PID to obtain a circulation reference. Finally, I let the circulation reference and the load current reference as the input of deadbeat control. Compared with the traditional integer-order PID control method, the dynamic response of the circulation reference that based on the fractional-order PID control method proposed in this paper is better and can be stabilized more quickly. What is more, the harmonic component of circulation and the capacitor voltage ripple of sub-module are lower. So the method proposed in this paper is effective.