Study Of Multi-level Converter Control System Based On FPGA In HVDC Light

HVDC Light is a new type of power transmission, which can commendably solve the problems such as how to merge the new energy into grid, to interconnect the local grid and to improve the power quality. With the development of power electronic technology, the voltage grade and capacity of the high-power device improve continuously, such as IGBT, GTO and IGCT. Thus, Voltage Source Converters (VSC) which makes use of the self-turn-off components is widely used in HVDC Light.Traditional HVDC Light systems adopted two-level voltage source converters. It has many disadvantages. For instance, there are larger harmonics in the side of AC, the device needs to be in series and the du/dt is too big. Multilevel converter is an effective way to solve these problems above. And it will be the main program in the high-voltage and high-power system. Therefore, studying the structure and controller of the multilevel converter in HVDC Light is of great importance.This paper includs the following aspects:Firstly, this paper introduces the research status at home and abroad and the development trend of HVDC Light. Besides, it interprets the main structure and application field of multilevel converter. In addition, this paper introduces the present situation and development direction of the power electronic control technology. The principle and control strategy of HVDC Light are briefly analyzed, as well as the theory and realization method of SPWM.Then, this paper focuses on the principle and control strategy of multilevel converter in HVDC Light system. The Diode-Clamped based Three-level Voltage Source Converters (VSC) is analyzed in detail. The simulation model based on the three-level converter VSC HVDC light system is established. In this model, the control strategy has fixed DC voltage on the rectifier side and fixed AC voltage on inverter side. It shows that the control strategy is efficient and the three-level structure is superior from the simulation results.Followed, the realization principle of the digital SPWM is analyzed. A comparative analysis of digital realization between natural sampling method and the regular ones is presented. Moreover, the realization method of the digital SPWM controller is researched in multilevel structure. Finally, an overall solution of multilevel VSC controller based on FPGA is proposed. It includes the data acquisition unit, All Digital Phase-Locked Loop (ADPLL), multiterminal digital SPWM module and various kinds of logic control circuit. All Digital Phase-Locked Loop frequency tracking and digital SPWM realization technology based on FPGA are emphasized in the research. The validity and feasibility of the system design are demonstrated by the simulation and experimental results. So the ADPLL takes the features of locking frequency with high precision and following the locking with fast speed, and so on.