Journal of Energy - Energija

A Novel Multi-Loop Base Carrier Mark PWM Strategy for Leakage Current Reduction in Grid-Connected Transformerless Inverters

2025-11-04T17:25:50+01:00

This paper presents a novel multi-loop Base Carrier Mark (BCM) pulse-width modulation strategy to address leakage current challenges in grid connected transformer-less photovoltaic inverters. The proposed approach introduces a combination of sequential level shift, single-loop, two-loop, and three-loop carrier rotation techniques in BCM generation, specifically designed to minimize common-mode voltage variations and suppress leakage current. The method’s effectiveness was validated through comprehensive simulation studies using Matlab/Simulink, evaluating eight distinct BCM configurations. Results demonstrate that the proposed multi-loop BCM strategy, particularly in STATE-V configuration, achieves superior leakage current suppression while maintaining high system performance. This configuration reduces leakage current significantly below the standard 300mA limit without compromising other performance metrics. The strategy also demonstrates favorable outcomes in Total Harmonic Distortion (THD < 2% in STATE-VI), common mode voltage stability (optimal in STATE-III), and system efficiency (peak performance in STATE-IV).These findings present a significant advancement in transformer-less inverter technology, oﬀering a practical solution to the critical challenge of leakage current in grid-connected PV systems.

An Economy Aspect of Different Nuclear Energy Development

2025-12-04T14:55:04+01:00

Humanity must face the reality that it cannot depend indefinitely on combustion of coal, gas and oil for most of its energy needs. In the long term, nuclear energy seems to be the only one capable of replacing fossil fuel energy in the production of electricity in the world. The specific greenhouses gases (GHG) emissions of nuclear power plants are among the lowest of any electricity generation method. Nuclear power is cost-competitive with other forms of electricity generation, except where there is direct access to low-cost fossil fuels.

Global primary energy needs rise more slowly than in the past, but still an increase of 19% between today and 2050 is expected according to World Energy Outlook 2022. Electrical energy needs will rise faster than primary energy needs and the electrical energy production has to be with low GHG emissions due to global warming mitigation. We assume in our scenarios that nuclear energy will be global electricity production leader with a percentage of 36.7 % in the year 2050. In addition, we assume that all thermal power plants will be replaced by uranium or thorium fuel cycle nuclear power plants by the year 2057.

This paper describes a comparison of different long term nuclear energy development scenarios according to costs. The calculated saving of GHG emissions in case of significant use of nuclear energy in the future in the world is emphasized.

Benchmark Calculation of FHR Fuel Assembly Phase I-C Depletion Exercises

2025-12-04T15:05:27+01:00

This paper presents our initial results for the Fluoride-salt High-temperature Reactor (FHR) physics benchmark calculations in Phase I-C, focusing on depletion exercises 5 and 6. In this Phase, the model is extended from the previous OECD benchmarks (Phases I-A and I-B) by transitioning from a pseudo-2D to a full 3D representation of a single FHR fuel assembly featuring TRISO fuel, graphite moderator, and FLiBe coolant. The pseudo-2D geometry is extruded axially, incorporating top and bottom reflectors (FLiBe and graphite), with radial periodic and axial vacuum boundary conditions applied. The benchmark’s challenging aspects, including the complex 2D geometry of the plate-type assembly with TRISO fuel, the double heterogeneity spectral calculation, and the use of novel materials (FLiBe coolant and europium as a burnable poison), necessitate the use of Monte Carlo methods. We used the Serpent 2 code (versions 2.1.32 and 2.2.1) with two versions of the ENDF/B library (VI.8 and VII.1). Exercises 5 and 6 subdivide the fuel assembly into 20 axial regions with distinct material temperatures, however the primary distinction between these two exercises is the inclusion of integral burnable absorbers (Eu-151 and Eu-153 oxides) in the latter. The paper presents the results for k_eff, recoverable energy per fission, fission density rate, and axial offset in selected burnup points up to the final burnup of 70 GWd/tU. Additionally, we assessed the impact of different cross-section libraries, xenon modeling (transient versus equilibrium), and the depletion step length on the benchmark results.

Verification of the IRIS Numerical Model for the Severe Accident Calculation

2025-12-04T15:25:56+01:00

The interest in the IRIS (International Reactor Innovative and Secure) reactor is revived by today's popularity of small modular reactors. The IRIS reactor project, led by Westinghouse Electric Corporation, was active in the first decade of the 21^st century. Different groups of institutions such as nuclear manufacturers, academic institutions, national laboratories, etc. from 10 countries around the world participated in the IRIS team.

IRIS is an integral, modular, medium sized (1000 MWt) pressurized water reactor. The IRIS reactor pressure vessel houses, beside the reactor core, also other major reactor coolant system components such as the pressurizer, reactor coolant pumps and steam generators. The lack of large pipes ensures high safety of the IRIS power plant and eliminates many causes of major accidents. This principle is known as “safety-by-design” approach.

Polytechnic of Milan and the University of Zagreb were leading institutions in performing safety analyses for the IRIS reactor. The explicit coupling of RELAP5 and GOTHIC codes has been set up to cover the sequence of most probable LOCA transient events. This was necessary because the reactor vessel and the containment, once when the LOCA is initiated, become one hydraulic system with strong interaction. They exchange mass and energy which affects both systems in short time period and therefore cannot be treated separately as in a conservative analysis of a classic PWR nuclear power plant. In addition, the ASYST code model was recently developed to cover possible severe accident sequences. The core heat structures were replaced with SCDAP components to simulate core degradation. A couple of different GOTHIC models were developed to represent various arrangements of passive safety systems. A steady state analysis was performed to confirm the applicability of the IRIS numerical model in the safety analyses.