Research on Common Rail (CR) injection systems has helped to increase the performance of Diesel engines in terms of available power and fuel consumption in compliance with the restrictions of noise and pollutant emissions. To accomplish these tasks, the last generation of electro-injectors is being developed to advance and improve structure and operation in achieving an accurate fuel metering. This paper presents a model of an electro-injector for common rail systems that is able to predict steady-state and transient behavior. Good results are obtained by simulation in different working conditions and match experimental data to a good extent.

This paper develops simple formulas directly relating performance specifications to control parameters of fractional-order proportional integral (PI) controllers for position servo systems. With the proposed controller settings, the open-loop frequency response achieves a good phase margin, that remains constant in a wide range around the crossover frequency. Consequently, the tuning results in high stability robustness to gain variations in the loop. Moreover, the fractional order integration also leads to limited overshoot and short settling time. Laboratory experiments confirm simulation results.\"""

This paper focuses on a design method for feedback and feedforward fractional order control of electromechanical systems. The architecture combines a fractional order proportional-integral controller and a set-point filter. First, the open-loop frequency response is shaped to obtain robustness specifications and to approximate an optimal feedback system in the input-output tracking, at least in a specified bandwidth. Secondly, the set-point filter is designed by dynamic inversion to minimize the difference between the ideal synthesized command signal, that provides a smooth monotonic response, and the filter step response. Tests on the position/speed control of DC and permanent magnet synchronous motors show the effectiveness of the methodology in comparison with PI controller tuned by symmetrical optimum and coupled with a smoothing filter.

This paper concerns fuel injection control of compressed natural gas engines. The main operating conditions are considered and for each one a fractional-order PI controller is designed. Then at each sudden change of rail pressure and injection timing, a change of the determined controller gains is scheduled. Switching between controllers is driven by step changes of the reference pressure. Robust stability of the designed closed-loop system is guaranteed by D-decomposition. Detailed simulation verifies both dynamic performance and robustness given by the controllers and stability of the switching.

This paper provides closed-form formulas for coefficients of convergents of some popular continued fraction expansions (CFEs) approximating $s^{nu}$, with $-1<nu<1$, and $(2/T)^{nu}((z-1)/(z+1))^{nu}$. The expressions of the coefficients are given in terms of $nu$ and of the degree $n$ of the polynomials defining the convergents. The formulas greatly reduce the effort for approximating fractional operators and show the equivalence between two well-known CFEs in a given condition.

The realization of fractional-order controllers is based on the approximation of the irrational operators by continuous or discrete transfer functions. However, at high sampling frequencies, discrete z-transfer functions approximations can be very sensitive even to small changes in coefficient values. This technical note proposes a realization of s^nu, in terms of transfer functions in the complex delta-domain, which improves considerably the robustness of the approximation to parameter changes and then to truncation in transfer function coefficients applied for implementation with finite word length.

This note ties the Laguerre continued fraction expansion of the Tustin fractional discrete-time operator to irreducible Jacobi tri-diagonal matrices. The aim is to prove that the Laguerre approximation to the Tustin fractional operator $s^{-nu}$ (or $s^{nu}$) is stable and minimum-phase for any value $0 < nu < 1$ of the fractional order $nu$. It is also shown that zeros and poles of the approximation are interlaced and lie in the unit circle of the complex $z$-plane, keeping a special symmetry on the real axis. The quality of the approximation is analyzed both in the frequency and time domain. Truncation error bounds of the approximants are given.

In this paper an integrated circuit (IC) design of the fractional order proportional-integral-derivative (PID) controller is proposed. The development of the IC device is realized in Cadence environment, using the switched capacitors (SC) technology in order to reduce the area on the silicon wafer and to improve the electrical controllability. In order to obtain transfer functions that describe the fractional order of the differ-integral operator it is necessary to use interpolation methods, in particular, the choice in this work has fallen on the Oustaloup interpolation. This procedure is aimed at implementing a series of pole-zero blocks that approximate the non-integer order. The realized approach is able to guarantee a good approximation of the fractional order PID and simultaneously propose a detailed circuit analysis of the influence of the non-idealities, in particular the phenomenon of warping. This takes into account the distortion introduced by the s-domain to the z-domain transition, acting on the positions of poles and zeros, especially those at a higher frequency. Time and frequency domain result tests confirm the feasibility and reliability of the SC implementation.

A rational approximation is the preliminary step of all the indirect methods for implementing digital fractional differintegrators s^nu, with nu in R, 0 < |nu| < 1, and where s in C. This paper employs the convergents of two Thiele’s continued fractions as rational approximations of s^nu. In a second step, it uses known s-to-z transformation rules to obtain a rational, stable, and minimum-phase z-transfer function,with zeros interlacing poles. The paper concludes with a comparative analysis of the quality of the proposed approximations in dependence of the used s-to-z transformations and of the sampling period.

Variable-Bit-Rate (VBR) video transmission over UMTS networks is assuming an ever growing importance, then scheduling VBR data over wireless channels attracts great interest today. This paper proposes an on-line PI control algorithm for easily and suitably scheduling interactive multimedia transmission of VBR video streams. It dynamically adapts the transmitted bit rate to the user’s actions that can suddenly and highly modify the client buffer level. The Real-time Transport Control Protocol (RTCP) packets periodically feed back the buffer level to the server for keeping the free buffer space at 50% of its capacity, so as to prevent both buffer overflow and underflow. Numerical results of different simulated scenarios show the effectiveness of the proposed controller in comparison with two well-established algorithms, enhanced with RTCP information.