https://www.um.edu.mt/library/oar/handle/123456789/52000 2026-04-26T22:12:53Z https://www.um.edu.mt/library/oar/handle/123456789/52771 Title: Transformerless inverters for grid-connected photovoltaic systems Abstract: Nowadays, solar energy generation has gained significant popularity in light of the increasing energy demands. Transformerless inverters have become an important alternative to interface photovoltaics with the grid for converting DC electricity to AC, since they are more reliable and have higher efficiencies of up to 98%. However, they are prone to leakage currents and their use is regulated by the local grid codes of individual countries. This project is concerned with the analysis and comparison of the operation of the H4, H5 and HERIC transformerless inverter topologies. The main objective of the project is the design, modelling and simulation of a 2.5kVA single phase inverter implemented with these three topologies. Simulations results will include a comparison of efficiencies at different power injection levels; common mode voltages and leakage currents. For the implementation of the transformerless inverters connected to the grid, first it was needed to design and simulate the Photovoltaic Array which was going to serve as the DC source for the inverters. The second phase was to design and simulate the inverter topologies under different DC input power levels. In order to perform these tests, control loops for the grid connected operation of the inverter were also designed and modelled. Third stage was to investigate their Common Mode Voltage and leakage currents. In order to achieve these tests, stray capacitances were used at the input side of the inverter. Finally, the simulation of the inverters including switching and conduction losses of the IGBTs and diodes were considered in order to determine the efficiency curves of the three topologies. In addition, the European Efficiency was also considered which takes into consideration the operation of the PV array. Description: B.ENG (HONS) 2019-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/52766 Title: Implementation and testing of paralleled droop controlled three phase inverters Abstract: The main grid is no exception to improvement and evolution. The grid’s main function is to transmit and distribute electricity, from both the suppliers to the consumers and vice versa. The later has become more prominent, such as with excess solar power generation in Malta. These last ten years, power engineers have researched and developed different types of microgrids to facilitate the integration of distributed energy resources (DERs). These microgrids are able to interconnect together and to the main grid, increasing the reliability and efficiency of the latter. Microgrids can perform in conjunction with the main grid (grid-tied mode) or autonomously (islanded-mode). Microgrids employ several power electronic converters (PECs) in order to connect the DERs and specific local loads to its main bus. Furthermore, these PECs such as inverters are controlled via certain load sharing techniques. The main focus of this dissertation is the study of droop controlled three-phase inverters and their paralleling to form an islanded AC microgrid. As part of the study, a lab-based prototype with two parallel inverters capable of sharing the load connected to the microgrid was designed, implemented and tested. The project may be sub-divided into four main stages. Firstly, Stage 1 is concerned with the system modelling and design for the droop controlled inverters. This also includes the ability of one inverter to synchronise with the microgrid voltage and to connect once the synchronisation criteria have been met. Consecutively Stage 2 consists of the simulation of the complete system model, verifying the correct operation of the designed control loops. In Stage 3, the hardware prototypes’ power circuitry and PCBs required for sensing and interfacing with the three-phase inverters were implemented. Furthermore, the control algorithms developed in stage 1 were programmed in the respective µCs of both inverters. Finally, Stage 4 encompassed the testing and analysis of the individual inverter prototypes’ ability to provide power to the local load, as well as their load sharing capabilities when connected in parallel. Paralleling between two three-phase inverters utilising hierarchical control was successfully achieved in the laboratory. Testing and analysis of the inverters’ ability to separately supply and share power when in parallel was conducted. Description: B.ENG (HONS) 2019-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/52743 Title: Study and implementation of home automation system with energy monitoring Abstract: Home automation is about “bringing life” into various devices installed in a building or apartment, giving home owners the access to control these devices using central hubs or smartphones. Home automations systems are quite common in both residential, commercial and industrial applications. The management and control of residential or commercial devices is relatively established but still lacks in the proper management of energy flows. Recently, home owners have become more aware of energy consumption and had started investing in energy monitoring systems to observe energy consumption and reduce energy waste. A real time power meter is an electronic device that is used to record the electric power being consumed by devices. The main objectives covered in this project is the design and construction of a single-phase electrical energy monitoring system compatible with the KNX system. Furthermore, the project also developed a graphical user interface (GUI) for energy monitoring and to provide a platform-based control of electrical equipment. This document describes the design, development and implementation of a low budget single-phase real time KNX power meter. In this project, an accurate power meter is built using the instantaneous power calculation method; 𝑝(𝑡) = 𝑉𝑚𝐼𝑚 cos(𝜔𝑡 + 𝜃𝑣)cos(𝜔𝑡 + 𝜃𝑖) A voltage and current sensing circuit was designed and constructed to sample the voltage and current of a connected load. These are then sampled using the KAIstack development board which carries out the power calculation and communication with the KNX system. The rms voltage, rms current, power, power factor and phase angle are transmitted in real-time to the KNX system and are displayed on a graphical user interface (GUI) over a HTTP connection. Thanks to the HTTP connection, users can easily control and monitor data from a tablet, computer, smartphone or any device which have access to Wi-Fi. The developed meter was targeted to be used on single phase electrical appliances. It can accurately measure true power regardless of the type of connected load being resistive, inductive, capacitive or a mixture of all. The designed KNX power meter, is aimed to set the basis for a system whereby energy management algorithms can be applied to increase energy efficiency inside a domestic application. Description: B.ENG (HONS) 2019-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/52711 Title: Design and implementation of a three phase thyristor phase controlled rectifier for a DC Motor Abstract: Variable speed control is a requirement found amongst various industrial high power DC motors. The three phase thyristor phase controlled AC/DC converter is a popular choice for DC motor adjustable speed drives (ASD). Phase angle control permits the adjustment of the DC average output voltage of the converter applied across the armature of the motor. This dissertation is concerned with the design and implementation of a six-pulse bridge rectifier to be used as a variable speed drive (VSD) for a separately excited DC motor. The main features within the design include; input supply AC voltage synchronization, design of a real time control firmware, thyristor gate triggering and a user interface. The converter demonstrated to work as expected and all elements within the system proved to be working correctly. The converter output DC voltage showed that the thyristors are being activated at accurate firing times. Adjusting the firing angle by means of the designed controller brought about a change in the output average voltage, thus regulating the speed of the motor. Description: B.ENG (HONS) 2019-01-01T00:00:00Z