Chimera states are spatiotemporal patterns in which coherence and incoherence coexist. We observe the coexistence of synchronous (coherent) and desynchronous (incoherent) domains in a neuronal network. The network is ...
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With more and more frequency-related devices interconnected into power grid, accurate frequency estimation becomes important for power system electro-mechanical simulations. This paper reviewed the methods for calcula...
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With more and more frequency-related devices interconnected into power grid, accurate frequency estimation becomes important for power system electro-mechanical simulations. This paper reviewed the methods for calculation of bus frequency including difference method, difference method with low-pass filter. Trapezoidal method and damping trapezoidal method which are commonly used in numerical computation are also discussed in this paper for the calculation of bus frequency. In order to analyze advantages and disadvantages of these methods in the aspect of numerical accuracy and stability, a comparison is made on their amplitude-frequency and phase-frequency characteristics. Voltage angle samples from both ideal function and numerical simulation are provided to test the performance of these methods on estimating bus frequency.
In recent years, cyber-physical systems (CPSs) have received much attention from both the academic world and the industrial world, which refer to a deep integration and coordination of physical and computational resou...
In recent years, cyber-physical systems (CPSs) have received much attention from both the academic world and the industrial world, which refer to a deep integration and coordination of physical and computational resources [1,2]. Typical examples of CPSs can be found in smart grids, smart transportation systems, industrial controlsystems, water supply systems, and so on. Furthermore, many military systems are also CPSs. The key characteristic of CPSs is the integration of computing, control and communication. The increased interconnection between the cyber and physical spaces make CPSs vulnerable to various malicious attacks. A well-known example of an attack of CPSs is the Stuxnet which infected the controlsystem of nuclear-fuel centrifuges of Bushehr nuclear power plant in Iran. Stuxnet makes people beware of the grave consequences of a cyber-attack on a CPS. Since many national critical infrastructures are applications of CPS, ensuring security and safety of such systems is of great importance.
The optimal operation of active distribution systems (ADSs) should address the issue of uncertainties caused by high penetration of renewable generation. A two-stage stochastic programming model is proposed for joint ...
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ISBN:
(纸本)9781538622131;9781538622124
The optimal operation of active distribution systems (ADSs) should address the issue of uncertainties caused by high penetration of renewable generation. A two-stage stochastic programming model is proposed for joint energy and reserve scheduling of ADSs with distributed generators (DGs). Reserve required is provided by upstream network, electrical energy storage (EES), and controllable loads (CLs). Soft normally open points (SNOPs) are installed in ADSs for relaxing power constraints on branches. The stochastic programming model is solved by using a convex relaxation method based on semi-definite programming (SDP). Simulation results of a 22-bus test system verify the validity of the proposed stochastic programming model and good performance of the convex relaxation method.
With a large quantity of distributed generators (DGs) integrated, the operation and control of distribution networks is faced with great challenges. Voltage regulation is a vital issue for active distribution networks...
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ISBN:
(纸本)9781538622131;9781538622124
With a large quantity of distributed generators (DGs) integrated, the operation and control of distribution networks is faced with great challenges. Voltage regulation is a vital issue for active distribution networks (ADNs). Optimal placement for energy storage system (ESS) units is determined to enhance their impacts on voltage regulation by solving a mixed integer linear programming model. A voltage regulation strategy is proposed by coordinating DGs, ESS units and on-load tap changer (OLTC). The ADN is partitioned into various zones by using the sensitivity information. For each zone, ESS units play a very active role in voltage regulation coordinating with DGs. The OLTC is activated to ensure achieving the voltage regulation goal when DGs and ESS units are out of control scope. Simulation results on a 33-bus test system demonstrate the effectiveness and good performance of the proposed regulation strategy.
Along with the rapid development of the power industry, grid structure gets more sophisticated. The validity and rationality of protective relaying are vital to the security of power systems. To increase the security ...
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Along with the rapid development of the power industry, grid structure gets more sophisticated. The validity and rationality of protective relaying are vital to the security of power systems. To increase the security of power systems, it is essential to verify the setting values of relays online. Traditional verification methods mainly include the comparison of protection range and the comparison of calculated setting value. To realize on-line verification, the verifying speed is the key. The verifying result of comparing protection range is accurate, but the computation burden is heavy, and the verifying speed is slow. Comparing calculated setting value is much faster, but the verifying result is conservative and inaccurate. Taking the overcurrent protection as example, this paper analyses the advantages and disadvantages of the two traditional methods above, and proposes a hybrid method of on-line verification which synthesizes the advantages of the two traditional methods. This hybrid method can meet the requirements of accurate on-line verification.
Establishing the accurate mathematical and simulation model of transformer is the basis of the power system steady state and transient state analysis, but the nonlinear of the transformer main magnetic circuit makes i...
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Establishing the accurate mathematical and simulation model of transformer is the basis of the power system steady state and transient state analysis, but the nonlinear of the transformer main magnetic circuit makes it difficult to accurate analysis of the transformer and its system. Jiles-Atherton hysteresis model as one of the classical model of ferromagnetic materials, is a physical basis of phenomenological model. It enables the mathematical description of hysteresis curves using five parameters that depend on the magnetic material characteristics. This paper introduces a modified Jiles-Atherton static hysteresis model, and the inverse model was deducted. And then this paper identifies of a hysteresis model parameters using the differential evolution algorithm, and the calculated results are well agreed with the date.
The frequency swings owing to the use of renewable sources shows that loss of rotational inertia may jeopardize the system stability. Numerous researches illustrate how synthetic inertia can be provided from various d...
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ISBN:
(纸本)9781538622131;9781538622124
The frequency swings owing to the use of renewable sources shows that loss of rotational inertia may jeopardize the system stability. Numerous researches illustrate how synthetic inertia can be provided from various devices to power grid, but few of them utilize the synchronous condenser, which is widely applied for reactive power regulation. This paper presents the analysis of the control scheme and operation characteristics of the variable speed synchronous condenser (VSSC) using doubly fed induction machine (DFIM). The IEEE nine bus system was used to validate the potential of the VSSC to provide inertia support for power grid. Simulation results obtained from two operation contingencies, sudden load changes, and variations of control parameter, demonstrated the effectiveness of this system to provide synthetic inertia under frequency oscillation.
Quadruped robot is considered to be the most practical locomotion machine to negotiate uneven terrain, and shows superb stability during static walking. To improve the ability to go over rough terrain, this paper is f...
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Quadruped robot is considered to be the most practical locomotion machine to negotiate uneven terrain, and shows superb stability during static walking. To improve the ability to go over rough terrain, this paper is focused on the stable walking and balance control of quadruped robots. 24 kinds of walking gaits are analyzed in order to derive the most stable and smoothest walking gait. Considering the inefficiency to model a terrain by its specified appearance, a uniform terrain model is established and by means of kinematic analysis, a method to adjust the body posture and center of gravity （COG） height is presented. Simulations demonstrate the effectiveness of the proposed meth- od and the improvement of the adaptation of quadruped robots on rough terrain.
Under frequency load shedding(UFLS) is an important measure to tackle with frequency drop caused by load-generation imbalance. In existing schemes, loads are shed by relays in a discontinuous way, which is the major r...
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Under frequency load shedding(UFLS) is an important measure to tackle with frequency drop caused by load-generation imbalance. In existing schemes, loads are shed by relays in a discontinuous way, which is the major reason leading to under-shedding and overshedding problems. With the application of power electronics technology, some loads can be controlled continuously, and it is possible to improve the UFSL with continuous loads. This paper proposes an UFLS scheme by shedding loads continuously. The load shedding amount is proportional to frequency deviation before frequency reaches its minimum during transient process. The feasibility of the proposed scheme is analysed with analytical system frequency response model. The impacts of governor droop, system inertia, and frequency threshold on the performance of the proposed UFLS scheme are discussed. Cases are demonstrated to validate the proposed scheme by comparing it with conventional UFLS schemes.
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