Development And Application Of Modular Multilevel Converter Platform For Versatile Use

Modular multilevel converter(MMC)has been widely used in high-power fields,especially in the field of HVDC applications,due to its high efficiency,excellent output waveform with low harmonic distortion and scalability.In this paper,a 25-level MMC prototype based on T-type full-bridge sub-module(TFBSM)has been developed to invertigate the operating feartures of MMC,which owns the cear advantage of versatility and high function expansion ability.Futhermore,an equivalent test scheme for simulating the operating conditions of sub-modules in MMC system is porposed.1.This paper introduces the design method of a 25-level MMC experimental platform which is combined with universal integration features.By using the T-type full-bridge sub-module(TFBSM),the topology of the converter can be reconfigured to investigate operating characteristics of different sub-module topolohgy.Futhermore,aiming at organizing and managing numerous I/O channels of the main controller of MMC,the design idea of industrial controller is adopted and the resources of main controller can be well configured by using the function board interface.2.This paper designs a set of MMC hierarchical control system based on serial communication in order to improve the reliability and efficiency of the MMC control system.First of all,according to the demand of system control tasks,the hierarchy of control system and functions is divided.Secondly,timing coordination mechanism of controllers at all levels are futher designed to ensure that controllers at all levels can coordinate and cooperate normally.Lastly,the number of optical fibers in the sub-module is reduced by adopting the idea of coding and decoding in serial communication and the reliability of data transmission is realized through the error correction mechanism of serial communication.3.An equivalent test scheme for sub-modules is proposed in this paper,which has the clear advantages of system simplicity and reduced facility requirements.The equivalent test circuit of the submodule is firstly proposed by analyzing the detailed output features of sub-modules in real MMC systems.Then,the capacitor voltage fluctuation and power loss of the sub-module in the equivalent test circuit are analyzed in depth to demonstrate the equivalence between the proposed testing circuit and the real MMC system.Filnally,the effectiveness of the porposed test scheme is verify by the simulation and experimental results.