Concept of a three phase AC power source with virtual output impedance for tests of grid connected components

This paper presents the concept of a three phase AC power source with virtual output impedance, which is mainly used for the development, validation and testing of grid connected components. The main advantage of the proposed system is the adjustability of the output voltage, frequency, harmonics and also the grid impedance. Based on the requirements and the related standards a LC-output filter is designed, which is improved with investigations of the the output impedance frequency response. For the realization of this system switching frequencies up to 200 kHz are required and therefore silicon carbide (SiC) semiconductors are preferred. Various offline simulations are presented to verify the proposed topology and its control scheme for the virtual output impedance. A first prototype of the controller was developed and validated using Controller Hardware in the Loop (C-HIL) simulation. In this paper a C-HIL simulation for the validation of the digital control unit is presented. The results show that the controller fulfils the required sample time of 5 μs and is able to emulate the grid impedance.