Research On Real-time Simulation And Efficient Modeling Of Modular Multilevel Converter

Modular Multilevel Converter(MMC)is widely used in the field of flexible DC transmission due to its strong expansibility,flexible DC bus,unbalanced operation capability and low harmonic output.The topological performance needs to be tested by simulation before the project is put into operation.Hardware in the loop simulation based on Field Programmable Gate Array(FPGA)has high-speed computing capabilities and parallel processing capabilities.The clock frequency of FPGA is relatively high,and its simulation step size can reach the level of nanoseconds,which quickly becomes the first choice for real-time simulation of power electronic systems.Since the number of MMC levels in actual projects is as high as several hundred,its topology is complicated.If the detailed switch model is built,the simulation speed will be slow and the processor will be greatly burdened.This shows that establishing an equivalent model for a highly modular MMC is the best solution.This article will start with the characteristics of MMC,with model accuracy and calculation speed as the guide,deeply study the efficient modeling method of MMC,and verify it through hardware in loop simulation experiments.First,the article analyzes the topology and operating principle of MMC in detail,studies the carrier phase-shift modulation and nearest level modulation of MMC,and summarizes the applicable scope of the two modulation strategies.After that,the basic control strategy of MMC was studied,including: the sub-module capacitor voltage balance control strategy and the circulating current suppression strategy.Then the article conducts offline simulation verification in MATLAB/Simulink for different modulation methods and control strategies.Secondly,based on the MMC topology characteristics,this paper studies the MMC Thévenin equivalent transient numerical solution model suitable for real-time simulation,and solves the related electrical quantities through model splitting and decoupling.Aiming at the delay link set in the model solution,Hermite + quadratic smooth wave interpolation prediction method is used to correct the error.Under the premise of ensuring the accuracy of the model,the optimization of the model is started from the optimization calculation speed and the corresponding equivalent model code is written.Finally,this article builds an offline simulation model to verify the correctness of the modeling method.Based on the MMC equivalent model,this paper studies multi-rate simulationtechnology with the purpose of optimizing FPGA computing resources,analyzes the data interaction principles of the fast subsystem and the slow subsystem at the simulation interface in detail,and performs offline simulation Verify model accuracy.After that,the resource consumption of multi-rate simulation in FPGA is analyzed and compared with the resource consumption of single-rate simulation.Compared with single-rate simulation,multi-rate simulation greatly optimizes FPGA computing resources.Finally,taking 5-level MMC as an example,the modeling method in this paper is verified by real-time simulation.In this paper,the MMC equivalent model is built.By connecting the corresponding digital controller,the hardware-in-the-loop simulation experiment is performed on the d SPACE real-time simulation platform,and compared with the experimental results obtained by the real MMC hardware platform.After that,it analyzes the FPGA resource consumption and observes the proportion of resource consumption of MMC equivalent models of different levels.The experimental results verify the correctness and effectiveness of the modeling method in this paper.