Establishing a PLC-based Power Hardware-in-the-Loop Setup for Power Grid Applications

Power-Hardware-in-the-Loop (PHIL) is a powerful tool for studying the behaviour between real Hardware under Test (HuT) and simulated grids in power grid applications. In addition to the utilised Interface Algorithm (IA) and the system impedances, the dead times of the system are crucial for stable operation. Large simulation step sizes can therefore lead to unstable operation and reduce the accuracy of the simulation. The choice of the appropriate Real Time Digital Simulator (RTDS) for the calculation of the simulation and other system components must therefore be selected according to the application. The paper presents a PHIL setup for three-phase power grid applications which is realised with a Beckhoff Programmable Logic Controller (PLC) at a closed loop time of 150 μs. The stability limits of the setup are analysed theoretically and practically. The paper presents an island grid frequency control model simulated in real time. In addition to the grid impedance and measurement of active power, this includes dynamic frequency modeling based on a swing equation coupled with primary and secondary power control. This allows the behaviour of real hardware on the grid to be investigated on a variable scale under safe laboratory conditions. New control strategies can be validated and their influence on the grid can be analysed flexibly. The complete PLC setup enables the implementation of independent digital twins and the coupling of the systems via linear power amplifiers.