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This paper presents an innovative method for reducing current distortion on the ac side of six-pulse parallel-connected ac/dc rectifiers. The principle of the method is to modify the current waveforms on the dc side of the rectifier by using two self-commutated switches (insulated-gate bipolar transistors). It is demonstrated that accurate shaping of currents on the dc side achieves low distortion levels in currents IA, IB, and IC on the ac side. The effectiveness of the method is confirmed by laboratory recordings, which are related to steady-state and transient studies. [ABSTRACT FROM AUTHOR]

This work presents the development of analytical models for thyristor-controlled reactors (TCRs). A nonlinear model for the TCR was developed based on the use of Generalized Switching Functions and from this model, a detailed linear model was derived. The linear model allows for the analysis and precise understanding of the behavior of the TCR under small disturbances both in the time and frequency domains, for frequency ranges up to some tens of hertz. This model clearly shows that the TCR dynamics are operating point dependent. System parameter variations are also correctly considered in the model. With the proposed model, it is possible to design static var compensators (SVC) controllers in an integrated form, avoiding risks of instabilities and guaranteeing a good overall dynamic performance for the system. Validation of the models was done by comparing simulated results obtained with the proposed model with those obtained with a traditional electromagnetic transients program (EMTP). [ABSTRACT FROM AUTHOR]

This paper presents a practical destruction-free parameter-extraction methodology for a new physics-based circuit simulator buffer-layer integrated gate-commutated thyristor (IGCT) model. Most key parameters needed for this model can be extracted by one simple clamped inductive-load switching experiment. To validate this extraction method, a clamped inductive-load switching experiment was performed, and corresponding simulations were carried out by employing the IGCT model with parameters extracted through the presented methodology. Good agreement has been obtained between the experimental data and simulation results. [ABSTRACT FROM AUTHOR]

Discrete wavelet transform is used to analyze faulty signals for a transmission system employing a thyristor controlled series capacitor at the midpoint of a line. Different frequency components of current signals are considered to select the phase(s) involved with a fault. To identify the fault section the new approach utilizes the difference in high frequency components of the current signals. For both phase selection and section identification tasks new energy and standard deviation-based indices are also calculated for the transmission system. [Copyright &y& Elsevier]

A misfire phenomenon taking place in a discharge circuit composed of a capacitor and thyristor has been investigated. This circuit was operated at a frequency of up to 198 Hz. A misfire was observed in a circuit with a PET capacitor at low temperatures, while no misfire was observed with a PP capacitor under any conditions. Transient currents in the range of 40 A to 1 mA were measured with a digital oscilloscope. In the case of a PET capacitor, the current initially decreased exponentially at a given time constant, but exhibited a slow decay which caused the misfire. This current is associated with residual charges trapped in the bulk of the PET film. © 2001 Scripta Technica, Electr Eng Jpn, 137(2): 1–7, 2001 [ABSTRACT FROM AUTHOR]

In power stations and substations of electric power companies, power semiconductor devices such as diodes and thyristors have been used in control power supplies and emergency power supplies since the 1970s. Such equipment is designed on the assumption that power semiconductor devices are semipermanent, since their service life is much longer than that of capacitors and resistors. Therefore, it is hard to find studies that have systematically examined the long-term reliability of semiconductor devices. Such studies are very important from the viewpoint of ensuring reliability and improving the renewal period by proper equipment maintenance. This paper discusses the long-term reliability of power semiconductor devices used in power station rectifiers and substation rectifiers. © 2001 Scripta Technica, Electr Eng Jpn, 136(3): 67–75, 2001 [ABSTRACT FROM AUTHOR]

Chaotic behaviors are observed in the anode current of the thyristors where their anodes were excited with an ac source and the constant dc current was supplied to the gate. Three aspects of chaos, i.e., period-doubling bifurcation, intermittency, and period-adding chaotic sequence, are observed with different combinations of control parameters. This paper discusses primarily the feature of period- adding chaos accompanied with intermittency. Also reported is the structure of its bifurcation by using a simple first return map model constructed from the experimental results. [ABSTRACT FROM AUTHOR]

For pulsed power systems such as lasers and accelerators, semiconductor switches with their longer service life have actively been developed as replacements for thyratrons. The MOS-driven thyristors are suitable for pulsed power applications because they have high-power handling and fast turn-on capabilities. The MOS-assisted gate-triggered thyristor (MAGT), designed especially for pulsed power, is a promising candidate in this field. This paper presents the results of an investigation into the performance of MAGTs. Using a pulse-forming network (PEN), the pulse-switching characteristics and the dynamic resistance characteristics during the current flow are investigated. A maximum current density of 21.8 kA/cm² and di/dt of 106 kA/μs/cm² with 1550-V anode voltage on a single-shot basis were obtained. Furthermore, a life test with 109 shots at a high repetition rate showed no degradation in the observed characteristics. Based on these experimental results, a carrier flow model of MAGT during turn-on process is proposed and the turn-on mechanism is considered. [ABSTRACT FROM AUTHOR]

Two design methods of ac/dc thyristor converter current control systems with MRAC (Model Reference Adaptive Control) have been designed, To linearize the input/output relation of the systems, the constant term of the model is considered in different ways. In the first method, a linear transformation of the control input is made while in the second method, the constant term and compensated modeling error are neglected by integral adaptation. Computer simulations and experiments have shown that the control performances of the MRAC systems are much better than that of PI controllers. However, in the first method, since the variable vector is not persistently spanning, the convergence rate of estimated parameters is not as high as expected. The second method has better dynamic characteristics but its stability has not been proved in theory. This paper suggests a new design method in which the constant term is considered as a deterministic disturbance. The feature of this method is that by introducing an equality equation which makes the term of disturbances apparently unobservable, the effect of disturbances can be eliminated and the existing adaptive control scheme without disturbances whose stability has been proved theoretically can be used. Computer simulations and experiments show that the new method can obtain better responses than the old ones. [ABSTRACT FROM AUTHOR]

Electronic devices can be damaged in an undesirable manner if the junction temperature achieves high values in order to cause thermal runaway and melting. This paper describes the mathematical model to calculate the power losses in power semiconductor devices used in bidirectional rectifier which supplies a resistive-inductive load. The obtained thermal model can be used to analyse the thermal behaviour of power semiconductors in steady-state conditions, at different values of the firing angle, direct current, air speed in the case of forced cooling, and different types of load. Also, the junction and case temperature of a power thyristor have been computed. In order to validate the proposed mathematical model, some experimental tests have been performed. The theoretical values are in good concordance with the experimental data and simulated results. [ABSTRACT FROM AUTHOR]

We have studied the mechanism of high-field domain formation in thyristor structures at ultrahigh current densities (J &Ge; 100 A/cm[SUP2]) and the related effect of anomalous buildup of the direct residual voltage. The analysis is based on the results of numerical simulation of the process of double injection with allowance for accompanying nonlinear effects. [ABSTRACT FROM AUTHOR]