Time Delay In Control Loop Research Articles

Robust Controller Synthesis and Analysis in Inverter-Dominant Droop-Controlled Islanded Microgrids

This work investigates the problem of controller design for the inverters in an islanded microgrid. Robust μ-synthesis controllers and local droop controllers are designed to regulate the output voltages of inverters and share power among them, respectively. The designed controllers alleviate the need for additional sensors to measure the states of the system by relying only on output feedback. It is shown that the designed μ-synthesis controller properly damps resonant oscillations, and its performance is robust to the control-loop time delay and parameter uncertainties. The stability of a droop-controlled islanded microgrid including multiple distributed generation (DG) units is analyzed by linearizing the nonlinear power flow model around the nominal operating point and applying theorems from linear algebra. It is indicated that the droop controller stabilizes the microgrid system with dominantly inductive tie-line impedances for all values of resistive-inductive loads, while for the case of resistive-capacitive loads the stability is conditioned on an upper bound on the load susceptances. The robust performance of the designed μ-synthesis controller is studied analytically, compared with the similar analysis in an H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> control (benchmark) framework, and verified by simulations for a four DG benchmark microgrid. Furthermore, the robustness of the droop controllers is analyzed by Monte Carlo simulations in the presence of local voltage fluctuations and phase differences among neighboring DGs.

СИНТЕЗ І НАПІВНАТУРНЕ МОДЕЛЮВАННЯ СИСТЕМИ УПРАВЛІННЯ ГІДРОПРИВОДУ З КОВЗНИМИ РЕЖИМАМИ

We consider the construction of servo-hydraulic drive of volumetric regulation system control relay type. A volumetric hydraulic actuator is used in agriculture, construction, transport machine, coal harvesters, rigs, airplanes, military machinery, etc. Hydraulic bulk drive have several advantages, most important of which are the possibility of obtaining a great effort, smooth operation, low inertia hydraulic machines, relatively high efficiency (up to 80%), high reliability. At the same time, he has a number of drawbacks, chief of which is the change in the properties of the working liquid during operation and under the influence of external factors. The disadvantages include loss of hydraulic oil, contamination of the liquid during operation. These shortcomings can lead to loss of quality control loss of accuracy, speed of working off of the set of control actions. One of the classes of systems which structurally provide high dynamic accuracy, there are systems operating in the sliding mode. In addition, due to the introduction of sliding mode in some cases it is possible to increase the degree of astaticism of the system, and hence to improve the playback quality of the input job. Proposed the implementation of a control system of hydraulic drive, is invariant to parametric and external disturbances through the use of sliding modes. To study the proposed control system with hydraulic drive constructed model of the developed system, which is the natural object of a hydraulic drive using its mathematical model, at the same time the control system is implemented physically is one that can be used in a real device. Hill simulation has allowed answering the questions of realization of sliding modes when controlling hydraulic drive of volumetric regulation through a DC motor. The behavior of a control system of hydraulic drive when changing the parameters of the control object (the moment of inertia, viscosity), which showed that the change of damping ratio within a wide range (up to 50% of the design) does not disrupt the sliding mode, the quality of the regulatory process does not deteriorate significantly. At the same time, the change to 100% conversion rate can lead to instability of the control system that allows to make a conclusion about the establishment of the position controller on the lesser of the possible damping coefficients. Also a study of digital implementation of the synthesized control law by introducing in the control loop time delay has been carried out, which is possible with the use of microprocessor-based calculator.

The time-delay coupling nonlinear effect in sky-hook control of vibration isolation systems using Magneto-Rheological Fluid dampers

The effect of the nonlinearity and time delay in the Magneto-Rheological fluid (MRF) damper on an isolator system is studied in this study. The mechanical model of the control force of the MRF damper in the skyhook control is introduced as nonlinear piecewise function. The displacement transmissibility of the isolation system is solved by employing the Averaging method. The isolation effectiveness for different values of control coefficients is demonstrated by the displacement transmissibility. The increasing of damping control force of MRF damper reduces the displacement transmissibility to a low level while time delay has different functions in different frequency bands. Moreover, by the analysis of eigenvalues in the manifold given by Averaging method, the unstable and stable region of the steady state can be decided on the parameter plane, which provides the bifurcation criterion induced by nonlinearity and time delay. The main results from theoretical analysis and experimental prototype give an insight into the analysis and design of semi-active control with time delay in control loop and signal processing for isolator system by exploiting nonlinear benefits in vibration suppression effectiveness.

Duty Ratio Predictive Control Scheme for Digital Control of DC-DC Switching Converters

The control loop time delay caused by sampling, the zero-order-holder effect and calculations is inevitable in the digital control of dc-dc switching converters. The time delay will limit the bandwidth of the control loop and therefore degrade the transient performance of digital systems. In this paper, the quantization time delay effects with different time delay values based on a generic second-order system are analyzed. The conclusion that the bandwidth of digital control is reduced by about 20% with a one cycle delay and by 50% with two cycles of delay in comparison with no time delay is obtained. To compensate the time delay and to increase the control loop bandwidth, a duty ratio predictive control scheme based on linear extrapolation is proposed. The compensation effect and a comparison of the load variation transient response characteristics with analogy control, conventional digital control and duty ratio predictive control with different time delay values are performed on a point-of-load Buck converter by simulations and experiments. It is shown that, using the proposed technique, the control loop bandwidth can be increased by 50% for a one cycle delay and 48.2% for two cycles of delay when compared to conventional digital control. Simulations and experimental results prove the validity of the conclusion of the quantization effects of the time delay and the proposed control scheme.

Wind tunnel test of an active mass damper for bridge decks

An active mass damper is implemented to a bridge section model test in a wind tunnel to enhance the flutter stability. Servo motors controlling the rotational motion of control masses serve as actuators. The torque generated by rotational acceleration is used to control the angular motion of the section model. The mechanical parameters of the uncontrolled and the controlled structures are identified by the modified Ibrahim time domain (MITD) method. The deterioration of the control performance through control loop time delay is determined. The critical wind speeds are determined experimentally by wind tunnel tests and numerically by flutter analysis. The experimental and numerical results are in good agreement. The experimental results underline the applicability of an active mass damper and can be seen as a first step towards an implementation in real bridges.

Improvement of transient stability limit in power system transmission lines using fuzzy control of FACTS devices

The objective of this paper is to investigate the application of FACTS devices to increase the maximum loadability of the transmission lines which may be constrained by a transient stability limit. Hence, the on-line fuzzy control of the superconducting magnetic energy storage (SMES) and the static synchronous series compensator (SSSC) are suggested. The fuzzy rule-bases are defined and explained. The validity of the suggested control strategies are confirmed by simulation tests. The simulation results show that by the use of the proposed method, the line power transfer can be increased via the improvement of the transient stability limit. Finally, the effect of the control loop time delay on the performance of the controller is presented.

Active vibration control synthesis for the control of flexible structures mast flight system

Pole-zero modeling and active vibration control synthesis for the Control of Flexible Structures Mast Flight System (COFS-I) are discussed. An analytical transfer function from the tip-mounted actuator force to the beam deflection at various sensor locations is derived for control synthesis. A new concept of generalized structural filtering for flexible-mode stabilization is applied to the COFS-I. The simplicity and practicality of the classical transfer-function approach to active structural vibration control are demonstrated for the COFS-I. In particular, nonminimum-phase structural filtering is proposed for the noncolocated control experiment of the COFS-I. The effects of proof-mass actuator dynamics and control-loop time delay on the phase/gain stabilization of the flexible modes are also discussed.