Independent Local Control Research Articles

Investigation on active vibration isolation with multi-axis control: Analysis and experiment

Vibration isolators are usually used to attenuate the transmission of vibration of power machinery to the flexible foundation. Since vibration energy is transferred nearly through all the degrees of freedom of an isolator, it is difficult to guarantee sufficient vibration attenuation by the single-axis control at each active isolator. In order to enhance attenuation at each vibration isolator, a novel configuration of active vibration isolation is proposed. Each active isolator is composed of two rubber isolators and one intermediate rigid mass in which eight electromagnetic actuators and six error accelerometers are attached. Six control forces are applied on the intermediate mass to suppress its multi-axis vibration. Moreover, the weakened interaction between isolators allows independent local control at each isolator. A numerical model is established to verify the proposed active vibration isolation and the results show that the transmission of vibration from the source to the flexible hull structure can be nearly cut off when the error vibrations of each intermediate mass are attenuated completely. The effectiveness is also proved by an experimental active vibration isolation system and the proposed isolation configuration with multi-axis control can achieve more significant attenuation of vibration of the hull structure than the commonly used active vibration isolation with only single-axis control.

Distributed Traffic Engineering for Multi-Domain SDN Without Trust

In software defined networking, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">flat</i> design of distributed control plane enables the management of multi-domain networks that are incapable of deploying a root controller. However, it is very difficult to avoid policy conflicts between independent local controllers due to the lack of centralized arbitration. Moreover, domains without trust may not be always cooperative and could even cheat to maximize their own interests. In this article, we first consider the cooperative scenario and address the problem of traffic engineering in a flat distributed control plane. We propose a fully distributed algorithm, called <monospace xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DisTE</monospace> , which can provide max-min fair bandwidth allocation for flows and maximize resource utilization. <monospace xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DisTE</monospace> also preserves the local topology of each domain and achieves policy consistency by multiple rounds of synchronization. We then consider the non-cooperative scenario, where selfish domains may discriminate bandwidth requests from other domains or overstate theirs owns to squeeze more bandwidths.

Local reactive power dispatch optimisation minimising global objectives

The number of distributed energy resources (DERs) deployed in distribution systems has been rapidly increasing in recent years. Consequently, many researchers have proposed to utilise the DERs for local reactive power support. Yet, the expansion of infrastructure necessary to allow communication among the DERs, and with a centralised controller, has not been as fast. This necessitates an independent local control method that is able to fulfil the objectives of a centralised controller. Therefore, this work proposes a data-driven local optimisation of global objectives (LOGO) algorithm to control the reactive power dispatch from DERs in distribution systems. The proposed method has been validated across different test systems with real topology, irradiance and load data, for steady-state undervoltage and overvoltage scenarios. The results have shown that LOGO performs almost as well as centralised optimisation without any communication and without any information regarding the grid topology. LOGO is able to satisfy the voltage constraints using only locally available information even when other algorithms fail to do so. Compared with distributed and other local reactive power controls, LOGO is much more stable and yields significantly better results. Moreover, LOGO’s superiority over other control methods increases with system size and complexity. Hence, this work provides a viable alternative for real-life dispatch optimisation and opens up new possibilities to optimise global variables without any communication. Lastly, this paper also highlights the importance of accurate solar forecasting and validation of reactive power control.

Time-varying partitioning for predictive control design: Density-games approach

The design of distributed optimization-based controllers for large-scale systems (LSSs) implies every time new challenges. The fact that LSSs are generally located throughout large geographical areas makes difficult the recollection of measurements and their transmission. In this regard, the communication network that is required for a centralized control approach might have high associated economic costs. Furthermore, the computation of a large amount of data implies a high computational burden to manage, process and use them in order to make decisions over the system operation. A plausible solution to mitigate the aforementioned issues associated with the control of LSSs consists in dividing this type of systems into smaller sub-systems able to be handled by independent local controllers. This paper studies two fundamental components of the design of distributed optimization-based controllers for LSSs, i.e., the system partitioning and distributed optimization algorithms. The design of distributed model predictive control (DMPC) strategies with a system partitioning and by using density-dependent population games (DDPG) is presented.

An effective computational design strategy for [formula omitted] vibration control of large structures with information constraints

In this paper, we present an effective computational strategy to design high-performance decentralized controllers with partial local-state information for vibration control of large building structures. Specifically, the building dynamical model is first decomposed into a set of approximate low-dimensional decoupled subsystems subject to the action of generalized disturbances, which include the effect of external physical disturbances, modeling approximation errors and mechanical subsystem interactions. Next, using the approximate decoupled subsystems, an overall structured state-feedback controller is obtained by designing a proper set of independent local controllers. The proposed computational strategy is applied to obtain two structured control systems for the seismic protection of a 35-story building: (i) a fully decentralized velocity-feedback controller with 35 interstory actuators that can be passively implemented by a set of viscous dampers, and (ii) a decentralized velocity-feedback controller with 15 interstory actuators, which can be implemented with a reduced set of collocated sensors and a system of five independent short-range communication networks. To assess the performance of the obtained structured controllers, the corresponding frequency and time responses are investigated and compared with the responses produced by optimal full-state H∞ controllers. Moreover, to evaluate the effectiveness of the computational procedure, both structured and full-state controllers are designed for a proper set of buildings with different number of stories and the corresponding computation times are recorded and compared. The obtained results show that the computational cost of the proposed design methodology is remarkably low and also indicate that, despite the severe information constraints, the synthesized structured controllers are practically optimal.

A two-layer networked learning control system using actor–critic neural network

Aiming at the fact that the controlled objects are becoming more and more complex, while the existing control strategies cannot fulfill the needs for higher quality control performance due to the limitations of the widely used single-layer networked control system architecture, a two-layer networked learning control system architecture is proposed. Under this architecture, independent local controllers are interconnected to form the lower layer, while a learning agent which communicates with the independent local controllers in the lower layer forms the upper layer. To implement such a system, a discard-packet strategy is firstly developed to deal with network-induced delay, data packet out-of-order and data packet loss. The cubic spline interpolator is then employed to compensate the lost data. Finally, the output of the learning agent using actor–critic neural network is used to dynamically tune the control signal of local controller. Control simulations of different ways for a nonlinear heating, ventilation and air-conditioning (HVAC) system are compared. Simulation results show that this new architecture can effectively improve the control performance.

Decentralized harmonic active vibration control of a flexible plate using piezoelectric actuator-sensor pairs

We have investigated decentralized active control of periodic panel vibration using multiple pairs combining PZT actuators and PVDF sensors distributed on the panel. By contrast with centralized MIMO controllers used to actively control the vibrations or the sound radiation of extended structures, decentralized control using independent local control loops only requires identification of the diagonal terms in the plant matrix. However, it is difficult to a priori predict the global stability of such decentralized control. In this study, the general situation of noncollocated actuator-sensor pairs was considered. Frequency domain gradient and Newton-Raphson adaptation of decentralized control were analyzed, both in terms of performance and stability conditions. The stability conditions are especially derived in terms of the adaptation coefficient and a control effort weighting coefficient. Simulations and experimental results are presented in the case of a simply supported panel with four PZT-PVDF pairs distributed on it. Decentralized vibration control is shown to be highly dependent on the frequency, but can be as effective as a fully centralized control even when the plant matrix is not diagonal-dominant or is not strictly positive real (not dissipative).

Two-Layer Control of Integrated Quality and Quantity in Dynamic Water Distribution Systems

An integrated approach to control of quantity and quality in water supply and distribution systems is proposed. The integrated control consists in optimising the operational cost, meeting a demand on water of desired quality and maintaining the constraints. This constrained optimising control problem is complex due to nonlinearities, large dimension, output constraints, mixed-integer structure of the variables involved, at least two time scales in the system dynamics and an uncertainty. A sub-optimal two-level hierarchical control structure is proposed that allows incorporating the desired controller functions and yet making the synthesis of these functions possible. The control trajectories optimising the operational cost over one day to one week horizon are generated by the upper layer. The upper layer controller operates according to a repetitive control strategy. Due to model-reality differences the prescribed bounds on chlorine residuals may not be met when the generated controls are applied to a real systems. The main objective of the lower control layer is to adjust on-line actions of the booster stations determined by the upper control layer so that the chlorine residuals are kept within the limits. The lower layer controller operates almost continuously as opposed to the upper layer one. Its design is very difficult as the dynamics between the chlorine injection nodes and monitored nodes involves time-varying delays and parameters that can abruptly change. A decentralisation of the lower layer controller into a number of independent local controllers allocated to selected sub-areas of a distribution system by using the interaction trajectories determined by the upper layer is discussed. The design of the lower layer controller and its performance are illustrated on an example water system.

Local and systemic control of the osteoblast.

Local and systemic control of the osteoblast.

Decoupled cushion control in ride control systems for air cushion catamarans

A well-known limit of air cushion catamarans is the so-called “cobblestone effect”, a resonance phenomenon due to the interaction between the ship body and the air cushion dynamics excited by the incoming waves. In this paper the problem of designing a ride control system for the attenuation of the wave-induced vertical accelerations of a surface effect ship (SES) is considered. It is shown that the damping of the two main resonant modes can be achieved by two independent control loops. Such a decoupled control scheme exploits the intrinsic orthogonality of the two oscillation phenomena, and provides better performances than classical control schemes based on two independent local control loops.

Gastric mucosal blood flow regulation in response to different stimuli.

We compared changes in gastric mucosal blood flow (GMBF) and left gastric artery blood flow (LGABF) in response to pharmacological, physiological, and pathological stimuli. GMBF and LGABF were measured by the hydrogen gas clearance and perivascular ultrasonic transit time techniques, respectively, under baseline conditions and following intravenous infusion of vasopressin or pentagastrin, isovolemic hemodilution, or gastric perfusion with HCl-taurocholate. Blood flow changes following vasopressin or hemodilution were significantly larger in the left gastric artery than in the gastric mucosa. In contrast, the increment in blood flow associated with pentagastrin-stimulated acid secretion was significantly greater in the gastric mucosa than in the extramural artery. Barrier disruption with acid-taurocholate induced similar changes in both measurement sites. The gastric hyperemia induced by either mechanism was significantly attenuated by blockade of NO synthesis. These data demonstrate that although functional changes in GMBF are primarily supported by changes in blood flow at the extramural gastric arteries, the gastric mucosal microvasculature is also under the influence of independent local control mechanisms.

Evaluation of the multiple offender alcoholism project: Quasiexperimental evaluation strategy with a focus on individual change and quality of life

The development, implementation, and evaluation of a treatment program for violent criminal offenders with alcohol abuse/alcoholism is described. The treatment program was based on a contingency management system that rewarded program attendance and participation. The evaluation of the program, using quasiexperimental techniques (including comparisons with national samples and two independent local control samples), indicated that active program clients engaged in significantly fewer violent crimes and showed significantly improved life functioning (“quality of life”) in areas of employment and social adjustment during participation in the program. These beneficial changes were correlated with program participation and were also predictive of desired social outcomes, as defined by the criminal justice system, such as reduced alcohol consumption and reduced violent crime. This presentation illustrates that the goals of mental health treatment programs and traditional criminal justice system agencies (and their associated definitions of “quality of life”) are not necessarily incompatible.

Series and parallel operation of hysteresis current-controlled PWM rectifiers

Different strategies for series and parallel connections of hysteresis current-controlled PWM rectifier have been investigated by experiments, computer simulations, and analyses. Each rectifier unit delivers near-sinusoidal current waveforms at unity (or even leading) power factor. Of particular concern are the questions of: (i) system stability; (ii) the capability of the modular units to share voltage (series connection) and current (parallel connection) under steady-state and transient operation; and (iii) sensitivity of performance characteristics to component tolerances. Experiments were made on 1 kW bipolar transistor modular units. Two configurations, having independent local control (type A) and common switching control (type B), respectively, were studied. The study shows that type B is more economical than type A and appears to give a satisfactory performance. >