Ideal Transformer Method Optimization for Power Hardware-in-the-Loop Simulations of Grid Connected Inverters

Abstract:
Power hardware-in-the-loop (PHIL) testing is increasingly being adopted as a testing tool for grid integration of distributed energy resources with power electronic interfaces. Conventionally, these PHIL setups use the ideal-transformer-method (ITM) as an interface algorithm between the device-under-test (DUT) and the real-time simulation model. The closed-loop PHIL interface with the DUT is usually stabilized using simple low-pass filters in the feedback path. Such filters stabilize the closed-loop PHIL interface, but with compromised accuracy. In order to improve the accuracy of the PHIL interface, this paper presents a method to design an optimal feedback compensator depending on the type of physical filter topology (L, LCL) of a photovoltaic inverter which is used as a DUT. In addition, a method to further improve the dynamic accuracy, with the help of damping resistors as part of the filter topology, is proposed in this paper. Accuracy analysis is provided based on error functions in the frequency domain. Simulation results are presented in this paper to prove the superior performance of the developed optimal compensator used within the PHIL interface. Experimental results are also presented to validate some of the proposed concepts with further analysis of stability with respect to source-to-load impedance ratios.