| The increasing penetration rate of new energy sources such as photovoltaics and wind power has had a huge impact on the stable operation of traditional power sys-tems.The power conversion system is considered to be an important way to greatly improve the ability of new energy dissipation and ensure the stable operation of large power grids because it can stabilize power fluctuations.At the same time,many large-scale industrial applications require energy storage systems to have independent power supply functions.Therefore,as an important part of energy storage,the power industry has higher requirements for the capacity of power conversion system.It is a feasible expansion mode of the power conversion system to realize capacity expan-sion and redundant power supply through multiple power conversion system in paral-lel.Therefore,it is of great practical significance to study the parallel control of power conversion system in off-grid mode.This paper takes the two-stage energy storage power converter as the research object,and mainly studies the parallel control strategy without interconnection in off-grid mode.The paper firstly describes the different topological classifications of power conversion system,summarizes the off-grid control strategies of power conversion system,including single control strategy and multiple parallel control strategies,compares the advantages and disadvantages of control strategies such as centralized control,master-slave control,decentralized logic,parallel control strategy without in-terconnection in off-grid mode,and selects the parallel control strategy without inter-connection in off-grid mode..The parallel connection strategy is selected to realize parallel connection of multiple machines,and then the mathematical model of single power conversion system in off-grid mode is established according to the main circuit of the device.The equivalent physical model of two energy storage power converters is connected in parallel.Through the analysis of the model,the circulation influencing factors of the parallel system and its power characteristics of parallel systems are studied.In order to realize the parallel connection of without interconnection between devices,the principle of parallel control for sagging control and its implicit commu-nication mechanism are studied in this paper.Aiming at the problems existing in the traditional droop control,the virtual synchronous machine control algorithm is adopt-ed,so that the power conversion system has the inertia and damping characteristics in addition to the droop adjustment characteristics of the traditional synchronous ma-chine,which ensures the stability of the parallel system in the event of load disturb-ance.For the problems of phase un-synchronization,inductive load characteristics in low voltage system,and power oscillation of the low-voltage system,the pre-synchronization and virtual impedance are added,and a power-based adaptive in-ertia parameter adjustment method is proposed to improve the parallel stability and rapidity of the system.In order to verify the feasibility of the parallel strategy in this paper,the Matlab/Simulink simulation and experiment of parallel operation of a single device and the parallel of multiple devices were carried out,and the results further verified the correctness of the control strategy of this project. |
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