Primary Control Loop Research Articles

Fully Integrated Capacitive DC–DC Converter With All-Digital Ripple Mitigation Technique

This paper presents an adaptive all-digital ripple mitigation technique for fully integrated capacitive dc-dc converters. Ripple control is achieved using a two-pronged approach where coarse ripple control is achieved by varying the size of the bucket capacitance, and fine control is achieved by charge/discharge time modulation of the bucket capacitors used to transfer the charge between the input and output, both of which are completely digital techniques. A dual-loop control was used to achieve regulation and ripple control. The primary single-bound hysteretic control loop achieves voltage regulation and the secondary loop is responsible for ripple control. The dual-loop control modulates the charge/discharge pulse width in a hysteretic variable-frequency environment using a simple digital pulse width modulator. The fully integrated converter was implemented in IBM's 130-nm CMOS process. Ripple reduces from 98 to 30 mV, when ripple control secondary loop is enabled for a load of 0.3 V and 4 mA without significantly impacting the converter's core efficiency. Measurement results show constant ripple, independent of output voltage. The converter achieves a maximum efficiency of 70% for Vin= 1.3 V and Vout= 0.5 V and a maximum power density of 24.5 mW/mm2, including the areas for the decoupling capacitor. The maximum power density increases to 68 mW/mm2 if the decoupling capacitor is assumed to be already present as part of the digital design.

Reactive Power Compensation in Single-Phase Operation of Microgrid

A coordinated control of distributed generators (DG) and distribution static compensator (DSTATCOM) in a microgrid is proposed in this paper. With high penetration of distributed sources and single-phase operation of the system, voltage unbalance can often go beyond the acceptable limit. With the feeders geographically spread out, it is not always possible to achieve reactive compensation at optimum location with the three-phase devices. In this paper, a simple control strategy for DSTATCOM with communication in loop is proposed. The proposed reactive compensation technique is based on the voltage sag and the power flow in the line. The power flow and the voltage at different locations of the feeders are communicated to the DSTATCOM to modulate the reactive compensation. The single-phase DSTATCOM compensates for the reactive power deficiency in the phase while the DGs supply “maximum available active power.” During reactive power limit of the DG, the “maximum available active power” is fixed to a value lower than maximum active power to increase reactive power injection capability of the DGs. A primary control loop based on local measurement in the DSTATCOM always ensures a part of reactive compensation in case of communication failure. It is shown that the proposed method can always ensure to achieve acceptable voltage regulation. The data traffic analysis of the communication scheme and closed-loop simulation of power network and communication network are presented to validate the proposed method.

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.

Current sensorless quick charger for lithium-ion batteries

An efficient, simple and low cost quick charger based on the double-loop controller is proposed for the charging of lithium-ion (Li-ion) batteries. With positive and negative feedback of the battery voltage, charging profile similar to the constant current and constant voltage (CC–CV) charging strategy can be performed without actually sensing the charging current. The charging time can easily be shortened by raising the level of saturation in the primary voltage control loop. Experimental results are included to demonstrate the effectiveness of the battery charger. The charger could be a low cost and high performance replacement for existing Li-ion battery chargers.

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.

Robust low-order controller design for multi-modal power oscillation damping using flexible AC transmission systems devices

Damping of multi-modal oscillation through supplementary control of a single flexible AC transmission system (FACTS) device is illustrated here. This often requires multiple feedback signals in a centralised multi-input single-output framework for which extension of the classical control design approaches is not straight forward. Past contributions have either focused on decentralised design of low-order PSS in an SISO or MIMO framework; or alternatively, on robust control design techniques which of course, result in higher order controllers. An attempt to design a fixed (low)-order controller, which is robust and is able to damp multiple swing modes with a single FACTS device is presented. The control design problem is formulated as a multi-objective parameter optimisation and solved using a standard evolutionary optimisation technique. Possible post-contingency operating conditions are considered explicitly during the design phase itself to reduce the conservativeness. The present exercise is a step forward towards use of wide area measurement systems for closed-loop supplementary control (around the primary voltage and/or power flow control loop) of the FACTS devices to improve the transfer capacity of the existing corridors.

Nonlinear model predictive control of SOFC based on a Hammerstein model

To protect solid oxide fuel cell (SOFC) stack and meet the voltage demand of DC type loads, two control loops are designed for controlling fuel utilization and output voltage, respectively. A Hammerstein model of the SOFC is first presented for developing effective control strategies, in which the nonlinear static part is approximated by a radial basis function neural network (RBFNN) and the linear dynamic part is modeled by an autoregressive with exogenous input (ARX) model. As we know, the output voltage of the SOFC changes with load variations. After a primary control loop is designed to keep the fuel utilization as a steady-state constant, a nonlinear model predictive control (MPC) based on the Hammerstein model is developed to control the output voltage of the SOFC. The performance of the MPC controller is compared with that of the PI controller developed in [Y.H. Li, S.S. Choi, S. Rajakaruna, An analysis of the control and operation of a solid oxide fuel-cell power plant in an isolated system, IEEE Trans. Energy Convers. 20 (2) (2005) 381–387]. Simulation results demonstrate the potential of the proposed Hammerstein model for application to the control of the SOFC, while the excellence of the nonlinear MPC controller for voltage control of the SOFC is proved.

Automatic Gain Controller for Variable Speed Wind Turbines

This paper presents a novel controller for DFIG based wind parks, designed to achieve more efficient voltage regulation, reactive power compensation and to enhance the transient stability margin of the interconnected power system. The supervisory-secondary voltage control is used to generate the local voltage reference, providing an improved overall voltage profile, while combining an automatic gain controller (AGC) to improve the transient response of the primary control loop. The controller is implemented and tested with a power system comprising of a lumped, fundamental frequency model of a DFIG based wind park, and hydro and diesel generators connected to the electric grid. The performance of the controller was investigated for both steady-state improvements as well as under extreme contingencies to demonstrate its benefits.

A simple dynamic model of the primary circuit in VVER plants for controller design purposes

A simple low dimensional nonlinear dynamic model of the primary circuit in a VVER-type nuclear power plant is developed from first engineering principles that is able to capture the most important dynamics of the system in normal operating modes. The model includes the description of the main control loops in the system, too. The model has been verified and validated by using measured data from three VVER-440 units of Paks Nuclear Power Plant in Hungary, and a good fit has been obtained. This qualifies the model to be the basis for the integrated re-design of the primary control loops.

A Novel Method for Selective Harmonic Elimination in Power Electronic Equipment

The algorithms for adaptive canceling of selected harmonic components have been well developed in digital signal processing. In those applications, "filtering" is a primary objective. However, in power electronic applications control, with objectives like fast response of system on reference and disturbance change, is of primary importance. This paper provides a novel and a systematic design approach for applying signal processing methods (like modified adaptive selective harmonic elimination algorithms) as an addition to conventional control. Thus, both control objectives like fast transient response and efficient harmonic (disturbance) filtering are achieved. The filtering algorithm does not interfere and has minimal impact on the stability of the primary control loop. Its sole function is to eliminate undesirable higher harmonic components from selected variable (current or voltage) and it requires only knowledge of the frequency of the component to be eliminated. The methodology is applicable for a wide range of equipment like uninterrupted power systems, regenerative converters, active power filters, etc. The application of the proposed method in a regenerative voltage source converter for dead time compensation is used as an example for illustrating its effectiveness and design procedure

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.

Simplified approach for modelling pilot pursuit control behaviour in multi-loop flight control tasks

A control-theoretic procedure for modelling human pilot pursuit control behaviour is presented. The procedure allows for the development of human pilot behavioural models in multi-loop flight control tasks in a simplified framework emphasizing frequency-domain techniques. Beginning with the primary control loops, each control loop is closed using a combination of output-rate feedback and output-error feedback. It is demonstrated that this approach can accommodate any vehicle dynamics that can be stabilized by a human pilot. In addition, the modelling approach identifies vehicle dynamics that approach the limits of human pilot controllability. The well-documented increase in pilot effective time delays that have been shown to accompany vehicle dynamics requiring lead compensation is also replicated by this modelling approach. A method for predicting handling-qualitiy levels that would be assigned to a particular vehicle and task is presented. A visual cue model is included, which can approximate the effects of degraded visual cues. It is shown that this model can be used to reproduce the three most important measurable effects of visual cue quality upon human operator dynamics, namely, an increase in ‘effective’ pilot time delay, a decrease in crossover frequency, and an increase in error-injected remnant. The ability of the modelling procedure to accommodate different levels of pilot aggressiveness in completing manoeuvres is demonstrated. Finally, an application to a multi-axis rotorcraft flight control problem is presented.

Modeling the effects of display quality upon human pilot dynamics and perceived vehicle handling qualities

A model-based technique addressing the effect of display or visual scene quality upon human pilot dynamics is introduced. The technique builds upon a methodology proposed for the preliminary assessment of flight simulator fidelity which uses a structural model of the human pilot. This model is incorporated in what is termed the primary control loop(s) for the task at hand. It is shown that the measured effects of degradations in display quality upon human pilot dynamics can be modeled by simple reductions in the gains associated with error and proprioceptive signals in the structural model. A control theoretic rationale for these gain reductions is presented. The effect of display quality upon perceived handling qualities is discussed and demonstrated in a simple example. Although the research had its genesis in flight simulator fidelity studies, the modeling procedure is applicable to any continuous control task involving degraded visual conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Closed-loop assessment of flight simulator fidelity

An analytical methodology is presented for the preliminary assessment of piloted flight simulator fidelity. The hypothesis that forms the central theme of the methodology is that many major simulator fidelity problems stem from simulator limitations that adversely affect the pilot's innermost feedback control loop, referred to here as the primary control loop. This loop is the most critical in terms of task performance and the pilot's evaluation of vehicle handling qualities. The proposed methodology, based on a pilot/vehicle analysis of the vehicle and tasks being simulated, has the potential for serving as a tool for the rapid diagnosis of simulator fidelity problems. Selected results from experiments involving both flight test and piloted simulation of a UH-60A rotorcraft in a pair of demanding vertical and lateral hover tasks are used to exercise the methodology and indicate its potential.

Improved process conditioning using internal control loops

Abstract Singular-value analysis is employed in the development of processes displaying good controllability properties. Excess manipulatable variables may be used in the form of internal control loops which enhance the process conditioning, giving improved performance in the primary control loops of a conventional multi-loop control system.

Automatic Generation Control of an Interconnected Power System Considering Generation Rate Constraint and Governor Deadband

The paper records the investigation of the effect of both the speed governor deadband and the generation rate constraint (GRC) on an optimal integral controller for the automatic generation control (AGC) of an interconnected power system. The effective application of the eigenvalue method for optimizing the primary control loop has been discussed. The investigation reveals that the presence of the speed governor deadband (DB) deteriorates the dynamic response considerably if the GRC is neglected but in the presence of the GRC, the deterioration in the dynamic response is tolerable. The present investigation compares the performance of the optimal integral controller with that of the Fosha-Elgerd optimal controller in the presence of the speed governor deadband.

Governing features and performance of the first 600-MW drogenerating unit at grand coulee

The Grand Coulee Power Complex contributes a new strong influence on system dynamics and control. Addition of the Third Powerplant, with the largest hydrogenerating units in the world, is an important feature. Its function is combined with those of the initial complement of generating units, pumping units, and pump/generating units. In this paper are described the design objectives and recent verification by field tests of the governor characteristics sought to benefit system dynamics, to coordinate all generation under local computer control in response to a single system control signal, and to effectively utilize the inherent capabilities of hydropower for daily peaking as well as for system control. The primary control loops for the system control hierarchy, those of the prime mover governors, are given special features for rapid response to their primary signals while maintaining single-time-constant response to local computer control.

On the speed of response of a model-reference adaptive control system†

An analytical evaluation of the adaptive loop response of a model-reference adaptive control system is presented using sinusoids as a test signal. A schematic diagram of the feedback system containing a primary control loop and an adaptive control loop are given.

MAGNETIC TORQUING SCHEME

T note presents a simple scheme to use the earth's magnetic field as an angular momentum reversal device in the attitude control of satellites. The basic control concept involved is the use of momentum storage devices supplemented on a discontinuous basis by magnetic torques for desaturation purposes. Reaction wheels are used to attitude control the vehicle by storing angular momentum, and the magnetic torques are used to remove angular momentum from the system. The system presented here performs only logical (not arithmetic) computations based upon angular momentum and magnetic field measurements and, therefore, is a simplification over the control techniques discussed in Refs. 2 and 3. This magnetic momentum removal system requires only a simple threshold measurement of both the reaction wheel speeds and the body axis components of the earth's magnetic field. These signals are combined using some simple logical operations to produce constant control moments. The concept discussed below is for three-axis attitude stabilization as opposed to those which control a spin stabilized vehicle. A block diagram of the attitude control system under consideration is shown in Fig. 1. The block diagram shows the primary control loop, consisting of attitude sensors, compensation, and reaction wheels to control the body rotational dynamics, and the magnetic torquing system, consisting of magnetometers, logic, and magnetic moment generators. Because of disturbance torques acting on the orbiting satellite, the reaction wheel angular momentum storage will be fluctuating periodically with a component of secular angular momentum buildup. The function of the magnetic system is to remove this secular component of angular momentum. A magnetic dipole moment in a magnetic field experiences a torque given by the cross product of the magnetic moment and the magnetic field vector. Written out in body coordinates, this relationship becomes

Adaptive control through sinusoidal response

An investigation has been made in the application of sinusoidal techniques to adaptive feedback control systems. The adaptive feature of this approach is an automatic gain control. These systems contain two loops: a basic or primary control loop and an adaptive control loop. The forward-path gain of the basic loop is adjusted by the adaptive loop. A sine wave test signal is added continuously to the basic loop input and to a model. The phase shift or the amplitude of the basic loop output is measured by an adaptive computer which adjusts the forward-path gain in an attempt to hold the measured amplitude or phase-shift constant. This paper contains derivations of the adaptive loop response to changes in the process gain factor for several cases. Some of the considerations pertaining to the design of the adaptive control loop are also given.