Modelling and Simulation of Hybrid Electric Vehicles

Abstract

Inclusion of real physics based dynamics instead of conventional charts and maps, while capturing the transient behavior of the overall powertrain is the primary objective of this research effort. The multi-body model of the longitudinal car is described in detail, including mathematical models of tyres, suspensions, aerodynamic behaviour and continuous variable transmission (CVT). The PMSM and PMSG along with DC/AC, AC/DC are modeled in the d - q frame. A novel frictional torque function, predicting all mechanical and electrical losses except resistance loss, is proposed. The results of the proposed frictional torque function compare well with the results obtained from empirical sources. Average models for AC/DC, DC/AC and DC/DC converters are used to ensure the simplicity and feasibility of the simulation in acceptable time scale. Bidirectional converters fed-back the recaptured mechanical energy during regeneration to the battery. A switching-frequency dependent average model for soft-switching isolated DC/DC converter is used in this research. A generic dynamic Li-ion battery model has been chosen which expresses the electrochemical parameters of the battery directly in terms of electrical parameters of the circuit. A control oriented, fast and simple 0D model of the turbocharged diesel engine, combining mean value model and filling and emptying models has been presented in this work. Inlet manifold and exhaust manifolds are modeled as filling and emptying model, engine cylinder dynamics with mean value model, engine torque as a three dimensional map of indicated torque (Teng = f (ωeng,λ)), engine speed ωeng and air-fuel ratio λ, and flow characteristics of the compressor and turbine are modelled with mean value model. A novel control mechanism is proposed to control the fuel mass flow rate and relative air-fuel ratio. Simulation results of the present engine model are validated against a high-fidelity commercial Ricardo-wave model of the same engine. A novel DC-link control mechanism is proposed to simulate the transient operation of the series HEV powertrain during different modes of operation. The supervisory control is implemented to meet the driver’s demand for the traction power, at the same time avoiding over-discharging of the battery below certain threshold level, and optimizing the drive train efficiency, fuel consumption and emissions. On the basis of thermostat control and power follower, a novel “load follower” supervisory control strategy is proposed in the present work. A PI controller based driver model is developed and performance seems satisfactory while tracking the standard NEDC cycle. Simulation results are validated by energy balance computations and available transient and steady state data points for individual components as well as the overall powertrain. The research has successfully achieved the goal of developing a complete model for a series hybrid powertrain while capturing the transient performance of the all the components involved in the powertrain with module based, control oriented and forward facing modelling approach.