Active Vibration Cancellation of a Free-Piston Linear Generator Engine

A free-piston linear generator engine (LG) is a device that couples a free-piston combustion engine with a linear electric generator. The engine is consisted with a part called piston-rod assembly (PRA), where two pistons are connected by a rod attached with permanent magnet. During the operation of LG, PRA will linearly reciprocate between two internal combustion chambers on the opposite sides. However, when the PRA is on one side of the engine, an unbalanced impact force is created. The unbalanced forces provide an undesirable impact force acting on the engine block, causing the engine to vibrate. The control of vibration for the LG becomes crucial, because proper vibration controls maintain a consistent electricity output and maximize the efficiency of the engine. Current work proposed using a linear motor (LM) to create an anti-phase momentum into the system to counter the impact forces created by PRA. The works are based on analytical modeling with MATLAB used for simulation. Simulation shows the system instability characteristics, the time and frequency responses for LG. The results showed the existence of a real pole at the right hand side of complex plane which contribute to the system instability. The non-proportional damped time response obtained using state-space approach shows the overall interaction between mass forcer and PRA decreased with respect to time. The frequency responses showed that with the application of active vibration cancellation, the resonance can be delayed and the magnitude of the resonance can be reduced. A lumped-mass quarter car suspension model is used for validation. Case study is carried out to decide the best available driven forces that drive the LG. The conclusion of current study showed that with proper vibration control for the LG, the vibration level of LG can be reduced to a desirable level while maintaining the optimum operating conditions

Safety Awareness for Rigid and Elastic Joint Robots: An Impact Dynamics and Control Framework

This thesis aims at making robots with rigid and elastic joints aware of human collision safety. A framework is proposed that captures human injury occurrence and robot inherent safety properties in a unified manner. It allows to quantitatively compare and optimize the safety characteristics of different robot designs and is applied to stationary and mobile manipulators. On the same basis, novel motion control schemes are developed and experimentally validated

Damping controller design for FACTS devices in power systems using novel control techniques

Power systems are under increasing stress as deregulation introduces several new economic objectives for operation. Since power systems are being operated close to their limits, weak connections, unexpected events, hidden failures in protection system, human errors, and a host of other factors may cause a system to lose stability and even lead to catastrophic failure. Therefore, the need for improved system damping in a wider operating range is gaining more attention. Among the available damping control methods, each approach has advantages and disadvantages in different systems. The effectiveness of damping control depends on the devices chosen, the system modal feature, and the applied controller design method;In the literature, many approaches have been proposed to undertake this task. However, some of these approaches only take a fixed operating point into consideration without describing the changing uncertainty in varying system conditions; computational effort. Furthermore, no systematic comparison of controller design methods has been conducted with regard to different system profiles. Attention has been drawn to the enhanced susceptibility to inter-area oscillations between groups of machines under large others require a great deal of variation of system operating conditions. The linear parameter varying (LPV) approach, which has been widely studied in the literature, provides a potential method for capturing the varying system condition precisely without formulation of system uncertainty. However, in some cases no solution can be achieved if the system variation is too large using the traditional LPV approach. Also, sometimes the system structure imposes limitations in the achievable damping performance. In general, there is a critical need for a cost-effective control strategy applicable to different systems from an economic point of view;In this dissertation, a comprehensive comparison among controller design methods has been conducted to study the damping effectiveness of different FACTS devices. Based on these, a robust regional pole-placement method is applied in a TCSC damping controller design in a 4-machine system; an interpolated LPV approach is proposed and applied to designing a SVC damping controller in the IEEE 50-machine system; finally with the advantage of an additional feedback signal, limitations in achieving satisfactory damping performance can be relieved using a two-input single-output (TISO) damping controller for a TCSC in the IEEE 50-machine system

Active Vibration Cancellation of a Free-Piston Linear Generator Engine

A free-piston linear generator engine (LG) is a device that couples a free-piston combustion engine with a linear electric generator. The engine is consisted with a part called piston-rod assembly (PRA), where two pistons are connected by a rod attached with permanent magnet. During the operation of LG, PRA will linearly reciprocate between two internal combustion chambers on the opposite sides. However, when the PRA is on one side of the engine, an unbalanced impact force is created. The unbalanced forces provide an undesirable impact force acting on the engine block, causing the engine to vibrate. The control of vibration for the LG becomes crucial, because proper vibration controls maintain a consistent electricity output and maximize the efficiency of the engine. Current work proposed using a linear motor (LM) to create an anti-phase momentum into the system to counter the impact forces created by PRA. The works are based on analytical modeling with MATLAB used for simulation. Simulation shows the system instability characteristics, the time and frequency responses for LG. The results showed the existence of a real pole at the right hand side of complex plane which contribute to the system instability. The non-proportional damped time response obtained using state-space approach shows the overall interaction between mass forcer and PRA decreased with respect to time. The frequency responses showed that with the application of active vibration cancellation, the resonance can be delayed and the magnitude of the resonance can be reduced. A lumped-mass quarter car suspension model is used for validation. Case study is carried out to decide the best available driven forces that drive the LG. The conclusion of current study showed that with proper vibration control for the LG, the vibration level of LG can be reduced to a desirable level while maintaining the optimum operating conditions

Development and experimental validation of direct controller tuning for spaceborne telescopes

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2000.Includes bibliographical references (p. 285-294).Strict requirements in the performance of future space-based observatories such as the Space Interferometry Mission (SIM) and the Next Generation Space Telescope (NGST), will extend the state-of-the-art of critical mission spaceflight-proven active control design. A control design strategy, which combines the high performance and stability robustness guarantees of modem, robust-control design with the spaceflight heritage of conventional control design, is proposed which will meet the strict requirements and maintain traceability to the successful controllers from predecessor spacecraft. Two principal tools are developed: an analysis algorithm that quantifies each sensor/actuator combination's effectiveness for control, and a design engine which tunes a baseline controller to improve performance and/or stability robustness. The sensor/actuator effectiveness indexing tool requires a reduced-order state-space model of the plant. A modification of the balanced reduction method is introduced which improves numerical conditioning so that the order of large models of flexible spacecraft may be decreased. For each sensor and actuator an index is computed using the modal controllability from an actuator weighted by the modal cost in the performance, and the model observability of a sensor weighted by the modal cost of the disturbance. The special case of actuators that are used for active output isolation is handled separately. The designer makes use of the sensor/actuator indexing tool to select which control channels to emphasize in the tuning. The tuning tool is based on forming an augmented cost from weighting performance, stability robustness, deviation from the baseline controller, and controller gain. The tuning algorithm can operate with the plant's state-space design model or directly with the plant's measured frequency-response data. Two differentiable multivariable stability robustness metrics are formed, one based on the maximum singular value of the Sensitivity transfer matrix and one based on the multivariable Nyquist locus. The controller is parameterized with a general tridiagonal parameterization based on the real-modal state-space form. The augmented cost is chosen to be differentiable and a closed-loop stability-preserving unconstrained nonlinear descent program is used to directly compute controller parameters that decrease the augmented cost. To automate the closed-loop stability determination in the measured-data-based designs, a rule-based algorithm is created to invoke the multivariable Nyquist stability criteria. The use of the tuning technique is placed in context with a high-level control design methodology. The tuning technique is evaluated on a sample problem and then experimentally demonstrated on a laboratory test article with dynamics, sensor suite, and actuator suite all similar to future spaceborne observatories. The developed test article is the first spacetelescope- like experimental facility to combine large-angle slewing with nanometer optical phasing and sub-arcsecond pointing in the presence of spacecraft-like disturbances. The technique is applied to generate an improved controller for a model of the SIM spacecraft.by Gregory J.W. Mallory.Ph.D

The Fifth NASA/DOD Controls-Structures Interaction Technology Conference, part 2

This publication is a compilation of the papers presented at the Fifth NASA/DoD Controls-Structures Interaction (CSI) Technology Conference held in Lake Tahoe, Nevada, March 3-5, 1992. The conference, which was jointly sponsored by the NASA Office of Aeronautics and Space Technology and the Department of Defense, was organized by the NASA Langley Research Center. The purpose of this conference was to report to industry, academia, and government agencies on the current status of controls-structures interaction technology. The agenda covered ground testing, integrated design, analysis, flight experiments and concepts

Proceedings of the 4th Annual SCOLE Workshop

This publication is a collection of papers presented at the Fourth Annual Spacecraft Control Laboratory Experiment (SCOLE) Workshop held at the U.S.A.F. Academy, Colorado Springs, Colorado, November 16, 1987. The papers address the modeling, systems identification, and control synthesis for the Spacecraft Control Laboratory Experiment (SCOLE) configuration

Evolutionary design of controlled structures

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1997.Includes bibliographical references (p. 209-213).by Brett P. Masters.Ph.D

Multi-agent persistent monitoring of a finite set of targets

The general problem of multi-agent persistent monitoring finds applications in a variety of domains ranging from meter to kilometer-scale systems, such as surveillance or environmental monitoring, down to nano-scale systems such as tracking biological macromolecules for studying basic biology and disease. The problem can be cast as moving the agents between targets, acquiring information from or in some fashion controlling the states of the targets. Under this formulation, at least two questions need to be addressed. The first is the design of motion trajectories for the agents as they move among the spatially distributed targets and jointly optimize a given cost function that describes some desired application. The second is the design of the controller that an agent will use at a target to steer the target's state as desired. The first question can be viewed in at least two ways: first, as an optimal control problem with the domain of the targets described as a continuous space, and second as a discrete scheduling task. In this work we focus on the second approach, which formulates the target dynamics as a hybrid automaton, and the geometry of the targets as a graph. We show how to find solutions by translating the scheduling problem into a search for the optimal route. With a route specifying the visiting sequence in place, we derive the optimal time the agent spends at each target analytically. The second question, namely that of steering the target's state, can be formulated from the perspective of the target, rather than the agent. The mobile nature of the agents leads to intermittencontrol, such that the controller is assumed to be disconnected when no agent is at the target. The design of the visiting schedule of agents to one target can affect the reachability (controllability) of this target's control system and the design of any specific controller. Existing test techniques for reachability are combined with the idea of lifting to provide conditions on systems such that reachability is maintained in the presence of periodic disconnections from the controller. While considering an intermittently connected control with constraints on the control authority and in the presence of a disturbance, the concept of 'degree of controllability' is introduced. The degree is measured by a region of states that can be brought back to the origin in a given finite time. The size of this region is estimated to evaluate the performance of a given sequence