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Fast high-voltage, high-current switching using stacked IGBTs

By: Zarir Ghasemi

Supervisor: Prof. S. J. Macgregor

Institute for Energy and Environment

University of Strathclyde

Glasgow

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Pulsed Power System with Examples of System Components

HVPowerSupply

Intermediate Energy Store

PFN Switch Load

Coaxial Cable,

Stripline Semiconductor Device,

Spark Gap

Plasma Drill,

Treatment Cell

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Comparison of solid-state switching devices

Voltage Rating

Current Rating

Speed Availability Cost

Thyristor High High Low Readily available

Low

GTO High High Low Medium Medium

MOSFET Low Low High Readily available

Low

MCT High Medium Medium Special order

only High

MAGT Medium High High Special order

only High

SIT Medium Medium High Special order

only High

IGBT Medium Medium High Readily available

Low

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An X2 Non-Inverting Blumlein Cable Generator

a b c d

OUTPUT

CABLE 1 CABLE 2

CHARGING ELEMENTHV

SWITCH

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Problems associated with stacking IGBTs

• Signal synchronisation • Signal isolation (Magnetic or Optical )• Voltage sharing (Passive or Active snubbers)• Current sharing• Stack configuration• Diagnostic• Protection

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Photograph of 55 IGBT stack with voltage and current ratings of 2.5 kV and 250 A, respectively.

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Voltage across the device and output pulse for two 1.2 kV IGBTs

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Photograph of 10 kV, 400 A stack of IGBT modules consisting of 105 1.2 kV IGBTs.

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Photograph of 10 kV, 400 A stack of IGBT modules,

optically triggered

Over-voltage protection circuit

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Photograph of 3 kV, 2 kA Marx

generator

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Conclusion

• The IGBT was determined to be the preferred device for stacking

• IGBT’s can handle a peak current of five times their normal rating during short-pulse conducting, if they are driven by fast gate pulses.

• The dual degradation of the collector-emitter voltage exists in some of available IGBT devices.

• A prototype stack at voltage and current ratings of 10 kV and 400 A, with a voltage fall-time of about 45 ns was successfully tested.

• An optically-coupled stack of IGBTs with voltage and current ratings of 10 kV and 400 A was built and operated in a generator, used for Pulsed Electric Field (PEF) inactivation of microorganisms.

• A modular Marx generator, having an output voltage rating of 3 kV and a peak current rating of 2 kA, was designed and evaluated.