The grid-connected photo-voltaic (PV) system is one of the most promising renewable energy solutions which offers many benefits to both the end user and the utility network and thus it has gained the popularity over the last few decades. However, due to the very nature of its invariability and weather dependencies, the large scale integration of this type of distributed generation has created challenges for the network operator while maintaining the quality of the power supply and also for reliable and safe operations of the grids. In this study, the behavioral impact of large scale PV system integration which are both steady and dynamic in nature was studied.  An aggregate PV model suited to study the impacts was built using MATLAB/Simulink.  The integration impacts of PV power to existing grids were studied with focus on the low voltage residential distribution grids of Mälarenergi Elnät AB (10/0.4 kV). The steady state impacts were related to voltage profile, network loss. It was found that the PV generation at the load end undisputedly improves the voltage profile of the grid especially for the load buses which are situated at farther end of the grid. Further, with regard to the overvoltage issue, which is generally a concern during the low load demand period it was concluded that, at a 50% PV penetration level, the voltage level for the load buses is within the limit of 103% as prescribed by the regulator excepting for few load buses. The voltage level for load buses which deviate from the regulatory requirement are located at distance of 1200 meter or further away from the substation. The dynamic impact studied were for voltage unbalancing in the grid, which was found to have greater impact at the load buses which is located farther compared to a bus located nearer to the substation. With respect to impact study related to introduction of harmonics to the grid due to PV system integration, it was found that amount of harmonic content which was measured as total harmonic distortion (THD) multiplies with integration of more number of PV system. For a 50 % penetration level of PV, the introduced harmonics into the representative network is very minimal. Also, it was observed from the simulation study that THD content are be less when the grid operates at low load condition with high solar irradiance compared to lower irradiance and high load condition.

The increase in electric vehicles and photovoltaic power production may introduce problems to the low-voltage distribution grid. With a higher number of electric vehicles, their accumulated charging power might breach the lowest allowed voltage level of the grid. Photovoltaic-modules can on the other hand exceed the highest allowed voltage level, by producing high accumulated power when the solar irradiance is high. Normally, electric distribution companies in Sweden reinforce the existing grid with more resilient infrastructure, such as stronger and larger cables or transformer stations. This is however a costly and time-consuming solution, which could be solved by using alternative means such as already existing resources. This Master's Thesis investigates how smart charging of batteries can support the low-voltage electrical grid with the increase in electric vehicles and photovoltaic power production. To do this, an optimization tool has been developed in Matlab. An existing model of a low-voltage grid is combined with the developed tool, where controllable batteries and photovoltaic-modules can be placed at specific households in the grid. The controllable batteries belong to either electric vehicles or stationary battery systems, and are intended to support the grid by the means of either reducing peak load powers, voltage variations, or a trade-off between them. Furthermore, this thesis investigates the maximum electric vehicle capability for a specific low-voltage electrical grid in Sweden. From the results, it can be concluded that smart charging of batteries can reduce the peak loads as well as voltage variations. The reduction of voltage variations for the entire low-voltage grid is greatest during the summer, when photovoltaic production generally is at its highest. The results also show that a stationary battery system can reduce the voltage variations to a greater extent, compared to an electric vehicle. Also, the introduction of multiple controllable batteries allows further support of the low-voltage grid. Regarding the maximum electric vehicle capability, the results show that the placement of the vehicles and the charging power strongly affect the maximum number of electric vehicles the low-voltage grid can manage. / Ökningen av elbilar och elproduktion från solceller kan ge problem i lågspänningsnätet. Med ett ökat antal elbilar kan den sammanlagrade effekten vid laddning underskrida den minsta tillåtna spänningsnivån i nätet. Solpaneler kan däremot leda till att den högsta tillåtna spänningsnivån överskrids, genom att producera en hög sammanlagrad effekt när solstrålningen är som högst. Vanligtvis förstärker elnätsbolag i Sverige det befintliga nätet med motståndskraftigare infrastruktur, såsom kraftigare och större kablar eller transformatorstationer. Detta är dock en kostsam och tidskrävande lösning, som skulle kunna lösas med alternativa medel, till exempel redan existerande resurser. Detta examensarbete undersöker hur smart laddning av batterier kan ge stöd till lågspänningsnätet, med en ökning av elbilar samt solcellsproduktion. För att undersöka detta har ett optimeringsverktyg utvecklats i Matlab. En befintlig modell av ett lågspänningsnät har kombinerats med det utvecklade optimeringsverktyget, där styrbara batterier samt solcellsproduktion kan placeras vid specifika hushåll i elnätet. De styrbara batterierna är antingen elbilar eller stationära batterisystem, och är ämnade till att stödja lågspänningsnätet genom att antingen reducera effekttoppar, spänningsvariationer eller en kompromiss av båda. Vidare undersöker detta examensarbete det maximala antalet elbilar som ett specifikt lågspänningsnät i Sverige kan hantera. Resultaten visar att smart laddning av batterier kan reducera effekttoppar samt spänningsvariationer. Reduceringen av spänningsvariationerna för hela lågspänningsnätet visar sig vara högst under sommaren, vilket är då solcellsproduktionen generellt är som högst. Resultaten visar även att stationära batterisystem kan reducera spänningsvariationer ytterligare, jämfört med en elbil. Att introducera flera styrbara batterier tillåter ett ännu större stöd till lågspänningsnätet. Angående det maximala antalet av elbilar som ett lågspänningsnät kan hantera visade resultaten att placeringen av elbilarna samt laddningseffekten har en stor påverkan.