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Improving the Direct Switching Method for High Voltage Applications to Improve the Load Voltage Waveform

Zarghani, Mostafa | 2021

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 54619 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Kaboli, Shahriyar
  7. Abstract:
  8. Pulsed power supplies are used in linear accelerators, pulsed lasers, nuclear welding, radar, some medical applications, etc. which require much more instantaneous power than average power. These sources store energy in an energy storage element for a relatively long period of time and then release this energy in a short period of time. Among the most important goals pursued in these power supplies are the quality of the output pulse, the reliability and lifetime, efficiency, and cost, which depending on their application, some of these features are more important. One of the important applications of pulsed wave power supplies is their use to power microwave lamps. In some applications of these lamps, the quality of the output RF waveform is very important. Also, in some applications, the frequency of the output pulse is variable, and in some cases, up to several tens of kHz for a short interval.Reducing size, long lifetime, the ability to achieve high pulse repetition frequencies, and good output pulse quality are some of the improvements that are only possible with the use of semiconductor switches in pulse power supplies. The most important limitation of using semiconductor switches in pulsed power supplies is the limitation on nominal values such as current and voltage. Among the available methods for achieving high voltage pulses using semiconductor switches, direct switch pulsed power supplies are the most efficient. For this purpose, different methods for series connecting switches are presented in articles in this field.DC link voltage quality and high voltage switch behavior in power supplies that work by direct switching method is the most important factors that affect the output pulse shape and frequency of the output pulse due to the effect on losses. Therefore, in this project, the main focus is on improving the behavior of the high voltage switch and improving the DC link voltage. To improve the switch behavior, it is necessary to control the losses and the on and off time of the high voltage switch. By controlling the on and off time of the switches, the required specifications for the pulse edges can be achieved. However, if we need to slow down the switches, their losses will increase, and thus we will be limited for higher frequency applications. Because these losses change the switches junction temperature and the change of junction temperature changes their switching behavior and thus changes the output pulse rise time. For this purpose, a part of this research is dedicated to improving the performance of high voltage switch, which can be used to shape the pulse edges to the expected load. In this research, a mechanism is proposed that can control the pulse rise time to the desired value.Also, to improve the DC link, it is necessary to control the amount of voltage in the pulse interval at a constant value by storing less energy in the DC link. In this project, in order to compensate for the voltage drop of the DC link, it is suggested to use a series compensator. This compensator must have a suitable speed to be able to respond properly to voltage changes due to pulsed load current. For this reason, the use of a linear regulator with a feedforward has been suggested so that it can have a suitable speed.
  9. Keywords:
  10. High Voltage Switching ; Pulse Shaping ; High Voltage Pulsed Power Supply ; Pulse Quality ; Switching Frequency

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