Blackstart Capability of Modular Multilevel Converters From Partially-Rated Integrated Energy Storage

This paper discusses blackstart provision enabled by Modular Multilevel Converters (MMC) with integrated partially-rated Energy Storage (ES) systems. It is demonstrated that ES units integrated in an MMC for ancillary service provision can be utilised to energise the auxiliary power supply electronics of the submodules (SMs), fully charge the converter capacitors, and establish voltage at the ac and dc terminals. This feature can prove especially useful during the converter start-up phase in passive grids or following a post-fault disconnection event. For an MMC with integrated ES, the added functionality of charging the converter capacitors and starting-up the adjacent networks requires no additional infrastructure – only an updated control scheme. The charging algorithm goes through successive steps: ES-SM charging,
activation of the Auxiliary Power Supplies in the SMs
, active charging of all SMs,
and finally,
connection to the grid. The effectiveness of the method is confirmed by simulation results where a fully disconnected MMC charges nominally within 2 seconds, and connects to
a passive
ac network.
By using a grid forming control scheme, the converter ramps up the voltage at the ac terminals and supplies 5% of active and reactive power with only 4% of ES-SMs per stack.