Development and Evaluation of a Plug-in HEV with Vehicle-to-Grid Power Flow             

This page updated November 23, 2005.

AC Propulsion

Development and Evaluation of a Plug-in HEV
with Vehicle-to-Grid Power Flow

CARB Grant Number ICAT 01-2

The statements and conclusions in this Report are those of the grantee and not necessarily those of the California Air Resources Board. The mention of commercial products, their source or their use in connection with material reported herein is not to be construed as actual or implied endorsement of such products.

The goal of this project was to develop a prototype plug-in hybrid vehicle that would combine characteristics of a pure electric vehicle with the unconstrained range of a conventional vehicle. This was accomplished by developing a compatible auxiliary power unit (APU), including an specially designed alternator, integrating the propulsion system and APU into a vehicle, and demonstrating emission reductions and commercialization potential.
A plug-in hybrid differs from the hybrid vehicles now in production in that it can connect to the power grid and use grid-supplied energy as well as energy from onboard storage of petroleum-based fuel such as gasoline or diesel. The plug-in hybrid developed for this project demonstrates four capabilities that differentiate it from plugless hybrids as well as from conventional vehicles. The project vehicle can:

    1. Provide full performance and 35-mile range with electric propulsion only.
    2. Substitute grid energy in place of petroleum energy.
    3. Serve as a distributed electric power resource.
    4. Use natural gas for generation of electric power.

The results of testing conducted under this project indicate that these capabilities can reduce vehicle emissions. Also, these capabilities demonstrate potential economic and energy benefits that can assist the commercialization of plug-in hybrids, so that emission benefits can be realized.
The Vehicle Technology
Volkswagen Jetta was converted to electric propulsion using a 100 kW drive system and an eight kWh lead-acid battery. The battery charger is integrated with the drive system and operates on grid power at 100 to 250 VAC. Charge power up to 20 kW is possible. The charger operates bi-directionally, allowing conversion of electricity from the high-voltage DC bus to 60 Hz AC current at up to 15 kW. The AC power can be fed to the grid or to other external loads.
A custom-built auxiliary power unit (APU) using a small automobile engine was designed and developed specifically for this project. The APU feeds the high-voltage bus with up to 30 kW of DC current. This power level allows charge-sustaining operation at any speed up to 80 mph. The APU is series-connected, it never drives the wheels directly. The APU can operate as a generation source, with its output fed from the vehicle to external loads including local or large area power grids.
Equipped with a wireless internet connection and control algorithms developed under a separate CARB research contract, the power system in the project vehicle can be controlled remotely to provide grid support functions.
Development of the APU was a major element of this project. The emission-controlled engine drives a light-weight, high-efficiency alternator designed and developed to meet the power, noise, and weight requirements of this application. The engine burns gasoline when it operates while the vehicle is being driven. The engine is also equipped to operate on low-pressure natural gas, and the vehicle is equipped with a gas connection that allows the APU to draw fuel directly from gas mains while it is parked. Connecting the project vehicle to an off-board gas source allows it to generate electric power continuously without depleting the onboard fuel supply or discharging the battery.
Vehicle Capabilities
The project vehicle was built to demonstrate usability, functionality, and convenience in daily use as well as the unique capabilities of plug-in hybrids. Driveability, simple controls, and seamless operation of the hybrid system all received development effort under this project. Vehicle features include cruise control, power brakes, regenerative braking, power steering, traction control, and bi-directional power. The vehicle has been tested and evaluated for emissions, efficiency, audible noise, and power quality in stationary operation; and emissions, range, fuel economy, acceleration, and driveability in mobile operation.
The completed vehicle provides 35 miles of range on batteries. The battery charger allows charging from 110V, 208V, or 240V outlets. A standard 50A electric outlet allows charging in one hour. Fuel economy of 30 to 35 mpg gives gasoline range of over 500 miles using gasoline. Up to 30 kW DC electric power is produced by the APU. This power level allows charge sustaining operation at up to 80 mph. Top speed is governed at 85 mph. Acceleration from 0-60 mph can be achieved in 8.5 seconds.
The project vehicle demonstrates full functionality as a replacement for a conventional car that may be used locally or for long-distance travel. (Storage capacity was compromised in the prototype vehicle, but this compromise is not inherent to plug-in hybrids.)
Emission Results
In dynamometer tests conducted by CARB at their El Monte, CA, test facility, the project vehicle produced emission levels near current ULEV standards over the standard UDDS test cycle. In separate tests, emissions were measured at steady state operating points, and these brake-specific emission rates, measured in gms/kWhr are very low as shown in the table.

Project Car APU Operating Data, Stationary Mode, Gasoline Fuel







Project Car APU 5 kW






Project Car APU 15 kW






Capstone Microturbine
30 kW
1 (natural gas,
max output)






 U.S. Generation Avg1
(fossil fuel)






 CA Generation Avg 2
(fossil fuel)






 CARB DG Standard3






 CARB DG Standard3






1 Source: Capstone White Paper March 6, 2000
2 Source: CEC Environmental Performance Report, 2001
3 Distributed Generation Certification Program, Section 94203, California Code of Regulations
It is interesting to note that, because APU operation is de-coupled to a some degree from the actual driving cycle, the UDDS emissions can be estimated just by multiplying the brake specific emmisions rates times the energy required by the vehicle over the driving cycle. Such theoretical calculations suggest that SULEV emission levels over the UDDS should be achievable, and that the relatively high emissions measured over the actual UDDS test are the result of poor cold-start emission control.
The measured brake specific emissions rates also can predict the emissions from the APU when it is used as a stationary power source. Comparing the brake specific emissions from the project APU to emissions from other power generating sources shows that the project APU operates with significantly lower emissions than microturbines or conventional gen-sets, neither of which benefit from the sophisticated and highly developed emission control systems that are typical of current automotive engines.

Funding Source

Funding Amount





South Coast Air Quality Management District and National Renewable Energy Laboratory




Click here for the entire final report.

ICAT Funded Projects