Vector-based accuracy measures in power-hardware-in-the-loop simulations

As real-time technology advances, so does the development of power-hardware-in-the-loop (PHIL) setups to test power electronic devices or generation systems. In academia, the stability and accuracy properties of PHIL simulations are often evaluated using the transfer functions of the open- or closed-loop systems. The results are then used to design the interfacing algorithm that couples the hardware with the software side. But this approach typically requires detailed prior knowledge, which is frequently different from practical applications where little or no information is available about the hardware under test. Lacking a benchmark model, it is therefore rather difficult to predict what accuracy can be achieved in practice with a given interface. To avoid modeling all components of the PHIL system, this paper aims to establish the interpretation of the interfacing algorithm as an isolated two-port network. Considering the inputs and outputs as vectors, it is shown how the transmission properties of PHIL interfaces can be predicted for different frequencies and steady-state inputs. In addition, a new measure for evaluating the accuracy via the cosine similarity is proposed, which automatically combines the amplitude and phase characteristics in the calculation. Finally, simulations illustrate the applicability of the presented methodology.