Black-start Capabilities of the Arholma Microgrid

Arholma, which is located in the Stockholm Archipelago in Sweden. The black-start function was tested and the results summarize eight different attempts of black-starting the microgrid, as well as its ability to stabilize in island operation after a successful black-start. In addition to the tests performed on the microgrid, Power Hardware-in-the-Loop (PHIL) testing was performed on a heat pump to observe its reaction to a black-start that utilizes a soft start function. Out of the eight attempts to black-start the Arholma system, only two were successful and one of those only partially successful. In all the unsuccessful attempts, at around the same voltage level, a current spike occurred, which caused the voltage to collapse. One hypothesis, that was investigated, is that household heat pumps, which represent a significant load on the island, could have connected during the black-start and contributed to this voltage collapse. To test this, PHIL testing was conducted on heat pumps at the Vattenfall R&D Laboratories in

Älvkarleby. The test results support the hypothesis, since similar current spikes were observed when the tested heat pump reached a voltage level similar as those current spikes were observed at during the tests on the island.