Secondary Control Loop Research Articles

PARTIC: Power-Aware Response Time Control for Virtualized Web Servers

Both power and performance are important concerns for enterprise data centers. While various management strategies have been developed to effectively reduce server power consumption by transitioning hardware components to lower power states, they cannot be directly applied to today's data centers that rely on virtualization technologies. Virtual machines running on the same physical server are correlated because the state transition of any hardware component will affect the application performance of all the virtual machines. As a result, reducing power solely based on the performance level of one virtual machine may cause another to violate its performance specification. This paper proposes PARTIC, a two-layer control architecture designed based on well-established control theory. The primary control loop adopts a multi-input multi-output control approach to maintain load balancing among all virtual machines so that they can have approximately the same performance level relative to their allowed peak values. The secondary performance control loop then manipulates CPU frequency for power efficiency based on the uniform performance level achieved by the primary loop. Empirical results demonstrate that PARTIC can effectively reduce server power consumption while achieving required application-level performance for virtualized enterprise servers.

Multiple Degrees of Freedom Control for Cascade Processes with Time Delay

A new cascade control of multiple degrees of freedom program based on modified internal model control is proposed for chemical and industrial cascade processes. Because the set-point tracking and disturbance rejection in the secondary control loop exercise influence on performance of primary loop simultaneously, they are decoupled completely and can be adjusted independently. A disturbance observer is added in the primary loop which realizes the decoupling control between set-point tracking and disturbance rejection, and there is no tradeoff any more. Simple and effective analytical method is adopted to devise the controllers. Finally, simulations example demonstrates the validity of the proposed control scheme.

Analytical Design for Parallel Cascade Control of Multiple Degrees of Freedom

A new parallel cascade control program of multiple degrees of freedom is proposed for chemical and industrial cascade processes. Firstly, the two degree of freedom IMC structure is adopted in the secondary control loop, and the set-point tracking and disturbance rejection are decoupled, therefore, the influence on performance of primary loop because of the coupling between the set-point tracking and disturbance rejection in the secondary loop is reduced. Then, based on a modified structure of the Smith predictor control, the primary loop realizes the decoupling control between set-point tracking and disturbance rejection, and simple and effective analytical method is adopted to devise the controllers. Finally, simulations example demonstrates the validity of the proposed control scheme.

PAUC: Power-Aware Utilization Control in Distributed Real-Time Systems

CPU utilization control has recently been demonstrated to be an effective way of meeting end-to-end deadlines for distributed real-time systems running in unpredictable environments. However, current research on utilization control focuses exclusively on task rate adaptation, which cannot effectively handle rate saturation and discrete task rates. Since the CPU utilization contributed by a real-time periodic task is determined by both its rate and execution time, CPU frequency scaling can be used to adapt task execution times for power-efficient utilization control. In this paper, we present PAUC, a two-layer coordinated CPU utilization control architecture. The primary control loop uses frequency scaling to locally control the CPU utilization of each processor, while the secondary control loop adopts rate adaptation to control the utilizations of all the processors at the cluster level on a finer timescale. Both the two control loops are designed and coordinated based on well-established control theory for theoretically guaranteed control accuracy and system stability. Empirical results on a physical testbed demonstrate that our control solution outperforms a state-of-the-art utilization control algorithm by having more accurate control and less power consumption. Extensive simulation results also show that our solution can significantly improve the feasibility of utilization control.

Cascade control parameterization for time delay plants

In industrial control engineering practice the cascade controller scheme represents a standard solution for plants with considerable time delays. The compensation of time delay impact is based on finding a purposely selected secondary control loop with a "slave" controller, as prompt as possible in response, and subordinated to a "master" controller feedback. An application of affine parameterization has been developed to derive the set of all stabilizing controllers for this control scheme applied to plants with significant delays. The parameterization technique, making use of the so-called RQ meromorphic functions, represents a novel approach to designing dynamics of cascade control that results in controller transfer functions with delays. Owing to the use of timeshifted data, this kind of controllers is referred to as anisochronic ones. Copyright © 2007 IFAC

Analytical method of PID controller design for parallel cascade control

An analytical method of PID controller design is proposed for parallel cascade control. Firstly, a general structure for parallel cascade control is proposed that takes both setpoint and load disturbance responses into account. Analytical tuning rules for the PID controllers are then derived for the general process model by employing the IMC design procedure. The proposed method offers a simple and effective way to obtain the PID controller rules for parallel cascade control system which takes into account the interaction between primary and secondary control loops. The simulation results illustrate the application of the proposed method and demonstrate its superiority compared to several alternatives.

Performance limitation improvement for a highly-integrated chemical process

Control systems can have inherent performance limitations that are independent of the controller design ( Seron et al., 1997). However, recent work ( Cao, Rossiter and Owens, 1998a) shows that such performance limitation can be improved by introducing several appropriately selected secondary control loops. Here, selection of secondary manipulated variables and measurements for thesesecondary controlloops iscritical to the performance improvements. In this work, a generic selection method is presented. This method represents the selection as a Linear Quadratic Gaussian problem and uses a global optimization technique, the Branch-and-Bound method to select the best control structure without exhaustive evaluation of all possible secondary control input/output combinations. A case study for a highly integrated chemical plant — the HDA process shows that by closing two temperature controlloops in the benzene column, the performance of the primary outputs: benzene production rate and purity of the process is dramatically improved.