Showing papers by "Lin Jiang published in 2013"

Delay-Dependent Robust Load Frequency Control for Time Delay Power Systems

Abstract: The usage of communication channels introduces time delays into load frequency control (LFC) schemes. Those delays may degrade dynamic performance, and even cause instability, of a closed-loop LFC scheme. In this paper, a delay-dependent robust method is proposed for analysis/synthesis of a PID-type LFC scheme considering time delays. The effect of the disturbance on the controlled output is defined as a robust performance index (RPI) of the closed-loop system. At first, for a preset delay upper bound, controller gains are determined by minimizing the RPI. Secondly, calculation of the RPIs of the closed-loop system under different delays provides a new way to assess robustness against delays and estimate delay margins. Case studies are based on three-area LFC schemes under traditional and deregulated environments, respectively. The results show that the PID-type controller obtained can guarantee the tolerance for delays less than the preset upper bound and provide a bigger delay margin than the existing controllers do. Moreover, its robustness against load variations and parameter uncertainties is verified via simulation studies.

Further Results on Delay-Dependent Stability of Multi-Area Load Frequency Control

Abstract: Further to results reported by Jiang , this paper investigates delay-dependent stability of load frequency control (LFC) emphasizing on multi-area and deregulated environment. Based on Lyapunov theory and the linear matrix inequality technique, a new stability criterion is proposed to improve calculation accuracy and to reduce computation time, which makes it be suitable for handling with multi-area LFC schemes. The interaction of delay margins between different control areas and the relationship between delay margins and control gains are investigated in details. Moreover, usage of delay margins as a new performance index to guide controller design is discussed, including tuning of the controller for a trade-off between delay tolerance and dynamic response, choosing the upper bound of the fault counter of communication channels and the upper bound of sampling period of a discrete realization of the controller. Case studies are carried out based on two-area traditional, two-area and three-area deregulated LFC schemes, all equipped with PID-type controllers, respectively. Simulation studies are given to verify the effectiveness of the proposed method.

Delay-dependent robust load frequency control for time delay power systems

Abstract: Summary form only given. The usage of communication channels introduces time delays into load frequency control (LFC) schemes. Those delays may degrade dynamic performance, and even cause instability, of a closed-loop LFC scheme. In this paper, a delay-dependent robust method is proposed for analysis/synthesis of a PID-type LFC scheme considering time delays. The effect of the disturbance on the controlled output is defined as a robust performance index (RPI) of the closed-loop system. At first, for a preset delay upper bound, controller gains are determined by minimizing the RPI. Secondly, calculation of the RPIs of the closed-loop system under different delays provides a new way to assess robustness against delays and estimate delay margins. Case studies are based on three-area LFC schemes under traditional and deregulated environments, respectively. The results show that the PID-type controller obtained can guarantee the tolerance for delays less than the preset upper bound and provide a bigger delay margin than the existing controllers do. Moreover, its robustness against load variations and parameter uncertainties is verified via simulation studies.

Stability analysis for control systems with aperiodically sampled data using an augmented Lyapunov functional method

Abstract: This study analyses the stability of aperiodically sampled-data control systems with and without communication delays by using a new augmented Lyapunov functional method. Compared with most of existing methods that commonly require each term of a Lyapunov-Krasovskii functional (LKF) to be non-negative, the proposed method waives this requirement by introducing an augmented term, which has zero value and zero derivative, into the LKF. Several stability criteria with less conservatism are obtained from the relaxation of constraint conditions for guaranteeing the non-negativeness of the LKF. These criteria are extended to investigate the stability of the systems with polytopic uncertainties and the exponential stability of the system. Three numerical examples are given to show the effectiveness of the proposed method.

Hybrid algorithm for dynamic economic dispatch with valve-point effects

Abstract: Dynamic economic dispatch problem in power system considering valve-point effects of generators is a non-smooth, non-convex and multi-dimensional constrained optimisation problem. In allusion to those characteristics, this study proposes a hybrid algorithm which integrates low-discrepancy sequences, improved shuffled frog leaping algorithm and sequential quadratic programming. The effectiveness of the proposed method has been verified by using case studies based on 5-unit, 10-unit and 30-unit test systems over a period of 24 h. The results show that the proposed method has improved solution quality and computation efficiency, compared with most current approaches.

Mapping of IEC 61850 to Data Distribute Service for digital substation communication

Abstract: Digital substation is one key component of smart grid and requires real-time and reliable data communication platform. This paper investigates the feasibility mapping of IEC61850 by using Data Distribution Service, which is a real-time, reliable, and data-centric middleware standard proposed by Object Management Group. The mapping is based on publish/subscribe mode which provides more flexibility than another message-based or client/server based mapping techniques such as MMS and CORBA-TAO. Moreover, middleware based implementation reduce the developing time and complexities and improve the code reliability. Several tests of QoS have been carried out to verify the mapping, based on tools provided by RTI-DDS.

A feedback linearization control strategy for maximum power point tracking of a PMSG based wind turbine

Abstract: This paper presents a feedback linearization control (FLC) scheme for maximum power point tracking (MPPT) of permanent magnet synchronous generator (PMSG) based wind turbine (WT). The FLC strategy can fully decouple and linearize the original nonlinear system and thus provide a optimal controller crossing a wide range operating conditions. It performs better than the conventional vector control (VC) with proportional-integral (PI) loops designed based one operation point as operation points varies. The Verified and performance of the proposed control strategy are confirmed by simulation studies in comparison with the VC.

Networked predictive control based wide-area supplementary damping controller of SVC with communication delays compensation

Abstract: This paper presents the design of a networked predictive control (NPC) based wide-area supplementary damping controller (WSDC) of SVC in order to damp the inter-area low frequency oscillations in large-scale interconnected power system. The major advantage of the proposed WSDC is that it can compensate constant and random communication delays existing in wide-area signals in an active way. Moreover, a recursive least-squares algorithm (RLSA) with a variable forgetting factor is applied to identify the predictive model of the power system to overcome the model inaccuracies and uncertainties. Case studies undertaken on a two-area four-machine power system with a SVC device installed show that the proposed WSDC can provide better damping performances than the conventional WSDC especially when the wide-area signals exist communications delays.

Adaptive passivity-based control of a TCSC for the power system damping improvement of a PMSG based offshore wind farm

Abstract: This paper proposes the adaptive passivity-based control of a thyristor controlled series capacitor (TCSC) for damping improvement of a permanent-magnet synchronous generator (PMSG) based offshore wind farm (OWF) fed to a one-machine infinite-bus (OMIB) system. The passivity-based control (PBC) is an energy-based approach whose aim is to render the closed-loop system passive with a given storage function. However, the standard PBC requires an accurate model to passivize the system, which is not realistic, in practise, as the active-power of PMSG based OWF is unknown because of the time-varying turbulent wind power inputs. By defining the system perturbation to represent the combinatorial effect of the model uncertainties and external disturbances, we designed a high-gain state and perturbation observer (HGSPO) to estimate the perturbation and angular speed, which are used as part of the adaptive passivity-based control (APBC) system. Simulation studies verify that the proposed approach can render better damping performance with only one state measurement.

Disturbance identification based on mathematical morphology and radial coordinate visualization

Abstract: This paper proposes a novel power quality disturbance identification algorithm based on mathematical morphology (MM) and radial coordinate visualization (Radviz). The algorithm firstly filters the noise out from the signals using mathematical median filter, and then extends the one-dimensional data to multi-dimensional data. Consequently, it is possible to use Radviz to decouple the normal part and the disturbance from each other, so that the disturbance can be identified more easily. Simulation studies have been conducted to test the performance of the proposed algorithm and the results have demonstrated its validity.

Support vector regression-based short-term wind power prediction with false neighbours filtered

Abstract: Wind power prediction has received much attention due to the development renewable energy sources using wind power. The paper presents a new approach which is a support vector regression (SVR) based local predictor (LP) with false neighbours filtered (FNF-SVRLP) to undertake short-term wind power perdition. The proposed predication method not only combines the powerful SVR with the reconstruction properties of time series, but also overcomes the drawback of the original local predictor by removing false neighbours. The proposed method (FNF-SVRLP) is evaluated with the real world wind power data, and the final performance is compared with the support vector regression based local predictor (SVRLP) and the autoregressive moving average (ARMA). The results demonstrate that the proposed method can achieve a better performance than the other methods.

Device for detecting lower limit of reservoir forming pore throat radius of compact sandstone reservoir

Abstract: The embodiment of the utility model discloses a device for detecting a lower limit of a reservoir forming pore throat radius of a compact sandstone reservoir. The device comprises a throat obtaining device, a carbon content obtaining device, a throat radius lower limit value obtaining device and an intersection getting device, wherein the throat obtaining device is connected with the carbon content obtaining device; the carbon content obtaining device is connected with the throat radius lower limit value obtaining device; the throat radius lower limit value obtaining device is connected with the intersection getting device; the throat obtaining device is used for obtaining a plurality of throats which are gradually thinned; the carbon content obtaining device is used for selecting 1, 2, 3, 4, ..., n and n+1 points in sequence from the thick ends of the plurality of obtained throats which are gradually thinned, detecting energy spectra of the n+1 points one by one and obtaining carbon content of each point; the throat radius lower limit value obtaining device is used for obtaining a plurality of reservoir forming pore throat radius lower limits of the compact sandstone reservoir, which correspond to the plurality of throats, according to the carbon content of each point; and the intersection getting device is used for getting an intersection of the plurality of value taking intervals so as to obtain the final reservoir forming pore throat radius lower limit of the compact sandstone reservoir.

Hardware implementation of smooth region switching for wind turbine control using PDF controller

Abstract: Control system for wind turbine will operate with different objectives throughout its complete wind speed regions: from cut-in speed to cut-out speed. This paper presents a method for smoothly switching of controllers between these operating regions. The controllers designed in this paper are based on Pseudo Derivative Feedback (PDF), which provides smoother dynamic and simpler tuning of parameters than general PI controllers. Simulations of the presented method are performed with a non-linear wind turbine model at first, followed by preliminary results of hardware-in-the-loop simulation. The simulation and hardware implementation results present a smooth performance of region switching between different controllers and verify the effectiveness of the controller proposed.