Design of a droop control scheme for programmable sources in a microgrid testbed

The Clean Energy Research Lab (CERL) in Nanyang Technological University, Singapore has a three-phase, 400V, 50Hz microgrid (MG) testbed to perform power system studies. The MG testbed comprises a 13.5kVA synchronous generator, 18kVA programmable source, 6kvar capacitor bank, 5kW solar photovoltaic (PV) system, 13.5kW wind simulator, 5kW battery energy storage system (BESS), 5kW fuel cell, 13.5kW programmable load as well as a 10kW simulated industrial load. The MG can operate either in islanded mode or in grid-connected mode. In the islanded mode, distributed generators such as the synchronous generator and the programmable source determine the frequency and voltage of the MG. A major difference between the synchronous generator and the programmable source is that the synchronous generator has inertia while the programmable source is inertialess. This means that the former has an inherent power-frequency droop associated with it whereby the synchronous generator frequency changes according to its power generated. Conversely, the programmable source does not have a power-frequency droop characteristic since it has no rotating parts. This paper demonstrates how the programmable source can be programmed to contain the power-frequency droop characteristics inherent to the synchronous generator. The experimental results presented in this paper are obtained from the CERL MG testbed. The results demonstrate the utility and performance of the developed droop scheme.Published versio