DC Equivalent of an AC Circuit Through an Inverter in a Symmetric Monopolar Configuration

Nowadays, the number of power electronic converters is growing on the power grid. Three-phase inverters/rectifiers are interfacing the High-Voltage DC links with the three-phase AC part of the system. They are also converting the DC voltage, produced by Photovoltaic panels into three-phase voltages, to connect the PV to the main grid, e.g. Moreover, the three-phase currents produced by offshore windfarms are converted in direct current to comply with the direct current lines. This work aims to model a DC-equivalent circuit of a three-phase circuit connected to an inverter. This DC-equivalent will help to understand the consequences of three-phase elements on the DC side of an inverter. Therefore, an ‘unified’ DC network is modeled. A systematic representation of the system as seen from the DC side is shown.To do so, this work is based on the DC side frequency study of an inverter to understand the impact of a three-phase Thévenin equivalent as seen from the DC side. This DC equivalent impedance depends on the PWM parameters (e.g., phase, modulating index). Therefore, this DC equivalent circuit can be used by the upper control layers (i.e. current controls, power controls) for a direct control method, e.g. The behaviour of its equivalent model in DC will be presented. The mathematical development is presented and the simulation results are illustrating the model in MATLAB/Simulink. Based on these results, the performance of this DC equivalent electrical circuit model will be shown along with some improvements possible on this model.