Improved dynamic phasor-based modeling and simulation of modular multilevel converter

An improved dynamic phasor modeling method for modular multilevel converter (MMC) in high voltage direct current (HVDC) transmission system is presented, verified and applied. The model developed in this paper consists of AC interface module, DC interface module, MMC control system, circulating current suppression module and the 8-order MMC improved dynamic phasor model. When the external circuit is updated, it just needs modifying the electrical parameters of interface modules and the control strategy of the MMC, thus it is convenient for the external circuit improvement to connect to the MMC model. Since the improved method avoids the integral and convolution operation, the computational cost of the MMC dynamic phasor modeling is greatly reduced. Finally, under the steady-state and three-phase-to-ground short-circuit fault conditions, the MMC dynamic phasor model is implemented in MATLAB using the ode45 solution and the MMC electromagnetic transient (EMT) model is implemented in PSCAD/EMTDC. The comparisons of the simulation results verify the validity of the proposed modeling method. As the salient feature, the dynamic phasor modeling approach can greatly accelerate simulation speed without sacrifice the simulation accuracy, therefore the dynamic phasor modeling is expected to be more widely used in the simulation of large-scale MMC-based AC/DC power grid.