Feedforward Control Loop Research Articles

Design of a linear motor-based shaker rig for testing driver's perceived ride comfort

In autonomous vehicles the driver will become a passenger. By ensuring a high level of ride comfort through active suspensions, the driver's ability to perform various tasks such as reading, drawing and texting can be enhanced. A high-performance shaker rig can conveniently be used to test the ride comfort improvement by means of various active suspensions under laboratory conditions. The paper deals with the design of such a rig, which employs a linear electric servomotor to impose accurately controlled vertical vibrations of driver seat. The reference time profiles of seat acceleration, velocity and displacement are generated off-line by using a half-car vehicle model and LQR control with a road preview option. The selection of linear motor comes from assessment of three characteristic shaker rig drive designs (hydraulic and two electric ones). To ensure high-precision seat motion, the proposed shaker control system includes: acceleration feedforward and feedback control loops, a state controller-like compensator of accelerometer offset to prevent drift of seat position and velocity, and feedforward compensation of linear motor cogging force mode. The designed shaker rig application is demonstrated through a case study related to ride comfort evaluation of various active suspension configurations and a drawing task. The drawing task results are employed to determine the root-mean-square vertical seat acceleration threshold, below which the active suspension drawing task performance remains similar to that obtained under standstill conditions.

ExoNet Database: Wearable Camera Images of Human Locomotion Environments.

ExoNet Database: Wearable Camera Images of Human Locomotion Environments.

Towards better understanding of the influence of process parameters in roll compaction/dry granulation on throughput, ribbon microhardness and granule failure load

A key quality attribute for solid oral dosage forms is their hardness and ability to withstand breaking or grinding. If the product is to be manufactured continuously, it can be of interest to monitor the hardness of the material at different stages of manufacturing. Using the controlled process parameters of roll compaction/dry granulation specific compaction force, roll speed and gap width, hardness of the resulting ribbons and granules can be predicted. For the first time, in this study two yield variables (corrected torque of the granulation unit and throughput of material) are used to predict the granules failure load. The increase in granule hardness was monitored in-line when the specific compaction force was increased during the compaction process. This opens the way for in-line control of material hardness, and its use for feedback and feedforward control loops for future continuous manufacturing processes.

Fault-Tolerant Control of Multirotor UAVs by Control Variable Elimination

This article presents to develop a fault-tolerant control (FTC) to cope with defective thrust systems in multirotor unmanned aerial vehicles (UAV). Faults can occur for a number of reasons in flight, including defective motor performance and damaged propellers. The faults deform both the thrust and torque outputs that could result in the UAV crashing and causing secondary accidents. The FTC method in the article is developed to reconfigure thrust systems using the optimal control when significant degrees of failure occur in a number of defective motors. Orientation control could be abandoned to maintain the controllability of altitude when the control output loss cannot be compensated for because of motor saturation. Specifically, yaw motion control is sacrificed, resulting in a rapid rotation and divergence of position control. The divergence can be resolved by a feed forward control loop on the roll and pitch angles. Both simulations and experiments are implemented to demonstrate the performance of the FTC. The results indicate that the proposed FTC can be implemented to minimize accidents from failures of main thrust systems.

Photovoltaic system operation as DSTATCOM for power quality improvement employing active current control

This paper presents photovoltaic (PV) system control as distributed static compensator (DSTATCOM), termed as PV-DSTATCOM, operated with active current control (ACC) and feed-forward control loop (FFCL). Besides active power injection into the utility grid, the proposed PV system autonomously transforms into a DSTATCOM to provide various ancillary services including source current harmonic suppression, load reactive current compensation, zero sequences component mitigation, and power factor correction. Since PV-DSTATCOM operates with ACC, it precisely extracts the fundamental in-phase and quadrature components of current. It introduces high-gain at the third-order harmonic and thereby alleviates stationary errors in the current control loop of PV inverter. The proposed ACC+FFCL structure is computationally efficient and unconditionally stable. Practically, FFCL addresses the challenges emerged due to nonlinearity introduced by the PV unit and ensure a rapid power balance between the PV unit and electric grid. Further, a simplified perturb and observe based maximum power point tracker has been employed to evacuate the maximum power from the PV array. The proficiency of the developed ACC+FFCL structure is investigated through a comprehensive set of transient studies using MATLAB/Simulink software. Finally, a laboratory setup has been developed using the dSPACE-1104 platform and experimental results are recorded with detailed comparative evaluation.

Intelligent coordinated control for improved voltage and frequency regulation with smooth switchover operation in LV microgrid

Abstract During demand changes and incidence of grid faults, the microgrid system is subjected to an imbalance between the generation and demand. The maintenance of power balance under such dynamic conditions is a major concern for the proper functioning of the microgrid network. During those dynamic periods, achieving voltage and frequency regulation, in particular, during islanded/standalone mode of operation is a challenging task. For reliable operation, in addition to power balance, voltage and frequency regulation, reduced switchover transients and fast switchover operations are necessary. Conventional coordinated controllers comprising of droop, voltage and current control loops, aim at achieving stability of the microgrid network but fails to ensure a quick and smooth response. This work proposes an Adaptive Neuro-Fuzzy Inference System based intelligent coordinated control strategy by combining control techniques namely, inverse droop control, virtual impedance control and current control. The proposed coordinated control scheme provides improved voltage and frequency regulation, reduced switching transients and quick adaptation of the system during demand changes and fault events. The proposed system uses an inverse droop control technique to achieve power decoupling. Additionally, a virtual impedance-based voltage control loop is implemented which ensures voltage regulation of the microgrid and a feed-forward current control loop is developed to minimize the transients during load switching and switchover operations. The reverse droop based PLL strategy is implemented for grid synchronization and smooth switchover operations. The proposed system is simulated in a 20-kVA grid-tied microgrid system in MATLAB/SIMULINK R2018b and tested in real-time of 5-kVA grid-tied solar PV system which demonstrated that the proposed approach is effective under varying irradiance, changing demand conditions and switchover operations. The experimental results prove that the proposed scheme is performing better under different system conditions with fast switching response when compared with other control algorithms.

Improved Position Control for an EGR Valve System with Low Control Frequency

An exhaust gas recirculation (EGR) valve position control system requires fast response without overshoot, but the low control frequency limits control bandwidth and results in poor position response. A novel EGR valve position control scheme is proposed to improve the position response at low control frequency. This is based on the feedforward controller, but the feedforward control loop is implemented without the position pattern generator or derivative. The proposed method estimates the acceleration command through the relationship between the position controller output, the speed command and the speed limiter, and compensates the cascaded proportional-proportional integral (P-PI) controller. In this method, many operations are not required and noise due to derivative is not generated. This method can improve the position response without much computation and derivative noise at the low control frequency. Experimental results are presented to verify the feasibility of the proposed position control algorithm.

Development and Test of a Fringe-Imaging Direct-Detection Doppler Wind Lidar for Aeronautics

DLR currently investigates the use of Doppler wind lidar as sensor within feedforward gust alleviation control loops on fast-flying fixed-wing aircraft. Such a scheme imposes strong requirements on the lidar system such as sub-m/s precision, high rate, high spatial resolution, close measurement ranges and sensitivity to mixed and pure molecular backscatter. We report on the development of a novel direct-detection Doppler wind lidar (DD-DWL) within these requirements. This DD-DWL is based on fringe-imaging of the Doppler-shifted backscatter of UV laser pulses in a field-widened Michelson interferometer using a fast linear photodetector. A prototype for airborne operation has been ground-tested in early 2018 against a commercial coherent DWL, demonstrating its ability of measuring close-range wind speeds with a precision of 0.5 m/s, independent of the actual wind speed.

How and where to use super-capacitors effectively, an integration of review of past and new characterization works on super-capacitors

Abstract The Electric double-layer capacitor (EDLC) or super-capacitors are becoming increasingly popular for their high specific power and for integrating that feature with batteries, which have a high specific energy. Due to the above reason, we have attempted to understand how to use super-capacitors and characterized them, so that both battery and super-capacitors can be used together, or for low power green energy applications, like various electronics gadgets, how to use only super-capacitors. In this paper, we described the known properties of a super-capacitor relative to a conventional lithium-ion battery. The structural design of the Super-capacitors and also various engineering-based applications, related to consumer electronics, transportation etc. are also described, as a review, in this paper. As we all know, that Super-capacitor's voltage would decay over time as we draw power from it, therefore maintaining the output voltage constant for any DC-DC converter without any battery is difficult. Thus, in this paper we have shown, how we have developed a DC-DC converter circuit, without any battery, which has both feed-back and feed forward control loop, in order to maintain constant output voltage. We also have developed a mathematical equation related to super-capacitor to show the requirement for having a feed-back loop can be eliminated while using super-capacitors which have very low Equivalent Series Resistance (ESR). We have also found that for some super-capacitors one cannot pump infinite current to charge a super-capacitor because the effective parallel resistance reduces as one try to pump large current and therefore charging these capacitors to a given desire voltage may not be possible. Therefore, in order to enhance the efficiency and to reduce the charging time of super-capacitor, we proposed and developed an algorithm having gamma function-based charging methodology for super-capacitor.

A Fully Synthesizable Ultra-${N}$ Audio Frequency Multiplier for HDMI Applications

This brief develops a highly programmable and fully synthesizable large-N frequency multiplier. It is based on Time-Average-Frequency Direct Period Synthesis (TAF-DPS) and its purpose is to generate audio frequencies in HDMI (high definition multimedia interface) applications in which frequency multiplication ratio is extremely large. The proposed multiplier is a full digital feed-forward frequency control loop. The output frequency is produced by performing a fractional frequency division of the oscillator clock with TAF-DPS. The source of electrical oscillation in the TAF-DPS is a free-running inverter ring that consists of inverters. The novel structure is implemented in a TSMC 0.18 μm 1P6M CMOS process. The implementation is fully digital HDL coding → simulation → synthesis → place & route without any need for analog simulation. The hardware cost is equivalent to 3150 two-input NAND gates. The proposed structure can achieve fast frequency switching within two input reference clock cycles. The multiplication ratio is evaluated experimentally to be as high as 106 with an input signal of 50 Hz; this is the largest ratio and lowest input frequency to be reported to the best of our knowledge. Besides generating an audio clock for HDMI applications, this frequency multiplier is very suitable for frequency measurements and system-on-a-chip applications.

Dynamical Model Based Contouring Error Position-Loop Feedforward Control for Multiaxis Motion Systems

Contouring motion control plays an important role in modern precision multiaxis motion systems. In order to enhance the coordination between each axis and promote contouring performance, many research works have been conducted that mainly focus on contouring error online estimation and control. Essentially, most of existing control strategies based on emerged contouring error belong to feedback control, which cannot achieve perfect performance due to inevitable delay or lag. To fundamentally tackle the above problem, a novel position-loop feedforward contouring control method is proposed in this paper. Specifically, according to the linear model of each axis and the kinematics characteristics of reference contour, a dynamical model of contouring error in multiaxis systems is firstly developed, which can explain the essential causes of contouring error quantificationally. Then, based on the proposed contouring error model, a position loop feedforward control strategy can be designed for contouring following tasks. The effectiveness of the proposed method is tested on a three-axis computerized numerical control systems. Various experimental results consistently demonstrate that the contouring error model can accurately predict actual contouring error to some degree. Compared with the conventional model-based feedforward approach, the proposed strategy can not only point out the essential causes of contouring error directly, but also achieve better contouring performance.

The engineering principles of combining a transcriptional incoherent feedforward loop with negative feedback

BackgroundRegulation of gene expression is of paramount importance in all living systems. In the past two decades, it has been discovered that certain motifs, such as the feedforward motif, are overrepresented in gene regulatory circuits. Feedforward loops are also ubiquitous in process control engineering, and are nearly always structured so that one branch has the opposite effect of the other, which is a structure known as an “incoherent” feedforward loop in biology. In engineered systems, feedforward control loops are subject to several engineering constraints, including that (1) they are finely-tuned so that the system returns to the original steady state after a disturbance occurs (perfect adaptation), (2) they are typically only implemented in the combination with negative feedback, and (3) they can greatly improve the stability and dynamical characteristics of the conjoined negative feedback loop. On the other hand, in biology, incoherent feedforward loops can serve many purposes, one of which may be perfect adaptation. It is an open question as to whether those that achieve perfect adaptation are subject to the above engineering principles.ResultsWe analyzed an incoherent feedforward gene regulatory motif from the standpoint of the above engineering principles. In particular, we showed that an incoherent feedforward loop Type 1 (I1-FFL), from within a gene regulatory circuit, can be finely-tuned for perfect adaptation after a stimulus, and that the robustness of this behavior is increased by the presence of moderate negative feedback. In addition, we analyzed the advantages of adding a feedforward loop to a system that already operated under negative feedback, and found that the dynamical properties of the combined feedforward/feedback system were superior.ConclusionsOur analysis shows that many of the engineering principles used in engineering design of feedforward control are also applicable to feedforward loops in biological systems. We speculate that principles found in other domains of engineering may also be applicable to analogous structures in biology.

Comparative analysis of MPPT algorithms bio‐inspired by grey wolves employing a feed‐forward control loop in a three‐phase grid‐connected photovoltaic system

It is well-known that performance of photovoltaic (PV) systems can be severely deteriorated when PV arrays are subjected to partial shading conditions, once the traditional techniques used for maximum power point tracking (MPPT) could not operate in the global maximum power point (GMPP). Thus, to overcome this problem and achieve the GMPP, four MPPT techniques bio-inspired in the grey wolf optimisation (GWO) are presented. These MPPT techniques, which are named as GWO, GWO-Beta, GWO-IC (Incremental Conductance), and GWO-P&O (Perturb and Observe), are evaluated and compared to each other by employing a double-stage three-phase grid-connected PV system, which is composed of DC/DC converter and three-phase inverter. Commonly, the DC-bus voltage regulation of double-stage PV systems presents slow dynamic behaviour to avoid disturbances in the currents injected into the grid. As a result, MPPT algorithms suffer with this problem since they must be executed considering this condition. To overcome this problem, a feed-forward control loop (FFCL) is implemented to improve the DC-bus voltage regulation during abrupt solar irradiance changes, as well as accelerating the MPPT algorithms dynamics. By means of extensive experimental and simulation results, the performance and effectiveness of the four MPPT techniques, as well as the FFCL, are evaluated.

An overview of isolation controls at LIGO

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment that aims at measuring gravitational waves emitted by astrophysical sources. The detection of black hole mergers and neutron star collision was made possible by the extreme level of isolation required to hold the optics still from external ground disturbances in a large band of the spectrum. From the low-frequencies (earthquakes, wind, microseism, below 1 Hz) to the higher frequencies (anthropogenic noise, above 1 Hz), the controls system must be tuned to meet the requirements for lock acquisition, lock stability, and sensitivity of the instrument. In this talk, I will describe the overall control scheme of the LIGO isolation platforms and mirror suspensions, and the challenges met to design the many feedback and feedforward control loops.The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment that aims at measuring gravitational waves emitted by astrophysical sources. The detection of black hole mergers and neutron star collision was made possible by the extreme level of isolation required to hold the optics still from external ground disturbances in a large band of the spectrum. From the low-frequencies (earthquakes, wind, microseism, below 1 Hz) to the higher frequencies (anthropogenic noise, above 1 Hz), the controls system must be tuned to meet the requirements for lock acquisition, lock stability, and sensitivity of the instrument. In this talk, I will describe the overall control scheme of the LIGO isolation platforms and mirror suspensions, and the challenges met to design the many feedback and feedforward control loops.

Design and fabrication of a linear broadband non-reciprocal acoustic waveguide using feedforward control

Acoustic metamaterials that exhibit non-reciprocal transmission have received substantial attention due to their wide range of applications such as noise control, diagnostic imaging, communications, and acoustic cloaking. Passive metamaterials achieve non-reciprocity through system resonances combined with nonlinearities or manipulation of phononic bandgap and are usually effective over a narrow band of frequencies. In this study, we describe the development of a new class of acoustic waveguides that exhibit linear non-reciprocal sound transmission over a wide range of frequencies. We use an open loop feedforward control mechanism where the measured local pressure is passed through an electronic controller and transmitted downstream to actuate an acoustic source. Analysis of the idealized one-dimensional model with a continuous distribution of probes and sources shows spatial asymmetry with attenuation in one direction and amplification in the other for frequencies ranging from one-half to five times the ratio of the active length of the segment to the acoustic wavelength. We show that such behavior can be replicated in a physical system with a finite array of acoustic probes and sources and develop the framework to compute the stability of this class of active waveguides. The experimental results for a simple feedforward model system are presented.

Dynamic performance comparison involving grid‐connected PV systems operating with active power‐line conditioning and subjected to sudden solar irradiation changes

This study presents a comparative performance analysis involving single- and double-stage photovoltaic (PV) systems, which are connected to a three-phase four-wire electrical system by means of a four-leg inverter topology. The double-stage PV system is composed of a step-up DC/DC converter and a four-leg grid-connected inverter, while in the single-stage PV system the PV array is directly connected to the inverter DC bus. In addition to the active power injection into the grid, both PV systems have two attractive features, described as follows: (i) power quality improvement due to their capability to perform active power-line conditioning, such as load harmonic current suppression, reactive power compensation, and load unbalance compensation; (ii) dynamic improvement in the occurrence of abrupt solar irradiation variations, which is achieved through the implementation of a feed-forward control loop (FFCL) acting directly in the inverter DC-bus voltage control loop, resulting in speeding up of the dynamics of both the DC-bus voltage and the injected grid-inverter currents. The referred comparative analysis addresses the static and dynamic performances considering the PV systems operating under the action of the FFCL, as well as performing active power-line conditioning. Simulation and experimental results are presented to evaluate and validate the proposed study.

Adaptive Neural Control of Underactuated Surface Vessels With Prescribed Performance Guarantees.

This paper presents adaptive neural tracking control of underactuated surface vessels with modeling uncertainties and time-varying external disturbances, where the tracking errors consisting of position and orientation errors are required to keep inside their predefined feasible regions in which the controller singularity problem does not happen. To provide the preselected specifications on the transient and steady-state performances of the tracking errors, the boundary functions of the predefined regions are taken as exponentially decaying functions of time. The unknown external disturbances are estimated by disturbance observers and then are compensated in the feedforward control loop to improve the robustness against the disturbances. Based on the dynamic surface control technique, backstepping procedure, logarithmic barrier functions, and control Lyapunov synthesis, singularity-free controllers are presented to guarantee the satisfaction of predefined performance requirements. In addition to the nominal case when the accurate model of a marine vessel is known a priori, the modeling uncertainties in the form of unknown nonlinear functions are also discussed. Adaptive neural control with the compensations of modeling uncertainties and external disturbances is developed to achieve the boundedness of the signals in the closed-loop system with guaranteed transient and steady-state tracking performances. Simulation results show the performance of the vessel control systems.

Particle swarm algorithm-based damage-mitigating control law analysis and synthesis for liquid-propellant rocket engine

The damage-mitigating control is a novel technique to ameliorate the reliability and safety of liquid-propellant rocket engines by achieving an optimized trade-off level between overall dynamic performance of the liquid-propellant rocket engine and structural durability of some selected critical damageable components under the condition of no impact on the achievement of the launch and flight mission. Thus, it is needed to be solved for the damage-mitigating control that the global optimization of the best trade-off between the damage of the critical damageable components and the performance of rocket engine. The major challenge should focus on: (i) to construct model of a certain rocket engine system dynamics, critical components structural dynamics, and damage dynamics; (ii) to optimize open loop feed-forward control law based on liquid-propellant rocket engine system dynamic model, structural and damage dynamics model, by using particle swarm optimization algorithm; (iii) to synthesize an intelligent damage-mitigating control system using the optimized open loop control law. In this paper, synthesis procedure of damage mitigation is introduced; structure and damage dynamic model of damageable components are formulated. The results of the simulation computation show that the synthesized control laws are implemented and achieve the effect of damage mitigating for the liquid-propellant rocket engine. It can provide important theoretical and practical value not only for improving the safety and reliability of the liquid-propellant rocket engine, but also for the complex thermo-flow-mechanical systems such as airplane engines, automobile engines, and fossil-fueled power plant because their service life is very critical too.

Active Passive Nature of Assistive Wearable Gait Augment Suit for Enhanced Mobility

In this paper we discuss the active and passive nature of the assistive wearable gait augment suit (AWGAS). AWGAS is a soft, wearable, lightweight, and assists walking gait by reducing muscle activation during walking. It augments walking by reducing the muscle activation of the posterior and anterior muscles of the lower limb. The suit uses pneumatic gel muscles (PGM), foot sensors for gait detection, and pneumatic valves to control the air pressure. The assistive force is provided using the motion in loop feedforward control loop using foot sensors in shoes. PGMs are actuated with the help of pneumatic valves and portable air tanks. The elastic nature of the PGM allows AWGAS to assist walking in the absence of the air supply which makes AWGAS both active and passive walking assist suit. To evaluate the active and passive nature of the AWGAS, we experimented to measure surface EMG (sEMG) of the lower limb muscles. sEMG was recorded for unassisted walking, i.e., without the suit, passive assisted walking, i.e., wearing the suit with no air supply and active assisted walking, i.e., wearing the suit with air supply set at 60 kPa. The results shows reduction in the muscle activity for both passive and active assisted walking as compared to unassisted walking. The pilot trials of the AWGAS were conducted in collaboration with local farmers in the Hiroshima prefecture in Japan where feedback received is complementing the results obtained during the experiments.

Continuous Friction Feedforward Sliding Mode Controller for a TriMule Hybrid Robot

This paper presents a continuous friction feedforward sliding mode controller (CFSMC) for a TriMule hybrid robot to improve its trajectory-tracking performance. The dynamic model depicts that the TriMule robot is a multivariable system with nonlinearity and strong coupling, which poses significant challenges in controller design. Hence, a novel CFSMC that consists of a friction feedforward control loop and a continuous sliding mode feedback control loop is specially developed. The feedforward control item calculated with a speed related function is used to handle discontinuous friction disturbance and achieve good transient performance. The feedback control item designed with a continuous sliding mode algorithm is applied to cope with other nonlinear dynamics and assure zero steady-state error. The robustness of the proposed hybrid control scheme is validated in the sense of Lyapunov. Comparative experimental studies with the double closed-loop controller, the sliding mode controller, and the continuous sliding mode controller are conducted, confirming that the CFSMC with the superior control accuracy is an effective and practical robust control scheme for the TriMule hybrid robot. Taking advantages of the CFSMC, a high-precision circular motion is achieved by the TriMule hybrid robot.