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Ultra Low Emission Vehicle – Transport Advanced Propulsion

U. Henning1, F. Thoolen2, M. Lampérth3, J. Berndt4, A. Lohner5, N. Jänig6

1Siemens AG, Erlangen, Germany, 2Centre for Concepts in Mechatronics CCM, Nuenen, Netherlands, 3Imperial College, London, Great Britain, 4 Vossloh Kiepe GmbH, Düsseldorf, Germany , 5FH, Köln, Germany, 6Transport Technologie – Consult Karlsruhe GmbH TTK, Karlsruhe, Germany

Abstract

The project ULEV – TAP 2, ultra low Emission vehicle – transport advanced propulsion, is funded by the European Commission within the 5th Framework Programme. It concentrates research and development efforts on the central hardware required for a series electric hybrid drive concept for the light rail application based on the flywheel technology energy storage system, diesel engine driven prime mover unit and a supervisory control unit for safe, reliable and optimised drive. Energy storage enables brake energy recovery and load levelling. This allows for energy efficient vehicles of high quality, able to meet strict emission limits and to provide a standard of performance expected of modern electrified systems without involving electric supply infrastructure.

Introduction

ULEV-TAP 2 is a European Commission sponsored project based on a series electric hybrid concept for the light rail application. The hybridisation of vehicles is about the combination of different power-sources and energy storage device. Depended on the duty-cycle of the vehicle the storage system will either be optimised for high power density or high energy density. Current technology unfortunately does not provide for an energy storage device that offers both good power and energy storage density. The main contenders for the hybridisation of a rail vehicle are ultra-capacitors (High Power density) and Flywheel (High Energy Density). The choice for the power source is also wide. For the case of a rail vehicle conventional diesel technology is predominately used at present. These engines run at a relatively low speed (up to 2500 rpm) and are heavy (low power-density). Alternatives in development are Fuel cells but they are a long way from being available for high volume production. With a faster running Diesel engine a higher power-density can be achieved adding to the benefits of the diesel technology over fuel-cell systems. Other combustion engine technologies do not offer benefits in terms of efficiency and gas system in particular can not be considered for safety reasons. The project ULEV-TAP 2 concentrates research and development efforts on the central hardware required for a series electric hybrid drive based on the flywheel technology energy storage system, diesel engine driven prime mover unit and a supervisory control unit for safe, reliable and optimized drive. Flywheel energy storage enables brake energy recovery and load leveling. This allows for energy efficient vehicles of high quality, able to meet strict emission limits and to provide a standard of performance expected of modern electrified systems without involving electric supply infrastructure. Flywheel technology combined with an automotive diesel based prime mover unit will offer the highest combined efficiency and lowest overall weight. The ULEV-TAP project set-out to demonstrate that this approach is feasible and proven the concept for light rail application. The 3-years-project ULEV-TAP 2 has been finished in 2005. In this paper details about the progress made on the Premium Power Unit (PPU), Prime mover Unit (PMU) and Supervisory Control Unit (SCU) developments are described. The consortium members and their project objectives are: • Siemens AG: project coordination, specification of modern modular hybrid light rail vehicles with roof

mounted hardware • Centre for Concepts in Mechatronics CCM: PPU - Premium Power Unit, flywheel construction,

bearing system Motor generator and power converter technology • Imperial College London IC: PMU - Prime Mover Unit, axial flux permanent magnet generator, power

and control electronics

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• Vossloh Kiepe GmbH: SCU - Supervisory Control Unit, communication and optimized control algorithms for energy management, safe control of power train and vehicle. Diagnostics and monitoring.

• TransportTechnologie-Consult Karlsruhe GmbH TTK: project management, dissemination and evaluation.

Elaboration of the component specifications

The bases are performance data of mu lti-system hybrid low-floor light rail vehicles. The developed specifications contain an overview of the propulsion system and explain the technical environment of the system; all necessary electrical data such as power, voltage and limits are defined. Mechanical requirements like the allowed dimensions, weights with tolerances, shock, vibrations, lacquering and transport instructions as well as safety, RAM, acoustics and environmental data were also determined. The main specification data are: • vehicle unit: low-floor 5-articulated tram train • propulsion system: 4 x 180 kW (160kW) (diesel-electric mode) • tare weight: appr. 60 t • rotating mass: appr. 10 % • passenger load (4P/m²): 15,4 t • passenger load (6P/m²): 23,0 t • low-floor part: appr. 70 % • drive adhesion: appr. 50 % • axis mode: Bo’ 2 2 Bo’ • wheel diameter (new): 660 mm The vehicle performance data are (see also Fig. 1): • operation speed limit - diesel-hybrid mode:100 km/h • operation speed limit - electric mode (DC-system): 70 km/h • maximum gradient: 4.5 % • initial acceleration: ≥ 0.90 m/s² • average acceleration from 0 kmph to 100 kmph: ≥ 0.17 m/s² • required adhesion coefficient for powered bogie: ≥ 0.21

Fig. 1. Vehicle performance An example of a roof arrangement of the PPU and PMU is shown in Fig. 2. Possible configurations depend mainly on the max. nominal power of PMU, max. continuous power and max. effective energy storage capability of the PPU.

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TC PPU PPUPMU TC

Fig. 2. Roof arrangement (example) of the diesel hybrid vehicle The specification data (target requirements per one unit) of the PMU (see also Fig. 3) are: • nominal electric power: ≥ 200 kW [e.g. VW 10 Z TDI (230kW)] • max. weight: 800 kg • max dimension (length / width / height): 1600 x 1850 x 583 mm.

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The specification data (target requirements per one unit) of the PPU (see also Fig. 4) are: • Continuous power capability: > 500 kW • Effective energy storage capability: 4 – 5 kWh • Charge and discharge efficiency: > 90 % • Max. weight: 800 kg • Max dimension (length / width / height): 1600 x 1850 x 583 mm

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The Premium power unit (PPU)

For the application in a light rail application where a long service life is paramount batteries can not be considered. Ultra-capacitors and flywheels are the only feasible options. If these two options are compared than it can be shown that ultra-capacitors offer good power-density and nearly as good energy density as conventional flywheel technology does (Fig. 5). This makes them suitable for application where

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short power-bursts are required. With new flywheel technology though similar power-densities can be achieved whilst offering better energy-density. This makes the technology suitable where longer accelerations time are required. When only power-density is concerned than the devices should be compared on the basis of live expectancy and efficiency.

Fig. 5. Comparison of energy storage technologies CCM has since 1986 developed and demonstrated flywheel energy storage technology as a viable energy saving and emission reducing resource for on-board public transport vehicles. In the ULEV-TAP 2 project CCM is tasked with developing a complete PPU (Premium Power Unit) for roof mounting on light rail vehicle. The step improvements required for this demonstrator have been major steps forward in the development of this PPU. The flywheel system of the proceeding ULEV-TAP project had therefore to be miniaturized. This has been realized by increasing the rotation speed up to 22,000 rpm. As a consequence all mechanical and electrical parts (flywheel, bearing system, motor/generator, power converter and control) had to be redesigned in order to withstand the higher speeds and in order to minimize energy conversion losses as conversion losses increase substantially with higher speeds. The main component of the PPU, the Flywheel-Motor/Generator-Unit (FMG Unit) has become very compact by its modular construction consisting of: a high speed carbon fiber flywheel; a fully integrated high power permanent magnet motor/generator; a compact bearing cartridge and vacuum/safety containment. The planned lifetime of the unit is 150,000 hrs with a bearing replacement every 50,000 hrs. Also the PPU safety has been addressed. A Flywheel Safety System has been developed and implemented, based on the product assurance system as already applied and approved in space industry. Implementation of this safety system has been a contribution to the improvement of the reliability, availability, maintainability and safety of this PPU. Passive safety is reached by the development of a safe construction and by the application of approved engineering parts. Active safety is reached by the integration of a guarding system continuously checking operational parameters. The progress in flywheel development and miniaturization during the last 50 years is displayed in next illustration, see Fig. 6. The progress in ULEV - TAP 2 has been exemplary with improvements in all areas such as power density improved to 800 W/kg, with an associated energy density of 10.6 Wh/kg (38 kJ/kg) and turnaround efficiency of 96% (flywheel motor-generator unit). The miniaturized flywheel system is specially designed to be packaged into a roof cabinet for light rail vehicle application. The challenge of the PPU packaging is the very restricted dimensioning of the roof cabinet, in particular the construction height. Taking into account the vehicle specifications, a packaging configuration has been realized as shown in Fig. 7.

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• 1955 Oerlikon, Switzerland, • 3.13 kWh / 130 kW, 3000 rpm • Ø1700 x 1100 mm, 3000 kg

• 2001, ULEV-TAP 1, CCM • 4 kWh / 300 kW, 15000 rpm • Ø900 x 900 mm, 850 kg

• 2005 ULEV-TAP 2, CCM • 4 kWh / 300 kW, 22000 rpm • Ø780 x 450 mm, 375 kg

Fig. 6. Flywheel history

The complete PPU package (Fig. 7) comprises the following modules: • Flywheel-Motor/Generator-Unit (FMG) incl uding a cardanic suspension for eliminating gyroscopic

forces to the vehicle and vibration insulation • Power converter • Choke as part of power converter • Controller for operating the complete PPU • Cooler for liquid cooling of FMG and power converter. Note that a lubrication and vacuum pump are

not required anymore • DC switch gear for coupling and decoupling PPU to vehicle drive system • AC switch gear including fuses as part of the safety system

Fig. 7. PPU box (300 kW continuously, 4 kWh, 1000 kg components only, 1650x1850x580 mm)

The Prime mover unit (PMU)

Available prime-movers in the near future will be Internal Combustion based. Diesel engines used in rail applications are usually low speed engines (up to 2,500 rpm). These engines distinguish themselves with their low maintenance requirements and reliability. The drawback is the low power density resulting in heavy machines. Automotive Diesels, on the other hand, have more than double the power density and

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also the potential for higher efficiency. Gas-turbine would offer the best energy density and also a high efficiency. The problem with this technology is the conversion from the turbine power to electrical power. Diesel engines can use low speed generator technology which is much easier. Automotive Diesels offer the next best power density. The Hybrid Power Research group at Imperial College London is building the PMU based on a high speed diesel engine coupled to an innovative axial flux generator. The use of permanent magnets for field excitation allows not only increasing the power-density of a generator but also its efficiency. Axial flux topology adds additional benefits allowing a further increase of the power density as shown in Fig 8. Axial flux permanent magnet machines pose a design and manufacturing challenge but offer the best performance. A combination of this generator with an Automotive Diesel engine is poised to give best power-density and exceptional efficiency. To even further improve the efficiency hybridization will help to operate the PMU at is optimal point and also reduce overall energy consumption due to regenerative breaking. Since the start of the project Imperial College has focused on the design of the generator. A prototype has been built and tested. Fig. 8 shows a comparison of the ULEV-TAP machine with a conventional high power-density generator. For the same size and speed-range four times as much power could be generated.

Fig. 8. Comparison of ULEV-TAP 2 machine with conventional generator Another innovation of the machine is the winding which is optimized for reduction of eddy current losses and minimal ripple torque. One of the six slices is shown in Fig. 9. It has been shown that is possible to more than double the power density of a diesel based Prime Mover Unit. The technical feasibility of a 200kW with an over efficiency of up to 36% and a weight of less than 800kg has been demonstrated (Fig. 10). In difference to the other aspects of the ULEV-TAP project this has only aimed at building a technology demonstrator and more work will be required to move the innovation into production.

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Fig. 9. Winding of ULEV-TAP II generator

Fig. 10 PMU demonstration

The Supervisory Control Unit (SCU)

Fig. 11 depicts the Vossloh Kiepe concept of the hybrid power train system. The vehicle can be supplied conventionally by overhead line or autonomously by diesel engines. The drive equipment is composed of two power trains each consisting of one PMU, one PPU, one Drive Brake Unit (DBU) and one SCU being master of its power train.

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Fig. 11. Basic structure of the power and the data connections between the units of the flywheel boosted

hybrid power train. The SCUs are responsible for a save vehicle operation and for the power management of the power trains due to a minimum fuel consumption and due to ultra low emissions. Additionally, according to the drivers demand each SCU controls its internal DC-bus voltage with assistance of its PPU. The PPU behaves like an ideal voltage source with low internal resistance receiving its load characteristic (no-load voltage, internal resistance, current limits) from the SCU. This DC-link set-point voltage, calculated by the SCU, mainly depends on the torque/speed characteristic of the diesel engine. In order to achieve the best usage and highest efficiency the engine varies speed with varying power demand. A typical system simulation result of the hybrid power-train is shown in Fig. 12. The system simulation considers the technical data of the tram train, the data of the storage system (PPU), the diesel generator (PMU) and the traction system (DBU). The basis for the simulation was a real drive cycle of the city of Karlsruhe. The research work shows that the best strategy is to drive the diesel engine in the defined hybrid configuration only in three different states: Engine off, best point of efficiency and max. power. The dynamic of power will be provided by the energy storage system (PPU). The control strategy can be verified in the side figure. The 1st diagram shows the speed (NPMU) of the diesel engine which has three states, zero (engine off), 2400 rpm (best point of efficiency) and 3300 rpm (max. power). Also the torque of the diesel engine (MPMU) is shown. The 2nd diagram shows the vehicle speed (VDBU) which varies between 0 and 90 km/h. EPPU represents the state of charge (SOC) of the flywheel. The EPPUmax shows the maximum set points of SOC for the storage unit (PPU) given by the Supervisory Control Unit (SCU). The fuel consumption of the vehicle during the drive cycle is shown. The comparison between the fuel consumption of the hybrid driven vehicle and the diesel electric driven tram train shows a reduction of more than 40 %. The 3rd diagram shows the electric parameter of the hybrid power system. UDC is the voltage of the DC-Bus which is nearly constant. Only in cases of max. speed of the diesel engine the DC-Bus voltage increases. The diagram shows that the high potential storage system (IPPU=PPU current) is feeding the traction system (IDBU=DBU current) in the acceleration phases. In braking phases, the storage system (PPU) will store the regenerative braking energy produced by the traction inverters. Only the difference of power between traction inverter and storage unit is given by the diesel generator.

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Fig. 12. Simulation result

Market prospects and outlook

The improvements to the power train efficiency and emissions pollutants, i.e. one of the main outcomes of ULEV-TAP 2, will make cost effective/clean prime movers for industrial and transportation applications possible. For transport, this will bring accessibility in peripheral regions which have so far been at a social and economic disadvantage in relation to areas with efficient or electrified transport (e.g. prohibitive costs of 500,000 Euros/km for electrified light rail). Rail tracks may be classified as electrified and non-electrified. Diesel vehicles have been used for non-electrified as well as mixed electrified/non-electrified lines. For electrified, there is an additional requirement for border crossing situations, where there is a mismatch of system parameters. Here electrical dual -mode vehicles for local regional public transport have not been available. Successful developments in dual mode operation (e.g. Karlsruhe 750V dc/15.000V ac, but also other German and now France cities/regions) has increased the potential for rail transport. This means that the dual-mode-LRT-vehicle can operate on regional, electrified heavy rail routes as well as in the city centres. Similar systems are actively being sought by city and regional transport authorities throughout Europe. Due to environmental restrictions the main advantages for a low emission hybrid power train are: • use of not electrified regional railway routes and inner city electrified tramway routs • LRT-systems in cities without the need for an overhead-system and without any visual intrusion • multi-modal-capability The project therefore supports EU policy promoting competitiveness and cohesion through the convergence of regional growth paths and through transport infrastructure development. A more detailed market study has been carried out within the project. This market study addresses the diesel/energy-on-board-storage tram train vehicles as well as energy-on-board-storage equipped trams. From the dissemination activities including the Europe wide market survey followed good prospective for future commercialization possibilities of the ULEV-TAP 2 technologies for rail application. There is even better market perspective for the individual components of the ULEV-TAP 2 drive system.