Ruggedized Power Electronics and Electric Drives for Off Highway Applications

1. Ruggedized Power Electronics and Electric Drives for Off Highway Applications By Brij N. Singh, Ph.D. May 22, 2009

2. Outline • Introduction • Electric drive system topology • System structure • Attributes and performance requirements • Application and implementation challenges • Field example • Conclusions

3. Introduction This talk is focused on the following example: LeTourneau Technologies L-1150 mining loader

4. Background • Electric drives using GTOs and SCRs have been used for the propulsion systems of large vehicles • Mining, Locomotive • poor switching response, turn-off gain, & efficiency • Development time at medium (V and I) power level • IGBT - a relatively newer technology (used in medium power applications) • high frequency, tighter and easier control with significant efficiency gains • Rising energy costs and falling power electronics cost have helped IGBTs to find their application in very cost-competitive automotive industry • Off-highway vehicles are deeply affected by R & D and growth in automotive industries

5. Background - Continued • Off-highway applications present many new challenges for power electronics • High performance expectations • Harsh operating conditions • High reliability goals • Reduced fuel consumption yet cost effective/completive • The efforts and technology used to meet these challenges can be termed as “Ruggedized Power Electronics for Off Highway Applications”.

6. Electric Drive System Topology • Internal-combustion engine (typically diesel) • Generator drive (gear, machine, and power converter) • Traction drive (machine and power converter) • HVDC link between power converters • Gear box / wheels

7. Electric Drive System Structure

8. Alternative Electric Drive System Structure

9. Single Generator / Multiple Traction Motor System • Machine/inverter scaling • Part commonality Single machine driving all four wheels can be another example

10. Attributes and Performance Expectations • Decreased Fuel Consumption • Performance, Productivity, and Vehicle Up-time/Maintenance Enhancements • Torque Control at Startup and Stall Conditions • Energy Density • Protection, Diagnostics, and Safety Move on 

11. Attributes and Performance Expectations Decreased Fuel Consumption • Higher efficiency with electric drives • Automatic energy recovery schemes • Example of drive system - Operation in a work cycle of loader: • Forward, stop, push through a material pile to fill the bucket, reverse, transport to destination, and unload • Variable speeds but constant speeds between modes • Vehicle’s kinetic energy can theoretically be captured for later use – further fuel efficiency gains possible • Power electronics system, control theory, and signal processing could enable a cost-effective high voltage energy storage system – Future

12. Attributes and Performance Expectations Performance, Productivity, and Vehicle Up-time/Maintenance Enhancements • Electric drive can execute same task with far superior performance, productivity, and vehicle up-time. • Fast dynamic response and stable steady-state operation • Low inertia of machine & energy storage devices–possible improvements • Electric machine, inverter, and control algorithm, and careful system design result in vehicle productivity and traction control. • Dynamic braking possible with electric drive – fast response and energy • No need to apply mechanical brake resulting in simplified control and ease to the operator. • Inverters move energy at fast rate during acceleration, braking, and speed reversal and DC bus energy rate is tens of kV / second. • Control system manages energy flow as there is limited high voltage energy storage capability. Energy storage devices and cost targets • Far less maintenance needed for electric drive vehicles resulting in less vehicle down-time and lost productivity.

13. Attributes and Performance Expectations Torque Control at Startup and Stall Conditions • Heavy-duty off-highway vehicles require maximum torque delivery in both directions upon startup, in loaded and /or stall conditions • This places extra challenges on the control system, position sensors/circuitry, power converter design, gate drive design, and machine design • The system needs to be designed to have good robustness and reliability when repeatedly faced with these challenging conditions

14. Attributes and Performance Expectations Energy Density • Electric vehicle applications requires/desires a small and lightweight powertrain to compete with well-developed and advanced technology for mechanical propulsion systems. • Greater energy density is needed for power converters and machines. • Greater power processing per unit volume of the system requires extreme power and temperature cycling of power devices and an effective thermal management and advanced cooling systems for both inverters and machines. • Energy density (and the resulting system costs) becomes a very important design criterion in vehicle optimization with reduction in the operating temperature as an objective function.

15. Attributes and Performance Expectations Protection, Diagnostics, and Safety • Drive system protects itself and safely shutdown in the event of overvoltage, overcurrent, over temperature, cable/wiring faults, etc. • Protections for di/dt and dv/dt events • Detection and accurate diagnosis of these problems raises vehicle robustness • Proper precautions contribute to uptime benefits, as small problems can be quickly and easily identified and fixed, and larger problems and cascading failures are avoided • Faults may not be apparent until higher voltage levels • Breakdown of insulation on cables or motor windings or leakage paths that are created by conductive contaminant build-up between high voltage terminals.

16. Attributes and Performance Expectations Protection, Diagnostics, and Safety • Diagnostics methods that can operate safely at different voltage levels • Real-time diagnosis (and eventually prognosis) of the inverter and machines can prolong the system’s life and infuse confidence in system’s reliability • The operator, bystanders, & service technicians must be protected at all times from the high voltage circuitry and vehicle itself • Possible high voltage safety measures include: • Reinforced insulation between high and low voltage electronics or the vehicle frame • Automatic high voltage discharge/shutdown systems • Warning indicators, product labeling • Operator training • Use of isolation monitoring system resulting in safe shut down if leakage current exceeds safety level

17. Ruggedized Power Electronics and Electric Drives for Off Highway Applications Application & Implementation Challenges

18. Application & Implementation Challenges • Competition with mechanical drive propulsion systems • very mature, high performance, and cost effective • Off-highway application provides new challenges for electric drives (vs. industrial applications) • Environmental • Operational • Safety & Field/Service

19. Application & Implementation Challenges Environmental Challenges • Operating temperature extremes (-40C to 85C) • Temperature cycles due to working shifts, as well as daily and seasonal climate changes resulting from the geographical location of the vehicle • High humidity conditions (accentuates thermal cycling effects and accelerates wear mechanisms) • Product exposure to a variety of uncontrolled chemicals that exist in the field or in the vehicle environment • Dusty/dirty/conductive/corrosive environmental issues (such as operating in coal dust in a mine or salt water atmosphere on a sea coast) • High pressure washing, especially while high voltage electronic circuits are powered

20. Application & Implementation Challenges Environmental Challenges • Exposure to rain, including possible submersion • Extreme vibration and shock requirements, along with continuous vehicle movement and flexing due to exposure to rough terrain • Enclosure must be environmentally sealed and robust against external forces – sealing creates extra challenges during extreme temp cycling and max loading • Exposure to electro-static discharge (ESD), especially in low humidity environments - the system needs to be protected from this without undermining high speed signal integrity

21. Application & Implementation Challenges Operational Challenges • Absence of regulated AC mains source on mobile vehicle • Fault conditions, such as winding short circuits, phase to ground or phase to phase short circuits, over temperature, over-speed, over-voltage, under-voltage, etc. • Power cycle due to the continuously cycling nature of the application • EMC (conducted and radiated emissions and susceptibility) sensitive electronics such as analog sensor and low voltage digital signals and components must be robust in the presence of high E and H field strengths. • The electric drive system must also not affect other systems on vehicle, electrical, communication, or entertainment systems.

22. Application & Implementation Challenges Safety & Field/Service Challenges • Vehicle and machine grounding issues, including safety bonding (connections between electric machines, inverters, and vehicle frame) • High voltage safety • Service personnel and operator training • Vehicle performance and reliability vs. cost tradeoffs / considerations • Safely handling failure modes and limiting vehicle down-time/lost productivity • Limp home capability under fault conditions • Field issues (vehicles are often located in extremely remote areas which are difficult to access) • Ease of maintenance, preferably on-site with no special training

23. Example of Ruggedized Electric Drive Vehicle

24. Example of Ruggedized Electric Drive Vehicle • Mining class loader model L-1150 by LeTourneau Technologies • On-board engine with 898 kW power • Four wheel drive train based on high efficency SR traction motors and SR generator requiring reduced maintenance • High power IGBTs in chopper configuration • Maximum speed of 12mph in either direction • Electric drive with on-board electric braking system enhances productivity with decreased fuel consumption while providing capability of full stop without use of any mechanical brake • Power electronics system (gate driver board, control board, and software) was designed, developed, and manufactured by Phoenix International – A John Deere Company

25. Ruggedized Power Electronics On Display

26. Energy Recovery with SR system

27. Fuel Savings with SR Electric Drive vs. Mechanical Drive

28. Conclusions • Rising energy costs - need for more efficient vehicles while meeting/exceeding performance, productivity, and cost metrics • Use of electric drives is apparent path • Demand for robust, high performance electric drive systems to replace existing mechanical systems • Challenges, design issues, implementation issues • Performance improvements can be achieved if electric drives is carefully designed. • Future work is needed in electric drive reliability, product packaging / thermal management, and cost competiveness • Improved energy recovery technologies and methods can optimize electric drive system • Efforts in automotive area will accelerate implementation of robust & low-cost electric drives for off-highway vehicles

29. Ruggedized Power Electronics and Electric Drives for Off Highway Applications Thank you Questions?