Design And Experiment Of Control Strategy And Monitoring System Based On MMC-HVDC Low Voltage Physical Experiment Platform

The energy issue has become increasingly prominent in recent years. The renewable energy integration has come to be a widely argued issue in the smart power grid research, where voltage source converter based high voltage direct current (VSC-HVDC) is one of the crucial methods. As compared with traditional multilevel topologies in the VSC-HVDC application, a novel modular multilevel converter(MMC) receives much concern and becomes an important research focus, because of the easiness of modular design, low harmonics distortion and du/dt capability to cascade low-voltage level power switches in the middle/high application system.Firstly, this paper studied the working principle of MMC, designed the device parameters and main performance indices of the MMC-HVDC low-voltage physical experiment platform. This paper also put forward an open-looped synchronization method based on dq conversion in order to improve the problems in existing synchronization method. This method used the given frequency as the synchronous rotation frequency of dq conversion and eliminate the negative sequence component by the decoupling network. Both the simulation and the experiment results prove the effectiveness of the PLL method.Secondly, for monitoring the MMC-HVDC low-voltage physical experiment platform more efficiently, a client-server mode as a particular design plan for MMC-HVDC monitoring system is put forward, which was implemented by Labvew programming the man-machine interface and dual-core microprocessor F28M35processing the MMC data. The communication between the client and server is realized by Lwip network protocol. This proposed monitoring system mainly design for three basic functions:data monitoring and measuring, fault detection, power-on startup.At last, the relationship between the MMC-HVDC half-physical simulation platform and the low-voltage physical experiment platform is interpreting in this paper. And the hardware design plan of the platform involving the experiment testing and signal processing circuit, control system, main circuit are shown too. The parallel control scheme is proposed in MMC-HVDC control system by comparing the advantages and disadvantages with the serial control. The hardware-in-loop simulation platform can testify the feasibility of the scheme avoiding damages to the power switches due to the error algorithm. Thus, it is a reasonable and priority choice that the experiment is firstly done by hardware-in-loop simulation platform and lastly finished by the platform of low-voltage physical experiment platform, which can fully testify the feasibility and effectiveness of the MMC-HVDC control and monitoring system.