Design and implementation of an off-grid PV drive system for small scale fresh produce cooling

Samules, Jason Avron (2017-12)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: The implementation of a PV drive system is discussed in this thesis with the focus on fresh produce cooling for small-scale farmer. A background study is presented, which firstly addresses hunger and food insecurity through emphasis on one of the mentioned six causes of hunger, namely, food waste. Further focus is placed on cooling and, specifically, solar cooling. Therefore, the relevant factors pertaining to cooling and solar energy as a power source are presented, adding to the background study. Thereafter, the project details are outlined which states the research significance as the investigation of feasibility, in terms of cost and performance, of the design and implementation of PV drive systems, using the proposed development process. With that being said, the design of the PV drive system, elevation of low-voltage solar PV energy and cost-effective implementation were evaluated. In a high-level project overview the project parts are presented for the designed and implemented PV drive system, with the focus on the solar energy source and the cooling application. Similarly, the proposed development process is discussed through which the drive system was implemented. In effect, this process entails using off-the-shelf subsystems, as far as possible, to construct the drive system with only the necessary self-built subsystems. The drive system consists of the following self-built subsystems, namely the DC-DC converter and control module, and a commercial VSD, with integration between these subsystems. As the main means of voltage elevation, from the low-voltage solar PV source, the focus is placed on DC-DC converters. Furthermore, a comparison of DC-DC converters are made, with the defined criteria for the project, for the most suitable converter. For easier comparison, the converters are grouped and their advantages and disadvantages are presented. Ultimately, a converter choice was made. The chosen converter, the resonant push-pull converter, was thoroughly discussed, analysed and specifically designed for the project. Furthermore, this theoretical design of the converter was firstly simulated, for confirmation, before physical construction proceeded. Thereafter, converter tests were done to verify the design through various measurements. Most importantly, the converter output voltage range and efficiency were measured and verified to a satisfactory degree. The system control module allowed for proper operation of the converter and, moreover, the integration of the PV drive subsystems. Furthermore, the microcontroller-based control module is discussed and the implemented algorithms are presented for optimal energy transfer; these algorithms were expressed in flow diagrams. In addition, transient control results are shown for start-up and load variations for verification. After verification of the main subsystems, the complete PV drive system was operated throughout a whole day with an appropriate load, to ensure proper conclusions are made. Unfortunately, a cooling system could not be acquired for testing. Details for the demonstration are presented, which include the specific equipment used and results for the operation. Moreover, the results present a fully operational drive system from a lowvoltage solar PV energy source able to drive the appropriate load, which demonstrates successful performance. However, the drive system included performance shortfalls, which are discussed and for which recommendations were provided. With the drive system operational, conclusions were made, regarding cost and performance, in comparison with other similar systems. In addition, the research objectives and aims were evaluated. After evaluation, although the PV drive system could be designed and implemented to a successful measure with regards to performance, it fell short regarding cost in comparison with the compared systems. Therefore, the proposed PV drive system, with the development process followed, is not completely feasible in implementation -to the degree described- for fresh produce cooling for small-scale farmers.

AFRIKAANSE OPSOMMING: Die implementering van ’n fotovoltaïese (FV) aandryfstelsel word bespreek in die tesis met die fokus op die verkoeling van vars produkte in kleinskaalboerdery. ’n Agtergrondstudie is aangebied wat eerstens hongersnood en voedselonsekerheid aanspreek met die klem op een van die ses genoemde oorsake van hongersnood, naamlik, voedselvermorsing. Verdere fokus is geplaas op verkoeling, spesifiek sonverkoeling, en die relevante faktore van verkoeling en sonenergie as bron is aangebied, in byvoeging tot die agtergrondstudie. Daarna is die projek besonderhede getoon wat die navorsingsbelang verklaar as die uitvoerbaarheidsondersoek, in terme van koste en uitvoering, van die ontwerp en toepassing van FV aandryfstelsels, met die voorgestelde ontwikkelingsproses. Met dit gesê, is die ontwerp van die FV aandryfstelsel, die verhoging van die laespanning FV sonenergie bron en koste-effektiewe toepassing geëvalueer. In ’n hoëvlak projekoorsig is die projekdele aangebied vir die ontwerp en toepassing van die FV aandryfstelsel met die fokus op die sonenergie as bron en die voerkoelingstoepassing. Soortgelyk is die voorgestelde ontwikkelingsproses bespreek waardeur die FV aandryfstelsel toegepas is. In effek bevat die proses die gebruik van van-die-rak substelsels, so ver mootlik, om die FV aandryfstelsel saam te stel met net die nodige selfgeboude substelsels. Die aandryfstelsel bestaan uit die volgende selfgeboude substelsels, naamlik, die g.s.-g.s. omsetter en die beheermodule, en ’n kommersieële veranderbare spoed aandrywer (VSA), met integrasie tussen die substelsels. As hoof manier van spanningsverhoging, vanaf die laespanning FV sonenergiebron, is die fokus geplaas op die GS-GS omsetter. Nog meer is ’n vergelyking van g.s.-g.s. omsetters gemaak, met die gekose kriteria vir die projek, vir die mees gepaste omsetter. Om die vergelyking makliker te maak is die omsetters gegroepeer en hulle voordele en nadele getoon. Uiteindelik is ’n omsetterkeuse gemaak. Die gekose omsetter, die resonante stoot-trek omsetter, is deuglik bespreek, geanaliseer en ontwerp spesifiek vir die projek. Nog meer, is die teoretiese ontwerp van die omsetter gesimuleer, vir bevestiging, voordat die fisiese samestelling voortgegaan is. Daarna is omsettertoetse gedoen om die ontwerp te bevestig deur verskeie metings. Mees belanglik is voldoende bevestiging van die omsetter se uittreespanningsbereikmetings en doeltreffendheidmetings. Die stelselbeheermodule het toegelaat vir behoorlike werking van die omsetter en, nogmeer, die integrasie van die FV aandryfstelseldele. Boonop is die mikrobeheerdergebaseerde beheermodule bespreek en die toegepaste algoritmes aangebied vir optimale energieoordrag; hierdie algoritmes is deur vloeidiagramme uitgedruk. Verder is die oordragsbeheerresultate getoon, van die omsetteraanskakeling en lasvariasies, vir bevesting. Na bevestiging van die hoofsubstelsels is die volledige FV aandryfstelsel bedryf vir ’n volle dag met ’n toepaslike las om te verseker dat gepaste gevolgtrekkings gemaak is. Ongelukkig is ’n verkoelingsstelstel nie verkry vir toetse nie. Besonderhere vir die demonstrasie is aangebied wat die informasie oor die spesifiek toerusting en resultate van die volle dag se bedryf insluit. Nog meer is die resultate aangebied van ’n werkende aandryfstelsel van ’n laespanning FV sonenergiebron om ’n toepaslike las aan te dryf, wat suksesvolle uitvoering demonstreer. Alhoewel die FV aandryfstelsel suksesvolle werking toon, is tekortkominge in werksverrigting waargeneem en bespreek met die nodige aanbevelings. Met die FV aandryfstelsel operasioneel, is gevolgtrekkings gemaak met betrekking tot koste en uitvoering saam, in vergelyking met ander soortgelyke stelsels. Nog meer is die navorsingsuitsette en navorsingsdoelwitte geëvalueer. Na die evaluering, alhoewel die FV aandryfstelselontwerp en toepassing tot suksesvolle uitvoeringsmate getoon is, val dit kort in terme van koste in vergelyking met soortgelyke stelsels. Dus is die voorgestelde FV aandryfstelsel met die ontwikkelingsproses gevolg, nie volledig uitvoerbaar in toepassing -tot die mate beskryf- vir vars produk verkoeling by kleinskaalboerdery nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102874
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