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High-power current sources with high dynamic performance, ultralow current ripple, and absolute reference tracking accuracy are the key elements for magnets (bumper and septum) that are used in accelerators. Similar requirements are also encountered in plasma research applications in fusion reactors, as well as plasma research for the future high voltage direct current circuit breakers. Therefore, the current source must be able to drive resistive/inductive and highly fluctuating loads without any compromise in its performance. In this paper, such a flexible, dynamic, and accurate current source is introduced, which able to provide amplitudes up to 30 kA and bipolar voltages up to 10 kV. The system’s operating concept is presented and its design procedure in order to fulfill a list of demanding specifications is demonstrated. In addition, a detailed description of its near-optimal, advanced control system is presented. Finally, the theoretical considerations are verified by extensive simulation results for various operating scenarios, including driving chaotic arc loads. [ABSTRACT FROM AUTHOR]

In this paper, the results of a 2.88-MW solid-state long-pulse modulator, which has been designed for the new linear collider at the european spallation source in Lund, are summarized. The presented modulator generates an output voltage pulse of 115 kV with a pulselength of 3.5 ms. The main components of the modular system, which include a series–parallel resonance converter, a high-voltage high-frequency transformer, and an output rectifier, are discussed. The modulator design is verified by measurements performed with a full-scale prototype, which is operated under nominal load conditions. A detailed output voltage ripple evaluation is given, and in addition, the system design has been proven by a 7- and 2/3-h heat run test. All specifications are well within the given limits, and the maximum occurring temperatures in the transformer stay below 110 °C even under worst case assumptions. The system achieves a pulse efficiency (determined by the pulse shape) of 96.78%, an overall electrical system efficiency of 91.9%, and a combined pulse system efficiency of 89%. [ABSTRACT FROM AUTHOR]

This paper presents the design of an ultraprecise 127-MW/3- \mu \textrm s solid-state modulator with split-core transformer. The modulator consists of a power supply, 12 pulse generator modules with active core reset, and a split-core transformer with six cores. In addition, an $LC$ bouncer could be used to compensate the droop of the pulse. This paper includes the design and analysis of the pulse transformer. A volume minimal transformer is investigated for different load capacitances to investigate the achievable rise time and the parameters which can be used to adjust the damping. In addition, the influence of the pulse transformer on the synchronization of the switches is investigated using an enhanced reluctance model. In addition, an $LC$ bouncer circuit is investigated. A multiobjective optimization is performed which shows the required energy of the bouncer for a certain pulse ripple. The flat-top ripple of the presented modulator can be reduced to 0.2%. Because the bouncer degrades the flat-top stability, the bouncer is not implemented. Measurements of the overall system include short-circuit measurements and flat-top stability measurements. They show that the modulator is short-circuit capable. Furthermore, the flat-top stability is determined to be less than 10 ppm at an output voltage of 360 kV. [ABSTRACT FROM PUBLISHER]

In this paper, a high-dynamic and high-precise optical current measurement system based on the Faraday effect is presented. First, the sensor concept is presented and different sensor constructions are analyzed. Then, a measurement system based on a rare-earth iron garnet film is investigated. The measurement system uses multiple signal processing channels to increase the signal-to-noise ratio. Furthermore, the measurement range exceeds a rotation of 180° and therefore requires a counting mechanism to count the number of rotations. Finally, the precision of the presented system is analyzed. The precision is determined to be 4.9 ppm at a rotation range of 3300°. [ABSTRACT FROM PUBLISHER]

This paper presents the interleaved operation of a soft-switching boost converter operated in boundary conduction mode. First, the operating principle of the converter as well as the basic concept of the interleaving is presented. Then, the dynamic behavior is modeled using the z-transform to obtain a converter model that is independent of the switching frequency. With the model, the stability of the closed-loop system with a proportional–integral (PI) controller is analyzed. It is shown that an adaptive PI controller can be easily implemented to achieve a minimal settling time over a wide operating range. Finally, the controller is validated with two converters with a 40-kW nominal output power and an output voltage of 3 kV. The tests at different output voltages under different load conditions show a stable interleaved operation. [ABSTRACT FROM PUBLISHER]

Modern accelerator driven experiments like linear colliders or spallation sources are supplied by RF amplifiers using klystrons. The cathode voltage for these klystrons can be generated by long pulse modulators generating highly accurate voltage pulses in the length of milliseconds. Conventional designs using pulse transformers become huge for long pulses. The series-parallel resonant converter (SPRC) topology avoids this drawback as the transformer is operating at high frequencies. This paper presents a comprehensive design approach for SPRC modules, which is based on an optimization procedure containing an electrical model of the resonant circuit and a thermal model of the semiconductors. In addition, an insulation and a leakage design procedure and a thermal model of the transformer are also presented. Finally, this procedure provides the optimal design parameters of the resonant circuit elements. With these parameters, a global optimizer chooses the optimum amount of modules connected in series and/or in parallel to fulfill the given restrictions. The efficiency of a basic SPRC-module is 94.7% with a pulsed power density of 4.63 kW/l. [ABSTRACT FROM PUBLISHER]

In this paper, limitations of compact and durable solid state modulators, using a 4.5-kV IGBT in combination with a pulse compression (PC) circuit are evaluated. Two investigated modulators uses two separate paths: one for ignition voltage and one for high currents. In the first modulator, ignition voltage is generated with a PC circuit based on saturable transformers, which is used to charge a series capacitor. After saturation, the capacitor is connected to the output. The second modulator combines together pulse transformer and magnetic switch. Parasitics have been estimated to find the optimal modulator configuration. Measurement results for validating the models as well as the simulation results are presented. Main limitation factors are described and possible solutions are discussed. [ABSTRACT FROM PUBLISHER]

In this paper, the charging precision of a 40-kW 3-kV soft-switching boost converter for capacitor charging is investigated. At the beginning, an overview on the topology and the control of the converter is given. Then, two different feedback controllers are presented and compared analytically to determine their sensitivity on noisy input variables. An algorithm to investigate the charging precision is illustrated. This algorithm considers the signal-to-noise ratio (SNR) of all measured signals, the controller output limitations, quantization related errors, the finite resolution in the digital domain, and the switching signal jitter to calculate the charging precision. All effects mentioned before are analyzed separately. This analysis shows that the output voltage measurement SNR is the key parameter for the charging precision. Then, measurements are performed to verify the model used to calculate the precision. These measurements show that the measured precision is only 6% higher than the precision predicted by the model for the used setup. Finally, the charging precision of the presented converter is analyzed including all considered effects. The repetition accuracy of the converter is determined to be 8.3 ppm at an output voltage of 3 kV, neglecting the load connection and the input voltage variation during one switching cycle. [ABSTRACT FROM PUBLISHER]

In this paper, a procedure for optimal transformer design with a variable set of constraints for pulse transformers with a pulse range of 3–140 \mus is presented. During the optimization procedure, the pulse shape is analyzed in the time domain, ensuring that the pulse constraints, such as rise time and overshoot are met. For accurate prediction of the pulse shape, analytical approaches are proposed to estimate the distributed capacitance and leakage inductance of the transformer. The analytical approach is verified by 2-D-FEM simulations and measurements. The optimization procedure considers pulse, core, winding, demagnetization losses, and losses of the primary switches. First, the procedure is applied to an existing pulse transformer with specifications for SwissFEL. An improvement of 16.6% in conversion efficiency is achieved in comparison with the existing design. In a second step, the procedure is applied to specifications of the compact linear collider, which demands high conversion efficiency. The resulting optimal transformer consists of three cores with five primary turns and requires a tank volume of 0.915 m^3. In an optimal configuration, an overall conversion efficiency of 97.7% is achieved for the considered system including pulse losses. [ABSTRACT FROM AUTHOR]

Solid-state modulators based on pulse transformers offer the advantage that, with the turns ratio of the transformer, the primary voltage could ideally be adapted to available switch technology, and a series connection of switches could be avoided. To increase the power level, several semiconductor switches must be connected in parallel, and a balancing between the different switches must be guaranteed. Here, the matrix transformer concept, which is based on multiple primary and/or secondary windings, as well as flux adding, offers superior performance with respect to the achievable rise times. However, the influence of the parasitic elements on the voltage and current distribution is quite involved. In this paper, the influence of the parasitic elements of the matrix transformer on the current balancing and on the winding voltages is investigated based on reluctance models. Additionally, the inherent current balancing of the matrix transformer for windings mounted on different cores is explained. Furthermore, the influence of parasitic load/transformer capacitances on the turnoff transient is discussed in detail. [ABSTRACT FROM PUBLISHER]

In many pulsed-power applications, the flatness of the output pulse is an important characteristic to enable proper system operation, whereas a pulse flatness within less than a few percent has to be achieved. In power modulators based on capacitor discharge, this voltage droop is mainly defined by the input capacitance. In order to overcome this problem, in power modulator systems, compensation circuits are added, whereby in spite of a smaller storage capacitor, a flat pulse top is achieved. Depending on the pulse duration, different approaches for voltage droop compensation exist. For short pulse durations, in the range of several microseconds, only passive solutions or bouncer circuits are applicable. In this paper, the design and optimization of a two-winding inductor bouncer circuit are presented in order to achieve an output voltage droop of less than 1%. Due to the realized galvanic isolation, a new degree of freedom is obtained, which allows an adaptation of the bouncer circuit's voltage and current ratings to standard semiconductor switches. With an optimal design of the two-winding inductor bouncer circuit for the existing system, the volume of the input capacitor is reduced by a factor of 10.5, and the stored energy is decreased by a factor of 24 compared to a system without a bouncer circuit. [ABSTRACT FROM PUBLISHER]

In modern pulsed power systems, often, fast solid-state switches like MOSFETs and insulated gate bipolar transistor (IGBT) modules are used to generate short high power pulses. In order to increase the pulsed power, solid-state switches have to be connected in series or in parallel. Depending on the interconnection of the switches, parameter variations in the switches and in the system can lead to an unbalanced voltage or current. Therefore, the switches are generally derated, which results in an increased number of required devices, cost, and volume. With an active gate control, derating and preselection of the switching devices can be avoided. In this paper, an active gate control of paralleled IGBT modules, which has been developed for converters with inductive load, is explained in detail and adapted to a solid-state modulator. This paper focuses on achieving a low-inductance IGBT current measurement, the control unit implementation with a field-programmable gate array and a digital signal processor, as well as the balancing of the pulse currents. [ABSTRACT FROM AUTHOR]

In power modulators for pulses in the microsecond range, transformers are often used for generating high output voltages. With standard topologies, the transformer is usually only excited in a unipolar direction, i.e., the flux density B swings between zero and a value close to the saturation flux density. By applying a reset circuit, the flux density B in the transformer is set to a value close to the negative saturation flux density before the pulse, so that the flux density could swing between the negative and positive saturation values during the pulse. This allows one to halve the core area and reduce the core volume/weight as well as the losses. In this paper, the operating modes of three different reset circuit topologies (the standard and a new advanced passive as well as an active one) and the corresponding waveforms are explained. Furthermore, the three topologies are compared with respect to the losses/complexity based on a design for a solid-state modulator with 20-MW output power and 200-ky output voltage. [ABSTRACT FROM AUTHOR]

A design and optimization procedure for high-voltage pulse transformers is presented. The procedure is enhanced by the integration of core loss measurements under pulsed excitation, by electrical peak field calculations and by checking of the isolation distances, which are compared to scaled high-voltage breakdown data. The procedure is applied with specifications of the compact linear collider, and the sensitivity of system parameters such as the number of primary turns, core material, transformer oil, and high-voltage cable length is investigated by comparing their Pareto fronts. With amorphous core material, the highest efficiency is achieved. Replacing mineral oil by natural ester results in an efficiency reduction of 0.5%, and an increase in HV cable length from 1.5 to 5 m reduces the efficiency by 0.6%. Finally, the optimized transformer’s pulse shape is investigated over the entire load range. [ABSTRACT FROM PUBLISHER]

Pulse loads, like solid-state pulse modulators, generate short pulses with a high peak power that exceeds the average power by 100-1000 times depending on the pulse repetition rate. There, the peak power usually is drawn from an energy buffer such as a capacitor bank. The pulse discharges the energy buffer, and it is fully recharged in the time between the pulses by a power supply, which is usually connected to the mains. Due to the worldwide variation in mains voltages and the desired ability to adapt to the capacitor voltage of the modulator, the power supply has to support a wide input and output voltage range. Additionally, the supply should draw a sinusoidal current from the mains while providing energy to the pulse modulator due to electromagnetic interference regulations. Therefore, a general control concept for pulse load applications, which guarantees continuous power consumption from the mains and power factor correction, is described in this paper. Furthermore, measurements of the control principle, which is independent from the converter topology, are presented for a three-phase buck-boost rectifier. [ABSTRACT FROM AUTHOR]

Medium and high beta cavities used in linear colliders or spallation sources are supplied by klystrons or inductive output tubes amplifiers. The cathode voltage for these amplifiers can be generated by long-pulse modulators generating highly accurate high voltage pulses in the length of milliseconds. With existing modulator topologies, all the demanding requirements like fast pulse rise time, high accuracy, and low voltage ripple hardly can be satisfied at the same time. Common designs like bouncer modulator topologies using pulse transformers become huge for long pulses. The series–parallel resonant converter (SPRC) avoids this drawback as the transformer is operated at high frequencies. In this paper, the comprehensive multidomain model of an SPRC including an electrical model of the inverter, a magnetic model, and an isolation design procedure of the transformer is verified with a prototype of a single module operated under full-load conditions. In addition, a comparison between the predicted parasitics like leakage inductance and stray capacitance of the transformer and the measured values are given. An evaluation of the isolation of the transformer, which is especially crucial for a series connection of the modules, is also performed. In addition, different possibilities to realize the desired series inductance are discussed. [ABSTRACT FROM PUBLISHER]

This paper presents a gate unit with short-circuit protection for a 4.5-kV press-pack insulated gate bipolar transistor (IGBT) designed for pulsed applications and operated at a pulse current of 4 kA and the results of short-circuit tests performed with the mentioned switch and the gate unit. Initially, an overview of the gate unit, the implemented gate boosting as well as the two-stage turn-off and active clamping is given. An over-di/dt as well as an over-current detection using a printed circuit board (PCB) Rogowski coil is used in the gate drive to protect the IGBT during operation. Then, the design of the PCB Rogowski coil is introduced including partial element equivalent circuit simulations to predict the coil parameters. Measurements were made to verify these simulations. Afterward, two types of short-circuit tests were performed. First, the over-di/dt detection was tested by turn-on into a short circuit. The tests show that the over-di/dt detection reacts very fast. The IGBT was always able to turn off the short-circuit current. The maximum short-circuit current was 4.4 kA. Second, tests using an auxiliary switch were made to investigate the short-circuit events during pulse top. The IGBT was able to turn off a maximum short-circuit current of 8.7 kA. [ABSTRACT FROM AUTHOR]