L.F. Beites

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 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 contribution for modeling controlled and uncontrolled AC/DC converters in harmonic power flows

The main object of this paper is to present a sequential method of adjusting the operating point of power converters within the framework of harmonic power flows. To do this, a unified formulation of previous work in the frequency domain has been developed, resulting in a set of compact and powerful analytical expressions for AC and DC magnitudes. Special attention has been paid to uncontrolled rectifiers. The proposed sequential method offers a more flexible and modular framework where AC and/or DC magnitudes can be used for defining the operating point. Moreover, it provides better convergence properties for iterative harmonic analysis (IHA). Newtons method or Gausss method can be applied for IHA without special considerations. Finally, the solution obtained has been verified by means of time domain simulation and measurements.

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.

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.

Arc furnace characterization from an off-line analysis of measurements

The object of this paper is to present an exhaustive analysis of power quality measurements performed in an arc furnace. Main disturbances produced by the arc furnace are taken into account in accordance with IEC recommendations. In this way, the typical magnitudes of power quality analysis are evaluated using a statistical treatment. Other magnitudes such as different power components and power factors are also calculated in order to provide a scheme by which the disturbances of the arc furnaces can be characterized.

Decoupled Newton Algorithms in the Harmonic Domain for the Harmonic Interaction of Line Commutated Converters With AC Systems

Under certain nonideal conditions, the harmonic interaction of line commutated converters with the ac network must be represented by suitable models with high level of detail. A complex and robust solution of this problem is achieved in previous works by means of an iterative procedure in the harmonic domain, where ac and dc harmonics and switching instants are updated simultaneously. This simultaneous method is a full Newton solution (FNS) and therefore it offers a very good convergence, but the integration of the converter model into the whole iterative process (WIP) is complicated due to the heterogeneous form of the Jacobian matrix. The main object of this paper is to present alternative procedures based on decoupled Newton solutions (DNS), where a sequential method of solving the iterative process is used. It leads to a much more modular approach for performing the WIP, since the integration of the converter in the WIP is significant simplified, even when the converter presents any dc side structure. Several critical cases and experiments have been tested in order to show the performance and the convergence properties of the DNS in comparison with FNS.

Iterative harmonic analysis of line side commutated converters used in high speed trains

This paper presents a model, in the frequency domain, of line commutated rectifiers used in traction applications. The model is described by means of powerful analytical expressions that take into account the operating point of such devices as single phase loads connected to three phase power systems. Special attention is paid to define the operating point in terms of power and DC current. The harmonic emission of each locomotive is represented by a harmonic current source coherent with the selected operating point. Several locomotives acting simultaneously at the same busbar are also considered. This model requires iterative harmonic analysis in order to obtain the final harmonic injections. Harmonic load flow calculations have been performed using this model in the IEEE 14 bus test system.

An Analytical Procedure for Calculating Harmonics of Three-Phase Uncontrolled Rectifiers Under Nonideal Conditions

Detailed analytical procedures (DAPs) are very efficient methods for obtaining the steady-state solution and the harmonic evaluation of three-phase diode bridges with finite capacitive dc smoothing. Until now, these DAPs are developed for balanced operation of the system. This paper presents a new DAP. The consideration of unbalanced operation, the inclusion of dc reactor, and the treatment of the operating point in terms of power are contributions with respect to previous DAPs.