EP/I038543/1 Leigh Murray University of Warwick 1
Objectives Facts & Figures Outputs 2
To develop new EV technologies. Meet challenges + opportunities facing the EV market. Integrate electrical motor + power electronics reduce cost/weight and increase power density improve reliability of electrical power systems maintain manufacturability for a mass market 3
EPSRC-funded project: 3.1 M + 745k for demo projects 4-year project: Oct 2011-Sep 2015. Extension to Mar 2016 10 partners 6 research themes 3 technology demonstrators (started Oct 2013) Low TRL (1-3) to support EV technology development 4
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Experts in power electronics, electrical machines, and mechanical engineering Prof Phil Mawby (Warwick) Prof Phil Mellor (Bristol) Prof Keith Pullen (City) Prof Patrick Luk (Cranfield) Prof Emil Levi (Liverpool John Moores) Prof Andrew Forsyth (Manchester) Prof Volker Pickert (Newcastle) Prof Mark Johnson (Nottingham) Prof David Stone (Sheffield) Prof Andrew Cruden (Southampton) 6
Car manufacturing companies Semiconductor manufacturers Component manufacturers Product designers Energy supplier Consultancies 7
Demo 1: Integrated Non-Rare-Earth High Performance Drive Demo 2: Integrated Power Conversion for Reduced EMI Demo 3: An Integrated Onboard Battery Charger using a Nine-phase Machine, with V2G Capability 8
Objective: To grow 3C-SiC on Si wafers for high current and high voltage power devices. Not 4H-SiC S because too expensive. Specific aims: Create lateral MOSFET devices with: o medium/high blocking voltages o high current permits high torque, high acceleration Target = 1200V and 10A = future requirement for higher performing EV power trains. Finger vs circular structure: Take up space /(non) uniform distribution of current. Passivation Oxide Gate Source Drain Al Gate Passivation Oxide Ti/Ni Source Ti/Ni Drain Achieved: Lateral MOSFET with a channel mobility of around 90 cm 2 /Vs which is much higher compared to 4H-SiC. So current density is expected to be high. Fabricated lateral MOSFET Commercial 4H- SiC: 40cm 2 /V.s 9
D Challenge: To achieve high voltage with current material quality because Interface strain from lattice mismatch. 3C-SiC lattice structure is smaller than Si. Si and SiC expand at different rates (Si expands faster than SiC when heated). 3C-SiC on Si 3C-SiC anti-phase boundary 3C-SiC Stacking faults Si Strain is partially released through film curvature (macro view) and defect formation (micro view). Stress-induced defects formed in 3C-SiC can cause leakage current. Si 10
Integrated Non-Rare-Earth High Performance Drive Total Funding: 311,982 Objectives: To develop a high performance ferrite motor with full functional integration with its converter. Mechanical and thermal integration of the motor and the controller. Theme 2: Design Tools (Newcastle, City, Manchester) Theme 4: Motors (Cranfield and Newcastle) 11
Experiments data correlations fed into design of software (enable thermal design of the electrical machine). Rotate rotor at various speeds and apply forced airflow from a fan blower. Forced flow results in a more uniform heat transfer (stator to air). For lower rotational speeds, more airflow causes heat transfer to increase. For higher rotational speeds, more airflow may cause heat transfer at the rim to decrease slightly. No forced flow Radial outflow: 8 g/s Radial outflow of 19 g/s 12
Power module failure: cracks in solder layer and bond wire lift-off. Newcastle have integrated a cooling medium to a power module to cool power chips individually. Results: Temperature fluctuation ( T) reduced by 10 o C by using liquid-metal material has potential to double chip lifetime compared to conventionally cooled power modules. Pipes containing the liquid-metal coolant. Power supply for the internal pump (no mechanical rotational component). 160 140 120 T junction ( o C) 100 Power module and cooling circuit 80 Red chip temp. cycle new module Blue chip temp. cycle traditional module 60 Proposed with periodic flowrate Conventional with constant flowrate 40 0 5 10 15 20 25 30 35 40 Time (s) 13
Rare-earth PM in-wheel machine (speed <1000 rpm) Relatively new concept of drive train. PE integrated inside the stator to directly turn the wheels. No gearbox or transmission system, so space for battery. Mass of in-wheel motors can t be large - stability. Disadvantages of rare-earth: high-temperature demagnetization; expensive; restricted supply. In-wheel Motor Energy Source Motor Controller Ferrite-based PM machine (speed ~5000 rpm) Working temperature 100⁰C higher than rare-earth PM. Disadvantages: low-temp. demagnetization; fragility; low-energy density (1/10 of rare earth). 14
Rotor Used multi-physics optimization to simulate structure. Decided on a small rotor diameter and pole number (8) to simplify the rotor structure and safeguard rotor integrity against high centrifugal force. Max speed: 20,000 rpm. Lamination stress reduced to <300MPa at 20,000 rpm. Stator Compared 4 stator configurations with different slot numbers. Assessed affect on torque output, torque ripple, and demagnetization. Used 3-D electromagnetic FEA determined the final optimal design. Stator with 48 slots and 156mm diameter. 30 slots 36 slots 42 slots 48 slots 15
High-strength, support pins used to reduce stress in the lamination steel. Optimal rotor has eight poles and is 95.4mm diameter. Employ Nippon Steel 0.35mm lamination 35H250 with 420MPa tensile strength to minimize rotor core loss. Rotor right cover Rotor left cover Rotor shaft tie pin Pin holders Lamination with pin holders Lamination support pins 16
Employ Nippon Steel 0.2mm lamination 20HTH1200 to minimize the stator core loss at high rotational speed. Stator lamination with windings Partially assembled stator Aluminium casing DC capacitor and power module (converter and DSP inside) mounted on Al casing on stator 17
Material weight Cost (inc. manufacture) Rare-earth motor (with Demo 1 specs) Lamination: 9.0 kg Cu wire: 1.2 kg Rare earth PM: 0.75 kg Total = ~11 kg Demo 1: Ferrite PM motor Lamination: 12.0 kg Cu wire: 1.7 kg Ferrite PM: 1.0 kg Total = ~15 kg High. Rare-earth PM = 50/kg Low. Ferrite PM = 7/kg Nominal rating: 20 kw at 10,000 rpm (max. 20,000 rpm). Cross-sectional view of the final assembly Overview of the final assembly. Integration of controller board on top. 18
Integrated Power Conversion for Reduced EMI Total Funding: 310,661 Objectives: Save weight and volume through having a sealed enclosure and shared cooling circuit. Reduce electromagnetic emissions by using filters and Al enclosure. Reduce the passive component size to reduce converter size and increase power density. Theme 3: Packaging (Nottingham) Theme 6: Passives (Bristol, Manchester, Sheffield) 19
Passive components represent ~50% of the mass of a power converter. Objective: investigate technologies to deliver compact and lightweight wound components, and to increase heat removal from them. Heat removal: Encase in a composite potting compound (epoxy). Adding Al 2 O 3 powder as filler material can improve thermal conductivity. Epoxy pumped in With filler get 20% more heat removal from inductor. Toroidal inductor E-core inductor Potted inductor with thermal sensors Heat extraction better with e-cores: end windings potted, and can mount on cold plate. 20
High-fidelity modelling to find best combination of coil and core dimensions. Consider electromagnetic performance AC losses from windings and core losses thermal behaviour simultaneously VESI inductor requirements: - 80 μh inductance - 200 A rated current - 400 Hz operating frequency Winding power loss [W] 250 200 150 100 50 Al Al conductors 20C Al conductors 40C Al conductors 60C Al conductors 80C Cu conductors 20C Cu conductors 40C Cu conductors 60C Cu conductors 80C Cu Inductor Design Commercial 0 1 2 3 4 5 6 Frequency [khz] Energy density for theoretical mass of 2.5 kg 0.1-0.2 J/kg Publications 0.2-0.8 J/kg Al windings in e-core. End windings to be potted in epoxy. VESI 1.2 J/kg 21
Alternative ways to package chips on a substrate instead of wire-bonding and soldering techniques. Employ integrated, modular assemblies, where electromagnetic, thermal and mechanical functions are treated together. Sintering process Multi-layer flex connect with sintered SiC JFETs AlN substrate with Ag nano-paste 4-channel integrated liquid cooler Integrated gate drive circuit Demo 3 uses 3 power modules to create a 9-phase converter Integrated CM and DM input filter Final module (12.8 x 16.3 x 3.3 cm) 22
By mounting the main power conversion elements within a single enclosure, with appropriate power and signal filtering, the associated EMI challenges can be eliminated. Integration at least a 20% reduction in volume and weight. COLD PLATE LAYOUT DC-DC converter Power module for traction motor FPGA control board Bi-directional DC-DC converter interface to 30kW supercapacitor buffer store 23
An Integrated On-board Battery Charger using a Nine-phase Machine, with V2G Capability Total Funding: 269,437 Objectives: To develop a working prototype system of an onboard charger with bi-directional power flow. To develop a high-power-density power converter, based on WBG devices. To design control software for charging and V2G functionality. Theme 3: Packaging (Nottingham) Theme 5: Converters (Manchester, LJMU, Newcastle, Southampton) 24
Investigate integrated on-board charger with bidirectional power flow for battery charging and V2G operation. Can use single-phase (slow), 3-phase, and multiphase charging (fast). No separate charger, instead RE-USE the pre-existing magnetic components and inverter installed for driving mode. No torque produced while charging. Advantages: Fewer new elements lower cost Lower weight faster vehicle Less space needed smaller vehicle Can use any type of power socket V2G operation helps with providing stored electricity to the grid 25
Concept is applied to 5,6, and to 9-phase configurations. three-phase grid v ag+ v bg+ v cg+ i ag i bg i cg EMI filter (onboard ) S 1 S 2 hardware reconfig. i ag i bg five-phase machine b i cg i bg /2 d c a i cg /2 i ag i bg /2 i cg /2 i c i b i a i e i d v c v b v a v e v d i dc i c v dc C i L BAT e Switches open grid is connected and can charge the battery. Switches closed grid is disconnected, so the inverter can perform propulsion control of the machine. 26
Oscilloscope displaying waveforms Laptop DSP control unit Grid voltage sensor 10 x 12V, 40Ah LiFePO 4 batteries 7.5kW DC/DC converter and ninephase inverter Nine-phase induction machine 27
A small-scale controller looking at communication between EVs and the grid. Connect all vehicles to a network. EV users notified about the demand on the grid, and can export to help meet demand, or charge up. Display of real-time data for speed and power flow. Shows whether demo supplies power to the grid (V2G, power is -ve) or charges battery (G2V, power is +ve). Shows how fast battery is being dis/charged. 28
VESI project focuses on integrating the electrical motor and power electronics Meeting the key aims: reduce cost, increase power density, improve reliability of electrical power systems. 36 publications. Underpinning basic research nearly complete. Work on physical outputs for the 3 technology demonstrators continuing. 29
VESI project information.. l.murray@warwick.ac.uk Semiconductors..p.a.mawby@warwick.ac.uk Demo 1/Motors... p.c.k.luk@cranfield.ac.uk Heat transfer...k.pullen@city.ac.uk Power module cooling. volker.pickert@newcastle.ac.uk Demo 2/Passives p.h.mellor@bristol.ac.uk andrew.forsyth@manchester.ac.uk Potting compounds... d.a.stone@sheffield.ac.uk Packaging. lee.empringham@nottingham.ac.uk mark.johnson@nottingham.ac.uk Demo 3/On-board charging. e.levi@ljmu.ac.uk V2G functionality..a.j.cruden@southampton.ac.uk 30