Development of a power-hardware-in-the-loop application — Power grid emulator by using ‘voltage source inverter cumulation’

The increasing use of complex grid-connected technological components in safety-critical applications like public transportation or distributed power systems requires a precise evaluation of the reliability and robustness of these pieces of equipment during their development. Direct on-field tests of high power systems are generally not possible. A conventional method of getting around this problem consists in using software-based simulation to analyse the behaviour of the electric equipment under test (EUT) under normal and transient operation conditions of the grid. However, signal-level simulation is not able to perfectly reproduce every detail of a physical phenomenon. This publication describes a cost-effective realization of a power-hardware-in-the-loop (PHiL) grid emulation system combining two inverters with different electrical characteristics (type of semiconductor, switching frequency, DC link etc.). The proposed grid emulator is a controllable power source not only capable of emulating low frequency (50 [Hz]) transient faults as voltage sags but also high-order harmonic components usually present in the voltage waveforms of the utility grid (e.g. noise). A downscaled 5-kVA laboratory prototype has been implemented and the experimental results shown in the paper demonstrate the emulator's ability to combine high power with high dynamics.