Degree Of Freedom Control Structure Research Articles

Design and comparison of model-based controllers for an automotive air conditioning system in an electric vehicle

The air conditioning system in an electric vehicle has to fulfill multiple tasks, which are ensuring thermal comfort for the passengers and tempering the battery. In this paper four model-based control approaches for the air conditioning system are developed. The approaches are compared regarding their ability to track desired references, reject disturbances and avoid windup effects. Two approaches are feedback controllers, a decentralized proportional-integral control strategy and a centralized linear-quadratic-integral control strategy. The other two approaches combine the feedback controllers with an inversion based feedforward controller in a two degree of freedom control structure. In addition, the four concepts are complemented by the Hanus-Conditioned anti-windup mechanism.Three of the four proposed controllers explicitly consider the couplings of the multiple-input-multiple-output system, which allows for a high-performance control. Additionally, all approaches have the benefit of being based on a physical model of the system to be controlled. The development and identification of this physical model is part of the paper. The physical basis for the controllers ensures a high level of reusability and therewith an efficient controller design process. The proposed control concepts are validated and compared by measurement data from a testbench.

Nonlinear Model Order Reduction for Feedforward Control of an Air Conditioning System in an Electric Vehicle

Air conditioning systems are indispensable in all modern production cars, as they ensure thermal comfort for the passengers. Besides that, extended air conditioning systems allow for additional tasks like tempering the battery in hybrid and electric vehicles. To fulfill these multiple tasks, an advanced control structure has to be applied. Since the components of the air conditioning system are constantly optimized and new structures are developed, an efficient controller design requires a model-based approach to handle the diversity and allow for a fast adaptation to different structures.This paper considers such an approach: For the usage in a two degree of freedom control structure a feedforward controller is derived. This controller is designed as a multiple-input-multiple-output controller with a flatness based approach. To apply the concept on the model of the air conditioning system, a nonlinear model order reduction is performed. The presented reduction method is extended by a frequency scaling on the reduction data and the reduced model is validated with experimental data.

Robust control for electric vehicle powertrains

This paper considers the application of robust control methods (μ- and H∞-synthesis) to the speed and acceleration control problem encountered in electric vehicle powertrains. To this end, we consider a two degree of freedom control structure with a reference model. The underlying powertrain model is derived and combined into the corresponding interconnected system required for μ- and H∞-synthesis. The closed-loop performance of the resulting controllers are compared in a detailed simulation analysis that includes nonlinear effects. It is observed that the μ-controller offers performance advantages in particular for the acceleration control problem, but at the price of a high-order controller.

Real‐time Trajectory Tracking of a Cable‐driven Parallel Robot Using Servo‐constraints

AbstractCable robots are widely applicable for various industrial tasks, where accurate trajectory tracking of the end‐effector is an essential control objective. This is especially challenging for underactuated cable robots since they possess less actuators than degrees of freedom. Trajectory tracking can be achieved by using an inverse model based on servo‐constraints. It is possible to solve the DAE problem in real‐time, which makes an implementation on experimental setups straightforward. Stabilization of the tracking error can be achieved by a feedback controller which augments the feedforward loop in a two degree of freedom control structure. Effectiveness of the described method is shown in experiments on a cable robot test bench. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Two degree of freedom control scheme for unstable processes with small time delay

In this work, a recently reported two degree of freedom control structure namely the Parallel Control Structure (PCS) is modified to achieve improved control performance for unstable processes. New tuning rules are proposed using a direct synthesis approach for unstable first order plus time delay (UFOPTD), unstable second order plus time delay (USOPTD) and integrating and unstable plus time delay (IUPTD) process models. The proposed method has two tuning parameters whose suitable values are recommended after studying their effect on the system performance and robustness. This is an advantage of the present work over the other reported control schemes where the authors provide suitable ranges of the tuning parameters values. Simulation examples show that the present scheme results in improved nominal and perturbed responses as compared to the recently reported methods. Also it is observed that satisfactory performance is achieved when the proposed tuning rules are applied on an isothermal chemical reactor which exhibits multiple steady state solutions.

Disturbance Observer in Robust DC Motor Control

The disturbance observer is a specific method of designing a two degree of freedom control structure to achieve insensitivity to modeling error and disturbance rejection. It has been successfully applied in a variety of motion control applications. In motion control, the major sources of uncertainties are friction, inertia, and external disturbances. These uncertainties should be taken into account by any robust motion controller. In this paper, this element is a PD (proportional-derivative) controller. The disturbance observer proves its advantages through the simulation and experiments. With disturbance observer, better tracking performance can be achieved with less control energy.

CONTROL LOOP PERFORMANCE ASSESSMENT FOR TWO DEGREE OF FREEDOM CONTROLLER: ANALYSIS OF MODEL-PLANT MISMATCH

Controllers are vehicles to implement decisions designed for improved productivity. Performance assessment of controllers is necessary to estimate the health of such controllers so as to maximize their ability to realize optimal decisions/ targets. Traditionally, such performance assessment algorithms have focused largely on the single degree of freedom control structure, and generate performance indices either for the servo or the regulatory case. However, in many applications such as grade transitions or batch processes, it is important to achieve good tracking in the presence of unknown disturbances. A two degree of freedom controller is eminently suited to realize these objectives. This paper therefore extends performance assessment strategies for control loops with single degree of freedom controller, to control loops with two degree of freedom controller (2DOFC) structure. The proposed methodologycalculates two performance indices (viz. for the servo and regulatory case each for set point change and disturbance change) that are based on the minimum variance benchmark. We also examine effect of model plant mismatch on the servo and regulator performance of the control loop system.

A QFT Framework for Antiwindup Control Systems Design

The paper is devoted to the robust stability problem of linear time invariant feedback control systems with actuator saturation, especially in those cases with potentially large parametric uncertainty. The main motivation of the work has been twofold: First, most of the existing robust antiwindup techniques use a conservative plant uncertainty description, and second, previous quantitative feedback theory (QFT) results for control systems with actuator saturation are not suitable to achieve robust stability specifications when the control system is saturated. Traditionally, in the literature, this type of problems has been solved in terms of linear matrix inequalities (LMIs), using less structured uncertainty descriptions as given by the QFT templates. The problem is formulated for single input single output systems in an input-output (I/O) stability sense, and is approached by using a generic three degrees of freedom control structure. In this work, a QFT-based design method is proposed in order to solve the robust stability problem of antiwindup design methods. The main limitation is that the plant has poles in the closed left half plane, and at most, has one integrator. The work investigates robust adaptations of the Zames–Falb stability multipliers result, and it may be generalized to any compensation scheme that admits a decomposition as a feedback interconnection of linear and nonlinear blocks (Lur’e type system), being antiwindup systems as a particular case. In addition, an example will be shown, making explicit the advantages of the proposed method in relation to previous approaches.

Decentralized Control of a Pilot Flotation Column: A 3×3 System

This paper details the application of a decentralized control strategy to a pilot flotation column working with a water-air system. The process is represented by a multivariable system composed of three inputs and three outputs. The selected control variables are the froth depth, air hold-up and bias-rate whereas the corresponding manipulated variables are the set-points of the local flow controllers of tailings, air and wash-water. All controlled variables are estimated using electrical-conductivity based techniques. Results of a new method for estimating bias-rate, based on the volumetric fraction of wash water under the interface, are presented. This method reduces the coupling problem associated to the bias estimation as a difference between feed and tailing water rates. Moreover, the nominal system transfer matrix can be represented by an upper triangular matrix, in such a way that the closed-loop system stability reduces to the stability of the independent control loops. A two degree of freedom control structure was implemented for the froth depth so that in the absence of disturbances the controller acts as a proportional controller whereas in the presence of a disturbance it becomes a PI controller. For gas hold-up and bias-rate, PI controllers were implemented considering the closed-loop time constants being equal to those in the open-loop case. The experimental results show expected closed-loop performances for froth depth and gas hold-up, however, the bias rate control loop was observed to be strongly dependent on the air flow rate, in some cases reaching the saturation point of the controller.

Halftone banding reduction for a class of electrophotographic systems – Part II: Closed-loop control

A new control configuration for laser printing process was proposed, which constructs a feedback controller for regulation of the motor/gear transmission subsystem using direct velocity measurement from the imaging component. Causal connection between banding artifact and transmission errors has been demonstrated previously. Two controller design approaches were suggested for reducing banding artifact. The proposed designs were based on the internal model principle and H ∞ robust control theories, both have two degree of freedom control structure. The controllers were implemented on a monochrome laser printer, for which latent images are formed on a cylindrical photoconductor drum. Experimental results showed significant reduction in the measured velocity error for the photoconductor drum as well as noticeable banding reduction on the printed images.