A model-based controller for a single-phase grid-tied modular multilevel inverter with regulation and balance of energy

© 2019 John Wiley & Sons, Ltd.A controller based on the model is presented for a single-phase grid-tied inverter of 2N + 1 levels, which is based on the modular multilevel converter (MMC) topology, where N is the number of cells per arm. This is referred to as an MMC-based inverter in this paper. The controller has the purpose to assure a good performance of the converter operation both internally and during grid connection. For this, the proposed controller involves four control loops, namely, overall energy regulation, energy balance between arms, circulating current, and injected current loops. Notice that the proposed controller by itself guarantees voltage regulation at the arms level only. To guarantee individual regulation of each cell capacitor voltage, the proposed controller is then combined with the phase-shifted carrier-based pulse-width modulation (PSC-PWM) scheme. Experimental evidence is exposed to assess the performance of the proposed control scheme. The experimental setup considers a grid-tied inverter based on an MMC of seven levels (N = 3). The proposed controller and the experimental prototype are implemented in a hardware-in-the-loop platform. The experimental tests include responses to step changes in the load power and unbalance in the initial capacitor voltages.