Light-triggered Thyristor Research Articles

Numerical study on light triggering characteristics of NiO/SiC heterojunction thyristor

In this paper, the performance of silicon carbide (SiC) light-triggered thyristor (LTT) with a p-type NiO emitter region is analyzed through numerical simulation. The conductivity modulation in SiC LTT is significantly enhanced with the help of high injection efficiency of holes in NiO/SiC heterojunction. The injected hole density at the surface of the p− long base is increased by ∼21.2 times and the corresponding specific on-state resistance (Ron,sp) is only 36.7 mΩ cm2, which is reduced by about 29%. Moreover, hole-injection enhancement by NiO/SiC heterojunction also exhibits excellent potential in improving the dynamic characteristics of SiC LTTs. The simulation results indicate that the turn-on time of SiC LTT can be reduced by ∼57.76% when triggered by 1.0 W/cm2 ultraviolet light. Furthermore, energy dissipations of SiC LTT during the turn-on and turn-off processes can be reduced by 91.4% and 21.9%, respectively.

Direct-Triggering LTT With Monolithic Structure

Light-triggered thyristor (LTT) has attracted considerable interest in power conversion and control systems because of its strong antiinterference ability and large power capacity. In this work, we propose a monolithic LTT that can be lighttriggered directly without an amplifying gate (AG) design, to improve the device reliability and operating speed. The cathode structure is redesigned into an interdigitated structure with a relatively large light-incident area. The cathode shorts are re-arranged to balance the trigger intensity and the light incident depth, so as to ensure optimal dV/dt capability. Devices are fabricated and adequate performances are obtained, verifying the feasibility of our design.

Hole-transmission enhancement in 4H-silicon carbide light triggered thyristor for low loss *

In this paper, a 20 kV silicon carbide (SiC) light triggered thyristor (LTT) with n-type blocking base is simulated using Synopsys Sentaurus TCAD. In order to reduce the power dissipation, a method that enhances the hole-transmission through electric field induced by gradual doping profile in the n-buffer layer is proposed. The results indicate that the method enhancing the hole-transmission is effective in reducing the power loss of SiC LTT with n-type blocking base. By changing the doping profile of n-buffer layer from uniform to gradual, both on-state loss and switching loss are efficiently reduced. Compared to the conventional SiC LTT with 2.5 μm thick n-buffer layer, when the doping gradient is 1.0 × 1021 cm−4, the on-state and the switching losses of the hole-transmission enhanced SiC LTT are reduced by 34.7% and 17.9%, respectively.

Light controlled (super) cascode, LC(S)C, a power device with optical turn-on and -off

ABSTRACTThe proposed light-controlled cascode is a power electronic device (or circuitry) which can be turned-on and -off by optical excitation. In contrast to the light-triggered thyristor, which can optically be turned-on but not -off, the proposed device allows optical turn-on and -off. Also, it allows a scalability of the blocking voltage by the extension to a light-controlled supercascode [1] which is also shown. After a brief theoretical consideration experimental set-ups will be presented and measurements are shown. Due to the difficulty to buy appropriate devices required for the experimental set-ups some compromises were necessary. Therefore, these first experiments show a very slow switching behaviour. However, this could become speeded up by an optimized photodiode made from wide band gap semiconductor material. In spite of these compromises pulses with a power of 1 kW were turned-on and – off by the experimental set-up. However, this device is far away from being ready for series production but the feasibility is demonstrated and the potentials are shown.

Analysis of corrosion and scaling in high-voltage direct-current valve cooling water system

In this paper, the problems of corrosion and scaling in the converter valve tower cooling water system based on the ± 500kV Baode HVDC transmission project with Siemens light-triggered thyristor HVDC transmission technology are analyzed in detail. The corrosion and scaling phenomenon can cause the closure or emergency shutdown of converter valves and bring potential dangers to the safe and stable operation of power grid. So far, there is no fundamental solution to this problem. Based on the investigation of scaling phenomenon of grading electrode and corrosion of thyristor aluminum alloy heat sinks, the scaling law of the grading electrode is proposed and the cause of scaling is put forward and analyzed. Some suggestions are given.

Shortening turn-on delay of SiC light triggered thyristor by 7-shaped thin n-base doping profile**Project supported by the National Natural Science Foundation of China (Grant No. 51677149).

A new 4H–SiC light triggered thyristor (LTT) with 7-shaped thin n-base doping profile is proposed and simulated using a two-dimensional numerical method. In this new structure, the bottom region of the thin n-base has a graded doping profile to induce an accelerating electric field and compensate for the shortcoming of the double-layer thin n-base structure in transmitting injected holes. In addition, the accelerating electric field can also speed up the transmission of photon-generated carriers during light triggering. As a result, the current gain of the top pnp transistor of the SiC LTT is further increased. According to the TCAD simulations, the turn-on delay time of the SiC LTT decreases by about 91.5% compared with that of previous double-layer thin n-base SiC LTT. The minimum turn-on delay time of the SiC LTT is only 828 ns, when triggered by 100 mW/cm2 ultraviolet light. Meanwhile, there is only a slight degradation in the forward blocking characteristic.

Design and Implementation of a Test Circuit of a Repetitive Critical Rate of Rise of ON-State Current for a High-Power Thyristor

A test circuit of a repetitive critical rate of rise of ON-state current ( di / dt ) for a high-power thyristor is designed and implemented. The operating principle of the test circuit specified in the standard IEC-60747-6 is explained in detail. The design example for the circuit to test repetitive di / dt of 300 A/ $\mu \text{s}$ for a thyristor having a mean ON-state current of 2200 A is presented. The value of the charging resistor is chosen by simulations considering the maximum charging current, power consumption of the charging resistor, maximum charging voltage of the capacitor, and the peak pulsed current of the thyristor. The best firing angles of the thyristor are decided based on the simulations focused on the pulsed current of the thyristor, charging diode current, apparent power of the step-up transformer, and reverse voltage of the charging diode. The repetitive di / dt test prototype of 300 A/ $\mu \text{s}$ , 60 Hz, and 60 shots is assembled with the Infineon light-triggered thyristor (T1503N). The design results are verified by an experiment.

Performance Comparison of ETT- and LTT-Based Pulse Power Crowbar Switch

High-voltage high-power pulse switches are built with semiconductor devices, preferably thyristor, due to the superior performance that they offer. Triggering methods classify the thyristor as electrically triggered thyristor (ETT) and light triggered thyristor (LTT). Due to the specialized gate constructions and many build-in protections, the cost of LTT is much higher than ETT. The operating modes in applications, such as crowbar, do not require all these build-in protections. In this paper, the operation of a crowbar is analyzed, and the build-in protections of LTT are reviewed. This paper proposes three experiments for the design selection of thyristor, between ETT and LTT, for crowbar applications. The experiments cover the electrical performance as well as electromagnetic emissions in a 10-kV, 1-kA crowbar built with both ETT as well as LTT, which can be used to benchmark the performance of the crowbar circuit. From the three experiments, the performance of ETT-based crowbar is found to be comparable with LTT-based crowbar. Based on the experiments carried out with the proposed benchmarking approaches, this paper shows that ETT-based crowbar is a cost-effective solution for crowbar applications.

Modulation Controller Design for the 1400 MW New Zealand Inter Island HVDC Link

Abstract The existing HVDC scheme connecting the North Island and the South Island of New Zealand is currently being upgraded. During this upgrade also known as the New Zealand Inter Island HVDC Pole 3 Project, the existing HVDC Pole 1 based on mercury arc valves is replaced by a new HVDC Pole 3 based on light triggered thyristor vales. Both poles, the existing Pole 2 and the new Pole 3 are then operated as a non balanced bipolar HVDC scheme. In this study, a power system stability analysis of the HVDC Pole 2 and Pole 3 connecting the North Island and the South Island is performed. Focus is hereby on the design of special power modulation controller to enhance the dynamic performance of the entire interconnected power system, especially during and shortly after faults and severe contingencies. The proposed modulation control functions are designed for frequency and transient AC voltage support.

The p/sup -/ layer punch-through structure with a thick, high concentration p emitter for a light-triggered thyristor

The on-state voltage reduction of a light-triggered thyristor was studied from the view-points of reducing the thyristor thickness and using a high-injection, low-lifetime structure. High-injection was achieved by increasing the thickness and concentration of the p emitter. The reduction in thyristor thickness was achieved by using a p/sup -/ layer punch-through structure in both the p base and p emitter. This structure consists of a shallow, high-concentration p layer and a deep, low-concentration p layer. The depletion layer extends through the low-concentration p layer, and it reaches and is stopped by the high-concentration p layer when a high voltage is applied. This structure reduces the thickness by about 5%. The on-state voltage can be reduced for a 6-kV, 5.5-kA light-triggered thyristor by the p/sup -/ layer punch-through structure and the thick, high-concentration region of the p emitter.

Overvoltage self-protection structure of a light-triggered thyristor

Overvoltage self-protection with a slight temperature dependence on triggering temperature was realized for a light-triggered thyristor. This thyristor had a narrow, low concentration p layer in the light-triggered region. This low concentration area was formed by ion implantation. The thyristor was triggered when the depletion layer extended to near the n-emitter. The triggering voltage could be controlled by the ion implantation dose.

Modelling of self-protected light-triggered thyristors

The paper describes the work carried out in modelling the self-protected light-triggered thyristor (SPELTT). In particular, a sophisticated quasi-three-dimensional model was developed for the structure, which included all the important circuit/device interactions. The model was used to investigate the sensitivity of critical operation timings to various processing parameters for the structure. Excellent agreement was found with experimental measurements on the device. The predictive capability of the model has led to identifying approaches which significantly improve the device performance.

Study on overvoltage protection in HVDC LTT valve

The light-triggered thyristor (LTT), which can be directly fired by light, does not need gate electronics on the high-voltage side and is thus a near-ideal semiconductor device for a HVDC valve. In providing overvoltage protection for an LTT without losing its advantage of simple circuits associated with the thyristor, the overvoltage protection system adopted in the conventional electrically triggered thyristor is not necessarily appropriate. The authors have shown that high-speed protective gate pulses generated from the valve base electronics together with the valve arrester are sufficient for the LTT valve overvoltage protection. The adequacy of this protection strategy is demonstrated by factory type tests and also excellent service experiences.

Power Electronics Equipment Development and Application Trends for Higher Reliability and Better Quality of the Electric Power Supply

This paper introduces the development on the power electronics equipment especially applicable to the high voltage power supply systems of the paper and pulp industries. The light-triggered thyristor (LTT), gate turn-off thyristor (GTO) and insulated gate bipolar transistor (IGBT) were firstly developed by Toshiba. These semiconductor devices realized robust and reliable power electronics equipment to directly handle the electric power of high voltage and large capacity.This paper also describes the examples of the power electronics applications to enhance the electric power supply reliability and to improve the power quality. The thyristor clipper (THC) or the thyristor limitter (THL) reduces adverse effect of the AC system faults. The uninterruptible power system (UPS) and the stand-by power system (SPS) rescues equipment from power shortage.Furthermore, applications to the energy savings and the environment preservation are also described. The photo-voltaic (PV) inverter and the re-generative convertor contribute to save fossil fuels and to reduce CO2 emission.Thus, the power electronics equipment will contribute to improve the electrical environment of the paper and pulp industries in aspects of security, quality, efficiency and productivity.

Progress in the development of an 8-kV light-triggered thyristor with integrated protection functions

Light-triggered 8-kV thyristors with an integrated breakover diode were fabricated. The adjustment of the breakdown voltage of the breakover diode (BOD) is realized by a well-defined curvature of the junction between the p-base and the n-base. A multiple amplifying gate structure, together with an integrated turn-on current limiting resistor, guarantees a safe turn-on behavior in the case of overvoltage triggering as well as during light triggering. These thyristors have successfully been put into service at the Celilo Converter Station of the Pacific Northwest-Southwest HVDC Intertie by Bonneville Power Administration in Portland/Oregon/USA. There, a mercury arc valve was replaced by a valve containing these light triggered thyristors with integrated overvoltage protection. In a further development, the amplifying gate structure was optimized in order to simplify the fabrication process and to maintain the high light sensitivity while obtaining a higher dV/dt and a higher dI/dt capability. This was realized by shrinking the optical gate, by carefully adjusting the triggering sensitivity of the amplifying gates and by widening of the turn-on current limiting thyristor. With these measures, initial investigations regarding the integration of a forward recovery protection were also performed.

Development of a Thyristor Valve for Next Generation 500 kV HVDC Transmission Systems

A high voltage thyristor valve is the basic component of an HVDC transmission system. Development of a 500 kV valve for next generation HVDC transmission systems is described. First, the power loss of the valve is analyzed to decide a reasonable wafer size for the light-triggered thyristor. From these results, a six inch diameter wafer size is selected. A light-triggered thyristor, with ratings of 8 kV and 3.5 kA, is developed using the six inch wafer. The design of the valve employing the thyristor and test results with a prototype valve prove that a 500 kV valve can be realized by this design method.

Design and type test of a light-triggered thyristor valve for back-to-back systems

The design of directly light-triggered, water-cooled thyristor valve was designed and manufactured as an extension for the Shin-Shinano frequency converter station (back-to-back system, 300 MW, 125 kV-2400 A) of Tokyo Electric Power Co. is described. The light-triggered thyristor, triggering LED and light guides, gating system, cooling, and structural design are covered. Various tests conducted in the factory and a seismic test on a full-scale valve model are reported. >

Development of VBO-free large capacity light-triggered thyristor valve

Following the recent development of 6 kV class VBO (voltage break-over)-free light-triggered thyristors (LTTs) in Japan, a field verification test has been conducted by applying these thyristors to an actual 100 MVA class SVC valve, and satisfactory results were obtained. The authors describe the characteristics of the VBO-free large-capacity LTTs, the effects that can be expected when it is applied to SVC or HVDC valves, design and manufacturing, the results of factory tests for the SVC and valve, and the results of a verification test in the field. >

Field evaluation of industry's first self-protected, light-triggered thyristor

A description is given of the industry's first self-protected, light-triggered thyristor to be developed, fabricated, and field-demonstrated. This device is installed on a 13.8 kV, 40 MVAr AC switch using 16 series-connected devices operating in one phase of a static VAr compensator at the Minnesota Power Co.'s Shannon substation. The light-triggered thyristor was designed with internal overvoltage protection (safe turn-on at a preset overvoltage level) and with significantly improved dv/dt withstand characteristics. In the process, the AC switch in the static VAr compensator was redesigned to incorporate 16 instead of the originally installed 24 series-connected thyristors. >

A 115-mm phi 6-kV 2500-A light-triggered thyristor

A 115-mm-diameter 6-kV 2500-A light-triggered thyristor developed for high-power converter applications and fabricated using ion implantation, large-diameter-element treatment, and cathode pattern design techniques is discussed. The device has an on-state voltage of 3.0 V at 7800 A, a minimum light-triggering power of 10 mW, a dv/dt capability of more than 3000 v/ mu s, and a turn-off time of less than 400 mu s.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>