Possible Bi-directional Switch Configurations

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High Voltage, High Power, High Frequency
Converters for Industrial Applications
Dr David Cook Power Electronics, Machines and
Control Group
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Applications of HV PSU

• High voltage power supplies are used in range of
  medical, scientific, industrial and defence
  applications
• Treatment of tumours
• Particles physics research, e.g. CERN, LANL,
  ORNL,
• Emerging power station technology, e.g. ITER
• Industrial processing of rock and mineral
• Radar and EW

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Conventional Power Supply
High Voltage Rectifier
Filter
Grid Voltage, Line Frequency Transformer
Crowbar
Load
AC LF input
x3
Shunt Thyristor Rectifier
High Voltage, Line Frequency Transformer
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Why HV, HF?

• Techniques used at the University of Nottingham
  utilise high frequency (20kHz) resonant circuits.
• High frequency operation significantly reduces
  the size of the high voltage transformer and
  input/output filters
• Estimated that 20kHz transformers may are
  approximately 1 the size of line frequency
  counterparts
• Resonant circuits allow for soft-switching
  (ZVS/ZCS), therefore allowing high power at high
  frequency
• Allows for highly compact power converter in many
  applications where space and weight are critical

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Current and RecentResearch Projects
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Long PulseExisting Technology

• Disadvantages
• Very large capacitor bank (energy storage 80kJ)
• Crowbars Required
• Large filter components required to limit
  flicker

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Long PulseExisting Technology

• Large Utility frequency transformer and
  rectifier
• Poor input quality
• Huge DC capacitor bank (need low droop during
  pulse)
• 2 Crowbars
• High voltage series switch

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Long Pulse New Technology direct modulation
(Mike Bland)
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Long Pulse Converter
Voltage gain / frequency characteristics of
resonant tank
Simulation result
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Long Pulse Converter Some key features

• Long Pulse or CW operation
• High power factor input (low harmonic content)
• Intelligent recharging of Cdc between shots
  eliminates flicker
• Soft switching high power, high frequency
  operation
• HF transformer for reduced size
• HF multiphase operation gives high ripple
  frequency
• Small output filter
• low energy storage small energy dump during
  fault
• Direct modulation of HF inverter for long pulse
  operation

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Long Pulse Modulator Assembly
Wave guide
Solenoid
Cathode Voltage Monitor
Magnetron
Input from Pulsed PSU
Control Unit
Auxiliary PSUs
Pulsed PSU (UoN)
Heater Supply
Industrial experimental prototype
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Long Pulse Modulator Results
Experimental result obtained from operation with
Magnetron load
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CW Converter
Direct Conversion Approach
CONTROL
3-phase to 1-phase matrix
Resonant tank and transformer
Rectifier filter
Filter
LOAD
AC Supply
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CW Converter
Resonant tank
Input matrix
Predictive control of resonant tank every ½ cycle
of resonance
Line Filter
S1
S3
S5
AC LF input
Output Filter/Rectifier
S2
S4
S6
HF transformer
Switches S1-S6 commutated when tank current
passes through zero soft switching
Bi-directional switch
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CW Converter Some Key Features

• No energy storage
• Potential for small size
• CW only
• Soft switching of matrix
• High efficiency
• High power factor input (low harmonic content)
• High operating frequency
• Small input filter
• HF transformer for reduced size
• Small output filter
• low energy storage small energy dump during
  fault

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CW ConverterResults
DC Output Waveform

• Experimental result
• Converter producing 25kV DC
• 25kW Output

• Simulation result
• Converter producing 25kV DC
• 25kW Output

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CW ConverterResults
Phase Current

• Experimental result
• Converter producing 25kV DC
• 25kW Output

• Simulation result
• Converter producing 25kV DC
• 25kW Output

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High Efficiency Pulsed Power Supplies (Fabio
Carastro)

• Scalability and reliability of pulsed power
  supplies utilising IGBTs
• Thermal cycling of IGBT during pulsed operation
• Asses reliability implications
• 250kW (500J) test rig to asses thermal cycling
• Consider different topologies for high power
  (500kW) units
• 500kW prototype in construction at partner company

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Electrostatic Precipitator(Vivek Tailor)

• Knowledge Partnership with Castlet Ltd.
• World leader in manufacture of Electro-Static
  Precipitators
• Used to remove particulate emissions from power
  station exhaust.
• Existing supplies are based on line-frequency
  approaches
• Competitors are starting to introduce supplies
  utilising high frequency techniques to the market
• More responsive
• Pulsed Operation
• Can be mounted on the chimney (space saving)

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Electrostatic Precipitator(Vivek Tailor)

• 100kV, 2Amp Unit
• LCC Resonant circuit
• Phase Control
• Highly demanding load (short and open circuits)
• Less stringent power quality and output ripple
  specifications

H-Bridge
High Voltage, High Frequency Transformer
Cockcroft-Walton Multiplier
Resonant Tank (LCC)
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Ultra Compact Capacitor Charging System

• Design of a 40kJ/s capacitor charging system for
  high voltage (20kV) applications
• Ultimate requirement is for minimised converter
  volume / height (100mm)
• Weight and efficiency are a secondary
  consideration
• Twin Shot Application Only required to charge
  the output capacitor twice.
• Then de-activated until converter has cooled
  sufficiently

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High Power, High Voltage, High Frequency
Transformers for Switching Converters (Todor
Filchev)

• Follows on from previous PPARC project, Power
  Supplies for High Power RF Systems .
• Optimal design of the transformer/rectifier was
  identified as a critical component in order to
  fulfil the potential of new converter concepts.
• In particular a reduction in size, weight and
  cost whilst maintaining reliability.
• Required to generate the knowledge and confidence
  such that industrial exploitation of compact (HF)
  power converters can become a reality

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Background to Project

• Key requirement of emerging high frequency high
  voltage converters is the requirement for step up
  transformers
• Present knowledge is based on (at best)
  experience at line frequency
• Many factors influencing transformer design are
  frequency dependant

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HVHF Transformer

• Main concern is the HVHF Transformer
• High voltage insulation requirements (Choice of
  materials is essential)
• Leakage inductance/stray winding capacitance (LC
  tank interaction)
• Core loss and heat dissipation (reduced
  efficiency)
• Rectification and output terminal connections

Equivalent transformer model.
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• Thank you
• Any questions?