Electrical source emulation using modular multilevel converter

Source emulation is a power level hardware-in-the-loop simulation of different electrical sources. In this method, the mathematical model for an electrical source is solved in real time, and power electronic converter is used to emulate the source characteristics. Source emulation helps in performing the realistic evaluation of different active front-end power electronic converters and grid connected power electronic converters for renewable energy generation systems. Thus, it ensures increased reliability and quality and more efficient development of systems, with reduced testing cost and risk. This paper discusses a source emulator using one of the multilevel converters called modular multilevel converter (MMC). MMC has a modular arm structure with cascade connection of multiple bidirectional chopper cells with floating capacitors. The control and modulation of MMC should be selected such that the sub-module capacitor voltages are equal and independent of load conditions. In the source emulator, an over-current limiting control by virtual resistance principle is implemented to avoid the test equipment damage. The simulation results for the source emulator acting as a grid emulator producing different conditions such as voltage dips, unbalanced voltages, over voltages, frequency changes and harmonic disturbances are presented. The emulation of a synchronous generator is also discussed with simulation results.