Control of the grid-connected modular multilevel converter based on capacitor energy

For the modular multilevel converter (MMC) connected with the grid is the most important application. In this paper, an equivalent model of the MMC in the dq synchronous reference is deduced. Different from traditional converter, this model indicates both the inductance and the equivalent capacitance in the ac side would influence the system control. In order to simplify the control to the input currents, the voltage of the inductor and resistor is selected as the control variable and others are taken as disturbance variables. In the outer control loop, the capacitor energy is brought to realize linear control to the system, at the same time, the system power response model is established to deduce the system transformation. Finally, experiment results verify the conclusions and the validity of the mentioned control strategy.