Enhanced Average-Value Modeling of Voltage-Source Inverters in Variable Frequency Drives for Efficient Simulation of Marine Propulsion Systems

Variable-frequency drive (VFD) systems utilize voltage-source inverters (VSIs) and are employed extensively in many applications, including marine propulsion. For efficient simulations and studies of such systems, average-value models (AVMs) of VSIs are indispensable. Recently, a so-called directly-interfaced AVM (DI-AVM) has been developed for line-commutated and voltage-source converters. In this paper, the DIAVM is developed for VSIs in the converter reference frame, which has advantages for machine-converter systems. The DI-AVM is implemented in electromagnetic transient (EMT) simulation programs as a resistance/conductance matrix instead of controlled voltage/current sources that are used conventionally. The advantages of the proposed DI-AVM are demonstrated on a ship propulsion system implemented in PSCAD/EMTDC. The proposed DI-AVM offers significant computational advantages compared to the conventional AVMs of VSIs by achieving higher numerical accuracy and allowing larger time step sizes.