Power control of grid-connected high-gain boost full-bridge modular multilevel converter

Conventional Modular Multilevel Converter (MMC) with half-bridge submodules (HB-SMs) can be used for gird-integration of renewable energy sources, but with limited voltage gain. To elevate the generated ac output voltage level, a bulky low-frequency step-up transformer can be employed at the converter ac side. Alternatively, single-stage dc-ac Boost Full­Bridge MMC (BFB-MMC) can be used effectively. In this paper, the performance of high-gain grid-connected BFB-MMC is investigated under active and reactive power control. The BFB-MMC can generate an ac output voltage with magnitude of kVdc where k is a positive integer number, and Vdc is the input dc voltage level. Each arm in the BFB-MMC contains (2k+1) Full-bridge submodules (FB-SMs) each rated at 0.5 Vdc. Each arm is controlled to generate bipolar sinusoidal stepped voltage ranged from (0.5+k) Vdc to (0.5-k)Vdc with steps of 0.5 Vdc while keeping the sum of upper and lower arm voltages in the same leg equals the input dc voltage. A Detailed illustration for BFB-MMC operational concept, capacitor voltage balancing technique, and active and reactive power controller is presented. Finally, simulation model for the grid-connected BFB-MMC has been built. The simulation results show the effectiveness of BFB-MMC in the grid-connected applications.