https://www.um.edu.mt/library/oar/handle/123456789/519 The Faculty of Engineering is located at the University's main campus and offers tuition and supervision to about 477 students at both undergraduate and postgraduate levels while conducting research in all fields covered by its departments. Wed, 19 Aug 2026 03:55:23 GMT 2026-08-19T03:55:23Z https://www.um.edu.mt/library/oar/handle/123456789/148487 Title: Grid-forming converters with frequency & voltage active support and distributed cooperative control for active and reactive power sharing Authors: Li, Guangdi; Zhang, Yaodong; Gao, Hao; Zhou, Bowen; Xiao, Zhaoxia; Micallef, Alexander; Apap, Maurice; Licari, John Abstract: In islanded AC microgrids, grid-forming converters (GFCs) often employ virtual synchronous generators (VSGs) with virtual inertia and droop characteristics. However, this approach can lead to deviations in frequency and voltage from their rated values, affecting power quality and potentially compromising the security of the power supply. In addition, the power allocation is influenced by line impedance, and due to the uneven parameters among GFCs, it cannot be fully evenly shared. This paper presents a distributed control strategy for GFC that integrates frequency-voltage active support with power coordination control. This distributed strategy is implemented using multi-agent consensus theory, which ensures that the frequency and voltage of the GFCs remain at their rated values while accurately distributing active and reactive power across each GFC. It addresses the limitations of VSG control while maintaining a lower communication burden. Furthermore, several Hardware-in-the-Loop (HIL) experiments were conducted across multiple cases, validating the effectiveness of the proposed strategy and further enhancing it through cross-case analysis. Sun, 01 Jun 2025 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/148487 2025-06-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/148478 Title: Sampling design of energy storage converter Authors: Xiao, Zhaoxia; Liu, Wenlong; Xiong, Junjie; Gao, Jian; Sun, Puhang; Fang, Hongwei; Micallef, Alexander Abstract: Energy storage converters are widely used in power systems, new energy vehicles, wind power generation and other fields, and are of great significance in grid peak shaving, valley filling, smoothing new energy fluctuations and other aspects. The sampling part plays an important role as a bridge between the primary and secondary side control of the energy storage converter device. The accuracy of the sampling part directly affects the accuracy of the control algorithm. The sampling part of this paper includes a sampling circuit, a conditioning circuit and a calibration design. The sampling circuit is composed of a Hall voltage and current sensor. The AC voltage and current signals output by the sensor cannot be directly input to the A/D converter of the DSP. The output values need to be converted into 0 to 3V signals through the signal conditioning circuit and then input to the A/D converter. The calibration design is to calibrate and normalise the digital quantity output by the A/D converter, and then apply it to the control algorithm to improve the speed of the control algorithm. Finally, the accuracy of the sampling is verified by comparing the oscilloscope waveform with the upper computer sampling waveform through precharging experiments and energy storage discharge experiments of the energy storage device. Wed, 01 Jan 2025 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/148478 2025-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/148476 Title: Mitigating power quality issues due to renewable energy in Maltese LV distribution networks with battery energy storage systems Authors: Galea, Semira; Licari, John; Micallef, Alexander Abstract: Traditional electricity distribution systems have predominantly relied on centralized generation, limiting their ability to integrate diverse energy sources. As the penetration of renewables increase further, innovative solutions are essential to maintain network reliability and efficiency. This study investigates the integration of Battery Energy Storage Systems (BESSs) into low-voltage networks, addressing the challenges posed by the increasing adoption of renewable energy sources. A detailed analysis of energy storage integration was conducted, including simulations of low-voltage feeders with integrated BESSs, along with the strategies used for optimal BESS placement and capacity sizing. Two discharge strategies (peak shaving and load following) were evaluated to assess their impact on power flow dynamics within the network. Simulation results show that peak shaving significantly enhances the voltage stability along the feeder. Additionally, the research highlights that peak shaving offers advantages over load following, primarily due to operational flexibility requirements. The integration of BESSs not only improves network performance by minimizing energy wastage and maximizing solar energy utilization but also promotes sustainability by improving power quality within low-voltage distribution networks. Sun, 01 Jun 2025 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/148476 2025-06-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/148475 Title: Renewable hydrogen production from reverse power flows in the Maltese medium voltage distribution network Authors: Gallo, Pierluigi; Licari, John; Massaro, Fabio; Micallef, Alexander; Ruffino, Salvatore; Spiteri Staines, Cyril Abstract: The continued growth of nonprogrammable renewable energy sources, such as wind and photovoltaics, which is necessary in the energy transition process, is leading to the emergence of a number of issues for electric grid operators. Among these are reverse power flows, which consist of power going up from the distribution grid to the transmission grid at the time generation exceeds demand. In mitigating this phenomenon, power-to-gas plants can make an important contribution. In this paper, an optimization study is presented for the sizing of a power-to-hydrogen plant consisting of a PEM electrolyzer, a compressed hydrogen storage system, and a fuel cell for local hydrogen-to-power capabilities. The model was applied to the case study of an industrial medium-voltage distribution network in Malta, evaluating a scenario in which the currently installed photovoltaic capacity was doubled from the current 2 MWp to 4 MWp, according to existing expansion plans. The optimal results obtained allow for an 81.52% reduction in reverse power flows, while producing 4 tons of renewable hydrogen per year. Sun, 01 Jun 2025 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/148475 2025-06-01T00:00:00Z