Virtual Reference Feedback Tuning Method Research Articles

Fractional data-driven control for a rotary flexible joint system

As one of the most promising topics in complex control processes, data-driven techniques have been widely used in numerous industrial sectors and have developed over the past two decades. In addition, the fractional-order controller has become more attractive in applied studies. In this article, a fractional integral control is implemented for a rotary flexible joint system. Moreover, an adjusted virtual reference feedback tuning (VRFT) technique is used to tune the fractional-order integrator. In this method, fractional integral control is designed based on state feedback control. Then, VRFT is adjusted and applied to the fractional integral controller. The effectiveness of the proposed adjusted VRFT method is discussed and presented through simulation and experimental results. The tracking performance of the rotary arm and the minimization of the vibration tip is evaluated based on the proposed method. In this article, the comparison of our proposed VRFT fractional scheme is made with the classical state feedback as well as a recently developed state feedback-based fractional order integral (SF-FOI) controller. The current investigations determine the performance improvement of our proposed scheme of comparable structure to the recent SF-FOI, with the introduction of the VRFT to the SF-FOI scheme.

Virtual Reference Feedback Tuning Applied to DC–DC Converters

This article presents the application of a data-driven control design to the output voltage regulation of dc–dc converters. Using only data collected on the plant, a proportional-integral-derivative (PID) controller is designed in order to achieve a desired closed-loop response, without deriving a mathematical model for the plant. Since an inverse response is typical on voltage signals of different dc–dc converters, the virtual reference feedback tuning (VRFT) method with flexible criterion is applied to estimate the controller gains, so the limitation due to the nonminimum phase zero, if it exists, is taken into account by the algorithm. We present appropriate choices for data collection, controller structure, and reference model definition in order to safely apply the VRFT method to design a controller for dc–dc converters. A practical application on a boost converter shows the effectiveness of the proposed method.

Hydrogen value chain and fuel cells within hybrid renewable energy systems: Advanced operation and control strategies

While macroscopic modelling and dynamic analyses are topics approached by many to improve the efficiency of hybrid energy systems, the optimization and control of operational strategies need to be studied to allow practicality of such configurations in an industrial setting. Simple implementation and reliable operability of any critical sub-system component of a hybrid energy module are critical requirements for the development of their control algorithms. In this paper, a state-of-the-art hybrid renewable energy system consist of different sub-systems is presented with resolved economically optimal dispatch strategies. The local control of one of its key exemplary sub-system, a Solid Oxide Fuel Cell (SOFC), is realized via two methods i.e. a model-based approach of shrinking-horizon Model Predictive Control (MPC) with constraints and a data-driven approach using Virtual Reference Feedback Tuning (VRFT) to identify controller parameters. Fixed current load and fixed conversion efficiency operations are assessed respectively for 1-h and 24-h spans. For both simulation cases, results show that both control methods provide robust power tracking performance within constrained boundaries with marginal to no overshoot and the VRFT method achieving stability at least 10 times faster than the MPC method. While the two juxtaposed methods are diametrically different, they are both technically viable and efficient under industrial power loads. The main contribution of this work is to demonstrate the feasibility of the hybrid energy system by providing the practitioners with a broad range of local control options, depending on operational realities and constraints.

Virtual disturbance feedback tuning

This paper presents a data-driven control method formulated for the disturbance rejection problem. Inspired on the Virtual Reference Feedback Tuning method, which is based on a tracking reference model, the proposed methodology, entitled Virtual Disturbance Feedback Tuning, is based on a disturbance model. Using only input/output data collected on the process (no process model) and a linearly parameterized controller, the optimal controller is obtained through least squares, resulting in a closed loop system as close as possible to the disturbance model. Experimental results show the efficiency of the proposed methodology.

Coordinated control design for a PEMFC power system using adaptive VRFT method

For a proton exchange membrane fuel cell (PEMFC) power system containing a methanol reformer and a DC–DC converter, it is necessary to coordinate the subsystem controllers to achieve effective power tracking control and prevent constraint violations. This study focuses on the controller design of coordinating control scheme for a PEMFC power system to maintain stable fuel utilization ratio and meet the load demand simultaneously. Because the system exhibits considerable nonlinear behavior, a process model is difficult to identify and is prone to modeling errors. Therefore, this study employs the virtual reference feedback tuning (VRFT) method to design the controllers directly using the process input–output data. To address the process nonlinearity, an improved adaptive VRFT method is developed and applied to the adaptive PID controllers design for a cascade control system. Furthermore, the design parameter of the fuel cell current controller is adaptively tuned according to the deviation of fuel utilization ratio, so that the coordinating control is realized by keeping the dynamics of the current loop consistent with that of the fuel flow loop. Simulation results show that this coordinated control design enables the PEMFC power system to track the load power demand effectively while maintaining the fuel utilization ratio constant.

Research on Nonlinear System Tuning Based on Virtual Reference Feedback

To avoid the complex modeling process of the system object and design the controllers for nonlinear systems fast and effectively, the design of the feedback controller of the nonlinear system draws lessons from the thinking of the virtual reference feedback tuning method. On this basis, in order to improve the system stability and eliminate the uncertain disturbance, adding a linear controller in the feedback loop can improve the tracking performance of the system, and the design is converted into the parameter identification of the nonlinear function under the expansion equation of a basis function. The simulation has verified the effectiveness of the proposed algorithm.

Tuning Nonlinear Controllers with the Virtual Reference Approach

Virtual Reference Feedback Tuning (VRFT) is a well established method for data-driven tuning of linear controllers. In VRFT the design is performed in “one-shot”, that is, with only one batch of input-output data, without the need of iterative data collection procedures. Its core concept consists in treating input-output data collected from the plant to be controlled as if they had been obtained from a virtual experiment , in which a particular reference signal - the virtual reference - would have been applied to the closed-loop system. A key feature of the VRFT method is that it greatly simplifies the design procedure with respect to standard model reference design: for linear and linearly parametrized controllers, it results in convexification of the design, so that its solution can be found by a single least squares method. In this paper this paradigm is applied to the tuning of nonlinear controllers. We propose specific design procedures for two classes of nonlinear plants: rational plants and plants of the Wiener type. Statistical properties of the controllers thus designed in noisy environments are also illustrated.

Virtual Reference Feedback Tuning for non-minimum phase plants

Model reference control design methods fail when the plant has one or more non-minimum phase zeros that are not included in the reference model, leading possibly to an unstable closed loop. This is a very serious problem for data-based control design methods, where the plant is typically unknown. In this paper, we extend the Virtual Reference Feedback Tuning method to non-minimum phase plants. This extension is based on the idea proposed in Lecchini and Gevers (2002) for Iterative Feedback Tuning. We present a simple two-step procedure that can cope with the situation where the unknown plant may or may not have non-minimum phase zeros.

AN APPLICATION OF THE VIRTUAL REFERENCE FEEDBACK TUNING METHOD TO A MULTIVARIABLE PROCESS CONTROL

This paper provides an application of the virtual reference feedback tuning (VRFT) method to a process control. The VRFT method is a direct method which determines parameters of a feedback controller using a set of input and output data of a plant. Originally, the VRFT method is presented for designing a single-input single-output control system. In this paper, the VRFT method is applied for a design of a multi-input multi-output control system. Experimental results show availability of the VRFT method.

Virtual reference feedback tuning for two degree of freedom controllers

AbstractThe virtual reference feedback tuning (VRFT) is a data‐based method for the design of feedback controllers. In the original formulation, the VRFT method gives a solution to the degree of freedom model‐reference control problem in which the objective is to shape the input–output transfer function of the control system. In this paper, the extension of the method to the design of 2 d.o.f. controllers is presented and discussed. Copyright © 2002 John Wiley & Sons, Ltd.