| With the continuous development of strategy of sustainable development, the new energy technology based on solar, wind and other renewable energy has become a hot research. The flexible HVDC technology based on voltage modular multilevel converter has become an inevitable choice for grid connecting distributed energy. Forever, the control system is the brain and nervous throughout the flexible HVDC system, so this paper made the control system of the Modular Multilevel Converter (MMC) as the core for study, and researched its control strategy combined with the experimental study.Combined with the existing instance of MMC flexible HVDC, this paper analyzed the research status of MMC control system, summed up the typical control system structure with the existing MMC control technology. For the typical MMC topology with half-bridge sub-module, this paper analyzed its working principle and four-quadrant operation condition, established a simplified equivalent model and the small-signal model to facilitate the subsequent design for control strategy.Based on the existing multi-hierarchy capacitor voltage control method, this paper proposed the MMC integrated control strategy employing the arm current direct control, and applied it to the back-to-back MMC system consisting of rectifier and inverter side. A Current feed forward scheme applied to the rectifier side was proposed, which increased the dynamic response speed of active current, improve the efficiency and stability of the system.In order to carry out the experiment of MMC, this paper developed a set of four modules of three-phase back-to-back MMC experimental platform. The control system consists of the main controller, auxiliary controller and the sub module controller. The control system using TI’s latest dual core chip composed of ARM and DSP, achieved MMC control algorithm and the convenient and rapid communication with host computer, displayed the module voltage and arm current information of MMC on the PC timely.In the debugging process of experimental platform, this paper carried on the design, debugging and verification with the control strategy firstly using the semi physical simulation system, and then debugged the main circuit, finally carried on the verification and experimental study with the control strategies of multilevel converter module. The experiment results verified the proposed control strategy. The experimental results demonstrated the practicability of the experimental platform and the validity of MMC integrated control strategy. |
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