Nino Stojković

Indices for Harmonic Distortion Monitoring of Power Distribution Systems

Among different power quality parameters, the voltage total harmonic distortion is important and often-analyzed category. Different indices have already been suggested to measure and to monitor both the current and the voltage distortion in power systems, but harmonic site characterization still cannot be performed in satisfactory way. The state of the harmonic distortion is difficult to predict due to variability and a large number of unknown, such as detailed consumer and system characteristics. In this paper a new index describing the total harmonic distortion in current measurements, total rated distortion (TRD), is suggested in order to simplify and standardize harmonic current measurements. Another index representing the increase of harmonic voltage distortion with TRD, equivalent harmonic impedance zeq, is proposed as an efficient way of characterizing a particular site. Finally, extensive harmonic measurements of a real distribution system were performed to prove the usefulness of the proposed indices.

Real amplifier influence on impedance tapere 2nd-order filters

In this paper, an influence of real parameters of operational amplifier to the impedance tapered filter transfer function is analyzed. As an example, a second-order-low-pass (LP) and high-pass (HP) Sallen and Key filters with Butterworth and Chebyshev transfer function approximations are considered. Design tables with normalized element values for both cases are given. The filter elements were calculated using three different design criteria: equal resistors, capacitors and impedance tapered elements. Filter transfer functions are obtained using ideal and real operational amplifier. Real model of common operational amplifier is presented. Active sensitivities for all presented filters are shown. The results obtained by the analysis show significant influence of real amplifier in the frequency ranges higher than 100 kHz. Reduction of active sensitivities is obtained using impedance tapering, which fortunately, reduces the passive sensitivities as well.

Realization of the all-pole third-order transfer function

Realization possibilities of the all-pole third-order transfer functions are discussed. For this purpose, the ladder network with a controlled voltage source in any shunt branch is used. The voltage source is controlled by the shunt branch voltage. The transfer functions are expressed with cumulants. Because of the high degree of symmetry, there are the rules for cumulant development. In this paper, the controlled voltage source with the controlling voltage placed in the shunt branch behind the source is considered. In this case, the transfer function contains only poles. The realization of the all-pole third-order transfer function is given in an example. The transfer function stability is analyzed using the Routh-Hurwitz criterion for the third degree polynomials.

Noise improvement using SC filters

In this paper noise analysis of three different filter designs is performed. Voltage noise spectral density and RMS noise voltage in simply designed active RC, noise optimized active RC and switched capacitor (SC) filter design are calculated for fifth order Chebyshev low pass filter, with a cut-off frequency fc=3.4kHz, and pass-band ripple αmax=-0.5dB. All three designs are realized as a cascade of two second order sections and one first order section. All filter analysis has been performed using MATLAB and SPICE program tools. Through the analysis it is shown that SC based filter has significantly lower noise when compared with active RC based filter.

The effect of IEC grouping algorithms on the measurement uncertainty of harmonic distortion indices

The influence of noise on the measurement uncertainty of different harmonic indices calculated according to IEC grouping algorithms is analyzed in this paper. The results of a previously published paper are extended to cases where the input noise is superimposed on to the harmonic signal. Probability density functions (pdf) of the harmonic indices are obtained by means of numerical integration and are used for assessment of the statistical properties of the output noise. The values of the offset errors and standard deviations are compared to uncertainties obtained by applying the uncertainty propagation law, as indicated by The Guide to the Expression of Uncertainty in Measurement (GUM).

Realization of the third-order high-pass transfer function with real zeroes

The realization possibilities of the third-order high-pass transfer functions with the real zeroes are discussed. The filter structure consists the CR ladder network with only one operational amplifier (OA), what will give the low sensitivity circuit with the low power consumption. In this paper, the OA provides the signal feedforward and in that case, the transfer function contains real zeroes, both in and out of the origin of complex plane. The frequency responses and the time responses are presented as well as the sensitivity and the noise analysis. The obtained results are confirmed with the SPICE.

Filter Designs for VDSL Analog Front End

In the paper different fourth order filter designs with different transfer function approximations are discussed. Specifications on the filters are given for VDSL signal processing. Transfer functions and filter elements are given and sensitivity and noise for each design are calculated. The lowest sensitivity is obtained using a cascade of Rauch biquads, the lowest noise gives Akerberg-Mosberg design and the best selectivity is obtained using an elliptic filter. That leads to compromise in VDSL filter design. Also, transfer function approximation significantly determine overall specifications

Filters for VDSL technology

In this paper, different the third order filters designs with different transfer function approximations are discussed. The filters should fulfill the specifications for the VDSL signal processing. The standard transfer function approximations are chosen: the Butterworth, the Chebyshev, the symmetric impulse response and the elliptic. The filters are designed using the fully differential sections with the small number of elements to obtain the low noise and the high dynamic range, and the low sensitivity. The transfer functions and the filter elements are given and the sensitivity and the noise for each design are calculated. The best results are obtained for the third order filter where the second order block follow the first order block.