José Manuel Bermúdez Cano

Improving the Dynamics of Virtual-Flux-Based Control of Three-Phase Active Rectifiers

Virtual flux (VF)-oriented control (VFOC) and VF-based direct power control (DPC) (VF-DPC) have been developed to improve voltage-oriented control and DPC of three-phase active rectifiers. The VF space vector is utilized in transformations between stationary and rotating coordinates in VFOC and in obtaining instantaneous power in VF-DPC. The VF space vector is calculated by integrating the grid voltage space vector. This integration is usually performed using a first-order low-pass (LP) (FOLP) filter, which counteracts the saturation and dc-drift problems associated with pure integrators. However, the dynamics of FOLP filters can be enhanced to a great extent. This paper presents a new, simple, and fast integration algorithm for VF-based control methods. Simulations and experimental tests on a VF-DPC-based system showed that the proposed algorithm leads to rapid recoveries after grid voltage sags occur. Moreover, the performance of VF-DPC under nonideal grids is discussed.

Modeling of LCC-HVDC Systems Using Dynamic Phasors

This paper presents an average-value model of a line commutated converter-based HVDC system using dynamic phasors. The model represents the low-frequency dynamics of the converter and its ac and dc systems, and has lower computational requirements than a conventional electromagnetic transient (EMT) switching model. The developed dynamic-phasor model is verified against an EMT model of the CIGRE HVDC Benchmark. Simulation results confirm the validity and accuracy of the average-value model in predicting the low-frequency dynamics of both the ac and dc side quantities. Merits and applicability limitations of the average model are highlighted.

Diagnosis of Electrical Distribution Network Short Circuits Based on Voltage Park's Vector

This paper proposes a short-circuit diagnosis tool for electrical low-voltage (LV) distribution networks. The tool relies on analyzing Parks vector representation of the LV phase voltage in the sag produced by a short circuit. Parks vector representation is considered to be an identification mark for the type of short circuit that the installation is exposed to and the phases that it affects. In addition, it shows whether the fault is located in the medium voltage or LV network. The characteristics of the vector representation corresponding to the different types of short circuits are analyzed in this paper. Finally, the relationship between Parks vector representation and the location of the defect is also studied. The results can be used as part of an expert system for the automatic classification of disturbances.

Finite Element Model for the Study of Inter-Turn Short Circuits in Induction Motors

This paper presents a finite element model for the study of the behavior of induction motors under inter-turn short circuit conditions. The main advantages of this model are its simplicity and the possibility of simulating different types of short circuits, involving different number of shorted turns located in different positions. This is achieved by means of the combination of a peculiar coil definition in the bi-dimensional finite element model with an external circuit coupled with it. The proposed model has been applied to a low-voltage random-wound induction motor, especially rewound for this study in order to allow the authors to introduce inter-turn short-circuits in any specific place of the windings. Experimental tests were performed on this machine in healthy and short-circuit conditions and, in both cases, measurements of supply currents and electromagnetic torque were taken. The spectral analysis of these magnitudes showed a good agreement between simulation and experimental results, validating the model for this kind of study.

Detection of stator winding insulation failures: On-line and off-line tests

Insulation faults in electrical rotating machines are a matter of great industrial interest since the economic losses associated with these events are usually equal or even higher than the cost of the machine itself. For this reason, the development of monitoring and diagnostic techniques to detect this failure during its earliest stages has been a subject of great interest. On the other hand, the accuracy of the quality controls applied to the manufacturing of insulation systems is an essential issue to reduce fault rate and increase machine life. The aim of this paper is to present a comprehensive review of the scientific literature in this field, including not only research papers but also existing standards for off-line tests. A critical review of their diagnosis capability, especially on low voltage machines, is essential to clarify the reliability of these techniques as well as the convenience of its generalized industrial use.

Dynamic Estimation of Electrical Demand in Hot Rolling Mills

This paper proposes a method capable of reproducing the particular operating conditions of a hot strip mill and predicting the evolution of the main electrical variables from both the characteristics of the steel to be milled and the specific features of the rolling mill. The method analyzes the load torque and the motor-speed evolution in the stands of the roughing and finishing mill drives, according to the steel to be milled. In this study, three types of carbon alloy steel are considered, thus involving dissimilar hardness characteristics. The main stands of the mill, the power network, and the filter banks have been modeled. The relationship between the grade of steel and both the electrical demand and various power quality parameters is discussed. The results can be used as a part of an expert system for the automatic estimation of the electrical demand in a hot rolling mill.

Dynamic estimation of electrical demand in hot rolling mills

This paper proposes a method capable of reproducing the particular operating conditions of a hot strip mill and predicting the evolution of the main electrical variables from both the characteristics of the steel to be milled and the specific features of the rolling mill. The method analyzes the load torque and the motor-speed evolution in the stands of the roughing and finishing mill drives, according to the steel to be milled. In this study, three types of carbon alloy steel are considered, thus involving dissimilar hardness characteristics. The main stands of the mill, the power network, and the filter banks have been modeled. The relationship between the grade of steel and both the electrical demand and various power quality parameters is discussed. The results can be used as a part of an expert system for the automatic estimation of the electrical demand in a hot rolling mill.

Modeling of LCC-HVDC systems using dynamic phasors

This paper presents an average-value model of a line-commutated converter-based HVDC system using dynamic phasors. The model represents the low-frequency dynamics of the converter and its ac and dc systems, and has lower computational requirements than a conventional electromagnetic-transient (EMT) switching model. The developed dynamic-phasor model is verified against an EMT model of the CIGRE HVDC Benchmark. Simulation results confirm the validity and accuracy of the average value model in predicting the low-frequency dynamics of the ac- and dc-side quantities. Merits and applicability limitations of the average model are highlighted.