Power Electronics Based Active Load for Unintentional Islanding Testbenches

The paper discusses the emulation of a parallel resonant RLC load by means of an electronic power converter. The main application of the analyzed approach is in the testing of grid connected resources (e.g., renewable sources), where it allows us to ease testing procedure, minimize wasted power, and reduce test-bench size. To this end, an effective control system is proposed, analyzed, and designed considering a current-controlled inverter as the basis of emulator development. The limitations of the control system are explored, highlighting the requirements of the controller in order to achieve desired emulation accuracies and avoid instability. The reported studies are verified by means of both simulations and experimental tests performed on a laboratory prototype. In particular, the proposed modeling is able to predict the presence of resonant peaks close to the current control bandwidth, giving in this way useful guidelines to minimize such an undesired effect, which is detrimental for stability when the load is connected to other systems. Finally, the experimental results from an unintentional islanding test are reported to show the equivalence of the developed active RLC load with respect to a passive one.