Abstract
A vehicle is a machine for transporting persons or loads from a starting place to destination. Energy efficiency improvement measures of a vehicle consist of mainly reducing unnecessary operation, energy recovering and improvement of propulsion efficiency. The cost effectiveness of measures is the described order. The first measure is idle stop that can be realized with a micro hybrid system, and vehicle weight reduction. The second measure is kinetic energy recovery that can be realized with a regeneration system or with a kinetic energy recovery system (KERS) in a racing car or waste heat energy recovery for an internal combustion engine (ICE). The third measure is hybrid propulsion or optimization of load point in an ICE.
Kinetic energy is an energy to be recovered. And vehicle velocity is an energy storage in other point of view. Velocity should be handled as a storage element in a hybrid propulsion vehicle and the stored energy can be recovered as electricity, velocity of a fly wheel or hydraulic pressure.
A computation model represents functionalities of a target system. Fewer parameters for rules of model behavior or model properties is preferable as far as the model can represent required functionalities. Time required for model construction and model verification is proportional to scale of a model. A mathematical equation requires only a few rules and parameters and meets above mentioned conditions. An electric motor and a generator are modeled with electrical – mechanical system equations in which main parameters are current to torque conversion coefficient and a resistance. Torque and energy efficiency can be calculated with those equations without conventional torque map and efficiency maps. Required parameters can be obtained from published papers.
A linear model is to be proposed to describe linear relationship between output torque and fuel consumption rate in an ICE. Output power of an ICE can be calculated without conventional maps. Required parameters or properties can be also obtained from published paper or common knowledge for an ICE.
Recovery ratio of the vehicle velocity is depending on target speed of a test cycle. Because a vehicle is not a lossless system during acceleration and deceleration. If capacity of a battery on a vehicle is sufficient for a certain part of a test cycle, battery charging slots can be allocated arbitrary in the test cycle. The model to be proposed is small size and can be applied even for an exhaustive search.
A framework of energy balance model, in which vehicle velocity is included as an energy storage, for hybrid propulsion vehicle energy management. To reduce the scale of model, an ICE and an electric motor are modeled as an energy transform gain. Those gains are described with simplified linear mathematical equations. Parameters for those equations were obtained from published papers. No map for coefficients are not required.
The model structure is transparent and evaluation of parameters and simulation result is easy because of smaller parameters. The model was realized with Matlab. HEV behavior in NEDC can be simulated within 30 seconds. The calculation speed is approximately 30 times higher than that of the model described with GT-suite and Matla.
The proposed model is suitable for iterative optimization for the energy management. Some iterative optimization strategies are under study.
KEYWORDS : EV and HV systems, energy control system, energy management, HPV system modeling