This project examines the implications of the photovoltaic power generation as well as the battery storage systems on the distribution network tariff structures. Different types of existing distribution tariffs were applied to the residential households’ demand patterns. Several scenarios of demand profiles were theoretically investigated. First scenario included households’ consumption under current situation without on-site power production and any storage, second scenario concerned penetration of average size of solar panel installations and the last demand profile with maximum possible size of photovoltaic panels complemented with battery storage use. The distribution tariffs included in the comparison are: power based tariff and two energy based tariffs, one with flat-rate and another with time-of-use structure. Distribution tariffs were normalized with the aim to research the implications of the on-site production and storage use. Normalization factors were used when comparing financial bills from the households under above mentioned scenarios. Energy distribution tariffs have higher potential for households to save on their energy bill with the introduction of the on-site solar power utilization. On the other hand power tariff provides higher incentive for the implementation of the demand response strategies in the households.

As distributed generation penetrates the electric power grid at higher power levels, grid interface issues with distributed generation must be addressed. The current power system consists of central power generators, while the future power system will include many more distributed resources. The centralized power generation system is controlled by utility operators, but many distributed resources will not be controlled by utility operators. Distributed generation must use smart control techniques for high reliability and ideal grid interface. This thesis discusses the grid interface issue of anti-islanding. An electric island occurs when a circuit breaker in the electric power system trips. The distributed resource should disconnect from the electric grid for safety reasons. This thesis will give an overview of the possible methods. Each method will be analyzed using the ability to detect under the non-detection zone and the economic feasibility of the method. This thesis proposes two addition cases for analysis that exist in the electric power system: the effect of multiple methods in parallel in the non-detection zone and the possibility of a false trip caused by a load step. Multiple methods in parallel are possible because the islanding detection method is patentable, so each grid interface inverter company is likely to implement a different islanding detection method. The load step represents a load change when a load is switched on. / Master of Science

In this dissertation, several volt-var optimization methods have been proposed to improve the expected performance of the distribution system using distributed renewable energy sources and conventional volt-var control equipment: photovoltaic inverter reactive power control for chance-constrained distribution system performance optimisation, integrated distribution system optimization using a chance-constrained formulation, integrated control of distribution system equipment and distributed generation inverters, and coordination of PV inverters and voltage regulators considering generation correlation and voltage quality constraints for loss minimization. Distributed generation sources (DGs) have important benefits, including the use of renewable resources, increased customer participation, and decreased losses. However, as the penetration level of DGs increases, the technical challenges of integrating these resources into the power system increase as well. One such challenge is the rapid variation of voltages along distribution feeders in response to DG output fluctuations, and the traditional volt-var control equipment and inverter-based DG can be used to address this challenge. These methods aim to achieve an optimal expected performance with respect to the figure of merit of interest to the distribution system operator while maintaining appropriate system voltage magnitudes and considering the uncertainty of DG power injections. The first method is used to optimize only the reactive power output of DGs to improve system performance (e.g., operating profit) and compensate for variations in active power injection while maintaining appropriate system voltage magnitudes and considering the uncertainty of DG power injections over the interval of interest. The second method proposes an integrated volt-var control based on a control action ahead of time to find the optimal voltage regulation tap settings and inverter reactive control parameters to improve the expected system performance (e.g., operating profit) while keeping the voltages across the system within specified ranges and considering the uncertainty of DG power injections over the interval of interest. In the third method, an integrated control strategy is formulated for the coordinated control of both distribution system equipment and inverter-based DG. This control strategy combines the use of inverter reactive power capability with the operation of voltage regulators to improve the expected value of the desired figure of merit (e.g., system losses) while maintaining appropriate system voltage magnitudes. The fourth method proposes a coordinated control strategy of voltage and reactive power control equipment to improve the expected system performance (e.g., system losses and voltage profiles) while considering the spatial correlation among the DGs and keeping voltage magnitudes within permissible limits, by formulating chance constraints on the voltage magnitude and considering the uncertainty of PV power injections over the interval of interest. The proposed methods require infrequent communication with the distribution system operator and base their decisions on short-term forecasts (i.e., the first and second methods) and long-term forecasts (i.e., the third and fourth methods). The proposed methods achieve the best set of control actions for all voltage and reactive power control equipment to improve the expected value of the figure of merit proposed in this dissertation without violating any of the operating constraints. The proposed methods are validated using the IEEE 123-node radial distribution test feeder.

The research focus of this thesis is on modelling techniques for river kinetic turbines, to develop predictive numerical tools to further the design of this emerging hydro technology. The performance benefits of enclosing the turbine in a shroud are quantified numerically and an optimized shroud design is developed. The optimum performing model is then used to study river kinetic turbines, including different anchoring systems to enhance performance. Two different turbine numerical models are studied to simulate the rotor. Four different computational fluid dynamics (CFD) turbulence models are compared against a series of particle image velocimetry (PIV) experiments involving highly-separated diffuser-flow and nozzle-flow conditions. The risk of cavitation is briefly discussed as well as riverbed boundary layer losses. This study is part of an effort to develop this emerging technology for distributed power generation in provinces like Manitoba that have a river system well adapted for this technology. / May 2007

The research focus of this thesis is on modelling techniques for river kinetic turbines, to develop predictive numerical tools to further the design of this emerging hydro technology. The performance benefits of enclosing the turbine in a shroud are quantified numerically and an optimized shroud design is developed. The optimum performing model is then used to study river kinetic turbines, including different anchoring systems to enhance performance. Two different turbine numerical models are studied to simulate the rotor. Four different computational fluid dynamics (CFD) turbulence models are compared against a series of particle image velocimetry (PIV) experiments involving highly-separated diffuser-flow and nozzle-flow conditions. The risk of cavitation is briefly discussed as well as riverbed boundary layer losses. This study is part of an effort to develop this emerging technology for distributed power generation in provinces like Manitoba that have a river system well adapted for this technology.

The research focus of this thesis is on modelling techniques for river kinetic turbines, to develop predictive numerical tools to further the design of this emerging hydro technology. The performance benefits of enclosing the turbine in a shroud are quantified numerically and an optimized shroud design is developed. The optimum performing model is then used to study river kinetic turbines, including different anchoring systems to enhance performance. Two different turbine numerical models are studied to simulate the rotor. Four different computational fluid dynamics (CFD) turbulence models are compared against a series of particle image velocimetry (PIV) experiments involving highly-separated diffuser-flow and nozzle-flow conditions. The risk of cavitation is briefly discussed as well as riverbed boundary layer losses. This study is part of an effort to develop this emerging technology for distributed power generation in provinces like Manitoba that have a river system well adapted for this technology.

We discuss a model of a virtual power plant (VPP) that provides market access to privately-owned distributed generations (DGs). The VPP serves passive loads, processes bids from generators, and trades in the wholesale market. The generators can be renewable or thermal, and they act strategically to maximize their own profit. The VPP establishes the rules of the internal market to minimize the cost of energy and the cost of balancing while ensuring generator participation and load balancing. We derive a heuristic mechanism for internal market and propose a dynamic programming approach for minimizing the VPP cost. We present illustrative simulations for both single and multistage market bidding and then compare the resulting performance to the centralized VPP model, where the DGs are assumed to be owned by the VPP. We show that the proposed design incentivizes the DG agents to behave the same as in the centralized case, but the optimal cost paid by VPP is higher due to the payments to the DG owners.

In recent years, the world has seen a significant growth in energy requirements. To meet this requirement and also driven by environmental issues with conventional power plants, engineers and consumers have started a growing trend in the deployment of distributed renewable power plants such as photovoltaic (PV) power plants and wind turbines. The introduction of distributed generation pose some serious issues for power system protection and control engineers. One of the major challenges are power system protection. Conventional distribution power systems take on a radial topology, with current flowing from the substation to the loads, yielded unidirectional power flow. With the addition of distributed generation, power flow and fault current are becoming bi-directional. This causes loss of coordination between conventional overcurrent protection devices. Adding power sources downstream of protection devices might also cause the upstream protection device to be blinded from faults. Conventional overcurrent protection is mainly based on the fault levels at specific points along the network. By adding renewable sources, the fault levels increase and become dynamic, based on weather conditions. In this dissertation, power system faults are modelled with sequence components and simulated with Digsilent PowerFactory power system software. The modeling of several faults under varying power system parameters are combined with different photovoltaic penetration levels to establish a framework under which protection challenges can be better defined and understood. Understanding the effects of distributed generation on three phase power systems are simplified by modeling power systems with sequence networks. The models for asymmetrical faults shows the limited affect which distributed generation has on power system protection. The ability of inverter based distributed generators to provide active control of phase current, irrespective of unbalanced voltage occurring in the network limits their influence during asymmetrical faults. Based on this unique ability of inverter based distributed generators (of which PV energy sources are the main type), solutions are proposed to mitigate or prevent the occurrence of loss of protection under increasing penetration levels of distributed generation. The solutions include using zero and negative sequence overcurrent protection, and adapting the undervoltage disconnection time of distributed generators based on the unique network parameters where it is used. Repeating the simulations after integrating the proposed solutions show improved results and better protection coordination under high penetration levels of PV based distributed generation. / Dissertation (MEng)--University of Pretoria, 2017. / Electrical, Electronic and Computer Engineering / MEng / Unrestricted

Η παρούσα διπλωματική εργασία έχει ως σκοπό την παράθεση και ανάλυση των μεθόδων που έχουν παρουσιαστεί αυτή τη στιγμή στη διεθνή βιβλιογραφία και αφορούν τον έλεγχο και συγχρονισμό σε δίκτυο των Διασπαρμένων Συστημάτων Παραγωγής Ισχύος (Δ.Σ.Π.Ι.). Στο πρώτο κεφάλαιο γίνεται μια εισαγωγή στη Διασπαρμένη Παραγωγή (Δ.Π.) και στα Δ.Σ.Π.Ι. Στο δεύτερο κεφάλαιο παρουσιάζονται και αναλύονται τα κύρια χαρακτηριστικά των στρατηγικών ελέγχου που σχετίζονται με τον έλεγχο των Δ.Σ.Π.Ι. Στο τρίτο κεφάλαιο γίνεται παρουσίαση και ανάλυση των μεθόδων που χρησιμοποιούνται για το συγχρονισμό των Δ.Σ.Π.Ι. με το δίκτυο. Στο τέταρτο κεφάλαιο, όμοια με προηγούμενα, έγινε προσπάθεια για παρουσίαση των στρατηγικών ελέγχου των Δ.Σ.Π.Ι. σε περίπτωση που έχουμε εσφαλμένο δίκτυο. / The aim of this master thesis , is the presentation and analysis of the control strategies which are implemented on the distributed power generation systems(grid connection. Moreover, grid synchronization methods of DPGS are presented and evaluated. Control strategies when running on grid faults are also presented.

The output power variability of intermittent renewable sources can cause significant fluctuations in distribution system voltages. A local linear controller that exploits the capability of a photovoltaic inverter to provide both real and reactive power is described. This controller substitutes reactive power for real power when fluctuations in the output of the photovoltaic source are experienced. In this way, the inverter can help mitigate distribution system voltage fluctuations. In order to provide real and reactive to the grid, a three-phase grid-connected single-stage photovoltaic system with maximum power point tracking and power control is described. A method of reducing the current harmonic caused by resonance of the LC filter and transformer is presented. The local linear controller is examined using an example distribution system, and it is found that the controller is effective at mitigating voltage violations. The photovoltaic control system is examined using three-phase single-stage PV inverter system. The power control and damping system show good performance and stability under rapid change of irradiance.