Given the merits of photovoltaic technology (PV), rooftop PV systems are becoming more prevalent in residential and commercial areas. As a result of the growing number of photovoltaic systems connected to low voltage (LV) distribution grids, a significant portion of power flow from photovoltaic arrays to the LV grid, As the PV penetration increases, this effect becomes more severe. This reversal of power flow (from the load side to the grid side) results in a voltage rise problem along the distribution feeder. Such an issue is more pronounced near the point of common coupling (PCC). Overvoltages are not desired as they can damage consumers’ electronic devices, burn the insulation and can trip protective equipment, causing sudden power outages. The principal objective of this study is to achieve 100% PV penetration in a low voltage distribution network while maintaining voltages within the grid constraints by employing numerous voltage control techniques. To conduct PV penetration studies, the European low-voltage distribution benchmark network developed by CIGRE is selected. PV systems of various configurations are designed and integrated into the CIGRE LV network. The results of the PV penetration analysis on the CIGRE network suggest that with the increase in the distance between the source and the load, the penetration level decreases drastically. The worst-case network model in which the penetration level is reduced to 65% is selected for employing voltage control strategies. Two main strategies have been used to improve PV penetration. In the first category of methods, the reactive power is controlled by the PV system so that voltages at the PCCs are within the grid voltage limits. Four different reactive power control methods are employed. The second category of methods are based on active power control, in which the voltages are controlled by batteries/electrolyzers by absorbing excess power generated by the PV system, avoiding reverse power flow into the grid. The results obtained reveal that all the techniques employed are successful at increasing PV penetration to 100% without violating grid voltage limits. However, it is concluded that, batteries/electrolyzer systems provide better value in terms of effectiveness in solving the voltage rise issue. They also offers lower losses, and multiple-use cases. ... Read more

With the current need of implementing renewable energy sources to combat climate change, significant developments are being done into storage options for these intermittent energy sources. Green Hydrogen can be produced by the connection of a renewable energy source to an electrolyser which produces hydrogen, in this project the Photovoltaic (PV) System is indirectly connected to the electrolyser as this gives the ability to control the different systems and flexibility in sizing the different systems. Several different dc/dc converters are simulated in Matlab Simulink and compared to each other while also taking into account the project requirements. First, an overview of the project is presented after which the main idea of the thesis is presented in which the dc/dc converters are selected for optimal operation of the system. Two converters are selected based on simulations and mathematical calculations (Component sizes, Voltage ripple & Current ripple), for the Maximum Power Tracking converter (Connected to the PV system) the buck-boost converter was selected. This was because of its ability to fully track the Current-Voltage curve of a PV system. And for the connection to the Electrolyser system a 3-level Interleaved Buck converter was selected, because of its increased reliability to be able to continue working after a power electronic switch failure. With the PV system maximum power point being between 580-582 V (depending on the irradiance) and a Electrolyser voltage range between 210 - 260 V, the voltage needed to be reduced. After selecting the different converters, a control system was modelled and simulated, this is to optimize and control the working points of the PV-Electrolyser system. This control system works on the idea of matching the electrolyser load working point to the available PV power from the input. This control algorithm selects the right reference voltage which then goes into a voltage controller to ensure the correct voltage is at the output for the electrolyser load. This control algorithm was modelled and simulated in Matlab simulink and tested against different changing inputs (Changing the irradiance & electrolyser temperature). Furthermore, the controller was checked for several different stepsizes and time delays (accounting for external effects) and the optimal combination was found to be a stepsize of 0.1V and timedelay of 1ms which gave an Converter+algorithm efficiency of 98.42%. The results demonstrate the controller’s ability to correctly follow the irradiance pattern and electrolyser temperature changes. ... Read more

Green hydrogen can be produced from various renewable energy sources like PV, wind, geothermal and biomass. Especially PV or wind sourced hydrogen production systems are becoming more prevalent as a solution to produce green hydrogen, owing to their regional abundance. In this master thesis project, a PV-grid powered electrolyser shall be taken into consideration. The electrolyser is an equipment that produces hydrogen through electrolysis. Here, an alkaline electrolyser is taken into consideration, which is a DC load and hence, it requires a rectifier to convert the AC power from the grid and from the PV plant (DC PV power will be converted to AC through an inverter) into DC power. The amount of hydrogen produced is proportional to the amount of current flowing into the electrolyser. As the electrolyser operates, the process of electrolysis will, more often than not, produce heat. The heat produced during electrolysis, along with the ambient conditions, will result in variation of the temperature of the electrolyser. Some systems make use of a thermostat to control the temperature of the electrolyser whereas some employ a cooling system to extract heat and utilise it to perform useful work. If there is no system to control or maintain its temperature, the electrolyser is bound to have varying temperature while it is operational. This research aims to develop a control strategy for a PV-grid powered electrolyser to ensure the optimal operation of the electrolyser despite its varying temperature. The need for such a control strategy for the electrolyser rises due to the dependence of the I-V characteristics of the electrolyser on the temperature. As the temperature of the electrolyser increases, the I-V curve shifts in such a way that a given current value will be produced at a lower value of voltage. Since the amount of hydrogen produced depends on the amount of current flowing into the electrolyser, the control strategy aims to maintain the input current to the electrolyser at the rated value irrespective of the change in the temperature of the electrolyser. The control strategy is tested on Simulink with the help of an electrolyser emulator into which data is fed through a look-up table. Real-time data for irradiance and ambient temperature has been used to perform day-long simulations. Based on the results obtained, the average efficiency of the converter was found to be 93.88%. ... Read more

Until recent times, electrical power grids have been dominated by conventional power plants run by fossil or nuclear fuels in order to cater to the electrical load demand. These power plants employ large generators that operate in synchronous with each other to maintain a stable frequency and voltage across the power grid. The frequency and voltage stability, which are respectively linked to active and reactive power serves as a backbone for a secure operation of the power system. Furthermore, since these classical generation sources promised support of ancillary services during unstable conditions, along with power generation, they were characterized as a reliable solution for maintaining the security of the power system. But, due to the high emission of carbon by-products from these fossil-fuelled generators, challenges of global warming and climate change have made it inevitable to decommission them. And more emphasis has been embarked on the adaptation of renewable energy sources (RES) which offer minimum carbon footprint. Geothermal heat, wind, sunlight, and tides constitute some of the Renewable energy sources since their availability are unlimited and involve the least emission of greenhouse gasses, hence Renewable Energy Sources have a minimal impact on the environment compared to traditional energy sources and can effectively tackle the problems which arise with fossil fuel usage. For all these reasons, during the last decades, there is fierce research on finding ways to produce the needed energy in a sustainable fashion. Synchronous Generators, which are dominant in the existing power grid, have the inherent characteristics to relate system’s frequency with load balance. This considerable advantage is found missing from Power Electronic interfaced renewable energy resources due to the following reasons. Firstly, since active power support was earlier the main purpose of using these devices, they were operated at Maximum power point tracking (MPPT). Secondly, in wind energy technology, isolation between electrical and mechanical circuits had to be introduced due to their variable behavior of energy production, and this has led to no inertia backing from the synthetically produced frequency. So with high penetration of RES in the future grids, the aforementioned problems pose huge risks for grid stability and reliability. The current research mainly focuses on the development, implementation, testing, and validation of frequency regulation strategies under the umbrella of Fast Active Power Regulation controllers specifically to support during large load frequency variation in low inertia power system grid. These controllers developed are very generic and can be implemented with slight modifications in all the renewable energy devices with ease. In order to simulate more real-time behavioral conditions, dynamic simulation studies are performed in RSCAD software interfaced with a Real-Time Digital Simulator (RTDS). Two Test benches have been considered in this thesis, one being an IEEE 9 bus system modified with 52% wind share and another is the North of Netherlands Network. In the first stage of the project, FAPR controller’s proof of concept has been tested on a Type-4 Wind generator setup connected to the modified IEEE 9 bus system. Here wind penetration is scaled up to 52% and a low inertia grid have been simulated. Later, the results obtained here were validated by Hardware in Loop setup utilizing a mock-up grid side converter. The next stage of the project aims at making FAPR controllers more generic. For this the North of Netherlands network was modified by adding FAPR integrated 300MW solar farm, FAPR integrated 82MW full converter based Type-4 Wind Turbine and lastly, a responsive load (Electrolyser) was modified to accommodate FAPR controllers. All together formed a Multi-Energy Hub and simulations were performed to check the practical feasibility and boundaries of operation of FAPR controllers in the future power grid. The results prove that the proposed topology and control strategies can effectively provide frequency ancillary services to the grid by providing support during dynamic load frequency variations. ... Read more