Ground controlled robotic assembly operations for Space Station Freedom

A number of dextrous robotic systems and associated positioning and transportation devices are available on Space Station Freedom (SSF) to perform assembly tasks that would otherwise need to be performed by extravehicular activity (EVA) crewmembers. The currently planned operating mode for these robotic systems during the assembly phase is teleoperation by intravehicular activity (IVA) crewmembers. While this operating mode is less hazardous and expensive than manned EVA operations, and has insignificant control loop time delays, the amount of IVA time available to support telerobotic operations is much less than the anticipated requirements. Some alternative is needed to allow the robotic systems to perform useful tasks without exhausting the available IVA resources; ground control is one such alternative. The issues associated with ground control of SSF robotic systems to alleviate onboard crew time availability constraints are investigated. Key technical issues include the effect of communication time delays, the need for safe, reliable execution of remote operations, and required modifications to the SSF ground and flight system architecture. Time delay compensation techniques such as predictive displays and world model-based force reflection are addressed and collision detection and avoidance strategies to ensure the safety of the on-orbit crew, Orbiter, and SSF are described. Although more time consuming and difficult than IVA controlled teleoperations or manned EVA, ground controlled telerobotic operations offer significant benefits during the SSF assembly phase, and should be considered in assembly planning activities

Experimental Issues in Testing a Semiactive Technique to Control Earthquake Induced Vibration

This work focuses on the issues to deal with when approaching experimental testing of structures equipped with semiactive control (SA) systems. It starts from practical experience authors gained in a recent wide campaign on a large scale steel frame structure provided with a control system based on magnetorheological dampers. The latter are special devices able to achieve a wide range of physical behaviours using low-power electrical currents. Experimental activities involving the use of controllable devices require special attention in solving specific aspects that characterize each of the three phases of the SA control loop: acquisition, processing, and command. Most of them are uncommon to any other type of structural testing. This paper emphasizes the importance of the experimental assessment of SA systems and shows how many problematic issues likely to happen in real applications are also present when testing these systems experimentally. This paper highlights several problematic aspects and illustrates how they can be addressed in order to achieve a more realistic evaluation of the effectiveness of SA control solutions. Undesired and unavoidable effects like delays and control malfunction are also remarked. A discussion on the way to reduce their incidence is also offered

Analysis And Mitigation Of The Impacts Of Delays In Control Of Power Systems With Renewable Energy Sources

ABSTRACT Analysis and Mitigation of the Impacts of Delays in Control of Power Systems with Renewable Energy Sources by Chang Fu Apr. 2019 Advisor : Dr. Caisheng Wang Major : Electrical and Computer Engineering Degree : Doctor of Philosophy With the integration of renewable resources, electric vehicles and other uncertain resources into power grid, varieties of control topology and algorithms have been proposed to increase the stability and reliability of the operation system. Load modeling is an critical part in such analysis since it significantly impacts the accuracy of the simulation in power system, as well as stability and reliability analysis. Traditional power system composite load model parameter identification problems can be essentially ascribed to optimization problems, and the identied parameters are point estimations subject to dierent constraints. These conventional point estimation based composite load modeling approaches suer from disturbances and noises and provide limited information of the system dynamics. In this thesis, a statistic (Bayesian Estimation) based distribution estimation approach is proposed for composite load models, including static (ZIP) and dynamic (Induction Motor) parts, by implementing Gibbs sampling. The proposed method provides a distribution estimation of coecients for load models and is robust to measurement errors. The overvoltage issue is another urgent issues need to be addressed, especially in a high PV penetration level system. Various approaches including the real power control through photovoltaic (PV) inverters have been proposed to mitigate such impact, however, most of the existing methods did not include communication delays in the control loop. Communication delays, short or long, are inevitable in the PV voltage regulation loop and can not only deteriorate the system performance with undesired voltage quality but also cause system instability. In this thesis, a method is presented to convert the overvoltage control problem via PV inverters for multiple PVs into a problem of single-input-single-output (SISO) systems. The method can handle multiple PVs and dierent communication delays. The impact of communication delays is also systematically analyzed and the maximum tolerable delay is rigorously obtained. Dierent from linear matrix inequality (LMI) techniques that have been extensively studied in handling systems with communication delays, the proposed method gives the necessary and sucient condition for obtaining a controller and the design procedure is explicitly and constructively given in the paper. The effectiveness of the proposed method is veried by simulation studies on a distribution feeder and the widely-used 33-bus distribution test system. The similar design strategy can be utilized to mitigate delay impacts in Load frequency control (LFC) as well. LFC has been considered as one of the most important frequency regulation mechanisms in modern power system. One of the inevitable problems involved in LFC over a wide area is communication delay. In this thesis, an alternative design method is proposed to devise delay compensators for LFC in one or multiple control areas. For one-area LFC, a sucient and necessary condition is given for designing a delay compensator. For multiarea LFC with area control errors (ACEs), it is demonstrated that each control area can have its delay controller designed as that in a one-area system if the index of coupling among the areas is below the threshold value determined by the small gain theorem. Effectiveness of the proposed method is veried by simulation studies on LFCs with communication delays in one and multiple interconnected areas with and without time-varying delays, respectively

Analysis And Mitigation Of The Impacts Of Delays In Control Of Power Systems With Renewable Energy Sources

ABSTRACT Analysis and Mitigation of the Impacts of Delays in Control of Power Systems with Renewable Energy Sources by Chang Fu Apr. 2019 Advisor : Dr. Caisheng Wang Major : Electrical and Computer Engineering Degree : Doctor of Philosophy With the integration of renewable resources, electric vehicles and other uncertain resources into power grid, varieties of control topology and algorithms have been proposed to increase the stability and reliability of the operation system. Load modeling is an critical part in such analysis since it significantly impacts the accuracy of the simulation in power system, as well as stability and reliability analysis. Traditional power system composite load model parameter identification problems can be essentially ascribed to optimization problems, and the identied parameters are point estimations subject to dierent constraints. These conventional point estimation based composite load modeling approaches suer from disturbances and noises and provide limited information of the system dynamics. In this thesis, a statistic (Bayesian Estimation) based distribution estimation approach is proposed for composite load models, including static (ZIP) and dynamic (Induction Motor) parts, by implementing Gibbs sampling. The proposed method provides a distribution estimation of coecients for load models and is robust to measurement errors. The overvoltage issue is another urgent issues need to be addressed, especially in a high PV penetration level system. Various approaches including the real power control through photovoltaic (PV) inverters have been proposed to mitigate such impact, however, most of the existing methods did not include communication delays in the control loop. Communication delays, short or long, are inevitable in the PV voltage regulation loop and can not only deteriorate the system performance with undesired voltage quality but also cause system instability. In this thesis, a method is presented to convert the overvoltage control problem via PV inverters for multiple PVs into a problem of single-input-single-output (SISO) systems. The method can handle multiple PVs and dierent communication delays. The impact of communication delays is also systematically analyzed and the maximum tolerable delay is rigorously obtained. Dierent from linear matrix inequality (LMI) techniques that have been extensively studied in handling systems with communication delays, the proposed method gives the necessary and sucient condition for obtaining a controller and the design procedure is explicitly and constructively given in the paper. The effectiveness of the proposed method is veried by simulation studies on a distribution feeder and the widely-used 33-bus distribution test system. The similar design strategy can be utilized to mitigate delay impacts in Load frequency control (LFC) as well. LFC has been considered as one of the most important frequency regulation mechanisms in modern power system. One of the inevitable problems involved in LFC over a wide area is communication delay. In this thesis, an alternative design method is proposed to devise delay compensators for LFC in one or multiple control areas. For one-area LFC, a sucient and necessary condition is given for designing a delay compensator. For multiarea LFC with area control errors (ACEs), it is demonstrated that each control area can have its delay controller designed as that in a one-area system if the index of coupling among the areas is below the threshold value determined by the small gain theorem. Effectiveness of the proposed method is veried by simulation studies on LFCs with communication delays in one and multiple interconnected areas with and without time-varying delays, respectively

Anesthesiologist in the loop and predictive algorithm to maintain hypnosis while mimicking surgical disturbance

Many regulatory loops in drug delivery systems for depth of anesthesia optimization problem consider only the effect of the controller output on the patient pharmacokinetic and pharmacodynamic response. In reality, these drug assist devices are over-ruled by the anesthesiologist for setpoint changes, bolus intake and additional disturbances from the surgical team. Additionally, inter-patient variability imposes variations in the dynamic response and often intra-patient variability is also present. This paper introduces for the first time in literature a study on the effect of both controller and anesthesiologist in the loop for hypnosis regulation. Among the many control loops, model based predictive control is closest to mimic the anticipatory action of the anesthesiologist in real life and can actively deal with issues as time lags, delays, constraints, etc. This control algorithm is here combined with the action of the anesthesiologist. A disturbance signal to mimic surgical excitation has been introduced and a database of 25 patients has been derived from clinical insight. The results given in this paper reveal the antagonist effect in closed loop of the intervention from the anaesthesiologist when additional bolus intake is present. This observation explains induced dynamics in the closed loop observed in clinical trials and may be used as a starting point for next step in developing tools for improved assistance in clinical care. (C) 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved

Predictive state feedback control of network control systems

Networked control systems have gained attention in the recent years due to their widespread applications to various real time systems. Controlling these systems poses several challenges which are currently still being investigated. A study of these issues is provided along with recent proceedings in technology to counter such issues like limited bandwidth, time delays and packet drop-outs. This thesis focuses on the problem of time delays in network control system which can cause instability of closed loop operation of these systems. A guaranteed cost approach is employed to achieve stability along with achieving a certain level of performance as defined by the cost function. A state feedback controller is used and along with it, a predictive control scheme is implemented to design variable gains of the feedback controller depending on the number of packets missed (packet drop-outs) and time delays of the received input sample or state of the plant, both of which can be random but bounded for a given communication channel. The controllers are connected to the plant via the network. They generate the appropriate input for the plant so that delays in the channel will not instabilize the system and thus they comprise the network delay compensator. The controller gains and the observer gain are determined by formulating a linear matrix inequality (LMI) problem and solving this problem by using the Robust Control Toolbox in MATLAB. Further, this technique is implemented on a fictitious system by modelling the networked system with constant delay in SIMULINK and the observer states as well as the plant output are shown to be stable

Time-Delay Switch Attack on Networked Control Systems, Effects and Countermeasures

In recent years, the security of networked control systems (NCSs) has been an important challenge for many researchers. Although the security schemes for networked control systems have advanced in the past several years, there have been many acknowledged cyber attacks. As a result, this dissertation proposes the use of a novel time-delay switch (TDS) attack by introducing time delays into the dynamics of NCSs. Such an attack has devastating effects on NCSs if prevention techniques and countermeasures are not considered in the design of these systems. To overcome the stability issue caused by TDS attacks, this dissertation proposes a new detector to track TDS attacks in real time. This method relies on an estimator that will estimate and track time delays introduced by a hacker. Once a detector obtains the maximum tolerable time delay of a plant’s optimal controller (for which the plant remains secure and stable), it issues an alarm signal and directs the system to its alarm state. In the alarm state, the plant operates under the control of an emergency controller that can be local or networked to the plant and remains in this stable mode until the networked control system state is restored. In another effort, this dissertation evaluates different control methods to find out which one is more stable when under a TDS attack than others. Also, a novel, simple and effective controller is proposed to thwart TDS attacks on the sensing loop (SL). The modified controller controls the system under a TDS attack. Also, the time-delay estimator will track time delays introduced by a hacker using a modified model reference-based control with an indirect supervisor and a modified least mean square (LMS) minimization technique. Furthermore, here, the demonstration proves that the cryptographic solutions are ineffective in the recovery from TDS attacks. A cryptography-free TDS recovery (CF-TDSR) communication protocol enhancement is introduced to leverage the adaptive channel redundancy techniques, along with a novel state estimator to detect and assist in the recovery of the destabilizing effects of TDS attacks. The conclusion shows how the CF-TDSR ensures the control stability of linear time invariant systems

Closed-Loop System Identification Experience for Flight Control Law and Flying Qualities Evaluation of a High Performance Fighter Aircraft

This paper highlights some of the results and issues associated with estimating models to evaluate control law design methods and design criteria for advanced high performance aircraft. Experimental fighter aircraft such as the NASA-High Alpha Research Vehicle (HARV) have the capability to maneuver at very high angles of attack where nonlinear aerodynamics often predominate. HARV is an experimental F/A-18, configured with thrust vectoring and conformal actuated nose strakes. Identifying closed-loop models for this type of aircraft can be made difficult by nonlinearities and high order characteristics of the system. In this paper, only lateral-directional axes are considered since the lateral-directional control law was specifically designed to produce classical airplane responses normally expected with low-order, rigid-body systems. Evaluation of the control design methodology was made using low-order equivalent systems determined from flight and simulation. This allowed comparison of the closed-loop rigid-body dynamics achieved in flight with that designed in simulation. In flight, the On Board Excitation System was used to apply optimal inputs to lateral stick and pedals at five angles at attack : 5, 20, 30, 45, and 60 degrees. Data analysis and closed-loop model identification were done using frequency domain maximum likelihood. The structure of identified models was a linear state-space model reflecting classical 4th-order airplane dynamics. Input time delays associated with the high-order controller and aircraft system were accounted for in data preprocessing. A comparison of flight estimated models with small perturbation linear design models highlighted nonlinearities in the system and indicated that the closed-loop rigid-body dynamics were sensitive to input amplitudes at 20 and 30 degrees angle of attack

Time-and event-driven communication process for networked control systems: A survey

Copyright © 2014 Lei Zou et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.In recent years, theoretical and practical research topics on networked control systems (NCSs) have gained an increasing interest from many researchers in a variety of disciplines owing to the extensive applications of NCSs in practice. In particular, an urgent need has arisen to understand the effects of communication processes on system performances. Sampling and protocol are two fundamental aspects of a communication process which have attracted a great deal of research attention. Most research focus has been on the analysis and control of dynamical behaviors under certain sampling procedures and communication protocols. In this paper, we aim to survey some recent advances on the analysis and synthesis issues of NCSs with different sampling procedures (time-and event-driven sampling) and protocols (static and dynamic protocols). First, these sampling procedures and protocols are introduced in detail according to their engineering backgrounds as well as dynamic natures. Then, the developments of the stabilization, control, and filtering problems are systematically reviewed and discussed in great detail. Finally, we conclude the paper by outlining future research challenges for analysis and synthesis problems of NCSs with different communication processes.This work was supported in part by the National Natural Science Foundation of China under Grants 61329301, 61374127, and 61374010, the Royal Society of the UK, and the Alexander von Humboldt Foundation of Germany