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Research On Unbalanced Load Of Parallel Inverter Based On Droop Control

Posted on:2018-07-16Degree:MasterType:Thesis
Country:ChinaCandidate:M A LiuFull Text:PDF
GTID:2322330536987512Subject:Power electronics and electric drive
Abstract/Summary:PDF Full Text Request
With the rapid development of the distributed generation technology,it has put forward higher requirements to the system capacity,reliability and hot-swap technique.One of the effective solutions is that inverters operate in parallel.Considering multiple inverters operate in parallel,the output power of each inverter needs to be allocated coordinately.The droop control is adopted to realize the independent control of each module without interconnection lines,which enhances the reliability of the system power supply.Recently,the key research of the conventional droop control is to realize the power sharing and solve the power coupling.But the power supply quality will be affected seriously and the output power of the inverters will be changed if the system operates with unbalanced loads,which will influence the effects of the droop control.Thus,the droop control and the power sharing strategies on the inverters in parallel with unbalanced loads are studied in this thesis.In order to equip inverters with ability to supply power for unbalanced loads,the three-phase four-wire inverter with split capacitor type structure was adopted as the main circuit topology in this thesis.In the first of all,the thesis established the relative mathematical models.Considering the single inverter operating with unbalanced loads,the cause of the unbalanced output was analyzed in detail by symmetrical component method,and the proportional integral(PI)controller with quasi-resonance control was used to suppress the negative sequence component resulting from the unbalanced loads.Besides,the suppression of the zero sequence component and the voltages sharing control of the split capacitor were realized by introducing a zero-axis loop integrated with 3D-SVPWM strategy,which avoided the additional circuit to balance the capacitor neutral point.Then,the influence of the unbalanced loads on the output power was analyzed in this thesis,and a droop control strategy based on dividing-sequence control was proposed.The conventional droop control loop was adopted in the positive sequence component to supply the references of the voltage and the frequency,which realized the positive sequence power sharing.The negative and zero sequence currents are sharing reasonably according to virtual impedance,which was formed by second-order generalized integral(SOGI)algorithm and mitigated the effect of line impedance mismatch.Simulations in Matlab were given to verify the validity of the droop control strategy based on dividing-sequence control.Finally,an experimental prototype with two three-phase grid-connected inverters in parallel was designed and built according to the system requirements,the hardware and software design of the prototype were introduced.The experimental results validated the effectiveness of the proposed droop control strategy.
Keywords/Search Tags:Unbalanced loads, Split capacitor voltages sharing, Droop control, Dividing-sequence control, SOGI virtual impedance
PDF Full Text Request
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