Abstract

When heating an industrial hall-type building, the following types of heat demand must be considered: for heating, for domestic hot water preparation, for ventilation, for technological purposes, and for losses related to transport and distribution. This paper analyzes aspects related to the heat demand for heating an industrial hall, starting from the existing situation (heating with static radiators, with hot water as the heat transfer medium taken from the urban heating network at a price of approximately 718 lei/Gcal) and rethinking the decentralized hot air heating system with wall-mounted air heaters.  Generally, heat requirements are based on a simplified estimate, the accuracy of which de-pends on the designer’s experience in the field.  In this paper, the energy performance of the industrial hall analyzed was assessed taking into account the methodologies specified in the regulations. The particularities related to the building’s purpose (industrial building), the climatic zone in which the building is located, and the specific features of the type of heating system used (static bodies or wall-mounted air heaters) were taken into account. All these particularities are explicitly specified in the chapter dedicated to the case study, which makes the issues discussed easier to under-stand.

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Abstract

This paper presents a comparative analysis of control strategies applied to active power filtering, aiming to compensate a nonlinear three-phase load with a current of 20 A per phase. The study focuses on the comparison between direct power control (DPC) and indirect current control, analyzed in two distinct configurations: (i) reference current calculation based solely on the voltage regulator, and (ii) reference current calculation including the active component of the load current. The active power filter system is modeled and simulated in the Matlab/Simulink environment and subsequently implemented in real time on the dSPACE DS1103 platform for experimental validation. The evaluations are carried out under identical load conditions, allowing for a relevant and fair performance comparison. Experimental results highlight the ability of both strategies to reduce harmonic distortions and compensate reactive power, while showing notable differences in terms of total harmonic distortion (THD), DC-link voltage stability, and dynamic response to load variations. The comparative analysis provides a clear perspective on the advantages and limitations of each method, emphasizing the impact of the reference current calculation approach on the overall performance of the active power filter and its relevance for practical power quality compensation applications.

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Abstract

The purpose of this work is the implementation and experimental validation of a quasi-oriented rotor flux control algorithm on a full scale, railway locomotive traction system. This control method can be useful for industrial applications based on DSPs which have limited computation power, given the fact that the real time flux-oriented control needs relatively high computation power, especially for the flux estimator. The advantage of this method is given by the elimination of flux estimation as it assumes the control system is oriented. This way, a processor hungry control section is avoided, the flux control loop being also avoided. The control algorithm had been implemented in the Matlab Simulink environment, using the dSPACE RTI toolbox, for the DS1103 prototyping board. The dSPACE board had been used for the control of the full-scale traction system experimental stand.

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Abstract

This paper presents an experimental demonstration of a basic bidirectional energy transfer consistent with the Vehicle-to-Everything (V2X) concept, using a commercial Battery Management System (BMS) not originally intended for automotive applications. A 14-series (14S) lithium-ion battery pack integrated with a 48 V BMS and a bidirectional inverter is experimentally evaluated under low-power operating conditions. The study focuses on practical system integration, protection behavior, and cell balancing functionality using minimal laboratory equipment. The results show that essential BMS functions are sufficient to support controlled bidirectional energy flow at low power levels, highlighting both the feasibility and limitations of low-cost BMS-based V2X experimental setups.

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Abstract

Accurate estimation of photovoltaic (PV) energy production is essential for ensuring the optimal design, operation, and economic viability of solar installations. However, discrepancies often arise between predicted and actual energy yields, particularly in regions characterized by variable meteorological conditions. The paper presents a synthesis of methods for estimating energy production of photovoltaic systems. For two types of residential systems located in Craiova, a comparative analysis is presented between the estimated values obtained using the most efficient methods and the actual measured values. The research combines simulation-based predictions with real operational data collected over a defined monitoring period to evaluate the accuracy of commonly used estimation models. To estimate solar radiation and energy production, some of the most common specialized software for renewable energy sources were used. The findings reveal that estimation tools tend to overpredict energy output during periods of high temperature and unstable atmospheric conditions, while performing more accurately during stable seasonal intervals. These results highlight the importance of localized calibration of prediction models and the integration of detailed climatic data for improving accuracy. The study contributes valuable insights for system designers, operators, and policymakers seeking to enhance PV system reliability and advance renewable energy planning in Romania and similar climatic regions.

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Abstract

Despite its inexhaustible nature, the use of solar energy is temporally limited. In addition, the efficiency of fixed photovoltaic panels is influenced by climatic conditions over a day, resulting in lower efficiency of energy production (about 15%). To operate close to the maximum production point, the photovoltaic panels must be kept perpendicularly to the solar radiation. Therefore, there is a need for solutions to improve the energy efficiency of the PV solar panel and a solar tracker system could be a solution. The paper presents the features of a bi-axial solar tracking system developed by the authors in the laboratory and based on an Arduino Uno microcontroller platform. A small solar panel is oriented in the direction corresponding to the maximum energy point by means of two servomotors controlled by the microcontroller platform, which receives the information from a system of 4 photodetectors.

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Abstract

Circuit-breakers are essential for the safety and reliability of electrical power systems by interrupting fault currents un-der various conditions. Circuit-breakers must be capable of breaking single-phase short-circuit currents which can occur in two distinct scenarios. The first scenario involves effectively earthed neutral systems, where single-phase faults can generate high fault currents that the circuit-breaker must safely interrupt to prevent equipment damage and ensure personnel safety. The second scenario occurs in non-effectively earthed neutral systems, where double earth faults can appear on two separate phases, with one fault occurring on one side of the circuit-breaker and the other on the opposite side. Such conditions pose significant challenges for circuit-breaker design and operation, requiring careful consideration of their dynamic response and fault current interruption capacity. This paper presents the expected behavior of the circuit breakers and the real-life situations encountered during high-power testing of this type of equipment. Real-life testing reveals critical insights into performance limitations, transient phenomena, and operational reliability, providing valuable information for both equipment manufacturers and system designers. The study high-lights the importance of accurate modeling, thorough testing, and adherence to standards to ensure that circuit-breakers perform reliably under all anticipated fault conditions. The most severe condition is identified as a double earth fault occurring under phase opposition. Although additional tests are planned to confirm this, preliminary assessment suggests that under normal operating conditions (0° < φ < 30°), the current at the final breaking pole should not exceed the generator’s short-circuit current.

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Abstract

The present paper presents an exhaustive optimization method based on screening and zoom techniques and its application in two case studies involving electromagnetic devices. The method is based on the design of experiments technique, combining optimization algorithms with numerical simulations. The solution of the optimization problem is performed in two stages: global modeling (coarse optimization) and actual optimization (fine optimization). In the first stage, a partitioning of the entire feasible domain is per-formed, especially in the areas where there are extrema of the objective function. Their location is signaled by the sign variations of the local effects of the design variables calculated by a screening technique. In the second stage, the actual optimization takes place using the zoom technique, initiated around the point found in the first stage. The paper concludes with two case studies in which the application of the method on 2-D models of electromagnetic devices is exemplified. The optimization problems are to maximize the developed forces while maintaining the overall dimensions and the cross-sections of the coils, depending on two geometric parameters. The method was applied up to zoom level 5, obtaining a considerable improvement in the performances of the electromagnetic devices. The great advantage of the exhaustive method is the determination of the global extremum of the objective function, which becomes all the more expensive the greater the number of design variables and the finer the partitioning.

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ANNALS OF THE UNIVERSITY OF CRAIOVA – Electrical Engineering Series, no. 49, vol. 49, Issue  1, 2025 (click to download)