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With widespread application of voltage source converter (VSC) as a key energy-conversion power electronic device by using the phase-locked loop (PLL) technique for synchronization, the system dynamics has become much complicated. In this paper, the nonlinear dynamics and transient stability of the PLL-based VSC system are investigated, within a unified framework of the (normalized) generalized swing equation. It is found that there are three different types of bifurcation, including the generalized saddle-node, Hopf, and homoclinic bifurcations. Within the coexistence parameter region, the basin boundary of the stable equilibrium point shows either a closed-loop or a fish-like pattern. With the help of the equal area criterion (EAC), the transient stabilities under different transient disturbances including short circuit, voltage dip, and power rise are analyzed. Because the equivalent damping of the VSC is state-dependent, the theoretical results based on the EAC are examined. Furthermore, based on the analytical results from the generalized swing equation, the principle for all major transient stability enhancement methods is uncovered. All these findings are well verified by extensive electromagnetic transient simulations. Therefore, the generalized swing equation provides a deeper physical insight and plays a crucial role in transient stability problems in power-electronic-dominated power systems, similar to the swing equation in traditional power systems. [ABSTRACT FROM AUTHOR]

In actual microgrids (MGs) networks, the information exchange between distributed energy resources (DERs) agents may be subject to various types of measurement noises and effected by communication time delays. This article proposes a resilient distributed multiagent control scheme for ac MG networks subject to additive noise and time-delay disturbances. The proposed multiagent control scheme is composed of three distributed consensus protocols, which is able to synchronize the output voltages and frequencies of inverter-based DERs to their reference values and achieve the optimal active power-sharing property by a low bandwidth communication network with noise and time-delay disturbances in almost sure convergence. By means of the stochastic analysis tools and algebraic graph theory, distributed consensus control protocols are designed to be employed for the secondary control level of MGs. On this basis, we deduce the stability criteria of the closed-loop MG system under noise and time-delay disturbances. As a result, the proposed consensus protocols can well restore the voltage and frequency’s derivation produced at the primary control level, meanwhile, can well achieve the optimal power sharing even though there exist communication disturbances. Several simulation scenarios on an islanded MG network are provided to verify the proposed control protocols’ performance. [ABSTRACT FROM AUTHOR]

The wide-area damping controller (WADC) using the remote signals obtained from wide-area measurement system (WAMS) as input is an effective measure to suppress interarea oscillations. Once the input signal of WADC is threatened by false data injection attacks (FDIAs), its performance will be decreased dramatically. To address this problem, this article proposes a resilient adaptive wide-area damping control (RAWADC) framework combined with linear state estimator (LSE) and goal representation heuristic dynamic programming (GrHDP). The LSE is proposed and adopted as a preprocessor to detect and correct the attacked data. By detecting and correcting FDIA, the integrity of the WAMS measurement signal is guaranteed. The GrHDP algorithm is employed to design the WADC, which not only does not require a detailed mathematical model of the system but can also adapt to variations of the operating conditions. Simulation results of the 16-machine 68-bus system with voltage source converter based HVdc indicate that the RAWADC can suppress interarea oscillation effectively under a wide range of operating conditions, different FDIA types and measurement noise. [ABSTRACT FROM AUTHOR]

This paper proposes a real-time coordinated scheduling method for active distribution networks (ADNs) with soft open points (SOPs) and plug-in electric vehicles (PEVs) via multi-timescale framework under uncertainties. Specifically, this method is achieved with day-ahead pre-scheduling and intra-day corrective control stages by coordinating various flexible resources at different timescales. The day-ahead stage is designed to reduce operational cost, regulate voltage profile and avoid risk exposure through joint scheduling of traditional devices, SOPs and PEVs on hourly basis. In intra-day corrective control stage, an hour is further divided into two timescales. The slow-timescale scheduling (STS) aims to corrective coordination of SOPs and across-time-and-space energy transmission of PEVs, and nested within the STS, the fast-timescale scheduling optimally coordinates the active & reactive power of SOPs and PV inverters to handle fast voltage fluctuations as well as against real-time uncertainties. The formulated three models are all transformed into second-order cone programming problems via sample weighted average approximation (SWAA), linearization and conic relaxation, which can be thus efficiently solved. Case studies based on three modified distribution systems (including two IEEE test systems and one actual distribution network) are performed to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Deception attacks that threaten communication networks will result in serious consequences ranging from the deterioration of damping performances to instability of power systems. To address this problem, this paper proposes a resilient wide-area damping control (RWADC) for inter-area oscillation based on a secure networked predictive control (SNPC), which is combined with information technology security system (ITSS) and the resilient control scheme based on networked predictive control (NPC). The ITSS including data encryption, data decryption and deception attack detection, is designed to guarantee data confidentiality, integrity, and authenticity. This security system is based on Data Encryption Standard (DES) and Message Digest Algorithm (MD5). The NPC part is used to provide optimal control sequences and compensate the impact of communication constraints and deception attacks, which includes modified generalized predictive control (MGPC), network delay compensator (NDC), and model identifier. Case studies are undertaken on the 16-machine 68-bus AC/DC hybrid power system. Simulation results show that the proposed RWADC can suppress inter-area oscillations, provide better damping performances than those of the conventional and robust WADC over different operating conditions and compensate adverse effects caused by deception attacks actively. [ABSTRACT FROM AUTHOR]

This article proposes a flexible event-triggered online scheduling (ETOS) method for residential multi-microgrid (MMG) systems integrating internal scheduling and external energy sharing levels. Our novelties lie in the flexible ETOS framework embedding customized functions and the fair energy sharing mechanism. Unlike time-triggered methods with a holistic controller and complex mechanisms, the presented ETOS framework achieves systematic management of MMG by simulating its real-life dynamics from the perspective of event-triggering. In the internal scheduling level, universal working logics are designed through active “demand response” interactions, which has high scalability and openness in function and makes event customization possible for future use. In the energy sharing level, the concept of energy level is introduced to organize a localized energy sharing, in which the sharing strategies can be decided through stimulation and transition with the advantages of fairness and low complexity. Moreover, we specify detailed function and algorithm for ETOS entities, helping to realize flexible online operation of MMG in a decentralized and natural way. Numerical simulations show that proposed ETOS is economically beneficial, computationally efficient, and is promising to facilitate the online scheduling of a practical real world MMG project. [ABSTRACT FROM AUTHOR]

This paper investigates the in-depth mechanism of commutation failure for a line-commuted converter-based high-voltage direct current (LCC-HVDC) system. The commutation failure prevention control (CFPREV) and the initial fault voltage angle (IFVA) are considered from the view of the voltage-time area (VTA) in the analysis. It is revealed that the IFVA is among the dominant factors for commutation failures when the voltage drop of the inverter bus is relatively small, and CFPREV further intensifies the impact of the IFVA on commutation failures, while the fluctuation of the direct current plays a dominant role in commutation failures under a greater voltage reduction at the inverter bus. A quantitative division of the severity of AC faults is proposed to determine dominant factors for commutation failures. The relationship between the chance of commutation failures to occur and the IFVA is built, and the method used for computing probability of commutation failures is proposed. The influence of the dynamic of CFPREV output on our research is studied. Simulations based on a typical monopole LCC-HVDC system using PSCAD/EMTDC software are conducted to verify the correctness of the theoretic analysis and the effectiveness of the proposed computing methods. [ABSTRACT FROM AUTHOR]

This paper proposes a variable proportion coefficient based control scheme for the doubly-fed induction generator based wind turbines (DFIG-WTs) to implement frequency support by regulating rotor speed. To reduce the adverse impact caused by regulating DFIG-WT on the dynamic characteristic of the grid frequency, a two-stage switching control scheme is employed for the proposed method. In the first stage, the variable proportion coefficient is designed for emulating the virtual inertia of the DFIG-WT to provide inertia response. In the second stage, a fuzzy control scheme is employed to design the variable proportion coefficient for both quickly restoring the maximum power point tracking (MPPT) operation of DFIG-WTs and avoiding the secondary frequency drop to system. Case studies are undertaken based on WSCC 9-bus and IEEE 39-bus power systems, respectively. Simulation results show that the proposed control scheme can not only make grid-connected DFIG-WTs provide the friendly frequency support, but also help them to fully use the frequency regulation ability of synchronous generators for quickly restoring the MPPT operation. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of power grid strength and phase-locked loop (PLL) parameters on small signal stability of grid-connected doubly fed induction generator (DFIG)-based wind farm. Modal analysis of the grid-connected DFIG wind turbine under different operating conditions and various power grid strengths are investigated at first. Modal analysis results reveal that the DFIG connected to a weak grid may easily lose stability under the heavy-duty operating conditions due to PLL oscillation. The object of this paper is to identify the PLL oscillation mechanism as well as influence factors and propose a damping solution for this oscillation mode. A simplified linear system model of the grid-connected DFIG wind turbine is proposed for analyzing the PLL oscillation. Through the complex torque coefficients method and using this model, the oscillation mechanism and influence factors including the power grid strength and the PLL parameters are identified. To suppress this PLL oscillation, a mixed $H_2/H_{\infty }$ robust damping controller is proposed and designed for the DFIG. Electromagnetic transient simulation results of both single-DFIG system and multiply-DFIG system verify the correctness of the analysis results and effectiveness of the proposed damping controller. [ABSTRACT FROM AUTHOR]

This paper develops a novel distributed iterative event-triggered control scheme for a master-slave-organized dc microgrid network with limited communication bandwidth. The proposed scheme can synchronize the voltage of multiple distributed energy resources (DER) to their desired value. Moreover, the optimal load sharing for their economic operation (e.g., minimize the total generation cost) can be achieved through a low bandwidth communication network. The designed controllers are fully distributed and only triggered at their own event time, which effectively reduces the frequency of controller updates compared with continuous-time feedback control. Eventually, each DER only requires the local voltage and current measurement from its own and some nearest (but not all) neighbors at given event-triggered time through limited-bandwidth communication links. The Lyapunov technique is employed to derive the event-triggered conditions that guarantee the stability. Furthermore, the lower bound of the interevent intervals is captured by the proposed iterative algorithm to exclude Zeno behaviors. Different cases in MATLAB/SimPowerSystems are investigated and results demonstrate the effectiveness and the performance of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper proposes a multiport dc–dc autotransformer (multiport dc auto) that is used to interconnect multiple HVDC systems with different voltage levels. The multiport dc auto is able to reduce 50–80% the converter cost compared with conventional dc–ac–dc technology. Different from the conventional dc–ac–dc technology using magnetic coupling at the ac sides of the converters, there is direct electrical connection between the interconnected dc systems in the multiport dc auto. Such direct electrical interconnection significantly reduces the used power converters in the multiport dc auto. Taking interconnecting a ±250, ±320, and ±400 kV dc system with the rated exporting/importing dc power at each of the dc system being 500, 1000, and 1500 MW as an example, the conventional multiport dc–ac–dc technology requires a total of 3000 MW power converters while only 775 MW power converter is required in the multiport dc–dc autotransformer. The required power converter in the multiport dc–dc autotransformer is only 26% of the converter used in the conventional multiport dc–ac–dc technology. Cost and operating power loss is therefore significantly reduced. [ABSTRACT FROM AUTHOR]

Wide-area damping controller (WADC) requires communication networks to transmit remote signals. The usage of communication networks will introduce time delays into the control loop of the WADC. Ignoring this time delay would deteriorate the damping performance provided by the WADC or even cause the whole system instability. This paper employs networked predictive control (NPC) to design a WADC for the generator exciter to enhance the damping of interarea oscillations in a large-scale power system. The NPC incorporates with a generalized predictive control (GPC) to generate optimal control predictions, and a network delay compensator to detect and compensate both constant and random delays. Moreover, model identification is used to obtain an equivalent reduced-order model of the large-scale power system and deal with the model uncertainties and variation of operating conditions. Case studies are based on the New England 10-machine 39-bus system. Effectiveness of the proposed WADC is verified by simulation studies and compared with a conventional WADC and a GPC-based WADC without delay compensation. [ABSTRACT FROM AUTHOR]

Calculation of the complex torque coefficient for multi-machine system subsynchronous resonance (SSR) assessment had been proven a hard task. In this paper the concept of complex frequency domain port-equivalence conductance matrix (CPCM) is introduced to model the individual system component which represents the relationship between the terminal voltage and current in frequency domain, and the model of the overall power system can be established easily. Thus the complex torque coefficients of the generator unit under investigation can be calculated for SSR assessment. The advantages of this proposed method are that it can take the shaft dynamics and the rotor angle interactions among the generator units into consideration for the multi-machine power system SSR analysis, as well as it can be used to analyze the effectiveness of SSR damping devices. The effectiveness of the proposed method has been verified by both the eigenvalue analysis and the time domain simulation. [ABSTRACT FROM PUBLISHER]

This paper gives the background and role of the market flow in the interregional congestion management process for market-based operating entity and describes the market flow methodology. It proposes that the market flow method calculates the same impact result on a flowgate as the unit dispatch system (UDS) flow does and proves it mathematically. The equivalence of market flow and UDS flow shows that the UDS flow change on a constraint due to the UDS binding will have the same effect on the change in the market flow under the electricity market operations. In addition, it proves that, in an interconnected system, the sum of the market flows of all of the market entities, the generation-to-load impacts of nonmarket entities, and the total tagged transaction impact among the entities is equal to the dc flow for any constraint. The assessment of market flow methodology demonstrates the effectiveness of using the market flow in the congestion management process and coordinated management of transmission constraints. The proposed methodology can help identify the cause of loop flow problem in power systems. The numerical results on a 23-bus test system and a 7917-bus system are also illustrated. [ABSTRACT FROM PUBLISHER]

The application of energy storage (ES) in power system is limited due to the high cost of the ES device, which exponentially increases with its capacity. This paper is to improve the saturation-dependent stability of the power system equipped with the energy storage based damping controller (ESDC), and hence, reduce the required size of the ES. The phenomenon that the capacity of ES is smaller than the required value produced by the ESDC, is modeled as actuator saturation using the saturation function. The proposed method is to design an anti-windup compensator (AWC), which in the event of saturation, produces a signal based on the output difference between the ESDC and saturated ES and then augment the signal to the ESDC to alleviate the adverse effect of saturation. The AWC is designed with the reduced-order model of power system and linear matrix inequality. Detailed design procedure is introduced. Case studies based on a modified 4-machine 2-area power system and 10-machine New England power system are carried out to demonstrate the effectiveness of the AWC design method. [ABSTRACT FROM PUBLISHER]

The usage of remote signals obtained from a wide-area measurement system (WAMS) introduces time delays to a wide-area damping controller (WADC), which would degrade system damping and even cause system instability. The time-delay margin is defined as the maximum time delay under which a closed-loop system can remain stable. In this paper, the delay margin is introduced as an additional performance index for the synthesis of classical WADCs for flexible ac transmission systems (FACTS) devices to damp inter-area oscillations. The proposed approach includes three parts: a geometric measure approach for selecting feedback remote signals, a residue method for designing phase-compensation parameters, and a Lyapunov stability criterion and linear matrix inequalities (LMI) for calculating the delay margin and determining the gain of the WADC based on a tradeoff between damping performance and delay margin. Three case studies are undertaken based on a four-machine two-area power system for demonstrating the design principle of the proposed approach, a New England ten-machine 39-bus power system and a 16-machine 68-bus power system for verifying the feasibility on larger and more complex power systems. The simulation results verify the effectiveness of the proposed approach on providing a balance between the delay margin and the damping performance. [ABSTRACT FROM PUBLISHER]

There is a concern over large, fluctuating wind power injected into a power system, which could affect stability, frequency and power quality of the power system. A method of using three-terminal HVDC system to bundle large scale wind farms with conventional power plants is proposed to overcome this problem. The wind power fluctuation is canceled by regulating the power from the conventional power plants. Topology of the scheme is described. A control strategy particularly suitable to cope with wind power fluctuation is designed. Novel fault ride through mechanisms are designed to enable safe operation of the system. Simulations using PSCAD/EMTDC verify the successful operation of the system during starting-up, steady state, wind power variations and faults. The proposed scheme provides a novel way to deal with the integration of large scale wind power. [ABSTRACT FROM PUBLISHER]

This paper proposed a probabilistic load flow method that can address the correlated power sources and loads. The proposed probabilistic load flow method is based on the Nataf transformation and the Latin Hypercube Sampling. The main advantage of the proposed method is that high accurate solution can be obtained with less computation. Also, it is almost unconstrained for the probability distributions of the input random variables. Considering the uncertainties of correlated wind power, solar energy and loads, the effectiveness and the accuracy of the proposed probabilistic load flow method are verified by the comparative tests in a modified IEEE 14-bus system and a modified IEEE 118-bus system. [ABSTRACT FROM PUBLISHER]

In the distribution network fault management, service restoration is a very important component. When a fault occurs, it is necessary to restore power to these deenergized loads as soon as possible. The restoration problem could be formulated as a multilevel, multi-objective optimization problem with constraints [1]. [ABSTRACT FROM PUBLISHER]

Variation is one of the most important inherent characteristics of wind power. Very few common methods exist to quantify the variations. This presents difficulty for the security and efficiency operations of power systems if large-scale wind power is included. Based on the analysis results from the large amounts of field measurements from nine aggregated wind farms, it is found that the t location-scale distribution and the Laplace distribution are able to cope with this problem. A systemic methodology is proposed accordingly. Therefore, the characteristic of the wind-power variations could be appropriately represented. [ABSTRACT FROM PUBLISHER]

A 35 kJ/7 kW conduction-cooled HTS SMES is developed. The magnet of the SMES is a solenoid type coil, made of Bi2223/Ag tapes, and cooled to about 20K by a cryocooler through conduction-cooled method. To evaluate the performance of the 35 kJ/7 kW SMES, system characteristics such as current carrying ability, power conditioning capability and dynamic operation for stabilizing power systems are investigated by experiments. In this paper, the temperature characteristic of the conduction-cooled HTS magnet for 35 kJ/7 kW SMES is analyzed. Experimental results verify that the thermal stability of the HTS magnet can meet the requirement of dynamic power compensation. Integrating with the analysis of the energy loss in dynamic operation of the magnet, the methods to reduce the energy loss and improve the thermal stability of the conduction-cooled HTS SMES magnet are discussed. [ABSTRACT FROM AUTHOR]

High temperature superconducting (HTS) power cables operated at 77 K temperature could carry a lot more current through the same old underground city pipes and could satisfy the requirements for use in electrical networks. As this new technology still lacks practical operating experience, power network planners are eager to come to know its technical and economic feasibility. Under the pressure of reducing the cost of electric power transmission, it is crucial to demonstrate their profitability over conventional cables besides their technical feasibility. In this paper, a network planning with HTS power cables are expected to offer an economic alternative to 220 kV level conventional cables. The study shows that the use of superconducting cables in an underground transmission circuit is promising from the technical and economic point of view. [ABSTRACT FROM AUTHOR]

Recent advances in signal processing methodologies have spawned the way for a high-speed home network power-line communication (PLC) system. In this paper, a novel signal processing method based on wavelet packet analysis is proposed to combat the adverse communication environment over power lines. A comparison research between wavelet transform and wavelet packet transform is presented. Since wavelet packet decomposition can provide more precise frequency resolution than wavelet decomposition, this paper proposes to use the wavelet packet analysis to deal with the highly polluted PLC communication signal. A hardware structure for the PLC system is presented as an experimental platform for sampling an actual communication signal. Simulation results based on these kinds of actual communication signals show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A novel approach based on genetic search is presented for the design of a supplementary subsynchronous damping controller (SSDC) that is capable of damping out subsynchronous oscillation (SSO) in a parallel AC/DC transmission system. The problem of selecting the parameters of the SSDC is converted to a minimax optimization problem, which is solved by genetic algorithms with an eigenvalue-based objective function. The aim of the proposed control strategy is to choose the best controller parameters in such a way that the dominant eigenvalues of the closed-loop system are shifted to the left-hand side of s-plane as far as possible. Both the eigenvalue analysis and the detailed simulation results demonstrate the effectiveness of the proposed SSDC. [ABSTRACT FROM PUBLISHER]

As the technique of orthogonal frequency-division multiplexing (OFDM) has the ability to overcome the effect of multipath and to obtain high spectral efficiency of the communication channel, it is generally considered as one of the most effective methods to realize the high-speed digital communication system over the low-voltage powerline. This paper proposes a novel OFDM method, in which the cosine carriers of the conventional OFDM system are replaced with the orthonormal wavelets. A quantitative index used to measure the multipath interference, including the intersymbol interference (ISI) and the interchannel interference (ICI), is induced with a filter bank-based multicarrier transmission system model. The effectiveness of the proposed OFDM over the conventional OFDM in reducing both the ISI and the ICI is verified on a model obtained from the measurements of a practical low-voltage powerline communication channel. [ABSTRACT FROM AUTHOR]

The low-voltage powerline communication (PLC net- work) is a technical and attractive innovation in the field of communication. PLC utilities can support energy distribution and provide a pipe for high-speed reliable communication traffic. Wide business opportunities can then be expected. Rut the question that re- mains is how to make the PLC network a commercial reality in the competitive broadband market. The low-voltage electrical network is an unfriendly environment and several factors inherent to the PLC concept itself present technical challenges to using it for data communication. Besides interference and low signaling impedance, PLC transmitters also require a highly linear operating environment. In this paper, a coupling unit topology and design methodology, which could provide gain equalization and wideband mitigation of the effects of low-impedance loads on PLC at the frequency ranging from 0.1 to 30 MHz are presented. Maximization of the network signaling and implementation of a high-speed PLC-oriented system are main objectives for the present work. Some experimental measurements have been performed at residential and industrial environments in China. Motivations to conduct this experiment are given; some compromise was obtained and results are presented. [ABSTRACT FROM AUTHOR]

Proposes a method for the design of an optimal fuzzy logic excitation controller for a generating unit. Important aspects in the performance of the fuzzy logic controller system; Method for design of an optimal fuzzy logic control; Problems with the conventional design method analyzed.

Analyzes the problems existing in the neural network based on-line self-learning control system. Principles of self-learning; Self-learning algorithm; Design of the self-learning power system stabilizer (PSS); Simulation results; Conclusions.