Journal of Energy - Energija

Adaptive PWM Control and Dynamic Switching Frequency for Leakage Current Suppression and THD Control in 3-Level NPC Inverters

2025-11-28T15:53:26+01:00

This paper presents an adaptive operation algorithm for 3-level NPC grid-connected inverters that simultaneously addresses leakage current suppression and total harmonic distortion (THD) control in transformerless photovoltaic systems. The proposed approach integrates intelligent PWM method selection with dynamic switching frequency optimization to achieve optimal inverter performance under varying operating conditions. The algorithm employs a hierarchical control structure where high-level decisions regarding PWM method selection between Phase Disposition (PD) and Phase Opposition Disposition (POD)
PWM are made based on real-time leakage current measurements, while low-level switching frequency adjustments using perturbation and observation (P&O)
technique maintain acceptable THD levels. Comprehensive PSIM simulation validation demonstrates that the algorithm achieves up to 40% reduction in leakage current under fault conditions while maintaining grid current THD below 3.5%, meeting international safety and power quality standards. The algorithm’s response time of 0.5 seconds for leakage current threshold violations and convergence within 1.5-2.0 seconds for THD optimization provides adequate protection for safety applications. The software-based solution requires no additional hardware components, making it suitable for both new installations and retroft applications in commercial inverter systems. The demonstrated performance under realistic fault conditions and grid disturbances confrms the algorithm’s practical viability for transformerless PV inverter applications.

Performance Based Risk Informed Fire Modelling Evaluation of Electrical Equipment Functionality in Nuclear Power Plants

2025-12-11T16:18:34+01:00

Introduction of risk-informed and performance-based analyses into fire protection engineering practice exists in both the general fire protection and the nuclear power plant fire protection applications. Risk-informed and performance-based approach relies on application of validated and verified fire modelling to estimate fire generated effects that are arising in predefined fire scenarios for fire protection related applications in nuclear power plant. Regulatory bodies have used risk-informed insights as a part of its regulatory decision making for the past thirty years. Before performance-based approach came out, all regulatory prescribed requirements relied on deterministic approach with ultimate condition that one complete shutdown train together with auxiliary support features is free of fire damage. Performance-based approach relies upon calculable performance results to be met but provides more flexibility in achieving established performance criteria during all phases of plant operations. Nevertheless, fire modelling is finding its benefits in design basis engineering, fire hazard analysis, nuclear safety capability assessment and probabilistic risk assessment. To demonstrate such capabilities, an example on fire development in Nuclear Power Plant Safety Related Pump Room with respect to possible loss of one safety shutdown path is modelled with a fire simulator computer tool.

Point-Kernel Shielding Applications of Sievert Integral

2025-12-04T15:15:01+01:00

The application of a point-kernel technique in gamma radiation shielding calculations has a long and successful history. Using this approach radiation sources of various shapes such as point, linear, planar, or volumetric can be subdivided using the linear superposition principle to calculate total radiation received at a detector. Mathematically, any form of a distributed source may be treated as a summation i.e. integration of the radiation received from an equivalent number of point sources, for which exponential point-kernel function is analytically known. Fundamental assumption is that there is no interaction of individual, point sources which together represent total distributed radiation source. The effects of geometrical boundaries and gamma scattering are not included in this treatment, so user should be aware of these inherent limitations when comparing with reference results, such as Monte Carlo (MC) solution. This paper presents specific case of gamma flux attenuation from a distributed line source of photons in front of a slab shield, but is actually part of a larger effort, whose final goal is a general-purpose point-kernel code development. The solution of a line source with slab shield is known as the secant or Sievert integral, which cannot be evaluated analytically, so auxiliary tabulated function is introduced to facilitate bilinear interpolation on angle and shield thickness. Such code written in C-language will provide graphical user interface to assist user with necessary input data preparation and selection of predefined shielding materials for which Taylor buildup factors are provided. This paper gives programming and numerical aspects of such point-kernel code for which results of the test cases are compared with a MC solution of SCALE6.1.3 code package.