Matlab-based modeling, simulation and design package for Eletric, Hydraulic and Flywheel hybrid powertrains of a city bus

Abstract

In this paper a package for designing, modelling and simulation of three hybrid powertrains are presented. These powertrains are Electric hybrid, Hydraulic hybrid and Flywheel hybrid. The differences among the proposed hybrid powertrains include the energy storage system components, the secondary power converter and also the powertrain configuration. The O457 city bus is considered as the benchmark vehicle. At first, the design process for each hybrid powertrain which is based on the power requirements of the bus in any driving condition is presented. Then, the powertrains modelling using MATLAB/Simulink as a powerful simulating tool is presented. The models are feed-forward and resemble the real world driving conditions. Each model has the blocks for the main components of the corresponding propulsion system. The most important stage in the modeling process is implementing of the components efficiency in each powertrain. Moreover, there is a block in each hybrid powertrain model for the energy management. Finally, the simulation results for comparing the usefulness of the hybrid powertrains are presented. The results indicate that the electric hybrid powertrain has the most effect on reducing the bus fuel consumption. But regarding the fabrication expenses and manufacturing complexity, the hydraulic hybrid powertrain is recommended. KEY WORDS : Series electric hybrid city bus, Parallel flywheel hybrid city bus, Parallel hydraulic hybrid city bus, Powertrain design and modeling NOMENCLATURE P EM : electric motor power (W) P E /G : engine/generator power (W) P Batt : battery pack power (W) P demand : driver's demand power (W) δ : mass factor M v : vehicle mass (kg) t a : accelerating time (s) V : vehicle speed (m/s) V b : vehicle speed corresponding to electric motor's base speed (m/s) V f : final acceleration speed (m/s) g : gravitational acceleration (m/s 2 ) f r : rolling resistance coefficient ρ α : air density (kg/m 3 ) C D : aerodynamic drag coefficient A f : vehicle frontal area (m 2 ) i : grade percentage (%) T : total cycle time (s) η t : efficiency of the mechanical transmission η EM : efficiency of the electric motor V Batt : battery pack voltage (V) I Batt : battery pack amperage (A) t PEM : pure electric mode duration (hr) I : battery output current (A) Q Batt : energy capacity of the battery pack (Ah) η v : volumetric efficiency of the hydraulic P/M η : total efficiency of the hydraulic pump/motor η mh : hydro-mechanical efficiency of the hydraulic P/M qv : hydraulic flow of hydraulic P/M (m3/s) n : rotational speed of hydraulic P/M (rpm) δ p: pressure difference between input and output port of the hydraulic P/M T pump : torque of hydraulic P/M in pumping mode (Nm) T motor : torque of hydraulic P/M in motoring mode (Nm) v g : displacement of hydraulic P/M (cm3/rev) G SP : gear ratio of simple gear p : hydraulic pressure (bars) v : gas Volume in accumulator (m3) R_int : battery internal resistance I_bat : battery current P_bat : battery power *

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