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Research On Parallel Control Technology Of Microgrid Inverter Based On Virtual Synchronous Generator Algorithms

Posted on:2021-02-15Degree:MasterType:Thesis
Country:ChinaCandidate:C ChenFull Text:PDF
GTID:2392330629987208Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
With the rapid development of power electronics technology and renewable energy generation,micro-grid technology based on distributed structure has changed the terminal power consumption mode in traditional power system,and promoted the friendly interaction and coordination among source-grid-load system.Due to the increasing quantity of micro-grid inverters and its own capacity limit,along with the developing needs of new energy generation,higher requirements have been placed on the intelligent construction of parallel inverter technology without interconnected control.As a distributed non-interconnected micro-grid control algorithm using inverters to simulate the external characteristics of synchronous generators(SG),Virtual Synchronous Generator(VSG)technology provides sufficient inertia and damping support for micro-grid,and encourages each parallel inverter to participate in the transient and dynamic grid regulation spontaneously.However,the stability of parallel inverter unit is easily affected by pre-synchronization and sudden load changes during off-grid,and voltage following during grid connection.Based on this control requirement,this paper mainly focuses on several problem of parallel VSG algorithm,such as the secondary frequency modulation,rotor inertia adaptive control under the island,and the parallel unit mode switching.The main contents are as follows:Firstly,according to the basic principle of traditional VSG algorithm,a small signal model of parallel VSG system was established.Based on the secondary frequency adjusting process of the power system,a new secondary frequency modulation control scheme for parallel VSG operation was proposed.The proposed scheme solves the problem of voltage drop and current oscillation when micro-grid inverters connected in parallel.Secondly,the parallel system characteristic root was solved according to the small signal model,and rotor inertia adaptive control strategy was derived from the root locus analysis,and the related parameters were optimized and set.Combined with the basic principle of equivalent synchronous generators,the inertia matching principle of parallel VSG system was proposed.The proposed method can not only suppress the power oscillation in the transient connection of the VSGs to the AC bus,but also improve the frequency support.In turn,it ensures that the load power is proportionally distributed among the VSGs.Then,the flexible mode switching technology for parallel VSG system was proposed according to the basic principle and conditions of quasi-synchronous control,the phase-locked loop based on cascading integral and the optimization of the double closed-loop control parameters.The proposed scheme can effectively suppress the power frequency oscillation of the parallel system while ensuring the power is evenly divided.Finally,an experimental platform for a parallel micro-grid inverter system based on VSG algorithm was built,and the experimental detection and evaluation of the VSG algorithm were performed to verify its feasibility.
Keywords/Search Tags:Virtual synchronous generator, Micro-grid inverter, Secondary frequency modulation, Rotor inertia adaptive control, Mode switching
PDF Full Text Request
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