Development and validation of a modularized average model for three-phase VSIs

This paper proposes and derives a general-formed average model for three-phase voltage source inverters (VSIs) that is suitable to implement modular simulations. During deriving the switching model, the inverter is divided into several units according to their functions. Every unit is maintained in the switching model, where the units are interfaced only by independent inductor currents and independent capacitor voltages. By applying the moving average technologies to the switching model, the average model is obtained. In addition, an equivalent circuit for the average model is established to reflect all real-circuit non-switching components in it. Benefited from the variable substitutions, the circuit model appears as a self-balanced system, in which each phase can be calculated separately. Compared with existing models, the proposed model removes the requirements to properties of three-phase ac waveforms. Moreover, due to that the load unit in the model is functionally isolated with other units except interfacing inductors via independent currents/voltages, after local modifications to this unit according to the real load, the model can be applied in situations where the load is non-linear and/or have harmonic current sources. Further discussions and simulation examples are provided to verify the models' validity.1