A high-voltage pulsed power modulator for fast-rising arbitrary waveforms

This work presents the design and testing of a new semiconductor-based pulsed power modulator meeting the challenging requirements of a pulsed electron beam device (GESA): a fast-rising (10^12 V/s) output voltage with arbitrary waveform of maximum 120 kV at a maximum current of 600 A for a pulse duration of up to 100 µs

A Method of Including Switching Loss in Electro-Thermal Simulations

Often, power electronics systems are simulated with ideal switching elements, perhaps augmented with conduction loss models. A behavioral model is proposed that also includes switching loss and is independent of switching frequency. Therefore, it is suitable for variable frequency control methods, including hysteresis, delta modulation, and random PWM. Models have been realized in Dymola using voltage-controlled voltage sources, current sources, logic, and additional ideal switches. Thermal ports are included to facilitate electro-thermal simulation. A method for parameter extraction is demonstrated using experimental data from standard PWM

Reverse-Conducting Insulated Gate Bipolar Transistor: A Review of Current Technologies

The Reverse Conducting IGBT has several benefits over a separate IGBT and diode solution and has the potential to become the dominant device within many power electronic applications; including, but not limited to, motor control, resonant converters, and switch mode power supplies. However, the device inherently suffers from many undesirable design trade-offs which have prevented its widespread use. One of the most critical issues is the snapback seen in the forward conduction characteristic which can prevent full turn-on of the device and result in the device becoming unsuitable for parallel operation (required in many high voltage modules). This phenomenon can be suppressed but at the expense of the reverse conduction performance. This paper provides an overview of the technical design challenges presented by the RC-IGBT structure and reviews alternative device concepts which have been proposed in literature. Analysis shows that these alternate concepts either present a trade-off in performance characteristics, an inability to be manufactured, or a requirement for a custom gate drive.EPSRC Doctoral Training Partnership scheme (grant RG75686) UK Innovate Project Number 10287

High power high frequency DC-DC converter topologies for use in off-line power supplies

The development of a DC-DC converter for use in a proposed range of one to ten kilowatt off-line power supplies is presented. The converter makes good use of established design practices and recent technical advances. The thesis begins with a review of traditional design practices, which are used in the design of a 3kW, 48V output DC-DC converter, as a bench-mark for evaluation of recent technical advances. Advances evaluated include new converter circuits, control techniques, components, and magnetic component designs. Converter circuits using zero voltage switching (ZVS) transitions offer significant advantages for this application. Of the published converters which have ZVS transitions the phase shift controlled full bridge converter is the most suitable, and assessments of variations on this circuit are presented. During the course of the research it was realised that the ZVS range of one leg of the phase shift controlled full bridge converter could be extended by altering the switching pattern, and this new switching pattern is proposed. A detailed analysis of phase shift controlled full bridge converter operation uncovers a number of operational findings which give a better and more complete understanding of converter operation than hitherto published. Converter design equations and guidelines are presented and the effects of the new improvement are investigated by an approximate analysis. Computer simulations using PSPICE2 are carried out to predict converter performance. A prototype converter design, construction details and test results are given. The results obtained compare well to the predicted performance and confirm the advantages of the new switching pattern

High Efficiency IGBTs through Novel Three-Dimensional Modelling and New Architectures

New Insulated Gate Bipolar Transistor (IGBT) designs are reliant on simulation tools, such as Sentaurus technology computer-aided design (TCAD) models, which allow for rapid device development that could not be achieved by manufacturing prototypes due to the cost and time associated with fabrication. These simulations are, though, computationally expensive and typically most design engineers develop these TCAD models only in two dimensions. This leads to inaccuracies in the model output since manufactured transistors are inherently three-dimensional (3D). Based upon a commercial IGBT, this thesis begins by outlining the development of a 3D TCAD model using design details provided by the manufacturer. Large variations between the experimental data from the manufactured device and the simulation model lead to the discovery of widespread birds-beaking within the IGBT – an uncontrollable processing defect that the manufacturer was unaware of. This thesis presents a new simulation technique to account for this processing error while minimising computational effort and investigates the consequence of this birds-beak on the reliability of the device. The verified 3D IGBT model was also used to determine an optimum cell design that considered critical 3D effects omitted from previous studies. An extensive literature review for the Reverse-Conducting IGBT (RC-IGBT) is provided. It is shown that despite the benefits of the RC-IGBT, the device suffers from many undesirable design trade-offs that have prevented its widespread use. The RC-IGBT designs that have currently been proposed in literature, either present a trade-off in performance, an inability to be manufactured, or a requirement for a custom gate drive. This thesis presents a new RC-IGBT concept, the ‘Dual Implant SuperJunction (SJ) RC-IGBT’ that addresses these concerns and is manufacturable using current state of the art techniques. The concept and proposed manufacturing method enables, for the first time, a full SuperJunction structure to be achieved in a 1.2kV device. In addition, an investigation into a coordinated switching scheme using both a silicon IGBT and silicon-carbide MOSFET was undertaken, which aimed to improve turn-off losses within the IGBT without sacrificing on-state losses. Thermal modelling of the power devices switching under inductive load was explored as the system was optimised to use a SiC MOSFET in excess of its nominal ratings, reducing the overall system cost.EPSRC Doctoral Training Partnership scheme (grant RG75686

IGBT:n hilaohjain hidastetun sammutuksen toiminnolla

The purpose of this thesis research was to develop a new gate driver circuit for IGBT semiconductor switches that are used in frequency converters. Frequency converters are widely used in industry and electrical systems of buildings, including elevators and es-calators, for energy efficient speed control of electric motors. The thesis is a part of larg-er research entity done in Danfoss Drives in order to enhance the short circuit protection of frequency converters. The research was based on existing simulations of the driver, done by another development engineer of Danfoss. The reference material used as back-ground information for the research consisted mainly of academic research articles and the fundamental literature regarding electric converters. The study consisted of performing further simulations for the driver circuit, building a prototype and performing measurements for it in a high voltage testing environment. The testing environment modelled the main circuit of a frequency converter. The target on the driver development was to achieve short delays, high gate currents and fast out-put voltage transitions, thus providing flexibility for the application-specific adjusting of the driver. The second section of the research consisted of developing an additional soft turn-off circuitry for the gate driver. Soft turn-off can be used for decreasing the turn-off voltage overshoots over the IGBT switch. Overshoots are caused by turning the IGBT off when a short circuit has appeared in the output of the converter. When using normal turn-off switching procedure for high currents, the momentary overvoltage can exceed the tolerance of the IGBT and cause damage to the converter. The theoretical section of the thesis includes introducing the main circuit of a frequency converter, the structure and controlling method of an IGBT and its behavior in fault situations. Also the general requirements for a gate driver are presented. The section considering the practical research focuses on the technical solutions of the developed driver and measurement results regarding the driver and the driven IGBT. Additionally, the behavior of the IGBT and the main circuit is studied with different configurations of soft turn-off circuit. For comparability of the driver’s performance, an existing driver is introduced and measured for reference. The developed gate driver reached the targets for the gate current and delays. It re-duced the delays caused by the driver by more than 50 % when compared to the refer-ence driver. In turn, chosen gate power supply voltages turned out to be rather low. Also the power rating of the IGBT module in the test setup was significantly lower than what the driver is designed for. The soft turn-off was reducing the turn-off overvoltage even more than expected. According to measurements performed with the final configura-tion, the overshoots were 82 % lower than when using the normal turn-off

Study of switching transients in high frequency converters

As the semiconductor technologies progress rapidly, the power densities and switching frequencies of many power devices are improved. With the existing technology, high frequency power systems become possible. Use of such a system is advantageous in many aspects. A high frequency ac source is used as the direct input to an ac/ac pulse-density-modulation (PDM) converter. This converter is a new concept which employs zero voltage switching techniques. However, the development of this converter is still in its infancy stage. There are problems associated with this converter such as a high on-voltage drop, switching transients, and zero-crossing detecting. Considering these problems, the switching speed and power handling capabilities of the MOS-Controlled Thyristor (MCT) makes the device the most promising candidate for this application. A complete insight of component considerations for building an ac/ac PDM converter for a high frequency power system is addressed. A power device review is first presented. The ac/ac PDM converter requires switches that can conduct bi-directional current and block bi-directional voltage. These bi-directional switches can be constructed using existing power devices. Different bi-directional switches for the converter are investigated. Detailed experimental studies of the characteristics of the MCT under hard switching and zero-voltage switching are also presented. One disadvantage of an ac/ac converter is that turn-on and turn-off of the switches has to be completed instantaneously when the ac source is at zero voltage. Otherwise shoot-through current or voltage spikes can occur which can be hazardous to the devices. In order for the devices to switch softly in the safe operating area even under non-ideal cases, a unique snubber circuit is used in each bi-directional switch. Detailed theory and experimental results for circuits using these snubbers are presented. A current regulated ac/ac PDM converter built using MCT's and IGBT's is evaluated

Modeling, Measurement and Mitigation of Fast Switching Issues in Voltage Source Inverters

Wide-bandgap devices are enjoying wider adoption across the power electronics industry for their superior properties and the resulting opportunities for higher efficiency and power density. However, various issues arise due to the faster switching speed, including switching transient voltage overshoot, unstable oscillation, gate driving and evaluation difficulty, measurement and monitoring challenge, and potential load insulation degradation. This dissertation first sets out to model and understand the switching transient voltage overshoots. Unique oscillation patterns and features of the turn-on and turn-off overvoltage are discovered and analyzed, which provides new insights into the switching transient. During the experimental characterization, a new unstable oscillation pattern is found during the trench MOSFET\u27s turn-off transient. The MOSFET channel may be falsely turned back on, resulting in severe oscillation and possible loss of control. Time-domain and large-signal analytical models are established, which reveals the negative impact of common-source inductances and unconventional capacitance curve of trench MOSFET. Besides the devices themselves, another determining part in their switching transient behavior is the gate driver. A programmable gate driver platform is proposed to readily adapt to different power semiconductors and driving schemes, which can greatly facilitate the evaluation and comparison of different devices and driving schemes. The faster switching speed of wide-bandgap devices also requires more demanding measurement and monitoring solutions. A novel combinational Rogowski coil concept is proposed, which leverages the self-integrating feature to further increase the bandwidth. Prototypes achieved more than 300 MHz bandwidth, while keeping the cross-sectional area less than 2.5 mm$^2$. Finally, the very high voltage slew rate of wide-bandgap devices may negatively impact the motor load insulation. Attempting to fully utilize the higher switching frequency capability, sinewave and $dv/dt$ filters are compared. It is shown that sinewave filters can achieve higher efficiency and power density than $dv/dt$ filters, especially for high frequency applications