DC–AC Power Conversion Based on Using Modular Multilevel Converter With Arm Energy Approximation Control

Power conversion from ultravoltage direct current (UVdc) to ultravoltage alternating current (UVac) is the biggest challenge facing industrial power application companies. Converting UVdc transmission systems with 2200 kV dc and distance up to 3000 km into UVac is the most challenging issue associated with transmitting power by UVdc transmission systems. This paper proposes an approximated arm energy control algorithm for a modular multilevel converter with a large scale of submodules per arm to convert UVdc of 2200 kV and more into UVac in order to achieve total harmonics distortion for UVac systems of <;1%. Generating insertion indices by utilizing upper and lower approximated arms' energies equations for the numbers of submodule per arm (N) is derived first. Second, the flooring switching pulsewidth modulation is explained in order to generate the number of inserted and bypassed submodules per arm. Third, submodules' selections are proposed and verified by the simulations. Fourth, a set of simulation results for a dc bus of 2200 kV and 481 levels for the output voltage conducted in the MATLAB/Simulink environment are presented to verify the proposed algorithm. Finally, the proposed algorithm is experimentally verified by the hardware and software designs of the prototype.