A New Fractional Order Hold and Its Capability in Frequency Response and Zero Placement

This paper introduces a new holder with application on digital control systems. This holder is a combination of fractional order hold (FROH) and zero-order hold (ZOH) that has the capability of both holders and a frequency response better than both of ZOH and FROH. For the stability of zeros of the sampled system two theorems are stated and proved with the assumption that the sampling period is very small. Also simulation results are studied to show the effectiveness of the proposed holder and better performance results in comparison with ZOH and FROH

Guided Lock of a Suspended Optical Cavity Enhanced by a Higher Order Extrapolation

Lock acquisition of a suspended optical cavity can be a highly stochastic process and is therefore nontrivial. Guided lock is a method to make lock acquisition less stochastic by decelerating the motion of the cavity length based on an extrapolation of the motion from an instantaneous velocity measurement. We propose an improved scheme which is less susceptible to seismic disturbances by incorporating the acceleration as a higher order correction in the extrapolation. We implemented the new scheme in a 300-m suspended Fabry-Perot cavity and improved the success rate of lock acquisition by a factor of 30

Approximation Algorithms for Energy Minimization in Cloud Service Allocation under Reliability Constraints

We consider allocation problems that arise in the context of service allocation in Clouds. More specifically, we assume on the one part that each computing resource is associated to a capacity constraint, that can be chosen using Dynamic Voltage and Frequency Scaling (DVFS) method, and to a probability of failure. On the other hand, we assume that the service runs as a set of independent instances of identical Virtual Machines. Moreover, there exists a Service Level Agreement (SLA) between the Cloud provider and the client that can be expressed as follows: the client comes with a minimal number of service instances which must be alive at the end of the day, and the Cloud provider offers a list of pairs (price,compensation), this compensation being paid by the Cloud provider if it fails to keep alive the required number of services. On the Cloud provider side, each pair corresponds actually to a guaranteed success probability of fulfilling the constraint on the minimal number of instances. In this context, given a minimal number of instances and a probability of success, the question for the Cloud provider is to find the number of necessary resources, their clock frequency and an allocation of the instances (possibly using replication) onto machines. This solution should satisfy all types of constraints during a given time period while minimizing the energy consumption of used resources. We consider two energy consumption models based on DVFS techniques, where the clock frequency of physical resources can be changed. For each allocation problem and each energy model, we prove deterministic approximation ratios on the consumed energy for algorithms that provide guaranteed probability failures, as well as an efficient heuristic, whose energy ratio is not guaranteed

Design and analysis of robust controllers for directional drilling tools

Directional drilling is a very important tool for the development of oil and gas deposits. Attitude control which enables directional drilling for the efficient placement of the directional drilling tools in petroleum producing zones is reviewed along with the various engineering requirements or constraints. This thesis explores a multivariable attitude governing plant model as formulated in Panchal et al. (2010) which is used for developing robust control techniques. An inherent input and measurement delay which accounts for the plant's dead-time is included in the design of the controllers. A Smith Predictor controller is developed for reducing the effect of this dead-time. The developed controllers are compared for performance and robustness using structured singular value analysis and also for their performance indicated by the transient response of the closed loop models. Results for the transient non-linear simulation of the proposed controllers are also presented. The results obtained indicate that the objectives are satisfactorily achieved

Requirements Study for System Implementation of an Atmospheric Laser Propagation Experiment Program, Volume II

Program planning, ground support and airborne equipment for laser space communication syste

Dual-Active-Bridge Model and Control for Supporting Fast Synthetic Inertial Action

This article proposes a dual-active-bridge control to support the fast synthetic inertial action in DC microgrids. First of all, the selection of the isolated DC/DC converter to link an energy storage system with the DC bus in a microgrid is analyzed and the advantages of the dual-active-bridge converter controlled by a single-phase shift modulation justify its selection. An active front-end can be then adapted to connect the DC bus with an AC grid. Secondly, this paper presents the design of a discrete PI controller for supporting fast synthetic inertial action. In particular, a discrete dual-active-bridge model based on the transferred power between both converter bridges, which overcomes the approximations of the output current linearization model, is proposed. Moreover, the article introduces a novel equation set to directly and dynamically tune discrete PI parameters to fulfill the design frequency specifications based on the inversion formulae method. In this way, during the voltage/power transients on the DC bus, the controller actively responds and recovers those transients within a grid fundamental cycle. Since the developed set of control equations is very simple, it can be easily implemented by a discrete control algorithm, avoiding the use of offline trial and error procedures which may lead to system instability under large load variations. Finally, the proposed control system is evaluated and validated in PLECS simulations and hardware-in-the-loop tests