IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 48, NO. 6, NOVEMBER 1999 1779 Application of Electrically Peaking Hybrid (ELPH) Propulsion System to a Full-Size Passenger Car with Simulated Design Verification Mehrdad Ehsani, Fellow, IEEE, Yimin Gao, and Karen L. Butler, Member, IEEE Abstract— An electrically peaking hybrid electric (ELPH) propulsion system is being developed that has a parallel configuration. A small engine is used to supply power approximately equal to the average load power. The operation of the engine is managed by a vehicle controller and an engine controller such that the engine always operates with nearly full load—the optimal fuel economy operation. An induction ac motor is used to supply the peaking power required by the peaking load (electrically peaking). The motor can also absorb the excess power of the engine while the load power is less than the peak. This power, along with the regenerative braking power, can be used to charge the batteries on board to maintain the battery state-of-charge (SOC) at a reasonable level. With the electrically peaking principle, two control strategies for the drive train have been developed. One is called MAXIMUM BATTERY SOC control strategy, by which the engine and electric motor are controlled so that the battery SOC is maintained at its top level as much as possible. This control strategy may be used in urban driving in which accelerating and decelerating driving is common and high-battery SOC is absolutely important for normal driving. The other control strategy is called ENGINE TURN-ON AND TURN-OFF control by which the engine is controlled to operate in a turn-on and turn-off manner. This control strategy may be used in highway driving. Based on the ELPH principle and the drive train control strategies, a drive train for a full-size five-seat passenger car (1700 kg of gross weight) has been designed and verified using the V-ELPH computer simulation package developed at Texas A&M University. The results show that the ELPH car can easily satisfy the performance requirement, and the fuel economy can be improved greatly over conventional vehicles. Index Terms—Design, electrically peaking, full-size passenger car, hybrid electric vehicle, simulation. I. INTRODUCTION I N VEHICLE development and design, the major issues are the marketability and the impacts on the environment. Conventional gasoline and diesel-fueled vehicles possess ad- vantages such as good performance, long driving range, ease in refueling, and lightweight energy source. These advantages have enabled the conventional vehicles to dominate the market. However, conventional vehicles have serious disadvantages in This work was supported by the Texas Transportation Institute and Texas Higher Education Coordinating Board. The authors are with the Department of Electrical Engineering, Texas A&M University, College Station, TX 77843-3128 USA. Publisher Item Identifier S 0018-9545(99)09275-0. regard to energy sources and environment protection, primarily the very inefficient usage of the petroleum sources and serious air pollution. The electric vehicles, which have been under development for many years, are considered to be important substitutes of the conventional vehicles that can overcome their disadvantages. But the acceptability of the electric vehicles in the automobile market has encountered major obstacles. Due to the heavy and bulky batteries on board, the electric vehicles usually have sluggish performance, limited loading capacity, short range and long battery recharging time, and high manufacturing cost. Hybrid electric vehicles under development in recent years are considered to be the best tradeoff between conventional and electric vehicles. In a hybrid vehicle, two power plants are available which commonly are an internal combustion engine and electric motor. The inclusion of two power plants provides flexibility to use either an internal combustion engine or electric motor or both together for traction according to their operation characteristics and driving requirement. This configuration increases the potential to optimize the overall drive train operation. It also, however, increases the complexity in the management of the powers supplied by both engine and motor. Therefore, the control strategy of the power plants is a crucial aspect in the development of hybrid electric vehicles. In this paper, a hybrid electric propulsion system, with a parallel configuration, referred to as EL ectrically P eaking H ybrid (ELPH) propulsion system, is introduced. The principle is illustrated through simulations performed using the V-ELPH software simulation program developed at Texas A&M Uni- versity [1]. The power plants available in the system are a spark ignition internal combustion engine and an ac induction motor. The power plants are managed (controlled) with an electrically peaking manner [2], [3], [7], [8]. The objectives of the application of the ELPH propulsion system to a full-size car are: 1) comparable performance to conventional vehicles; 2) similar mass production to that of the corresponding con- ventional one; 3) the same operation as driving conventional vehicles; 4) significant improvement of the fuel economy over the conventional vehicles; and 5) self-sustained battery SOC. II. ELPH PRINCIPLE For a full-size vehicle, the required acceleration perfor- mance usually constrains the reduction of the power capacity 0018–9545/99$10.00  1999 IEEE