Search

In this research, a 100% inverter-based resource (IBR)-penetrated bulk power system (BPS) is examined for possible interarea oscillations. A testbed of a BPS constructed in PSCAD, with both grid-forming inverter (GFM)-based IBRs and grid-following inverter (GFL)-based IBRs, is utilized for simulation. For linear analysis, a data-driven method is used to obtain the $dq$ admittance models of the IBRs. This information, combined with our knowledge of the network admittance, leads to eigenvalue analysis of the power grid. Furthermore, for the dominant 3-Hz mode, extended frequency-domain mode shape analysis, along with subgroup effect analysis, and network decomposition analysis are conducted. The analysis results can precisely tell the influencing factors of the oscillation mode. This mode is identified as an interarea oscillation mode. It has a different characteristics compared to the traditional electromechanical interarea mode. Specifically, the network decomposition analysis provides new insights on interarea oscillation modes. The analysis results are all confirmed by the electromagnetic transient (EMT) simulation results.

Tower cranes with slender jib transporting bulky loads are commonly applied in the construction site. Human-operated commands induce vibrations of the cantilever jib, swing, and twisting of the suspended load. Coupled oscillations among jib deflection, load swing and load twisting exhibit complex dynamic behavior. Furthermore, coupled-system frequencies significantly differ from uncoupled frequencies of the jib and pendulum. Unfortunately, little attention has been directed at the coupled-oscillation dynamics and control of jib deflection, load swing, and load twisting. A dynamic model of a tower crane slewing a slender jib and moving a distributed-mass load is derived. The fully coupled effects among jib deflection, load swing, and load twisting are described in the model. Then, an equation for predicting coupled-system frequencies is presented from the analytical model. Meanwhile, a hybrid piecewise smoother is proposed to filter out coupled oscillations among jib deflection, load swing and load twisting. Many experiments validate the utility of frequency-estimation equation and verify the success of the smoother. [ABSTRACT FROM AUTHOR]

A normally-off SiC-JFET/GaN-HEMT cascode device is recently proposed, featuring a cascode configuration that incorporates a high-voltage (HV, e.g., 1200 V) silicon-carbide (SiC) junction field effect transistor (JFET) delivering the HV blocking capability and a low-voltage (LV) enhanced-mode (E-mode) gallium-nitride (GaN) high electron mobility transistor (HEMT) providing the normally-off gate control. This all-wide-bandgap device exhibits superior thermal stability and high switching speed compared to its counterparts, e.g., the SiC/Si cascode device. In this article, we study short-circuit (SC) characteristics of a 1200-V/80-mΩ SiC/GaN cascode device by considering the interactions between the SiC and GaN devices. The single-event SC withstand time (SCWT) of the demonstrated SiC/GaN cascode device is tested to be ∼3 μs under a dc-bus voltage (Vdc) of 600 V when the turn-on gate voltage (VG-on) is set to 5 V. The SC failure occurs due to the formation of hot spots induced by thermal-runaway leakage currents inside the SiC JFET. The SCWT of the cascode device could be improved by applying a moderate VG-on (e.g., SCWT = ∼6.5 μs at VG-on = 3.5 V under v dc = 600 V) without affecting the on-state resistance (r on). However, it is identified that current oscillations tend to be triggered during the SC period when VG-on is too low (e.g., lower than 3 V). The oscillation behavior is attributed to the energy stored in the interconnection parts between the SiC and GaN devices. The harmful oscillations could be suppressed by applying higher VG-on, which drives the SiC JFET into low-transconductance mode by modulating the drain-to-source voltage (VDS-G) of the LV GaN HEMT. [ABSTRACT FROM AUTHOR]

The risk of unstable subsynchronous oscillations (SSO) in DFIG-based wind parks radially connected to transmission lines with series capacitive compensation is typically assessed with numerous electromagnetic transient (EMT) simulations, which is a time-consuming process. However, not all operating scenarios present risk of SSO and require such a detailed investigation. This paper proposes two charts based on impedance equivalents of wind generators obtained through frequency scans to quickly map which combinations of parameters can create unstable SSOs and which combinations are risk-free. With the information, engineers can immediately filter out scenarios with no risk of instability and conduct detailed studies on fewer scenarios that are truly critical. These charts can be obtained with simple equations that use only information readily available in practice to engineers, without the need to run any computer simulation. The charts also reveal the key operating conditions that can increase the risk of an unstable SSO and provide real-time quantitative insights into how close a wind park is to an instability. Application examples are provided to illustrate how this approach can help engineers speed up studies to identify the risk of SSO. [ABSTRACT FROM AUTHOR]

In recent years, very high frequency (VHF) converter has attracted much attention. However, with rich parasitic parameters and complex resonance links, there are some great difficulties to the modeling of such systems. Taking the on-off controlled VHF resonant boost converter as an example, this paper presents an accurate modeling and analysis method that considers multiple parasitic parameters. First, the closed-loop VHF converter system is divided into a main network and a parasitic oscillation network. Then, based on the operation analysis, an equivalent circuit model characterized by a time-varying input voltage source and two variable duty-cycle controlled switches is proposed. It worth noting that both the time-varying input and the controlled switches take into account the influences of the parameters. Furthermore, the periodic approximate analytical solution of the output voltage in the on stage is obtained by using the equivalent small parameter method to the proposed circuit model. And then combining the solution of the parasitic oscillation network and on-off state switching conditions, the steady-state waveform of output voltage can be obtained quickly. Finally, a prototype with operating frequency of 21.44 MHz is built to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The method of analytical study of the influence of impulse moments on nonlinear torsional oscillations of a homogeneous constant cross-section of a body under classical boundary conditions of the first, second, and third types have been developed. When the flexible material properties meet the body close to the power law of flexibility, mathematical models of the process have been obtained. It is the boundary value problem for an equation of hyperbolic type with a small parameter at the discrete right-hand side. The latter expresses the effect of pulse momentum on the oscillatory process. Under the effect of periodic pulse momentum on a flexible body, resonant and non-resonant processes are possible. Resonant processes occur when the amplitude of natural oscillations approaches a fixed value. The peculiarities of resonant oscillations are established. The amplitude of passing through the primary resonance is significant for larger values of the nonlinearity parameter and, in the case of the action of pulse momentum, closer to the middle of the body. If the initial perturbation amplitude is less than the amplitude at which the resonance occurs in the presence of only internal forces of viscous friction. So, the external periodic impulse moments of resonance processes have occurred. The extreme case confirms the reliability of the results obtained related to the dynamics of the respective objects under the continuous action of autonomous perturbation.

The static deflection compensation method of a planar multi-link flexible manipulator is proposed using the feedback from inertial sensors mounted at the tip of each link. The proposed compensation technique is validated experimentally using a high-precision laser tracker. The proposed strategy is experimentally verified using a three-link flexible manipulator. A strategy to compensate for the centripetal and tangential acceleration induced on the accelerometer mounted on the rotating link is proposed for correct inclination estimation. The improvement in the inclination estimation using the proposed compensation technique is verified both in simulation and experimental studies.

The high penetration of renewables has sparked new oscillatory concerns in hybrid AC/DC grids. Knowledge of the oscillation regarding its source and propagation mechanism, is crucial to system operation. In this respect, the frequency-domain modal analysis (FMA) provides a way (e.g., participation factor) to extract these oscillation properties, and has been widely applied in converter-based AC grids. Compared to AC grids, oscillation properties of hybrid AC/DC grids are much more complex. Such complexity mainly originates from the diversity of oscillation propagation behaviors in hybrid AC/DC grids, where a distinctive local-area oscillation will emerge. Therefore, a dedicated oscillation propagation analysis for hybrid AC/DC grids is desired, which is the main focus of this paper. First, the mechanism of the distinctive local-area oscillation is analyzed considering AC/DC coupled dynamics of converters. Then, a systematic method for the oscillation propagation analysis is presented, where indices for characterizing the local-area oscillation and its impact area are established. Finally, some propagation properties are discussed, by which a strategy for the online oscillation source locating is designed. Case studies are carried out in a typical hybrid AC/DC grid to validate the propagation analysis in this paper. [ABSTRACT FROM AUTHOR]

Online condition monitoring of winding insulation has been proved to be an effective means to improve the reliability of an inverter-fed machine, but little work has been done on the insulation of line-end coil subjected to much higher transient voltage stress with a higher risk of premature insulation break down. In this article, the inverter self-excited high-frequency switching oscillations are utilized for the line-end coil insulation condition monitoring. To improve the condition monitoring sensitivity and its robustness to dynamic operating conditions, a switching oscillation mode decomposition method is proposed. First, the condition-sensitive mode, i.e., high-frequency common-mode (HFCM) current is selected and separated by the variation mode decomposition algorithm among three dominant modes in switching oscillation current. Then, the amplitude-frequency features of HFCM current are extracted for condition monitoring. Finally, the overall insulation condition of three-phase line-end coils and the degree of asymmetric degradation are quantitatively evaluated by the frequency and amplitude features respectively. Experimental work was carried out and the results demonstrate the good performance of high sensitivity, good robustness, and non-contract safety. [ABSTRACT FROM AUTHOR]

With the loss of a large number of space vectors under switch open-circuit faults, the neutral point potential (NPP) control of T-type three-level converters is faced with a huge challenge. It becomes harsh to balance the NPP and maintain the symmetry of line voltages under switch open-circuit faults simultaneously. In order to improve the NPP control performance and stable operation of T-type three-level converters, this article presents a hybrid modulation strategy that can enhance the NPP control ability even under switch open-circuit faults. Through a carrier-based analysis tool, two candidate modulation strategies are first evaluated from the perspective of the adjustment range of the neutral point current. The first one maintains the conventional three-level modulation in two nonfault phase arms. The second one degrades the mode of modulation from three-level modulation to two-level modulation in two nonfault phase arms. By making full use of the NPP oscillation characteristics of the two candidate methods, a hybrid modulation strategy based on transition duty-cycle and enabled bridge-arm adjustment is put forward to achieve a comprehensive optimal control performance. Numerical analysis and experiments are carried on to prove the correctness and feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

Multiconverters connected to grid can induce subsynchronous oscillation (SSO). This article proposed an analytical damping contribution assessment method that can explicitly reveal how (positively or negatively) and to which degree each converter in the multiconverters system changes the system stability level. First, the energy network model of the multiconverters system that satisfies energy conservation is proposed. On this basis, a theory proof is presented that the real part of eigenvalue of SSO mode in the multiconverters system is equal to the sum of coefficient in the aperiodic components of the derivative of dynamic energies injected by each converter and dissipation energy of network, which illustrates analytically how the SSO stability level is shaped. The dynamic energy showing a decreasing trend is good for the oscillation to disappear, and the faster the dynamic energy decreases, the faster the oscillation amplitude decreases. Thus, how and to which degree converter changes stability level can be revealed by the changing trend and rate of its dynamic energy, respectively. Moreover, the expression of dynamic energy is brief, which is, thus, readily for online use, and is universal for converters with different control strategies. Finally, hardware in loop tests verifies that, eliminate converters’ rapidly increasing dynamic energy, the unstable SSO converges rapidly, and eliminate converters’ slowly increasing dynamic energy, the unstable SSO converges but slowly, and eliminate converters’ decreasing dynamic energy, unstable SSO diverges more rapidly, which demonstrates that dynamic energy can precisely assess damping contribution of converter. [ABSTRACT FROM AUTHOR]

Virtual synchronous generator (VSG) control introduces active power oscillation especially under the condition of multi-VSG. This article proposes a decentralized mutual damping control method that suppresses power oscillation in the multi-VSG grid. The idea is that as the local frequency is greater than the frequency of the VSG other than itself, the input energy of the local VSG is reduced, and thus dωi/dt increases. On the contrary, when the local frequency is less than others, the input energy is increased, and thus dωi/dt decreases. In this way, all frequencies get close to each other in the dynamic process with the method. The idea is verified by the stability analysis. Participation factor analysis and sensitivity analysis are presented to guide parameter design. Finally, the effectiveness of the decentralized mutual damping method is verified through the simulation results and experimental results. [ABSTRACT FROM AUTHOR]

The increasing use of voltage-source converters (VSCs) in modern power systems has led to extensive studies on their frequency response and stability, which are characterized by power-frequency oscillations and overshoots following a disturbance. However, the existing small-signal analysis models do not adequately describe the impact of the types of disturbance on the torque-frequency dynamics of the multi-VSC parallel system. In this paper, based on the principle of electromechanical analogy, a unified equivalent admittance modeling method is proposed by analogizing the rotor dynamic model of a synchronous generator (SG) to the circuit network, which has the advantages of simple modeling, clear physical meaning and easy expansion. Firstly, the equivalent admittance model of a single SG/VSC is established, and then easily extended to the multi-VSC system. The proposed modelling method not only applicable to a variety of VSCs, but also can handle different types of disturbance. More importantly, the circuit theory can be applied to analyze the torque-frequency dynamic characteristics. Subsequently, the equivalence between the proposed model and the state-space model under different damping terms is compared. In addition, the response characteristics of two different damping terms are compared. Next, the dynamic response characteristics of single VSC and multi-VSC parallel systems under different disturbances are analyzed. Finally, related simulations and experiments are executed to verify the accuracy and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The switching oscillations and voltage overshoots excited by ultrafast switching transients are urgently required to be overcome for SiC mosfet. Herein, the C-RC snubber is employed to address these adverse issues. An optimized C-RC snubber design is proposed, which can not only suppress the switching oscillation and overvoltage, but also effectively reduce the snubber loss compared with the dc-link RC snubber. This will be beneficial to the actual application of this snubber into the high-power and high-frequency field. For the turn-off overvoltage, the varying tendency of the overshoot with snubber parameters are analyzed according to the equivalent impedance network so that the parameter selection principle can be obtained preliminarily. Then, the C-RC snubber parametric region where both oscillations and overvoltages can be sufficiently suppressed is established using the root locus. Distinctive from the prior-art C-RC design to seek the peak impedance, the proposed switching ringing suppression method is developed by the way of actively assigning poles of fifth-order system to tune an optimal damping ratio. Then, the final design can be determined by minimizing the snubber loss within the obtained parametric range. Finally, the influence of snubber circuit on overvoltage, switching oscillation, and snubber loss are illustrated and verified in detail using the double-pulse tests. Moreover, the application of C-RC snubber in the chopper circuit further highlights its superiority of low snubber loss. [ABSTRACT FROM AUTHOR]

Ignoring parts of the dynamics of a multiterminal DC (MTDC) power system can simplify its stability analysis but may miss some instability risks in the analyzed results. This study analyzed the stability of DC voltage oscillation by considering comprehensive dynamics of an MTDC system in a DC voltage time scale to reveal the stability mechanism of the DC voltage oscillation accurately. It demonstrated that a DC voltage oscillation loop is first formed by the DC voltage control of the voltage source converter (VSC). Subsequently, it is affected by the dynamics of the remaining DC system (RDCS) through two paths: (1) the equivalent conductance of the RDCS is equal to an additional damping added to the DC voltage oscillation loop, and (2) the equivalent susceptance forms a mirrored subsystem and results in an open-loop modal resonance, which always induces negative effects on DC voltage oscillation stability. These conclusions are also correct in parts of the MTDC system using DC voltage droop control. Moreover, a method was proposed to quickly determine the stable operating region of the RDCS. Finally, accuracy of the stability mechanism of the DC voltage oscillation and effectiveness of the proposed method are verified based on the SIMULINK platform. [ABSTRACT FROM AUTHOR]

Synchronization is the key of AC power system operation, but its mechanism becomes unclear with the large-scale integration of voltage-source converters (VSCs). As an important feature distinguishing VSCs from synchronous generators (SGs), the current-source characteristics of VSCs have hardly been focused from the perspective of synchronization. In this letter, a synchronization mechanism between power-synchronized voltage-source (VS) and PLL-controlled current-source (CS) is clarified. Based on this mechanism, negative damping oscillations of SGs caused by VSCs are disclosed. [ABSTRACT FROM AUTHOR]

In this letter we propose an extension of the Dissipating Energy Flow (DEF) method for locating sources of forced oscillations (FOs), based on an energy function constructed by the complex integral approach, which we call Complex DEF (CDEF). To trace sources of FO, we study the scalar projection of CDEF in a specific direction on the complex plane. We show by simulated cases that this alternative has a good performance in cases where the original DEF fails. [ABSTRACT FROM AUTHOR]

The control plant model of multiple grid-connected converters is a multivariable coupling model. There is complex coupling interaction between the control loops of the multiple converters, resulting in poor current control quality or interaction oscillation issues when the grid impedance is high or the number of converters is large. This article proposes a novel multivariable decoupling control method based on a summation difference coordinate for eliminating the current control interaction between multiple converters. With a summation difference coordinate transformation matrix, the multivariable model of multiple converters can be transformed to be multiple single-variable models. By designing specific current regulators for the summation current and the difference current loops in the summation difference coordinate, the summation current and each difference current can be regulated independently. Compared with the conventional methods, the proposed method can improve the current control bandwidth and stability without introducing any high-frequency oscillation especially when the grid impedance is high or the number of converters is large. Moreover, based on the proposed approach, the classical single variable control theory is enough to designthe regulator parameters for any number of converters under the new coordinate system. Experimental results of four three-phase 2 kW two-level converters have been presented, which validates the proposed approach. [ABSTRACT FROM AUTHOR]

Road irregularities induce vertical and longitudinal vibrations of the sprung and unsprung masses, which affect vehicle comfort. While the vertical dynamics and related compensation techniques are extensively covered by the suspension control literature, the longitudinal dynamics on uneven road surfaces are less frequently addressed, and are significantly influenced by the tires and suspension systems. The relatively slow response of internal combustion engines does not allow any form of active compensation of the effect of road irregularities. However, in-wheel electric powertrains, in conjunction with pre-emptive control based on the information on the road profile ahead, have some potential for effective compensation, which, however, has not been explored yet. This paper presents a proof-of-concept nonlinear model predictive control (NMPC) implementation based on road preview, which is preliminarily assessed with a simulation model of an all-wheel drive electric vehicle with in-wheel motors, including a realistic tire model for ride comfort simulation. The major improvement brought by the proposed road preview controller is evaluated through objective performance indicators along multiple maneuvers, and is confirmed by the comparison with two benchmarking feedback controllers from the literature. [ABSTRACT FROM AUTHOR]

A large number of experiments have proved that the ring structure is a common phenomenon in neural networks. Nevertheless, a few works have been devoted to studying the neurodynamics of networks with only one ring. Little is known about the dynamics of neural networks with multiple rings. Consequently, the study of neural networks with multiring structure is of more practical significance. In this article, a class of high-dimensional neural networks with three rings and multiple delays is proposed. Such network has an asymmetric structure, which entails that each ring has a different number of neurons. Simultaneously, three rings share a common node. Selecting the time delay as the bifurcation parameter, the stability switches are ascertained and the sufficient condition of Hopf bifurcation is derived. It is further revealed that both the number of neurons in the ring and the total number of neurons have obvious influences on the stability and bifurcation of the neural network. Ultimately, some numerical simulations are given to illustrate our qualitative results and to underpin the discussion. [ABSTRACT FROM AUTHOR]

The trust-region-based sequential convex programming (TSCP) method is designed to solve the nonlinear trajectory planning problem using successive linearization and trust region. The TSCP method has a good real-time performance suitable for onboard aerospace applications. However, the main challenge in practical applications is its poor convergence. In this article, we reveal an oscillation phenomenon, which is an important factor affecting the convergence. The main contribution of this article is threefold: 1) the oscillation phenomenon is proved to be an inherent property of the TSCP method for the nonlinear trajectory planning problem; 2) the oscillation condition that determines whether oscillation occurs is obtained; and 3) the oscillation-condition-based remedy to address the oscillation is presented. The effectiveness and robustness of the proposed remedy have been verified via a complex reentry trajectory planning problem. [ABSTRACT FROM AUTHOR]

In the presence of multiple power converters in a power system the total current may exhibit zero-crossing distortion in the form of recurrent damped oscillations with high magnitude. These oscillations are synchronized with the power system frequency. This paper presents a comprehensive analysis of the input current of single-phase ac-dc converters fitted with power factor correction (PFC) controllers. Emphasis is given on the impacts of the source impedance, and on how the number of converters connected to a common coupling point (PCC) impacts the PFC controller’s performance. A system model is developed followed by simulation and measurements in a real installation with electronic ballasts used to drive fluorescent lighting tubes. Results show that the recurrent damped oscillations originating from PFC controllers are close to the harmonic range and with a very low level of cancellation between devices. The magnitude therefore increases proportionally with the number of devices. As the source impedance increases, instability may occur. Possible explanations for these observations are discussed. [ABSTRACT FROM AUTHOR]

Most of the existing stability analysis methods are capable of determining the oscillatory stability of black-box converter interfaced generators (CIGs) under given operating conditions only but can hardly identify the critical operating conditions. In this letter, an oscillatory stability region (OSR) is defined with the short-circuit ratio and output power as variables, and a method to obtain the OSR for the black-box CIG is proposed. First, the CIG is modeled as a variable-operating-point impedance model (VOPIM) through perturbation tests. Then, the critical operating points, for which the CIG system has a zero-damping oscillation mode, are determined by VOPIM-based oscillatory stability analysis so as to obtain the OSR. Finally, the accuracy of the OSR is verified through control hardware-in-the-loop tests. The OSR is of significant meaning for the control strategy and operation plan optimization of the CIGs. [ABSTRACT FROM AUTHOR]

Damping control plays an important role in suppressing the oscillation modes of virtual synchronous generators (VSGs). The most widely used damping control method through a frequency deviation feedback path is confronted with multiple challenging inherent contradictions among the different control objectives, resulting in seriously degraded control performance of VSGs. To resolve these contradictions fundamentally, this article proposes a novel phase feedforward damping (PFD) control method for VSG from the perspective of restructuring the damping controller. It replaces the traditional frequency deviation feedback path with a novel damping controller utilizing a phase feedforward path. Then, considering the grid-connected and islanding operation modes, respectively, a detailed comparative study of the traditional damping-based VSG (Tra-VSG) and the PFD-based VSG (PFD-VSG) is conducted. Both the theoretical and experimental results demonstrate convincingly that the proposed PFD control method can reconcile the different control objects of VSG, and thus, compared with Tra-VSG, PFD-VSG exhibits vastly superior response performance of the active power and the frequency in both grid-connected and islanding operation modes. [ABSTRACT FROM AUTHOR]

This article proposes an improved tubular single-phase permanent magnet linear oscillation actuator (SP-PMLOA) considering eliminating detent force for direct drive compressor applications. First, the flux tube method and Maxwell stress tensor are used to derive the end force and cogging force formulations based on the magnetic flux leakage of the magnet rings. Then, a novel model with minimum detent force is presented by finite element parametric sweeping. Finally, the electromagnetic performance of the three SP-PMLOAs is compared using 2-D finite element analysis (FEA), whose merits are evaluated, and the thermal distribution of the optimal PMLOA is analyzed using 3-D FEA. The predicted results show that the proposed structure not only can significantly reduce the detent force and the mover axial length but also can increase the thrust force-moving magnet mass ratio. [ABSTRACT FROM AUTHOR]

This letter discusses performance degradation of traditional supervisory control and data acquisition (SCADA)-based static state estimation (SSE) caused by violation of the static assumption. The sensitivity of non-synchronized sampling errors against oscillations is tested through real measurement data and grid model from a subsystem of the North American power gird. The test results show that as an important reason leading to the failure of SCADA-based SSE, the non-synchronized sampling error of SCADA is sensitive to oscillations in that the error rapidly increases when oscillations occur and vanishes when the oscillations cease. [ABSTRACT FROM AUTHOR]

To enhance the real-time monitoring of sub-/super-synchronous oscillation dynamics by utilizing the advantages of wide-area time-synchronization and dynamic measurement of synchrophasor measurement data, the idea of a parameter identification algorithm with synchrophasor trajectory fitting (PTF) is proposed in this letter to identify the parameters of each component of the instantaneous signal during sub-/super-synchronous oscillations. Simulated PMU data are used to demonstrate the proposed idea and verify the performance of PTF compared with the interpolated DFT algorithm. Discussions are also provided for further improvements. [ABSTRACT FROM AUTHOR]

This article presents an L2 norm-enabled variable step-size adaptive least mean square controller for grid-connected photovoltaic converter. The variable step size is adopted to damp out the weight oscillations and to enable faster convergence under exposure to disturbances in the load and solar insolation. More precisely, to achieve oscillations free response, a nonlinear relationship is developed between step size and estimated error. This way, it significantly improves the convergence speed and stability. The iteration function of the presented variable step-size feature includes the input signal to study the impact of harmonically polluted load current on the weight extraction performance. Besides, the designing procedure of step size considers both current and previous error states, thereby ensuring noise immunity. With the inclusion of these features, the devised controller is applied to accurately extracting the fundamental weight component of the load current and in turn enabling various ancillary services. The proposed control algorithm is designed in matlab/Simulink software and its effectiveness is examined under both steady-state and transient conditions during grid disturbances. Furthermore, the practicability of the proposed controller is verified and compared with conventional controls using ARM cortex M4 microcontroller-based laboratory test bed. In a nutshell, the results confirm the oscillations free weight component with higher convergence and better stability under various operating conditions. [ABSTRACT FROM AUTHOR]

Objective: Beta bursts of local fields potentials (LFPs) recorded from subthalamic nucleus (STN) have been recently proposed as a new temporal feature for patients with Parkinson's disease (PD). We introduce a new technique for the adaptive time-domain segmentation of STN-LFP recordings such that the constructed time segments are proportional to the duration of stationary beta activity. We investigated whether the spectral entropy of the adaptively captured beta oscillations can describe the improvement in motor signs following dopaminergic medication. Methods: STN-LFP recordings from externalized chronic deep brain stimulation (DBS) leads were obtained in 9 PD patients. During this monitoring, each patient underwent 3 medication intake cycles where short acting agents (L-DOPA equivalent dose) were administered. We analyzed 2-minute resting state LFP data in each OFF and L-DOPA-induced ON medication states and constructed time domain segmentation of LFP signal in which the length segmentations are adapted to time-varying nature of the oscillatory activity. Results: Adaptively constructed segments were noted to be significantly longer in OFF- and shorter in ON-state (p<0.001). Interestingly, in the OFF state, the peak frequency of long beta bursts (>375 ms) was in the low range (12-23 Hz) of the beta spectrum, whereas shorter beta bursts (<375 ms) were widespread in the 13-30 Hz band. Measured clinical improvement was highly correlated with the difference in the spectral entropy of beta bursts between OFF and ON states (r = −0.83, p<0.01). Conclusion and significance: Our findings suggest that beta oscillations can be adaptively segmented without the use of a predetermined amplitude threshold, thereby allowing for objective quantification of burst itself. Compared to the shorter ones, longer oscillations with duration ≥ 375 ms were highly correlated with the clinical improvement, supporting a pathological role for them. Overall, these findings coupled with our adaptive approach could enable the quantitative use of temporal dynamics of beta activity in assessing severity of PD and improvements in motor features. [ABSTRACT FROM AUTHOR]

Virtual synchronous generator (VSG) has been a grid-friendly integration control technique for the integration of grid-connected inverters. However, the emulated inertia and damping of VSG control technique can also be used in the field of dc systems. In this article, a virtual synchronous control is proposed to dampen the wideband oscillation of dc voltage in a dc microgrid. The proposed control strategy contributes to maintaining the synchronous operation of dc converter with the network. Besides, the relationships among damping, inertia, wideband oscillation, rate of change of voltage (RoCoV) as well as DC voltage nadir (DCVN) are studied. It is concluded that the RoCoV and DCVN are similar as the oscillation frequency and fluctuation ranges of poorly-damped oscillation, respectively. A unified concept is proposed by connecting the oscillation-related stability with the inertial transient response originated from the imbalanced powers/mismatched currents. Besides this, the inertia plays the same role as damping because the inertia contributes to maintaining the original state and damping to impeding further change. A new feedback analytical method is proposed to clarify the important role of RoCoV and DCVN on the motion of dc voltage. Finally, the theoretical results are compared with simulations and experiments. [ABSTRACT FROM AUTHOR]

Virtual synchronous generator (VSG), recognized as a grid-friendly control technique, contributes to providing inertia and damping support from the grid-tied power electronic systems. However, similar to the conventional synchronous generator, the VSG is vulnerable to wideband oscillations and can even become unstable when the system is subjected to a variety of disturbances. To tackle this issue, this article proposes a magnitude-phase motion equation (MPME) for grid-forming VSG attached to a weak grid. Besides, a feedback analytical method is introduced to identify the frequency dynamic stability, judged by the sign of (dω/dt)/δω. Besides, the rate of change of frequency (RoCoF) and frequency nadir (FN) are evaluated by the two indices, i.e., dω/dt and δω. In addition, the relationship between the low-inertia-RoCoF-FN-related stability and the weak-damping-oscillation-related stability is illustrated by the feedback analysis. Moreover, in the framework of MPME, a reactive-power feedforward (RPFF) decoupling control strategy is proposed for the enhancement of stability and robustness performance of the VSG system. Finally, the proposed modeling and the RPFF decoupling control strategy are demonstrated with the experiments. [ABSTRACT FROM AUTHOR]

Closed-loop stimulation for targeted modulation of brain signals has emerged as a promising strategy for episodic memory restoration. In parallel, closed-loop neuromodulation strategies have been applied to treat brain conditions including drug-resistant depression, Parkinson’s Disease, and epilepsy. In this study, we seek to apply control theoretical principles to achieve closed loop modulation of hippocampal oscillatory activity. We focus on hippocampal gamma power, a signal with an established association for episodic memory processing, which may be a promising ‘biomarker’ for the modulation of memory performance. To develop a closed-loop stimulation paradigm that effectively modulates hippocampal gamma power, we use a novel data-set in which open-loop stimulation was applied to the posterior cingulate cortex and hippocampal gamma power was recorded during the encoding of episodic memories. The dataset was used to design and evaluate a linear quadratic integral (LQI) servo-controller in order to determine its viability for in-vivo use. In our simulation framework, we demonstrate that applying an LQI servo controller based on an autoregressive with exogenous input (ARX) plant model achieves effective control of hippocampal gamma power in 15 out of 17 experimental subjects. We demonstrate that we are able to modulate gamma power using stimulation thresholds that are physiologically safe and on time scales that are reasonable for application in a clinical system. We outline further experimentation to test our proposed system and compare our findings to emerging closed-loop neuromodulation strategies. [ABSTRACT FROM AUTHOR]

The generation of self-sustaining oscillations at the output of nonlinear systems without tracking a reference signal is under investigation. In this study, we proposed an internal double fuzzy inference system to generate an asymptotically stable limit cycle or self-oscillations for the second-order systems. The fuzzy system has been synthesized by invoking the Poincaré–Bendixson theorem, which states sufficient and necessary conditions of existence of an attracting periodic orbit at the output of the closed-loop system. This theorem was also used for design; that is, we set the tuning rules of the fuzzy controller. The effectiveness of the proposed controller is corroborated by numerical simulations and experiments made in a single-link pendulum system. [ABSTRACT FROM AUTHOR]

As a terahertz (THz) radiation source, the frequency-tunable gyrotron is promising in application and attractive to researchers. In this article, the nonstationary phenomenon in a frequency-tunable gyrotron operating in different regimes—gyromonotron, transition, and gyro-backward-wave oscillator (BWO)—has been investigated in detail by 3-D particle in cell (PIC) simulation. Simulated results demonstrate that among the three regimes, gyromonotron has the strongest capability to keep stationary, and nonstationary oscillations are most likely to occur in the transition regime. Moreover, in the gyro-BWO regime, the capability of the system to maintain steady-state operation gets slightly improved with the increase in the axial mode. The corresponding interpretation is based on detuning frequency and feedback mechanism. Finally, the effect of the velocity spread on the nonstationary behavior has also been studied. Investigations reveal that the stability of stationary oscillations would be weakened when velocity spread is considered. The results in this article may be of benefit of a deeper insight into the nonstationary phenomenon in a frequency-tunable gyrotron. [ABSTRACT FROM AUTHOR]

In grid-connected photovoltaic (PV) systems, grid inductance greatly influences the performance of grid-connected inverters. However, the grid inductance usually varies with the changes of the grid operation conditions. Therefore, accurate grid inductance detection is one of the key technologies to achieve an adaptive control of the grid-connected inverters under different operation conditions. In this article, an equivalent circuit model of a grid-connected PV system which includes the controller, filter, and grid impedance is established. The oscillation characteristic of the inverter terminal voltage caused by the sudden change of the inverter output power is analyzed. The oscillation mechanism of the inverter terminal voltage caused by the interaction of the controller, filter, and grid impedance is investigated. A grid inductance detection method based on the oscillation characteristic of the inverter terminal voltage is proposed. The main advantage of the proposed method is that it does not need complicated signal processing and calculation procedures. A 10-kW grid-connected PV system was built for both simulations and the experimental setup. Finally, simulation and experimental results validate the correctness and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Dual-active-bridge series-resonant converter (DABSRC) is increasingly used in many emerging power electronics applications requiring fast dynamic responses. However, under conventional transient phase-shift modulation strategy, DABSRC generally suffers from large-amplitude transient oscillations when its phase-shift angle is changed abruptly by a high-gain controller. These oscillations occur at the beat frequency, which results from the interaction between the switching-frequency and resonant-frequency components in the series-resonant tank during transient states. Besides incurring high voltage and current stresses on the power-stage devices, these transient oscillations also span many switching cycles between the original and new steady states and cause perturbations to the output voltage of DABSRC, thereby degrading its dynamic performance and output voltage quality. To mitigate these problems, a new transient modulation strategy, known as trajectory-switching modulation (TSM), is proposed for achieving an accurate and computationally efficient trajectory planning of the resonant voltages and currents of DABSRC during transient states, and its basic operation is to govern the transient switching patterns of the gating signals according to a simple set of closed-form equations. The proposed TSM strategy can guarantee convergence to the next new steady state within about one switching cycle and avoid needing costly sensors and complex computation for implementation, and it is inherently compatible with high-gain controllers for realizing oscillation-free fast dynamic responses. [ABSTRACT FROM AUTHOR]

Due to the absence of the natural current zero-crossing point, the dc interruption has been a critical issue in the dc system. The interruption schemes currently used are based on power electronics or precharged capacitors, leading to the high cost and complicated control strategy. In this article, a passive oscillation dc load current breaking scheme based on a vacuum interrupter is proposed. The external transverse magnetic field (ETMF) is applied to the vacuum interrupter to excite the oscillation of the arc voltage. According to the spectrum analysis of the arc voltage, a passive LC path is designed to realize resonant oscillation with the interrupter, by which 2 kA/10 kV interruption is realized within 2 ms. The influence of the gap separation, ETMF intensity, and arcing energy on the resonant oscillation process is investigated. At last, the practicability of applying the proposed scheme in HVdc interruption is discussed. [ABSTRACT FROM AUTHOR]

This letter presents a novel global asymptotic stability (GAS) criterion for fixed-point digital filters (DFs) employing saturation overflow arithmetic. The criterion is developed using an improved characterization of saturation nonlinearities (as prevailing in the DF under study) and Lyapunov theory. The criterion outperforms a series of existing criteria. [ABSTRACT FROM AUTHOR]

Oscillations of grid-connected voltage source converter (VSC) usually reaches sustained state because of the limiters in controller. Describing function has been adopted to analyze the amplitude and frequency of the sustained oscillations, but high-order oscillation components caused by the limiter are ignored in previous literatures. This letter proposes an analysis method for sustained oscillations which considers high-order oscillation components. This method could obtain a more precise oscillation frequency and the amplitude of 1st, 2nd, and 3rd order components. The proposed method is verified by case studies and simulations in PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

The existing inertia estimation based on electromechanical oscillation relies on a single mode, which is limited in complex systems. In this letter, the inertia is estimated without worrying about the number of modes in the oscillation. The inertia expression is derived based on the swing equation in the frequency domain, which considers the mode coupling in the electromechanical bandwidth using a summation calculation. The effectiveness of the proposed inertia estimation method is validated through simulation data and real measurements. [ABSTRACT FROM AUTHOR]

Conventional full-bridge and half-bridge (HB) converters are quite popular for front-end power factor preregulation (PFP) in electric vehicle (EV) battery chargers. Discontinuous conduction mode (DCM) operation at high power causes increased oscillation in the circuit. These oscillations increase with parasitic components of circuit. During deep DCM operation, these oscillations are seen to be significant and contribute to harmonic content in the input current. Therefore, a PFP bridgeless isolated HB converter based EV charger with reduced LC oscillation in DCM is presented in this article. To reduce LC oscillation, two diodes are used in series with minimum number of magnetic components. The design of proposed charger in DCM is illustrated to facilitate uniform battery current during constant current/constant voltage charging. The inherent advantage of reduced conduction loss with bridgeless topology is achieved. The performance of this isolated HB converter based charger is shown for improved oscillation characteristics and power quality operation at steady state and over a range of varying input voltages. [ABSTRACT FROM AUTHOR]

With a high proportion of new energy and power electronic equipment connected to the modern power system, a new type of subsynchronous oscillation (SSO) is triggered, which affects the safe and stable operation of the system. Accurate analysis and identification of the SSO source becomes the key to studying this problem. This article presents a novel method to analyze SSOs. First, multisynchrosqueezing transform is applied to the signal to get the concentrated time–frequency analysis results. Then, the ridge tracking method is utilized to identify and reconstruct the subsynchronous component signals. The method of dissipating energy flow is applied to locate the source and sink of the SSO in the subsynchronous component signals. The performances of the proposed method are verified using electromagnetic transient simulations in a three-wind farms system and a modified IEEE 10-generator 39-bus New England power system. [ABSTRACT FROM AUTHOR]

High-stability optoelectronic oscillators (OEOs) are attained using self-forced oscillation techniques using long optical delays. Free-running InP-based multi-mode laser (MML) diodes with free-spectral range (FSR) of 11.7 GHz is stabilized using self-electrical injection-locked (SEIL) and dual self-phase-locked loop (DSPLL) (SEILDPLL) approach; phase noise of the free-running OEO of −52.8 dBc/Hz at 10-kHz offset was improved by 36 dB experimentally. Self-forced stabilization of MML-based OEO results in timing jitter of 0.9 ps, a factor of 33 times reduction in the free-running performance. A fully integrated solution using Si-photonics (SiP) is more environmentally stable and amenable to a reduced large volume manufacturing. A heterogeneously integrated MML combined with self-forced function is designed on an approximately 91-cm2 SiP chip using 325- and 975-ns time delays. [ABSTRACT FROM AUTHOR]

Rate control is the most used operation method for master–slave hydraulic manipulators. However, the trajectory from the master controlled by the operator cannot completely meet the dynamic limitations and flow restriction of the hydraulic manipulator. Continuous large errors and oscillation will occur due to flow restrictions and high-order dynamics beyond the dynamic boundaries that significantly limits the velocity tracking performance of a hydraulic manipulator. In this article, we propose a flow-limited rate control scheme for the master–slave hydraulic manipulators. The variable velocity mapping is developed, adjusting the velocities to meet the pump and valves’ flow limits. An adaptive robust rate controller of hydraulic manipulators is designed. An adaptive boundary estimator is introduced to estimate the hydraulic manipulator acceleration boundaries, and a variable structure controller is used to plan the velocities to meet dynamic limits. The proposed control scheme is tested on a hydraulic manipulator. The results show that the control scheme reduced velocity error and avoid the manipulator vibration, so the performance is improved for the hydraulic manipulator. [ABSTRACT FROM AUTHOR]

We employ a novel data-enabled predictive control (DeePC) algorithm in voltage source converter (VSC)-based high-voltage DC (HVDC) stations to perform safe and optimal wide-area control for power system oscillation damping. Conventional optimal wide-area control is model based. However, in practice, detailed and accurate parametric power system models are rarely available. In contrast, the DeePC algorithm uses only input-output data measured from the unknown system to predict the future trajectories and calculate the optimal control policy. We showcase that the DeePC algorithm can effectively attenuate interarea oscillations even in the presence of measurement noise, communication delays, nonlinear loads, and uncertain load fluctuations. We investigate the performance under different matrix structures as data-driven predictors. Furthermore, we derive a novel Min-Max DeePC algorithm to be applied independently in multiple VSC-HVDC stations to mitigate interarea oscillations, which enables decentralized and robust optimal wide-area control. Further, we discuss how to relieve the computational burden of the Min-Max DeePC by reducing the dimension of prediction uncertainty and how to leverage disturbance feedback to reduce the conservativeness of robustification. We illustrate our results with high-fidelity, nonlinear, and noisy simulations of a four-area test system. [ABSTRACT FROM AUTHOR]

In this work, the accuracy of row–column tensor velocity imaging (TVI), i.e., 3-D vector flow imaging (VFI) in 3-D space over time, is quantified on a complex, clinically relevant flow. The quantification is achieved by transferring the flow simulated using computational fluid dynamics (CFD) to a Field II simulation environment, and this allows for a direct comparison between the actual and estimated velocities. The carotid bifurcation flow simulations were performed with a peak inlet velocity of 80 cm/s, nonrigid vessel walls, and a flow cycle duration of 1.2 s. The flow was simulated from two observation angles, and it was acquired using a 3-MHz 62+62 row–column addressed array (RCA) at a pulse repetition frequency (${f}_{prf}$) of 10 and 20 kHz. The tensor velocities were obtained at a frame rate of 208.3 Hz, at ${f}_{prf} = {10} ~\mathrm{kHz}$ , and the results from two velocity estimators were compared. The two estimators were the directional transverse oscillation (TO) cross correlation estimator and the proposed autocorrelation estimator. Linear regression between the actual and estimated velocity components yielded, for the cross correlation estimator, an ${R}$ 2 value in the range of 0.89–0.91, 0.46–0.77, and 0.91–0.97 for the ${x}$ -, ${y}$ -, and ${z}$ -components, and 0.87–0.89, 0.40–0.83, and 0.91–0.96 when using the autocorrelation estimator. The results demonstrate that an RCA can, with just 62 receive channels, measure complex 3-D flow fields at a high volume rate. [ABSTRACT FROM AUTHOR]

Virtual synchronous machine (VSM) based high voltage dc systems enhance the inertia of the power system. However, the dynamic interactions between the VSM-based rectifier station, the inverter station, and the grid could induce the system oscillation, which has been investigated in this article. At first, the hybrid ac–dc impedance models of the VSMs considering the coupling between the ac and dc dynamics are established. Then, the relationships between the dc impedance, dq-frame impedance, and the hybrid ac–dc impedance are presented. It is found that the dc impedance of the VSM-based inverter station and the d-d channel impedance of the dq-frame impedance of the rectifier station behave as negative resistors in the low-frequency range. Moreover, a five-dimensional impedance stability criterion based on the hybrid ac–dc impedance and generalized inverse Nyquist criterion is proposed to assess the system stability. The analysis results show that the low-frequency oscillation occurs when the grid short-circuit ratio of the rectifier station is small. Finally, the simulation and experimental results verify the impedance models and the stability criterion. [ABSTRACT FROM AUTHOR]

Sudden torque change caused by the TM (traction motor) of HEV (hybrid electric vehicle) can lead to severe driveline oscillation, furthermore the backlash between engaging components in the driveline could increase the vibration amplitude. This paper focuses on the driveline oscillation of a series-parallel hybrid vehicle on launch condition. An analytic model of driveline torsional vibration considering disturbance brought by nonlinear backlash is established and simplified for the convenience of controller design. Based on the simplified model, a feedforward control strategy is proposed to suppress HEV launch vibration. However, the control effect will deteriorate sharply with the increase of equivalent backlash in the driveline system. To improve vibration attenuation performance, a feedback compensator is established and incorporated into the control system, with a robust sliding mode observer which is designed to estimate unknown disturbances as feedback signal. Numerical simulation is applied to validate vibration attenuation performance of the feedforward-feedback hybrid control strategy. Simulation results demonstrate that the feedforward-feedback control strategy has better robustness to cancel the unwanted effects of disturbance brought by nonlinear backlash compared with other control methods, which can be regarded as an effective approach to attenuate driveline oscillation and thus improve ride comfort on launch condition. [ABSTRACT FROM AUTHOR]

The power oscillation damper (POD) in the doubly-fed induction generator (DFIG) is to damp the low- frequency oscillation (LFO) in the power systems. But the POD will introduce the LFO to the DFIG and intensify the oscillation of the latter. In this paper, open-loop subsystems of the DFIG with the POD and the rest part of power system are derived to describe the interaction between them. The balanced truncation method is used to reduce the transfer function of the DFIG and derive the analytical description to the oscillation of the DFIG. Considering the impact of the POD on the DFIG, the constraint to the DFIG is newly incorporated in the optimization model to the POD parameters, with the aim to alleviate the oscillation of both the DFIG and power system. The simulation verifies the accuracy of the reduced model of the DFIG, and validates the effectiveness of the improved optimization to the POD of the DFIG. [ABSTRACT FROM AUTHOR]

Fundamental sensor feedback limitations for improving rotor angle stability using local frequency or phase angle measurement are derived. Using a two-machine power system model, it is shown that improved damping of inter-area oscillations must come at the cost of reduced transient stability margins, regardless of the control design method. The control limitations stem from that the excitation of an inter-area mode by external disturbances cannot be estimated with certainty using local frequency information. The results are validated on a modified Kundur four-machine two-area test system where the active power is modulated on an embedded high-voltage dc link. Damping control using local phase angle measurements, unavoidably leads to an increased rotor angle deviation following certain load disturbances. For a highly stressed system, it is shown that this may lead to transient instability. The limitations derived in the paper may motivate the need for wide-area measurements in power oscillation damping control. [ABSTRACT FROM AUTHOR]