Showing papers on "Frequency response published in 2020"
TL;DR: A virtual synchronous generator control based on adaptive virtual inertia based on Lyapunov stability theory combines the merits of large inertia and small inertia, which contributes to the improvement of dynamic frequency response.
Abstract: A virtual synchronous generator (VSG) control based on adaptive virtual inertia is proposed to improve dynamic frequency regulation of microgrid. When the system frequency deviates from the nominal steady-state value, the adaptive inertia control can exhibit a large inertia to slow the dynamic process and, thus, improve frequency nadir. And when the system frequency starts to return, a small inertia is shaped to accelerate system dynamics with a quick transient process. As a result, this flexible inertia property combines the merits of large inertia and small inertia, which contributes to the improvement of dynamic frequency response. The stability of the proposed algorithm is proved by Lyapunov stability theory, and the guidelines on the key control parameters are provided. Finally, both hardware-in-the-loop and experimental results demonstrate the effectiveness of the proposed control algorithm.
152 citations
TL;DR: The concept of frequency security margin is proposed to quantify the system frequency regulation ability under contingency as the maximum power imbalance that the system can tolerate while keeping frequency within the tolerable frequency range.
Abstract: The power system inertia is gradually decreasing with the growing share of variable renewable energy (VRE). This may jeopardize the frequency dynamics and challenges the secure operation of power systems. In this paper, the concept of frequency security margin is proposed to quantify the system frequency regulation ability under contingency. It is defined as the maximum power imbalance that the system can tolerate while keeping frequency within the tolerable frequency range. A frequency constrained unit commitment (FCUC) model considering frequency security margin is proposed. Firstly, the analytical formulation of system frequency nadir is derived while considering both the frequency regulation characteristics of the thermal generators and the frequency support from VRE plants. Then, the frequency security margin is analytically formulated and piecewise linearized. A novel FCUC model is proposed by incorporating linear frequency security constraints into the traditional unit commitment model. Case studies on a modified IEEE RTS-79 system and HRP-38 system are provided to verify the effectiveness of the proposed FCUC model. The impacts of VRE penetration on system frequency security are analyzed using frequency security margin.
102 citations
TL;DR: In this article, the vibrational behavior of porous functionally graded magneto-electro-elastic (P-FGMEE) circular and annular plates is explored through finite element procedures.
86 citations
TL;DR: In this paper, the Nusselt number fluctuations are examined, revealing that the dynamical relations between the inlet flow fluctuations as the input and those of the Reynolds number as the output, can be nonlinear.
79 citations
TL;DR: The results demonstrate that the proposed control scheme can ensure the stable operation of the system under a larger sampling period so as to reduce the communication network burden and show that the controller designed by a large exponential decay rate can provide a fast frequency response to alleviate the impact of thesystem’s frequency response due to the high penetration of wind power.
77 citations
TL;DR: The result shows that the cascade control produced better transient and steady state performances than those of the other classical controllers, and the system overshoots/undershoots in frequency response pertaining to random change in wind power generation and load perturbations were significantly reduced by the proposed cascade control.
Abstract: This paper presents the automatic load frequency control (ALFC) of two-area multisource hybrid power system (HPS). The interconnected HPS model consists of conventional and renewable energy sources operating in disparate combinations to balance the generation and load demand of the system. In the proffered work, the stability analysis of nonlinear dynamic HPS model was analyzed using the Hankel method of model order reduction. Also, an attempt was made to apply cascade proportional integral - proportional derivative (PI-PD) control for HPS. The gains of the controller were optimized by minimizing the integral absolute error (IAE) of area control error using particle swarm optimization-gravitational search algorithm (PSO-GSA) optimization technique. The performance of cascade control was compared with other classical controllers and the efficiency of this approach was studied for various cases of HPS model. The result shows that the cascade control produced better transient and steady state performances than those of the other classical controllers. The robustness analysis also reveals that the system overshoots/undershoots in frequency response pertaining to random change in wind power generation and load perturbations were significantly reduced by the proposed cascade control. In addition, the sensitivity analysis of the system was performed, with the variation in step load perturbation (SLP) of 1% to 5%, system loading and inertia of the system by ±25% of nominal values to prove the efficiency of the controller. Furthermore, to prove the efficiency of PSO-GSA tuned cascade control, the results were compared with other artificial intelligence (AI) methods presented in the literature. Further, the stability of the system was analyzed in frequency domain for different operating cases.
76 citations
TL;DR: In this paper, the authors studied the unit commitment problem in a power network with low levels of rotational inertia and derived frequency-related constraints from a uniform system frequency response model that incorporates dynamics and controls of both synchronous generators and grid-forming inverters.
Abstract: In this paper, the Unit Commitment (UC) problem in a power network with low levels of rotational inertia is studied. Frequency-related constraints, namely the limitation on Rate-of-Change-of-Frequency (RoCoF), frequency nadir and steady-state frequency error, are derived from a uniform system frequency response model that incorporates dynamics and controls of both synchronous generators and grid-forming inverters. These constraints are then included into a stochastic UC formulation that accounts for wind power and equipment contingency uncertainties using a scenario-tree approach. In contrast to the linear RoCoF and steady-state frequency error constraints, the nadir constraint is highly nonlinear. To preserve the mixed-integer linear formulation of the stochastic UC model, we propose a computationally efficient approach that allows to recast the nadir constraint by introducing appropriate bounds on relevant decision variables of the UC model. This method is shown to be generally more accurate and computationally more efficient for medium-sized networks than a piece-wise linearization method adapted from the literature. Simulation results for a modified IEEE RTS-96 system revealed that the inclusion of inertia-related constraints significantly influences the UC decisions and increases total costs, as more synchronous machines are forced to be online to provide inertial response.
76 citations
TL;DR: The findings demonstrated that the second order optimal weighted contribution rate has a high application value in the fault diagnosis of rub-impact and the new index shows better superiority.
71 citations
TL;DR: In this article, a novel control framework for SI provision from wind turbines (WTs) is proposed, which eliminates the secondary frequency dip and allows the dynamics of SI from WTs to be analytically integrated into the system frequency dynamics.
Abstract: The undergoing transition from conventional to converter-interfaced renewable generation leads to significant challenges in maintaining frequency stability due to declining system inertia. In this paper, a novel control framework for Synthetic Inertia (SI) provision from Wind Turbines (WTs) is proposed, which eliminates the secondary frequency dip and allows the dynamics of SI from WTs to be analytically integrated into the system frequency dynamics. Furthermore, analytical system frequency constraints with SI provision from WTs are developed and incorporated into a stochastic system scheduling model, which enables the provision of SI from WTs to be dynamically optimized on a system level. Several case studies are carried out on a Great Britain 2030 power system with different penetration levels of wind generation and inclusion of frequency response requirements in order to assess the performance of the proposed model and analyze the influence of the improved SI control scheme on the potential secondary frequency dip. The results demonstrate that the inclusion of SI provision from WTs into Unit Commitment (UC) can drastically impact the overall system costs.
68 citations
TL;DR: Results confirm that the proposed dual-adaptivity inertia control strategy not only achieves rapid frequency response with slight dynamic deviations under disturbances but also strikes a balance between the frequency and power and leads to improved overall control.
Abstract: The virtual synchronous generator (VSG) improves the robustness of the inverter-interfaced distributed generator (IIDG) against instability by introducing a virtual inertia. However, the transient response of the active power and the angular frequency conflict with each other for the IIDG with fixed inertia control. It is necessary to adopt adaptive control to improve overall performances of power and frequency as the operating condition changes. This paper analyzes the impact of the inertia on power and angular frequency. A dual-adaptivity inertia control strategy is proposed to offer a responsive and stable frequency support and also achieve the balance between power regulation and frequency regulation according to different operating conditions. The principle of parameter design is given to obtain the range of adaptivity. Quantitative assessment considering the cumulative effect of the output deviation and its duration is also presented to evaluate the proposed strategy intuitively. The strategy is further verified based on PSCAD/EMTDC and a hardware-in-loop experiment platform based on RTDS. Results confirm that the proposed strategy not only achieves rapid frequency response with slight dynamic deviations under disturbances but also strikes a balance between the frequency and power and leads to improved overall control.
64 citations
TL;DR: In this paper, the authors proposed a "rainbow" metamaterial to achieve broadband multi-frequency vibration attenuation, which is constituted of a Π-shaped beam partitioned into substructures by parallel plates insertions with two attached cantilever-mass acting as local resonators.
TL;DR: The configurations of spatially-varying connectable graded microstructures at microscale and their distribution at macroscale are simultaneously optimized, which ensures a sufficiently large design space to minimize the frequency response of cellular composites.
TL;DR: In this paper, a nonlinear inertance mechanism (NIM) was proposed for vibration mitigation and the performance of nonlinear vibration isolators employing such mechanism was evaluated. But the NIM was not applied to a linear spring-damper isolator and to nonlinear quasi-zero-stiffness isolators.
Abstract: This paper investigates a nonlinear inertance mechanism (NIM) for vibration mitigation and evaluates the performance of nonlinear vibration isolators employing such mechanism. The NIM comprises a pair of oblique inerters with one common hinged terminal and the other terminals fixed. The addition of the NIM to a linear spring-damper isolator and to nonlinear quasi-zero-stiffness (QZS) isolators is considered. The harmonic balance method is used to derive the steady-state frequency response relationship and force transmissibility of the isolators subjected to harmonic force excitations. Different performance indices associated with the dynamic displacement response and force transmissibility are employed to evaluate the performance of the resulting isolators. It is found that the frequency response curve of the inerter-based nonlinear isolation system with the NIM and a linear stiffness bends towards the low-frequency range, similar to the characteristics of the Duffing oscillator with softening stiffness. It is shown that the addition of NIM to a QZS isolator enhances vibration isolation performance by providing a wider frequency band of low amplitude response and force transmissibility. These findings provide a better understanding of the functionality of the NIM and assist in better designs of nonlinear passive vibration mitigation systems with inerters.
TL;DR: In this article, an analytical model for the frequency nadir prediction was developed to predict the maximum frequency deviation and the time at which the maximum occurs with high efficiency and accuracy following a major disturbance.
Abstract: The frequency nadir is a significant indicator for the primary frequency response monitoring and control. It is imperative to predict the maximum frequency deviation and the time at which the maximum occurs with high efficiency and accuracy following a major disturbance. To develop an analytical model for the frequency nadir prediction, the closed-loop is broken and a parabolic frequency deviation is input for decoupling the calculation of governor response and frequency deviation. Following which, the polynomial fitting is adopted to depict the primary frequency response characteristic of each governor. The iterative numerical solution for the frequency nadir prediction model is carried out based on the insight into the features of governor response. Case studies are presented to verify the performance of the analytical model over WSCC 9-bus system, New England 39-bus system and practical provincial power system, where the frequency nadir prediction model demonstrates its advantages of easy implementation, minimum computation, and high accuracy.
TL;DR: A data driven-based equivalent model of battery energy storage systems, as seen from the electrical system, is proposed, which takes advantage of the energy storage system special attributes to contribute to inertial response enhancement, via the virtual inertia concept.
Abstract: In this paper, the problem of optimal placement of virtual inertia is considered as a techno-economic problem from a frequency stability point of view. First, a data driven-based equivalent model of battery energy storage systems, as seen from the electrical system, is proposed. This experimentally validated model takes advantage of the energy storage system special attributes to contribute to inertial response enhancement, via the virtual inertia concept. Then, a new framework is proposed, which considers the battery storage system features, including annual costs, lifetime and state of charge, into the optimal placement formulation to enhance frequency response with a minimum storage capacity. Two well-known dynamical frequency criteria, the frequency nadir and the rate of change of frequency, are utilized in the optimization formulation to determine minimum energy storage systems. Moreover, a power angle-based stability index is also used to assess the effect of virtual inertia on transient stability. Sensitivity and uncertainty analyses are further conducted to assess the applicability of the method. The efficiency of the proposed framework is demonstrated on a linearized model of a three-area power system as well as two nonlinear systems. Simulation results suggest that the proposed method gives improved results in terms of stability measures and less ESS capacity, when compared with other methods proposed in the literature.
TL;DR: In this paper, an analytical study of nonlinear vibratory energy harvesting via a two-span piezoelectric beam was performed using the Galerkin truncation method and harmonic balance method.
TL;DR: In this paper, an optimization scheme for the resonator distribution in rainbow metamaterials was proposed, aiming at minimizing the maximum and average receptance values respectively, with the objective function for both single and multiple frequency ranges optimization set up with the frequency response functions predicted by an analytical model.
TL;DR: A light-responsive elastic metamaterial whose transmission spectrum can be tuned by light stimuli is introduced, and it is demonstrated that an appropriate laser illumination is effective in reversibly widening an existing frequency band gap, doubling its initial value.
Abstract: The metamaterial paradigm has allowed an unprecedented space-time control of various physical fields, including elastic and acoustic waves. Despite the wide variety of metamaterial configurations proposed so far, most of the existing solutions display a frequency response that cannot be tuned, once the structures are fabricated. Few exceptions include systems controlled by electric or magnetic fields, temperature, radio waves and mechanical stimuli, which may often be unpractical for real-world implementations. To overcome this limitation, we introduce here a polymeric 3D-printed elastic metamaterial whose transmission spectrum can be deterministically tuned by a light field. We demonstrate the reversible doubling of the width of an existing frequency band gap upon selective laser illumination. This feature is exploited to provide an elastic-switch functionality with a one-minute lag time, over one hundred cycles. In perspective, light-responsive components can bring substantial improvements to active devices for elastic wave control, such as beam-splitters, switches and filters. Here, the authors present a light-responsive elastic metamaterial whose transmission spectrum can be tuned by light stimuli. More specifically, we demonstrate that an appropriate laser illumination is effective in reversibly widening an existing frequency band gap, doubling its initial value.
TL;DR: In this article, a permanent magnet (PM) resolver has been proposed, which is equipped with low-price Hall Effect sensors to measure the magnetic flux density and has a robust performance in high electromagnetic disturbance environments.
Abstract: Resolvers as position sensors need a high frequency AC excitation voltage, and the induced voltage in their 2-phase perpendicular windings are amplitude modulated (AM) signals. For calculating the position, it is required to demodulated the output signals and calculate their envelopes. Then, inverse tangent can be used for calculating the position. Despite the advantages of resolvers, there are some drawbacks in their application. Calculating the envelopes is always one of the deep concerns in using resolvers. Furthermore, due to low-amplitude of the excitation flux, the performance of the resolvers is strongly affected by electromagnetic interference by the stray fields of motor and brake. Complicated winding process is the next challenge of resolvers. The last concern is referred to the high speed applications where to maintain the accuracy of the sensor it is required to increase the excitation frequency. While, the maximum frequency of excitation is limited by the frequency response of the employed ferromagnetic core and the employed resolver to digital converter (RDC). To overcome all the mentioned worries, a new permanent magnet (PM) resolver is proposed in this paper. The presented resolver has no copper winding and no need to the high frequency excitation. It is equipped by low-price Hall Effect sensors to measure the magnetic flux density and has a robust performance in high electromagnetic disturbance environments. All the analysis is done using time stepping finite element method (TSFEM) and verified by experimental measurements on a built prototype.
TL;DR: The results show the effectiveness and robustness of the proposed intelligent fault diagnosis and prognosis method based on NARMAX-FRF and PCA for nonlinear defect signal analysis and the performance of the experiment of intelligent RFID system of corrosion monitoring and the TOFD experimental system are analyzed.
TL;DR: In this article, the nonlinear primary resonance in the vibration control of a cable-stayed beam with time delay feedback was investigated. And the effect of control gain and time delay on the amplitude and frequency response behavior were investigated.
TL;DR: A novel method based on NOFRFs and the CNN-LSTM model for detecting the early damages in structures is proposed, motivated by the powerful learning abilities of convolutional neural networks (CNN) and long short-term memory (L STM) networks.
Abstract: Frames, shells, and hybrid structures with early damages, such as early cracks, often behave as extremely weak nonlinear systems, among which the nonlinearity is difficult to be detected, especially if the system response is affected by the noise. To avoid these damages becoming catastrophic failures, developing effective incipient damages detection methods is important. The nonlinear output frequency response functions (NOFRFs) and associated indexes can be considered as one kind of the prospective detection tools, which are usually determined from the established nonlinear autoregressive with exogenous inputs (NARX) model. However, the hyperparameters in the NARX model are difficult to be determined so that the identification accuracy cannot be guaranteed. Therefore, it is important to develop more accurate methods to estimate the NOFRFs and their associated indicators for damage detection. Motivated by the powerful learning abilities of convolutional neural networks (CNN) and long short-term memory (LSTM) networks, a novel method based on NOFRFs and the CNN-LSTM model for detecting the early damages in structures is proposed. By applying the beat excitation, the response of the structure is divided into two components, where the approximately linear component is used to estimate the frequency characteristic of the linear component by the classical linear model and the nonlinear component is used to establish the CNN-LSTM model. By calculating the responses of the two models, the NOFRFs and associated indexes can be accurately estimated, and then the early damage can be detected. Simulation and experimental studies verify the potential and effectiveness of the novel method proposed in this article.
TL;DR: A practical secondary frequency control strategy for virtual synchronous generator (VSG) with predictable rotor frequency response is proposed in this letter and the complexity of parameter design is reduced obviously.
Abstract: A practical secondary frequency control (SFC) strategy for virtual synchronous generator (VSG) with predictable rotor frequency response is proposed in this letter. The relationship between rotor inertia, damping factor, integral coefficient and the time constant of low-pass filter is revealed, moreover, the complexity of parameter design is reduced obviously. Finally, the proposed concept is verified by Simulation results.
TL;DR: Comparison between the electrical properties of different devices should be made using high frequency impedance measurements performed in the steady-state voltage regime in which the cell is expected to operate, and it is shown that the high frequency response contains all the key information relating to the Steady-state performance of a PSC.
Abstract: Interpreting the impedance response of perovskite solar cells (PSCs) is significantly more challenging than for most other photovoltaics. This is for a variety of reasons, of which the most significant are the mixed ionic-electronic conduction properties of metal halide perovskites and the difficulty in fabricating stable, and reproducible, devices. Experimental studies, conducted on a variety of PSCs, produce a variety of impedance spectra shapes. However, they all possess common features, the most noteworthy of which is that they have at least two features, at high and low frequency, with different characteristic responses to temperature, illumination and electrical bias. The impedance response has commonly been analyzed in terms of sophisticated equivalent circuits that can be hard to relate to the underlying physics and which complicates the extraction of efficiency-determining parameters. In this paper we show that, by a combination of experiment and drift-diffusion (DD) modelling of the ion and charge carrier transport and recombination within the cell, the main features of common impedance spectra are well reproduced by the DD simulation. Based on this comparison, we show that the high frequency response contains all the key information relating to the steady-state performance of a PSC, i.e. it is a signature of the recombination mechanisms and provides a measure of charge collection efficiency. Moreover, steady-state performance is significantly affected by the distribution of mobile ionic charge within the perovskite layer. Comparison between the electrical properties of different devices should therefore be made using high frequency impedance measurements performed in the steady-state voltage regime in which the cell is expected to operate.
TL;DR: In this paper, a bending-torsion L-shaped bimorph harvester with large face shear piezoelectric coefficients (d36) was proposed to increase the levels of harvested energy and increase the frequency bandwidth.
TL;DR: No prior knowledge of power system model is required in this work, including generator configuration, operation condition, and frequency response of each component, and the overall system frequency characteristic is approximated online by the proposed estimator.
Abstract: With the advantage of quick response and flexible ramp, energy storage system (ESS) offers a promising capability of fast frequency control for power systems, especially under a severe disturbance. This paper proposes an ESS control strategy using local measurement in order to provide fast frequency support right after a sufficiently severe disturbance is observed. The proposed strategy includes online frequency characteristic estimator and online optimization controller. Distinguished from existing approaches, no prior knowledge of power system model is required in this work, including generator configuration, operation condition, and frequency response of each component. Instead, the overall system frequency characteristic is approximated online by the proposed estimator. Then, the power setpoint of ESS is determined adaptively to participate in frequency control by the proposed model predictive controller. Finally, the effectiveness of the proposed method is verified via real-world data of a provincial power grid in China.
TL;DR: In this paper, the authors developed a semi-analytical model for solving the transient and steady-state contact responses of a rigid sphere sliding/rolling on a viscoelastic layer-elastic substrate system.
Abstract: This paper reports the development of a novel semi-analytical model for solving the transient and steady-state contact responses of a rigid sphere sliding/rolling on a viscoelastic layer-elastic substrate system. The displacement transmissions at the layer-substrate interface are affected by spring-like or dislocation-like defects. The analytical transient and steady-state viscoelastic frequency response functions (FRFs) are derived from the elastic solutions with imperfect interfaces. Instead of using the integration form of the creep function, viscoelastic modulus E(ω) is directly incorporated into the viscoelastic FRFs by a frequency-velocity transform that links the time-related frequency, ω, and sliding velocity, V, with the space-related frequency number, m, i.e. ω=−mV. The solutions are so formulated that fast numerical techniques, such as the conjugate gradient method (CGM) and the discrete convolution-fast Fourier transform (DC-FFT) algorithm, can be incorporated for computation efficiency. The developed model is employed to investigate the effects of layer thickness, modulus, sliding velocity, and the degree of interface imperfection on the viscoelastic contact response of the material system, including pressure distributions, displacements, viscoelastic dissipation, and subsurface stresses.
TL;DR: A control method that takes into account the WT fatigue load and the frequency response of the power system is proposed and the differential evolution (DE) algorithm is used to optimize the PID parameters based on multi-cost functions.
TL;DR: In this paper, an equivalent circuit-based design was proposed to synthesize second-order band-pass frequency selective surfaces (FSSs) with wide out-of-band rejection and fast roll-off characteristics.
Abstract: In this article, we proposed an equivalent circuit-based design to synthesizing second-order band-pass frequency selective surfaces (FSSs) with wide out-of-band rejection and fast roll-off characteristics. An equivalent circuit model (ECM) is established in order to depict the desired frequency response. Then, based on the ECM, a generalized composite structure comprised of three FSS arrays separated by two dielectric substrates is proposed. The main advantage of this method is that it allows us to acquire optimized structural parameters according to the desired frequency response. With this method, an FSS based on the proposed composite structure is designed. The designed FSS can provide a second-order pass-band within the stop-band ranging from 1 to 40 GHz and the pass-band is operating at 10 GHz with 12% fractional bandwidth. Meanwhile, the bandwidth of the two transitional bands on both sides of the pass-band is only 0.26 and 0.6 GHz, respectively. Also, the frequency response of the designed FSS is stable at 60° for both TE and TM polarizations. For further verification, an FSS prototype is fabricated and experimentally characterized. Good agreements between the simulated and measured results can be observed.
TL;DR: A control strategy for the multi-terminal VSCs aiming at PLL-less synchronization and autonomous frequency response of the MTDC system is proposed, which exhibits advantages in weak grid operation andonomous frequency response.
Abstract: Recent analyses have shown that the grid-integration of offshore wind farms through MTDC systems has brought low inertia and small-signal stability issues, in which the dynamics of phase-locked-loop (PLL) play a crucial role. To address this issue, this article proposes a control strategy for the multi-terminal VSCs aiming at PLL-less synchronization and autonomous frequency response of the MTDC system. One of the significant features of the proposed control is that the deviation of the grid frequency can be instantaneously reflected on the deviation of the DC voltage without ancillary control. Based on this feature, a fast inertia response and primary frequency regulation among wind farms and AC systems interconnected by the MTDC system can be achieved. A small-signal model is established to evaluate the overall system stability using the proposed control. Finally, comparative studies of this proposed control with the conventional PLL-based vector control are conducted in PSCAD/EMTDC based on a practical MTDC system in China, the Zhangbei four-terminal HVDC transmission system. The analysis shows that the proposed control exhibits advantages in weak grid operation and autonomous frequency response.