Gate Turn-off Thyristor Research Articles

Hong Kong Metro's Traction Equipment: The Drive for Efficiency

This paper describes the evolution of the electric multiple unit traction equipment of the Hong Kong Mass Transit Railway Corporation (MTRC). Traction energy efficiency is particularly important to the MTRC and has been improved by 46 per cent on the most recently supplied cars. The justification for the conversion of the existing camshaft cars to chopper control and the relative merits of different types of drives in MTRC's application are discussed. The utilization of energy, the method used to optimize coasting for energy saving, life-cycle costs and the design features of the gate turn-off thyristor chopper cars are described.

A large-scale PWM solid-state synchronous condenser

The description, steady-state analysis, and control design of a microcontroller-based large-scale pulse-width modulated solid-state synchronous condenser (PWM-SSSC) for reactive power compensation is presented. The key feature of the proposed compensator is the low switching frequency of the PWM pattern, which allows the utilization of high-power GTO thyristors. The PWM-SSSC has the additional advantage that large passive magnetic components are substituted with silicon. Closed-loop operation of a high-power PWM-SSSC (having a poor inherent damping) with a PI controller is investigated. Cumbersome z-domain methods for pulse stability analysis are completely avoided by using direct s-domain computations. A systematic approach for tuning the controller parameters is introduced by extending the concept of absolute stability. Selected predicted results are experimentally verified on a scaled-down laboratory prototype.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Benefits of GTO-based compensation systems for electric utility applications

The performance of reactive compensation systems based on gate-turnoff thyristors offers potential benefits compared to conventional compensators. The authors describe these benefits in applications involving increased steady-state loadability of heavily stressed systems; in improving the security of systems with heavy motor loads; in improving the transient stability of systems experiencing large power swings; and in adding damping to power swings. These performance benefits lead to the ability to solve specific application problems with less rating and with better stability than with conventional devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A novel control scheme of a parallel current-controlled PWM inverter

A parallel technique for current-controlled pulse-width-modulated (PWM) inverters is described. Two voltage source inverters, the output terminals of which are connected in parallel through current balancers, are used as a main circuit. In this scheme, excellent characteristics both in steady states and in transient states are obtained, keeping the average values of the cross current and zero sequence current at zero level. This current control scheme is applicable to large-capacity GTO inverters because good performance is attained even if the switching frequency is only a few hundred hertz, as is shown in the experimental results. >

FGTO — A fine structured GTO-thyristor with improved switching characteristics

A fine structured GTO thyristor, abbreviated FGTO, has been developed to improve the switching characteristics. The new device has a cathode finger width of only 20 μm and can be turned off without a negative gate bias at an anode current level of more than 200 A/cm2. The turn-off time can be shortened down tot off ≦500 ns by increasing the negative gate current. A snubber circuit is not necessary to turn off the FGTO's. The maximum rate of rise of anode voltage du/dl reaches more than 10 kV/μs. Analytical models are developed to describe the turn-off transients of the FGTO's. Good agreement between the theoretical and experimental results could be achieved.

Microprocessor based simulation and digital logic model of gate turn-off thyristor

A digital logic model of a gate turn-off thyristor is developed considering the turn-on and turn-off mechanisms of the device. A commonly used R-C-D snubber circuit is also included in the proposed model. Relations between different delay times, e.g. storage time, Tall time, turn-off time and tail time, become apparent from the model. The model is simulated with the help of a microprocessor to establish the validity of the proposal.

A high frequency AC/DC converter with unity power factor and minimum harmonic distortion

A novel forced commutated AC/DC converter and control strategy is proposed that is able to draw nearly sinusoidal currents at unity power factor from three-phase power lines. The power factor is controlled by adjusting the relative position of the fundamental component of an optimized pulse-width-modulation (PWM) type voltage with respect to the supply voltage. Current harmonic distortion is minimized by the use of optimized firing angles for the converter at a frequency where gate turn-off thyristors (GTOs) can be used. This feature makes this approach attractive at power levels of 100 kW to 600 kW. An 8096 microcontroller is used to minimize the interface hardware requirements. The theoretical analysis of the converter, the control energy, and experimental results for a low-power prototype are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low-harmonic GTO converter for fundamental power factor compensation

A low-harmonic GTO (gate turn-off) thyristor AC-to-DC converter with line current lead-lag phase shift control ability is proposed and analyzed. The converter can be used either as a low-harmonic GTO-controlled rectifier or a fundamental input power factor compensator in a power supply system. The effect of PWM (pulse width modulation) current phase number on the harmonic contents and converter output voltage control range is investigated. Lower order input current harmonics are eliminated over a wide range, using a specially designed PWM current pattern. The effect of the PWM current pulse number on the power factor compensation characteristic is investigated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A PWM Current-Source Inverter for High Quality Drives

SummaryWith fast microprocessors and suitable switching devices such as GTO thyristors CSI-drives are considerably improved. Sinusoidal input and output currents are replacing the block-shaped currents of sequentially commutated inverters and a sophisticated control permits fast dynamic response. To achieve this goal, the resonant circuit consisting of the capacitors at the invener terminals and the machine inductances has to be kept under close control. With an online calculation of the PWM switching times, not only the voltages but also the Currents are maintained very close to the reference value, even at limited switching frequency. Measurements at the machine-side converter show the distinctive features of this drive system at various operating points.

6000-V gate turn-off thyristors (GTOs) with n-buffer and new anode short structure

6000-V gate-turn-off thyristors (GTOs) were developed for high-power inverters and choppers. In order to attain a high blocking voltage simultaneously with low turn-on and turn-off losses, a combination of an n-buffer layer and a cylindrical anode short structure was implemented. A 500- mu m n-base width, achieved by the n-buffer structure, can decrease turn-on loss to approximately 2/3 that of a conventional anode short structure. The proposed structure is effective in sweeping away excess carriers during turn-off transient without increasing the on-state voltage very much. An average anode current of 200 A can be continuously switched at a 900-Hz operational frequency by a 33-mm-diameter device. A simultaneous diffusion process for p-base and n-buffer layers was proposed and implemented to realize the newly developed device structure. >

Analytical model for the destruction mechanism of GTO-like devices by avalanche injection

A unified analytical model is derived from very basic principles. It allows the qualitative and-with certain restrictions-also quantitative description of all essential features characteristic of critical turn-off of devices based on the gate-turn-off-thyristor (GTO) principle and thus gives insight into the details of the destruction mechanism. In particular, it reflects that the turn-off capability is principally limited by the fundamental phenomenon of avalanche injection. Though idealized and simplified, the model correctly predicts or reproduces results from exact 2-D simulations and experiments-for example, the simultaneous pinning of voltage and current at high levels, the dynamic steepening and bending of the electric field profile, and the occurrence of traveling current filaments. The model is useful for estimating the safe operating area (SOA) of GTO-like devices. >

Demonstration of compact solid-state opening and closing switch utilizing GTOs in series

A compact opening and closing solid-state switch was designed, constructed, and demonstrated. The switch repetitively switches over 4 MW of peak power and yet is only 0.45 m by 0.12 m by 0.32 m and has a mass of 13 kg. The switch uses commercially available gate turn-off thyristors (GTOs), arranged in series to enable the collected devices to switch a voltage five times the rating of an individual device. The system uses commercially available components exclusively, yet takes advantage of state-of-the-art components. These include multilayer ceramic capacitors which are arrayed to produce a snubber capacitor, and small high-voltage isolated power transformers that protect each of the seven GTO stages from breakdown damage via their power supplies. Each stage is controlled via a fiber-optic link, and turn-on and turn-off times are adjustable for each of the seven stages. System dV/dt exceeded 1 kV/ mu s and system di/dt exceeded 200 A/ mu s, for both turn-on and turn-off. The system was only limited in the amount of power it could switch by thermal considerations. A much higher power could be switched if there were advanced cooling. The cooling devices were quite modest, in that this was only a demonstration of the principle. >

Simulation of wafer-scale GTO thyristors in circuits

A simulation technique that allows the study of large area power devices composed of many outwardly identical elements operating in a realistic power circuit has been developed. Results are presented showing the transient redistribution of current between a pair of GTO thyristor elements during turn-off under the influence of the power circuit. The method is validated by comparing simulated results with experimental measurements. Variations in carrier lifetime. diffusion uniformity, and gate contact position are studied, and they are shown to significantly alter the turn-off performance. Conclusions are drawn concerning the reliability of large area latching power devices with process inhomogeneity. >

A new physical model for calculating storage time in GTO thyristors

A two-dimensional analytical model, developed from first principles, to substantiate the dependence of storage time on the nature of the gate current ramp, anode current, and device geometry, as observed in experimental studies on single-element gate turn-off thyristors (GTOs), is discussed. The model originates in the solution of the continuity equation in the p base for evaluation of the plasma squeezing rate. It addresses realistic issues, such as high injection effects, variation in the base transport factors, and the physical basis for the minimum ON region dimension, that are not considered in any previous treatment.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Switching losses in a GTO inverter for induction heating

The application of gate-turn-off thyristors (GTOs) to parallel resonant inverters for induction heating is investigated. Three different modes of operation of the GTOs are explained and tested in a test circuit. The optimum mode is selected by switching loss measurement. It is shown that due to the small inductance in the commutation circuit, the gate-assisted turn-off technique leads to very high turn-on losses and is not the optimum way to drive the GTO in this application. However, it can be used under different conditions in order to reduce turn-off losses. It is suggested that a mixed turn-off of the devices by both gate action and natural commutation is the optimum mode of operation. Then, the load is driven at unity power factor. In this mode of operation, no snubbers are necessary in principle. A small capacitor in parallel to the GTO is recommended for only the staring procedure. An estimation of the total power loss in the GTOs leads to the result that the GTO tested can be operated at frequencies between 10 kHz and 20 kHz with a reasonable inverter efficiency.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

GTO Converters

In this paper, the important characteristics of gate turn-off thyristors (GTOs) which differ from those of conventional thyristors are briefly discussed. The protection of a GTO against switching stresses is explained with a simple snubber circuit. The importance of regenerative snubbers and snubberless operation are pointed cut. Few prominent GTO converter/inverter circuits as reported in literature are very briefly reviewed. Some successful commercial GTO applications are mentioned.

A new simultaneous gating GTO dual converter-fed DC motor drive without circulating current

A new dual power converter, comprised of two three-phase AC-DC pulse width modulated (PWM) gate turn-off thyristor (GTO) converters, is proposed. The gating pulse pattern of the converters is chosen such that no circulating current flows between the converters when they are operated simultaneously. In addition, a good input power factor is obtained with less ripple in the output current. A symmetrical type of gating is worked out in which all the GTOs in the converter are switched an equal number of times during each cycle of the source voltage. The motor current is free to reverse naturally at any moment, and hence, the possibility of discontinuous conduction of the motor current does not arise. A four quadrant, closed loop, speed controlled DC motor drive fed from the proposed dual converter is designed, constructed, and tested. The experimental results obtained are shown to be in good agreement with theory. >

Evolution of Power Semiconductor Devices in the Modern Era and Trend of Converters

Power semiconductor devices are undergoing dynamic evolution in the recent years. Modern power electronics era started by the invention of thyristor (or silicon controlled rectifier) in Bell Telephone Laboratory in 1956, and it was then commercially introduced by General Electric Company in 1958. Since then, we have seen the advent of triac, gate turn-off thyristor (GTO), bipolar power transistor and power MOSFET. The power semiconductors that appeared in the 1980's are insulated gate bipolar transistor (IGBT), static induction transistor (SIT), static induction thyristor (SITH) and MOS-controlled thyristor (MCT). The characteristics of these modern power devices have been discussed and compared from the viewpoint of power electronics applications. For completeness of description, other devices, such as thyristor, triac, GTO, bipolar transistor and power MOSFET have also been briefly reviewed. Finally, the trend of power converters has been discussed.

Transient model for gate turn-off thyristor in power electronic simulations

A two-level device model for a gate turn-off thyristor (GTO) is presented to predict its transient behaviour especially for turn-off. The model is developed mainly on the basis or the semiconducting phenomenon and is represented in a subcircuit form for easy adaption to currently used circuit simulators. The level 1 model is formed by a switching network paralleled with a recovery circuit and is able to simulate the GTO switching with short simulation time but acceptable accuracy. The level 2 model incorporates the Hu-Ki SCR model and additional charge control, anode-cathode and gate-cathode resistance modulation networks to simulate turn-off phenomena more precisely. The validity of the model is verified by comparing with experimental results. Methods for determination of the model parameters are described.

A three-phase AC-DC GTO thyristor converter employing equal pulse-width modulation (EPWM)

A comparative study of equal, triangular, stepped, sinusoidal, and inverted sinusoidal pulse-width modulation (PWM) schemes on the source and load performances of a three-phase AC-DC gate turn-off (GTO) thyristor converter-fed DC motor is presented. The two-quadrant GTO thyristor converter employing an equal pulse-width modulation (EPWM) scheme is studied in detail. This scheme has been found to offer better overall performance among the PWM schemes considered. A new symmetrical gate pulse pattern that reduces the total number of switchings and allows switching GTOs an equal number of times in each supply cycle is reported. The symmetrical gate pulse pattern has a beneficial effect on the switching loss, especially when the switching frequency is high. Smooth and continuous transition is obtained between rectification and inversion with a single GTO converter. The proposed converter was designed, constructed, and tested using a 3 HP laboratory-sized separately excited DC motor. The exponential results are shown to be in good agreement with the theory.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>