Study Of HVDC Light Based On Modular Multilevel Converter

There are great advantages in solving the non-synchronous AC system interconnection, supplying power to the remote passive loads, satisfying the demanding of protecting environment by applying HVDC Light in power transmission. Traditional HVDC Light systems adopt two-level or three-level voltage source converters. These converters need bulky filters, many power electronics devices in direct series, which need large space and reduce the efficiency of the converters.In this paper, a new modular multilevel converter is used as a converter of HVDC Light, which avoids those disadvantages above effectively. Firstly, the principle of modular multilevel converter is analyzed. Secondly, the modulation arithmetic and control strategy of HVDC Light which adopts modular multilevel converter is introduced. Thirdly, the realization scheme of the control system is proposed, too. Finally, the simulation results have been performed to validate modulation algorithm and control strategies. The main aspects of this dissertation are summarized as follows:1. The topology of modular multilevel converter, the topology and principle of sub-modular are analyzed in detail, and the modulation algorithm is explained.2. The principle of voltage source converter is introduced, and the strategies of indirect current control and direct current control are analyzed.3. Simulation is performed to validate the control strategies of HVDC Light which consist of modular multilevel converter.4. The average and balance control of sub-modular capacitor voltages is discussed, and a simple control method is given.5. The realization scheme of HVDC Light control system based on modular multilevel converter is discussed, specifically the digital implementation of sub-modular is focused on.