The Hybrid Electric Vehicle Analysis (HEVA) computer program numerically simulates the performance of an automotive vehicle -- especially a hybrid vehicle. A vehicle is said to be hybrid if (1) it contains an energy-storage device (a battery, flywheel, or ultra-capacitor) that is charged with energy from a heat engine that burns natural gas or another fuel and (2) the energy-storage device is part of a system that provides electricity to a traction motor for propulsion.

HEVA can mathematically model the performance of a conventional nonhybrid vehicle, which lacks an energy-storage device. It also accounts for energy recovered by regenerative brakes. For a given vehicle design and given operating conditions, HEVA calculates fuel economy and estimates itemized power flow, wheel and motor moments, and behavior of the energy-storage system. The algorithms in HEVA incorporate the assumption that the only direct source of motive power is an electric motor. HEVA cannot be used to analyze a hybrid vehicle with a parallel configuration, in which either an electric motor or a fuel-burning engine can propel the vehicle.

HEVA comprises a simulation subprogram and nine file-editor subprograms, which are used to modify the various input files. Each file-editor subprogram is dedicated to one of nine types of input files. The input data fall into the following categories:

  • Operating conditions (velocity profile, road inclination, and environmental conditions);
  • Some general vehicle parameters (including weight and aerodynamic characteristics)
  • Engine parameters (including efficiency, power ratings, and fuel characteristics)
  • Drive-train efficiency as a function of speed ratio
  • Torque supplied by the motor vs. motor speed ratio
  • Auxiliary power unit (APU) control parameters (adjusted APU power output vs. state of charge)
  • Battery characteristics (open-circuit voltage and resistance vs. state of charge, rated voltage, and charge capacity in ampere·hours)
  • Flywheel characteristics; an Capacitor characteristics (capacitance, efficiency, and maximum voltage).

HEVA is written in C++ for IBM-PC-compatible computers running Windows 95/NT. Executable code is provided. IBM Visual Age C++ is necessary for compiling any modifications of the code. The standard distribution medium for HEVA is a set of two 3.5-in. (8.89-mm), 1.44MB MS-DOS-format diskettes. An electronic copy of the documentation in HTML format is included on the distribution medium. HEVA was released to COSMIC in 1998.

This program was written by D. K. Stalnaker and L. Viterna of Lewis Research Center. For further information, access the Technical Support Package (TSP) free on-line at under the category.

NASA Tech Briefs Magazine

This article first appeared in the January, 1999 issue of NASA Tech Briefs Magazine.

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