Underpinning Research
Converters Theme
Andrew Forsyth
The University of Manchester
Overview
Underpinning Research
● Research team
● Vision, objectives and organisation
● Update on technical activities / achievements





Topologies
Structural and functional integration
Design tools and optimisation
Operational management and control
Deliverables and outputs
Research Team
Underpinning Research
● Bristol - Dr Xibo Yuan and Dr Neville McNeill
 Dr Iain Laird (RA), and Bosen Jin
● Imperial – Dr Paul Mitcheson and Prof Tim Green
 Dr Michael Merlin (RA)
● Manchester – Prof Andrew Forsyth and Dr Rebecca Todd
 Dr James Scoltock (RA), and Rishad Ahmed
● Nottingham – Prof Jon Clare, Prof Mark Johnson and Dr
Alberto Castellazzi
 Dr Xi Lin (RA)
● Strathclyde – Prof Stephen Finney and Dr Derrick Holliday
 Dr TC Lim (RA) and Dr Grain Adam (RA)
Vision and Objectives
Underpinning Research
● Focus on two areas where we have established capability /
strength and there is potential for UK exploitation
To extend the performance and operating envelopes of high voltage
AC-DC and DC-DC converter systems to 800 kV and beyond
To transform the performance of compact power converters to
achieve power densities of 30 kW/litre
Structural
and
functional
integration
Design tools
and
optimisation
Operational
management
and control
Organisation Diagram
Underpinning Research
● Four inter-linked work packages
WP1. Topologies
(Bri, Imp, Mcr, Nott, Str)
WP2. Structural &
Functional
Integration
(Bri, Mcr, Nott)
WP3. Design Tools
& Optimisation
(Bri, Imp, Mcr, Str)
Demonstrator D1
Ultra Compact
Converter
WP4. Operational
Management &
Control
(Imp, Mcr, Str)
Demonstrator D2
HV Converter
Organisation Diagram
Underpinning Research
● Four inter-linked work packages
WP1. Topologies
(Bri, Imp, Mcr, Nott, Str)
WP2. Structural &
WP3. Design Tools
Functional
& Optimisation
 DC-DC
converters for HVDC
grids (Strath)
Integration
(Bri, Imp, Mcr, Str)




WP4. Operational
Management &
Control
(Bri, Mcr,multi-level
Nott)
(Imp,(Strath)
Mcr, Str)
Hybrid
topologies for AC-DC conversion
Multi-level techniques for <1kV converters (Bris)
Soft-switching for compact multi-kW DC-DC conversion (Mcr)
Demonstrator D1
Demonstrator
Advanced AC-AC
converter concepts
(Notts) D2
Ultra Compact
Converter
HV Converter
Organisation Diagram
Underpinning Research
● Four inter-linked work packages
WP1. Topologies
(Bri, Imp, Mcr, Nott, Str)
WP2. Structural &
Functional
Integration
(Bri, Mcr, Nott)
WP3. Design Tools
& Optimisation
(Bri, Imp, Mcr, Str)
Demonstrator D1
Ultra Compact
Converter
WP4. Operational
Management &
Control
(Imp, Mcr, Str)
Demonstrator D2
HV Converter
Organisation Diagram
Underpinning Research
● Converters theme
WP1. Topologies
(Bri, Imp, Mcr, Nott, Str)
WP2. Structural &
Functional
Integration
(Bri, Mcr, Nott)
WP3. Design Tools
& Optimisation
(Bri, Imp, Mcr, Str)
Demonstrator D1
Ultra Compact
Converter
WP4. Operational
Management &
Control
(Imp, Mcr, Str)
Demonstrator D2
HV Converter
Organisation Diagram
Underpinning Research
● Four inter-linked work packages
WP1. Topologies
(Bri, Imp, Mcr, Nott, Str)
WP2. Structural &
Functional
Integration



(Bri, Mcr, Nott)
WP3. Design Tools
& Optimisation
(Bri, Imp, Mcr, Str)
WP4. Operational
Management &
Control
(Imp, Mcr, Str)
Device wear-levelling for modular MMC (Imp)
Variable overload ratings for modular MMC
D1
dependentDemonstrator
on device state-of-health
(Imp)
Demonstrator
D2
Ultra
Compact
Control techniques for very high freq.
HV Converter
Converter
converters (Mcr)
Recent Achievements
Underpinning Research
● Topologies for HV DC-DC systems
 Range of options being evaluated through detailed simulation
 Single converter topologies
» Based around the MMC
 Modular transformer-coupled systems
» Based on two-level, low-voltage modules
Recent Achievements
Underpinning Research
● Topologies for HV systems
 Quasi two-level MMC DC-DC converter
» Reduced capacitor size, low switching losses and controlled dv/dt
Recent Achievements
Underpinning Research
● Topologies for HV systems
 Quasi two-level MMC DC-DC converter
» Reduced capacitor size, low switching losses and controlled dv/dt
Average simulation of 800 kV / 640 kV,
1.3 GW system with 250 Hz transformer
Primary voltages
Primary currents
Recent Achievements
Underpinning Research
● Topologies for HV systems
 Modular transformer-coupled DC-DC converter
» Series and parallel connections, unidirectional and bi-directional options
» Transformer design and isolation is a challenge
V1
Input
Converter
Array
Transformer
Array
Output
Converter
Array
V2
Recent Achievements
Underpinning Research
● Topologies for HV systems
 Modular transformer-coupled DC-DC converter
» Series and parallel connections, unidirectional and bi-directional options
» Transformer design and isolation is a challenge
V1
Input
Converter
Array
Front-end Inverter
Unit
M1
Transformer
Unit
Inductor
Unit
M2
M22
85mH
Lout1
Lk
Cin
M4
M3
V2
Output Rectifier/Inverter
Unit
M11
10mH
Vin = 1kVdc
Output
Converter
Array
Transformer
Array
Cout
T1
1:2
Lout2
85mH
M44
M33
Vout = 1kVdc – 1.5kVdc
Iout = 10A
Recent Achievements
Underpinning Research
● Topologies for compact converters
 Multi-level techniques for low voltage DC-AC conversion
» Improved waveform quality, reduced filter requirements and reduced
switching losses
» Ultra-high efficiency NPC converter using super-junction MOSFETs
– Switching aid networks to supress body diode
– Efficiency >99% in 3 kVA, 20 kHz prototype
Recent Achievements
Underpinning Research
● Topologies for compact converter
 Multi-level techniques for low voltage DC-AC conversion
» Improved waveform quality, reduced filter requirements and reduced
switching losses
» Comparison of semiconductor losses in 5 kW 380 V AC applications
Converter efficiency(%)
100
Pi-type converter
98
iC 3
E
96
94
N2
iC 2
E
92
90
88
86
0
2 level
3 level T-type
3 level npc
4 level pi-type
20
40
60
80
Switching frequency(kHz)
100
N1
iC1
E
T1
C3
T3
T2
C2
T5
T4
C1
iN 2
iN 1
T6
Recent Achievements
Underpinning Research
● Topologies for compact converter
 Multi-level techniques for low voltage DC-AC conversion
» Improved waveform quality, reduced filter requirements and reduced
switching losses
» Validation of Pi-type converter (5 kW, 380 V)
Pi-type converter
iC 3
E
N2
iC 2
E
N1
iC1
E
T1
C3
T3
T2
C2
T5
T4
C1
iN 2
iN 1
T6
Recent Achievements
Underpinning Research
● Topologies for compact converters
 Soft-switching DC-DC conversion techniques
» SiC devices enable increased switching frequencies and reduced size
passives, but frequency still limited by switching losses
– Switching losses accounted for well over 50% of semiconductor
losses in recent 60 kW, 75 kHz converter
Recent Achievements
Underpinning Research
● Topologies for compact converters
 Soft-switching DC-DC conversion techniques
» Evaluation of ZVS / ZCS techniques combined with dual interleaved
converter
» 50% reduction in total switching losses and 50% reduction in dv/dt
compared with hard switching in 12.5 kW, 112 kHz prototype
Recent Achievements
Underpinning Research
● Topologies for compact converters
 Soft-switching DC-DC conversion techniques
» Modelling and analysis of soft switching transients in SiC converters
– Include non-linear capacitances and dominant stray / mutual
inductances
Input power
supply
Load
inductor
DC link
capacitor
Gate driver for the
upper leg MOSFET
Current shunt
resistor
DUT
Recent Achievements
Underpinning Research
● Structural and functional integration
 Understanding current manufacturing practice
» Company visits to review processes (applications ranging from 3 W to
3 MW) and identify bottlenecks that compromise yield, reliability,
opportunities for miniaturisation
» Strong similarities observed
Recent Achievements
● Structural and functional integration
 Understanding current manufacturing practice
 Supply chain strategy
Underpinning Research
Recent Achievements
Underpinning Research
● Structural and functional integration
 Understanding current manufacturing practice
 Bottlenecks in power electronics manufacturing
Assembly of premanufactured discrete
components
Non-standardised,
custom designed,
mostly bulky parts
Generic components
(R, L, C)
Technology driven deep into maturity
Increased volume
of package
Labour intensive
processes
Small profit margin
Recent Achievements
Underpinning Research
● Structural and functional integration
 Low inductance interconnect techniques to eliminate screw-type
terminals
»
»
»
»
Ultra low parasitic inductance
Low component count
High degree of component integration
More applicable for automated manufacture
Recent Achievements
Underpinning Research
● Structural and functional integration
 Low inductance interconnect techniques to eliminate screw type
terminals
»
»
»
»
Ultra low parasitic inductance
Low component count
High degree of component integration
More applicable for automated manufacture
Bus terminal receptacle
Double-sided DC
bus terminal tab
Recent Achievements
Underpinning Research
● Design tools and optimisation
 Systematic optimisation of SiC MOSFET based converters
Recent Achievements
Underpinning Research
● Design tools and optimisation
 Systematic optimisation of SiC MOSFET based AC-DC converters
» Integration of trade-off models into optimisation routine
» Variation of volume for 5 kW active rectifier with switching frequency
6000
Natural
Forced
Total
Line
DM
CM
2000
5000
Total volume (cm3)
EMI filter volume envelope (cm3 )
2500
1500
1000
500
0
0
4000
3000
2000
1000
50
100
150
Switching frequency (kHz)
200
250
0
0
50
100
150
Switching frequency (kHz)
200
250
Recent Achievements
Underpinning Research
● Design tools and optimisation
 Systematic optimisation of SiC MOSFET based AC-DC converters
700
» Optimum design of 5 kW active rectifier with natural and forced air
cooling
1.5
600
500
Line
DM
CM
Heatsink
400
300
Mass (kg)
Volume (cm3)
1
Line
DM
CM
Heatsink
0.5
200
100
0
0
Natural
Forced
Natural
Forced
a) Volume optimisation
b) Mass optimisation
Natural cooling = 7.581 kW/L
Forced cooling = 8.308 kW/L
Natural cooling = 3.425 kW/kg
Forced cooling = 3.650 kW/kg
Recent Achievements
Underpinning Research
● Design tools and optimisation
 Systematic optimisation of SiC MOSFET based DC-DC
converters
» Variation of component weight against switching frequency for a twophase, 30 kW, interleaved boost converter (200 V- 600 V) using SiC
devices with efficiency constraint of 96%
Weight vs.switching frequency
2.6
Total component weight (kg)
2.5
2.4
2.3
2.2
2.1
2
1.9
1.8
80
90
100
110
120
130
140
150
Switching frequency (kHz)
160
170
180
Recent Achievements
Underpinning Research
● Operational management and control
 Construction and commissioning of MMC / AAC lab prototype
Rated Power
15 kW
AC Frequency
50 Hz
DC bus
1,500 V
AC voltage
918 V (MMC)
1070 V (AAC)
Number of SM
10 SM per stack
SM voltage
150 V (MMC)
106 V (AAC)
SM Capacitance
1.13 mF
Director Switches
2 DS per stack
Phase Inductor
0.1 mH (MMC)
24 mH (AAC)
Arm Inductor
24 mH (MMC)
1.3 mH (AAC)
Recent Achievements
● Operational management and control
 Laboratory test bed
Underpinning Research
Recent Achievements
Underpinning Research
● Operational management and control
 AC and DC current waveforms (left) and SM voltages (right)
Recent Achievements
Underpinning Research
● Operational management and control
 DC fault imposition and recovery
- DC Fault
- Rapid discharge
of the DC bus
- STATCOM operation
- End of the DC Fault
- Recharge of the DC
bus
- Resume normal operation
Deliverables and Outputs
Underpinning Research
● Six project deliverables completed. On course to produce
seven more this year
 Report and publications on high power / voltage DC-DC topologies
(WP1.1)
 Publication on soft-switching multi-kW DC-DC converters using WBG
devices (WP1.3)
 Report on current manufacturing techniques (WP2)
 Report and publications on trade-off models and generic design
processes (WP3)
 Report / publications on wear levelling techniques (WP4)
 Operational MMC / ARC test rig (WP4)
● Publications
 13 conference papers
 2 journal papers
 3 papers in review
Underpinning Research
Converters Theme