Nestled secondary power loops in multilevel modular converters

A limitation of the conventional modular multilevel converter is that it relies on positive and negative half cycles of the ac output voltage waveform in order to achieve a charge balance on the sub-module capacitors. This constraint can be overcome by introducing secondary power loops that exchange power with the primary power loops by employing the principle of orthogonality of power flow at different frequencies. Converter topologies that use nestled secondary loops are proposed that give more possibilities to couple power between primary loops. Nestled loops facilitate the conversion of dc in multiple stages with transformerless modular multilevel converters and make it possible to add of sources and batteries to individual cells. Analytical simulations based on the power and energy balance of a multi-port modular converter system for interconnecting LVDC, MVDC and MVAC illustrate the power flow control capability offered by nestled secondary loops.