Efficient and accurate dynamic average-value modeling of current source modular multilevel converter

Current source modular multilevel converters (CSMMCs) in high-power applications can consist of large number of submodules. Simulations of such systems using full-size traditional detailed model in electromagnetic transient-type (EMT-type) simulation tools involve computational complexity and require very large computing time. This paper presents a computationally efficient and accurate average-value model (AVM) of CSMMC. In the proposed approach, the individual arm of CSMMC is represented by a controlled current source and the dc-side of the converter is represented by the controlled voltage sources. The submodule inductances are represented by a single equivalent inductance on the dc-side. The harmonic contents of the switching events are included using the modulation function in the arm level model while the variations in the submodule inductor currents are ignored. To validate the proposed model, detailed simulation studies of CSMMC based STATCOM is carried out with the proposed AVM and the traditional model in PSCAD/EMTDC. The results of various studies, obtained from both the models, are compared. The close matching of the results proves the validity of the proposed AVM. Moreover, the comparison of simulation time of both the models clearly demonstrates very high computational efficiency of the proposed AVM.