Converters Theme Andrew Forsyth

Converters Theme Andrew Forsyth The University of Manchester

Overview 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 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 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 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) Demonstrator D1 Ultra Compact Converter Demonstrator D2 HV Converter

Organisation Diagram Four inter-linked work packages WP1. Topologies (Bri, Imp, Mcr, Nott, Str) WP2. Structural & Functional Integration WP3. Design Tools & Optimisation DC-DC converters for HVDC grids (Strath) WP4. Operational Management & Control (Bri, Imp, Mcr, Str) Hybrid (Bri, Mcr, multi-level Nott) topologies for AC-DC conversion (Imp,(Strath) Mcr, Str) Multi-level techniques for <1kV converters (Bris) Soft-switching for compact multi-kw DC-DC conversion (Mcr) Advanced AC-AC converter concepts (Notts) Demonstrator D1 Ultra Compact Converter Demonstrator D2 HV Converter

Organisation Diagram 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) Demonstrator D1 Ultra Compact Converter Demonstrator D2 HV Converter

Organisation Diagram Converters theme 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) Demonstrator D1 Ultra Compact Converter Demonstrator D2 HV Converter

Organisation Diagram 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) Device wear-levelling for modular MMC (Imp) Variable overload ratings for modular MMC dependent Demonstrator device state-of-health D1 (Imp) Control techniques Ultra Compact for very high freq. converters (Mcr) Converter Demonstrator D2 HV Converter WP4. Operational Management & Control (Imp, Mcr, Str)

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

Topologies for HV systems Quasi two-level MMC DC-DC converter» Reduced capacitor size, low switching losses and controlled dv/dt

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

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 Input Converter Array Transformer Array Output Converter Array V 1 V 2 Front-end Inverter Unit Transformer Unit Inductor Unit Output Rectifier/Inverter Unit M1 M2 M11 M22 85mH 10mH L out1 V in = 1kV dc C in L k C out V out = 1kV dc 1.5kV dc I out = 10A M4 M3 T1 1 : 2 L out2 85mH M44 M33

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

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 98 96 94 92 90 2 level 3 level T-type 88 3 level npc 4 level pi-type 86 0 20 40 60 80 100 Switching frequency(khz) i C3 E N2 i C 2 E N1 i C1 E Pi-type converter C 3 C 2 C 1 T3 T5 T2 T4 T1 T6 i N 2 i N1

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

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

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 DUT Current shunt resistor

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

Structural and functional integration Understanding current manufacturing practice Supply chain strategy

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 Increased volume of package Labour intensive processes Generic components (R, L, C) Small profit margin Technology driven deep into maturity

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

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

Design tools and optimisation Systematic optimisation of SiC MOSFET based converters

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 EMI filter volume envelope (cm 3 ) 2500 2000 1500 1000 500 Total Line DM CM Total volume (cm 3 ) 6000 5000 4000 3000 2000 1000 Natural Forced 0 0 50 100 150 200 250 Switching frequency (khz) 0 0 50 100 150 200 250 Switching frequency (khz)

Design tools and optimisation 700 Systematic optimisation of SiC MOSFET based AC-DC converters» Optimum design of 5 kw active rectifier with natural and forced air cooling 1.5 600 500 1 Volume (cm 3 ) 400 300 200 Line DM CM Heatsink Mass (kg) 0.5 Line DM CM Heatsink 100 0 Natural a) Volume optimisation Forced 0 Natural b) Mass optimisation Forced Natural cooling = 7.581 kw/l Forced cooling = 8.308 kw/l Natural cooling = 3.425 kw/kg Forced cooling = 3.650 kw/kg

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% 2.6 Weight vs.switching frequency 2.5 Total component weight (kg) 2.4 2.3 2.2 2.1 2 1.9 1.8 80 90 100 110 120 130 140 150 160 170 180 Switching frequency (khz)

Operational management and control Construction and commissioning of MMC / AAC lab prototype Rated Power AC Frequency DC bus AC voltage Number of SM SM voltage SM Capacitance Director Switches Phase Inductor Arm Inductor 15 kw 50 Hz 1,500 V 918 V (MMC) 1070 V (AAC) 10 SM per stack 150 V (MMC) 106 V (AAC) 1.13 mf 2 DS per stack 0.1 mh (MMC) 24 mh (AAC) 24 mh (MMC) 1.3 mh (AAC)

Operational management and control Laboratory test bed

Operational management and control AC and DC current waveforms (left) and SM voltages (right)

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 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

Converters Theme