Showing papers on "Open-loop controller published in 2008"
TL;DR: This work proposes a Lyapunov-based model predictive controller which is designed taking data losses explicitly into account, both in the optimization problem formulation and in the controller implementation.
Abstract: In this work, we focus on model predictive control of nonlinear systems subject to data losses. The motivation for considering this problem is provided by wireless networked control systems and control of nonlinear systems under asynchronous measurement sampling. In order to regulate the state of the system towards an equilibrium point while minimizing a given performance index, we propose a Lyapunov-based model predictive controller which is designed taking data losses explicitly into account, both in the optimization problem formulation and in the controller implementation. The proposed controller allows for an explicit characterization of the stability region and guarantees that this region is an invariant set for the closed-loop system under data losses, if the maximum time in which the loop is open is shorter than a given constant that depends on the parameters of the system and the Lyapunov-based controller that is used to formulate the optimization problem. The theoretical results are demonstrated through a chemical process example.
271 citations
TL;DR: An analog fractional order PIλ controller, using a circuit element with fractional-order impedance, a Fractor (patent pending), was demonstrated in both a simple temperature control application and a more complex motor controller as discussed by the authors.
Abstract: An analog fractional order PIλ controller, using a circuit element with fractional order impedance, a Fractor (patent pending), is demonstrated in both a simple temperature control application and a more complex motor controller. The performance improvement over a standard PI controller was notable in both reduction of overshoot and decreased time to stable temperature, while retaining long term stability. In the motor controller, set point accuracy was considerably improved over conventional control. The modification of the standard controller to a fractional order controller was as simple as replacing the integrator capacitor with a Fractor. Mixing (i.e., hybridization) of digital and analog control was demonstrated.
246 citations
TL;DR: In this paper, a new control strategy for islanded (autonomous) operation of an electronically coupled distributed generation (DG) unit and its local load is presented, which utilizes an internal oscillator for frequency control and a voltage feedback signal to regulate the island voltage.
Abstract: This paper presents a new control strategy for islanded (autonomous) operation of an electronically coupled distributed generation (DG) unit and its local load. The DG unit utilizes a voltage-sourced converter (VSC) as the coupling medium. In a grid-connected mode, based on the conventional dq-current control strategy, the VSC controls real- and reactive-power components of the DG unit. Subsequent to an islanding detection and confirmation, the dq-current controller is disabled and the proposed controller is activated. The proposed controller utilizes (1) an internal oscillator for frequency control and (2) a voltage feedback signal to regulate the island voltage. Despite uncertainty of load parameters, the proposed controller guarantees robust stability and prespecified performance criteria (e.g., fast transient response and zero steady-state error). The performance of the proposed controller, based on time-domain simulation studies in the PSCAD/EMTDC software environment, is also presented.
232 citations
TL;DR: The key element in this work is the employment of an infinite-dimensional "backstepping" transformation, and the resulting complete Lyapunov function, for the infinite dimensional systems consisting of the state of the ODE plant and the delay state, which allows to establish inverse optimality of the modified feedback and its disturbance attenuation properties.
214 citations
TL;DR: In this paper, the authors proposed a proximate time-optimal digital (PTOD) controller, which is a combination of a constant-frequency PWM controller employing a linear PID compensator close to a reference point, and a linear or nonlinear switching surface controller (SSC) away from the reference, together with smooth transitions between the two.
Abstract: This paper introduces an approach to near time-optimal control for synchronous buck dc-dc converters. The proposed proximate time-optimal digital (PTOD) controller is a combination of a constant-frequency pulsewidth modulation (PWM) controller employing a linear PID compensator close to a reference point, and a linear or nonlinear switching surface controller (SSC) away from the reference, together with smooth transitions between the two. A hybrid capacitor current estimator enables switching surface evaluation and eliminates the need for current sensing. The SSC, which is implemented as a small Verilog HDL module, can be easily added to an existing digital PWM controller to construct the PTOD controller. In steady state, the controller operates exactly the same as a standard constant-frequency PWM controller with a linear PID compensator. Simulation and experimental results are shown for a 6.5 V-to-1.3 V, 10A synchronous buck converter.
211 citations
TL;DR: The real-time hardware-in-the-loop (HIL) test results show that with a set of fixed controller design parameters, the TLC robot controller is able to follow a large class of 3-degrees-of-freedom (3DOF) trajectory commands accurately.
174 citations
TL;DR: In this article, a novel control method is presented which utilizes the concept of capacitor charge balance to achieve optimal dynamic response for buck converters undergoing a rapid load change, which is implemented with analog components and is cheaper and more effective than its digital counterparts.
Abstract: A novel control method is presented in this paper which utilizes the concept of capacitor charge balance to achieve optimal dynamic response for buck converters undergoing a rapid load change. The proposed charge balance method is implemented with analog components and is cheaper and more effective than its digital counterparts since complex arithmetic and sampling delay is eliminated. The proposed controller will consistently cause the buck converter to recover from an arbitrary load transient with the smallest possible voltage deviation in the shortest possible settling time. Since the controller is nonlinear during transient conditions, it is not limited by bandwidth/switching frequency. Unlike conventional linear controllers, the dynamic response (voltage deviation, settling time) of the proposed controller can be estimated using a set of equations. This greatly simplifies the design process of the output filter. Simulation and experimental results show the functionality of the controller and demonstrate the superior dynamic response over that of a conventional linear controller.
170 citations
TL;DR: In this article, a linear parametrization of the feed-forward controller in a two-degree-of-freedom control architecture is chosen, which results in a feedforward controller that is applicable to a class of motion profiles as well as in a convex optimization problem, with the objective function being a quadratic function of the tracking error.
Abstract: In this paper, the feedforward controller design problem for high-precision electromechanical servo systems that execute finite time tasks is addressed. The presented procedure combines the selection of the fixed structure of the feedforward controller and the optimization of the controller parameters by iterative trials. A linear parametrization of the feedforward controller in a two-degree-of-freedom control architecture is chosen, which results in a feedforward controller that is applicable to a class of motion profiles as well as in a convex optimization problem, with the objective function being a quadratic function of the tracking error. Optimization by iterative trials avoids the need for detailed knowledge of the plant, achieves the controller parameter values that are optimal with respect to the actual plant, and allows for the adaptation to possible variations that occur in the plant dynamics. Experimental results on a high-precision wafer stage and a desktop printer illustrate the procedure.
162 citations
TL;DR: The input-to-state stability (ISS) property of the overall nonlinear control system is proven and leads to a major contribution of construction of a theoretically guaranteed robust nonlinear controller with DOB.
Abstract: In this brief, a novel robust nonlinear motion controller with disturbance observer (DOB) for positioning control of a nonlinear single-input-single-output (SISO) mechanical system is proposed. The controller is designed in a backstepping manner. First, a proportional-integral (PI) controller is designed to stabilize the position error. Consequently, a novel robust nonlinear velocity controller with DOB is designed to stabilize the velocity error. With the help of nonlinear damping terms, the input-to-state stability (ISS) property of the overall nonlinear control system is proven, which leads to a major contribution of construction of a theoretically guaranteed robust nonlinear controller with DOB. The performance of the proposed controller is verified through application to a magnetic levitation system. Comparative studies with an adaptive robust nonlinear controller are also carried out. It is shown that the proposed novel controller while being simple is superior over the adaptive robust nonlinear controller for the experimental setup under study.
160 citations
TL;DR: A robust fuzzy sliding-mode controller for active suspensions of a nonlinear half-car model and it has been shown that the designed controller does not cause any problem in suspension working limits.
Abstract: In this paper, a robust fuzzy sliding-mode controller for active suspensions of a nonlinear half-car model is introduced. First, a nonchattering sliding-mode control is presented. Then, this control method is combined with a single-input-single-output fuzzy logic controller to improve its performance. The negative value of the ratio between the derivative of error and error is the input and the slope constant of the sliding surface of the nonchattering sliding-mode controller is the output of the fuzzy logic controller. Afterwards, a four-degree-of-freedom nonlinear half-car model, which allows wheel hops and includes a suspension system with nonlinear spring and piecewise linear damper with dry friction, is presented. The designed controllers are applied to this model in order to evaluate their performances. It has been shown that the designed controller does not cause any problem in suspension working limits. The robustness of the proposed controller is also investigated for different vehicle parameters. The results indicate the success of the proposed fuzzy sliding-mode controller.
156 citations
TL;DR: This paper deals with the application of the adaptive control structure for torsional vibration suppression in the drive system with an elastic coupling and the on-line adaptation law for the chosen element of the state covariance matrix of the NEKF is proposed.
Abstract: This paper deals with the application of the adaptive control structure for torsional vibration suppression in the drive system with an elastic coupling The proportional-integral speed controller and gain factors of two additional feedback loops, from the shaft torque and load side speed, are tuned on-line according to the changeable load side inertia This parameter, as well as other mechanical variables of the drive system (load side speed, torsional and load torques), are estimated with the use of the developed nonlinear extended Kalman filter (NEKF) The initial values of the Kalman filter covariance matrices are set using the genetic algorithm Then, to ensure the smallest state and parameter estimation errors, the on-line adaptation law for the chosen element of the state covariance matrix of the NEKF is proposed The described control strategy is tested in an open and a closed-loop control structure The simulation results are confirmed by laboratory experiments
TL;DR: In this article, a new systematic tuning method with a new structure to design a robust PID load frequency controller for multimachine power systems is presented, which is mainly based on a maximum peak resonance specification that is graphically supported by the Nichols chart.
TL;DR: The design and experimental results of a novel output feedback controller for slender-body underwater vehicles derived using model-based design techniques and proved to be asymptotically stable using Lyapunov and cascaded systems theory are presented.
Abstract: This paper presents the design and experimental results of a novel output feedback controller for slender-body underwater vehicles. The controller is derived using model-based design techniques. Two separate control plant models are employed: a 3-degree-of-freedom (DOF) current-induced vessel model accounting for the current loads acting on the vehicle and a 5-DOF model describing the vehicle dynamics. The main design objective behind this strategy is to incorporate the vehicle dynamics when estimating the current influence on the vehicle. Furthermore, the transit model is based on the notion of constant propeller revolution resulting in a partly linearized model, which subsequently leads to perspicuous and implementable controller and observer structures. The controller is derived using the observer backstepping technique, and the closed loop is proved to be asymptotically stable using Lyapunov and cascaded systems theory. The control objective is to track the desired pitch and heading angle generated by the line-of-sight guidance system while keeping constant forward thrust. Experimental results demonstrate successful performance of the proposed output feedback controller implemented on the Minesniper MkII AUV/ROV.
TL;DR: Simulation and experimental results indicate that the proposed neuro-fuzzy controller (NFC) is reliable and effective for the speed control of the PMSM over a wide range of operations of thePMSM drive.
Abstract: This paper introduces a neuro-fuzzy controller (NFC) for the speed control of a PMSM. A four layer neural network (NN) is used to adjust input and output parameters of membership functions in a fuzzy logic controller (FLC). The back propagation learning algorithm is used for training this network. The performance of the proposed controller is verified by both simulations and experiments. The hardware implementation of the controllers is made using a TMS320F240 DSP. The results are compared with the results obtain from a Proportional+Integral (PI) controller. Simulation and experimental results indicate that the proposed NFC is reliable and effective for the speed control of the PMSM over a wide range of operations of the PMSM drive.
Patent•
04 Feb 2008TL;DR: In this article, the authors describe a haptic feedback system that includes a controller, a memory coupled to the controller, an actuator drive circuit coupled with the controller and a controller coupled with a memory.
Abstract: A haptic feedback system that includes a controller, a memory coupled to the controller, an actuator drive circuit coupled to the controller, and an actuator coupled to the actuator drive circuit. The memory stores at least one haptic effect that is executed by the controller in order to create a haptic effect.
TL;DR: A repetitive-based controller for the compensation of 6 lscr plusmn 1 harmonic components is proposed, which is more appropriate for processes that involve the use of six-pulse converters or other converters that mainly produce harmonic components at those frequencies.
Abstract: In this paper, a repetitive-based controller for the compensation of 6 lscr plusmn 1 harmonic components is proposed. This control scheme is more appropriate for processes that involve the use of six-pulse converters or other converters that mainly produce harmonic components at those frequencies. The control scheme is based on the feedback array of two delay lines plus a feedforward path that compensates only the 6 lscr plusmn 1 multiples of the fundamental frequency, thereby reducing the possibility of reinjecting unnecessary distortion into the system. The proposed scheme is, then, plugged into a generic feedback control system where a stability analysis is carried out. In addition, the passivity properties of the proposed scheme are presented, which open the possibility of control design following the passivity-based approach. Experiments that are based on a simple digital implementation are provided to illustrate the merits of our solution. These results include the open-loop responses of the proposed scheme and the responses in a practical example to validate its effectiveness in an application. For this latter result, the proposed scheme has been used in the controller of a 2-kVA shunt active filter to compensate the current harmonic distortion.
TL;DR: An adaptive controller that requires limited model information for stabilization, command following, and disturbance rejection for multi-input, multi-output minimum-phase discrete-time systems is presented and it is proved global asymptotic convergence for command following and disturbance rejected.
Abstract: We present an adaptive controller that requires limited model information for stabilization, command following, and disturbance rejection for mult-input multi-output minimum-phase discrete-time systems. Specifically, the controller requires knowledge of the open-loop system's relative degree as well as a bound on the first nonzero Markov parameter. Notably, the controller does not require knowledge of the command or the disturbance spectrum as long as the command and disturbance signals are generated by a Lyapunov-stable linear system. Thus, the command and disturbance signals are combinations of discrete-time sinusoids and steps. In addition, the Markov-parameter-based adaptive controller uses feedback action only, and thus does not require a direct measurement of the command or disturbance signals. Using a logarithmic Lyapunov function, we prove global asymptotic convergence for command following and disturbance rejection as well as Lyapunov stability of the adaptive system when the open-loop system is asymptotically stable.
TL;DR: In this paper, the voltage and frequency controller of a wind turbine driven isolated asynchronous generator is presented to control the system voltage with variation of consumer loads and the speed of the wind turbine.
Abstract: This paper deals with the voltage and frequency controller of a wind turbine driven isolated asynchronous generator. The proposed voltage and frequency controller consists of an insulated gate bipolar junction transistor based voltage source converter along-with battery energy storage system at its dc link. The proposed controller is having bidirectional active and reactive powers flow capability by which it controls the system voltage and frequency with variation of consumer loads and the speed of the wind turbine. It is also having capability of harmonic elimination and load balancing. The proposed electro-mechanical system along with its controller is modeled and simulated in MATLAB using Simulink and power system block-set toolboxes. Performance of the proposed controller is presented to demonstrate voltage and frequency control of a wind turbine driven isolated asynchronous generator along with harmonic elimination and load balancing.
16 May 2008
TL;DR: In this article, a unified current controller is introduced for a bidirectional dc-dc converter which employs complementary switching between upper and lower switches to avoid the current sensing related issues.
Abstract: In this paper, a unified current controller is introduced for a bidirectional dc-dc converter which employs complementary switching between upper and lower switches The unified current controller is to use one controller for both buck and boost modes Such a controller may be designed with analog implementation that adopts current injection control method, which is difficult to be implemented in high power applications due to parasitic noises The averaged current mode is thus proposed in this paper to avoid the current sensing related issues Additional advantage with the unified digital controller is also found in smooth mode transition between battery charging and discharging modes where conventional analog controller tends to saturate and take a long delay to get out of saturation The unified controller has been designed based on a proposed novel third- order bidirectional charging/discharging model and implemented with a TMS320F2808 based digital controller The complete system has been simulated and verified with a high-power hardware prototype testing
TL;DR: Simulation and experimental results for the steady-state operating condition and transient operating conditions for the system subjected to a reactive current reference step change, a three-phase line to neutral fault, and a step load change are presented to demonstrate the effectiveness of the proposed controller.
Abstract: In this paper, a novel controller with fixed modulation index (MI) and variable dc capacitor voltage reference to minimize voltage and current harmonics is presented for a distribution static synchronous compensator (STATCOM). The STATCOM with the proposed controller consists of a three-phase voltage-sourced inverter and a dc capacitor and is used to provide reactive power compensation and regulate ac system bus voltage with minimum harmonics. A systematic design procedure based on pole-zero cancellation, root locus method, and pole assignment method has been developed to determine proper parameters for the current regulator, the dc voltage controller, and the ac voltage controller of the STATCOM. With the proposed STATCOM controller, harmonic distortions in the inverter output current and voltage can be reduced since the MI is held constant at unity in steady state. In addition, a fast adjustment in the STATCOM output reactive power is achieved to regulate the ac bus voltage through the adjustment of the dc voltage reference during the transient period. Simulation and experimental results for the steady-state operating condition and transient operating conditions for the system subjected to a reactive current reference step change, a three-phase line to neutral fault, and a step load change are presented to demonstrate the effectiveness of the proposed controller.
TL;DR: In this article, a hybrid controller consisting of a parallel connected sliding mode controller (SMC) and a neuro-fuzzy controller (NFC) for the speed control of a permanent magnet synchronous motor (PMSM) drive is presented.
TL;DR: Simulation studies using PSIM program are carried out and the results are compared to the results of the conventional loop gain design method for which MATLAB program is used.
Abstract: Fuzzy logic controllers (FLC's) have the following advantages over the conventional controllers: they are cheaper to develop, they cover a wider range of operating conditions, and they are more readily customizable in natural language terms. A self-organizing fuzzy controller can automatically refine an initial approximate set of fuzzy rules. Application of PI-type fuzzy controller increases the quality factor. In this paper, the voltage raising type-pulse controller is considered. Two types of fuzzy controllers used for the control of boost converter are investigated; the simulation results confirm the above mentioned advantages. In order to prove the dynamic characteristics of the PID fuzzy controller being fast and robust, simulation studies using PSIM program are carried out and compared to the results of the conventional loop gain design method for which MATLAB program is used.
TL;DR: In this paper, an open-loop, finite-time, optimal control problem for a nonlinear distributed parameter system is formulated using extremum seeking, and a controller is proposed to achieve high fusion gain and non-inductive sustainment of the plasma current for steady-state operation.
Abstract: In a magnetic fusion reactor, the achievement of a certain type of plasma current profiles, which are compatible with magnetohydrodynamic stability at high plasma pressure, is key to enable high fusion gain and non-inductive sustainment of the plasma current for steady-state operation. The approach taken toward establishing such plasma current profiles at the DIII-D tokamak is to create the desired profile during the plasma current ramp-up and early flattop phases. The evolution in time of the current profile is related to the evolution of the poloidal flux, which is modeled in normalized cylindrical coordinates using a partial differential equation usually referred to as the magnetic diffusion equation. The control problem is formulated as an open-loop, finite-time, optimal control problem for a nonlinear distributed parameter system, and is approached using extremum seeking. Simulation results, which demonstrate the accuracy of the considered model and the efficiency of the proposed controller, are presented.
TL;DR: In this paper, a static synchronous series compensator (SSSC)-based damping controller is investigated for power system stability improvement by minimizing a timedomain-based objective function, in which the deviation in the oscillatory rotor speed of the generator is involved.
Abstract: Power-system stability improvement by a static synchronous series compensator (SSSC)-based damping controller is thoroughly investigated in this article. The design problem of the proposed controller is formulated as an optimization problem, and the particle swarm optimization technique is employed to search for the optimal controller parameters. By minimizing a time-domain-based objective function, in which the deviation in the oscillatory rotor speed of the generator is involved, stability performance of the system is improved. The performance of the proposed controller is evaluated under different disturbances for both a single-machine infinite-bus power system and a multi-machine power system. Results are presented to show the effectiveness of the proposed controller. It is observed that the proposed SSSC-based controller provides efficient damping to power-system oscillations and greatly improves the system voltage profile under various severe disturbances. Furthermore, the simulation result...
TL;DR: A hybrid controller, consisting of a model-based feedforward controller and a proportional-integral feedback compensator, for a solid-rotor synchronous reluctance motor/generator in a high-speed flywheel-based uninterruptible power supply application is proposed.
Abstract: A hybrid controller, consisting of a model-based feedforward controller and a proportional-integral feedback compensator, for a solid-rotor synchronous reluctance motor/generator in a high-speed flywheel-based uninterruptible power supply application is proposed in this paper. The feedforward controller takes most of the control output of the current regulator based on the machine model, and the PI controllers compensate the possible inaccuracies of the model to improve the performance and robustness of the complete control system. The machine current tracking error caused by parameter inaccuracy in the model-based controller is mathematically analyzed and utilized to dynamically compensate the estimated flux linkage to eliminate the steady-state error in current regulation. Stability analysis is also presented, and it can be seen that the regulation performance and robustness of the system are improved by the proposed hybrid controller. Simulation and experimental results consisting of a flywheel energy storage system validates the performance of the controller.
TL;DR: Experimental results show that the proposed FPID controller-based genetic optimization produces better control performance than the conventional PID controllers, particularly in handling nonlinearities and external disturbances.
Abstract: This paper presents a real-time implementation of a genetic-based hybrid fuzzy-proportional-integral-derivative (PID) controller for industrial motor drives. Both the design of fuzzy-PID (FPID) controller and its integration with the conventional PID in global control system to produce a hybrid design are demonstrated. A genetic optimization technique is used to determine the optimal values of the scaling factors of the output variables of the FPID controller. The objective is to utilize the best attributes of the PID and FPID controllers to provide a controller which will produce better response than either the PID or FPID controller. The principle of the hybrid controller is to use a PID controller, which performs satisfactorily in most cases, while keeping in the background a FPID controller, which is ready to take over the PID controller when severe disturbances occur. The hybrid controller is formulated and implemented in real time, using the speed control of a brushless drive system as a testbed. The design, analysis, and implementation stages are carried out entirely using a dSPACE DS1104 digital-signal-processor-based real-time data acquisition control system and MATLAB/Simulink environment. Experimental results show that the proposed FPID controller-based genetic optimization produces better control performance than the conventional PID controllers, particularly in handling nonlinearities and external disturbances.
TL;DR: A new approach for current control that uses integral-sliding-mode (ISM) controllers to achieve decoupling is proposed, which shows satisfactory results on a 0.25-hp three-phase induction machine.
Abstract: This paper discusses the problems of current decoupling control and controller tuning associated with sensorless vector-controlled induction-motor (IM) drives. In field-oriented control, the d-q synchronous-frame currents should be regulated to have independent dynamics such that the torque production of the IM resembles that of a separately excited dc motor. However, these currents are not naturally decoupled, and decoupling compensators should be used. Current loop tuning is an additional problem, since controller gains obtained by theoretical methods or simulation, quite often, do not work well on the real system. This paper proposes a new approach for current control that uses integral-sliding-mode (ISM) controllers to achieve decoupling. The synchronous-frame control voltages are synthesized as the sum of two controller outputs: a traditional one (PI) that acts on an ideal plant model and an ISM controller. The ISM controller decouples the d-q currents and compensates the parameter variations in the current loops of the machine. Simulations and experimental tests on a 0.25-hp three-phase induction machine show satisfactory results.
TL;DR: A new adaptive neuro controller for trajectory tracking is developed for robot manipulators without velocity measurements, taking into account the actuator constraints, and the computational complexity of the proposed controller is reduced as compared to the multilayered neural network controller.
Abstract: In this paper, a new adaptive neuro controller for trajectory tracking is developed for robot manipulators without velocity measurements, taking into account the actuator constraints. The controller is based on structural knowledge of the dynamics of the robot and measurements of joint positions only. The system uncertainty, which may include payload variation, unknown nonlinearities and torque disturbances is estimated by a Chebyshev neural network (CNN). The adaptive controller represents an amalgamation of a filtering technique to generate pseudo filtered tracking error signals (for the elimination of velocity measurements) and the theory of function approximation using CNN. The proposed controller ensures the local asymptotic stability and the convergence of the position error to zero. The proposed controller is robust not only to structured uncertainty such as payload variation but also to unstructured one such as disturbances. Moreover the computational complexity of the proposed controller is reduced as compared to the multilayered neural network controller. The validity of the control scheme is shown by simulation results of a two-link robot manipulator. Simulation results are also provided to compare the proposed controller with a controller where velocity is estimated by finite difference methods using position measurements only.
TL;DR: In this article, an integrated fuzzy controller is proposed to achieve a synchronous positioning objective for a dual-cylinder electro-hydraulic lifting system with unbalanced loadings, system uncertainties, and disturbances.
11 Jun 2008
TL;DR: In this article, the problem of inverse-optimal re-design of the predictor-based feedback law was studied for LTI finite-dimensional, completely controllable, but possibly open-loop unstable, plants, with arbitrarily long actuator delay.
Abstract: We consider LTI finite-dimensional, completely controllable, but possibly open-loop unstable, plants, with arbitrarily long actuator delay, and the corresponding predictor-based feedback for delay compensation. We study the problem of inverse-optimal re-design of the predictor-based feedback law. We obtain a simple modification of the basic predictor-based controller, which employs a low-pass filter, and has been proposed previously by Mondie and Michiels for achieving robustness to discretization of the integral term in the predictor feedback law. The key element in our work is the employment of an infinite-dimensional "backstepping" transformation, and the resulting complete Lyapunov function, for the infinite dimensional systems consisting of the state of the ODE plant and the delay state. The Lyapunov function allows us to establish inverse optimality of the modified feedback and its disturbance attenuation properties. For the basic predictor feedback, the availability of the Lyapunov function also allows us to prove robustness to small delay mismatch (in both positive and negative directions).