HIGH-PERFORMANCE QUASI-Z-SOURCE SERIES RESONANT DC-DC CONVERTER FOR PHOTOVOLTAIC MODULE LEVEL POWER ELECTRONICS APPLICATIONS

 

Abstract

 This paper presents the high-performance quasi-Z-source series resonant DC-DC converter as a candidate topologyfor the PV module level power electronics applications. Theconverter features a wide input voltage and load regulation rangethanks to the multi-mode operation, i.e. when the shoot-throughpulse-width modulation and phase-shift modulation arecombined in a single switching stage to realize the boost and buckoperating modes, respectively. Our experiments confirmed thatthe proposed converter is capable of ensuring ripple free 400 Voutput voltage within the six-fold variation of the input voltage(from 10 to 60 V). The converter prototype assembled achieved amaximum efficiency of 97.4%, which includes the auxiliarypower and control system losses.

EXISTING SYSTEM:

For the last 20 years, the MLPE application was an objectof increased research interest all over the world. An insight tothe MLPE technology trends is given in several review papers. Except the efficiency, power density, reliabilityand price per watt issues, one of the recent challenges in thedesign of a good MLPE system is a wide input voltageregulation range. A high-efficiency DC-DC converter withextended input voltage regulation range will support theimplementation of the global MPP tracking algorithms, which can substantially improve the energy yield from the PVmodule under the partial shading conditions [8]. The majorityof commercial microinverters today feature the minimum levelof the MPP voltage in the range from 22 V to 27 V .To feed power to the grid in European conditions, the gridsideDC-linkvoltageshouldbearound400V,thereforethemaximumDCvoltagegainoftheseconverters lies in the range from 14.8 to 18.2. Afurther decrease of the MPP voltage, for example, to 10 V,could bring the performance level of the microinverters to thatof the PV power optimizers. Next, emerging topologies ofthe high step-up galvanically isolated DC-DC converters forMLPE applications are discussed.

PROPOSED   SYSTEM:

The main focus of this paper is on thefull-power converters for the parallel connection of PVmodules. In this approach, each PV panel is equipped with amicroconverter (µCON) with outputs connected in parallel tothe central DC bus of the PV power system (Fig. 1a). µCON isa self-powered high efficiency step-up DC-DC converter withgalvanic isolation that operates with autonomous control andis integrated to the PV panel for tracking the MPP locally. Thegalvanic isolation is essential to reduce ground leakagecurrents and grid current total harmonic distortion. As seen from Fig. 1a, the central inverter feeds PV power to the grid.The microinverter (µINV) concept presented allows parallel connection of PV modules at the grid side. In that case, each PV module features direct AC connectivitysince µINV integrates both the galvanically isolated step-upDC-DC converter and the grid-tied inverter. This concept iscommon now in residential and small commercial PV powersystems mostly because of its expandability as well assimplicity of installation and maintenance

CONCLUSIONS

This paper has introduced a novel single-stage galvanically isolated high step-up DC-DC converter for the photovoltaicMLPE applications. Thanks to the multi-mode operation, theproposed quasi-Z-source series resonant DC-DC converterwith synchronous quasi-Z-source network and series resonanttank integrated to the secondary part of the converter featuresa wide input voltage and load regulation range. Moreover, theproposed topology achieves high efficiency through the fullZCSoftheVDRdiodesovertheentireoperatingrange,anddependingontheoperatingmode,ZVSand/orZCSoftheprimarysideswitches.The multi-mode operation principle of the proposedconverter was described along with steady-state waveforms  and analysis of operating states. Next, selected designguidelines were presented for the integrated magneticcomponents and realization of the control system. To verifythe theoretical assumptions, the experimental prototype wasassembled and tested. It was confirmed that the proposedconverter is capable of ensuring the ripple free 400 V outputvoltage within the six-fold variation of the input voltage (from10 to 60 V). Moreover, it features the continuous input currentover the entire voltage and load variation range without addingthe buffering capacitors to its input terminals. The converterprototype based on the generic Si MOSFETs and SiC SBDsachieves the maximum efficiency of 97.4% in the nominalmode and at the rated power of 250 W. It was also shown howthe part- and light-load efficiency of the proposed convertercan be improved considerably by the use of the cycle skipping modulation technique.

REFERENCES

[1] M. Kasper, D. Bortis, and J.W. Kolar, “Classification and comparativeevaluation of PV panel-integrated DC–DC converter Concepts,” IEEETrans. Power Electron., vol. 29, no. 5, pp. 2511-2526, May 2014.

[2] M. Acanski, J. Popovic-Gerber and B. Ferreira, “Design of a flexiblevery low profile high step-up PV module integrated converter,” in Proc.ECCE’2012, Raleigh, NC, 2012, pp. 2942-2948.

[3] B. Gu, J. Dominic, J. S. Lai, C. L. Chen, T. LaBella and B. Chen, “Highreliability and efficiency single-phase transformerless inverter for gridconnectedphotovoltaicsystems,”IEEETrans. Power Electron., vol. 28,no. 5, pp. 2235-2245, May 2013.

[4] S. B. Kjaer, J. K. Pedersen and F. Blaabjerg, “A review of single-phasegrid-connected inverters for photovoltaic modules,” IEEE Trans. Ind.Appl., vol. 41, no. 5, pp. 1292-1306, Sept.-Oct. 2005.

[5] Quan Li, and P. Wolfs, “A review of the single phase photovoltaicmodule integrated converter topologies with three different DC linkconfigurations,” IEEE Trans. Power Electron., vol. 23, no. 3, pp. 13201333,May2008.

[6] S. Harb, and R.S. Balog, “Reliability of candidate photovoltaic moduleintegrated-inverter(PV-MII)topologies-a usage model approach,”IEEE Trans. Power Electron., vol. 28, no. 6, pp. 3019-3027, June 2013.

[7] S. Kouro, J.I. Leon, D. Vinnikov, and L.G. Franquelo, “Grid-connectedphotovoltaic systems: an overview of recent research and emerging PVconverter technology,” IEEE Ind. Electron. Mag., vol. 9, no. 1, pp. 47 61, March 2015.

[8] A. Bidram, A. Davoudi, and R.S. Balog, “Control and circuit techniques to mitigate partial shading effects in photovoltaic arrays,” IEEE J.Photovoltaics, vol. 2, no. 4, pp. 532-546, Oct. 2012.

[9] APsystems YC500A Microinverter Datasheet [available online:https://usa.apsystems.com].

[10] Enphase S280 Microinverter Datasheet [available online:https://enphase.com].