Double Control Strategy Research Articles

A double-controller fuzzy scheme for intelligent resource discovery on IaaS cloud systems

A double-controller fuzzy scheme for intelligent resource discovery on IaaS cloud systems

On coherently driven group index of probe pulse at double-frequency regimes: An analytical formulation

The group index and its lineshape of a relatively weak double-resonance probe pulse (signal) propagates through an open doubly driven N-type five-level atomic system are analytically formulated. It is shown that the signal can be controlled by manipulating the driving contribution of the two coupling fields, so that both superluminal and subluminal propagation can take place simultaneously at two different (probe field induced transition) frequency regimes with reduced absorption/gain. Hence the proposed double-control scheme may be exploited to observe the double-switching effect (i.e. from superluminal to subluminal and vice versa) with negligible distortion. In our realization this double-controlling mechanism may be regarded as simultaneous tuning of two knobs, to regulate the group index of the signal at double-frequency regimes.

Semi-active drilling drawworks heave compensation system

Abstract In order to simplify the structure of the ocean drilling heave compensation system and reduce the energy consumption of active drawworks heave compensation system, a new type of semi-active drawworks heave compensation system was designed through structure design, system modeling and internal model PID robust displacement controller design. Then the feasibility of the system was verified by non-linear time domain simulation and experimental study. The structure design realizes decoupling control of heave compensation and automatic bit feed, reduces energy consumption of the system. The system is simplified to build simulation model by lumped mass method and energy conservation principle. The double control scheme of hook displacement closed loop in the outer loop and motor speed closed loop in the inner loop is put forward, the internal model PID robust displacement controller of outer loop is designed. The steady-state deviation of internal model control is zero when the model is matching or mismatching. The dynamic performance and resisting disturbance capacity of the internal model control is better when the filter time constant is smaller. The compensation rate is above 90% by simulation and experimental research results, the compensation effect is good and the system is feasible.

Control of pH process using double-control scheme

Control of pH is mostly needed in continuous process industries and is difficult and challenging due to its time-varying and nonlinear nature of the chemical or biological process. Conventional controllers do not incorporate nonlinear dynamics of the entire pH range (both acid and alkali) and do not show good performance. Dynamics based on specific process nonlinearity of two different ranges is used to design double-control scheme in a feedback structure to enhance the performance of pH process. The mathematical model of pH for a weak acid-strong base is used to design IMC based PID double-controller scheme which provides outstanding set-point tracking and disturbances rejection simultaneously to control pH processes.

A discrete double-controller scheme for delayed processes with both load and set-point disturbances

Using a double-controller strategy and a design approach related to Dahlin’s controller, a new sampled data control scheme is presented that is suitable for handling both set-point change and load disturbances. This control scheme has two controllers, a set-point controller and a load controller, which result in the separation of the load response from the set-point response in a closed-loop system. These two controllers can be designed independently to achieve good system performance for both set-point tracking and load rejection. The control scheme is applicable to processes that can be approximated by first-order plus time delay dynamics. For set-point changes, the set-point controller is a generalized Dahlin controller that has an extra tuning parameter TLC and has more ‘exibility and more robustness than Dahlin’s controller. For load disturbances, the load controller is also a generalized Dahlin controller and shows a significant improvement over the performance of Dahlin’s controller. The new double-controller scheme also alleviates a difficult compromise that the generalized Dahlin controller makes between the set-point tracking performance and load rejection performance. A simulation study is used to evaluate the performance of this new double-controller scheme in the presence of noise and model errors, and to compare it to Dahlin’s controller and the generalized Dahlin controller. The results show that the proposed double-controller scheme is superior to both Dahlin’s controller and the generalized Dahlin controller.

A new modified Smith predictor: the concept, design and tuning

The paper presents a new modified Smith predictor (MSP) for processes with a long time delay. The MSP appears as an extension of the double controller-scheme (DCS) proposed by Tian and Gao. The important feature of the MSP is that the trade-off between disturbance rejection and robustness to variations in process parameters can be adjusted by means of a single free parameter. The main contribution of the paper concerns tuning of the MSP, which relies on a combination of magnitude optimum criterion with process parameterisation based on multiple integrals of the open-loop step response. In a simulation study the performance of the MSP is compared with that of two known controllers for time delay systems, i.e. DCS of Tian and Gao and Hägglund's predictive PI controller. The results show the advantage of the MSP compared to the two other controllers.

Injection Velocity Control of Thermoplastic Injection Molding via A Double Controller Scheme

Injection velocity has been recognized as a key variable in thermoplastic injection molding. Its closed-loop control is, however, difficult due to the complexity of the process dynamic characteristics. The basic requirements of the control system include tracking of a predetermined injection velocity curve (defined by a velocity profile), load rejection, and robustness. It is difficult for a conventional control scheme to meet all of these requirements. Injection velocity dynamics are first analyzed in this paper. Then, a novel double-controller scheme is adopted for the injection velocity control. This scheme allows an independent design of set-point tracking and load rejection and has good system robustness. The implementation of the double-controller scheme for injection velocity control is discussed. Special techniques such as profile transformation and shifting are also introduced to improve the velocity responses. The proposed velocity control has been experimentally demonstrated to be effective for a wide range of processing conditions.

Double-controller scheme for control of processes with dominant delay

A double-controller structure is proposed for control of processes with dominant time delay. In contrast to the Smith predictor, the proposed control scheme contains two controllers, a setpoint controller and a load controller, and a process model. With this structure, the setpoint and load responses of the closed-loop system are no longer coupled, and the two controllers can be separately designed to obtain good performance in both setpoint tracking and load rejections. Any errors resulting from the inevitable mismatch between the model and the process can be viewed as additional load disturbances, and are compensated by the load controller. The load controller is tuned to be insensitive to the model structure and parameters, to accommodate large model uncertainty, for which the standard Smith predictor may give poor regulatory performance and even fail to work. Extensive simulations show that the proposed scheme is superior to the Smith predictor in the presence of large uncertainty in process dynamics.

A Double-Controller Scheme for Controlling Dominant Delay Processes

A double-controller structure is proposed for processes with dominant time delay. It consists of two separate controllers, a set-point controller and a load controller, and a process model. With this structure, the load response of the closed-loop system is decoupled from the set-point response. The two controllers can then be separately designed to obtain good performance both in set-point tracking and in load rejection. The two controllers are taken to be PI controllers for simplicity. The double-controller scheme is insensitive to the process model and superior to the Smith predictor in presence of large process uncertainty.

Double-Controller Scheme for Separating Load Rejection from Set-Point Tracking

In the design of a conventional feedback control system, a difficult compromise has to be made between the set-point tracking performance and load rejection performance. A novel double-controller scheme is proposed in this paper to alleviate this compromise. This control scheme has two controllers, a set-point controller and a load controller, which result in the separation of the load response from the set-point response in a closed-loop system. These two controllers can be designed independently to achieve good system performance for both set-point tracking and load rejection. Also, good robustness of the double-controller scheme to variations in system dynamics can be obtained by properly designing the load controller. The proposed scheme is applied to two difficult problems, set-point tracking in the presence of process uncertainty and control of a process with dominant time delay. The results show that the proposed double-controller scheme is superior to a conventional single controller system.