Selim Solmaz

On Padé Approximations, Quadratic Stability and Discretization of Switched Linear Systems

In this note we consider the stability preserving propertie s of diagonal Pade approximations to the matrix exponential. We show that while diagonal Pade approximations preserve quadratic stability when going from continuous-time to discrete-time, the converse is not true. We discuss the implications of this result for discretizing switched linear systems. We also show that for continuous-time switched systems which are exponentially stable, but not quadratically stable, a Pade approximation may not preserve stability.

Design of a multiple-model switching controller for ABS braking dynamics

The purpose of this study is to design high-performance active braking control and observer algorithms for passenger vehicles equipped with electromechanical brake systems. These algorithms are designed to be adaptive with changing driving and road conditions in a switched multiple-model manner to ensure high performance and robustness. The effectiveness of a set of multiple-model switching lead-lag controllers is evaluated during transitions between different road friction coefficients. Meanwhile, a multiple-model switching observer algorithm is developed to estimate the shape of the tyre braking force curve with respect to the longitudinal slip. Each switched observer predicts signals according to its preset tyre model. The observers are designed based on different Burckhardt tyre models that are parameterized for different road conditions. In our simulations, the value of the friction coefficient is assumed to be unknown and our switching algorithms are observed to estimate successfully the varying friction coefficients by comparing a quadratic cost function of measured signals from the vehicle with signals generated by observers. We demonstrate that our algorithms provide high reliability and fast response, thus ensuring a stopping distance close to the theoretical minimum.

A Novel Method for Indirect Estimation of Tire Pressure

In this paper, a novel algorithm for indirect tire failure indication is described. The estimation method is based on measuring changes in the lateral dynamics behavior resulting from certain types of tire failure modes including excessive deflation or significant thread loss in a combination of tires. Given the fact that both failures will notably affect the lateral dynamics behavior, quantifying these changes constitutes the basis of the estimation method. In achieving this, multiple models and switching method are utilized based on lateral dynamics models of the vehicle that are parametrized to account for the uncertainty in tire pressure levels. The results are demonstrated using representative numerical simulations.

Parametric Analysis and Compensation of Ride Comfort for Electric Drivetrains Utilizing In-Wheel Electric Motors

In this paper we study the effects of increased unsprung mass that result from the use of in-wheel electric motors used in hybrid and/or electric drive trains. For this purpose we reduce the problem to the analysis of the quarter car suspension model to assess how increasing unsprung mass affects the ride comfort. In order to see the change in the ride comfort level according to ISO 2631 the analysis was done in frequency domain using random road profile inputs generated according to ISO 8608. Also the results were assessed using a commercial multi body vehicle simulation software. Finally we suggest empirical solutions regarding modified suspension and tire parameters to compensate the detrimental effects of increased unsprung mass.

Dual stator/rotor brushless DC motors: A review of comprehensive modelling based on parametric approach and coupled circuit model

This paper proposes a dual-rotor brushless direct-current motor design specifically realized for unmanned underwater vehicles. Brushless DC motors are known for their high torque capacity and power density specs which are also suitable for underwater drive trains known as “thrusters”. Proposed brushless DC motor model having double rotor and double stator structure is basically designed by applying typical design procedure including sizing equations followed by detailed parametric analysis approach and coupled circuit model. Design of a dual-rotor brushless DC thruster having foregoing structure utilizes modular concentrated winding, optimized slot-opening and pole/slot ratio, outer and inner diameter and etc. Main output parameters such as rated torque, rated power, rated speed and total loss parameter of each brushless DC motor for different rotor positions are computed and compared. Additionally, a coupled-circuit analysis is employed to show the impact of the proposed design to evaluate rated power and torque capability.

Lateral Stability Control Based on Active Motor Torque Control for Electric and Hybrid Vehicles

This paper describes a method for lateral stability control of electric and hybrid vehicles utilizing multiple electric motors connected to independent wheels of the vehicle. Independent motor torque control based on LQR and PID are used to generate positive drive and negative brake torques for imposing an aligning moment around the yaw axis resulting in the lateral stability functionality. The developed algorithms were implemented and performance tested in Matlab-Simulink environment and the dynamic performance characteristics were reported with numerical simulation results.

A novel method for indirect estimation of tire pressure

In this paper a novel algorithm for indirectly estimating predetermined levels of tire deflation of an automotive vehicle is described. The estimation method is based on measuring varying levels of lateral dynamics behavior due to certain types of tire failures that may include excessive deflation or significant thread loss. Given the fact that both failures will notably affect the lateral vehicle behavior, quantifying these levels of alteration in the lateral dynamical response forms the basis of the estimation method. In achieving this, multiple models and switching method is utilized based on linearized lateral dynamics models of the vehicle that are parametrized to account for the uncertainty in tire pressure levels. The results are demonstrated using representative numerical simulations.