Symmetric GTO and snubber component characterization in PWMcurrent-source inverters

The pulsewidth-modulated (PWM) current-source inverter (CSI) used in AC motor drive applications can be implemented with symmetric gate turn-off thyristors (GTOs). One of the major difficulties in the optimization of the GTO switch and the snubber components of the inverter is the variation in different switching conditions encountered during normal operation. Past work has concentrated on the GTO and snubber components in voltage-source applications, where commutation of the GTO device is an independent process and does not affect the operation of the other inverter devices. This paper proposes the characterization of the GTO and the snubber components by formulation of the CSI equivalent circuit during the device commutation period. From the equivalent circuit, the state equations are derived, thereby obtaining accurate voltage and current waveforms of the GTO and associated snubbers. From the analysis, the component power loss can be calculated and optimization performed. Simulation results are verified by using both a laboratory prototype and medium-voltage drive system     

一种带有注入增强缓冲层的4H-SiC GTO晶闸管

门极可关断(GTO)晶闸管是应用在脉冲功率领域中的一种重要的功率器件。目前,由于常规SiC GTO晶闸管的阴极注入效率较低,限制了器件性能的提高。提出了一种带有注入增强缓冲层的碳化硅门极可关断(IEB-GTO)晶闸管结构,相比于常规GTO晶闸管结构,该结构有着更高的阴极注入效率,从而减小了器件的导通电阻和功耗。仿真结果表明,当导通电流为1 000 A/cm^2时,IEB-GTO晶闸管的比导通电阻比常规GTO晶闸管下降了约45.5%;在脉冲峰值电流为6 000 A、半周期为1 ms的宽脉冲放电过程中,器件的最大导通压降比常规GTO晶闸管降低了约58.5%。     

Zero-current and zero-voltage soft-transition commutation cell for PWM inverters

This paper presents a universal auxiliary commutation cell for pulse-width modulated (PWM) inverters termed zero current and zero voltage transition (ZCZVT) commutation cell. It provides zero current and zero voltage commutation, simultaneously, during main power devices turn-on and turn-off, with controlled di/dt and dv/dt. As a result, commutations of the main power devices occur without any losses. This unique characteristic is not achieved by any other soft-switching commutation cell for inverters hitherto presented in the literature, making it a strong candidate for use in low-power (MOSFET), medium-power (IGBT) or high-power applications (GTO, thyristor). Furthermore, reverse recovery losses of main diodes are minimized and auxiliary switches commutate at zero current. To demonstrate the operation of the proposed universal auxiliary commutation cell, a ZCZVT PWM full-bridge inverter is analyzed. To evaluate the operation of the auxiliary circuit in different conditions, prototypes with both IGBTs and MOSFETs for different output powers levels were implemented and their performances compared. Experimental results confirm that there is no overlap between main switch current and voltage, and that waveform ringing is practically eliminated.     

A simple snubber configuration for three-level GTO inverters

A simple snubber configuration for three-level gate turn-off thyristor (GTO) inverters is proposed. The proposed snubber has a single resistor per arm for stored energy dissipation, while the conventional RLD/RCD snubber contains six. This implies that the proposed snubber needs only one chopper circuit per arm for snubber energy recovery. This helps reduce the size, cost, and number of components. Besides the single resistor, the proposed snubber requires two less diodes per arm than the RLD/RCD snubber. Furthermore, the proposed snubber resolves the voltage imbalance problem between inner and outer GTOs without additional components. We have analyzed the proposed circuits and proven its performance through simulations and experiments     

4H-SiC power devices for use in power electronic motor control

Silicon carbide (SiC) is an emerging semiconductor material which has been widely predicted to be superior to both Si and GaAs in the area of power electronic switching devices. This paper presents an overview of SiC power devices and concludes that the MOS turn-off thyristor (MTO™), comprising of a hybrid connection of SiC gate turn-off thyristor (GTO) and MOSFET, is one of the most promising near term SiC switching device given its high power potential, ease of turn-off, 500°C operation and resulting reduction in cooling requirements. The use of a SiC and an anti-parallel diode are primary active components which can then be used to construct an inverter module for high-temperature, high-power direct current (d.c.) motor control.     

Measurements of failure phenomena in inductively loadedmulti-cathode GTO thyristors

The free-carrier absorption (FCA) technique is used for mapping of the carrier content in a dual-cathode gate turn-off thyristor (GTO) at different stages of the turn-off cycle. The FCA technique outputs 3-D maps based on 2-D measurements of local carrier concentration. The measurements are time resolved, thus making a transient response converted into a corresponding sequence of carrier maps. The dual-cathode device is shown to be sufficient for determining the transient behavior in a multicathode structure. The destruction mechanism and reasons for turn-off failure are investigated. The GTO device is inductively loaded and asymmetrically gate contacted in order to emulate a realistic mode of operation. The gate-driving conditions are altered, and the importance of the turn-off gain for turn-off failure is established. The case of equal ON-state cathode currents in both segments is particularly highlighted. The influence of snubber circuits is also discussed     

Turn-off operation of a MOS-gate 2.6 kV 4H–SiC gate turn-off thyristor

The turn-off operation of a 4H–SiC gate turn-off thyristor (GTO) with 2.6 kV breakover voltage has been investigated using an external Si-MOSFET as a gate-to-emitter shunt (MOS-gate mode), in the temperature interval 293–496 K. The maximum cathode current density j_cmax that can be turned off in such a mode decreases from 1850 A/cm² at 400 K to 700 A/cm² at 496 K. The room temperature j_cmax value is estimated to be about 3700 A/cm². The above j_cmax values are essentially higher than those observed when turning this thyristor off in the conventional GTO mode. Turn-off transients in the MOS-gate mode have been studied in both quasi-static and pulse regimes. Temperature dependencies of the turn-on and turn-off times, as well as those of the turn-on and turn-off energy losses have been measured. The upper switching frequency of the GTO is estimated to be about 700 kHz.     

A NOVEL PASSIVE DUAL ENERGY RECOVERY SNUBBER FOR HIGH POWER GTO CONVERTERS

A novel passive dual energy recovery snubber circuit is presented where energy trapped in the snubber inductor and capacitor is recovered into the both DC rail and load, without any active devices or resistors. The maximum over-shoot voltage on the switch is fixed, peak switch current is low, circuit reset is fast and the operational range of load current is wide. This circuit is suitable for use in high frequency, single ended power gate turn-off (GTO) thyrister choppers. Main design equations, some simulations and practical results are included.     

A new buried-gate GTO structure having a large safe operating area

A novel structure of a buried-gate GTO (gate turn-off thyristor) was proposed for expanding the safe operating area (SOA) of unit-GTOs. The SOA of unit-GTOs in a test sample GTO and the spike voltage at the limit of turn-off of the test sample were investigated experimentally. The SOA was calculated by means of a simple model in order to study the mechanism of the expansion of SOA in the structure. The SOA was expanded due to the reduction of the sheet resistance of the p-base layer by the fine mesh pattern of the buried layer. Corresponding to the increased size of the SOA, the spike voltage increased to 1000 V     

A new gate drive circuit for high-speed operation of GTO thyristors

This paper presents a new gate turn-off drive circuit for GTO thyristors, which can accomplish faster turn-off switching for high-speed operation of the GTO. The switching characteristics of GTO's can be improved by use of the gate drive circuit that is able to make a very high rate of the negative gate current. The major disadvantage of the conventional gate turn-off driving technique is that it has a difficulty in realizing higher negative di_G/dt due to the maximum reverse gate-cathode voltage and the stray inductances within the gate turn-off drive circuit. This paper shows that this problem can be overcome by adding another gate turn-off drive circuit to the conventional gate turn-off drive circuit. Simulation and experimental results in conjunction with chopper circuit verify the performance of the proposed gate drive circuit     

RBSOA characterization of GTO devices

GTO devices are characterized using a nondestructive RBSOA (reverse bias safe operating area) tester. Breakdown phenomena observed in GTO testing are very much different from those of a BJT. Explanation of the cause of the loss of device voltage blocking capability during turn-off is given     

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     

GTO逆变型量化电荷充电式脉冲激光器电源

介绍一种用 GTO 作为开关元件的脉冲激光器用逆变电源装置。引入了量化电荷充电概念,并设计了实现最化电荷充电的具体电路。     

Improvements to the passive lossless snubbers for power bridge legs

The paper considers three common snubber circuits used on gate turn-off thyristor and/or insulated gate bipolar transistor inverters. The three snubbers are passive lossless circuits for power bridge legs, and the improvements and modifications to these snubber circuits are presented. The comparative features and operation of the three improved energy recovery snubbers are discussed and supported by PSPICE simulations and experimental results.     

A novel single gate MOS controlled current saturated thyristor

A novel single gate MOS controlled current saturation thyristor (MCST) device is proposed. In the on-state the MCST operates in thyristor-like mode at low anode voltage and enters the IGBT-like mode automatically with increasing anode voltage, offering a low on-state voltage drop and current saturation capability. Simulation results based on 6.5 kV trench devices indicate the turn-off energy loss of the MCST is reduced by over 35% compared to the IGBT. The saturation current density of the MCST is strongly dependent on the on-set voltage of the p ⁺ buffer/n-well junction, leading to its excellent safe operation area (SOA) and making it suitable for high power applications     

Behavior of thyristors under transient conditions

The capability of gate-triggered thyristors to withstand steep wavefront, high-current pulses (i.e., di/dt capability) is a function of both junction temperature and frequency of operation. Localized internal heating occurs during turn-on and may lead to thermal runaway. The conditions required for this to occur have been determined by destructively testing many devices. The initial conducting area of a thyristor largely determines di/dt capability, which is not necessarily related to the size of the device but is a function of the design of the gate region. Gate drive is very important for determining the di/dt capability of a thyristor having a conventional gate design. Two devices which have been designed to increase the initial conducting area are discussed. One of these devices, if improperly designed, can lose its effectiveness with high gate drive. This characteristic can be studied by observing the reverse recovery current immediately following short forward current pulses.     

Demonstration of compact solid-state opening and closing switchutilizing 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/μs and system di/dt exceeded 200 A/μs, 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     

Current state-of-the-art and future prospects for power semiconductor devices in power transmission and distribution applications

Since the first commercially viable thyristors appeared in the early 1960s, there has been a dramatic increase in the switched power ratings and versatility of high-voltage power semiconductor devices. By the mid 1970s, thyristors with switched power ratings of several MVA were being applied in high voltage dc transmission systems and static VAr compensators. The introduction, in the 1980s, of controlled turn-off devices, such as the gate turn-off thyristor (GTO) and insulated gate bipolar transistor (IGBT), broadened the application of high-voltage power devices to hard-switched converters and, by the start of the 21st century, controllable silicon power devices were available with voltage ratings of 12?kV and switched power capabilities of up to 40?MVA. A review of the current state-of-the-art in silicon high-voltage power semiconductor technology covers gate-commutated thyristors (GCT, IGCT) and IGBT devices, including the injection-enhanced IGBT or IEGT. Despite these considerable achievements, there is now mounting evidence that silicon-based power semiconductors are reaching their limit, both in terms of voltage rating and of switched power capability. The introduction of wide-band-gap semiconductor materials such as silicon carbide offers the potential to break through the voltage-switching frequency limitations of silicon, with power-switching frequency products more than two orders of magnitude higher. An analysis of the current status and future prospects for silicon carbide power electronic devices is presented, together with a case study comparing a variety of silicon and silicon carbide solutions in a 10?kV hard-switched converter application. It is shown that an all-silicon carbide switch offers the best electrical performance and lowest cost solution, in spite of higher per unit area device costs.     

High-energy pulse-switching characteristics of thyristors

Experiments were conducted to study the high energy, high di/dt pulse-switching characteristics of silicon controlled rectifiers (SCRs) with and without the amplifying gate. High di/dt, high-energy single-shot experiments were first done. Devices without the amplifying gate performed much better than the devices with the amplifying gate. A physical model is presented to describe the role of the amplifying gate in the turn-on process, thereby explaining the differences in the switching characteristics. The turn-on area for the failure of the devices was theoretically estimated and correlated with observations. This allowed calculation of the current density required for failure. Since the failure of these devices under high di/dt conditions was thermal in nature, a simulation using a finite-element method was performed to estimate the temperature rise in the devices. The results from this simulation showed that the temperature rise was significantly higher in the devices with the amplifying gate than in the devices without the amplifying gate. From these results, the safe operating frequencies for all the devices under high di/dt conditions was estimated. These estimates were confirmed by experimentally stressing the devices under high di/dt repetitive operation     

3100 V, asymmetrical, gate turn-off (GTO) thyristors in 4H-SiC

A 2-mm×2-mm, 4H-SiC, asymmetrical npnp gate turn-off (GTO) thyristor with a blocking voltage of 3100 V and a forward current of 12 A is reported. This is the highest reported power handling capability of 37 kW for a single device in SiC. The 5-epilayer structure utilized a blocking layer that was 50 μm thick, p-type, doped at about 7-9×10¹⁴ cm^-3. The devices were terminated with a single zone junction termination extension (JTE) region formed by ion-implantation of nitrogen at 650°C. The device was able to reliably turn-on and turn-off 20 A (500 A/cm²) of anode current with a turn-on gain (I_K/I_{G, on}) of 20 and a turn-off gain (I_K/I_{G, off}) of 3.3