Bidirectional three-level DC-DC converters: Sum-difference modeling and control

This paper proposes a modeling and control approach for the three-level DC-DC converter. The converter is described in a sum and difference (ΣΔ) framework. It is shown that the formulation is useful to model the inverter and derive design-specific equations. The Σ component is responsible for the inductor current, i.e. the power flow, and the Δ component is used to balance (or unbalance) the DC-link capacitor voltages. It is shown that there are cross-coupling terms between the Σ and Δ axes that can be compensated. The proposed model is validated using high fidelity simulations with a proportional-integral controller. Two- and three-level converter operation is shown and it is proven that the passive components can be reduced by 50% to 75% using three-level operation without affecting the control performance. The control is verified by introducing load current and DC voltage steps.