Interfacing challenges in PHIL simulations for investigations on P-Q controls of grid connected generation units in electric power systems

Abstract

Real-time simulation and in particular power hardware-in-the-loop (PHIL) technology allows for the testing of power electronic inverters acting as grid-connected generation units in a simulation environment that closely mirrors existing and future smart grid networks. The interface between the realtime simulation model and physical devices is a system theoretic challenge as its design implies significant impact on both stability and accuracy of the real-time control system. In general, small time steps of the PHIL simulation model support either way stability and accuracy and these limitations are defined by well-given real-time constraints by the digital real-time simulator (DRTS). Different interface designs address this issue by using a minimum time-step at the power interface (PI) in combination with applying a staged adaptation related to stability for the digital model in accordance with given real-time constraints. The stability of the resulting closed-loop PHIL simulation system is verified by means of the classical Nyquist stability criterion. A test setup is built up with multiple photovoltaic inverters connected to different nodes within a distribution network and investigations of the behaviors of active and reactive power delivery with respect to the P-Q trajectories are discussed. Simulation results with different interface topologies are compared with waveforms obtained by a hardware test setup with the same network configuration. Statements on interactions of the inverter control algorithms and the impact on the grid voltage stability can be made and represent a basis for future analysis of smart grid testing platforms.