A single-phase 5-level inverter with FACTS capability using modular multi-level converter (MMC) topology

Renewable energy systems have become a major part of the modern power systems. Clearly, to connect renewable energy systems to the main grid, a power inverter is needed. There are two major topologies for renewable energy inverters, namely conventional two-level topology and multi-level topology. The modular multilevel converter (MMC) is one of the most advanced multi-level topologies that have gained increasing attention recently. In addition to an inverter in a renewable energy system, capacitor banks or STATCOMs are needed to compensate the reactive power of the grid. In this paper a novel single-phase MMC-based inverter with STATCOM capability for grid connection is proposed. The proposed inverter is designed for grid-connected wind turbines in the mid-sized range. In the proposed control strategy, active and reactive power is controlled by the power angle and the modulation index, respectively. The function of the proposed inverter is to transfer active power to the grid as well as keeping the power factor of the local grid constant at a target power factor regardless of the incoming active power from the renewable energy source, especially from a wind turbine. Generally, the main goal of this paper is to present a new inverter with FACTS capability in a single unit without any additional cost. The simulations have been done in MATLAB/Simulink for a 5-level inverter. A scaled prototype model of the proposed inverter has been built and tested to verify the simulation results.