https://www.um.edu.mt/library/oar/handle/123456789/101849 Mon, 20 Apr 2026 22:08:06 GMT 2026-04-20T22:08:06Z https://www.um.edu.mt/library/oar/handle/123456789/103009 Title: Control of DC microgrids for distributed generation including energy storage Abstract: In recent years DC microgrids have attracted significant interest in research, with various literature published covering areas such as system design, control systems, and energy management. This interest can be attributed to the increase in use of DC energy generation systems, such as photovoltaics (PVs), and energy storage systems, such as battery banks. The aims of this research were: (a) to build a laboratory-based DC microgrid system on which control algorithms can be developed, applied, and tested, (b) to implement and improve the primary control system, and (c) to develop a battery management system. A lab-based 48V DC microgrid consisting of two 2.5kW Buck converters, a 1.5kW Bidirectional converter connected to a 24V battery bank, and a resistive load bank was built. Detailed modelling of the Buck and Boost converters was performed, deriving the small signal models and the transfer functions for both converters, which were needed to design the control systems. The two Buck converters and the Bidirectional converter were designed, built, and tested. The converters were connected in parallel and shared a common resistive load using droop control. Three droop control methods were implemented and tested: V-I droop, I-V droop, and a newly proposed method called Combined Voltage and Droop (CVD). A battery management system (BMS) was developed to provide high-level control to the Bidirectional converter. The Buck and Bidirectional converters operated successfully both as standalone units and within a DC microgrid configuration. V-I droop control provided correct current sharing capability with good results, however its load sharing response was slower than CVD control. I-V droop control resulted to be unstable during practical implementation due to the high gain and bandwidth of the voltage control loop, which interacted with the bandwidth of the anti-aliasing filter in the voltage feedback path. The proposed CVD method solved the instability issues experienced by using I-V droop, making the control system work in a stable way by providing a means to adjust the bandwidth of the voltage control loop. Successful operation was also attained from the DC microgrid setup, which was operated in two scenarios: (1) with the two Buck converters and the Bidirectional converter (operated as a Boost converter) all sharing the resistive load among them, and (2) with the Bidirectional converter (operated as a Buck converter) charging the battery bank and the two Buck converters supplying the load current and input current of the Bidirectional converter. The BMS was successfully tested with simulations, utilizing the load current and state of charge (SOC) of the battery bank to select the mode of operation of the Bidirectional converter among battery charging, load sharing/supplying, and idle modes. Through this project, an experimental lab-based DC microgrid was built, serving as a valuable setup for further research on control algorithms of renewable energy conversion systems. By using the lab-based DC microgrid, the new CVD droop control method was developed, which offers advantages over the other droop methods. The BMS developed set up the basis for further development in the area. From this thesis there are two main contributions: (1) the novel droop control method (Combined Voltage and Droop method) which offers an alternative to the standard I-V droop control system, and (2) an algorithm for a BMS which provides simple but effective control of the Bidirectional converter and its storage system. Description: Ph.D.(Melit.) Sat, 01 Jan 2022 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/103009 2022-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/101931 Title: Plant automation with motion control Abstract: Automation technology in manufacturing is continuously advancing to boost productivity. Continuous advances in technology aims to decrease human error significantly. In fact, by time, human intervention has drastically reduced and on the other side flexibility in the process control has significantly increased. In this dissertation, a plant automation system was designed. The aim of the designed system was to continuously cut pieces from a material according to the length specified by the operator while the material was constantly moving on a conveyor belt system. The plant includes several variable speed drives with position control. All drives must simaltaneously work together in an automation task. A dedicated motion control profile was first designed to achieve the designed functionality for the operation of the automation plant. Safety features for the plant were taken into account to ensure reliable operation. Eventually, the motion control profile for all drives was implemented via the various motion control blocks within the PLC’s programming software. Furthermore, two user interfaces were developed for both control and monitoring purposes. These include an HMI panel and a user designed web-page. Continuous monitoring of the movement and position of the drives was presented on each control platform respectively. Both designs were designed to match the operator’s objectives and abilities so that all essential information is displayed in an effective way. This will aid plant operators to observe the plant operation more easily, while eliminating the possibility of systems malfunction. The system’s performance was measured by several encoders to verify correct operation. It was ensured that all drives travelled the required distances precisely, and at the stated velocity. Several cases were tested on the designed system, each time varying the cutting length and the diameter of the material to be cut. The results obtained were compared to investigate the effects on the synchronized velocities and the distances moved by all drives respectively. Lastly, it was confirmed that irrespective of the number of cutting cycles performed, the system’s accuracy was still within defined limits. Description: B.Eng. (Hons)(Melit.) Sat, 01 Jan 2022 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/101931 2022-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/101930 Title: Energy optimisation of the control of motors used for water boosting applications Abstract: The use of pumps for water boosting is a common application in process cooling systems within industrial plants. In the past, the control side of such pumping systems simply used to be a Direct On Line (DOL), Open Loop (OL) system that required additional manpower to control the flow mechanically. As time passed, such systems were replaced by a Closed Loop (CL) system that made use of a Variable Frequency Drive (VFD) and a number of sensors such that the system is fully automated and therefore requires minimal human intervention. Therefore, the aim of this project was to investigate and go through a commissioned process cooling system, and identify areas where the system could operate in a more efficient manner. This was carried out by implementing a simulation model on Matlab/Simulink and investigating several operating scenarios which are currently being applied within the process cooling system, and also propose additional changes which would result in an improved efficiency of the system. The simulations carried out included a comparison between the operation of pump using DOL or a VFD, and also a comparison between the operation as currently implemented and the proposed change of adding a common header to the process cooling system. From the results achieved it was concluded that by operating using a VFD surely is much more efficient than DOL. Moreover, the change which proposes an additional common header is advantageous at certain operating points and therefore to make full use of this change the control system must also be updated. Finally, the effect of changing the pump rating from 11kW to 7.5kW was explored and the results yielded show that by changing to 7.5kW is advantageous as the pumps are correctly sized. Description: B.Eng. (Hons)(Melit.) Sat, 01 Jan 2022 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/101930 2022-01-01T00:00:00Z