Simulation of switching processes in turn-off thyristors

Ultra-high voltage (>10 kV) power devices based on SiC are gaining significant attentions since Si power devices are typically at lower voltage levels. In this paper, a world record 22kV Silicon Carbide (SiC) p-type ETO thyristor is developed and reported as a promising candidate for ultra-high voltage applications. The device is based on a 2cm2 22kV p type gate turn off thyristor (p-GTO) structure. Its static as well as dynamic performances are analyzed, including the anode to cathode blocking characteristics, forward conduction characteristics at different temperatures, turn-on and turn-off dynamic performances. The turn-off energy at 6kV, 7kV and 8kV respectively is also presented. In addition, theoretical boundary of the reverse biased safe operation area (RBSOA) of the 22kV SiC ETO is obtained by simulations and the experimental test also demonstrated a wide RBSOA.

The gate turn-off (GTO) thyristor has the highest voltage and current rating among the semiconductor power switches used extensively today. The insulated-gate bipolar transistor (IGBT) is used to improve switching performance of a GTO in a cascode switch. This paper documents the switching performance of the different power semiconductor devices used in an IGBT-gated GTO-cascode switch. The cascode switch was tested and simulated using SPICE. Experimental waveforms are presented and show good agreement with simulation results.

A large-capacity inverter using high-power gate turn-off (GTO) thyristors that can be used instead of a cycloconverter in AC drives is presented. With the techniques of multiple configuration and GTO series connection, the inverter capacity is increased effectively. High conversion efficiency is obtained by using low-loss snubber circuits for GTOs. It is confirmed that the low-loss snubber circuits using energy recovery units (ERUs) have good performance in pulse-width modulated (PWM) operation. High-energy recovery efficiency is obtained, especially in leading operation (turn-on operation when freewheeling diodes conduct). These snubber circuits have superior ability for clamping overvoltage at GTO turn-off. A 2750 kVA inverter with low-loss snubber circuits using high-power GTOs has been fabricated and evaluated. >

New devices that are challenging the silicon-controlled rectifier are considered. Among them are the high-power bipolar-junction transistor (HPBT), the power MOS field-effect transistor (MOSFET), the gate turnoff (GTO) thyristor, and the insulated-gate bipolar transistor (IGBT), sometimes called a conductivity-modulated field-effect transistor (COMFET). Also important are the static-induction or short-channel junction-effect transistor, and its cousin, the static-induction thyristor. Applications for these devices are outlined, and their characteristics are briefly sketched. The use of MOSFETs in automobiles and IGBTs for motor drives is examined in more detail. Packaging issues are discussed.

Over the last few years high power semi-conductor devices with intrinsic turn-off capability have become available. These devices, called gate turn-off (GTO) thyristors, consist of several layers of silicon with appropriate dotations; they are able to turn off currents of 1000 Amperes at thousands of volts within microseconds. In circuits used in power electronics the usual resistive, inductive and capacitive circuit elements are combined with thyristors which may simply be considered as switches. This technology is still an active field of research, and it has many important applications such as AC/DC conversion (both ways), speed control of locomotives and electric cars, control of power stations and power networks, etc.

Potential, field and carrier distribution in the channel of junction field-effect transistors

The authors review the fundamental mechanism by which rotating electrical machines develop torque and draw conclusions as to which configuration offers inherent advantages in this regard. Development of a DC machine with a continuous armature winding where gate turn-off (GTO) thyristors replace the traditional copper-segment-carbon-brush commutator is described. Operation of a separately excited machine with 12 armature tapping points and 18 GTO thyristors is demonstrated, and waveforms are presented to illustrate the switching duties involved. >

The use of an insulated-gate bipolar transistor (IGBT) to improve the switching performance of a gate turn-off (GTO) thyristor in a cascode switch is documented. The IGBT-gated GTO-cascode switch features simple drive requirement, fast switching, robustness, and overcurrent protection. The cascode switch was applied in a quasi-resonant buck power converter and simulated on a computer using PSpice. The IGBT-gated GTO-cascode switch is suitable for high-power (1200 V, 140 A) and high-frequency operation up to 30 kHz. The turn-off time of the main switch, GTO, is reduced significantly due to the reverse current gain of unity in cascode configuration.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In view of the many system planning uncertainties faced by the UK National Grid Company (NGC), there is a clear need for readily relocatable reactive power compensation systems with enhanced system performance. To date 12 relocatable SVCs (RSVCs) have been installed as part of a planned programme of work to meet these changing system needs. Developments in the rating capabilities of gate turn-off (GTO) thyristors have enabled power electronic converters using GTOs to be proposed as serious competitive alternatives to the well proven thyristor controlled reactor (TCR) and thyristor switched capacitor (TSC). GTO-based STATCOM convertors have a number of benefits which are of value to NGC, such as reduction in required site area and ease of relocation. The authors describe the East Claydon project, which is viewed as an important step towards long-term objectives which could see the deployment of a range of compact power electronic devices on NGC's system.

A numerical two dimmensional simulation has been used to demonstrate the effect of IGFET channel width on threshold voltage. The computed results agree well with experiments and are used to build an understanding of the mechanism. Potential, field and carrier concentration distributions are used to provide a picture of the geometric interactions.

For almost three decades, InGaN (indium gallium nitride) quantum well (QW) lasers have received a lot of interest from the scientific research community. Recently, this material system has become probably the most intensively studied among all the material systems used for quantum well lasers. We simulated the characteristics of an In_0.02Ga_0.98N QW laser at a wavelength of 462 nm, particularly the carrier concentration distribution, the potential distribution, the energy band diagram, the wave intensity profile, the I-V and L-I characteristics, the background absorption, the radiative, Auger, Shockley-Read-Hall (SRH) and stimulated recombination, threshold current density, slope efficiency and external differential quantum efficiency, to gain an almost exhaustive general view of the performance characteristics of this structure, constituting in a more useful reference for applications than previous incomplete data gathered for this structure.

Chapter 2 - Power Semiconductors

Power semiconductor devices (MOSFET, IGBT, SIThy, and SOS) have been studied for applications in repetitive pulsed power generation. These switching devices are expected to be used in pulsed high-voltage modulators for accelerators and power supplies for pulsed atmospheric discharges. MOSFET and static-induction thyristor (SIThy) are investigated for their performance in high-voltage modulation at repetition rate on the order of MHz, which is demanded by applications in high-energy particle accelerators. Although the peak voltage and current are not very high (usually a few kV and a few 10s of A respectively), the repetition rate poses fatal problems to the devices due to the thermal effect. The system cooling and waveform control had been the main efforts in this study. IGBT and semiconductor opening switch (SOS) are studied for applications to atmospheric gas discharge, which has become very attractive recently due to its applications in gas-treatment, laser pumping, and sterilization. The electrical circuit scheme is based on inductive energy storage with opening switch, which gives pulsed output high-voltage up to 100 kV for high-impedance load. The study has concentrated on repetition rate and energy efficiency. These developments are joint studies between universities, national laboratories, and industrial companies.

With the introduction and wide acceptance of gate turn off power devices (e.g. Bipolars, Power Fets, GTO's, etc.), the switching behavior of converters has reached the point where further improvements in firing and switching networks bring only marginal benefits. Consequently, the research interests in the area of static converters have been shifting toward improving the process of power conversion through a combination of new circuit topologies and improved voltage and harmonic control PWM techniques. As a result several such techniques have been proposed lately.

A new all-optical emitter-turn-off (ETO) configuration is proposed in this paper which is operated under 15 kV single bias and a current of 10 A. This ETO is completely controlled by two optical signals, one for the 15 kV SiC gate-turn-off (GTO) thyristor and the other one for a triggering low-voltage optically controlled Si switch. The latter, called optically-triggered power transistor (OTPT), is used in series with the anode contact of the SiC GTO thyristor in order to handle the current switching between anode and gate path of the SiC GTO thyristor. This OTPT is triggered with a 5-W laser of 808-nm wavelength and the main SiC GTO thyristor is triggered with a laser having a low wavelength of 266 nm. The voltage drop on the OTPT during the on-state is controlled by the power of the laser. For an optical power of 5 W, the structure is optimized to have an on-state voltage of 0.2 V at the junction temperature of 200 °C. This is less than 0.002% of the total bias of 15 kV.