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Control Strategies Of Microgrid Inverters And Microgrid System

Posted on:2016-06-21Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y ShiFull Text:PDF
GTID:1222330473461645Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
Microgrid technology has become one of research hotspots in recent years along with the rapid development of renewable energy distributed generation systems, and the microgrid inverter control technology and the microgrid system coordinate control are two key technologies in Microgrid research area. In this paper, the key technologies of microgrid were discussed from both the perspectives of microgrid inverter and microgrid system. The main contents of this paper are as follows:(1) A detailed overview of research status on microgrids was presented. The key technologies of microgrid were summarized, and the control strategies of microgrid inverter were classified and comparatively analyzed. The secondary frequency control and pre-synchronization control based on hierarchical control structure were introduced and summarized.(2) In this paper, microgrid inverters were controlled in droop control mode in both islanded and grid-connected mode, to avoid the switch of inverter control algorithm during the microgrid mode transfer period. Small signal model of single inverter and parallel inverters were established, and the influences of the controller and network parameters on microgrid system stability were analyzed through the small signal model.(3) In the third chapter, in order to avoid the effects that other inverters or loads made on line impedance measurement, a line impedance detection method based on high precision system clock synchronization was proposed. Then a virtual impedance parameters selection method which considering power capacity, decoupling factor and the stability and dynamic performance of the microgrid was proposed. At last taking the Ethernet communication between the microgrid equipment into account, an improved reactive power sharing control method based on Ethernet communication was proposed.(4) The influence of unbalanced load on microgrid was summarized, and the necessary condition for unbalanced load sharing between the microgrid inverters was discussed, then a negative sequence current sharing control method was proposed. Furthermore, the reasons of the unbalanced load leading to micro-grid voltage unbalance were analyzed, and an unbalanced voltage compensation method was proposed.(5) The microgrid secondary frequency modulation principle has been analyzed and a secondary frequency modulation control method based on hierarchical control structure was proposed to achieve the recovery of voltage and frequency. At last, the microgrid pre-synchronization control method based on the secondary frequency recovery control was proposed.(6) A microgrid experimental platform contains renewable energy, storage system, MGCC, smart switch and communication system was established. The design concept and prototype of key equipment were introduced in details. At last, based on this microgrid experimental platform, the effectiveness of the proposed algorithms was confirmed by simulation and experiment.
Keywords/Search Tags:microgrid small-signal modeling, droop control, reactive power sharing, virtual impedance, unbalanced load, voltage compensation, coordinated control
PDF Full Text Request
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