Showing papers by "Lin Jiang published in 2016"
TL;DR: In this article, a systematic study on the relationship between the time delay and stability of single-loop controlled grid-connected inverters that employ inverter current feedback or grid current feedback (GCF) was carried out, and the ranges of time delay for system stability were analyzed and deduced in the continuous s-domain and discrete z-domain.
Abstract: LCL filters have been widely used for grid-connected inverters. However, the problem that how time delay affects the stability of digitally controlled grid-connected inverters with LCL filters has not been fully studied. In this paper, a systematic study is carried out on the relationship between the time delay and stability of single-loop controlled grid-connected inverters that employ inverter current feedback (ICF) or grid current feedback (GCF). The ranges of time delay for system stability are analyzed and deduced in the continuous s -domain and discrete z -domain. It is shown that in the optimal range, the existence of time delay weakens the stability of the ICF loop, whereas a proper time delay is required for the GCF loop. The present work explains, for the first time, why different conclusions on the stability of ICF loop and GCF loop have been drawn in previous studies. To improve system stability, a linear predictor-based time delay reduction method is proposed for ICF, while a time delay addition method is used for GCF. A controller design method is then presented that guarantees adequate stability margins. The delay-dependent stability study is verified by simulation and experiment.
315 citations
TL;DR: Two novel integral inequalities based on the combination of Wirtinger-based inequality and reciprocally convex lemma can provide smaller bounding gap without requiring any extra slack matrix in linear systems with a time-varying delay.
252 citations
TL;DR: In this article, a feedback linearisation controller based on the detailed model of the doubly fed induction generator based wind turbine (DFIG-WT) is proposed to maximize energy conversion for this system.
243 citations
TL;DR: A new Lyapunov-Krasovskii functional with simple augmented terms and delay-dependent terms is constructed, and its derivative is estimated by several techniques, including free-weighting matrix and inequality estimation methods.
Abstract: This paper investigates delay-dependent stability for continuous neural networks with a time-varying delay. This paper aims at deriving a new stability criterion, considering tradeoff between conservativeness and calculation complexity. A new Lyapunov–Krasovskii functional with simple augmented terms and delay-dependent terms is constructed, and its derivative is estimated by several techniques, including free-weighting matrix and inequality estimation methods. Then, the influence of the techniques used on the conservativeness and the complexity is analyzed one by one. Moreover, useful guidelines for improving criterion and future work are briefly discussed. Finally, the advantages of the proposed criterion compared with the existing ones are verified based on three numerical examples.
211 citations
TL;DR: A generalized free-weighting-matrix (GFWM) approach is proposed to estimate summation terms in the forward difference of Lyapunov functional, and theoretical study shows that the GFWM approach encompasses several frequently used estimation approaches as special cases.
Abstract: This note is concerned with the stability analysis of linear discrete-time system with a time-varying delay. A generalized free-weighting-matrix (GFWM) approach is proposed to estimate summation terms in the forward difference of Lyapunov functional, and theoretical study shows that the GFWM approach encompasses several frequently used estimation approaches as special cases. Moreover, an augmented Lyapunov functional with a delay-product type term is constructed to take into account delay changing information. As a result, the proposed GFWM approach, together with the augmented Lyapunov functional, leads to a less conservative delay-variation-dependent stability criterion. Finally, numerical examples are given to illustrate the advantages of the proposed criterion.
130 citations
TL;DR: In this article, a nonlinear pitch angle controller (N-PI) is proposed to reduce the power captured above the rated wind speed and release the mechanical stress of the drive train.
102 citations
TL;DR: An improved summation inequality is proposed to estimate the summation terms appearing in the forward difference of Lyapunov-Krasovskii functional to establish a relaxed stability criterion of a linear discrete-time system with a time-varying delay.
102 citations
TL;DR: An improved Beta-parameter-based MPPT method is proposed in this paper, which can identify and maintain the middle point of the three-level perturbations, which eliminate the oscillations at a steady state and enhances the tracking speed and is easily applied for any PV power system.
Abstract: Maximum power point tracking (MPPT) is essential for photovoltaic (PV) systems to ensure the highest power output of PV arrays under any environmental condition. Comparing to other techniques, the Beta method shows advantages in terms of tracking speed, steady-state performance, and simple implementation. However, the conventional Beta can further be improved by minimizing oscillations around the maximum power point under a steady state and an increasing tracking speed in response to rapid changing of irradiance or temperature. An improved Beta-parameter-based MPPT method is proposed in this paper to achieve the above-mentioned objectives. An adaptive scaling factor is introduced and utilized in the MPPT mechanism, which enhances the tracking speed and is easily applied for any PV power system. Furthermore, the proposed method can identify and maintain the middle point of the three-level perturbations, which eliminate the oscillations at a steady state. The control mechanism is not limited by specific operating conditions and illustrates superior performance over traditional methods with regards to transient response and steady-state performance, which contributes to effective solar power harvesting. Followed by theoretical analysis, the simulation and experimental evaluation validate the claimed advantages of the proposed MPPT solution.
89 citations
TL;DR: In this article, a nonlinear interval optimization (NIO) model is proposed to solve optimal power system dispatch (OPSD) with uncertain wind power integrated. But the model is not suitable for the case of large-scale systems, where the average and deviation of the dispatching objective are also taken into account.
Abstract: This paper presents the nonlinear interval optimization (NIO) model to solve optimal power system dispatch (OPSD) with uncertain wind power integrated. In this model, not only the average of the dispatching objective, but its deviation are also taken into account. Therefore, the NIO model based on OPSD is formulated as a multi-objective optimization problem. An optimization algorithm, group search optimizer with multiple producers (GSOMP) is applied to obtain Pareto solutions, which show the tradeoff relationship between the average and deviation of the dispatching objective. Then, a decision-making method, the evidential reasoning (ER) approach, is applied to determine the final dispatch solution. Simulation results based on the modified IEEE 30-bus system prove the applicability and effectiveness of the NIO model to deal with the OPSD, considering the integration of the uncertain wind power.
74 citations
TL;DR: In this article, a proportional-integral-derivative-type load frequency control (LFC) scheme design method was developed by using linear matrix inequality and particle swarm optimisation algorithm.
Abstract: Dynamics of vehicle-to-grid service to frequency regulation may suffer from the uncertainties arising from the spatial and temporal diversities of the large-scale plug-in vehicles (PEVs). Communication delays incurred both in the aggregation of the PEVs and in load frequency control (LFC) loop also degrade the dynamics and even destabilise the system. This study designs the LFC scheme considering those uncertainties. First, a dynamic model of individual PEV based on equivalent circuit and an aggregated model for PEVs group considering driving behaviours, battery characteristics, and delays are developed. Then, a state-space model with time delays and uncertainties is constructed to model the closed-loop LFC scheme with PEVs in primary control loop. After constructing the relationships among control gains, robust performances, and delays, a robust proportional–integral–derivative-type LFC scheme design method is developed by using linear matrix inequality and particle swarm optimisation algorithm. Case studies based on a three-area LFC system demonstrate that the PEVs contribute to the frequency regulation under different load disturbances and that the proposed LFC scheme successfully suppresses frequency fluctuations in the presence of delays and provides robustness against the uncertainties arising from the PEVs.
56 citations
TL;DR: In this paper, a pseudo-derivative feedback (PDF) controller is applied to the current control of three-phase grid-connected inverters with LCL filters, which significantly improves the transient response of the system to a step change in the reference input through the elimination of overshoot and oscillation.
Abstract: Pseudo-derivative-feedback (PDF) control is, for the first time, applied to the current control of three-phase grid-connected inverters with LCL filters, which significantly improves the transient response of the system to a step change in the reference input through the elimination of overshoot and oscillation. Two PDF controllers with different terms in the inner feedback path are developed for an inverter current feedback system and a grid current feedback system, respectively. For the inverter current feedback system, a simple PDF controller with a proportional term is used. The influence of the controller parameters on the transient performance is discussed in detail. Compared with a PI controller, the PDF controller is able to eliminate the transient overshoot and oscillation easily, while maintaining a fast response. For the gird current feedback system, a PDF controller with a proportional term and a second-order derivative is developed. The implementation and design of the PDF controller are presented. Active damping is achieved with only the feedback from the grid current, and at the same time, the system transient response is improved. Both theoretical analysis and experimental results verify the advantages of the PDF control over PI control methods.
TL;DR: In this article, the authors proposed an improved version of the beta method to further improve the overall performance, especially for practical applications, by using an autoscaling factor instead of manually tuning key parameters such as the range of the β parameter and scaling factor.
Abstract: Maximum power point tracking (MPPT) is essential to improve the energy yield of solar energy systems. However, conventional MPPT algorithms show obvious problems such as the conflict of the steady-state oscillations and dynamic speed, and the clash of high computational burden and accuracy. Originated from the beta method, which shows the advantages of fast tracking speed in the transient stage, small oscillations in the steady-state, and medium complexity of implementation, this paper proposed an improved beta method to further improve the overall performance, especially for practical applications. Instead of manually tuning key parameters such as the range of $\beta$ parameter and scaling factor $N$ for different operating conditions, an autoscaling factor is used, which make the method easier in practical implementation and suitable for wider conditions. The meteorological data of two distinct locations are used to verify that the $\beta$ parameters derived from photovoltaic (PV) modules are valid for one whole year under different environmental conditions. A PV system with the proposed MPPT method was built in MATLAB/Simulink, and different indices such as the rise time, the setting time, and the tracking energy loss are used to evaluate the performance of various MPPT algorithms. Finally, two experimental tests were carried out, including the indoor test with solar array emulator and the outdoor test with an actual PV module, respectively, to show the effectiveness of the proposed MPPT algorithm.
TL;DR: An algorithm based on alternating direction method of multipliers is proposed to solve the sparsity-constrained OPF problem and employs Lq(0 <; q ≤ 1) norms to enforce sparsity on FACTS devices setting values to achieve solutions with desirable device numbers and sites.
Abstract: Although there are vast potential locations to install FACTS devices in a power system, the actual installation number is very limited due to economical consideration. Therefore the allocation strategy exhibits strong sparsity. This paper formulates FACTS device allocation problem as a general sparsity-constrained OPF problem and employs $L_{q}(0 norms to enforce sparsity on FACTS devices setting values to achieve solutions with desirable device numbers and sites. An algorithm based on alternating direction method of multipliers is proposed to solve the sparsity-constrained OPF problem. The algorithm exploits the separability structure and decomposes the original problem into an NLP subproblem, an $L_{q}$ regularization subproblem, and a simple dual variable update step. The NLP subproblem is solved by the interior point method. The $L_{q}$ regularization subproblem has a closed-form solution expressed by shrinkage-threholding operators. The convergence of the proposed method is theoretically analyzed and discussed. The proposed method is successfully tested on allocation of SVC, TCSC, and TCPS on IEEE 30-, 118-, and 300-bus systems. Case studies are presented and discussed for both single-type and multiple-type FACTS devices allocation problems, which demonstrates the effectiveness and efficiency of the proposed formulation and algorithm.
TL;DR: In this article, a perturbation observer based sliding-mode control (POSMC) scheme for voltage source converter based high voltage direct current (VSC-HVDC) systems is proposed.
TL;DR: In this article, a sub-module synchronous buck converter (SBC) with distributed maximum power point tracking (DMPPT) control is presented to achieve optimal output power of the PV module, low system cost, and high efficiency even under partial shading conditions.
TL;DR: A series of NiII, CoII, ZnII and CdII tetramers with polytopic Schiff base ligands have been synthesized in this article, and the results showed that tetranuclear NiII tetramer has common face-shared defective dicubane cores.
Abstract: A series of NiII, CoII, ZnII and CdII complexes 1–9 with polytopic Schiff base ligands have been synthesized The single-crystal X-ray crystallography results show that tetranuclear complexes 1–6 have common face-shared defective dicubane cores, whereas trinuclear CdII complexes 7–9 are almost linear entities Synthesis methods (solvent evaporation and hydrothermal synthesis), reaction conditions (pH, solvents and dosage) and coligands (azide, methanol, chloride and acetate) play vital roles in determining the final structure of the complexes and therefore their magnetic properties In complexes 1–6, the terminal and central M2+ ions are connected through mixed bridges, μ-phenoxido/μ1,1,1-X and μ-Oalphatic/μ1,1,1-X, while central two M2+ ions are linked by double bridges, μ1,1,1-X (X = azido and methoxido groups for 1 and 2–6 respectively) For complex 1, two central NiII ions are connected through two μ1,1,1-N3− which is relatively less reported For complexes 7–9, there are two kinds of CdII, the centre CdII ions are eight-coordinated with triangle dodecahedral geometries, while the two side CdII ions are six-coordinated with trigonal prism geometries using chlorides or acetates as terminal ligands Magnetic susceptibility measurements (χM) for compounds 1–6 have been performed, and they reveal predominant ferromagnetic exchange interactions in CoII and NiII tetramers The photoluminescence studies show that the ZnII complex 6 and three CdII complexes 7–9 have strong fluorescence, and the lifetimes are measured to be in the 102 nanosecond timescale
TL;DR: In this paper, an adaptive power oscillation damping (APOD) scheme for the superconducting magnetic energy storage (SMES) device to suppress the interarea oscillation in the inter-connected power system is designed based on the generalized predictive control (GPC) and model identification.
TL;DR: In this article, a modified β-parameter-based method was proposed for photovoltaic (PV) power system application to extract the maximum possible power under changing irradiation and temperature conditions.
Abstract: Maximum power point tracking (MPPT) is necessary for photovoltaic (PV) power system application to extract the maximum possible power under changing irradiation and temperature conditions. The β-parameter-based method has many advantages over conventional MPPT methods; such advantages include fast tracking speed in the transient stage, small oscillations in the steady state, and moderate implementation complexity. However, a problem in the implementation of the conventional beta method is the choice of an appropriate scaling factor N, which greatly affects both the steady-state and transient performance. Therefore, this paper proposes a modified β-parameter-based method, and the determination of the N is discussed in detail. The study shows that the choice of the scaling factor N is determined by the changes of the value of β during changes in irradiation or temperature. The proposed method can respond accurately and quickly during changes in irradiation or temperature. To verify the proposed method, a photovoltaic power system with MPPT function was built in Matlab/Simulink, and an experimental prototype was constructed with a solar array emulator and dSPACE. Simulation and experimental results are illustrated to show the advantages of the improved β-parameter-based method with the optimized scaling factor.
01 Jul 2016
TL;DR: In this article, an alternating direction method of multipliers is proposed to solve the sparsity-constrained OPF problem, which exploits the separability structure and decomposes the original problem into an NLP sub-problem, an Lq regularization subproblem, and a simple dual variable update step.
Abstract: Although there are vast potential locations to install FACTS devices in a power system, the actual installation number is very limited due to economical consideration. Therefore the allocation strategy exhibits strong sparsity. This paper formulates FACTS device allocation problem as a general sparsity constrained OPF problem and employs Lq(0
TL;DR: In this article, a multi-agent smart generation control (SGC) scheme for the coordination of automatic generation control in power grids with system uncertainties is proposed, which can achieve AGC coordination in a highly uncertain environment resulting from the increasing penetration of renewable energy.
Abstract: This paper proposes a multiagent (MA) smart generation control (SGC) scheme for the coordination of automatic generation control (AGC) in power grids with system uncertainties. Under the control performance standards, SGC will undergo a non-Markov random process, of which the optimal solution can be resolved online by the reinforcement learning. Therefore, an MA decentralized correlated equilibrium Q(λ)-learning algorithm, and an MA stochastic dynamic game-based SGC simulation platform (SGC-SP) have been proposed for its implementation, which can achieve AGC coordination in a highly uncertain environment resulting from the increasing penetration of renewable energy. Single-agent Q-learning, Q(λ)-learning, R(λ)-learning, and proportional integral control are implemented and embedded in SGC-SP for the control performance analysis. Two case studies on both a two-area power system and the China Southern Power Grid model have been done, which verify its effectiveness and scalability.
TL;DR: In this article, a multi-objective demand side scheduling is investigated with consideration to the appliances' operational safety together with the electricity cost and the operational delay, and the relationship between the operational safety and the other two objectives are investigated through the approach of finding the Pareto-optimal front.
TL;DR: In this paper, the authors proposed a comprehensive decision-making method considering voltage risk to coordinate preventive and corrective control for voltage stability of power system, and the proposed method is significant not only to achieve the optimum balance between the security and economy of stability control, but also improve the decision efficiency.
Abstract: This study proposes a comprehensive decision-making method considering voltage risk to coordinate preventive and corrective control for voltage stability of power system. The voltage risk is quantified in the form of economic index with considering the uncertainty of postulated contingencies. Then, a non-linear optimisation model with the objective of minimising voltage risk is performed to coordinate the preventive and corrective control. The positive constraint relaxation algorithm (PCRA) is presented to determine the integrated countermeasures. Based on the principle of PCRA, the failure with the smallest severity factor in the set of preventive fault is selected as an emergency fault. With the changes of the fault sets, the voltage risk and the countermeasures are recalculated until that the risk is no longer reduced for the expected contingencies. The proposed method is significant not only to achieve the optimum balance between the security and economy of stability control, but also improve the decision efficiency. Finally, the proposed method is demonstrated on the New-England 39-bus system, and the results validate the effectiveness of the proposed method.
TL;DR: In this paper, a range of nanomaterials are obtained depending upon the tetra(4-sulfonatophenyl)porphyrin (TPPS) anion(s) used in the reaction.
TL;DR: A low-complexity and adaptive nonlinearity estimation module is proposed and experimentally demonstrated based on Godard's error and low-pass filter (LPF) and the computational complexity is significantly reduced.
Abstract: A low-complexity and adaptive nonlinearity estimation module is proposed and experimentally demonstrated based on Godard's error and low-pass filter (LPF). The computational complexity of the proposed adaptive estimation module is significantly reduced by avoiding utilizing the polarization demultiplexing, frequency offset compensation, and carrier phase recovery in the process of finding the optimal value $\gamma\xi_{\mathrm{opt}}$ compared with the previous approach based on phase noise variance. The performance of the proposed module is experimentally verified in a 40-Gb/s polarization-division-multiplexing-quadrature-amplitude modulation (PDM-QPSK) coherent optical communication system over 720-km single-mode fiber (SMF). Experimental results show that the computational complexity of the proposed nonlinearity estimation module is only ∼7.35% of the previous approach and ∼27.8% of that with an LPF inserted.
17 Jul 2016
TL;DR: In this paper, the authors investigated sub-synchronous resonance (SSR) phenomena inside a doubly-fed induction generator (DFIG) based wind farm, considering the impact of the spatial distribution of wind speed.
Abstract: This paper investigates sub-synchronous resonance (SSR) phenomena inside a doubly-fed induction generator (DFIG) based wind farm, considering the impact of the spatial distribution of wind speed. Firstly, the impedance model of a one-DFIG aggregated model based wind farm is presented to analyze the induction generator effect. Then, a two-DFIGs aggregated impedance model, considering DFIGs in both low wind speed and high wind speed is developed to analyze the influence of wind speed spatially distribution on SSR in a wind farm. The number of DFIGs under different wind speeds, which represented to the wind speed spatially distribution, will influence the SSR. When there are more DFIGs in low wind speed, SSR will occur simultaneously in all DFIGs in a wind farm; while there are more DFIGs in high wind speed, SSR will be damped for all DFIGs. Analysis based on the impendence models and the simulation tests are given.
TL;DR: In this paper, an effective polarization demultiplexing algorithm based on Stokes space is proposed to realize the de-noising of two nonorthogonal polarization states.
Abstract: The minimization of polarization multiplexing angle in a polarization-division-multiplexed (PDM) transmission system is explored. An effective polarization demultiplexing algorithm based on Stokes space is proposed to realize the demultiplexing of two nonorthogonal polarization states. Both simulation and experimental results verify the effectiveness of the proposed algorithm for the transmission of a 56-Gb/s PDM-dual phase-shift keying (DPSK) signal over different polarization multiplexing angles (i.e., $\theta=23^{\circ}$ , 45°, 67°, 90°) and different lengths of transmission links (i.e., back-to-back, 320 km, 400 km).
TL;DR: The first transmission of three-polarization-division-multiplexed DPSK signals at a rate up to 3×25 Gb/s over 300-km fiber link by using a single-carrier is experimentally demonstrated.
Abstract: Polarization is one of the key parameters to be utilized for large capacity and high spectral-efficient optical communication systems, especially the widely deployed polarization-division-multiplexing (PDM) scheme. To break the limitation of only two orthogonal polarization states that could be used for carrying data signals over the same wavelength, we experimentally demonstrate the first transmission of three-polarization-division-multiplexed DPSK signals at a rate up to 3×25 Gb/s over 300-km fiber link by using a single-carrier.
01 Oct 2016
TL;DR: This paper presents a new method for the detection and classification of power disturbances in power distribution systems using Half Multi-resolution Morphology Gradients (H-MMG), but the process only uses half the MMG strategy.
Abstract: This paper presents a new method for the detection and classification of power disturbances in power distribution systems using Half Multi-resolution Morphology Gradients (H-MMG). This method is based on multi-resolution morphology gradients (MMG), but the process only uses half the MMG strategy. In addition, this strategy will operate in level 1 only, so this will reduce the processing and increase the speed of detection. The location of disturbances can be detected as the difference between the input signal and the ascending and descending edges of the waveform. This strategy has been simulated using Matlab for sag, swell, voltage interruption, flicker, notch and transients. The results show accurate detection when disturbances occurred in the system.
22 May 2016
TL;DR: In this paper, a cooperative control strategy for a battery-supercapacitor based hybrid ESS (HESS) for both improving the transient performance of MG bus voltage and reducing the battery loss is presented.
Abstract: In an island Microgrid (MG), energy storage system (ESS) is required to balance the power generation and load demand. Battery is the most commonly used energy storage device, but it has its longevity adversely affected by accumulated depth of discharge (DOD). This paper presents a cooperative control strategy for a battery-supercapacitor based hybrid ESS (HESS) for both improving the transient performance of MG bus voltage and reducing the battery loss. In this control strategy, the power generated by different devices in HESS are distributed as that battery is controlled to provide the balanced power in steady-state, while supercapacitor (SC) is controlled to generate transient and unbalanced power for a single phase load demand. Simulations are implemented in the PSCAD/EMTDC software environment, and the results show that the transient response of MG bus voltage has been improved under the unbalanced load disturbance. Simultaneously, the battery loss is reduced by the proposed control strategy with lower DOD, less internal power loss, and higher entire efficiency than the conventional control method for battery on the base of frequent charging and discharging conditions in MG applications.
17 Jul 2016
TL;DR: In this paper, a novel convex relaxation based decomposeition algorithm is proposed to solve the full AC multi-period OPF with energy storages and renewable sources, based on alternating direction method of multipliers (ADMM), the original time-correlated nonconvex optimization problem is decomposed into two subproblems.
Abstract: Multi-period optimal power flow (OPF) is a basic tool to achieve optimal operation of a power system with energy storages devices and renewable sources. A novel convex relaxation based decomposeition algorithm is proposed in this paper to solve the full AC multi-period OPF with energy storages and renewable sources. Based on alternating direction method of multipliers (ADMM), the original time-correlated non-convex optimization problem is decomposed into two subproblems. The first subproblem is non-convex and separable among different time slots. Moment relaxation can be constructed and solved for each time slot in parallel. The second subproblem is a convex quadratic program (QP) and separable among different buses, which can be solved in parallel by standard interior point (IPM) solver. Case study on a benchmark system demonstrates the effectiveness of the proposed algorithm.