Control Systems Viewpoint Research Articles

Bi-directional impulse chaos control in crystal growth.

Mono-silicon crystals, free of defects, are essential for the integrated circuit industry. Chaotic swing in the flexible shaft rotating-lifting (FSRL) system of the mono-silicon crystal puller causes harm to the quality of the crystal and must be suppressed in the crystal growth procedure. From the control system viewpoint, the constraints of the FSRL system can be summarized as not having measurable state variables for state feedback control, and only one parameter is available to be manipulated, namely, the rotation speed. From the application side, an additional constraint is that the control should affect the crystallization physical growth process as little as possible. These constraints make the chaos suppression in the FSRL system a challenging task. In this work, the analytical periodic solution of the swing in the FSRL system is derived using perturbation analysis. A bi-directional impulse control method is then proposed for suppressing chaos. This control method does not alter the average rotation speed. It is thus optimum regarding the crystallization process as compared with the single direction impulse control. The effectiveness and the robustness of the proposed chaos control method to parameter uncertainties are validated by the simulations.

Improvement of Small Wind Turbine Control in the Transition Region

Wind energy conversion systems are very challenging from the control system viewpoint. The control difficulties are even more challenging when wind turbines are able to operate at variable speed and variable pitch. The contribution of this work is focused on designing a combined controller that significantly alleviates the wind transient loads in the power tracking and power regulation modes as well as in the transition zone. In a previous work, the authors studied the applicability of different multivariable decoupling methodologies. The methodologies were tested in simulation and verified experimentally in a lab-scale wind turbine. It was demonstrated that multivariable control strategies achieve a good closed-loop response within the transition region, where the interaction level is greater. Nevertheless, although such controllers showed an acceptable performance in the power tracking (region II) and power regulation (region IV) zones, appreciable improvement was possible. To this end, the new proposed methodology employs a multivariable gain-scheduling controller with a static decoupling network for the transition region and monovariable controllers for the power tracking and power regulation regions. To make the transition between regions smoother, a gain scheduling block is incorporated into the multivariable controller. The proposed controller is experimentally compared with a standard switched controller in the lab-scale wind turbine. The experiments carried out suggest that the combination of the proposed multivariable strategy for the transition region to mitigate wind transient loads combined with two monovariable controllers, one dedicated to region II and other to region IV, provide better results than traditional switched control strategies.

Accurate Modeling of the Nonlinear Characteristic of a Voltage Source Inverter for Better Performance in Near Zero Currents

In a sensorless vector control method, at low speeds and self-commissioning for AC motors, it is necessary to model dead time, rise/fall time, parasitic capacitors, and semiconductors’ voltage drop accurately. In this paper, voltage drop in each phase due to the nonlinear behavior of the inverter from the control system's viewpoint is precisely modeled by using two lookup tables. These lookup tables make the proposed model robust against the dc-link voltage and carrier frequency variations in the entire current range. In conventional methods at standstill, the measured voltage in the dc current test contains the nonlinearity of two phases. Therefore, to obtain the nonlinear voltage of each inverter phase, it is assumed that the values of inverter nonlinearity voltage at both high current and low current are equal. This simplification leads to distortion in measured voltage in the low currents. However, in this paper, the voltage drop equation of each phase is solved by numerical method that is realizable in conventional processors. The results obtained in actual voltage measurement show the superiority of the proposed method over traditional methods in the low currents. The proposed method is verified by using a voltage source inverter feeding a 2.2-kW three-phase induction motor.

Micro/nanoscale research: a control systems viewpoint

Micro/nanoscale research: a control systems viewpoint

Controller Design for Mechanical Impedance Reduction

Mechatronic systems that physically interact with humans should guarantee safety, as well as stability and control performance. Mechanical impedance is an effective means to evaluate the safety of such systems. The mechanical impedance represents the magnitude of reaction forces by mechanical system when it is moved. Therefore, low mechanical impedance is one of the requirements of safe mechatronic systems. However, there exists a tradeoff between mechanical impedance, stability, and control performance. In this paper, a methodology to design control algorithms for reduction of the mechanical impedance with guaranteed stability is proposed. For the controller design, the mathematical definition of the mechanical impedance for open- and closed-loop systems is introduced in this paper. Various analyses on the mechanical impedance from the viewpoint of control systems are given. Then, the controllers are designed for systems with/without right-half complex plane poles and zeros such that they effectively lower the magnitude of mechanical impedance with guaranteed stability. The proposed method is verified through case studies including simulations and experiments.

Modeling for control of a kinematic wobble-yoke Stirling engine

In this paper we derive the dynamical model of a four-cylinder double-acting wobble-yoke Stirling engine. In addition to the classical thermodynamics methods that dominate the literature of Stirling mechanisms, we present a control systems viewpoint to analyze the dynamic properties of the engine. We show that the Stirling engine can be viewed as a closed-loop system, in which the pressure variations in the cylinders behave as the feedback control law.

Analysis and suppression of Q-switching instabilities in mode-locked lasers-a control systems approach

We investigate the origin of Q-switching instabilities in a mode-locked laser from a control systems viewpoint. The laser is represented as a linear control system, and we consider active laser stabilization either by gain or by loss control as well as passive stabilization via inverse saturable absorption. Gain control stabilization compensates for low-pass filtering in the gain relaxation branch of the system, while control of intracavity losses directly counteracts the destabilizing effect of the saturable absorber. For both stabilization approaches, design rules are derived for controller gain and bandwidth, and their applicability to different laser systems is investigated. Our discussion is concluded with a control systems analysis of passive laser stabilization via inverse saturable absorption. The control systems representation makes the established methods of control theory available to active and passive laser stabilization.

State space modeling and experimental verification of a single channel, moving load cell structural test

Full-scale aircraft structural fatigue tests are extremely complex from a control systems viewpoint. There are usually a large number of actuators with significant interactions between them. Control is made more difficult because the load cells usually move with the actuators. In order to better understand these tests and improve the control, some modeling of the tests is required. This paper presents a linear state space model of a single channel structural test that can be simply expanded to a multi-channel configuration. The model is verified by comparing the predicted frequency response with measured data for several physical systems. The model predictions are shown to be sufficiently accurate to allow a greater understanding of these systems and predict the relative stability of different systems.

Adaptive Control of Rotary System with Nonlinear Frictions.

This paper is concerned with the design of a Model Reference Adaptive Control System (MRACS) for motion with unknown nonlinear frictions. From the control system viewpoint, the static friction and Coulomb friction are characterized by a nonlinear deadzone element and constant disturbance for the control input signal, respectively. Then, the MRACS for the nonlinear frictions is considered for a nonlinear system which is a cascade combination of an unknown deadzone block or disturbance and a linear dynamic block. In order to verify the validity of the theoretical results, the design method described above is applied to a servo system influenced by friction. Experimental results show the high performance of the constructed MRACS and the effectiveness of the proposed method.

Adaptive Control of Rotary System with Unknown Dead Zone.

This paper is concerned with the design of a Model Reference Adaptive Control System (MRACS) for motion with unknown nonlinear friction. From the control system viewpoint, the static friction is characterized by a nonlinear dead zone element for the control input signal. Thus, the MRACS is considered for a nonlinear system which is a cascade combination of an unknown dead zone block and a linear dynamic block. In order to verify the validity of the theoretical results, the design method described above is applied to a servo system influenced by friction. Experimental results have shown the high control performance of the constructed MRACS and the effectiveness of the proposed method.

A Metasystem Approach to Organizational Decision-Making

The metasystem approach to organizational decision-making presented in this paper is set in a control systems framework. Decision-making is approached from a control systems viewpoint. The concept of metasystem is introduced as a framework for decision-making about decision-making, that is, the structuring of a decision-nuking process and the determination of organizational objectives. The metasystem framework is illustrated by means of examples drawn from a case study.

Control systems model of the spontaneous and light-evoked patterns of the compound action potentials in the eye of Aplysia.

The spontaneous and light-evoked firing patterns of the compound action potentials (CAPs) in the isolated eye of Aplysia are experimentally observed from a control systems viewpoint. The eye, exhibiting an endogenous bursting activity and a marked circadian rhythm in darkness, is a self-excited system and responds to illumination with a controlled electrical activity. It is represented by the nonlinear systems model predicting the firing-rate variation of the CAPs. Construction of the model is based on the eye's biological model reported in the literature, and involves an experimental analysis of the system characteristics using linear approximation and conventional control systems techniques. The model is simulated and found to adequately conform to the observed behavior of the eye under various experimental conditions.