J. P. Karunadasa

The increasing demand for compact, efficient, and cost-effective power conversion systems across sectors such as renewable energy, industrial automation, and telecommunications has highlighted the need for high-performance DC-DC converters. This paper presents the design, implementation, and experimental validation of a 500 W half-bridge LLC resonant DC-DC converter for 63-75 V input and a regulated 14.5 V output. A key feature of the design is resonant-tank optimization to maintain inductive-region operation and allow soft switching, with experimental evaluation of the soft-switching margin that identifies where ZVS degrades near high-load operation. The incorporation of GaN FETs allows 100 kHz operation with peak efficiency above 90%, and a controlled GaN-versus-MOSFET comparison on the same platform under identical conditions shows a load-dependent efficiency improvement that increases toward higher output power, ranging from approximately 1% to 10%. Practical high-frequency hardware effects, including gate-drive and auxiliary-winding oscillations, are characterized and mitigated using a simple decoupling-and-gate-tuning approach. In addition, an adaptive protection framework is integrated, including configured input over- and under-voltage thresholds and multi-level over-current protection, to provide safe operation. Experimental validation through efficiency measurements and dynamic-load testing confirms stable behaviour over the tested operating range.

As the power system continues to evolve, the dynamic nature of synchronous generator control systems, excitation, and governor systems play important roles in determining the power system’s behaviour and performance. These systems consist of specific parameters, and their values change over time due to factors such as regular maintenance, frequent start-ups and shutdowns, and aging equipment. Hence, a standardized and locally applicable methodology is essential for parameter estimation, mainly in aged power plants of Sri Lanka. Recent research focuses on improving and optimizing existing parameter estimation techniques. In contrast, this research proposes a systematic approach for parameter estimation combined with field tests, which are conducted using customized test kits developed for the available excitation system in the Sapugaskanda power station. The proposed methodology is applied to a 20 MW heavy fuel synchronous generator in the power station, which has been in operation for about 40 years. The parameter estimator tool in MATLAB was used for parameter estimation methodology. The results evidenced that the proposed methodology is suitable to address the challenges of parameter estimation, especially in aged power plants. This can provide a practical and cost-effective solution, and the findings of this study can be adapted to other power plants that are facing similar challenges.

Lithium-ion batteries (LIBs) play a critical role in electric vehicles (EVs) and hybrid electric vehicles (HEVs) and degradation of LIBs influences lifetime, reliability, safety and dependability. The ability to assess and quantify degradation enables assessment of LIB’s true state of health. This paper investigates LIB degradation using a pseudo two-dimensional (P2D) model, particularly focusing on the changes to Electrochemical Impedance spectroscopy (EIS) results due to degradation. Three key degradation mechanism are considered and the impact of State-of-Charge (SoC) and temperature on EIS results are discussed. This paper also identifies the need for a more realistic approach to assess degradation. Simulations are conducted considering four repetitive standard drive cycles (viz., HTDDT, HWFET, US06 and OCTBC) for a vehicle travel distance of 150,000 km for each case. The cycle counting method is used to convert partial SoC variations during a drive cycle to an equivalent full cycle count which is then used within the degradation model to modify the parameters to represent the P2D model. This study demonstrates a robust process for analyzing degradation dynamics. The methodology presented here can guide future researchers with experimental data, enabling validation and refinement of model parameters to advance LIB degradation analysis and improve battery life predictions under operational scenarios.

Majority electronic fan regulators available in the market feed significant amounts of harmonics into the fan, which leads to fan overheating and frequent failures of fan capacitors. This paper presents a design and development of a new electronic fan regulator that feeds negligible amounts of harmonics into the fan, and hence offers more reliable fan operation with smooth control and ripple free speed.The paper first reviews different forms of power electronic based control applicable to single-phase induction motors, and then identifies six topologies suitable for ceiling fans, based on the simplicity and cost effectiveness in meeting the performance targets. Final topology for the new design was selected after simulation of each short-listed topology to assess relative performances in terms of lesser harmonics, ripple free speed, smooth control, and cost. Finally, a prototype was built of the selected topology for a 70W single phase ceiling fan and test results verified the simulation results. Details of investigations, design, simulation, and test results are given and discussed.