MODIFIED SINGLE-PHASE SINGLE-STAGE GRIDTIED FLYING INDUCTOR INVERTER WITH MPPT AND N SUPPRESSED LEAKAGE CURRENT
Abstract
In this paper, an improved transformer-less single-phase single-stage grid-tied flying inductorinverter is presented. The negative terminal of the PVarray is grounded in the improved topology, whichincreases reliability and suppresses the leakagecurrent. The proposed topology has buck-boostcapability without increasing the number of requiredcomponents and has a high efficiency. An improvedcontrol algorithm for proper operation of the proposedtopology which decreases switching losses has beeninvestigated. Moreover, P&O MPPT algorithm hasbeen adapted to the proposed inverter, which doesn’tutilize PI controllers, for the purpose of the maximumpower point tracking. Furthermore, design procedureof the passive elements of the converter based on thecorresponding operating has been demonstrated.Simulation in Matlab Simulink plus an experimentalprototype is developed to reconfirm the designedresults. Finally, a comparison study has beeninvestigated for better clarification of the advantagesand disadvantages of the proposed inverter.
EXISTING SYSTEM:
Three mainmethods of reducing the leakage current value have beenproposed as follows: separating the PV array from the ACside during the freewheeling mode, clamping the commonmode voltage (CMV) by connection of the neutral pointof the grid to the middle point of the two input DC linkcapacitors and connecting the grid neutral point to thenegative terminal of the PV array, directly. Differentstructures and control schemes have been investigated toapproach the standard value of the leakage current fornon-isolated grid-tied inverters. In the H5 circuit,which is a conventional topology, an additional switch isapplied to the full bridge inverter for the development ofthe constant CMV. However, the power dissipationvalue of the additional switch is almost double of the fullbridge inverter’s switches losses, which is not suitable forthermal design. An extended structure of the H5 inverteris presented in, which is named as oH5 with anadditional switch for clamping of the CMV to the valueequal to the half of the input voltage for leakage currentreduction. In spite of its advantages, oH5 demands a deadband between gating signals to prevent the short circuit ofsplit capacitors which leads to fluctuation of the CMV inthe dead band. Besides, due to simultaneous conductionof three switches, conduction losses remain high. The H6inverter has low leakage current and proper thermaldistribution. However, the H6 converter has a highconduction loss. HB-ZVR topology which has beenpresented in, keeps the CMV constant by adding zerovoltage mode rectifiers to the conventional full bridgeinverter. The total Conduction loss of this inverter islower than the H6 inverter, however high number ofapplied diodes is not desirable. Furthermore, HB-ZVRDis presented in with an additional diode compared toHB-ZVR which causes further reduction of the leakagecurrent. The HERIC inverter is presented in withmore reliability and efficiency compared to HB-ZVR byreplacing six power elements of the AC side in HB-ZVRwith only two switches. A current source H5 inverter hasbeen presented in named as CH5 with reducedleakage current but not eliminated completely.
PROPOSED SYSTEM:
A neutralpoint clamped transformer-less inverter is presented in with buck-boost ability suitable for MPPT of the PVarray with decreased leakage current. However,simultaneous conduction of four switches increases theconduction loss. The presented converter in uses thecharge pump circuit idea to present a new topology.Mentioned converter is doubly grounded and has thecapability of reactive power flow. However, it does nothave the buck-boost ability and its input current is notsymmetrical. Presented topology in is an integratedtwo-stage converter, which studies new aspect of grid tiedinverters as low frequency ripple. However the converterhas an extra energy storing level which adds a highvoltage capacitor to the topology, needs a large outputfilter, rather high number of passive elements and highswitching frequency. The proposed converter in hasbeen depicted in The mentioned inverter eliminatesthe leakage current, however needs a chopper to track themaximum power of the PV panel below the voltage of thegrid, which lowers the efficiency and increases thenumber of active and passive elements. Although thisconverter has low number of active elements, it utilizeshigh number of passive components. Furthermore, highvoltage stress of the switches and low efficiency are otherdisadvantages of the presented inverter. In this paper, an improved topology is proposed fornon-isolated grid-tied inverter with negative terminal ofthe PV array connected to the neutral point of the grid,which increases the reliability and eliminates the leakagecurrent. In addition, the presented structure has buckboostability, which eliminates the need to a DC-DCchopper to work in the voltages of PV below the voltagesof the grid. The proposed inverter, utilizes IGBTs withoutbody diodes, operates as a current source inverter anddemands acceptable number of active and passivecomponents, which makes the proposed inverter moreefficient and attractive. The proposed system considers asuitable switching strategy which makes the converterwork in discontinuous conduction mode (DCM) and aperturbation and observation (P&O) method withoututilizing PI controllers for acquiring MPPT.
CONCLUSION
An improved flying inductor transformer-less single- phase single-stage grid-tied inverter has been proposed. A modifiedcontrol algorithm compatible with the proposed converter hasbeen presented. An MPPT algorithm suitable for the proposedconverter has been illustrated and the design procedure for allof the converter’s passive devices has been investigated andvalidated by the simulation and experimental results. Acomparison between the proposed converter and similarstructures has shown that the converter has acceptable numberof switches and low number of passive elements, almost zeroleakage current, buck-boost capability, high efficiency andexcellent dynamics in case of the input voltage variation.Therefore, the proposed circuit can be utilized andcommercialized as the interface device between the PV arrayand the distribution system.
REFERENCES
[1] J. F. Ardashir, M. Sabahi, S. H. Hosseini, F. Blaabjerg, E. Babaei and G.B. Gharehpetian, “Transformerless Inverter with Charge Pump CircuitConcept for PV Application,” IEEE Emerg. Select. Topics PowerElectron.., doi. 10.1109/JESTPE.2016.2615062, Oct. 2016.
[2] Sh. R. Aghdam, E. Babaei, S. Gh. Zadeh, “Improvement theperformance of switched-inductor Z-source inverter,” in Proc. IECON,2013, Vienna, Austria, pp. 876-881.
[3] Sh. R. Aghdam, E. Babaei, , “Maximum constant boost control methoodfor switched-inductor Z-source inverter by using battery,” in Proc.IECON, 2013, Vienna, Austria, pp. 984-989.
[4] W. Li, Y. Gu, H. Luo, W. Cui, X. He, C. Xia, “Topology Review andDerivation Methodology of Single Phase Transformerless PhotovoltaicInverters for Leakage Current Suppression,” IEEE Trans. Ind. Elect.,vol. 62, no. 7, pp. 4537-4551, Feb. 2015.
[5] L. Zhang, K. Sun, Y. Xing, M. Xing, “H6 Transformerless Full -BridgePV Grid-Tied Inverters,” IEEE Trans. Power Electron., vol. 29, no. 3,Mar. 2014.
[6] Automatic Disconnection Device between a Generator and the PublicLow-Voltage Grid, DIN Electrotechnical Standard DIN VDE 0126-1-1,2005.
[7] S. Saridakis, E. Koutroulis, F. Blaabjerg, “Optimization of SiC-BasedH5 and Conergy-NPC Transformerless PV Inverters,” IEEE Emerg.Select. Topics Power Electron., vol. 3, no. 2, pp. 555-567, June. 2015.
[8] X. Huafeng, X. Shaojun, C. Yang, and H. Ruhai, “An optimizedtransformerless photovoltaic grid-connected inverter,” IEEE Trans. Ind.Electron., vol. 58, no. 5, pp. 1887–1895, May. 2011. [9] R. Gonzalez, J. Lopez, P. Sanchis, and L. Marroyo, “Transformerlessinverter for single-phase photovoltaic systems,” IEEE Trans. PowerElectron., vol. 22, no. 2, pp. 693–697, Mar. 2007. [10] T. Kerekes, R. Teodorescu, P. Rodriguez, G. Vazquez, and E. Aldabas,“A new high-efficiency single-phase transformerless PV invertertopology,” IEEE Trans. Ind. Electron., vol. 58, no. 1, pp. 184-191, Jan.2011.