The Research Of Control Strategy And The Development Of Controller Prototype For Modular Multilevel Converter

HVDC (high voltage direct current transmission) based on MMC (modularized multilevel converter) has become one of the most attractive VSC-HVDC technology because of its modularity and scalability. MMC-HVDC can be widely used in conecting renwable source to power grid, power supply for the passive grid, power supply for the city grid and asynchronous AC grid interconnection.Currently, the research on MMC system has been very extensive, most studies have focused on mathematical modeling, modulation method and control strategy. Due to a large number of power semiconductors in modularized multilevel converter (MMC) and its complicated coordination control, the physical verification for MMC is facing many difficulties. To solve this problem, a Hardware-in-the-Loop simulation platform for high level MMC is established between the RTDS simulator and the physical MMC controller. On this platform, the converter valves is simulated with the small time step of 2.5 microsecond, which is quite qualified for high precision simulation of hundred level MMC system. By adopting the multicore technology and distributing the parallel vale control between different cores, the designed controller meets the requirements of real-time control. Several steady and transient experiments are carried out to verify the functions of the designed platform and the rationality of the designed controller. The results show that different modulation and control strategies can be implemented on the simulation platform and each control objective has good tracking accuracy and quickly dynamic response. The proposed platform can be used for many fields, such as the design of main circuit for MMC-HVDC, the study and test of control strategies, the optimization of control parameters, the research of interaction between MMC-HVDC and large power grid and so on.