Digital Library University of West Bohemia
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Recent Submissions
Quality Assessment of Noisy and Enhanced Speech with Limited Data: UWB-NTIS System for Voicemos 2024
(IEEE, 2026) Kunešová, Marie; Pražák, Aleš; Lehečka, Jan
Voltage Space of Five-Phase Voltage-Source Inverters
(IEEE, 2025) Laksar, Jan; Komrska, Tomáš
Multiphase systems offer several advantages over their three-phase counterparts, such as torque enhancement, fault-tolerant operation, etc. In five-phase systems, the inverter output voltage can be increased using the third harmonic, which produces the voltage vector in the x−y plane with additional torque and the zero-sequence, torque-non-producing component. The maximum voltage is obtained with a non-circular trajectory of the voltage vector in the x−y plane, while the machine's optimal operation requires its circular trajectory. The paper focuses on analyzing the space for the voltage increase with respect to the constraints given by the dc-link voltage on the one hand and by the x−y and non-zero voltage component on the other. Theoretical conclusions are verified by simulations and experimental measurements.
Sensitivity analysis of digital twin model for energy community PV system
(2025) Bělík, Milan; Rubanenko, Olena
The current energy situation in Ukraine is researched, considering the analysis of damages from missile attacks during the war. One of the ways to improve Ukrainian energy security is defined as decentralization of energy resources comprised with digitalization, decarbonization, democratization and deregulation (5D) increasing flexibility of the sector. The objectives are to examine in detail the 5D strategy. Distributed renewable energy sources are defined within the frame of Energy Community (EC) which was developed to adapt to current shortages in Ukrainian centralized grid. The EC digitalization is based on Digital Twin (DT) concept targeting design, monitoring, operational modifications and developing recommendations for the stable and optimal operation of photovoltaic systems. Energy community development and optimization include technical, meteorological, social, financial and environmental factors. Criterion programming was chosen as an effective solution to complex optimization problems. Sensitivity theory application is the basis for simplifying and optimizing the process of EC management. A model energy community ‘shelter city’ was created. The article highlights the problem of PV modules biological corrosion and suggests ways to eliminate it. In cases when biological corrosion cannot be avoided, approaches reducing its harmful effects are proposed to help during the design stage of a PV plant.
Voltage Zero-Sequence Components in Optimal Control of Five-Phase PMSM Drives
(IEEE, 2025) Laksar, Jan; Komrska, Tomáš; Suchý, Ondřej; Šmídl, Václav
This paper investigates the utilization of the zero-sequence component (ZSC) to increase the voltage and enhance the operation area of five-phase electric drives with permanent magnet synchronous machines (PMSM). Although the ZSC allows reaching higher voltage, its application in multiphase drives is constrained by the usage of x-y planes activated by harmonic components. Since some odd harmonics allow torque enhancement, these planes are typically involved in voltage and current control as part of field-oriented control strategies (FOC) to maximize the torque while minimizing the losses (e.g., Joule losses in the Maximum Torque per Ampere strategy). In five-phase systems, the third harmonic is used for torque enhancement, which affects the maximum value and shape of the resulting voltage waveform across the torque-speed map. Consequently, the space available for ZSC injection is limited and depends on the actual operation point. This paper presents an analysis of how ZSC can be leveraged within these constraints to improve the torque-speed operating map of a five-phase PMSM drive, especially in the field-weakening region. Experimental results obtained on a laboratory five-phase PMSM setup validate the theoretical findings and demonstrate the practical benefits of the proposed approach.
Application of Composite Materials for Thermal Storage in the Heat Supply System in the Czech Republic
(Trans Tech Publications Ltd., 2025) Volf, Michal; Nezbedová, Eva; Kottner, Radek
This paper investigates the application of polymer materials for low-temperature, pressure-less thermal storage in Czech district heating systems integrated with high-performance heat pumps. A dynamic simulation was conducted for a residential building of 180 occupants, equipped with a 32 kW heat pump, 10 kW photothermal panels, and 200 m³ of stratified water storage divided into preheating and high-temperature sections. Composite tanks for thermal storage can provide lower cost per cubic meter of storage, superior structural resilience under thermal cycling, and competitive environmental performance relative to polypropylene alternatives. The findings highlight composite storage as a technically and economically viable pathway for enhancing flexibility, efficiency, and decarbonization in Czech district heating networks.