The aim of this work is to assess the technical and economic efficiency of using hybrid photovoltaic-thermal (PV-T) panels in the energy supply system of an urban residential complex in the Republic of Moldova, to improve energy efficiency and relieve centralized energy supply networks. This aim is achieved by developing a mathematical model of PV-T system integration into urban infrastructure in Simulink MATLAB, selecting and justifying the main equipment (PV-T panels, inverters, heat pumps, energy storage), simulating characteristic operating modes, and a comparative techno-economic analysis of the existing and proposed supply strategies. The proposed hybrid system uses solar energy to simultaneously generate electricity, provide domestic hot water and support space heating in a multi-apartment complex. The most important result is the substantiation of the technical feasibility and economic viability of integrating PV-T panels into urban buildings, reducing grid energy use during peak load with an acceptable payback period. The significance of the results lies in a comprehensive method for assessing the efficiency of hybrid solar systems under regional conditions. The study showed that PV-T panels not only increase solar energy conversion efficiency through effective cooling of the photovoltaic cells, but also relieve transformer capacity and reduce losses in distribution networks. The results can support regional programmes for renewable energy in the housing and utilities sector of the Republic of Moldova, the design of autonomous and hybrid energy supply systems for social facilities, and further research on optimizing distributed generation within an urban Smart Grid.
The objective of the study was to determine the feasibility of improving the energy efficiency and environmental performance of autonomous refrigerated transport by replacing the conventional diesel–generator set with an ammonia–hydrogen power plant. The relevance of the work is conditioned by the need to decarbonize and improve the reliability of autonomous refrigerated transport while ensuring the quality preservation of perishable products by partially or completely replacing air (oxygen) in the cargo compartment of the car with an inert gas (nitrogen). The use of liquid ammonia as a chemical carrier of hydrogen within the rolling stock was substantiated, and a coupled model was described for the joint operation of a catalytic cracking reactor, a hydrogen internal combustion engine with an electric generator, a heat-recovery system, and a nitrogen utilization unit. The material and heat balances of the power plant were compiled, and its operating and mass-and-size limits of applicability were determined. The conditions for thermal autonomy of the catalytic ammonia decomposition process via exhaust gas heat recovery and the afterburning of residual combustible components were established, ensuring a significant reduction of the required on-board ammonia reserve compared with the non-recovery scheme. The material balance regularities of ammonia dissociation were determined, substantiating the complete in-system utilization of the associated nitrogen flow. The obtained results confirm the possibility of replacing the diesel–generator set with an ammonia–hydrogen power plant without reducing the useful carrying capacity of the car at an operational cargo density of 0.3–0.4 t/m3.
The Tennessee-Eastman Process (TEP) model has served as a globally recognized standard for evaluating advanced control methods for unstable technological processes for over 20 years. Research data published in leading scientific journals are used to evaluate modern control algorithms and are accumulated in a dedicated repository. Analysis shows that the problem of eliminating unwanted oscillations in control actions caused by measurement noise and sensor discreteness, without reducing robustness and cost-effectiveness, remains unresolved. To achieve this goal, the following tasks were solved: a multi-faceted analysis of the physical, dynamic, and economic characteristics of the process was performed, based on which a hierarchical control structure with decentralized PI controllers was synthesized; advanced filtering methods have been developed and implemented, including discrete Kalman filters with constant-rate models for reconstructing continuous concentration signals, second-order setpoint filters in cascaded loops, and Smith predictors for delay compensation. Cross-coupling compensation and pressure stabilization schemes using additional control channels have been proposed. The most important results include the virtually complete suppression of high-frequency noise from level, flow, and concentration sensors without introducing critical phase delays; the elimination of excessive oscillations in valves and pumps, which radically reduces their mechanical wear; and the successful compensation of typical process disturbances while maintaining process operability. The significance of the obtained results lies in the fact that the proposed approach demonstrates for the first time the possibility of integrating observers and filters into a classical circuit architecture for controlling an unstable chemical engineering process.
The main objective of this study is to assess the effectiveness of Organic Rankine Cycle (ORC) turbines for recovering surplus thermal energy from cogeneration units during the non-heating season. To achieve this objective, the following tasks were addressed: municipal energy supply conditions in countries with extended summer periods were analyzed; international ORC experience was systema-tized by facility type, heat source, and power range; a conceptual scheme for integrating an ORC turbine with a thermal energy storage (TES) system was developed to smooth fluctuations in the waste-heat profile; and an analytical criterion for the techno-economic feasibility of ORC–TES systems at distributed generation facilities was derived, relating annual waste-heat availability to in-vestment payback. The most important results are as follows: TES integration increases the ORC turbine capacity factor by stabilizing the supplied heat flow while reducing required rated capacity; the generated electricity can cover peak summer air-conditioning loads without increasing equip-ment loading in the centralized power system; and criteria were formulated for preliminary screening of territories and industrial facilities suitable for such systems. The significance of the obtained results lies in developing a scientifically substantiated approach for converting seasonal waste-heat losses into additional electricity generation without increasing fuel consumption. Unlike previous studies, where thermal storage is mainly used to shift electrical or thermal load profiles, the proposed approach couples TES directly with an ORC turbine to convert otherwise unrecovered non-heating-season heat into electricity and introduces a quantitative payback criterion and a five-criteria procedure for facility selection.
Main objectives of the study have been formulated as the creation of the modified Red Deer Algorithm for optimal coordination of directional overcurrent relays in closed loop power systems, taking into account their total operating time under the coordination time interval constraints. These objectives were achieved by solving the following tasks: (1) obtaining an exact linear-programming solution for the time dial setting subproblem, replacing the heuristic sequential-update procedure used previously; (2) formulating a slack-penalized objective function to guarantee reliable convergence of the population-based search; (3) establishing an independent, non-circular criterion for breakpoint selection in looped coordination structures, applied to an eight-relay test network containing a six-relay ring and a mutually backed-up relay pair; and (4) performing a statistically grounded comparison with Particle Swarm Optimization under identical decision variables, objective function, and evaluation budget. The most important results are the following: the proposed algorithm converged to feasible solutions in every independent run, with a mean total operating time of 8.5244 s and a standard deviation of 0.0029 s over eight runs; there have been no constraint violations, confirmed for all six active relay pairs; the comparison algorithm also converged fully, and the difference between the best objective function values of the two algorithms was equal to 0.0002 s. The significance of the obtained results lies in demonstrating that the exact linear-programming evaluation combined with the slack-penalty and breakpoint concepts provides reliable, reproducible coordination for looped-network relay protection, achieving a 100% feasibility rate without requiring conservative or ad hoc penalty tuning.
