This paper investigates the voltage and phase dynamics of a low inertia inverter based Microgrid in islanded operation. In such case, the network is less robust to disturbances due to the lack of associated inertia within an inverter. In islanded operation, the assumption of a stiff grid is no longer valid due to the voltage and phase adjustment based on conventional droop control have a resulting effect on the power flows throughout the network where voltage and frequency stability of the network may be compromised. Other approaches neglect the network dynamics when there are power imbalances in the system and how each node is affected and if the resulting increase in demand can be met with the available power generation. This paper uses the fact that the phase dynamics of coupled inverters that employ droop control closely resemble the phase dynamics proposed by the Kuramoto model. Using this model allows the network stability to be analyzed under the true nonlinear operation. It Is observed through the strong coupling impedance of the secondary distribution transmission lines and the implementation of proportional droop control will provide an appropriate means for rural and suburban neighborhoods to operate independently, given the proportional droop gain is tuned appropriately.

As the world moves towards a more sustainable development, the energy coming from fossil fuels still produces the greenhouse gases that threaten the world’s climate. The UK government has established targets for the penetration of renewable energy generation and low-carbon alternatives for the electricity production. One of these technologies is microgeneration. In 2006, the UK government launched the Microgeneration Strategy pushing forward micro and small-scale generation as a supplementary source of energy for the country’s growing electricity demand. The proposal is focused on several technologies, including micro-wind and micro-PV, among others. These microgeneration technologies are now a reality and widespread across the distribution networks. Therefore, the analysis of the impact of these systems connected to distribution grids and the benefits of these technologies, alongside with their negative effects on the network is an important research area. Correct modelling of micro and small-scale renewablebased generation technologies implemented in urban areas, however, is not a simple task, as it requires an adequate representation of highly dispersed and uncontrolled generation systems. These systems are small in size, but high in numbers and usually experience large variations in available renewable energy inputs. This thesis presents aggregate models of urban micro and small-scale PV and wind generation systems, which are connected to low-voltage networks. The thesis analyses impact of urban PV and wind generation on the steady-state network performance (power flows and voltage profiles), taking into account variability of energy inputs. The presented analysis is of particular importance for the analysis of the future of power system supplies, which will have significantly higher penetration levels of renewable-based distributed generation technologies, resulting in a much wider range of interactions between microgeneration systems, loads and transmission/distribution networks. In order to perform this analysis, the resource assessment for urban areas has to be carried out to both quantify the potential for each technology and help in their modelling. This has been a challenge since the aggregation of microgeneration systems is far from simple, as the parameters, performance and size varies between different technologies. A solution presented in this thesis is an approach for simple yet accurate aggregation of microgeneration technologies. This approach allows to quantify and analyse their impact and effect on the power supply systems directly in terms of penetration levels and general technology characteristics.

The ambitious governmental policies, particularly in Europe, in pursuit of established energy targets require an increase in distributed generation. As a result, photovoltaic (PV) technologies have emerged, predominantly at residential Low Voltage (LV) feeders. However, PV rich LV feeders are highly likely to pose technical challenges such as significant voltage rise and thermal overloading. This inevitably limits the volume of PV systems that can be hosted on LV feeders. Therefore, the deployment of solutions that can enable feeders to accommodate greater volumes of PV systems without having any technical issues is crucial. This thesis, consequently, thoroughly investigates one of the potential solutions: transforming the radial operation of LV feeders into ring operation. European-style LV feeders are typically operated in a radial fashion and yet are designed to be reconfigurable with neighbouring feeders. It is, therefore, essential to identify the best pairing option (of PV rich LV feeders) in a practical and straightforward manner due to the large number of existing LV feeders in a given Distribution Network Operator (DNO) area. This thesis proposes a generic innovative methodology to enable DNOs to straightforwardly identify the best pairing feeder; a decision-making tool to facilitate the rapid uptake of PV systems. To accomplish this goal, an impact assessment of a set of real residential LV feeders is carried out to identify the first technical issue/constraint that limits their hosting capacity. Next, regression analyses are carried out to gain an understanding of the relation between this first occurrence of technical issue/constraint and the corresponding level of PV penetration. The most practical and adequately accurate metric needs to be chosen. Feeders are then classified based on the range of metrics to cover all possible pairing cases. Finally, the ring operation of feeders in each class is analysed and hosting capacities are compared to those of radial ones. This process creates a practical matrix from which DNOs can easily identify the best pairing feeders. DNOs are likely to be hesitant to adopt permanent ring operation as it is not typically adopted in traditional LV feeders. Therefore, the switch located between feeders can be operated over time (i.e., dynamic ring operation) to reduce the duration for which ring operation is in place. It is, however, challenging to identify the most favourable control strategy. This thesis proposes different strategies for dynamic ring operation. Note that the most preferable control strategy is that which preserves the benefits of permanent ring operation with the minimum duration of ring operation and minimum number of switching. To achieve this, four different control strategies are explored-using different control cycles and considering hosting capacity, duration and switching. The best control strategy is found to be able to increase hosting capacity as permanent ring operation, reduce switching actions and minimise duration of ring operation compared to other proposed strategies and, crucially, operate ring operation only when it is truly needed. Finally, this thesis investigates the use of ring operation with an LV on-load tap changer (OLTC) as this is recently available voltage control technologies and is increasingly drawing the attention of DNOs. Two approaches are investigated to increase hosting capacity and limit ring operations: the use of the switch and OLTC are controlled separately using local measurements (i.e., localised) and their simultaneous control at the LV transformer level (i.e., centralised). The latter gives the priority to the OLTC to minimise the duration of the ring operation. The assessments are extended to cover an integrated medium and low voltage network to obtain more realistic results. The results show that centralised approach provides better performance considering hosting capacity, the number of switching/tap actions and the duration of ring operation.

The main outcome of this research is the development of a Probabilistic Impact Assessment methodology to comprehensively understand the effects of low carbon technologies (LCTs) in low voltage (LV) distribution networks and the potential solutions available to increase their adoption. The adoption of LCTs by domestic customers is an alternative to decreasing carbon emissions. Given that these customers are connected to LV distribution networks, these assets are likely to face the first impacts of LCTs. Thus, to quantify these problems a Monte Carlo-based Probabilistic Impact Assessment methodology is proposed in this Thesis. This methodology embeds the uncertainties related to four LCTs (PV, EHPs, µCHP and EVs). Penetration levels as a percentage of houses with a particular LCT, ranging from 0 to 100% in steps of 10%, are investigated. Five minute time-series profiles and three-phase four-wire LV networks are adopted. Performance metrics related to voltage and congestion are computed for each of the 100 simulations per penetration level. Given the probabilistic nature of the approach, results can be used by decision makers to determine the occurrence of problems according to an acceptable probability of technical issues. To implement the proposed methodology, electrical models of real LV networks and high resolution profiles for loads and LCTs are also developed. Due to the historic passive nature of LV circuits, many Distribution Network Operators (DNOs) have no model for them. In most cases, the information is limited to Geographic Information Systems (GIS) typically produced for asset management purposes and sometimes with connectivity issues. Hence, this Thesis develops a methodology to transform GIS data into suitable computer-based models. In addition, thousands of residential load, PV, µCHP, EHP and EV profiles are created. These daily profiles have a resolution of five minutes. To understand the average behaviour of LCTs and their relationship with load profiles, the average peak demand is calculated for different numbers of loads with and without each LCT.The Probabilistic Impact Assessment methodology is applied over 25 UK LV networks (i.e., 128 feeders) for the four LCTs under analysis. Findings show that about half of the studied feeders are capable of having 100% of the houses with a given LCT. A regression analysis is carried out per LCT, to identify the relationships between the first occurrence of problems and key feeder parameters (length, number of customers, etc.). These results can be translated into lookup tables that can help DNOs produce preliminary and quick estimates of the LCT impacts on a particular feeder without performing detailed studies. To increase the adoption of LCTs in the feeders with problems, four solutions are investigated: feeder reinforcement, three-phase connection of LCTs, loop connection of LV feeders and implementation of OLTCs (on-load tap changers) in LV networks. All these solutions are embedded in the Probabilistic Impact Assessment. The technical and economic benefits of each of the solutions are quantified for the 25 networks implemented.

Diplomová práce se zabývá dopadem nabíjení elektrických vozidel a bateriových úložišť na schopnost distribučních sítí nízkého napětí absorbovat fotovoltaické systémy. Převážně venkovské, příměstské a převážně městské regiony s různými stupni penetrace nekontrolovaně i kontrolovaně nabíjených elektromobilů jsou analyzovány Monte Carlo simulacemi. Hostingová kapacita je také analyzována, jestliže jsou elektrická vozidla jak nahrazena, tak doplněna domácími bateriovými úložišti. Práce je zakončena krátkou analýzou využitelnosti BESS.

Power losses are always a cause of worry for any power grid. In India, the situation is even worse. Though recent reports by Ministry of Power shows that Aggregate Technical and Commercial losses (AT &C losses) have come down from 36.64% in 2002-03 to 27% in 2011-12, yet they are much higher than the losses seen in many of the developed nations. The reduction shown in power loss is because of the Electricity Act, 2003 and the amendments made to it in 2007 which controlled the commercial losses rather than the technical losses. According to Ministry of Power, technical losses (Transmission & Distribution losses or T&D losses) in India are reported to be 23.65% in 2011-12. However, according to the study done by EPRI, for systems deployed in developed countries, these losses are estimated to be in the range of 7-15.5%. T & D losses occur in four system components namely step-up transformers and high voltage transmission (0.5-1%), step down to in intermediate voltage, transmission and step down to sub transmission voltage level (1.5-3%), sub-transmission system and step down to low voltage for distribution (2-4.5%), and distribution lines (3-7%). 1% of power loss is approximately equivalent to annual loss of Rs 600 million for a single state. Hence, in a year, loss in distribution line alone causes approximate loss of Rs 1.8-4.2 billion per state. Understanding and reducing power losses in distribution lines which contribute nearly 50% of the total T&D losses assume significance and has formed the motivation for the work reported in the thesis. In recent years, the trend has been to encourage users to generate solar power predominantly at residential complexes and captive power plants at industrial complexes. It has been suggested in the literature that Distributed Generation (DG) can not only reduce the load demanded from the power grid but also the power loss. In this thesis, it has been shown that by the choice of proper size and location of DG, the power loss can be reduced substantially as compared to unplanned deployment of DGs. The objective of the thesis is to design strategy for location of distributed user generated power to maximize the reduction in power loss. The thesis begins with a study of distributed generation in primary distribution networks and proceeds to problem formulation, with the aim being to develop an algorithm that can find out the optimal locations for DG allocation in a network. A greedy approximation algorithm, named OPLODER (i.e. Optimal Locations for Distributed Energy Resources), is proposed for the same and its performance on a benchmark data set is observed, which is found to be satisfactory. The thesis then moves on to describe the actual data of 101,881 commercial, residential and industrial consumers of Bangalore metropolitan area. A loss model is discussed and is used to calculate the line losses in LV part of the grid and loss is estimated for the said actual data. The detailed analysis of the losses in the distribution network shows that in most cases the losses are correlated with the sanctioned load. However there are also some outliers indicating otherwise. The analysis concludes that the distributed generated sources need to be optimally located in order to benefit fully. Also presented thereafter is a study about the impact of electrical properties and the structure of the network on power loss. In the second part of the thesis, OPLODER was again used to process the BESCOM data of 101,881 consumers by modeling them to be connected in three topologies namely Bus (i.e. linear structure), Star (i.e. directly connected) and Hybrid (i.e. tree structure). In case of Bus topology, when DG capacity available is 5% of the demand in substation, OPLODER reduced the loss from 14.65% to 10.75%, from 11.63% to 7.71% and from 13.33% to 9.24% for IISc, Brindavan, and Gokula substations respectively. Similarly, for the same amount of DG in case of star topology, OPLODER reduced loss from 1.75% to 1.26%, from 3.39% to 2.59% and from 2.96% to 1.99% for IISc, Brindavan, and Gokula substations respectively. Thereafter, the available real world data is re-modeled as a tree-type structure which is closer to the real world distribution network and OPLODER is run on it. The results obtained are similar to those presented above and are highly encouraging. When applied to the three substations viz. IISc, Brindavan and Gokula, the power loss dips from 9.95% to 7.42%, from 6.01% to 4.44% and from 8.07% to 5.95%, in case of DG used is 5% of the demand in substation. For the optimal strategies worked out in the thesis, additional overheads will be present. These overheads are studied and it has been found that the present infrastructure and technologies will be sufficient to handle the smart distribution network and the optimal strategy for distributed sources.