Controller Development for Closed-Loop Feedback Control of Flows

Stochastic dynamic programming has been. extensively used in the optimization of long term hydrothermal scheduling problems due to its ability to cope with the nonlinear and stochastic characteristics of such problems, and the fact that it provides a closed-loop feedback control policy. Its computational requirements, however, tend to be heavy even for systems with a small number of hydroplants, requiring some sort of modeling manipulation in order to be able to handle real systems. An alternative to closed-loop optimization is an approach that combines a deterministic optimization model with an inflow forecasting model in a partial open-loop feedback control framework. At each stage in this control policy, a forecast of the inflows during the period of planning is made, and an operational decision for the following stage is obtained by a deterministic optimization model. The present paper compares such closed-loop and partial open-loop feedback control policies in long term hydrothermal scheduling, using a single hydroplant system as a case study to focus the comparison on the feedback control performance. The comparison is made by simulation using data from historical and synthetical inflow sequences in the consideration of three different Brazilian hydroplants located in different river basins. Results have demonstrated that the performance of the partial open-loop feedback control policy is similar to that of the closed-loop control policy, and is even superior in dry streamflow periods.

Multi-degree-of-freedom robots are widely used in various industries. In order to improve the stability of multi-degree-of-freedom robots, this paper proposes a motion trajectory optimization method based on PSO optimization algorithm and a closed-loop feedback control method for multi-degree-of-freedom robots based on error feedback. The standard D-H parameter method is used for kinematics analysis, combined with the multi-factor constraint parameter fusion method to establish the closed-loop feedback adaptive control law of the robot, and the robot's pose is adaptively adjusted according to the parameter optimization results to realize the stability control of the robot. The analysis results show that the multi-degree-of-freedom robot control with the analysis method in this paper has less error, strong robustness and accuracy of the kinematics method.

Closed-loop feedback control and command shaping are often used together to achieve superior control performance. In many cases, the feedback control is designed and implemented first. Then, the command shaping is designed to improve the resulting closed-loop dynamics. However, there is an often-overlooked advantage of optimally combining these two control schemes. This study will show that proportional and derivative feedback control can be intelligently used to create a closed-loop system that is particularly advantageous when input shaping is used as a filter outside of the loop. Experimental results are shown to verify the theoretical developments.

Based on a continuum theory, we investigate the manipulation of the nonequilibrium behavior of a sheared liquid crystal via closed-loop feedback control. Our goal is to stabilize a specific dynamical state, that is, the stationary "flow alignment," under conditions where the uncontrolled system displays oscillatory director dynamics with in-plane symmetry. To this end we employ time-delayed feedback control (TDFC), where the equation of motion for the ith component q(i)(t) of the order parameter tensor is supplemented by a control term involving the difference q(i)(t)-q(i)(t-τ). In this diagonal scheme, τ is the delay time. We demonstrate that the TDFC method successfully stabilizes flow alignment for suitable values of the control strength K and τ; these values are determined by solving an exact eigenvalue equation. Moreover, our results show that only small values of K are needed when the system is sheared from an isotropic equilibrium state, contrary to the case where the equilibrium state is nematic.

Track switches are essential in order to enable railway vehicles to change routes however they are also the largest single cause of failure on the railway network and remain a single point of failure. This thesis focusses on modelling and fault tolerant control of a new type of electromechanical railway track switch. Unlike conventional track switch machines, this switch needs closed loop feedback control. Firstly, a detailed simulation model of the switch is developed and validated against experimental results. Two model-based control designs are then developed and tested: a classical cascaded P/PI controller and a modern state feedback LQR controller. The two controllers are compared and it is found that, whilst there are some performance differences, both meet the requirements for use in a redundantly actuated track switch. Following this, a fault tolerant control scheme for sensor faults is developed and validated using fault detection, identification and accommodation methods applied to a detailed non-linear simulation model and then validated on the experimental test rig. The results demonstrate that using a reliable fault tolerant control configuration could increase the availability and reliability of the switch in the presence of sensor faults. Finally, a fault tolerant control approach to actuator faults on the switch with triplex redundancy is developed and validated. In order to achieve this, a dynamic model of a railway track is developed in simulation as the basis for load application to the system. Three parallel actuators with their associated controllers are used to actuate the switch showing good performance in meeting the position control requirements. Different actuator faults are applied and their control performance results are shown. A summary of the control performance is also presented highlighting the differences in performance with different permutations of actuator faults. Overall, it is shown that redundancy in actuation with a suitable control scheme provides benefits in achieving post-fault availability of a redundantly actuated electromechanical railway track switch in the presence of actuator faults.

Maximal L-regularity for an abstract evolution equation with applications to closed-loop boundary feedback control problems

The paper is devoted to the application of fractional calculus concepts to modeling, identification and control of discrete-time systems. Fractional difference equations (FAE) models are presented and their use in identification, state estimation and control context is discussed. The fractional difference state-space model is proposed for that purpose. For such a model stability conditions are given. A fractional Kalman filter (FKF) for this model is recalled. The proposed state-space model and fractional order difference equation are used in an identification procedure which produces very accurate results. Finally, the state-space model is used in closed-loop state feedback control form together with FKF as a state estimator. The latter is also given in an adaptive form together with FKF and a modification of recursive least squares (RLS) algorithm as a parameters identification procedure. All the algorithms presented were tested in simulations and the example results are given in the paper

When an equilibrium state of a physical or biological system suffers a loss of stability (e.g., via a bifurcation), it may be both possible and desirable to stabilize the equilibrium via closed-loop feedback control. Significant effort has been devoted towards using such control to prevent oscillatory or chaotic behavior in dynamical systems, both continuous-time and discrete-time. Regarding control in discrete-time systems, most prior attempts to stabilize unstable equilibria require that the system be perturbed once during each time step. However, there are examples of systems for which this is neither feasible nor possible. In this paper, we analyze a restricted feedback control method for discrete-time systems (restricted in the sense that the controller's perturbations may be applied only in every other time step). We apply our theoretical analysis to a specific example from cardiac electrophysiology in which this sort of restricted feedback control is especially relevant. The example is a useful test case for the theory, and one for which an experimental setup is rather straightforward.

The wet granulation route of tablet manufacturing in a pharmaceutical manufacturing process is very common due to its numerous processing advantages such as enhanced powder flow and decreased segregation. However, this route is still operated in batch mode with little (if any) usage of an automatic control system. Tablet manufacturing via wet granulation, integrated with online/inline real time sensors and coupled with an automatic feedback control system, is highly desired for the transition of the pharmaceutical industry toward quality by design as opposed to quality by testing. In this manuscript, an efficient, plant-wide control strategy for an integrated continuous pharmaceutical tablet manufacturing process via wet granulation has been designed in silico. An effective controller parameter tuning strategy involving an integral of time absolute error method coupled with an optimization strategy has been used. The designed control system has been implemented in a flowsheet model that was simulated in gPROMS (Process System Enterprise) to evaluate its performance. The ability of the control system to reject the unknown disturbances and track the set point has been analyzed. Advanced techniques such as anti-windup and scale-up factor have been used to improve controller performance. Results demonstrate enhanced achievement of critical quality attributes under closed-loop operation, thus illustrating the potential of closed-loop feedback control in improving pharmaceutical tablet manufacturing operations.

Real-time observation and control of particle size and production rate in microfluidic devices are important capabilities for a number of applications, including the production, sorting, and manipulation of microbubbles and droplets. The production of microbubbles from flow-focusing microfluidic devices had been investigated in multiple studies, but each lacked an approach for on-chip measurement and control of microbubble diameter in real time. In this work, we implement a closed-loop feedback control system in a flow-focusing microfluidic device with integrated on-chip electrodes. Using our system, we measure and count microbubbles between 13 and 28 m in diameter and control their diameter using a proportional-integral controller. We validate our measurements against an optical benchmark with and achieve a maximum production rate of /s. Using the feedback control system, the device enabled control in microbubble diameter over the range of 14-24 m.

In order to improve the efficiency of underground mining and tunneling operations and to realize automatic drilling, it is necessary to develop the automation system for large drill jumbos. This work focuses on one such mining drill jumbo which is actually a redundant robotic manipulator with eight degrees of freedom, because it has six revolute joints and two prismatic joints. To realize the autonomous drilling operation, algorithms are proposed to calculate the desired pose of the end-effector and to solve the inverse kinematics of the drill jumbo, which is one of the key issues for developing the automation system. After that, a control strategy is proposed to independently control the eight joint variables using PID feedback control approaches. The simulation model is developed in Simulink. As the closed-loop controllers corresponding to all joints are local and independent of each other, the whole system is not a closed-loop feedback control. In order to estimate the possible maximal pose error, the analysis of the pose error caused by the errors of the joint variables is conducted. The results are satisfactory for mining applications and the developed automation system is being applied in the drill jumbos built by Mining Technologies International Inc.

This paper deals with a theoretical analysis and experiments of a non-contact active feedback control, which is based on flow and aero-dynamical control, to suppress a leakage-flow-induced vibration of translational 1DOF system. In the proposed active feedback control method, the leakage-flow-induced vibration is suppressed by using a movable plate, as an actuator, set at inlet and outlet of the passage to control fluid force acting on the controlled target and fluid flow in the passage actively. The strategy of this active control method is based on active flow and aero-dynamical control which cancels the exciting fluid force acting on the rigid body. The root locus and critical flow velocity with and without control are calculated with changing the controller gain and phase-shift to evaluate the control performance, and experiments are conducted to verify the theoretical calculations. As a result, it is indicated that the leakage-flow-induced vibration is effectively suppressed by the proposed non-contact active control method and the suppression effect is very sensitive to the phase-shift and actuator position. For the inlet flow control, the vibration is effectively suppressed when the phase-shift is positive, and for the outlet flow control, the vibration is suppressed when the phase-shift is negative. The suppression effect of the inlet flow control is greater than that of outlet flow control.

This paper studies the problem of target control and how a virtual ellipsoid can avoid the static obstacle. During the motion to the target set, the virtual ellipsoid can achieve a motion under collision avoidance by keeping the distance between the ellipsoid and obstacle. We present solutions to this problem in the class of closed-loop (feedback) controls based on Hamilton–Jacobi–Bellman (HJB) equation. Simulation results verify the validity and effectiveness of our algorithm.

Percutaneous interventions have attracted significant interest in recent years, but most approaches still rely on straight line trajectories between an entry site and a soft tissue target. Thus, to this day, a flexible probe able to bend along predefined curvilinear trajectories within a highly compliant medium without buckling is still an open research challenge. In this paper, we describe the concept of a “programmable bevel” tip, which is inspired by the ovipositor of certain wasps: the offset between two parts of a probe determines the steering direction of the tip thanks to a set of bevels included at the tip of each segment. A kinematic model of the flexible probe and programmable bevel arrangement is derived. Several parameters of the kinematic model are calibrated experimentally using our first prototype of the flexible probe, codenamed STING. Open- (feed-forward) and closed-loop (feedback) control strategies are then derived and implemented in simulation using the chained form representation, originally developed to control car-like robots. Simulated results demonstrate accurate two-dimensional needle steering in the presence of velocity, position, and initial posture disturbances.

Voltage source inverters (VSIs) with output LCL filters are the key interfaces for today's distributed energy resource. There are mainly two groups of current control methods of a VSI: direct error tracking control with PWM, and closed-loop feedback control. Direct current error control, such as predictive control and hysteresis control, has some drawbacks like system parameter sensitivity, variable switching frequency, etc. On the other hand, the closed-loop feedback control could eliminate many drawbacks of direct error tracking PWM method while with the limited of control bandwidth. Closed-loop current control of a VSI can be of two types namely single-loop and multiple-loop VSI control. According to the feedback currents or number of current sensors used, the closed-loop current control can also be classified into single current sensor and two current sensors feedback system. The stability and dynamic performance of these control schemes differs from each other. However, a thorough understanding of the differences and the reasons behind is not available. This paper presents a comparative analysis of different closed-loop current control method for a VSI with output LCL filters. Effect of LCL filter parameter variation on their stability is investigated. Recently proposed generalized closed-loop control (GCC) platform is used to explain the comparison results. Simulation and experimental results of different VSI control systems are presented.