Series valve groups control strategy and power balance method of MMC Connected to Large-scale Islanded Renewable Energy

As a new type of converter, modular multilevel converter (MMC) has some outstanding advantages compared with line commutated convert (LCC), such as independent control of active and reactive power, provide stable voltage and power to a passive network. It is widely used in large-scale islanded renewable energy grid-connected application scenario. In large-scale renewable energy transmission systems, MMC is usually in the form of a series connection on the DC side. This paper analyses the issues of V/F control of the series valve groups from the perspective of the MMC control system and system power equation and proposes combination control to solve V/F control issue of series valve groups. In order to maintains power balance between series valve groups when the output power of renewable energy fluctuates, proposing a power deviation control based on dc current under the combination control. This approach can adjust varying energy output and eliminates the need for intricate PI parameter debugging. Finally, the proposed control strategy is verified based on PSCAD/EMTDC.