A large-capacity GTO inverter with low-loss snubber circuits

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     

Turn-On and Turn-Off Characteristics of a 4.5-kV 3000-A Gate Turn-Off Thyristor

A 4.5-kV 3000-A gate turn-off (GTO) thyristor has been developed for use in high-power motor drive control equipment such as inverters and choppers. The high gate turn-off current of 3000 A is achieved by decreasing the variation of on-state voltages as well as turn-off times between segments which compose the GTO thyristor. This idea is supported by observation of infrared radiation during the turn-off process in the parallel operation of two segments with different on-state voltages or turn-off times. The parallel operation behavior is well simulated by a two-dimensional numerical simulation. Such design considerations and electrical characteristics of the newly developed high-power GTO thyristor are described. The device has a forward blocking capability of 4.5 kV, a maximum gate turn-off current of 3000 A, on-state voltage of 3.0 V at 3000 A, turn-on time of 10 ?s, and turn-off time of 25 ?s.     

Parallel Operation Techniques of GTO Inverter Sets for Large AC Motor Drives

Techniques are presented for using a high-power GTO in a PWM inverter and operating inverter sets in parallel to increase the inverter equipment capacity. The high-power GTO has both a very large turn-off gate current and turn-on gate current for overdrive. It is best to employ an isolation pulse transformer for current amplification as the gate circuit. Also, the high-power GTO, which has a relatively small nonrepetitive controllable current compared with that of a medium- or low-power GTO, in principle can be protected effectively against short circuit faults using fuses. In parallel set operation, the inverter equipment has four typical behavior patterns which arise from differences in GTO switching characteristics. Of these, the behavior pattern in which the current balance is optimized is explained. In addition, the method for designing an interphase reactor as a current balancer and the combination region of GTO characteristics have been given. By means of a parallel set operation test, it has been confirmed that a current unbalance can be suppressed to below ten percent of the peak load current.     

A nondissipative snubber circuit for high-power GTO inverters

A novel snubber circuit for high-power GTO inverters is composed of only passive components which, idealized, produce no losses. The stored energy in the turn-on and turn-off snubbers is completely recovered during a switching cycle. In the absence of a permanent circulating current in the recovery transformer, the minimum on-time duration of one half-bridge is very low. The nondissipative operation of the snubber circuit permits a liberal design of the snubber components by which the switching losses in the power semiconductors are greatly reduced     

Untersuchungen und Erfahrungen mit abschaltbaren Leistungshalbleitern

Übersicht Vorgestellt werden neue abschaltbare Leistungshalbleiter (GTO, bipolare Transistoren, IGT, MOSFET, SIT und schnelle Dioden), die in den letzten Jahren die Leistungselektronik in allen Leistungsbereichen entscheidend verändert haben. Diskutiert werden das Schaltverhalten (Ein- und Ausschalten) und der sich daraus ergebende Frequenzbereich. PWM-Wechselrichter mit 20 kHz Pulsfrequenz mit verschiedenen Transistortypen werden verglichen: hier hat der IGT die besten Eigenschaften. Steuergeneratorschaltungen und Steuerleistungsbedarf werden angegeben. Für GTOs werden verlustarme Beschaltungen erörtert. Anwendungen und Entwicklungstrends werden aufgezeigt.

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Measurements and experiences with turn-off semiconductor power devices

Contents Presented are new turn-off semiconductor power devices (GTO, bipolar transistor, IGT, MOSFET, SIT and fast recovery diodes), which have changed decisively power electronics in all power ranges during the last years. Discussed are the switching behavior (turn-on and turn-off) and the applicable frequency range. PWM-inverters with different types of transistors are compared; here the IGT has the best properties. Gate driver circuits and gate power demand are given. Low-loss snubbers for GTOs are presented. Applications and development trends are shown.

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Herrn Prof. Dr. phil. nat. W. Gerlach zum 60. Geburtstag gewidmet.     

Distribution of linear control-current density over the area of a power thyristor

A model is suggested, and calculation of the distribution of the control-current linear density along the cells of the emitter n ⁺ layer of a power gate turn-off thyristor (GTO thyristor) is performed. It is shown that with numerous rings, linear control-current densities for the cells of the n ⁺ layer in the rings adjoining the gate electrode and in peripheral rings can differ by a factor of 2 or more. Means to increase the switching-on uniformity of GTO thyristor cells are proposed.     

Double-stage gate drive circuit for parallel connected IGBT modules

Solid state modulators are increasingly being used in pulsed power applications. In these applications IGBT modules must often be connected in parallel due to their limited power capacity. In a previous paper, we introduced a control method for balancing the currents in the IGBTs. In this paper, we investigate techniques to minimize the modules' rise and fall times, which can positively impact the modulator's output pulse parameters, which in turn must meet the application's specifications. Further, a reduction in rise and fall times lowers switching losses and thus increases the modulator's efficiency. To reduce the voltage rise time of the pulse without increasing the maximal over-voltage of the parallel IGBTs we have investigated a double-stage gate driver with protection circuits to avoid over-voltages and over-currents. Additionally voltage edge detection has been implemented to improve current balancing. Our measurement results reveal the dependency of the rise-time and turnoff losses on the design parameters of the gate drive. We show that our design achieves a 62% reduction in the turn-off rise time, and a 32% reduction in the turn-off losses.     

Improved current source GTO inverter-fed induction motor driveswith PWM-controlled thyristor converter

An improved current-source GTO (gate turn-off) inverter system for driving an induction motor at high frequency was developed. This system is composed of an inverter using GTOs and a PWM (pulsewidth-modulated)-controlled thyristor rectifier. The energy rebound circuit in the inverter is used to turn off the thyristors in the rectifier and to apply PWM control techniques. This circuit plays an important role in the treatment of reactive power in a load. The capacitors connected to the AC input terminal to improve PWM control also function as a filter. Thus, the waveforms of the input voltage and current become almost sinusoidal. Principles and circuit operations of the rectifier section are described in detail. The current-source GTO inverter is used to drive a 5.5 kW induction motor. The experimental waveform and characteristics for the tested motor drives are given. It is shown that the harmonic components of the input voltage and current are eliminated or reduced by using the PWM control technique without spoiling the inherent characteristics of the current-source GTO inverter     

A new regenerative snubber circuit for large-capacity three-level GTO inverter systems

Increase in the capacity of GTOs has made remarkable progress in recent years. At present, 4.5-kV, 4.0-kA GTOs are commercially available, and 6.0-kV, 6.0-kA GTOs made from 6-inch silicon wafers are appearing. The 6-inch GTOs will be applied to our three-level GTO inverter system. In order to apply GTOs to voltage-source inverters, snubber circuits are necessary for limiting on the turn-on di/dt and turn-off dv/dt. To realize high efficiency of the system, regenerative snubber circuits are often applied. A conventional circuit applied to three-level GTO inverters had the problem of long paths created for snubber circuits of the inner GTOs. Another circuit using a current transformer for recovering the energy trapped in the snubber circuits of the inner GTOs has been presented. In this paper, a new regenerative snubber circuit is proposed, which is more suitable for three-level GTO inverter systems with many phase-legs. By applying the snubber circuit, all snubber energy generated by each GTO switching can be regenerated to the dc link. In addition, high current turn-off performance of both the inner and the outer GTOs is verified by several successful experimental results using 6-inch 6.0-kV, 6.0-kA GTOs. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(2): 41–48, 1997     

New Approach to a High-Power GTO PWM Inverter for AC Motor Drives

A control method for GTO PWM inverter parallel-set operation and a new protection system for prevention of short-circuit faults caused by turn-off failure, both to realize a high-power drive system are described. Timing control of GTO gate pulse command provided by a feedback loop, and a reactor at the output of the inverter can minimize the cross current flowing between inverters and can balance the output current of each inverter in inverter parallel-set operation. This method eliminates the necessity of selecting GTO's of equal characteristics, and can apply to parallel-set operation of three or more inverters. The new protection system judges the on and off states of the GTO from the GTO gate-cathode voltage and detects turn-off failure of the GTO. This method positively stops the inverter system safely and reliably upon turn-off failure of the GTO. Experiments are carried out on a 30-kVA inverter and two sets of 450-kVA GTO inverters.     

零电压零电流谐振极型软开关逆变器

提出了一种新型的零电压零电流谐振极型软开关逆变器。在主功率器件开通和关断时,实现零电压和零电流,减小了电路损耗。同时,续流二极管的反向恢复损耗被降低到最小,辅助开关也实现了零电流开关。对其工作原理进行了分析,给出了不同工作模式下的等效电路图。制作了一个1 k W的试验样机,结果验证了该软开关逆变器的有效性。     

Three-Phase Static Power Supplies for Air-Conditioned Electric Coaches using High Power GTO

The electrical design, characteristics, construction, and test results of a 170-kVA static power supply using 2500-V 600-A gate turn-off (GTO) thyristors developed for a wide range of electric railway applications are discussed. This power supply is principally composed of a thyristor chopper at an elementary frequency of 360 Hz and three-phase gate turn-off thyristor inverters in the form of a twelve-phase bridge configuration. It is capable of stabilizing a 60-Hz ac voltage and twelve-phase waveform. The bulk and weight of this power supply are ascribed to the avoidance of an inverter commutating circuit, which contains parasitic thyristors, capacitors, and inductances. The applied strategy is derived from the trend of the state of the art regarding switching cells and commuter trains.     

Active power filters using resonant pole inverters

The use of a new soft switching inverter topology, the resonant pole inverter (RPI), for harmonic compensator realization, is proposed. Using resonant transitions to minimize switching losses, the topology is suitable for use with GTOs and other gate turn-off devices. Switching frequencies on the order of 10-20 kHz at multikilowatt power levels are feasible. A current-mode modulation strategy is proposed and is seen to realize good spectral characteristics. Extensive simulation and experimental results of a 10 kVA GTO resonant pole inverter switching between 10 and 20 kHz confirm the validity of the approach     

On-the use of IGBT-gated GTO-cascode switches in quasi-resonantconverters

The gate turn-off (GTO) thyristor has the highest voltage and current rating among the semiconductor power switches used extensively today. This paper documents the use of an insulated gate bipolar transistor (IGBT) to improve switching performance of a GTO in a cascode switch. 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 converter and simulated on a computer using PSPICE. Results indicate that IGBT-gated GTO-cascode switches are promising candidates for high-power and high-frequency applications     

2.5 kV 2000-A monolithic reverse conducting gate turn-off thyristor

A 2.5 kV 2000 A monolithic reverse-conducting gate turn-off thyristor (RC-GTO) has been developed using a precise lifetime control technique, a precise gate etching control technique, and an electrical separation technique between the GTO part and the diode part. It is most important for the RC-GTO to separate electrically the GTO part from the diode part. A very high separation resistance of 100-150 Ω is attained by applying a double diffused profile, and a high turn-off current of 2000 A is achieved by applying the precise lifetime control technique and the precise gate etching control technique. The development of the 2.5 kV 2000 A RC-GTO has been aided by the use of computer simulation and an image-converter camera     

Multilevel Converter Topology Using Two Types of Current-Source Inverters

A multilevel power-converter topology based on two types of current-source inverters (CSIs) has been proposed for large induction motor drives. The topology utilizes the combination of the load-commutated inverter (LCI) using thyristors and the CSI using gate turn-off thyristors (GTOs). As a result, the multilevel-inverter operation takes advantage of a soft switching of the LCI and hard switching of the CSI. The output capacitor is required to generate the leading power factor for load commutation of the LCI. It is shown that the proposed multilevel operation contributes to the leading-power-factor generation by providing the effective phase shift. Thus, the leading power factor required for the load commutation of the LCI is obtained with significantly smaller capacitors at the inverter's output terminals. As a result, the proposed approach can employ the LCI and utilize its soft-switching operation, yielding a cost-effective solution compared with the conventional multilevel CSI using two GTO CSIs. The switching losses are curtailed due to the natural commutation of the LCI and the six-step operation of the GTO CSI. Therefore, the proposed multilevel inverter can both increase the output power level and decrease the output capacitor size for LCI. The simulation and experimental results have been shown to verify the feasibility of the proposed multilevel topology and its operation     

三电平逆变器窄脉冲补偿方法研究

二极管箝位三电平逆变器在中压大功率场合应用很广泛。采用可关断晶闸管GTO(Gate Turn-off Thyristor)或集成门极换向晶闸管IGCT(Integrated Gate Commutated Thyristor)时存在窄脉冲NPW(Narrow Pulse Width)问题。窄脉冲问题与中点电位波动问题相互交织在一起,目前的算法还没有非常成功地在一种PWM方法中解决好这两个问题的方法。SVPWM方法也都无法扩展到三电平以上。基于三电平SPWM方法。提出了零序电压注入ZSVI(Zero-Sequence Voltage Iniection)窄脉冲补偿方法。零序电压注入即在三相参考电压中注入零序电压分量。仿真结果表明。采用ZSVI方法输出电压总谐波畸变率THD(Total Harmonic Distortion)大大减小,输出电压THD不再受增加最大、最小窄脉冲宽度影响。因此可以通过增加最大、最小窄脉冲宽度提高系统的可靠性。而不影响系统的性能．提出的ZSVI方法可以推广到任意电平的逆变器的控制．     

桥式电路中不同封装SiC MOSFET串扰问题分析及低栅极关断阻抗的驱动电路

由于SiC MOSFET开关速度较快,使得桥式电路中串扰问题更加严重,这样不仅限制了SiC MOSFET开关速度的提升,也会降低电力电子装置的可靠性。针对SiC MOSFET的非开尔文结构封装和开尔文结构封装的串扰问题分别进行分析,栅漏极结电容的充放电电流和共源寄生电感电压均会引起处于关断状态开关管的栅源极电压变化。提出一种用于抑制串扰问题的驱动电路,该驱动电路具有栅极关断阻抗低、结构简单、易于控制的特点。分析该驱动电路的工作原理,提供主要参数的计算方法。最后通过实验测试了两种结构封装SiC MOSFET的串扰问题,并且对提出的驱动电路进行了实验,验证了其正确性以及对串扰问题的抑制效果。     

GTO thyristor applications for HVDC transmission systems

Conceptual designs for convertor substation equipment for a HVDC (high-voltage direct current) transmission system using current- as well as voltage-source-type GTO (gate turn-off thyristors) power convertors (referred to as VSTGC and CSTGC) are presented. A study indicates that the VSTGC is preferable to the CSTGC. Also presented is a preliminary economic comparison between two HVDC-system alternatives for applying power to a weak AC system, one using a self-commutated GTO power convertor and the other combining a line-commutated convertor and a synchronous condenser. The result indicates that the two HVDC convertor substation alternatives cost about the same     

Device simulation of carrier lifetime-controlled GTO

Recent development of power semiconductor devices has produced remarkable advances in power electronics. Among them, the gate turn-off thyristor (GTO) is one of the most important devices. Carrier lifetime-controlled devices have been proposed recently to realize low turn-off switching loss. Thus, computer simulation for the device is now necessary to predict its characteristics. In this study, we simulated a carrier lifetime-controlled GTO with the FEM program. Lifetime control, such as heavy metal diffusion and electron beam irradiation, showed a trade-off relation between on-state and turn-off conditions. Partial lifetime control, which generates lattice defects locally by light ion irradiation, showed the possibility of reducing turn-off loss and improving the trade-off relations. Furthermore, the numerical analyses showed relations between the location of the irradiated point and variations of the internal carrier distributions. © 1997 Scripta Technica, Inc. Electr Eng Jpn 119(1): 82–89.