Julio G. Mayordomo

A new frequency domain arc furnace model for iterative harmonic analysis

This paper presents a new frequency domain arc furnace model for iterative harmonic analysis by means of a Newton method. Powerful analytical expressions for harmonic currents and their derivatives are obtained under balanced conditions of the power system. The model offers a three-phase configuration where there is no path for homopolar currents. Moreover, it contemplates continuous and discontinuous evolution of the arc current. The solution obtained is validated by means of time domain simulations. Finally, the model was integrated in a harmonic power flow where studies have been performed in a network with more than 700 busbars and 7 actual arc furnace loads.

A Harmonically Coupled Admittance Matrix Model for AC/DC Converters

This paper proposes a new method to model the harmonic generating characteristics of AC/DC converters. The model transforms the time domain nonlinear characteristic of the converter into a frequency domain linear admittance matrix. The matrix represents the coupling among the converter AC side harmonic voltages and currents accurately and it does not vary with the harmonic conditions of the system. The proposed model opens up a new way to conduct harmonic power flow studies. This paper presents the theoretical foundation and analytical derivation of the admittance model for both single-phase and three-phase bridge rectifiers. Potential applications of the model are discussed.

A new frequency domain approach for flicker evaluation of arc furnaces

In this paper, flicker magnitudes of rapidly varying loads are evaluated by means of a new frequency domain method. Analytical expressions of the instantaneous flicker sensation are obtained in terms of interharmonic voltages. The dynamic response of flicker magnitudes of such loads can be clearly described with this analysis, as well as the individual contribution of each interharmonic to the flicker sensation. The proposed method, applied to the voltages of DC and AC arc furnaces, provides very satisfactory results that have been validated with measurements performed with the standardized IEC flickermeter.

A method based on interharmonics for flicker propagation applied to arc furnaces

In this paper, propagation in the network of flicker produced by rapidly varying loads is analyzed by means of a new frequency domain method. By this method, the flicker level can be determined at any bus of the network when one or several loads operate simultaneously. Flicker summation effect is considered and the results obtained are compared with the summation laws proposed by IEC. The propagation algorithm has been applied to the 14-buses IEEE network and to the Spanish transmission system. The method has been validated with measurements performed with the standardized IEC flickermeter.

A unified theory of uncontrolled rectifiers, discharge lamps and arc furnaces. I. An analytical approach for normalized harmonic emission calculations

Under certain assumptions, similar models can be applied for rectifiers and devices with electric arc characteristic. The analysis considers single and three-phase uncontrolled rectifiers with continuous and discontinuous evolution of the AC current. It leads to four possible situations which fit with the harmonic behaviour of discharge lamps, arc furnaces and rectifiers with capacitive DC smoothing. A very useful set of compact and powerful analytical expressions for different magnitudes as well as for the harmonics currents are derived. It offers a direct method of selecting different operating points with their corresponding harmonic emissions. Normalized diagrams and tables of these magnitudes are depicted in a friendly way. Over these diagrams, harmonic emission limits of standard IEC 1000-3-2 and IEC 1000-3-4 are specified for Class C and Class D single-phase equipment and for three-phase equipment. Passive solutions applied to the aforementioned rectifiers to comply IEC 1000-3-2 and 1000-3-4 are obtained in a direct and normalized way.

Load and voltage balancing in harmonic power flows by means of static VAr compensators

In special applications, static VAr compensators (SVC) with thyristor controlled reactors (TCR) are used to balance unbalanced loads or to eliminate voltage unbalances at the terminals of the SVC. In both cases, load balancing and voltage balancing, the TCR can present a significant unbalanced behavior that produces important quantities of noncharacteristic harmonics. In this paper, the formulation and solution of the load and voltage balancing problems are developed for harmonic power flows obtained from a combination of two blocks: a conventional load flow (CLF) and an iterative harmonic analysis (IHA). In both blocks, the treatment of load and voltage balancing is described in detail. Load flow calculations and harmonic analysis show the presence of noncharacteristic harmonics in these two situations.

A contribution for modeling static VAr compensators in iterative harmonic analysis

Static VAr compensator (SVC) with thyristor-controlled reactors (TCR) are used to control the voltage at bus SVC, while the nonlinear harmonic source is connected to the TCR busbar. This specific situation requires special treatment of the voltage control characteristic in the iterative harmonic analysis (IHA). A voltage control characteristic reduced to the TCR busbar is proposed. Under this condition, the operating point of the TCR in the IHA is treated in a way so the firing angle is adjusted to satisfy the voltage regulation characteristic. In this paper, a frequency domain TCR model is presented by means of a set of analytical expressions for harmonic currents and their sensitivities with respect to the harmonic voltages. An additional nonlinear equation is also derived for obtaining the firing angle under distorted voltage. A scheme of checking coherent operating points of TCR is also included for IHA.

New transfer functions for an accurate estimation of harmonic distortion in AC/DC converters working under unbalanced conditions

In this paper, new transfer functions for the estimation of harmonic distortion in six-pulse AC/DC controlled converters working in continuous mode are proposed. One of the objectives of the paper is extending the use of transfer functions for the case of distorted and/or unbalanced supply voltages. Moreover, important changes in the structure of these transfer functions are proposed, with the aim of achieving higher accuracy in the estimations. With this technique, it is possible to predict the harmonic components of currents not only at the DC side, but also at the AC side, even for noncharacteristic harmonics. This paper deals only with the AC/DC transfer phenomenon. The new algorithm proposed in this paper is especially suitable to distinguish between the DC current harmonic components caused by the converter and those caused by the interaction of the load.

Iterative harmonic analysis for controlled and uncontrolled AC/DC converters under unbalanced conditions: a compromise between model accuracy and flexibility

In a previous paper, the authors presented a method for treating very efficiently controlled and uncontrolled power converters under balanced conditions. A sequential method of adjusting the operating point of such converters was proposed. It improves the convergence as well as the flexibility of the model in order to be included in the harmonic power flow. These results have been extended here to unbalanced power systems. Compact expressions of harmonic currents and their sensitivities are also developed. The model accuracy is conditioned by the DC busbar representation: a finite reactance and a DC voltage. It provides good results in many high powered applications and makes possible to reach the aforementioned flexibility of the model.

A Frequency Domain Approach for Modeling DC Arc Furnaces under Fluctuating Conditions

This paper presents a direct method in the frequency domain for modeling DC arc furnaces (DCAF) under fluctuating conditions. The procedure takes advantage of the switching function approach for obtaining a detailed representation of the DCAF. The model provides very fast calculations of the flicker interharmonic voltages and currents as well as it offers a basis for estimating the fluctuations of the arc from measurements on the AC side. With this procedure, an exhaustive analysis is developed where a deep insight is provided for better understanding the process by which flicker interharmonic components are generated. With this, flicker power flow in terms of Pst values is possible not only for the DCAF installation but also for large systems where the DCAF is connected. The method has been validated with measurements and with time domain simulations.