Harmonics analysis is established by international standards as well as national norms [6], [7]. There are also definitions and calculus relationships for the indicators considered representative for this non quality aspect of the electric power. Among the harmonics analysis methods, the authors have dealt with application of DFT, given the fact that were to be analyzed acquired waves experimentally, using data acquisition boards. Experiences in using DFT, difficulties and highlighted errors as well are materialized in this paper, which is of great use to practitioners in this field.

Next, there is made a distinction between the a.c. and d.c. current waves in defining the harmonics indicators, which gives accuracy and expressivity to the harmonic analysis.

The paper deals with techniques to accelerate the DWT power quality analysis. A brief description of a non-spline interpolation schematic is provided firstly. It is used for the evaluation of the first components near the right border of the signal. Comparisons were made between power quality indices, shape of details waveforms and runtimes, considering data acquired on stand, corresponding to a driving system using chopper and DC motor and respectively waveforms acquired from the secondary winding of the excitation system used to supply a generator. FFT and 3 distinct original functions were used for comparison. Similar results were generated by all methods. The spline-free interpolation technique, which used mean slopes, proved to be a better option when the analyzed signal’s periodicity is questionable, because it exhibited halved runtimes as compared to the spline interpolation technique. Two multithreading techniques, relying on a horizontal and respectively on an interleaved schematic, were afterward analyzed considering their performances relative to the DWT decomposition and respectively re-composition of single-phase currents or voltages. The analyzed filters had different lengths: 4, 6 and 8. 10 sets of 300 consecutive decompositions of signals consisting in 36864 samples were used as input data. Our Java programs implementing the horizontal technique revealed the diminishing of runtimes for all analyzed filters during the decompositions by 16%…23%, the technique being more efficient for shorter filters. Another multi-threading technique, relying on an interleaving schematic, was considered for the reconstruction of signals. It proved to be non-effective, revealing increases of runtimes in the range 19%…23%. Similar results were obtained with the horizontal technique. Finally a multithreading technique, relying on a vertical schematic is presented. Using it, savings of 45% of runtimes were revealed by tests made on three-phase systems.

The paper deals with MATLAB/Simulink models of single-phase active filters used for reducing the harmonic level and electromagnetic interference and to get compliance with the power quality standards. Four cases are modeled and studied in order to design and tune the best configuration for the active filter. Two of them are determined by the configuration of the load, which consists of a single-phase rectifier which feeds a resistive load, having a capacitive dc filter as a first setup and an inductive dc filter as the second setup. The single-phase active filtering system is based on a single-phase Voltage Source IGBT inverter with dc-link capacitor and a complete current control system that uses two different pulse-width modulation techniques. The two switching techniques, triangular carrier and hysteresis, determine the third and the fourth cases. The power quality and the existing standards are discussed, including the disturbances in a power system for a single-phase rectifier. The harmonics, how they are generated, and what problems they may introduce in the power system, are presented. The reference current for the power active filter is generated by the means of a resonant sinusoidal signal integrator filter implemented with a transfer function block. All simulations performed in MATLAB/Simulink validate the theoretical considerations but not all of them reveal a good agreement with the existing standards. The sinusoidal signal integrator integral coefficient it’s tuned in order to obtain a good compromise between grid THD current and transient response to load change. The results are interpreted and centralized so they can be useful in possible hardware implementation.