Feedforward Control Design Research Articles

Effects on oscillation mechanism and design of grid‐voltage feedforward in grid‐tied converter under weak grid

Grid-voltage feedforward control is widely used in grid-tied converters. The reported studies show that the grid-voltage feedforward may reduce the system stability margin, and may lead to oscillation problem in renewable power generation system. This study revisits the effect of voltage feedforward control on system stability and especially focuses on low frequency oscillation with impedance-based method. The low frequency oscillation usually happens in industry around 100 Hz and shows frequency coupling characteristics. A converter equivalent impedance which includes the effects of voltage feedforward and also covers the frequency coupling introduced by phase locked loop (PLL) is established. Based on the built impedance, the effect on oscillation mechanism with voltage feedforward and PLL is revealed. The results show that the voltage feedforward could increase the system stability margin and may be employed to improve the system stability. Then how to design an optimal proportional voltage feedforward control is demonstrated. Experimental results verify the theoretical analysis and the design of the proportional grid-voltage feedforward control.

Optimal Controller Design for Virtual Sensing With Independent Noise Source Measurement

In certain applications, when the placement of sensors at the target location is not feasible, a common practice is to obtain the target information indirectly via sensors at other locations. This technique is known as virtual sensing (or soft sensing), and involves various signal processing techniques. Virtual sensing is applied to such systems to estimate the error signal for feedback control. However, issues regarding both stability and performance degradation become significant because the estimation is not precise. In this brief, we propose a virtual sensing control (VSC) method using a feedforward controller to compensate the mismatch between an error sensor and virtual sensor under the feedback control. The results show that when an independent noise source measurement is available, a feedforward controller is more appropriate than estimation as it maintains the stability of the feedback system while achieving a good performance enhancement. For such a VSC system, the design of both feedforward and feedback controllers is coupled. In this brief, we derive an optimal controller design method to maximize the noise reduction capability. We show the advantages of the proposed VSC method by applying it to the implementation of an active noise control system.

Tube-Based Internal Model Control of Differentially Flat Input-Affine SISO Systems under Input Constraints

In this paper an optimal control approach based on a combination of the flatness theory and the internal model control (IMC) concept is designed to keep the controlled state within a predefined tube while respecting input constraints. This contribution uses ideas developed in the design of flatness-based feedforward IMC controllers for setpoint tracking and extends them to ‘tube tracking’. It shows the interesting result that for flat input-affine systems the control task of remaining within a tube while minimizing energy consumption and respecting input constraints can be expressed by a convex quadratic optimization problem. The computational feasibility of the developed control strategy is ensured by a purely analytical solution for the quadratic optimization problem derived based on the Karush-Kuhn-Tucker (KKT) optimality conditions. The control approach is illustrated by a simulation example.

Flatness-Based Feed-Forward Control Design for Solenoid Actuators Considering Eddy Currents

Flatness-based feed-forward control of solenoid actuators is considered. For precise motion planning and accurate steering of conventional solenoids, eddy currents cannot be neglected. The system of ordinary differential equations including eddy currents, that describes the nonlinear dynamics of such actuators, is not differentially flat. Thus, a distributed parameter approach based on a diffusion equation is considered, that enables the parametrization of the eddy current by the armature position and its time derivatives. In order to design the feedforward control, the distributed parameter model of the eddy current subsystem is combined with a typical nonlinear lumped parameter model for the electrical and mechanical subsystems of the solenoid. The control design and its application are illustrated by numerical and practical results for an industrial solenoid actuator.

Towards Automatic Steering of Underactuated Ships

Simple control solutions for steering underactuated ships have been seldom studied in literature. This paper provides a control method for automatic steering of underactuated ships in presence of disturbances and in uncertain environmental conditions. A mathematical model of ship dynamics is developed and validated. Our control method involves introduction of a preparation phase consisting of three algorithms. Waypoints leading to every desired set-point are defined and a continuous Dubins path is generated between these waypoints. A second-order motion profile is assigned to the path to suggest the speed with the best timing for the voyage. The control objective is reformulated from a tracking problem to a regulating problem by changing coordinates of the reference signal. PD-controllers are employed in closed loop to reduce position and heading error. The controller parameters are set in the design phase and do not need additional tuning for different trajectories and ship parameters. Weather information together with the planned motion profile are used in a feedforward controller design to achieve better disturbance rejection and higher accuracy. Performance and robustness of the design are evaluated in simulation by Course-keeping and Course-changing experiments in extreme and uncertain environmental conditions. While the developed control method is simple compared to the methods in literature, it can still achieve quite satisfactory steering performance.

A Nonlinear Feedforward Controller Design Taking Account of Dynamics of Turbocharger and Manifolds for Diesel Engine Air-Path System

Abstract In this study, we propose a design method of a model-based nonlinear feedforward controller for a diesel engine air-path system. First, a physical air-path model of the diesel engine was developed. Then, a feedforward controller was developed based on the inverse characteristics of the developed physical model. To improve the transient responses of the boost pressure and EGR ratio, the response delay of the turbocharger and manifolds dynamics were considered while designing the feedforward controller. The effectiveness of the proposed method was evaluated by conducting experiments using a real diesel engine. The experimental results indicated a good tracking performance for both the boost pressure and EGR ratio.

Beyond Performance/Cost Tradeoffs in Motion Control: A Multirate Feedforward Design With Application to a Dual-Stage Wafer System

Motion systems with multiple control loops often run at a single sampling rate for simplicity of implementation and controller design. The achievable performance in terms of position accuracy is determined by the data acquisition hardware, such as sensors, actuators, and analog-to-digital/digital-to-analog converters, which is typically limited due to economic cost considerations. The aim of this paper is to develop a multirate approach to go beyond this traditional performance/cost tradeoff, i.e., to use different sampling rates in different control loops to optimally use hardware resources. The approach appropriately deals with the inherent time-varying behavior that is introduced by multirate sampling. A multirate feedforward control design framework is presented to optimize the tracking of a dual-stage multirate system. The application of the proposed approach to an industrial dual-stage wafer system demonstrates the advantages of multirate control, both in simulations and experiments.

Design of feedforward and feedback position control for passive bilateral teleoperation with delays

Bilateral teleoperation systems connected to computer networks such as the internet must be able to operate with varying time delays since such systems can easily become unstable. A passivity concept has been used as the framework to solve the stability problem in the bilateral control of teleoperation systems. Passivity and tracking performance are recovered using a control architecture that incorporates time varying gains into the transmission path, feedforward, and feedback position control. The proposed architecture has an inner component that can accommodate any configuration but still remain stable and passive even with varying time delay. The simulation results for a single degree of freedom master/slave system demonstrate the performance of the proposed control architecture.

Adaptive feed-forward controller of piezoelectric actuator for micro/nano-positioning

In this paper, design and implementation of an adaptive feed-forward controller for micro/nano-positioning control of piezoelectric actuator (PEA) is described. Discrete-time Dahl hysteresis-based mathematical model of the PEA is developed and the values of the model parameters are estimated through an autoregressive with exogenous terms (ARX) model identification technique using experimental input–output data. A recursive least-square estimator (RLSE)-based adaptive feed-forward (FF) controller is proposed, which takes into account the parameter uncertainty. The FF controller has also been implemented in a DsPIC30F4011 microcontroller. The established PEA model and the controller are validated by simulation and experimental results including parameter variation.

Control strategy of optimal deployment for spacecraft solar array system with initial state uncertainty

A control strategy combining feedforward control and feedback control is presented for the optimal deployment of a spacecraft solar array system with the initial state uncertainty. A dynamic equation of the spacecraft solar array system is established under the assumption that the initial linear momentum and angular momentum of the system are zero. In the design of feedforward control, the dissipation energy of each revolute joint is selected as the performance index of the system. A Legendre pseudospectral method (LPM) is used to transform the optimal control problem into a nonlinear programming problem. Then, a sequential quadratic programming algorithm is used to solve the nonlinear programming problem and offline generate the optimal reference trajectory of the system. In the design of feedback control, the dynamic equation is linearized along the reference trajectory in the presence of initial state errors. A trajectory tracking problem is converted to a two-point boundary value problem based on Pontryagin’s minimum principle. The LPM is used to discretize the two-point boundary value problem and transform it into a set of linear algebraic equations which can be easily calculated. Then, the closed-loop state feedback control law is designed based on the resulting optimal feedback control and achieves good performance in real time. Numerical simulations demonstrate the feasibility and effectiveness of the proposed control strategy.

Data-based approach for feedback–feedforward controller design using closed-loop plant data

Feedforward control of measurable disturbances is a useful complement to feedback control because feedforward control performs control actions before a disturbance response occurs in a process output. In contrast to the typical model-based design approach, a novel data-based method for designing both the feedback and feedforward controllers is presented in this paper. The controller design directly exploits closed-loop plant data and does not require an identification of process and disturbance models. A feedback proportional–integral–derivative controller and feedforward lead-lag compensator are sequentially designed on the basis of the closed-loop response data for a set-point change and for a disturbance input, respectively. Because the controller design process uses plant data integrals, the proposed method is robust against measurement noise. Moreover, the proposed design method can be applied to improve existing underperforming feedback and feedforward controllers using routine closed-loop operating data. Simulation studies demonstrated that the proposed method outperforms existing methods in designing a feedback–feedforward control system.

Modeling and simulating the thermoelastic deformation of mirrors using transient multilayer models

We present a dynamic model with distributed parameters for the thermoelastic transfer behavior in multilayer structures, which are motivated by optically addressed deformable mirrors (OADMs). These are encountered in adaptive optics and utilized for correcting wavefront disturbances of high-power radiation. Our modeling approach is based on a continuum-mechanic multilayer model which distinguishes between an addressing heat load – the control input – and a boundary disturbance evoked by the high-power primary radiation. Thus, the model without control action can be used for passive mirrors as well. The relevant transient effects are investigated with physically motivated assumptions, the plate-like geometry, and parametric rheological analogue models. Furthermore, an efficient simulation scheme is established using Fourier methods in conjunction with model order reduction. The model’s accuracy and the validity of all assumptions is demonstrated by means of an experimental setup. The parametric model is a first step towards feedback and feedforward control designs and disturbance compensation algorithms for OADMs.

A Generic Function for Automated Modeling and Feedforward Control of Planetary Gear Sets

This paper introduces a generic function for automated modeling and feedforward control of planetary gears (PGs). Given the information on configuration, namely, the internal connection relationship between each PG, location of external torques, location and locking state of each clutch, this function outputs a ready-to-use kinetic model. The derived model can then be converted into numeric form by substituting the symbols in the matrix with real values and used for simulation, analysis or controller design. Since the output of the function is in symbolic form, it provides the theoretically most accurate results. Furthermore, compared to other kinds of automated modeling techniques for PG, the proposed function is: (a) more “straightforward” in a sense that it relies solely on direct matrix formulation and no other methods such as system identification are needed and therefore can be implemented in a single environment such as matlab; (b) more “generic” since it is capable of deriving both full-degrees-of-freedom (DOF) and reduced-DOF models for virtually any configuration regardless of the number, connection, and location of input/output shafts or clutches. By exchanging certain variables in the list of unknowns and knowns, the function can also be used to facilitate the design of feedforward controllers.

Flatness-based feedforward control design and two-degrees-of-freedom tracking control for semilinear plug flow reactors

Flatness-based feedforward control design for semilinear plug flow reactors is considered in combination with an easily tunable PI controller to achieve the tracking of desired output trajectories. The approach is based on a subdivision of the relevant time–space region along the characteristic curves of the underlying partial differential equations and a parameterization of the solution in terms of summable formal power series. An approximation for the solution is retrieved by applying an adequate summation method to the power series. Simulations illustrate the applicability of the approach to achieve finite time transitions between operating points along prescribed transient paths and its robustness with respect to uncertainties in the parameters of the reactor.

Industrial feedforward control technology: a review

In the control field, most of the research papers focus on feedback control, but few of them have discussed about feedforward control. Therefore, a review of the most commonly used feedforward control algorithms in industrial processes is necessary to be carried out. In this paper, in order to benefit researchers and engineers with different academic backgrounds, two most representative kinds of feedforward controller design algorithms and some other typical industrial feedforward control benchmarks are presented together with their characteristics, application domains and informative comments for selection. Moreover, some frequently concerned problems of feedforward control are also discussed. An industrial data driven example is presented to show how feedforward controller works to improve system performance and achieve the maximum economic profits.

PID2018 Benchmark Challenge: learning feedforward control

The design and application of learning feedforward controllers (LFFC) for the one-staged refrigeration cycle model described in the PID2018 Benchmark Challenge is presented, and its effectiveness is evaluated. The control system consists of two components: 1) a preset PID component and 2) a learning feedforward component which is a function approximator that is adapted on the basis of the feedback signal. A B-spline network based LFFC and a low-pass filter based LFFC are designed to track the desired outlet temperature of evaporator secondary flux and the superheating degree of refrigerant at evaporator outlet. Encouraging simulation results are included. Qualitative and quantitative comparison results evaluations show that, with little effort, a high-performance control system can be obtained with this approach. Our initial simple attempt of low-pass filter based LFFC and B-spline network based LFFC give J=0.4902 and J=0.6536 relative to the decentralized PID controller, respectively. Besides, the initial attempt of a combination controller of our optimized PI controller and low-pass filter LFFC gives J=0.6947 relative to the multi-variable PID controller.

Causal IIR Audio Precompensator Filters Subject to Quadratic Constraints

Infinite impulse response (IIR) Wiener precompensator design, with constraints on causality, is here also extended to incorporate general quadratic constraints. A method for finding a linear quadratic optimal, causal discrete-time multiple-input multiple-output filter subject to a set of user defined constraints is proposed and analyzed. A method for designing causal filters subject to constraints on the power gains in a large number of small frequency intervals is also proposed. The resulting set of methods provide constrained stable IIR filters with optimal parameterization. Compared to finite impulse response Wiener filtering, the computational complexity is much lower; and compared to noncausal frequency domain designs, we gain control of the time-domain properties of the compensated system. The design methods are applied to a room compensation audio problem subject to filter power gain constraint(s) and are compared to a corresponding noncausal per-frequency method. The results are presented with audio filtering and sound field control as main motivating applications but the methods extend to other areas of linear feedforward controller design and Wiener filtering.

Real time implementation of socially acceptable collision avoidance of a low speed autonomous shuttle using the elastic band method

This paper presents the real time implementation of socially acceptable collision avoidance using the elastic band method for low speed autonomous shuttles operating in high pedestrian density environments. The modeling and validation of the research autonomous vehicle used in the experimental implementation is presented first, followed by the details of the Hardware-In-the-Loop connected and autonomous vehicle simulator used. The socially acceptable collision avoidance algorithm is formulated using the elastic band method as an online, local path modification algorithm. Parameter space based robust feedback plus feedforward steering controller design is used. Model-in-the-loop, Hardware-In-the-Loop and road testing in a proving ground are used to demonstrate the effectiveness of the real time implementation of the elastic band based socially acceptable collision avoidance method of this paper.

Design of A Novel Feed-Forward Control Strategy for A Non-Minimum Phase System

This paper proposes a new feed-forward control strategy for a plant with non-minimum phase dynamics. A Feed-Forward controller is very essential for controlling plants with time-varying reference signals. However, designing this type of controller is a non-trivial problem in case the plant dynamics is non-minimum-phase. This is because, this controller design involves the concept of inversion of the plant model and inverse of a non-minimum-phase plant model is unstable or non-causal. For this problem, usually an approximate inversion of a plant model is applied. An approach with corrected-approximate-inverse (CAI) method is available for feed forward controller design. After analyzing the results and discussion of this CAI technique, it is seen that although it seems to be working perfectly for small duration of time but its performance is unsatisfactory in case of large span of time. Therefore, in this paper, a new feed-forward control strategy has been designed to erase the above said problem. This method has adopted a simple version of an internal plant-model structure in its time domain. The fixed-structure feed forward controller that is constructed using this method is usually a linear amalgamation of a reference trajectory and its time-derivatives with suitable weighting factors. This control strategy has been verified with appropriate simulation results applied to a studied plant and results are compared with that of the CAI technique.

Model based controller design for the compensation of thermally induced deformations

Modern industries demand the production of smaller and yet more complex parts requiring the machine tool itself to fulfill increasing precision standards. Thermal stability is crucial to satisfy the producer’s and the client’s expectations regarding the product’s quality and reliability. Using high-tech materials with very low coefficients of expansion, integrating water cooling or insulation can improve the thermal stability but is not always possible due to geometric constraints. In this paper, a systematic approach is suggested to compensate the thermally induced deformations by controlling a small number of additional cooling elements. The analytic description of the thermal-mechanical behavior is derived from a Finite Element system that allows the modeling of very complex machine geometries. The Balanced Truncation method is then applied to determine a reduced order model that is used for an optimization based feed-forward controller design. It will be shown that this controller not only significantly reduces the deformations but can also be successfully applied to the original high-order model. As perfect knowledge of both the model and the disturbances can rarely be guaranteed, a feedback controller is finally introduced to improve the compensation of thermally induced deformations.