Control of Modular Multilevel Converters for integration of distributed generation sources into the power grid

This paper presents a control technique for control of a Modular Multilevel Converter (MMC) based DG system in the grid-connected mode. Circulating currents of MMC are considered as a state variable, besides the AC currents and dc-link voltage of interfaced converter, which is the main novelty and contribution of the proposed control technique over the other potential control techniques in DG technology. By this assumption, the proposed control technique is included by three outer, central and inner control loops for regulating the operation of interfaced MMC under steady state operating conditions, and during load and parameter variations. Passivity based controller, sliding mode method and reference currents calculator are employed as outer loop controller (OLC), central loop controller (CLC) and inner loop controller (ILC), respectively, in the proposed control technique. Simulation results confirm the effectiveness of the proposed control technique in the proposed DG model during dynamic and steady-state operating conditions.