DOE’s National Energy Technology Laboratory (NETL) recently issued a solicitation for the development of power electronics and electric motors for use in plug-in hybrid (PHEV), hybrid (HEV) or fuel-cell (FCV) vehicles.
DOE estimates that $16 million will be available over three or four years to support two to six awards selected in four areas of interest. The projects will be phased, with Phase I consisting of design, modeling, and initial research and development (R&D). Based on evaluation of the concept and a go/no-go assessment, the project may proceed to Phase II for continued development, demonstration and testing and analysis.
The four areas of interest are:
High Temperature Three-Phase Inverter for Advanced Hybrid Electric Vehicles (HEV) including Internal Combustion Engine HEV, Plug In HEV (PHEV), and Fuel Cell Vehicle (FCV) Traction Drive Applications.
High Speed Motors for Advanced Hybrid Electric Vehicles including Internal Combustion Engine HEV, Plug In HEV (PHEV), and Fuel Cell Vehicle (FCV) Traction Drive Applications.
Integrated Traction Drive System for Advanced Hybrid Electric Vehicles including Internal Combustion Engine HEV, Plug In HEV (PHEV), and Fuel Cell Vehicle (FCV) Traction Drive Applications.
Bi-directional DC/DC Converter for PHEV Applications.
Inverters. Inverters convert direct-current (DC) battery power into alternating current (AC). The inverters in current hybrids require cooling, which add to the cost of the system. An inverter able to operate at high temperatures would reduce hybrid system costs.
Advanced inverters are needed in all three classes of hybrid vehicle application (plug-in, combustion engine, and fuel-cell). DOE notes that high-temperature inverters are especially important for combustion engine and plug-in hybrid applications because the mid- and long-term paths involve a transition to higher-temperature coolants.
Future availability of advanced, high temperature (together with lower cost, weight, and volume) inverters will advance the marketplace application of highly fuel efficient and environmentally beneficial hybrid vehicles.
Currently, inverters in hybrids use 70° C coolant supplied via a separate cooling loop in the automobile. DOE’s goal is to produce an inverter that can operate reliably using ambient air without mechanical augmentation (e.g., fans, air compressors, etc.) as the cooling fluid.
Among the requirements for the inverters are:
- Reliable operation for 15 years;
- Rating of 55 kW peak at the coolant temperature;
- To be no larger than 4.6 liters in volume and weigh no more than 4.6 kg to enable successful integration into the drive system of an automobile;
- Total cost not to exceed $275 in large (100,000 units per year) production quantities; and
- Baseline voltage of 325V nominal, with provision for scaling to higher voltage levels.
High-speed motors. Although DOE says that it favors interior permanent magnet (IPM) motors for hybrid designs in which the electric traction drive system is used for a significant portion of the duty cycle, it will also consider other advanced motor technologies.
The goals for this area of interest are to develop advanced motor technology that achieves reductions in size, weight, and cost compared to current IPM motors. The specific goals are for a brushless DC motor that:
- Produces 55 kW peak power for 18 seconds and 30 kW of continuous power;
- Weighs no more than 35 kg;
- Occupies no more than 9.7 liters in volume;
- Costs no more than $275 in production volumes of 100,000 units per year;
- Uses a design that is scalable to 120 kW peak power for 18 seconds and 65 kW continuous;
- Operates at 325V nominal, with consideration given to operation at higher voltage levels; and
- Can be driven by a standard three-leg inverter with no additional circuitry.
The most promising method for attaining these targets is to increase the operating speed of the motor. The power level of the motor (at constant torque) is directly proportional to speed. Thus doubling the motor speed produces a motor with double the power. Over the past several years motor speeds have increased from 6,000 rpm to 14,400 rpm. This has resulted in the traction drive motor becoming smaller and lighter. It is anticipated that motor technology developed under this area of interest will leap frog current trends and focus on the development of a brushless dc traction drive motor with an operating speed in excess of 14,000 rpm.
Integrated Drive System. The electric drive system consists of the electric motor, power electronic inverter, and DC/DC converter (if needed. While current electric traction drive systems “are acceptable for the early adopter market...they are too costly, heavy, and bulky to allow the HEV to become a mass market option,” according to DOE.
DOE is seeking an integrated traction drive system that can:
- Produce 55 kW peak power for 18 seconds and 30 kW of continuous power;
- Be based on a design that can scale to 120 kW peak power for 18 seconds and 65 kW continuous power to accommodate a variety of automotive platforms;
- Operate reliably for 15 years;
- Cost no more than $660 to produce in quantities of 100,000;
- Weigh less than 46 kg and occupy a total volume of less than 16 liters;
- Operate with the use of engine coolant at a nominal temperature of 105° C;
- Offer a system efficiency of greater than 90% at 20% of rated torque over 10% to 100% of maximum speed; and
- Operate at 325V nominal with consideration to operating at higher voltage levels.
Converters. DC-to-DC converters transfer DC power between a low-voltage battery pack and the high-voltage electronics used in hybrid vehicles, allowing the use of a smaller battery pack that operates at a lower voltage.
DOE is asking that Phase I activity include a systems optimization study to determine the vehicle system tradeoffs associated with higher-voltage operation of the electric traction drive system in a PHEV application. The purpose of this study is to establish the need for and level of voltage boost that should be included in the converter. Phase II work would focus on design and testing of a prototype unit.
The converters should:
- Be capable of transferring at least 5 kW of power between low- and high-voltage buses and provide the necessary voltage boost to the traction drive system;
- Cost no more than $75/kW;
- Have a power density of at least 1.0 kW/liter and a specific power of at least 0.8 kW/kg; and
- Operate with an inlet coolant temperature of 105° C
Applications are due by 15 November. Full details are in the solicitation on the NETL Web site.