Averaged model of modular multilevel converter in rotating DQ frame

This paper proposes an average model of Modular Multilevel Converter (MMC) in rotating DQ frame. The proposed MMC model has a modular structure and can be linked with other power elements such as AC and DC subsystems. Modelling in DQ frame has numerous advantages over traditional ABC frame in terms of simulation speed and convenience for linearization. The main challenge of developing DQ model of MMC is to deal with the multiplication terms of dynamic equations of MMC. To overcome this complexity, a generic form is first introduced for each product variable mathematical equations of the average MMC model in ABC frame and then the multiplication results are transferred to DQ frame after ignoring the higher harmonics. The detailed model and the proposed DQ average model are implemented in PSCAD/EMTDC. The simulation results of the two models show very good matching which in turn confirms the accuracy of the proposed model. Also, the DQ average model is considerably faster than the detailed and even ABC average models.