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We report microsecond timescale switching between the superconducting and normal states of commercially manufactured high-T c superconducting wires using optical radiation to heat the conductor above T c. The achieved voltages and switching times have significant implications for a new class of thermal switches. The report contains experimental data for photo-induced microsecond scale voltage transients as well as numerical analysis of heat propagation through the material in response to optical radiation. The microbridges are etched into commercially manufactured coated conductors and submerged in liquid nitrogen. By varying the magnitude of the transport current, two different optical responses are identified. At low transport currents, short-lived voltage transients occur, transitioning to persistent latching once the current is increased above a threshold value. The microbridge, therefore, behaves as a fast opening and closing switch when carrying low currents or an optically latched thyristor at high currents. This is understood to occur due to critical current suppression as a result of heating from the optical pulse. Optically induced heating reduces the superconducting volume fraction, and Joule heating due to the transport current interaction with the high temperature superconducting occurs, which either causes short-lived or stable self-heating normal regions dependent on the magnitude of the transport current. This study is concluded with an estimate of the energy necessary to drive the microbridge into the resistive state. The observed behavior can potentially be utilized as a switching element in superconducting transformer rectifiers where high frequency switch operation is required. [ABSTRACT FROM AUTHOR]

Industrial water electrolyzers mainly use old thyristor-based rectifiers to obtain the DC current required to run because of the low voltage level and high current requirements of the processes. These rectifiers cause significant ripple in the electrolyzer input current, leading to dynamic operation of the electrolyzer. Even though industrial-scale water electrolyzers are operated under such dynamic conditions, the effect on the electrolyzer performance is not well explored. In this study, current measurements from an industrial alkaline electrolyzer plant were used to define the common current ripple amplitude and frequency caused by the thyristor-based rectification. Based on the parameters obtained, laboratory measurements were conducted using an alkaline water electrolyzer to define the power losses incurred at various ripple amplitudes and frequencies. Additionally, the linearization of the electrolyzer current–voltage behavior as a function of frequency was studied using two electrode sets made of different materials. The laboratory measurements carried out in the study show that the ripple amplitude has a significant effect on increasing the losses, whereas the ripple frequency counteracts this. Thus, dynamic operation can have a large impact on losses, especially at partial loads, where the ripple current amplitudes increase significantly when using thyristor rectifiers. Lastly, the frequencies where the electrolyzer starts to behave linearly were observed to be at 68 Hz with the first electrode set and at 5 Hz with the second one. The considerable difference between the electrode sets indicates that the electrode materials and microstructure play a significant role in defining the electrolyzer frequency behavior. Because common thyristor-based power delivery systems operate at 300 Hz or 600 Hz, the results also imply that when modeling these systems, a linear model can be used for the electrolyzer to simplify the simulation. [Display omitted] • Large amplitude current ripple on alkaline electrolyzers is studied. • Ripple amplitude increases power losses, while frequency counteracts it. • As ripple frequency is increased, the electrolyzer starts to behave linearly. • The linear slope is determined purely based on the impedance. • At high frequencies, power usage can be determined from EIS measurement. [ABSTRACT FROM AUTHOR]

Conventionally, DC arc furnaces are fed by thyristor rectifiers to control the level of current or power transferred to the load. With the advancement of high-power transistors, other structures such as diode rectifiers and DC choppers have been introduced and developed for the feeding system of DC electric arc furnaces. In this paper, the effect of different power supply systems on power quality indexes is discussed. In this regard, two types of feeding systems are considered, including a power supply system based on thyristor rectifiers and a power supply system based on diode rectifiers and DC choppers. In addition, different control methods, including constant current control (CCC) and constant power control (CPC), on DC electric arc furnaces are applied. For evaluating the power quality indexes, voltage and current harmonic distortion, unbalance of voltage and current, and power factor on the AC side are investigated for different power supply systems. Simulation results were performed with PSCAD/EMTDC software. It is shown that the power supply systems with diode rectifiers and DC choppers have superiority in comparison to the types based on thyristor rectifiers. According to the results, the average current THD is reduced from 16.55% in the thyristor rectifier to 8.40% in the chopper rectifiers with the CCC method and from 19.27% in the thyristor rectifier to 7.38% in the chopper rectifiers with the CPC method. Moreover, the average voltage THD is reduced from 5.67% in the thyristor rectifier to 3.02% in the chopper rectifiers with the CCC method. The result is similar to the CPC method. Furthermore, for a specific power supply system, the harmonic distortion is lower in the case of the CPC method than in the CCC method. [ABSTRACT FROM AUTHOR]

This article presents a hybrid five-level converter (H5LC) with cascaded full-bridge submodules (FBSMs) for high voltage direct current (HVdc) transmission. A five-level converter operates at a fundamental switching frequency to generate symmetric five-level square wave output voltages which are shaped into smooth sinusoidal voltages by the ac-side FBSMs. Using a proposed third-order harmonic voltage injection scheme, the FBSMs’ total blocking voltage is limited to one-eighth of the dc-side voltage, reducing the H5LC's losses, footprint, and capital costs. dc pole-to-pole fault blocking is enabled using a bypass branch consisting of bidirectional thyristor valves and fast mechanical switches to suppress the ac-side fault contribution within half a fundamental cycle. Full-scale HVdc simulation studies show the H5LC's ability to control real and reactive powers and additionally, its dc fault resilience. A lab-scale hardware implementation of an H5LC with 30 FBSMs is presented to verify its operating principle. In contrast to the half-bridge submodule based modular multilevel converter, the H5LC has improved efficiency, fewer semiconductor devices, and significantly reduced energy storage requirements. [ABSTRACT FROM AUTHOR]

Gate driver circuits to ensure proper turn-on and turn-off for power switches are essential parts of a power converter design. They become significantly challenging for multilevel converters, where multiple switches are operated at active voltage domains. The recent favorable use of gallium nitride devices for power switches makes gate driving even more difficult as the switch performance and reliability are very sensitive to the variations of the gate driving signals and power rails compared with traditional power MOSFETs. This article discusses gate driving methods using a multilevel multi-inductor hybrid (MIH) converter as the demonstration prototype to address two key challenges in designing gate drivers: 1) providing level-shifted pulsewidth modulation signals to active voltage domains and 2) powering schemes for gate driver circuits. To solve the first challenge, an optimal use of available half-bridge drivers is proposed to eliminate the need for separate signal isolator chips. This method was implemented and verified in an MIH converter prototype for 48-V point-of-load applications using three different powering schemes for gate drivers, including isolated power modules, regulated supplies from switch blocking voltages, and cascaded bootstrap power rails with regulations. The gate driver techniques and powering schemes are compared experimentally in terms of performance to illustrate their benefits and tradeoffs. [ABSTRACT FROM AUTHOR]

For variable frequency induction motor drive application, conventional modular multilevel converter (MMC) faces some issues, like high capacitor voltage ripple at low frequency, high circulating current, and high component count. This article proposes a novel configuration to address these issues, where a six-pulse thyristor-based controlled rectifier is combined with a waveshaper-based MMC (WS–MMC). Each phase of the converter consists of a WS and director valve, and then the phases are connected in series to create a common dc-link. The use of a thyristor-based controlled rectifier as a front-end converter increases reliability and reduces component count to a large extent. Unlike conventional MMC, circulating current does not exist in this converter, and the capacitor voltage ripple does not depend on the operating frequency. As a consequence, the current rating of the switching devices is reduced for the same power output, and capacitor voltage ripple at low frequency stays within the specified limit. Besides this, the component count of the proposed configuration is far less than the MMC-based topologies available so far. The operation principle, relevant control techniques, and analysis of the converter are discussed in detail in this article. The complete system is simulated in MATLAB/SIMULINK, and the performance of the control methods has been validated at different operating frequencies with various load torques. The results show satisfactory performance. [ABSTRACT FROM AUTHOR]

High-voltage direct current (HVDC) circuit breaker development and deployment strongly depend on the testing process, which ensures that the HVDC circuit breakers will satisfy design requirements. This article presents an HVDC circuit breaker test bench circuit configuration that can provide controllable large output currents to simulate different fault conditions for the current breaking test and high output voltage for the dielectric withstand test. The current breaking test circuit is based on multiple cascaded power converters connected in parallel to provide the necessary output current capability. Each cascaded power converter is composed of multiple cells that are operated by a phase-shifted pulsewidth-modulated signal for greater controllability and higher quality of the output waveform. The dielectric withstand test circuit is a simple high-voltage source with a low power rating that can also be used to charge the test bench and the internal circuitry of the circuit breaker that is to be tested. The proposed test bench ensures that fault conditions can be replicated accurately and offers greater flexibility by being able to test mechanical, semiconductor-based, or hybrid HVDC circuit breakers with different current and voltage ratings on the same hardware without any changes. The idea and the operating principle of the proposed test bench are verified experimentally on a downscaled system that consists of three cascaded power converters connected in parallel with three cells per cascaded power converter and with a total equivalent switching frequency of 92.5 kHz. [ABSTRACT FROM AUTHOR]

This paper treats a parallel 12-pulse rectifier as the study subject. The influence of unbalanced terminal voltage, the triggering angle, as well as the commutation angle of a thyristor-controlled rectifier circuit are considered in switching functions. Then, a frequency-domain harmonic coupled admittance matrix under the effect of positive sequence and negative sequence voltages are proposed, respectively. With the integration of the above matrices, a harmonic coupled admittance matrix model of a parallel 12-pulse rectifier under unbalanced voltage is proposed. On this basis, a simplified harmonic model of a 12-pulse rectifier is established, which only considers the effect of major elements through analyzing the elements' distribution and magnitude of the harmonic coupled admittance matrix, as well as the AC current harmonic producing mechanism. All the models proposed in this paper are verified with high accuracy through simulation in MATLAB/Simulink. The models proposed in this paper can be used to guide the selection of harmonic suppression measures and equipment. [ABSTRACT FROM AUTHOR]

A novel zero voltage switching (ZVS) interleaved high step-up converter for renewable energy systems is proposed in this article. By applying a switched capacitor mixed with coupled inductor and built-in transformer, the proposed converter achieves high voltage gain and minimized voltage stress across power switches. Both of the voltage gain and the voltage stress can be adjusted by the turns ratio of the coupled inductor and built-in transformer, which gives an extra degree of freedom for the converter design. Hence, operating at high duty cycles is avoided and low voltage rated semiconductors can be adopted, which reduce conduction losses and improve the circuit performance. Furthermore, an active clamp scheme is utilized to guarantee ZVS turn-on for the power MOSFETs and the leakage inductances of the magnetic means help to provide zero current switching of the diodes. In such a case, switching losses are minimized and the reverse current recovery is alleviated. Accordingly, the proposed converter with reduced counterparts is a suitable candidate for high step-up and high power applications. Finally, a 600-W prototype with 24 to 480 V voltage conversion is built to demonstrate the performance of the proposed converter. [ABSTRACT FROM AUTHOR]

In a hard switched mosfet based converter, turn-on energy losses is predominant in the total switching loss. At higher junction temperature the turn-on energy loss further increases due to the reverse recovery effect of the complementary mosfets body diode in a half-bridge configuration. Estimation of the switching loss under different operating conditions at an early design stage is essential for optimizing the thermal design. Analytical switching loss models available in literature are generally used for estimating the switching losses due to its accuracy and simplicity. In this article, the inaccuracy in the reported loss models due to non-inclusion of temperature-dependent reverse recovery characteristics of body diode, is investigated. A structured method to determine the temperature-dependent switching loss of a SiC mosfet in a half-bridge is presented. A simple methodology has been proposed to analyze the carrier lifetime's temperature dependencies of a SiC mosfets body diode. Device parameters from a $\text{1.2}\,\text{kV}/36\,\text{A}$ SiC mosfets datasheet are used for developing the loss model and experimental validation of the model. [ABSTRACT FROM AUTHOR]

This article presents a high‐gain DC–DC converter consisting of a quadratic boost converter and a voltage multiplier, which helps to lift up the voltage gain. The gain will be further enhanced by increasing the turn's ratio of the coupled inductor. The key features include ultrahigh gain, low voltage stress across switching devices, low input current ripple, and hence, it is preferably suitable for renewable energy applications. A passive clamp lowers the voltage stress across MOSFET, so allowing switch with lower Rds(on) reduces the system cost. Besides this, input inductor makes current continuous and reduces input current ripple. The reverse recovery problem of diodes also gets diminished with the usage of leakage energy of the coupled inductor. The operating principle with different modes of operation is also explained. Zero current switching (ZCS) turn‐on is achieved for power switch, and ZCS turn‐off is achieved for diodes, which helps to reduce the switching losses. This improves the overall system efficiency. A 250‐W prototype is built up to validate the converter. [ABSTRACT FROM AUTHOR]

This article presents a methodology for the time-frequency characterization of switching losses in Gallium nitride field effect transistors used in power electronics applications, particularly in dc–dc converters. Typically, switching losses are measured in the time-domain through the integration of the instantaneous power, that is, the product of the voltage multiplied by the current, during the turn-on and turn-off transients. Nonetheless, as novel power transistors allow for switching times in the nanosecond range, the accuracy of such measurements is compromised by the limitations of the probe-oscilloscope systems in terms of bandwidth and dynamic range. Here, we analyze the time-domain switching loss measurement method, and then, through a complementary setup we demonstrate how to validate the results in the frequency domain. A dc–dc half-bridge buck converter circuit based on the EPC2001C was used as a representative test sample. Less than 1% of difference in critical parameters such as rise-time, pulse width, state-levels and, switching frequency, is encountered between the time- and frequency-domain approaches. Moreover, the measurement uncertainty was analyzed and estimated to be between ±1% and ±8%. This article allows for highly confident switching loss measurements, a better understanding of the switching phenomena and of the measurement system performance. [ABSTRACT FROM AUTHOR]

This article puts forward a high repetition rate and high-voltage resonant pulse generator for plasma-assisted milling. This circuit uses only one semiconductor switch with an antiparallel diode and works in the resonant mode with the help of a resonant inductor, a resonant capacitor, and a pulse transformer to generate high-voltage pulses. An equivalent circuit of the proposed topology considering parasitic elements is established. Based on the equivalent circuit, the working principle of the pulse generator is analyzed in detail. In order to verify the theoretical analysis and circuit operation, a laboratory prototype with a 150-V dc input is implemented. The pulse repetition rate can be adjusted from 5.32 to 18.90 kHz, and the peak output voltage correspondingly varies between 8.84 and 11.7 kV. The pulse generator is used to drive a dielectric barrier discharge plasma-assisted milling chamber. Experimental results show that the pulse generator can work stably. [ABSTRACT FROM AUTHOR]

Utilization of the integrated gate-commutated thyristor as a semiconductor switch in the series resonant converter for isolated medium-voltage dc–dc conversion offers an opportunity for high conversion efficiency while operating at the high switching frequency. Low conduction losses of the switch as well as decreased switching losses due to zero-voltage turn-on and low-current turn-off in the subresonant operating regime are reflected in the efficiency increase of the converter. This article explores the switching behavior of the semiconductor device under low currents while giving insight into the achievable turn-off energy losses and duration of the turn-off transients, as information required during the design process of series resonant converter. Experimental measurements confirm trends observed with simulation results related to turn-off delay process, providing further understanding of the switching losses and achievable performances under resonant mode of operation. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive analysis of the generation mechanism and suppression methods of common-mode (CM) touch current when employing semiconductor-based galvanic isolation (SGI). SGI achieves galvanic isolation by utilizing semiconductor switches to deliver differential-mode (DM) power during their on states while sustaining CM isolation voltage during their off states. In SGI converters, the touch current (TC) is generated as the switch output capacitance is charged by the CM voltage during each turn-on transient. The TC rises as the switching frequency increases, which limits the system power density. This process is modeled by the proposed high-frequency pulse current model and the low-frequency equivalent resistance-based average model. Passive TC suppression approaches are reviewed, and an active TC compensation method has been proposed. A 2-kW EV battery charger with a GaN-based Totem-pole power factor correction stage and an SGI-based dc/dc stage has been built and tested. The touch current has been effectively reduced by 27 dB. It allows the converter to operate at a higher switching frequency to achieve higher power density while meeting the safety standards’ touch current requirement. [ABSTRACT FROM AUTHOR]

This paper proposes a high-step-down dc–dc converter with continuous output current which utilizes coupled-inductors. Another main feature of this converter is applying the same number of switches as the synchronous buck converter. The introduced converter is suitable for non-isolated low-voltage high-current applications, especially voltage regulator modules (VRMs) with 12-V-input. Owing to extension of the duty cycle, the main mosfet current stress and the synchronous rectifier switch voltage stress are significantly reduced. However, the discharge of the leakage inductance energy increases the main mosfet voltage stress. By employing a simple lossless clamp/snubber circuit the leakage inductance energy is recovered, the voltage spike across the main mosfet is clamped, and the turn-off switching losses are reduced. There is at least one inductor in all current paths which creates an intrinsic protection against current shoot-through and provides zero-current-switching (ZCS) turn-on for the main mosfet. High efficiency is attained by the proposed converter due to extended duty cycle, low number of switches, and soft switching operation while the converter driver is just like the conventional buck converter. Due to the single-phase structure of the proposed converter, this converter is a viable alternative to the buck VRM. Similar to the other converters using coupled-inductors, the complexity of coupled-inductors design and the space occupied by coupled-inductors can be considered as drawbacks. A prototype of the proposed converter is implemented to verify the converter operation and the theoretical analysis. [ABSTRACT FROM AUTHOR]

The interest in green hydrogen has been increasing in recent years for several applications, such as energy storage and different industrial sectors. The green hydrogen is produced from water electrolysis supplied by renewable electricity. The operation of industrial large-scale water electrolysis is characterized by a high DC current in the kiloampere range and a few hundred volts. Therefore, the rectifier unit plays an important role in converting AC current of the electricity grid into DC current supplied to the electrolyzer. The power electronic converters are also considered as one of the main cost components of the water electrolyzer system. The objective of this paper is to study whether the operation at a higher voltage than typical values (200 V–300 V) can be beneficial both for the cost and energy efficiency of the power converters in water electrolyzer systems. In this study, three different rectifier topologies considered for an industrial-scale electrolyzer are analyzed and compared in terms of energy efficiency and cost. The simulation models of each topology are carried out in the Matlab/Simulink environment. • The effect of voltage elevation on industrial water electrolyzer system is studied. • Thyristor and transistor-based rectifiers for water electrolyzers are analyzed. • Voltage elevation improves the energy efficiency and cost of rectifiers. • Buck-rectifier provides lowest specific energy consumption of electrolyzer stack. [ABSTRACT FROM AUTHOR]

Suspended thyristor valves are widely used in ultra high voltage (UHV) direct current transmission projects all over the world nowadays. However, the seismic performance of the 800 kV thyristor valve, which has longer hangers, larger air clearance requirement and is heavier than its lower voltage counterparts, has not been fully investigated. This study firstly established a finite element (FE) model of an 800 kV thyristor valve and its corresponding hall building to evaluate the seismic response of the valve. Subsequently, a restraint system consisting of rods, springs and viscous dampers was introduced to reduce the seismic response of the valve. Parametric analysis was carried out on a simplified model to determine the optimal design parameters of the restraint system. The FE model of the restrained valve, making use of the optimal parameters, was investigated. The results show that the system with the optimal parameters can effectively reduce the horizontal displacement of the valve. It is proposed to apply the restraint system to the valves, or other types of suspended equipment, to reduce the horizontal displacement and accordingly increase the seismic resiliency of this types of suspended equipment. [ABSTRACT FROM AUTHOR]

We proposed a two-terminal-electrode vertical thyristor and investigated its suitability as a cross-point memory cell without a selector from the viewpoints of p+- and n+-base region width and a vertically stacked doped-epitaxial-Si layer structure such as p++-emitter/n+-base/p+-base/n++-emitter or n++-emitter/p+-base/n+-base/p++-emitter. The proper p+- and n+-base-region width (i.e., 160 nm) and p++-emitter/n+-base/p+-base/n++-emitter layer structure could enable the development of a cross-point memory cell using the half bias concept by preventing misfit dislocations at the junctions between the n++-emitter and p+-base or n+-base and p++-emitter. It was also found that generation of the misfit dislocations originating from B or P atom segregation at junctions during doped-Si epitaxial-layer growth enhanced the strain at the junctions. The misfit dislocations at the junctions were produced when the strain at the junctions was greater than ∼4 × 10−4. [ABSTRACT FROM AUTHOR]

Recent technological developments have caused a renewed interest in the brushless excitation system. With the application of wireless communication, the conventional diode bridge has been replaced with fully controllable thyristors on the shaft. It offers the same dynamic performance as the conventional static excitation system. The thyristor bridge of the conventional three-phase exciter needs to be controlled with a high firing angle in normal operation in order to fulfill a requirement of both a high ceiling voltage and a high ceiling current. A high firing angle causes high torque ripple to be absorbed by the exciter stator and a low power factor results in a low utilization of the designed exciter. In this contribution, we present a strategy that solves this problem by looking into combinations of thyristor configurations of a double-star six-phase connection of the exciter. Experimental results are used to verify the circuit models implemented for this investigation. A hybrid-mode 12-pulse thyristor bridge configuration seems to be a good solution for implementations in commercial apparatus. An additional switch interconnects two separate thyristor bridges from parallel- to series connection at the rectifier output, and utilizes the advantages of both topologies. [ABSTRACT FROM PUBLISHER]

A parametric dynamic phasor (PDP) model of diode rectifiers has been recently proposed, which uses a computer-aided approach to effectively represent the rectifier dynamics including ac-side harmonics that change with system conditions. This letter extends the PDP methodology to thyristor-controlled rectifier systems where the dc-link voltage is regulated via the thyristor firing control. Steady state and large-signal transient studies demonstrate that the new/extended model is accurate even for prediction of harmonics for various operating modes. [ABSTRACT FROM AUTHOR]

The conventional “Delta” connected thyristor-controlled reactor (TCR) bank used for static var compensation and other applications is proposed to be split into two identical “Delta” banks each having kvar capacity half of the total TCR capacity. The study presented shows that such combination of two identical “Delta” connected reactor banks, one with phase switching by thyristors and the other with line switching thyristor arrangement can effectively reduce the harmonic generation of the TCR. Since both the three-phase banks are connected in delta, the zero sequence triplen harmonics generated due to phase control of thyristors remain trapped inside the delta, thus reducing the harmonic injection into the power system. Further, some other major characteristic harmonics are also minimized in the TCR line current. Thus, the proposed TCR yields a low current THD which meets the requisite harmonics standards and it can therefore be used as an economic solution for reactive power control over a reasonable range in high power grid without using any external harmonic filter or special phase shifting transformer. This paper describes in detail the modeling, analysis, and performance assessment of the proposed scheme. Simulation results are furnished to evaluate the output characteristics of the scheme under varying operating conditions. Finally, experimental results are presented, which proves the theoretical proposition. [ABSTRACT FROM PUBLISHER]

In this paper, a novel protection method based on time-time (TT) transform for thyristor-controlled series- compensated lines is presented. First, current signals at both sides of the sending and receiving ends are retrieved and processed through time-time domain transform (TT-transform), and a TT-matrix is produced. A proposed index is then compared with a defined threshold (THD) in order to determine fault occurrence and faulted phases. Within less than three cycles of the fault inception, a tripping signal can be sent that is acceptable for the speed of digital relays. After faulted phase selection, considering the TT-matrix of the faulted phases of both the sending and receiving ends, another index is introduced for estimation of the fault section. Simulation results show that this approach determines fault occurrence, faulted phase, and fault section under different fault conditions such as fault type, fault location, fault resistance, fault inception angle, source impedance, reverse power flow, different levels of compensation, and different locations of the compensator in the line. The test results in the presence of high noise (with SNR up to 15 dB) confirm the effectiveness of the proposed method. The results also indicate that the proposed method is more robust to fault resistance compared to previous studies. [ABSTRACT FROM AUTHOR]

Controllable three terminal high voltage ($>$ 10 kV) power switches based on silicon carbide (SiC) material are gaining significant attentions since silicon (Si) power switches such as insulated gate bipolar transistors (IGBTs) are typically designed for much lower blocking voltages. After more than 30 years of commercial development, there is a fundamental limitation in designing Si IGBTs with more than 6.5 kV voltage rating. On the other hand, the voltage barrier for SiC power devices could easily exceed 10 kV. In this paper, a world record 22 kV SiC p-type emitter turn-OFF (ETO) (p-ETO) thyristor is reported and analyzed as a promising candidate for high-voltage applications, such as solid-state circuit breaker, HVdc, flexible alternating current transmission system (FACTS), and motor drives. The device is based on a 2 cm2 22 kV p-type SiC gate turn-off thyristor (p-GTO) structure. Its static performances are analyzed exhibiting a high voltage (22 kV) blocking characteristic, ultralow leakage current, and a low forward voltage drop ( $\sim$7 V at 100 A) for a broad range of temperatures. The dynamic performances including turn-on and turn-off are studied. Key switching characteristics such as turn-off storage time, turn-off loss, dv/dt, and di/dt are presented and analyzed. In addition, the large reverse biased safe operation area (RBSOA) of the 22 kV SiC ETO is theoretically analyzed and verified by simulations and experimental tests. [ABSTRACT FROM AUTHOR]

The majority of the industrial motor drive systems are equipped with the conventional line-commutated front-end rectifiers and being one of the main sources of harmonics in the power line. While a parallel combination of these drive units elevates current quality issues, a proper arrangement of them can lead to the cancellation of specific harmonics. This paper proposes a new cost-effective harmonic mitigation solution for multidrive systems using a predictive pulse pattern current modulation control strategy. The proposed technique applies suitable interaction among parallel drive units at the rectification stage to synthesize sinusoidal input currents. The input voltage sensing is avoided in order to minimize the number of required sensors, and the grid synchronization also has been implemented based on a common phase-locked loop (PLL) using the dc-link capacitor voltage ripple. Experimental results validate the effectiveness of the proposed strategy. [ABSTRACT FROM PUBLISHER]

A new electrostatic discharge (ESD) protection device, called quad-silicon controlled rectifier (QSCR), is proposed and verified in a 0.25- \mu \textm CMOS process. The QSCR is designed to be used as ESD protection between separated power domains. Since the QSCR embeds four SCRs between its four terminals, no extra ESD clamps are needed to protect the interface circuits between two separated power domains. Implementations with different circuit topologies were also analyzed to achieve a comprehensive ESD protection design for different applications. From the experimental results, the QSCR can withstand 8-kV HBM and 600-V MM ESD stresses with a silicon area of 75 \mu \text m \times 100~\mu \textm . [ABSTRACT FROM PUBLISHER]

It is well-known that rectifiers are used widely in many applications required AC/DC transformation. With technological advances, many studies are performed for AC/DC converters and many control methods are proposed in order to improve the performance of these rectifiers in recent years. Pulse width modulation (PWM) based rectifiers are one of the most popular rectifier types. PWM rectifiers have lower input current harmonics and higher power factor compared to classical diode and thyristor rectifiers. In this study, neuro-fuzzy controller (NFC) which has robust, nonlinear structure and do not require the mathematical model of the system to be controlled has been proposed for PWM rectifiers. Three NFCs are used in control scheme of proposed PWM rectifier in order to control the dq-axis currents and DC voltage of PWM rectifier. Moreover, simulation studies are carried out to demonstrate the performance of the proposed control scheme at MATLAB/Simulink environment in terms of rise time, settling time, overshoot, power factor, total harmonic distortion and power quality. [ABSTRACT FROM AUTHOR]

This paper presents an application of model predictive control to a variable-speed drive system operating in the multi-megawatt range. The variable-speed drive system comprises a synchronous machine fed by a line-commutated rectifier and a load-commutated inverter. The control task is to regulate the dc-link current, and hence the machine torque, to ensure the machine speed follows a given reference. The proposed control approach is model predictive control, where both the rectifier- and inverter-firing angles are considered as control inputs. The nonlinear model predictive torque controller has been implemented on an embedded system and applied in an industrial-scale pilot plant installation. The experiments show the successful operation of model predictive control on a plant with more than 48 MW power. [ABSTRACT FROM PUBLISHER]

This letter proposes a harmonic mitigation strategy to cancel out current harmonics induced by the front-end rectifiers in multidrive systems, which consist of diode rectifiers, silicon-controlled rectifiers (SCR), and boost converters in the dc-link. The proposed strategy is a combination of a new dc-link modulation scheme with a phase-shifted current control enabled by the SCR. The dc-link current modulation scheme is implemented by adding and subtracting specific modulation levels, which makes the total currents drawn from the grid “multilevel,” resulting in an improved current quality. Simulations and experiments have validated the effectiveness of the proposed harmonic mitigation solution for multidrive systems. [ABSTRACT FROM PUBLISHER]

A compact torus (CT) injector operated at high repetition rates has been developed. A system consisting of a stack of insulated-gate bipolar transistors and storage capacitor banks (slow banks) for repetitive operation has been installed on the circuit of both CT formation and acceleration. Following the installation of silicon-controlled rectifiers for the purpose of triggering ignitrons at CT discharge circuits, a repetition rate of 10 Hz was achieved on the University of Saskatchewan CT Injector. [ABSTRACT FROM PUBLISHER]

The ac and dc drives commonly used on land and offshore drilling rigs produce extremely high levels of harmonic distortion. With voltage distortion often exceeding 20%, equipment associated with the drilling operation can experience erratic operation and equipment damage. Repeated damage to one or several ac drives is common. One land rig in Northern Alberta was experiencing failures with its centrifuge equipment on a weekly basis. During one visit to the site, a drive in the centrifuge was found to have tripped off causing the centrifuge to plug up. After cleaning out the centrifuge and restoring the drive, it tripped off again shortly after drilling operations resumed. A power quality analyzer was connected, which revealed extremely high levels of voltage distortion during drilling operations. Deep notches, which are visible in the voltage waveform, were found to be the result of silicon-controlled rectifiers in the mud pump dc drives. Total harmonic voltage distortion (v_\mathrmTHD) reached 25%. A series-connected passive filter was installed ahead of the centrifuge equipment to reduce the voltage notching and lower voltage distortion. The filter reduced the notch depth by more than half and lowered overall voltage distortion at the centrifuge panel to $<$ 9% during the most severe drilling operations. With line-side voltage distortion levels remaining in the 20% range, the filter proved to be extremely effective in eliminating all centrifuge operational and premature failure issues. [ABSTRACT FROM AUTHOR]

This paper presents a parallel combination of a shunt-connected passive filter and a distribution static compensator (DSTATCOM) for a 12-pulse thyristor rectifier feeding a high-current variable-voltage electrolyzer load. Since the process requires variation of voltage and current over a wide range, the reactive power consumed by the thyristor rectifier also varies enormously. As the passive filter is only able to provide a fixed compensation, the DSTATCOM is used to meet variable reactive power demand to keep the input power factor high even at partial load. In order to keep the DSTATCOM rating small, the bulk of reactive power is supplied by the dominant harmonic passive filter. Moreover, DSTATCOM does not provide any harmonic compensation, which is also taken care by the passive filter. Design and control of this system are discussed briefly, and more emphasis is laid on the implementation of the hybrid filter. An experimental system is tested rigorously, and detailed results are presented. [ABSTRACT FROM PUBLISHER]

Due to the repeated switching, the detailed switch-level models of electrical machines coupled with power-electronic converters are computationally expensive and hard to linearize for small-signal frequency-domain analysis. Average-value modeling (AVM) has become an effective tool for small-signal analysis of power electronic systems and time-domain transient studies where the details of switching are not important and can be neglected. Recently, a parametric AVM (PAVM) approach has been developed for machine/diode rectifier systems. This paper extends the parametric approach to the machine/thyristor-controlled-rectifier systems, where the thyristor firing may be referenced to either the line voltages or the rotor position. An analytical average model for this system is also developed based on the recently proposed constant-parameter voltage-behind-reactance synchronous machine model. The new PAVM is compared against the original switching system, as well as the analytical AVM. It is shown that the PAVM can accurately predict both small-signal characteristics and large-signal transients of the original switching system in light and heavy modes, which represents an advantage over the analytical models which are typically implicit. [ABSTRACT FROM AUTHOR]

One of the most important power quality issues is related to current harmonics generated by nonlinear loads such as diode and thyristor front-end rectifiers. Well-established solutions to overcome this problem, such as active power filters (APFs), have the required high power rating components as a major disadvantage. An alternative, called hybrid power filter (HPF), mixes low power rating active filters with passive filters. Unfortunately, many of these HPF topologies have, as a common disadvantage, a great number of passive components and/or transformers. Based on this fact, new concepts of HPFs, consisting of small-rated inverters and $LC$ filters, have been introduced with wide acceptance. The advantage comes from the fact that these HPFs are connected to the grid without any matching transformer. Recently, some topologies based on dual-converter configurations have been shown to be very attractive, where the APF (or HPF) must deal with highly nonlinear loads with high values of $di/dt$ and supplying the reactive power together with harmonic compensation. On the other hand, the drawback of dual converters is the high number of switch devices. Therefore, this paper proposes a transformerless HPF based on a new six-switch two-leg inverter with an enhanced harmonic compensation capability. Aside from presenting a reduced number of switches when compared with dual topologies, the proposed solution is capable of providing fully compensation even for loads with high harmonic content. Experimental results are presented for an HPF inverter prototype in order to demonstrate that the harmonic compensation performance meets the IEEE 519 standard. [ABSTRACT FROM PUBLISHER]

Fundamental features of the arc stability in a dc arc furnace of 720 V/100 kA/72 MW have been investigated. The Cassie-Mayr arc model has been employed and applied for the target dc arc furnace. In order to characterize the parameters of the Cassie-Mayr arc model and the behavior of unstable arc dynamics, the advanced arc simulations of magneto-hydrodynamics (MHD) have been performed. From the results of MHD simulation, the dc arc dynamic resistance is proposed to be an effective arc stability function reflecting the instability of dynamic arc behavior. A control strategy of the 12-pulse thyristor rectifier system to regulate the arc stability function is also proposed in this paper. The simulation and experimental results confirm the usefulness of the proposed dynamic arc resistance as the arc stability function along with the active control strategy. The proposed arc stability function can be regarded as an effective criterion for the overall power conversion system to maintain highly stable arcing operation leading to better productivity and reliability in a dc arc furnace. [ABSTRACT FROM AUTHOR]

Two-electrode graphite spark gap switch (TGSGS) is used as the main discharge switch and triggered by a reliable trigger generator in pulsed power conditioning system (PPCS). There would be 108 energy modules in PPCS working at the same time. The reliable operating and jitters of the trigger generators will have impact on the PPCSs performance. In this paper, the working modes of the TGSGS are discussed and the performance of trigger generators in PPCS is tested and presented. A protection strategy of the trigger generator in PPCS is introduced, and effect of the blocking capacitor on the trigger pulse transmission is analyzed and tested. The protection strategy of the trigger generator based on blocking capacitor and fuse can effectively prevent the energy anti-irrigation failure when the pulse transformer core saturated. The blocking capacitor has some effect on the trigger pulse transmission, and has the larger capacitance, getting the higher peak amplitude on the cathode of the TGSGS. It is tried to discuss the working characteristics of the thyristors, and proposes a selection reference of the thyristors in this and other similar applications. The combination of analysis and measurement would be useful for the selection of thyristors and other components. [ABSTRACT FROM PUBLISHER]

Presents the cover/table of contents for this issue of the periodical. [ABSTRACT FROM AUTHOR]

A lot of large-scale industrial critical loads suffer from voltage interruptions and sags which can cause a significant financial loss. The thyristor-based solid-state transfer switch (STS) and mechanical-based automatic transfer switch (ATS) are used to protect loads against these power quality problems. However, the STS has a great deal of loss consumption because of the forward voltage drop of the thyristors, and ATS can hardly satisfy the voltage-sensitive load due to the long transfer time. This paper proposes a 400 V/1000 kVA hybrid ATS (thyristor switch in parallel with mechanical switch) (HATS) to realize low power consumption under normal situation and transfer fast when required. The proposed HATS has four transfer strategies which can be chosen according to different applications, it realizes the overlapping transfer of the neutral wire, and it can make a decision to transfer or not according to the different fault locations (transfer on the source side and not transfer on the load side). The design details of the prototype are presented, and laboratory tests and field experiments show the prototype good performance. [ABSTRACT FROM PUBLISHER]

Three-level active neutral-point-clamped (NPC) (ANPC) (3L-ANPC) voltage-source converters (3L-ANPC VSCs) offer three additional switch states and an increase of commutations by a factor of four, compared to the three-level NPC voltage-source converter. This paper presents, for the first time, a detailed analysis of all 3L-ANPC VSC commutations using high-power 5SHY55L4500 integrated gate-commutated thyristors. Starting with a description of the switching states and commutations, a new 3-kV 5-kA medium-voltage 3L-ANPC testbench is described. To verify the function of all commutations, this paper derives suitable switching sequences and analyzes the commutations and switching transients in detail for dc-link voltages of 2.13–2.43 kV and load currents of 3.95–4.36 kA. The experimental investigations show that, although the ANPC commutations substantially differ from NPC commutations, the ANPC commutations do not present critical operating conditions for the power semiconductors or the converters. Thus, all 32 ANPC commutations can be applied in a new medium-voltage converter realization. [ABSTRACT FROM PUBLISHER]

This paper presents a novel large-power voltage source converter (VSC) arrangement suitable for flexible alternating current transmission system applications, achieved by combining four three-level three-phase neutral-point-clamped inverters by means of intermediate magnetic elements with lower VA rating and size than those of similar existing installations. The 12 inverter poles forming the VSC share a common dc bus and are implemented using standard power electronic building blocks of well-proven reliability. The output voltage is doubled by using an H-bridge configuration, and only a single-secondary grid coupling transformer is required. In addition, the intermediate magnetic elements ensure an equal power sharing between the four inverters. Since they also allow for the harmonic cancellation between the inverter poles and eliminate any third harmonic component created by the modulation, the output voltage waveform has a high quality, often eliminating the need for additional filtering. In this paper, the converter components and its operation are explained, and experimental results for several modulation strategies are provided. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel 12-pulse hybrid-mode thyristor rectifier (HMTR) that can operate in either parallel mode or series mode with the help of a switch. No matter in which mode it operates, the proposed 12-pulse HMTR keeps the same pulses in the load current. It is designed to operate in parallel mode when low output voltage is required and in series mode when high output voltage is required. This way, the firing angle of the thyristor is reduced and thereby the total harmonic distortion (THD) in the input current is improved. The predictive current control strategy is also proposed to achieve the hybrid-mode operation. Fast current response is achieved both in parallel and series modes as well as in transitions between parallel and series modes. The concept of the proposed predictive current control scheme is quite simple and understandable, and easy to be implemented by a microprocessor. This paper includes analysis, simulation, experiment, and a comparison of the proposed control method with the conventional PI controller. Results from both simulation and experiment demonstrate the validity of the proposed 12-pulse HMTR and the effectiveness of the predictive current control algorithm. [ABSTRACT FROM AUTHOR]

Abstract: A set of in-vessel saddle coils has been installed on J-TEXT tokamak. They are proposed for further researches on controlling tearing modes and driving plasma rotation by static and dynamic resonant magnetic perturbations (RMPs). The saddle coils will be energized by DC with the amplitude up to 10kA, or AC with maximum amplitude up to 5kA within the frequency range of 1–5kHz. At DC mode two antiparallel 6-pulse phase thyristor rectifiers are chosen to obtain bidirectional current, while at AC mode an AC–DC–AC converter including a series resonant inverter can generate current of various amplitudes and frequencies. The paper presents the design of the power supply system, based on the definition of the power supply requirements and the feasibility of implementation of the topology and control strategy. Some simulation and experimental results are given in the end. [Copyright &y& Elsevier]

Technical details about intermittent pulse rectifiers for large-capacity pulsed power supply have rarely been reported in the literature. In this paper, a new thyristor triggering scheme for this application is proposed. This proposed scheme adjusts gate trigger pulses according to the real-time variation of thyristor anode-to-cathode voltage to optimize the triggering performance. Accurate triggering is possible under big line voltage distortions and large frequency changes. Integrated real-time diagnostics can provide valuable information regarding thyristor triggering. The scheme can also prohibit unnecessary trigger pulses to reduce the gate power dissipation. Thus, gate trigger pulses can be designed with high amplitude to enhance the thyristor turn-on characteristics. The validity and superiority of the proposed scheme is verified through experiments. In actual operation, the scheme performs satisfactorily even under sudden load changes. [ABSTRACT FROM PUBLISHER]

The operation of offshore drilling rigs and production platforms requires the extensive use of variable-speed drives. Historically, this involved dc drives almost exclusively, but more recently, ac drives have begun to find their way onto these facilities. Often, combinations of dc and ac drives are used. Silicon-controlled rectifier- or thyristor-bridge-based dc drives will distort the supply voltage by creating commutating notches. These notches can become quite deep if the source is weak, the dc drive load is heavy, and line reactors are not installed. Excessive voltage notching can cause operational problems and/or failures in other loads connected to the bus. When system resonance causes the ringing of these notches, the problem becomes even more severe. One such susceptible load is the ac drive. Wide-spectrum filters designed to reduce the harmonic currents being drawn by the ac drive can also be used to protect the drive from the harmful effects of commutation notching and other associated disturbances. [ABSTRACT FROM PUBLISHER]

A resistor-less power-rail electrostatic discharge (ESD) clamp circuit realized with only thin-gate-oxide devices and with a silicon-controlled rectifier (SCR) as the main ESD clamp device has been proposed and verified in a 65-nm CMOS process. By skillfully utilizing the gate leakage current to realize the equivalent resistor in the ESD-transient detection circuit, the RC-based ESD detection mechanism can be achieved without using an actual resistor to significantly reduce the layout area in I/O cells. From the measured results, the new proposed power-rail ESD clamp circuit with an SCR width of 45 \mu\m can achieve 5-kV human-body-model and 400-V machine-model ESD levels under the ESD stress event while consuming only a standby leakage current of 1.43 nA at room temperature under the normal circuit operating condition with 1-V bias. [ABSTRACT FROM AUTHOR]

An ultralow-leakage power-rail electrostatic discharge (ESD) clamp circuit realized with only thin gate oxide devices and with silicon-controlled rectifier (SCR) as the main ESD clamp device has been proposed and verified in a 65-nm CMOS process. By reducing the voltage difference across the gate oxide of the devices in the ESD detection circuit, the proposed power-rail ESD clamp circuit can achieve an ultralow standby leakage current. In addition, the ESD-transient detection circuit can be totally embedded in the SCR device by modifying the layout structure. From the measured results, the proposed power-rail ESD clamp circuit with an SCR width of 45 \mu\m can achieve 7-kV human-body-model and 350-V machine-model ESD levels under the ESD stress event while consuming only a standby leakage current in the order of nanoamperes at room temperature under the normal circuit operating condition with 1-V bias. [ABSTRACT FROM PUBLISHER]

The high-field quasi-continuous magnets (QCM) are of great interest for scientific experiments that require long pulse duration and in particular a field pulse with a flat-top. For the QCM, the power supply is a real challenge. At the Wuhan National High Magnetic Field Center (WHMFC), it is planned to realize a 45 T/500 ms flat-top field by the series combination of a 0.6 kV/35 kA battery bank and a 12-pulse rectifier that is powered by a 100 MVA/100 MJ flywheel pulse generator (FPG). In order to reduce the dc current ripple, a dc passive filter is connected in parallel with the rectifier. The simulation of the pulse shape with respect to the voltage profile supplied by the power supply takes the resistance of the magnet into account; this increases with temperature as a function of coil current. The configuration and the associated control strategy are presented in this paper. A simulation model of the combined power supply system is developed and compared with the model of a single rectifier supply system. Results are provided to validate the proposed method. [ABSTRACT FROM PUBLISHER]

A model of the turn-on spread has been developed for the axisymmetric configuration characteristic of the optical triggering of power SiC thyristors. Results for plane- and axisymmetric cases are compared. It is shown that the initial stage of the spread, during (2-3)τ , where τ is the current rise time constant for the thyristor turn-on, is characterized by a relatively low spread velocity, especially in the axisymmetric case. It is demonstrated that, even for a comparatively large thyristor structure, self-similarity conditions are not valid even for the plane case. [ABSTRACT FROM AUTHOR]

This paper investigates occupational exposure to time-varying magnetic field generation in high-power rectifier systems. Two different kinds of high-power rectifier systems rated for 25 kA are modeled and analyzed. The performance is compared and evaluated on the basis of exposure guidelines from the International Commission on Non-Ionizing Radiation Protection (ICNIRP). In order to focus on the qualitative effect of rectifier operation, the mechanical structure of the current-carrying conductors is simplified as an infinite long busbar model and low-frequency harmonic contents up to 65 kHz are considered. A thyristor rectifier generates a significant amount of low-frequency magnetic field harmonic contents, both at the ac and dc sides of the rectifier, infringing the limit from ICNIRP. The multilevel IGCT-type rectifier has almost negligible field generation from the ac input side and smaller harmonic contents in the dc load side, complying with ICNIRP guidelines. This remarkable advantage of multilevel rectifier-IGCT type can lead to a simpler site layout design for installation and cost-effective compliance to the guidelines of occupational exposure against the magnetic field. [ABSTRACT FROM AUTHOR]

The predictive current controller presented in this paper provides fast current control for thyristor converters without relying on the accurate load model. Unlike load-model-based predictive methods of current control, this method does not use load parameters in the calculations of the firing angle. Instead, thyristors are fired when the sum of the measured instantaneous load current and the load current rise, which is predicted from the voltage–time area on the dc-side inductor, is equal to the current reference. This way, accurate current control is achieved just by knowing the dc-side inductor parameters and by measuring line voltages, the load current, and the load voltage. The proposed predictive current controller exhibits a practically negligible steady-state error, the fastest possible transient response, and the fastest possible and smooth transitions between continuous- and discontinuous-current conduction modes, for both the rectification and inversion modes of operation of the converter. It shows great stability and robustness. The controller also compensates for sudden changes in both line and load voltages, as well as for voltage drops due to the commutation process. Based on the proposed algorithm, the computer simulation model and the laboratory prototype of the system were developed. Both the simulation and experimental results demonstrated an excellent dynamic performance of the proposed controller. [ABSTRACT FROM PUBLISHER]