Feedforward Action Research Articles

A formal method for improving the transient behaviour of a non-linear flexible link

This article presents a procedure for improving the transient response of a boundary-controlled non-linear flexible elastic beam through a feed-forward action. It is shown that it is possible to obtain a formal analytic solution of an infinite-dimensional linear system, which approximates the non-linear dynamics, under time-varying boundary conditions in terms of the free vibration modes of the structure, whose calculation is a relatively easy task. The feed-forward action is then obtained by inverting the relationship between input and output variables. A numerical example is presented and some simulation results are discussed.

Robust and Fast Three-Phase PLL Tracking System

This paper presents a simple, robust, and fast synchronization method to detect the phase angle of the positive sequence of a three-phase ac system. The algorithm was derived from a standard phase-locked-loop (PLL) circuit based on the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pq</i> theory, but a feedforward action is implemented to guarantee high dynamic performance in conjunction with a modified feedback action to reduce the phase-angle estimation error to zero. The result is a fast tracking system that improves the start-up stage and rapid input variations. It guarantees accurate phase locking and is robust with respect to ac distortions such as harmonics, subharmonics, and voltage imbalance. The control model for the proposed PLL system was based on the standard <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> PLL structure. A linear analysis was performed to show the benefits of the proposed solution, and recommendations are given for tuning its parameters. The proposed technique was tested and compared with other algorithms by means of simulations. The experimental and simulation results are shown and compared.

Predictive Control with Disturbance Forecasting for Greenhouse Diurnal Temperature Control

AbstractThis work is devoted to analyze the Generalized Predictive Control (GPC) strategy considering measurable disturbances. This well known control architecture is extended using Double Exponential Smoothing (DES) technique to perform future disturbance estimation. The disturbance models are obtained, validated, and embedded within a GPC controller to compensate for future disturbances. The proposed system is compared with a typical GPC without feedforward action, a GPC with feedforward considering constant disturbances in the future, and a GPC with feedforward taking the original real data in the future. The proposed control scheme was tested by simulation of a greenhouse inside temperature control. The obtained results show that the GPC with disturbance forecasting provide improved behavior that standard techniques.

Three degrees of freedom Virtual Reference Feedback Tuning design and its application to wastewater treatment plant control

AbstractIn this paper, a three degrees of freedom (two degrees of freedom plus disturbance feedforward action) controller, tuned with the Virtual Reference Feedback Tuning is presented and applied to a wastewater treatment plant. The chosen framework is the one established in the Benchmark Simulation Model 1. Two loops were applied: control of nitrate concentration at the last anoxic section of the plant by manipulating the internal recycle flow rate using a two-degrees of freedom PI and a cascade plus feedforward approach to control ammonia at the last aeration section by manipulating the setpoint of the dissolved oxygen controller at the last aeration section using ammonia measurements from the influent. The results are very close to other more advanced approaches applied to the plant in the same conditions, therefore showing the usability of model-free approach for wastewater treatment plant control.

Gain-Scheduled Yaw Control for Aircraft Ground Taxiing

Abstracta gain scheduled yaw controller is proposed to control low speed rolling and manoeuvring of an aircraft on ground. This method is based on local linearisation of a nonlinear model and the synthesis of a family of local controllers. A parallel feedforward action is added to achieve the setpoint tracking and let the feedback controller perform the regulation task. Simulation results show attractive and robust performances regard to the adopted control method.

Digital Time-Optimal Phase Shedding in Multiphase Buck Converters

This letter proposes a time-optimal digital controller for the phase shedding (PS) in multiphase buck converters. PS is an established technique to improve the efficiency of multiphase converters at light load by changing the active number of phases depending on the load-current level. In order to minimize the output-voltage deviation and the transient time during PS, a minimum time algorithm is investigated. The proposed technique is insensitive to the power stage parameters, as its operation relies only on a feedforward action, depending on the steady-state duty cycle and the number of phases to be turned on or turned off. The proposed approach is validated through experimental tests on a synchronous buck converter.

Predictor Design for Altitude Control of a Seaweed Harvester

Abstract In this paper, the predictor design, for altitude control of a seaweed harvester, is investigated. The harvesting system consists of a vessel and a suspended harvester device, the altitude of which is controlled by a winch. The control approach of Gallieri and Ringwood (2010), including a feedforward action, which requires a single step disturbance prediction, is investigated further, focusing on the disturbance prediction, for noisy sensors. The prediction is performed using AR and ARMA models, identified online, by using the Recursive Least Squared with Forgetting Factor (RLSFF) algorithm and the Kalman Filter (KF). The dependance between the error spectrum and the quality of the control is shown, and the prediction performances are evaluated, using an FFT-based criterion, oriented to the feedforward application. The control performances are then evaluated, and the results are compared to Gallieri and Ringwood (2010).

Comparing rear wheel steering and rear active differential approaches to vehicle yaw control

A comparison between two different approaches to vehicle stability control is carried out, employing a robust non-parametric technique in the controller design. In particular, an enhanced internal model control strategy, together with a feedforward action and a suitably generated reference map, is employed for the control of a vehicle equipped either with a rear wheel steering (RWS) system or with a rear active differential (RAD) device. The uncertainty arising from the wide range of operating conditions is described by an additive model set employed in the controller design. Extensive steady state and transient tests simulated with an accurate 14 degrees of freedom nonlinear model of the considered vehicle show that both systems are able to improve handling and safety in normal driving conditions. RAD devices can make the vehicle reach higher lateral acceleration values but they achieve only slight stability improvements against oversteer. On the other hand, 4WS systems can greatly improve both vehicle safety and manoeuvrability in all driving situations, making this device an interesting and powerful stability system.

Disturbance and Friction Compensations in Hard Disk Drives Using Neural Networks

In this paper, we show that by using two adaptive neural networks (NNs), each of which is tailored for a specific task, the tracking performance of the hard-disk-drive (HDD) actuator can be significantly improved. The first NN utilizes accelerometer signal to detect external vibrations and compensates for its effect on HDD position via feedforward action. The second NN is designed to compensate for pivot friction. The appealing advantage of the NN compensators is that the design does not involve any information on the plant, sensor, disturbance dynamics, and friction model. The stability of the proposed scheme is analyzed by the Lyapunov criterion. Experimental results show that the tracking performance of the HDDs can be improved significantly with the use of the NN compensators as compared to the case without compensation.

Functional Coupling Between Motor and Sensory Nerves Through Contraction of Sphincters in the Pudendal Area of the Female Cat

The question of whether skin receptors might help in the perception of muscle contraction and body movement has not been settled. The present study gives direct evidence of skin receptor firing in close coincidence with the contraction of the vaginal and anal sphincters. The distal stump of the sectioned motor pudendal nerve was stimulated. Single shocks induced a wavelike increase in the lumen pressure of the distal vagina and the anal canal, as well as constriction of the vaginal introitus and the anus. The constriction pulls on and moves the surrounding skin, which was initially detected visually. In the present experiments, a thin strain gauge that pressed on the skin surface detected its displacement. Single shocks to the motor nerve induced a wave of skin movement with maximal amplitude at 5 mm from the anus and propagated with decrement beyond 35 mm. The peripheral terminals of the sensory pudendal nerve and the posterior femoral nerve supply the skin that moves. Sensory axons from both nerves fired in response to both tactile stimulation and the skin movement produced by the constriction of the orifices (motor-sensory coupling). In cats with all nerves intact, a single shock to the sensory nerves induced reflex waves of skin movement and lumen pressure (sensory-motor coupling). Both couplings provide evidence for a feedforward action that might help to maintain the female posture during mating and to the perception of muscle contraction.

MiR156-Regulated SPL Transcription Factors Define an Endogenous Flowering Pathway in Arabidopsis thaliana

The FT gene integrates several external and endogenous cues controlling flowering, including information on day length. A complex of the mobile FT protein and the bZIP transcription factor FD in turn has a central role in activating genes that execute the switch from vegetative to reproductive development. Here we reveal that microRNA156-targeted SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes not only act downstream of FT/FD, but also define a separate endogenous flowering pathway. High levels of miR156 in young plants prevent precocious flowering. A subsequent day length-independent decline in miR156 abundance provides a permissive environment for flowering and is paralleled by a rise in SPL levels. At the shoot apex, FT/FD and SPLs converge on an overlapping set of targets, with SPLs directly activating flower-promoting MADS box genes, providing a molecular substrate for both the redundant activities and the feed-forward action of the miR156/SPL and FT/FD modules in flowering control.

Mitochondrial Ca 2+ uptake is inhibited by a concerted action of p38 MAPK and protein kinase D

Angiotensin II elicits cytosolic Ca 2+ signal that is transferred into the mitochondria. Previously we found in H295R cells that this signal transfer is enhanced by both the inhibition of p38 MAPK and a novel isoform of PKC [G. Szanda, P. Koncz, A. Rajki, A. Spät, Participation of p38 MAPK and a novel-type protein kinase C in the control of mitochondrial Ca 2+ uptake, Cell Calcium 43 (2008) 250–259]. Now we report that simultaneous activation of these protein kinases (by TNFα and PMA + an inhibitor of the conventional PKC isoforms, respectively) attenuates the transfer of cytosolic Ca 2+ signal, elicited by depolarisation or store-operated Ca 2+ influx, into the mitochondria. The Ca 2+ uptake enhancing effect of the p38 MAPK inhibitor SB202190 is due to the inhibition of p38 MAPK and not to a direct mitochondrial action. Protein kinases reduce mitochondrial [Ca 2+] by inhibiting the uptake mechanism. The threshold of mitochondrial Ca 2+ uptake may depend on the activity of p38 MAPK. The silencing of protein kinase D (PKD) also results in enhanced transfer of Ca 2+ signal from the cytosol into the mitochondria. Our data indicate that Ca 2+ mobilising agonists, through the simultaneous activation of p38 MAPK, a novel PKC isoform and PKD, exert a negative feed-forward action on mitochondrial Ca 2+ uptake, thus reducing the risk of Ca 2+ overload.

A Control Methodology and Characterization of Dynamics for a Photovoltaic (PV) System Interfaced With a Distribution Network

This paper proposes a control strategy for a single-stage, three-phase, photovoltaic (PV) system that is connected to a distribution network. The control is based on an inner current-control loop and an outer DC-link voltage regulator. The current-control mechanism decouples the PV system dynamics from those of the network and the loads. The DC-link voltage-control scheme enables control and maximization of the real power output. Proper feedforward actions are proposed for the current-control loop to make its dynamics independent of those of the rest of the system. Further, a feedforward compensation mechanism is proposed for the DC-link voltage-control loop, to make the PV system dynamics immune to the PV array nonlinear characteristic. This, in turn, permits the design and optimization of the PV system controllers for a wide range of operating conditions. A modal/sensitivity analysis is also conducted on a linearized model of the overall system, to characterize dynamic properties of the system, to evaluate robustness of the controllers, and to identify the nature of interactions between the PV system and the network/loads. The results of the modal analysis confirm that under the proposed control strategy, dynamics of the PV system are decoupled from those of the distribution network and, therefore, the PV system does not destabilize the distribution network. It is also shown that the PV system dynamics are not influenced by those of the network (i.e., the PV system maintains its stability and dynamic properties despite major variations in the line length, line X/R ratio, load type, and load distance from the PV system).

Model predictive control of glucose concentration in type I diabetic patients: An in silico trial

In this paper, the feedback control of glucose concentration in type I diabetic patients using subcutaneous insulin delivery and subcutaneous continuous glucose monitoring is considered. A recently developed in silico model of glucose metabolism is employed to generate virtual patients on which control algorithms can be validated against interindividual variability. An in silico trial consisting of 100 patients is used to assess the performances of a linear output feedback and a nonlinear state-feedback model predictive controller, designed on the basis of the in silico model. More than satisfactory results are obtained in the great majority of virtual patients. The experiments highlight the crucial role of the anticipative feedforward action driven by the meal announcement information. Preliminary results indicate that further improvements may be achieved by means of a nonlinear model predictive control scheme.

An optimal feedforward control design for the set-point following of MIMO processes

In this paper we propose a new methodology for the design of a feedforward action for the improvement of the set-point following performance of feedback controlled square MIMO processes. In particular, by exploiting an analytical decoupling technique, the feedforward signals are determined in order to achieve predefined output transition times, by assuming that the transfer function matrix of the system consists of first order plus dead time transfer functions. An analytical expression of the feedforward signal is derived and this allows to solve easily a multiobjective optimisation problem in order to minimise the transition time of each output subject to constraints of the actuators. Simulation as well as experimental results demonstrate the effectiveness of the method.

A sliding mode predictive control approach to closed-loop glucose control for type 1 diabetes

The development of robust and efficient glucose control algorithms is key to making the artificial pancreas a reality. In this paper a sliding mode predictive control (SMPC) is obtained by combining the design technique of a sliding mode control with a model based predictive control (MPC). The SMPC combines the main advantages of the two control methods: the robust features of SMC and the good performance of MPC, including the handling of constraints on manipulated and controlled variables. Control action is composed by three parts: a predictive one from an optimization problem, a discontinuous one given by the switching term and finally, a feed-forward action given by an insulin bolus that is injected when a meal is ingested. The prediction model is linear and it is represented by a second order model with time delay. In order to test the controller in silico experiments, the Hovorka model has been considered. The proposed control algorithm shows considerable robustness for intra-patient variability, as well as an enhanced ability to handle measurement uncertainties and disturbance rejection, especially focusing on postprandial behaviour.

Antenna Robust Controller Design Using Feedforward Action for Accurate Pointing Onboard a Spacecraft1

A controller for a spacecraft mounted flexible antenna is designed. The antenna/plant has a high order and disturbances from the host spacecraft are transmitted to the antenna and need to be attenuated, while a high degree of pointing accuracy must be achieved. The design concept explored herein entails feedforward control to slew the antenna. Feedback control is then exclusively used to compensate for plant uncertainty and disturbance rejection. A tight feedback control loop is designed to meet performance specifications while minimizing the control gains. It is shown that the integration of feedforward control action and feedback compensation produces better responses than feedback control alone.

Timing feedback-inhibition of the male reproductive hormone axis

Hormonal methods of male contraception have addressed feedback-inhbition of the cascade of hormones that has evolved to regulate sperm production but high concentrations of testosterone (T) in the blood have not worked satisfactorily. We hypothesized that an episodic event, such as degranulation of gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus, could be as well inhibited by episodic interference as by continuously-applied suppression. We used a computational model of hypothalamus-pituitary-gonad axis described by Veldhuis et al. to test the hypothesis that episodic administration of T would inhibit GnRH and/or luteinizing hormone (LH) secretion. A set of stochastic differential equations model feedback as well as feed-forward actions of GnRH, LH and T. The model predicted feedback-inhibition of GnRH pulses in a dose and frequency dependent manner when transdermal patches or injections delivering pulsatile T were applied. Since the published model did not address the effect of chronic GnRH deprivation on the viability of pituitary gonadotrophes, we introduced a function to address this issue. Incorporation of this function in the model allowed the prediction of a “holiday period” in the contraceptive regimen, during which exogenous T would not be needed to protect from conception. Pulsatile T delivered by real-life transdermal delivery system applied as per a parsimonious regimen reduced secretion of LH and T and fertility. The vitality function, proposed to account for survival and proliferation of pituitary gonadotrophes correlated with in vivo observations as extensive apoptosis in the anterior pituitary was observed after application of transdermal T.

Timing feedback-inhibition of the male reproductive hormone axis

AbstractHormonal methods of male contraception have addressed feedback-inhbition of the cascade of hormones that has evolved to regulate sperm production but high concentrations of testosterone (T) in the blood have not worked satisfactorily. We hypothesized that an episodic event, such as degranulation of gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus, could be as well inhibited by episodic interference as by continuously-applied suppression. We used a computational model of hypothalamus-pituitary-gonad axis described by Veldhuis et al. to test the hypothesis that episodic administration of T would inhibit GnRH and/or luteinizing hormone (LH) secretion. A set of stochastic differential equations model feedback as well as feed-forward actions of GnRH, LH and T. The model predicted feedback-inhibition of GnRH pulses in a dose and frequency dependent manner when transdermal patches or injections delivering pulsatile T were applied. Since the published model did not address the effect of chronic GnRH deprivation on the viability of pituitary gonadotrophes, we introduced a function to address this issue. Incorporation of this function in the model allowed the prediction of a “holiday period” in the contraceptive regimen, during which exogenous T would not be needed to protect from conception. Pulsatile T delivered by real-life transdermal delivery system applied as per a parsimonious regimen reduced secretion of LH and T and fertility. The vitality function, proposed to account for survival and proliferation of pituitary gonadotrophes correlated with in vivo observations as extensive apoptosis in the anterior pituitary was observed after application of transdermal T.

Complex Events Initiated by Individual Spikes in the Human Cerebral Cortex

Synaptic interactions between neurons of the human cerebral cortex were not directly studied to date. We recorded the first dataset, to our knowledge, on the synaptic effect of identified human pyramidal cells on various types of postsynaptic neurons and reveal complex events triggered by individual action potentials in the human neocortical network. Brain slices were prepared from nonpathological samples of cortex that had to be removed for the surgical treatment of brain areas beneath association cortices of 58 patients aged 18 to 73 y. Simultaneous triple and quadruple whole-cell patch clamp recordings were performed testing mono- and polysynaptic potentials in target neurons following a single action potential fired by layer 2/3 pyramidal cells, and the temporal structure of events and underlying mechanisms were analyzed. In addition to monosynaptic postsynaptic potentials, individual action potentials in presynaptic pyramidal cells initiated long-lasting (37 ± 17 ms) sequences of events in the network lasting an order of magnitude longer than detected previously in other species. These event series were composed of specifically alternating glutamatergic and GABAergic postsynaptic potentials and required selective spike-to-spike coupling from pyramidal cells to GABAergic interneurons producing concomitant inhibitory as well as excitatory feed-forward action of GABA. Single action potentials of human neurons are sufficient to recruit Hebbian-like neuronal assemblies that are proposed to participate in cognitive processes.