Francis Assadian

A Novel Method for the Parameterization of a Li-Ion Cell Model for EV/HEV Control Applications

This paper presents a Li-ion cell model parameterization technique for hybrid electric and electric vehicle control applications. The proposed method is based on an equivalent electrical circuit (EEC) model of the Li-ion cell and combines the advantages of the two main strategies employed for cell model parameterization, namely, the offline and online procedures. Offline methods are based on the identification of relevant EEC parameter values using a limited set of test data specific to the target cell chemistry. Conversely, online techniques employ adaptive algorithms that update the cell model as it is being used. The novel method presented in this paper employs recurrent offline updates of the EEC parameterization set, and thus, it integrates the advantages of the offline approach, such as flexibility, reduced complexity, and improved run-time performance, with the main benefit of the online counterpart, which is the capacity to adapt the model parameterization to uncharacterized operating conditions. Based on an extensive set of experimental and simulation results obtained from tests specified in the IEC 62660-1 standard, it is shown that the proposed approach offers a significant accuracy improvement over simple offline methods, as well as enhanced runtime speed in comparison with commonly employed online strategies.

Modeling and Analysis of Active Differential Dynamics

Active differentials are used to improve the overall performance of traction control and vehicle dynamics control systems. This paper presents the development of a unified mathematical model of active differential dynamics using the bond graph modeling technique. The study includes active limited slip differential and various common types of torque vectoring differentials. Different levels of model complexity are considered, starting from, a second-order model with lumped input and output inertia toward higher-order models including the gear inertia and half-shaft compliance. The model is used for a theoretical analysis of drivability and time response characteristics of the active differential dynamics. The analysts is illustrated by simulation results.

Quasi-steady-state linearisation of the racing vehicle acceleration envelope: a limited slip differential example

In the motorsport environment, passive limited slip differentials are a well-established means of improving the traction limitation imposed by the open differential. Torque sensing types are highly adjustable, and can alter both the stability and agility of the vehicle in the various cornering phases of a typical manoeuvre. In this paper, an adjustable clutch plate or ‘Salisbury’ differential model is presented, which can significantly alter its torque bias characteristics through adjustments in the drive/coast ramp angle, the number of friction faces and preload. To allow robust evaluation of differential parameter changes on ultimate vehicle performance and handling balance, a unified acceleration or ‘GG’ diagram framework is then described. This builds on traditional GG diagram approaches, by using nonlinear constrained optimisation to define both the vehicle acceleration limits and a ‘feasibility’ region within the performance envelope. By linearising a seven degrees of freedom vehicle model at multiple operating points, eigenvalue and yaw rate response analysis is then used to establish contours of stability and agility throughout the GG envelope. This brings new insights into the way in which handling balance changes below and up to the vehicles acceleration limits.

A methodology to determine drivetrain efficiency based on external environment

In this paper a statistical method for establishing the efficiency of the drivetrain under different real-world usage conditions has been proposed. The method is based on real-world driving data from an electric vehicle (EV) trial conducted in the UK. It was found that the external environment (road-type and traffic) causes distinct operating regions in the drivetrain. This paper makes use of a neural network to predict the road-type and introduces two new variables (start-stop index and congestion index) to establish the external environment. Based on this external environment a new metric called frequency weighted distribution is introduced to evaluate the performance of the drivetrain. This methodology of design based on the driving environment is of importance to newer advanced powertrains such as hybrids and EVs. The end result would be a design which caters to a specific usage profile.

Bond Graph Modeling of Automotive Transmissions and Drivelines

Abstract The paper presents an overview of the bond graph models of advanced automotive transmission and driveline systems. This includes one-mode and two-mode series-parallel hybrid electric vehicle transmissions, a continuous variable transmission, active-limited slip and torque vectoring differentials in 2WD and 4WD configurations, and electromechanical actuator-based wet and dry clutch actuation systems. It is illustrated that the bond graph method can be effectively used to gain valuable insights about the system dynamics structure and behavior.

Optimal control of motorsport differentials

Modern motorsport limited slip differentials (LSD) have evolved to become highly adjustable, allowing the torque bias that they generate to be tuned in the corner entry, apex and corner exit phases of typical on-track manoeuvres. The task of finding the optimal torque bias profile under such varied vehicle conditions is complex. This paper presents a nonlinear optimal control method which is used to find the minimum time optimal torque bias profile through a lane change manoeuvre. The results are compared to traditional open and fully locked differential strategies, in addition to considering related vehicle stability and agility metrics. An investigation into how the optimal torque bias profile changes with reduced track-tyre friction is also included in the analysis. The optimal LSD profile was shown to give a performance gain over its locked differential counterpart in key areas of the manoeuvre where a quick direction change is required. The methodology proposed can be used to find both optimal passive LSD characteristics and as the basis of a semi-active LSD control algorithm.

Design of an optimized charge-blended energy management strategy for a plugin hybrid vehicle

This paper introduces the design of a charge blended energy management control system for use within a plugin hybrid electric vehicle. The approach taken extends the local cost function optimization routine associated with an Equivalent Fuel Consumption Method (EFCM) in which the charge-sustaining penalty factor is calculated online from an integrated PI controller rather than being derived from a pre-calibrated lookup table. The performance of the controller for a hybrid vehicle exercised over a number of different drive-cycles is presented. The powertrain model used to design and evaluate the system is derived from data logged onboard a number of different electric vehicles under real-world driving conditions.

Modelling of electromechanically actuated active differential wet-clutch dynamics

The paper presents a lumped-parameter dynamic model of an electromechanically actuated wet clutch found in an active limited slip differential. The bond graph modelling technique is used to describe the multi-physical clutch system including the clutch actuator dynamics, the axial dynamics with the fluid film squeeze effect, the thermal dynamics, and the torque development dynamics with a multi-functional clutch friction coefficient static characteristic. Different variants of the individual subsystem models are considered, ranging from first-principle models to simplified and numerically more efficient models. The proposed models are parameterized and thoroughly validated on the basis of the experimental data collected by using an active differential and clutch test rig. The modelling results are used for the purpose of analysis of the clutch steady state and transient behaviour under various operating modes.

Optimization of Global Chassis Control Variables

Abstract The paper presents a global chassis control (GCC) optimization approach using a gradient-based optimal control algorithm. The goal is to find optimal actions of various actuators such as active steering and active differential, which ensure satisfying the optimization criterion (e.g. trajectory following error minimization) subject to different equality and inequality constraints on state and control variables. The optimization algorithm is based on an exact gradient method, where the cost function gradient is calculated by using a backpropagation-through-time-like algorithm. The proposed GCC optimization approach is illustrated on an example of double lane change maneuver using rear active steering and/or rear active differential actuators.

The design and development of multivariable controls with the application for energy management of hybrid electric vehicles

In this paper, we overview the importance and design of robust feedback control in challenging application of Hybrid Electric Vehicle (HEV) energy management. The HEV dynamic is highly-coupled two-input two-output with severe interactions between internal combustion engine and electric motor. Moreover, it is subjected to parametric uncertainties (engine lag, rotational moment of inertia and damping), unmodeled dynamic (ignition/combustion delay) and unmeasurable exogenous disturbances (engine torque loss and clutch torque). We demonstrate that a robust multivariable design has great potential to provide guaranteed stability- and performance-robustness for this challenging application. Simulation results also verify the above leading towards reduced calibration cost and time.