Periodic Load Disturbances Research Articles

Virtual coupling control of photovoltaic-energy storage power generation system for efficient power support

The key to achieving efficient and rapid frequency support and suppression of power oscillations in power grids, especially with increased penetration of new energy sources, lies in accurately assessing the inertia and damping requirements of the photovoltaic energy storage system and establishing a controllable coupling relationship between the virtual synchronous generator and the main network. In this paper, the inertia and damping requirements of the photovoltaic energy storage system are estimated using frequency safety warnings and power oscillation suppression constraints. Furthermore, the oscillation characteristics of the power system, which include photovoltaic and energy storage in the presence of periodic load disturbances, are analyzed. Based on this analysis, a coupled virtual synchronous controller for energy storage is proposed. This controller employs a forced oscillation suppression technique through natural frequency shifting, and establishes a controllable power coupling relationship between the photovoltaic energy storage system and the main network to achieve the desired frequency shift. Finally, a simulation system incorporating conventional generators and a photovoltaic energy storage system controlled with the proposed strategy is built to test the frequency support and power oscillation suppression behaviors of the grid-connected power generation system.

Fixed-/Preassigned-Time Stability Control of Chaotic Power Systems

A power system shows chaotic oscillation when it is subjected to periodic load disturbance, which makes it a challenging and interesting problem for stability control of chaotic power system. In this paper, a unified controller is designed to solve the fixed-time and preassigned-time stability problems of fourth-order chaotic power systems. In addition, based on Lyapunov stability theory, sufficient conditions are established for the fixed-time and preassigned-time stability of the underlying chaotic power systems, and a more accurate estimation of the settling time is also derived. Finally, according to numerical simulations, we validate the theoretical results.

Extended state observer-based model predictive temperature control of mechanically pumped two-phase loop: An experimental study

Mechanically pumped two-phase loop (MPTL), as an emerging two-phase heat dissipation transformational technique, has made booming progress in some critical but tough cases such as space stations and high-performance chips. However, accurate temperature regulation of MPTL is intractable due to periodic heat load disturbance, measurement noise, and micro-channel boiling nonlinearity. To address these issues, an extended state observer-based model predictive control (ESOMPC) strategy is developed in this paper. To describe the process model, this paper builds an MPTL platform equipped with a micro-channel evaporator, based on which a series of sinusoidal heat load variation is carried out to show the effects on the wall temperature. Open-loop step experiments are then conducted in terms of flow rate of the working fluid so that the process model can be identified and the nonlinearity can be analyzed. Then, the ESOMPC is developed by incorporating the disturbance information in the optimization framework of the MPC. The ESO part is utilized to estimate the unknown disturbances and compensate the nonlinearity of MPTL, and thus enhance the disturbance mitigation property of the MPC algorithm. Finally, the closed-loop experiments verifies the efficacy of the proposed solution, showing smaller temperature fluctuation and shorter settling time than the conventional controller. The results indicate the great potential of the proposed ESOMPC in enhancing the temperature control accuracy of MPTL in terms of thermal management performance.

Advances in Fault Diagnostics and Post‐Fault Operation of Electrical Drives

Advances in Fault Diagnostics and Post‐Fault Operation of Electrical Drives

Fractional-Order Hyperbolic Tangent Sliding Mode Control for Chaotic Oscillation in Power System

Chaotic oscillation will occur in power system when there exist periodic load disturbances. In order to analyze the chaotic oscillation characteristics and suppression method, this paper establishes the simplified mathematical model of the interconnected two-machine power system and analyzes the nonlinear dynamic behaviors, such as phase diagram, dissipation, bifurcation map, power spectrum, and Lyapunov exponents. Based on fractional calculus and sliding mode control theory, the fractional-order hyperbolic tangent sliding mode control is proposed to realize the chaotic oscillation control of the power system. Numerical simulation results show that the proposed method can not only suppresses the chaotic oscillation but also reduce the convergence time and suppress the chattering phenomenon and has strong robustness.

An adaptive smooth second-order sliding mode repetitive control method with application to a fast periodic stamping system

This paper proposes an adaptive smooth second-order sliding mode repetitive control method for a class of non-linear systems with unknown disturbances and uncertainties. The key point is that the control law combines the advantages of adaptive second-order sliding mode control with the benefits of repetitive control. When both periodic and aperiodic disturbances exist in the system, the proposed method forces the sliding mode into a smaller pre-specified region in finite time, and when only periodic disturbance exists, the proposed method forces the sliding mode to converge to zero. Compared with pure sliding mode control, the proposed method is especially suitable for systems with sudden periodic load disturbances, for example from periodic impacts. Pure sliding mode control needs to adjust at each impact. Repetitive control knows each impact is coming and learns how to handle it, while sliding mode control can be dedicated to addressing aperiodic disturbances. This can result in smaller error levels. The stability of the proposed method is proved based on a Lyapunov approach. The performance is evaluated on a hydraulic press system via simulations.

Speed Fluctuation Suppression for the Inverter Compressor Based on the Adaptive Revised Repetitive Controller

Repetitive operation is extensively present in the inverter compressor refrigeration field. Research illustrates that an approximate periodic load disturbance deteriorates its self-sensing and efficiency in a low frequency range. According to an internal model theorem, a repetitive controller can realize periodic signal tracking or suppression; however, ideal repetitive control (IRC) can not be directly employed in practical application owing to its excessive sensitivity to period-time uncertainties or aperiodic component, etc. In addition, the ratio between period delay to sampling time can not always maintain an integer which causes the resonant frequencies to deviate from the interested. Even if the ratio is a fixed integer, the auxiliary function for stabilization in a conventional repetitive controller can result in the steady state tracking error. In this paper, a revised repetitive controller with a novel Savitzky–Golay (S–G) filter is proposed, the S–G filter cascaded with a traditional delay element can approximate the delay element with any ratio. Aiming at a different operating condition, a second order generalized integrator (SOGI) based observer is employed to extract disturbance fundamental component, and Steiglitz–McBride based adaptive notch filter (SM-ANF) is adopted for frequency estimation. The proposed scheme varies the S–G filter according to variable fundamental frequency and maintains its resonant frequencies corresponding with the fundamental and harmonic disturbance. In the end, simulations and experiments are implemented and results illustrate that speed fluctuation can be effectively suppressed by the proposed method.

Study on the control strategy of chaotic oscillation of synchronous generator based on the linear feedback adaptive fuzzy sliding mode control

In the case of periodic load disturbance, the chaos oscillation phenomena may be caused by synchronous generator to threaten the safety operation of the network. In order to solve this problem, this paper presents the strategy on the control of linear feedback adaptive fuzzy siding mode. Under the action of the controller, the system output track the desired trajectory, and the fuzzy control rules are used to suppress the high frequency chattering in conventional sliding mode controller. The theoretical analysis and simulation results show that the designed controller can effectively control the power system oscillation, and it has certain robustness.

Fuzzy-based Sliding Mode Control of Chaotic Oscillation in Power System

Power system will occur chaotic oscillation when it is exist periodic load disturbances. As for it, the simplified mathematical model of interconnected two- machine second-order power system is established based on the modelling and analysis of nonlinear system theory, and the dynamic behaviour of chaotic oscillation in power system is analysed. According to the sliding mode control and fuzzy control theory, the fuzzy-based sliding mode control is proposed, it is also analysed and proved theoretically. Simulations results show that the proposed method can suppress the chaotic oscillation in power system effectively. It not only reduce the convergence time, but also reduced the chattering of the system, and has strong robustness.

Robust Voltage Regulation of a DC–AC Inverter With Load Variations via a HDOBC Approach

In this brief, a harmonic disturbance observer (HDOB) based control approach is proposed for the robust voltage regulation design of a dc-ac inverter system. In distributed generation systems, wide range of load variations and effects of nonlinear loads result in significant degradations of control performance. Moreover, the loads, as the mismatched disturbances, impose adverse influences on the inverter system via a channel different from the control input. Toward that end, an HDOB is proposed to estimate the periodic load disturbances. By constructing new disturbance compensation gains, the effects of the mismatched periodic disturbances are removed from the output voltage channel. Rigorous stability analysis for the closed-loop system is presented. Experimental results are explored to illustrate the feasibility and capacity of the proposed control scheme.

Rejection of varying-frequency periodic load disturbances in wind-turbines through active disturbance rejection-based control

Wind turbines are complex mechatronic systems subject to different kinds of disturbances. Among all disturbance sources, those from periodic nature are the most relevant and important for maintaining the structural health of the entire wind turbine. However, periodic disturbances in wind turbines, mainly given by wind shear, tower shadow and rotational sampling of turbulence, have a variable fundamental frequency that changes as function of the turbine angular speed. In consequence, conventional controllers have issues to mitigate such varying-frequency periodic loads. This paper proposes two individual pitch control schemes to attenuate the main periodic load components of blade flap-wise and hub yaw/tilt-wise bending moments in horizontal-axis wind turbines under varying-frequency conditions. Both proposals are founded on the paradigm of Active Disturbance Rejection Control (ADRC): the former is formulated in the time-domain using a Linear-Time-Invariant (LTI) standard controller, while the latter is designed in the angular position domain using a Linear-Position-Invariant (LPI) approach. Several realistic simulations with different wind turbulence intensities and average wind speeds are performed using a 5 MW three-bladed horizontal-axis wind turbine implemented in the FAST code by NREL. Simulation results of the proposed control schemes show improved load reductions compared with other control techniques.

Nonlinear dynamic analysis of a single-machine infinite-bus power system

This study focuses on the nonlinear dynamic characteristics of a single-machine infinite-bus (SMIB) power system under a periodic load disturbance. The qualitative behavior of this system is described by the well-known “swing equation”, which is a nonlinear second-order differential equation. Compared with the existing results, the generator damping in this paper, which is more close to the practical engineering, is related to the state variables of this system. In addition, Melnikov’s method is applied to obtain the threshold for the onset of chaos. The efficiency of the criteria for chaotic motion is verified via numerical simulations. Comparisons between the theoretical analysis and numerical simulation show good agreements. The results in this paper will contribute a better understanding of the nonlinear dynamic behaviors of the SMIB power system.

Analyse and Research on Motion Control for Helical CT Scanner

This study mainly focuses on the synchronization problems of whole-body CT scanner. A master-slave synchronous control method is used to achieve synchronism between the gantry rotation motor and the bed moving motor in helical scanning mode, while the cascade control method is used to enhance the stability of each motor. In order to keep synchronous control, a control law is designed by the eigenstructure assignment method, which insures the accuracy of the signal tracking of the periodic load disturbance during the dual-motor synchronous control, and eliminates the adverse effects brought by periodic load. The proposed algorithm is simulated on MATLAB, and compared with the traditional PID algorithm. In addition, the algorithm is implemented on ARM9 and evaluated on a realistic synchronization control experimental platform designed by us. Both the simulation and realistic experimental results indicate that the algorithm is feasible for helical scanning.

Energy Storage Based Adaptive Control of Disturbed Load Interconnected Power Systems

A simple interconnected power system with periodic load disturbance is considered, an energy storage based adaptive controller is proposed to output tracking and disturbance completely rejection for the system. Since the periodic load disturbance is uncertain with both amplitude and frequency, by constructing a new exosystem, the output tracking and disturbance rejection problem is solved with output regulation theory. By designing an internal model for the complicated system and introducing an appropriate transformation, the output regulation problem is changed into the stabilization problem of a new augmented system. With the help of adaptive control technique, the designed dynamic energy storage controller can solve stabilization problem of the augmented systems as well as the output tracking and disturbance rejection problem for the original system. Finally, the simulation results show the effectiveness of the proposed control strategy.

Controlling Chaos in Power System Based on Tridiagonal Structure Matrix Stability Theory

In the case of periodic load disturbance, the chaos oscillation phenomena may caused by power system to threaten the safety operation of the network. In order to solve this problem, this paper presents the strategy on tridiagonal structure matrix stability theory. Using the designed controller, the chaotic system operation state turn into a stable operation state, and system is stabilized an unstable nonzero equilibrium point.

Wind turbine load reduction by rejecting the periodic load disturbances

ABSTRACTFor the cost per kilowatt hour to be decreased, the trend in offshore wind turbines is to increase the rotor diameter as much as possible. The increasing dimensions have led to a relative increase of the loads on the wind turbine structure; thus, it is necessary to react to disturbances in a more detailed way, e.g. each blade separately. The disturbances acting on an individual wind turbine blade are to a large extent deterministic; for instance, tower shadow, wind shear, yawed error and gravity are depending on the rotational speed and azimuth angle and will change slowly over time. This paper aims to contribute to the development of individually pitch‐controlled blades by proposing a lifted repetitive controller that can reject these periodic load disturbances for modern fixed‐speed wind turbines and modern variable‐speed wind turbines operating above‐rated. The performance of the repetitive control method is evaluated on the UPWIND 5 MW wind turbine model and compared with typical individual pitch control. Simulation results indicate that for relatively slow changing periodic wind disturbances, this lifted repetitive control method can significantly reduce the vibrations in the wind turbine structure with considerably less high‐frequent control action. Copyright © 2012 John Wiley & Sons, Ltd.

A robust disturbance reduction scheme for linear small delay systems with disturbances of unknown frequencies

A robust disturbance reduction scheme for linear small delay systems with disturbances of unknown frequencies is presented in this paper. Unlike other methods, the proposed scheme does not require disturbance frequencies to be known. The linear systems modeled in this study are nominally stable and minimum phase systems with relative degree. The control structure is an integration of Astrom’s modified Smith predictor and the proposed scheme. The proposed scheme consists of an input disturbance reduction controller (IDRC) and a residual disturbance reduction controller (RDRC). The IDRC using an artificial neural network (ANN) is proposed to reduce unknown load disturbances and modeling uncertainties in stable systems and unstable systems. The ANN can appropriately approximate the product of an inverse time delay and a nonnegative gain in the IDRC. The residual signals including residual disturbances and residual uncertainties are suppressed by the RDRC based on a disturbance observer. Simulation examples are illustrated to show the effectiveness of the proposed robust disturbance reduction scheme for linear delay uncertain systems with periodic or non-periodic unknown load disturbances.

Modified Smith predictor with a robust disturbance reduction scheme for linear systems with small time delays

AbstractThis paper presents a robust disturbance reduction scheme using an artificial neural network (ANN) for linear systems with small time delays. It is assumed that the nominal linear systems are stable, minimum phase and relative degree one systems. The proposed structure is an integration of a modified Smith predictor and an ANN‐based disturbance reduction scheme. Unlike other disturbance rejection methods, the proposed approach does not require information about unknown load disturbance frequencies. An ANN is used to approximate the unknown load disturbances and to enhance the robustness of the proposed disturbance reduction scheme against modelling errors in the estimated time delay and the process model. Connective weights of the ANN are trained on‐line using a back‐propagation algorithm until uncertainties resulting from unknown load disturbances and modelling errors are minimized. The simulation results show the effectiveness of the presented disturbance reduction scheme for controlling linear delay systems subjected to step or periodic unknown load disturbances.

Simulation Research of Inverted Plasma Cutting Power Supply Based on Fuzzy Control

Focusing on load characteristics of inverted plasma cutting power supply, this paper puts forward a nonlinear control method. This method integrates fuzzy control technology into the controller of power supply, thereby optimizing dynamic characteristics of power supply. The SIMULINK simulation technology is also used. To compare steady-state precision, robustness, response speed and other control indexes between fuzzy control and conventional PI control, the comparative simulation experiments were made respectively under constant non-disturbance steady-state condition, aperiodic load disturbance condition, and periodic load disturbance condition. The simulation results show that power supply with fuzzy controller has perfect steady robustness, fast system response and strong harmonic suppression ability. The simulation model is accurate and reliable, and it can be an efficient tool for further studying mechanism and algorithm optimization of plasma cutting power supply.

A disturbance reduction scheme for linear small delay systems with modeling uncertainties

A disturbance reduction scheme for linear delay systems with modeling uncertainties is presented in this paper. The linear systems in this study are assumed to be nominally stable, minimum phase and relative degree one systems. The control structure is based on Astrom's modified Smith predictor with a disturbance reduction scheme and an artificial neural network (ANN). Unlike other disturbance rejection methods, the proposed scheme does not require information about unknown disturbance frequencies. The ANN is used to approximate a product of an inverse of a time delay and a nonnegative gain and to augment the robustness of the proposed approach against modeling uncertainties including a time-varying delay. Connective weights of the ANN are trained on-line using a back-propagation algorithm according to a disturbance estimation error function. Simulation results show the effectiveness of the presented disturbance reduction scheme for linear delay systems with modeling uncertainties, subjected to both periodic and non-periodic unknown load disturbances.