Cheng Zeng

Chaotic Vibration and Comfort Analysis of Nonlinear Full-Vehicle Model Excited by Consecutive Speed Control Humps

When vehicles are driven on consecutive speed control humps, the parameters of speed control humps such as height, width, and space and vehicle’s speed are the important factors to affect safety and comfort of passengers. The paper assumes that the excitation function of the consecutive speed control humps is a half-sine wave and a SCHs-speed coupling excitation model called 7-DOF nonlinear full-vehicle model and differential equation are established by introducing the time delay of incentive input and then by using numerical simulation to analyze chaotic vibration in 7-DOF nonlinear full-vehicle model excited by consecutive speed control humps. The numerical simulation results show that chaotic vibration phenomenon possibly appears as vehicles are driven on consecutive speed control humps. Further studies indicate that the influence of nonlinear running state of vehicle on driving comfort becomes manifest as the state changes from chaotic motions to the periodic motion of the high speed and the periodic motion of the low speed, and this phenomenon can be avoided by changing the parameters of consecutive speed control humps. The results can be applied in design of vehicle and road humps pavement.

Nonlinear Fault Separation for Redundancy Process Variables Based on FNN in MKFDA Subspace

Nonlinear faults are difficultly separated for amounts of redundancy process variables in process industry. This paper introduces an improved kernel fisher distinguish analysis method (KFDA). All the original process variables with faults are firstly optimally classified in multi-KFDA (MKFDA) subspace to obtain fisher criterion values. Multikernel is used to consider different distributions for variables. Then each variable is eliminated once from original sets, and new projection is computed with the same MKFDA direction. From this, differences between new Fisher criterion values and the original ones are tested. If it changed obviously, the effect of eliminated variable should be much important on faults called false nearest neighbors (FNN). The same test is applied to the remaining variables in turn. Two nonlinear faults crossed in Tennessee Eastman process are separated with lower observation variables for further study. Results show that the method in the paper can eliminate redundant and irrelevant nonlinear process variables as well as enhancing the accuracy of classification.

Improving the stability of discretization zeros with the Taylor method using a generalization of the fractional-order hold

Abstract Remarkable improvements in the stability properties of discrete system zeros may be achieved by using a new design of the fractional-order hold (FROH) circuit. This paper first analyzes asymptotic behaviors of the limiting zeros, as the sampling period T tends to zero, of the sampled-data models on the basis of the normal form representation for continuous-time systems with a new hold proposed. Further, we also give the approximate expression of limiting zeros of the resulting sampled-data system as power series with respect to a sampling period up to the third order term when the relative degree of the continuous-time system is equal to three, and the corresponding stability of the discretization zeros is discussed for fast sampling rates. Of particular interest are the stability conditions of sampling zeros in the case of a new FROH even though the relative degree of a continuous-time system is greater than two, whereas the conventional FROH fails to do so. An insightful interpretation of the obtained sampled-data model can be made in terms of minimal intersample ripple by design, where multirate sampled systems have a poor intersample behavior. Our results provide a more accurate approximation for asymptotic zeros, and certain known results on asymptotic behavior of limiting zeros are shown to be particular cases of the ideas presented here.

Improvement of the Asymptotic Properties of Zero Dynamics for Sampled-Data Systems in the Case of a Time Delay

It is well known that the existence of unstable zero dynamics is recognized as a major barrier in many control systems, and deeply limits the achievable control performance. When a continuous-time system with relative degree greater than or equal to three is discretized using a zero-order hold (ZOH), at least one of the zero dynamics of the resulting sampled-data model is obviously unstable for sufficiently small sampling periods, irrespective of whether they involve time delay or not. Thus, attention is here focused on continuous-time systems with time delay and relative degree two. This paper analyzes the asymptotic behavior of zero dynamics for the sampled-data models corresponding to the continuous-time systems mentioned above, and further gives an approximate expression of the zero dynamics in the form of a power series expansion up to the third order term of sampling period. Meanwhile, the stability of the zero dynamics is discussed for sufficiently small sampling periods and a new stability condition is also derived. The ideas presented here generalize well-known results from the delay-free control system to time-delay case.

Improving the Asymptotic Properties of Discrete System Zeros in Fractional-Order Hold Case

Remarkable improvements in the asymptotic properties of discrete system zeros may be achieved by properly adjusted fractional-order hold (FROH) circuit. This paper analyzes asymptotic properties of the limiting zeros, as the sampling period tends to zero, of the sampled-data models on the basis of the normal form representation of the continuous-time systems with FROH. Moreover, when the relative degree of the continuous-time system is equal to one or two, an approximate expression of the limiting zeros for the sampled-data system with FROH is also given as power series with respect to a sampling period up to the third-order term. And, further, the corresponding stability conditions of the sampling zeros are discussed for fast sampling rates. The ideas of the paper here provide a more accurate approximation for asymptotic zeros, and certain known achievements on asymptotic behavior of limiting zeros are shown to be particular cases of the results presented.

A sufficient and necessary condition for stabilization of zeros in discrete-time multirate sampled systems

It is well known that the presence of unstable zeros limits the control performance, which can be achieved, and some control schemes cannot be directly applied. This manuscript investigates a sufficient condition for stabilization of zeros in the discrete-time multirate sampled systems. It is shown that the discretization zeros, especially sampling zeros, can be arbitrarily placed inside the unit circle in the case of relative degree being greater than or equal to three and multirate input and hold, such as generalized sampled-data hold function (GSHF), for the linear continuous-time systems when the sampling period T tends to zero. Moreover, the authors further consider the multivariable case, which has a similar asymptotic behavior. Finally, the simulation proves the validity of the method, and we also propose a hold design that places the sampling zeros asymptotically to the origin for fast sampling rates.

Asymptotic behavior of sampling zero dynamics for a 3-DOF tandem-rotor model helicopter

This paper derives an approximate discrete-time model for a nonlinear 3-DOF (degree-of-freedom) tandem-rotor model helicopter in the case of the multirate input and hold, which is accurate to some order in the sampling period. More importantly, the proposed model has more accurate than the classic Euler approximation. We also show how a particular strategy can be used to approximate the system outputs and its derivatives in such a way as to obtain a local truncation errors, between the outputs of the resulting sampled-data model and the true continuous-time system outputs, of order T5, where T is the sampling period. An insight interpretation of the obtained sampled-data model can be made in terms of sampling zero dynamics, and their explicit characterization are also given. Moreover, we show a condition which assures the stability of the sampling zero dynamics for the resulting model helicopter.

Sampled-data models and zero dynamics for nonlinear systems with relative degree two

This paper derives a more accurate sampled-data model than the Yuz and Goodwin type model for nonlinear systems in the case of the relative degree two, and analyzes the sampling zero dynamics of the sampled-data model to show a condition which assures the stability of the sampling zero dynamics of the proposed model. It is a nature extension of Ishitobi et al.s result from a single-input single-output (SISO) nonlinear systems to a multi-input multi-output (MIMO) nonlinear systems.