Showing papers on "Transient (oscillation) published in 2020"
TL;DR: A design-oriented transient stability analysis of the grid-forming VSCs is presented, revealing that the PSC and the basic droop control can retain a stable operation as long as there are equilibrium points, due to their noninertial transient responses, while thedroop control with LPFs and the VSG control can be destabilized even if the equilibrium points exist.
Abstract: Driven by the large-scale integration of distributed power resources, grid-connected voltage-source converters (VSCs) are increasingly required to operate as grid-forming units to regulate the system voltage/frequency and emulate the inertia. While various grid-forming control schemes have been reported, their transient behaviors under large-signal disturbances are still not fully explored. This article addresses this issue by presenting a design-oriented transient stability analysis of the grid-forming VSCs. First, four typical grid-forming control schemes, namely, the power-synchronization control (PSC), the basic droop control, the droop control with low-pass filters (LPFs), and the virtual synchronous generator (VSG) control, are systematically reviewed, whose dynamics are characterized by a general large-signal model. Based on this model, a comparative analysis on the transient stabilities of different control schemes is then carried out. It reveals that the PSC and the basic droop control can retain a stable operation as long as there are equilibrium points, due to their noninertial transient responses, while the droop control with LPFs and the VSG control can be destabilized even if the equilibrium points exist, due to the lack of damping on their inertial transient responses. With the phase portrait, the underlying stability mechanism is explicitly elaborated, and the quantitative impacts of the controller gains and the virtual inertia are clearly identified. Subsequently, controller design guidelines are proposed to enhance the system damping as well as the transient stability. Finally, experimental results are provided to verify the theoretical analysis.
244 citations
TL;DR: An adaptive PLL that switches between the second-order and the first-order PLL during the fault-occurring/-clearing transient is proposed for preserving both the transient stability and the phase-tracking accuracy.
Abstract: Differing from synchronous generators, there are lack of physical laws governing the synchronization dynamics of voltage-source converters (VSCs). The widely used phase-locked loop (PLL) plays a critical role in maintaining the synchronism of current-controlled VSCs, whose dynamics are highly affected by the power exchange between VSCs and the grid. This article presents a design-oriented analysis on the transient stability of PLL-synchronized VSCs, i.e., the synchronization stability of VSCs under large disturbances, by employing the phase portrait approach. Insights into the stabilizing effects of the first- and second-order PLLs are provided with the quantitative analysis. It is revealed that simply increasing the damping ratio of the second-order PLL may fail to stabilize VSCs during severe grid faults, whereas the first-order PLL can always guarantee the transient stability of VSCs when equilibrium operation points exist. An adaptive PLL that switches between the second-order and the first-order PLL during the fault-occurring/-clearing transient is proposed for preserving both the transient stability and the phase-tracking accuracy. Time-domain simulations and experimental tests, considering both the grid fault and the fault recovery, are performed, and the obtained results validate the theoretical findings.
180 citations
TL;DR: Comparisons show that the proposed transient-extracting transform method can provide a much more energy-concentrated time–frequency representation, and the transient components can be extracted with a significantly larger kurtosis.
Abstract: In industrial rotating machinery, the transient signal usually corresponds to the failure of a primary element, such as a bearing or gear. However, faced with the complexity and diversity of practical engineering, extracting the transient signal is a highly challenging task. In this paper, we propose a novel time–frequency analysis method termed the transient-extracting transform, which can effectively characterize and extract the transient components in the fault signals. This method is based on the short-time Fourier transform and does not require extended parameters or a priori information. Quantized indicators, such as Renyi entropy and kurtosis, are employed to compare the performance of the proposed method with other classical and advanced methods. The comparisons show that the proposed method can provide a much more energy-concentrated time–frequency representation, and the transient components can be extracted with a significantly larger kurtosis. The numerical and experimental signals are used to show the effectiveness of our method.
134 citations
TL;DR: It is indicated that loss of synchronism (LOS) of PLLs is responsible for the transient instability of grid-connected RECSs during LVRT, and the LOS is essentially due to the transient interaction between the PLL and the weak terminal voltage.
Abstract: Grid-connected renewable energy conversion systems (RECSs) are usually required by grid codes to possess the low voltage ride through (LVRT) and reactive power support capabilities so as to cope with grid voltage sags. During LVRT, RECS's terminal voltage becomes sensitive and changeable with its output current, which brings a great challenge for the RECS to resynchronize with the grid by means of phase-locked loops (PLLs). This paper indicates that loss of synchronism (LOS) of PLLs is responsible for the transient instability of grid-connected RECSs during LVRT, and the LOS is essentially due to the transient interaction between the PLL and the weak terminal voltage. For achieving a quantitative analysis, an equivalent swing equation model is developed to describe the transient interaction. Based on the model, the transient instability mechanism of RECSs during LVRT is clarified. Furthermore, a transient stability enhancement method is proposed to avoid the possibility of transient instability. Simulations performed on the New England 39-bus test system verify the effectiveness of the method.
105 citations
TL;DR: The transient angle stability of a paralleled synchronous and virtual synchronous generators (SG-VSG) system is investigated by comparing it with that of the paralleled VSGs system and a control method is proposed to improve the transient stability.
Abstract: With the development of virtual synchronous generator (VSG) techniques, parallel operations of synchronous generators (SGs) and VSGs become increasingly common in a microgrid. The differences between paralleled systems will affect the transient stability of the system, which probably threatens stable operation of the system, especially under fault conditions. In this article, the transient angle stability of a paralleled synchronous and virtual synchronous generators (SG-VSG) system is investigated by comparing it with that of the paralleled VSGs system. It is observed that the paralleled SG-VSG system is more prone to transient instability due to the differences between their speed governors. Then, a control method is proposed to improve the transient stability of the paralleled SG-VSG system. Furthermore, a Lyapunov method is employed to establish the nonlinear model of islanded microgrid, by which the attraction domain of paralleled system is quantified. The hardware-in-loop experiment is performed to validate the theoretical analysis.
99 citations
TL;DR: A fault location method based on the analysis of the energy of the transient zero-sequence current in the selected frequency band (SFB) is proposed and the implementation scheme is illustrated with the distribution level phasor measurement units.
Abstract: As a result of small fault current, high level of noise and a large penetration of distributed generators (DG), in the neutral non-effectively grounded medium-voltage (MV) distribution networks, it is quite difficult to locate the faulted line section for single phase to ground faults. In this paper, using a technique based on synchronized measurements in distribution networks, a fault location method based on the analysis of the energy of the transient zero-sequence current in the selected frequency band (SFB) is proposed. The equivalent impedance of the distribution network with lateral branches is studied with an equivalent network, and the phase-frequency characteristics of the equivalent impedance are analyzed. The SFB, within which the transient energy of the faulty line section is larger than that of the healthy line sections is determined. A combined fault-section location criterion is proposed and the implementation scheme is illustrated with the distribution level phasor measurement units. Numerical simulations of the IEEE 34 node system and the field experiments of a 10kV distribution network validate the feasibility and effectiveness of the proposed method.
93 citations
TL;DR: This article analyzes the large-signal synchronization stability of grid-connected VSGs, and proposes a mode-adaptive power-angle control method for enhancing the transient stability, which prevents the VSG-based system from collapsing due to the delayed fault clearance or the malfunction of protective relays.
Abstract: The virtual synchronous generator (VSG) is emerging as an attractive solution for interconnecting converter-based resources with the power grid. However, due to the nonlinear power-angle relationship, VSGs are, similar to synchronous generators, prone to the loss of synchronization (LOS) under large grid disturbances. This article, thus, analyzes the large-signal synchronization stability, i.e., the transient stability of grid-connected VSGs, and then proposes a mode-adaptive power-angle control method for enhancing the transient stability. In this approach, the positive-feedback mode of the power-angle control of the VSG is detected and adaptively switched to the negative-feedback mode after large disturbances. Thus, the LOS of the VSG can be avoided when there are equilibrium points after the disturbance. Moreover, during severe grid faults without any equilibrium points, a bounded dynamic response of the power angle can be obtained with the mode-adaptive control, and the VSG can still be stabilized even if the fault-clearing time is beyond the critical clearing time. These superior features prevent the VSG-based system from collapsing due to the delayed fault clearance or the malfunction of protective relays. Finally, the time-domain simulations and experimental tests are performed to verify the effectiveness of the control method.
91 citations
TL;DR: The proposed generalized state space average model (GSSAM) for multi-phase interleaved buck, boost and buck-boost converters can describe the operation at any number of operating phases with switching dynamics of phases and is validated by comparing the transient and steady-state dynamics between the GSSAM and a switching model from PLECS.
Abstract: This paper presents a generalized state space average model (GSSAM) for multi-phase interleaved buck, boost and buck-boost converters. The GSSAM can model the switching behavior of the current and voltage waveforms, unlike the conventional average model which can model only the average value. The GSSAM is used for the converters with dominant oscillatory behavior such as resonant converters, high current ripple converters, and multi-converter systems. The maximum current and voltage through the system can be predicted by modeling the switching behavior of voltage and current. The GSSAM in the literature is introduced for single-phase converters only, and it is not introduced for multi-phase converters due to the high complexity associated with it. Hence, the GSSAM for multi-phase buck, boost and buck-boost converters are introduced in this paper and the proposed models can fit with converters of any number of phases. The number of operating phases in the multi-phase interleaved converters is proportional with the output power to achieve the maximum efficiency over the operating range. Therefore, the proposed GSSAMs can describe the operation at any number of operating phases with switching dynamics of phases. The proposed GSSAM is validated by comparing the transient and steady-state dynamics between the GSSAM and a switching model from PLECS.
82 citations
TL;DR: The simulated and experimental results show that the proposed method can not only much faster extract the fault characteristics than the traditional K-SVD method, but also more accurately detect the repetitive transients than the infogram method and the traditional SVD method.
Abstract: To detect the incipient faults of rotating parts used in electromechanical systems widely, a novel transient feature extraction method based on the improved orthogonal matching pursuit (OMP) and one-dimensional K-SVD algorithm is explored in this paper. First, the stopping criterion of adaptive spark is developed, and then the corresponding OMP algorithm is used to remove the modulated and harmonic signals adaptively. Second, the residual signal is reformulated as a signal matrix by period segmentation and circulating shift, and the initial transient dictionary is constructed via the time-domain average technique. Subsequently, a novel K-SVD algorithm is proposed to get the optimized transient dictionary for the one-dimensional signal. Finally, the repetitive transient signal is recovered by the optimized dictionary. The simulated and experimental results show that the proposed method can not only much faster extract the fault characteristics than the traditional K-SVD method, but also more accurately detect the repetitive transients than the infogram method and the traditional K-SVD method.
81 citations
TL;DR: In this article, a commercial p-gate GaN high-electron-mobility transistor (HEMT) with Ohmic-and Schottky-type gate contacts is studied.
Abstract: An essential ruggedness of power devices is the capability of safely withstanding the surge energy. The surge ruggedness of the GaN high-electron-mobility transistor (HEMT), a power transistor with no or minimal avalanche capability, has not been fully understood. This article unveils the comprehensive physics associated with the surge-energy withstand process and the failure mechanisms of p-gate GaN HEMTs. Two commercial p-gate GaN HEMTs with Ohmic- and Schottky-type gate contacts are studied. Two circuits are developed to study the device surge ruggedness: an unclamped inductive switching circuit is first used to identify the withstand dynamics and failure mechanisms, and a clamped inductive switching circuit with a controllable parasitic inductance is then designed to mimic the surge energy in converter-like switching events. The p-gate GaN HEMT is found to withstand the surge energy through a resonant energy transfer between the device capacitance and the load/parasitic inductance rather than a resistive energy dissipation as occurred in the avalanche. If the device resonant voltage goes below zero, the device reversely turns on and the inductor is discharged. The device failure occurs at the transient of peak resonant voltage and is limited by the device overvoltage capability rather than the surge energy, dV/dt , or overvoltage duration. Almost no energy is dissipated in the resonant withstand process and the device failure is dominated by an electric field rather than a thermal runaway. These results provide critical understandings on the ruggedness of GaN HEMTs and important references for their qualifications and applications.
81 citations
TL;DR: In this article, the authors investigated the accelerating up transient vibrations of a rotor system under both the random and uncertain-but-bounded parameters, and used the Polynomial Chaos Expansion (PCE) coupled with the Chebyshev Surrogate Method (CSM) to analyze the propagations of the two categorizes of uncertainties.
TL;DR: It is well demonstrated here that the proposed method is able to prevent the increase in irreversible distance angle of VSGs relative to each other, which is the main factor in preventing VSGs reaching to instability point.
Abstract: This paper examines a completely novel method for improving the transient stability of multi virtual synchronous generator (VSG) grids. In this method, it has been tried to control the oscillation of VSGs with respect to the center of inertia frequency (COI-frequency) of the grid, during short-circuit. It is also well demonstrated here that the proposed method is able to prevent the increase in irreversible distance angle of VSGs relative to each other, which is the main factor in preventing VSGs reaching to instability point. The method can enhance both the synchronizing and damping terms efficiently. Detailed analyzing of the direct Lyapunov method illustrates the non-linear proof of the method. Also, non-linear algebraic equations for a two-VSG system have been derived to prove the possibility of corroborating simulation results. Equal area criterion is also used to clarify this method further. One interesting feature of the method is that there is no conflict between the requirements of the low voltage ride-through and transient stability improvement.
TL;DR: In this paper, a real-time detection algorithm of decaying dc component is first developed for a generic single-phase distorted ac signal, and fast and robust elimination of both decaying dc transient and harmonics can be performed simultaneously in three-phase grids, by adoption of moving average filters in $d$ − $q$ frame and subsequent calculations.
Abstract: Active power filters are conventionally utilized to compensate steady-state harmonic currents and reactive power in the utility, yet their capabilities are usually limited if the elimination of undesirable effects associated with decaying dc components during transients is the target, especially under the weak grid condition. In this letter, active cancellation of the typical first-order decaying dc-mode transients is explored. To this end, a real-time detection algorithm of decaying dc component is first developed for a generic single-phase distorted ac signal. Furthermore, fast and robust elimination of both decaying dc transient and harmonics can be performed simultaneously in three-phase grids, by adoption of moving average filters in $d$ – $q$ frame and subsequent calculations. Hardware-in-the-loop experiment results verified the effectiveness of the proposed technique.
TL;DR: The proposed ITPS is proved as a promising solution in eliminating the dc-bias current, minimizing the transient current stress by using an improved triple-phase-shift (ITPS) control for DAB converters.
Abstract: A transient dc-bias current due to the voltage-second imbalance of isolated bidirectional dual-active-bridge (DAB) converters for the disturbance in line or load may result in the transformer saturation and oscillations in both sides dc currents. This article focuses on the transient dc-bias current elimination by using an improved triple-phase-shift (ITPS) control for DAB converters. The inductor peak current stress optimization is adopted in the proposed ITPS to determine the steady-state phase-shift variables. Originated from the dc-bias current model of DAB converters with the TPS control, the transient phase-shift adjustment strategy can be determined, which has the ability to improve the inductor current changing slope and shorten the settling time. Both simulation and experiments for different conditions are provided to evaluate main dynamic indexes such as the transient period, dc-bias current, and inductor current stress for three different transition cases. The proposed ITPS is proved as a promising solution in eliminating the dc-bias current, minimizing the transient current stress.
TL;DR: In this paper, the impact load and instantaneous fluid pressure of transient flow on pump station system under the nonregulative operating conditions, the transient characteristics of an axial flow pump during start-up process are investigated experimentally and numerically.
TL;DR: The robust output voltage regulation problem of DC-DC boost converter system is addressed by using a continuous nonsingular terminal sliding mode control (CTSMC) technique based on finite-time disturbance observer to achieve better voltage tracking performance.
Abstract: DC-DC converters work as one of the crucial components in DC microgrid intergraded power systems. In this brief, the robust output voltage regulation problem of DC-DC boost converter system is addressed by using a continuous nonsingular terminal sliding mode control (CTSMC) technique based on finite-time disturbance observer. By integrating the disturbance estimations into the controller design, an improved sliding mode control (SMC) approach is developed to achieve better voltage tracking performance. The proposed control method admits the properties of fast transient responses, strong suppression ability against time-varying disturbances and small steady state oscillations of output voltage. Experimental results in the presence of both load variations and supplied voltage fluctuations are provided to validate the effectiveness of the proposed algorithm.
TL;DR: In this paper, an artificial neural network (ANN) based on feedforward back-propagation multilayered perceptron (MLP) was utilized to predict transient heat transfer coefficient.
TL;DR: An output-capacitorless low-dropout regulator (OCL-LDO) using a dual-active feedback frequency compensation (DAFFC) scheme with both transient and stability enhancement has been presented in this article.
Abstract: An output-capacitorless low-dropout regulator (OCL-LDO) using a dual-active feedback frequency compensation (DAFFC) scheme with both transient and stability enhancement has been presented in this paper. The DAFFC scheme consists of two parallel active feedback paths, which creates two pole-zero pairs to effectively enhance the stability and transient response for the proposed OCL-LDO. Compared to the conventional single-path active-feedback frequency compensation method, the proposed DAFFC technique has provided one more design freedom with one more active feedback loop deployed and has been proved to be capable of obtaining better compensation effects with the same capacitor budget. Besides, the induced extra ac currents by the two active feedback loops have also enhanced the transient response of the proposed OCL-LDO. To substantiate the proposed DAFFC, a telescopic cascode output stage for error amplifier, and two on-chip compensation capacitors (5 and 1 pF, respectively) are needed. The proposed OCL-LDO has been implemented in 65-nm CMOS technology and the active chip area is 0.0105 mm2. The output voltage is 0.8 V, and the minimum input voltage is 0.95 V at 100-mA loading current. The proposed OCL-LDO can work stably in a load range of 0 to 100 mA with 14-μA quiescent current.
TL;DR: Simulation results demonstrate that the proposed scheme, with low computational complexity, can distinguish internal faults from external ones and protect the entire line reliably and can also identify high-impedance faults and select the faulted pole correctly.
Abstract: To overcome shortages in the traditional current differential protection for HVDC transmission lines, a pilot protection based on transient energy ratio is proposed. The fault identification criterion is put forward based on the impedance-frequency characteristic of the line boundary, and the fault analysis which shows that under internal faults, with regard to either terminal of the dc line, the transient energy within a specific frequency band on the line side of the boundary is much greater than that on the valve side of the boundary, whereas after rectifier-terminal (inverter-terminal) external faults, the transient energy on the line side of the rectifier-terminal (inverter-terminal) boundary is much less than that on the valve side of the boundary. Moreover, the lightning disturbance identification criterion is implemented based on the magnitude ratio of fault components of high- and low-frequency band currents. Fault-pole selection is constructed by using the fault components of pole voltages. Simulation results demonstrate that the proposed scheme, with low computational complexity, can distinguish internal faults from external ones and protect the entire line reliably. It can also identify high-impedance faults and select the faulted pole correctly. Besides, it is not subject to lightning interferences and the dc line distributed capacitor.
TL;DR: In this paper, an active voltage balancing control for series-connected MOSFETs is proposed, which has no penalty of sacrificing the switching performance of SiC MOSFs.
Abstract: Limited by low availability, high price, and poor switching performance of high-voltage power devices, connecting low-voltage devices in series to block much higher voltages is always an option. However, severe voltage unbalance during turn-off transient remains to be solved. Most of the existing methods designed for low-speed silicon (Si) insulated gate bipolar transistor (IGBT) cannot be directly transplanted to the series-connected silicon carbide (SiC) MOSFETs with high switching speed. To maximum the switching performance of SiC MOSFETs, an elegant implementation of adjusting driving signal time delay method is proposed. In addition, a simplified model during drain–source voltage rising transient is discussed to basically reveal features and problems of the series-connected SiC MOSFETs. The factors affecting the appropriate time delay are discussed as well, especially the influence of the load current. The simplified model and the implementation are both verified by experiments. Indeed, the proposed active voltage balancing control works well and has no penalty of sacrificing switching performance of SiC MOSFETs.
TL;DR: A novel low-latency device-level power converter modeling approach is proposed for field programmable gate array (FPGA)-based real-time simulation and the accuracy of FPGA-based simulation results is validated by the error evaluation with respect to the results from offline simulation tools.
Abstract: The device-level real-time simulation of power converters is constrained by the contradiction between the required short simulation time step to describe the transient behaviors and the large computational amount caused by the nonlinearities of switches’ models. In this paper, a novel low-latency device-level power converter modeling approach is proposed for field programmable gate array (FPGA)-based real-time simulation. A piecewise linear insulated-gate bipolar transistor (IGBT)/diode transient model is proposed based on the inductive switching behaviors. The switching transient is modeled into four phases, which are identified by the boundaries between three operating regions of IGBT and between two operating modes of a diode. Moreover, each phase is approximated by a linear continuous behavior in order to reduce the real-time computational amounts. Accompanied by the effective boundary identification, the device-level IGBT/diode model can be efficiently integrated into the real-time simulation with low computational latency. A dc–dc–ac topology model is implemented on the FPGA-based real-time platform, as a case study to verify the effectiveness and practicability of the proposed approach. With the help of circuit partitioning techniques, the device-level converter model can be simulated with a 50-ns time step on FPGA. Moreover, the accuracy of FPGA-based simulation results is validated by the error evaluation with respect to the results from offline simulation tools.
TL;DR: Experimental results show that onboard device aging can successfully be achieved during systems start-up in the order of microseconds, and imply that device turn-on time is a viable aging precursor and can be used to monitor device health at system start- up.
Abstract: This paper presents an silicon carbide (SiC) MOSFET health condition monitoring method based on the switching transient measurements. Specifically, the device's turn -on time is used as the aging precursor, and a detection circuit is developed with picosecond resolution to detect the variations of the turn -on time. For this purpose, power cycles with constant junction temperature swings are applied on sample devices to accelerate their thermally triggered degradation. Over the aging process, device parameters are measured periodically using automated curve tracer to observe degradation-related changes. Also, a double pulse tester is used to evaluate devices’ switching transient changes throughout aging. Based on these results, both the theoretical discussions and experimental results imply that device turn -on time is a viable aging precursor and can be used to monitor device health at system start-up. High-resolution capture module of readily available system microcontroller is employed to measure the turn -on time through a simple auxiliary interface circuit on a buck converter. Experimental results show that onboard device aging can successfully be achieved during systems start-up in the order of microseconds.
TL;DR: In this paper, an autocorrelation function was proposed to distinguish transient time crystals from infinitely long-lived ones, which can increase the lifetime of time crystals by orders of magnitude.
Abstract: Optimal application of a magnetic field can increase the lifetime of transient time crystals by orders of magnitude, and autocorrelation functions can distinguish transient time crystals from infinitely long-lived ones.
TL;DR: Simulation results show that the MOPSO and penalization of both electrical and mechanical variables in the OF led to improved mechanical oscillations damping and voltage performance during a fault event, enhancing the LVRT capability even for the more critical condition of the flexible mechanical coupling.
TL;DR: This study focuses on the mitigation of rotor overcurrents and DC-link voltage variations by modifying the control structure of the DFIG converter, thereby enhancing its LVRT capability.
TL;DR: A new type of neural network architecture is developed by combining the long short-term memory (LSTM) network with the autoencoder structure to suppress noise in TEM signals, capable of enhancing the quality of the T EM signals at later times, which enables us to better resolve deeper electrical structures.
Abstract:
Late-time transient electromagnetic (TEM) data contain deep subsurface information and are important for resolving deeper electrical structures. However, due to their relatively small signal amplitudes, TEM responses later in time are often dominated by ambient noises. Therefore, noise removal is critical to the application of TEM data in imaging electrical structures at depth. De-noising techniques for TEM data have been developed rapidly in recent years. Although strong efforts have been made to improving the quality of the TEM responses, it is still a challenge to effectively extract the signals due to unpredictable and irregular noises. In this study, we develop a new type of neural network architecture by combining the long short-term memory (LSTM) network with the autoencoder structure to suppress noise in TEM signals. The resulting LSTM-autoencoders yield excellent performance on synthetic data sets including horizontal components of the electric field and vertical component of the magnetic field generated by different sources such as dipole, loop and grounded line sources. The relative errors between the de-noised data sets and the corresponding noise-free transients are below 1% for most of the sampling points. Notable improvement in the resistivity structure inversion result is achieved using the TEM data de-noised by the LSTM-autoencoder in comparison with several widely-used neural networks, especially for later-arriving signals that are important for constraining deeper structures. We demonstrate the effectiveness and general applicability of the LSTM-autoencoder by de-noising experiments using synthetic 1-D and 3-D TEM signals as well as field data sets. The field data from a fixed loop survey using multiple receivers are greatly improved after de-noising by the LSTM-autoencoder, resulting in more consistent inversion models with significantly increased exploration depth. The LSTM-autoencoder is capable of enhancing the quality of the TEM signals at later times, which enables us to better resolve deeper electrical structures.
TL;DR: In this article, the authors provide an overview of the types of transients to consider, from the transients that occur during switching at the chip surface all the way to the system-level transients which transfer heat to air.
Abstract:
There are many applications throughout the military and commercial industries whose thermal profiles are dominated by intermittent and/or periodic pulsed thermal loads. Typical thermal solutions for transient applications focus on providing sufficient continuous cooling to address the peak thermal loads as if operating under steady-state conditions. Such a conservative approach guarantees satisfying the thermal challenge but can result in significant cooling overdesign, thus increasing the size, weight, and cost of the system. Confluent trends of increasing system complexity, component miniaturization, and increasing power density demands are further exacerbating the divergence of the optimal transient and steady-state solutions. Therefore, there needs to be a fundamental shift in the way thermal and packaging engineers approach design to focus on time domain heat transfer design and solutions. Due to the application-dependent nature of transient thermal solutions, it is essential to use a codesign approach such that the thermal and packaging engineers collaborate during the design phase with application and/or electronics engineers to ensure the solution meets the requirements. This paper will provide an overview of the types of transients to consider—from the transients that occur during switching at the chip surface all the way to the system-level transients which transfer heat to air. The paper will cover numerous ways of managing transient heat including phase change materials (PCMs), heat exchangers, advanced controls, and capacitance-based packaging. Moreover, synergies exist between approaches to include application of PCMs to increase thermal capacitance or active control mechanisms that are adapted and optimized for the time constants and needs of the specific application. It is the intent of this transient thermal management review to describe a wide range of areas in which transient thermal management for electronics is a factor of significance and to illustrate which specific implementations of transient thermal solutions are being explored for each area. The paper focuses on the needs and benefits of fundamentally shifting away from a steady-state thermal design mentality to one focused on transient thermal design through application-specific, codesigned approaches.
TL;DR: This paper proposes a new reference-generation-strategy for direct torque control (DTC) of doubly fed induction generator (DFIG), under symmetrical voltage-dips, which prevents overcurrent in the rotor side converter, by damping the transient-flux and modifying the references of rotor- flux and torque, during voltage dip and recovery.
Abstract: This paper proposes a new reference-generation-strategy for direct torque control (DTC) of doubly fed induction generator (DFIG), under symmetrical voltage-dips. Since DTC has no current-control loop, it cannot prevent overcurrent during voltage-dips. The proposed method prevents overcurrent in the rotor side converter, by damping the transient-flux and modifying the references of rotor-flux and torque, during voltage dip and recovery. The analysis of DTC for DFIG is presented by a λ-i equivalent circuit, which is decomposed into forced and natural circuits. Based on the natural λ-i circuit, the method adds a transient compensation term to the rotor-flux reference, which is obtained by multiplying the stator-natural-flux with a proposed decaying-ramp function. Moreover, this method reduces the forced component of rotor-flux proportional to the grid voltage. As a result, this method adjusts the transient-flux damping time and ensures overcurrent prevention in the rotor and stator windings. The torque reference is modified to maintain the torque-angle (between rotor and stator flux vectors) constant, which results in stable control of the DFIG during grid faults. The effectiveness of the proposed method is confirmed by experimental results of a 3-kW test set-up and simulation results of a 2-MW DFIG.
TL;DR: An efficient strategy to improve the voltage quality of sensitive loads with the optimal utilization of a dynamic voltage restorer (DVR) based on energy-optimized compensation strategies and completes the smooth transition of the transient process during the voltage compensation and recovery stages.
Abstract: This paper introduces an efficient strategy to improve the voltage quality of sensitive loads with the optimal utilization of a dynamic voltage restorer (DVR). Traditional control strategies mainly focus on the voltage compensation stage to reduce the voltage rating of the DVR or minimize the required capacity of the energy storage device. In addition, the phase jump correction in the early stage of the compensation has attracted more attention as well. In reality, phase jump issues may occur in the initial and final stages of compensation, and they must be avoided for most loads, but few works focus on how a DVR can smoothly exit the system after the fault elimination. With the main objective of mitigating the phase jump in the load side voltage while improving the overall sag compensation time, this paper demonstrates that: 1) based on energy-optimized compensation strategies, the proposed approach aims at completing the smooth transition of the transient process during the voltage compensation and recovery stages and ensuring effective linkage from the former to the latter and 2) the mode operation boundaries in the two stages are derived and compared, and the updated procedure of a new injected reference voltage is activated to prevent the system from going outside its operating limits. Furthermore, the operation logic and the overall control scheme are elaborated, which ensure that the proposed approach preserves superior controllability to provide flexible voltage support. Finally, a combination of simulation and experimental results is used to validate the performance of the proposed method.