Abstract. Some of parameters in electrical systems cannot be considered as constants. In particular, some electrical loads should be described as unsteady because of physical reasons, e.g. arc and arc-resistance furnaces. One of the method to describe parameters of such loads is description by fuzzy numbers. Moreover, this description enables to determine optimal current of the system with unsteady parameters by an application of the optimisation technique called as fuzzy mathematical programming. The optimisation problem has been presented for one-phase system with sinusoidal waveforms. The obtained solution (optimal current) can be determined as crisp one (real numbers) in frequency domain in the numerical way. The determined optimal current has minimal RMS value in this case when the power constraints do not have to be fulfilled strictly because of changes of system parameters. It means simultaneously the minimisation of power losses in the system. This solution generalizes the classical optimisation solution obtained for the systems with constant parameters. In order to illustrate the problem the appropriate example has been presented.

No abstract

PurposeThe purpose of this paper is to deal with the problem of symmetrization of asymmetrical three‐phase delta connected nonlinear load. In the model of the three‐phase sinusoidal voltage source have also been included inner impedances. The purpose is to obtain symmetrical line currents of the voltage source, to minimize RMS values of currents and to minimize higher harmonics generated by nonlinear loads.Design/methodology/approachThis symmetrization of the system is realized by means of a symmetrizing system, which is composed of LC one‐ports. In order to solve the problem the symmetrical component theory is applied. The structure of symmetrizing system is consisted of two components: parameters determined for the basic harmonic and the filter for elimination of the higher harmonics generated by nonlinear loads.FindingsAfter symmetrization line currents of the source will be symmetrical with lower RMS values than before symmetrization, and the source will generate the greater active power than beforehand.Research limitations/implicationsThis approach can be used for inertialess (non‐reactive) elements in systems, where currents are periodical.Practical implicationsThe results of symmetrization can be useful for high‐power systems where LC one‐ports can be used, e.g. for arc furnaces.Originality/valueApplication of presented methods makes possible to improve the working point of the system, i.e. voltage source can generate greater active power than before symmetrization and line currents can be symmetrical.

Purpose -The problems presented in the paper concern a three-phase four-wire system with periodical non-sinusoidal voltage sources with inner impedances and asymmetrical linear three-phase loads. Generally, the line currents of the system are asymmetrical. The purpose of the paper is to improve the working conditions of the system by means of symmetrization. Design/methodology/approach -A method of symmetrization of these systems has been proposed. In this paper, the symmetrization problem has been solved by using the symmetrical components theory and compensation of reactive power for each of voltage harmonics under consideration. Findings -After symmetrization currents become symmetrical and their RMS values and active power on source impedances become lower. The realization of symmetrization makes possible: reduction of RMS values of source currents, an assurance of equal loads for individual phases of the system supplied from sources with inner impedances, after symmetrization the voltage source generates and load consumes greater useful active power. Originality/value -The simplified structure of the compensator has been proposed in the paper. The symmetrization has been presented with reference to new structure of the compensator.

No abstract

Glass fiber (GF) Sheet Molding Compound (SMC) composites are popular lightweight materials due to their good processability. Hybrid SMCs expand the field of operation, combining the high stiffness of unidirectional carbon fibers (CF) with the economic efficiency of GF. Combinations of manufacturing deviations (delamination, varying GF content, CF misorientation) occur during the production of hybrid SMCs and impede the mechanical performance of the part. A function-oriented quality assurance instead of strict tolerances is proposed. Finite element (FE) simulations are computationally too expensive for an assessment within the cycle time. Hence, surrogate models are trained on multiple parameterized FE simulations. The surrogate models shall allow for an individual functional assessment in real-time based on integrated measurement inputs. This work focuses on the generation of parametrized FE simulations for measurement inputs and surrogate modeling. Simulations and surrogate models show acceptable deviations from tensile tests for multiple combinations of manufacturing deviations. The measurement uncertainty of the stiffness prediction is assessed for both the FE simulation and the surrogate models in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM).

The research work has principally been related to selected problems in the field of analysis and synthesis of systems aimed at symmetrisation and improvement of some power quality parameters. This paper constitutes the second part of the report on the research. It has been devoted to three-phase system symmetrisation as well as effective elimination of higher harmonics and substantial improvement of power quality by means of hybrid active power filters.

The research work has principally been related to selected problems in the field of analysis and synthesis of systems aimed at symmetrisation and improvement of some power quality parameters. This paper constitutes a first part of the report on the research. It has been devoted to effective elimination of higher harmonics and reactive power compensation by means of parallel active power filters. The other problem discussed in this paper is related to this issue and it is very important from the economic point of view; it addresses optimal sizing and placement of active power filters in investigated power networks.