Modeling of a three level converter used in a synchronous rectifier application

In this paper we present a model that describes the dynamics of a three level neutral point clamped converter used in a synchronous rectifier application. The highly nonlinear model, originally in abc-coordinates, is also expressed in its αβγ-coordinates. Special attention is given to the γ-component of the control input, which represents a degree of freedom crucial for the balancing of the capacitors voltages. We show that the arithmetic difference and sum of the capacitors voltages are two natural states of the system and, indeed, they reduce considerably the model expressions. We also show that the controller γ-component has a minimum influence on the sum of the capacitors voltages, but it has a strong influence on the difference, hence its importance in the capacitor voltage balance. Simulations are presented to validate the proposed model. We expect that this model will stimulate new control proposals in the future.