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Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To address the challenges in establishing the state transfer matrix and the complexity of eigenvalue calculation in determining the multi-parameter stability boundaries of high-order nonlinear Vienna rectifiers, a novel numerical computation method is proposed in this paper. This method leverages a numerical stability criterion and a grid variable step search to efficiently calculate these stability boundaries. The small-signal model of the Vienna rectifier is derived by constructing the time-varying state transfer matrix using the periodic solution of the harmonic balance method. Eigenvalues are rapidly calculated via the periodic numerical solution of the state transfer matrix. The proposed parameter sensitivity-based grid variable step search method ensures a fast and accurate determination of stability boundaries. A hardware experimental setup is established to validate the stability boundaries of the Vienna rectifier under various parameter variations, including load, component, and control changes. The experimental results closely match the simulations, confirming the correctness and superiority of the proposed method. [ABSTRACT FROM AUTHOR]

This paper focuses on the analysis and control strategy of a four-switch boost-buck AC/DC converter utilized in power factor correction applications with a wide output voltage range. Given the increasing importance of electric vehicles and the need for high reliability, this study addresses the internal dynamic stability problem that can arise in the converter system. The analysis begins with a thorough examination of the system's min-phase characteristic. Despite this, internal dynamic stability issues persist, requiring a solution to ensure a higher power factor and reliability. To address this challenge, this paper proposes the utilization of a damping RC circuit instead of reducing the loop gain bandwidth. To demonstrate the internal dynamic behavior of the converter, small-signal modeling is employed. This modeling highlights the importance of mitigating internal dynamic instability to achieve the desired power factor and reliability. This study emphasizes the significance of proper analysis and control strategies for boost-buck AC/DC converters in power factor correction applications. By addressing internal dynamic stability using a damping RC circuit, the converter can achieve a higher power factor and enhanced reliability, ultimately contributing to the development of more efficient and dependable EV systems. Finally, the feasibility of the proposed analysis and control strategy is confirmed through comprehensive simulations. The simulation results validate the effectiveness of using a damping RC circuit to address the internal dynamic stability problem, leading to an improved power factor and enhanced reliability. [ABSTRACT FROM AUTHOR]

Copyright of Electric Drive is the property of Electric Drive Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper focuses on the analysis and control strategy of a four-switch boost-buck AC/DC converter utilized in power factor correction applications with a wide output voltage range. Given the increasing importance of electric vehicles and the need for high reliability, this study addresses the internal dynamic stability problem that can arise in the converter system. The analysis begins with a thorough examination of the system’s min-phase characteristic. Despite this, internal dynamic stability issues persist, requiring a solution to ensure a higher power factor and reliability. To address this challenge, this paper proposes the utilization of a damping RC circuit instead of reducing the loop gain bandwidth. To demonstrate the internal dynamic behavior of the converter, small-signal modeling is employed. This modeling highlights the importance of mitigating internal dynamic instability to achieve the desired power factor and reliability. This study emphasizes the significance of proper analysis and control strategies for boost-buck AC/DC converters in power factor correction applications. By addressing internal dynamic stability using a damping RC circuit, the converter can achieve a higher power factor and enhanced reliability, ultimately contributing to the development of more efficient and dependable EV systems. Finally, the feasibility of the proposed analysis and control strategy is confirmed through comprehensive simulations. The simulation results validate the effectiveness of using a damping RC circuit to address the internal dynamic stability problem, leading to an improved power factor and enhanced reliability.

Grid-forming (GFM) inverters are dc–ac converters that regulate their ac terminal voltage and frequency in response to real-time measurements. Recent developments on GFM controls have focused on a particular dispatchable virtual oscillator control whose implementation features a nonlinear Andronov–Hopf oscillator at its core. In this article, we systematically model and study this controller, its synchronization dynamics, as well as its stability. We show that system voltages and frequency are regulated in a decentralized and autonomous manner while exhibiting nonlinear droop-like behavior. Small-signal models are formulated for an individual inverter connected to an infinite voltage bus in addition to systems of interconnected GFM inverters. These models allow us to characterize dynamical stability and synchronization. Robustness is shown after sweeping key system parameters under the aforementioned models that capture system performance. Numerical simulations and experimental results validate the analytical developments. [ABSTRACT FROM AUTHOR]

It has been found in existing research works that the dc-link dynamics are significant internal dynamics in the type-IV wind turbine system, which can shape system characteristics and influence system stability. If dc-link dynamics are weakly damped, this dynamic behavior may reduce system damping and worsen system stability. Considering that dc-link dynamics are determined by the interaction effects of controllers and different control structures can be adopted to regulate dc-link voltage in the type-IV wind turbine system, analytical models are needed to accurately evaluate and analyze dc-link dynamics under different control structures, which are lacked in existing publications. In this article, the mechanism of dc-link dynamics in the system is described at first. A single-in-single-out indicator function is proposed to model the dc-link dynamics, based on which a linearized state-space model of dc-link dynamics is obtained. Then, the eigenvalue sensitivity matrix is applied to determine the influencing factors of dc-link dynamics and possible causes of weakly damped dc-link dynamics. DC-link dynamics under different control structures are compared. The influenced system characteristics can also be modeled by the proposed model of dc-link dynamics and the system stability with weakly damped dc-link dynamics is also investigated with experiments based on control-hardware-in-loop platform. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this article, a set of autonomous ac microgrids, interconnected by back-to-back converters, is taken into account, where they are supplied fully using voltage source converter-based distributed energy resources. A comprehensive and generalized small-signal model of the interconnected autonomous microgrids as a large-scale system is proposed using the interconnection method. The modeling is based on detailed module models to show the impact of each module on the dynamic modes, especially the dominant critical modes. It is generalized and scalable due to separate modeling of modules as well as using unlimited and expandable interconnecting. The proposed interconnection method deals with all electrical and control connections between individual modules including feedback, feed-forward, augmentation, and the order of module inputs and outputs. The model is validated employing Prony analysis method and using output results of an OPAL-RT real-time simulator. Using the proposed modeling method, the small-signal stability analysis and controller design can be realized simply for interconnected microgrids with any number of microgrids and different structures. Typically, for two interconnected microgrids, all dynamic modes and participant state variables in different frequency ranges are identified using the eigenvalue analysis and participation matrix in MATLAB. [ABSTRACT FROM AUTHOR]

This paper proposes a small-signal model and Floquet-theory-based method for analyzing small-signal stability of a single-phase asymmetric cascaded H-bridge multilevel inverter (ACHMI) operating in the stand-alone mode. The studied ACHMI system consists of the power stage and cascaded control loops, which includes the voltage loop in the synchronous reference frame (SRF), capacitor current feedback control, and hybrid modulation scheme. Due to the SRF voltage control, the derived small-signal model under linear and nonlinear load conditions are inherently periodically time-variant. Therefore, the Floquet theory is employed to analyze the stability regions of the dual-loop control parameters of the ACHMI. Furthermore, the loci and moduli of Floquet multipliers are calculated to accurately evaluate the respective effects of control parameters on the stability of the system. With the stability analysis based on the small-signal model and Floquet-theory-based method, an effective selection range of control parameters of the multilevel inverter can be obtained. Finally, the experimental results from a reduced-scale laboratory prototype ACHMI are presented to validate the theoretical analysis, and the effectiveness of proposed analysis method in high-power applications is verified by the simulation results from a 10-kV medium-voltage ACHMI. [ABSTRACT FROM AUTHOR]

In recent years, the Oil & Gas industry has been subjected to a progressive electrification process aiming to comply with global environmental requirements on CO2 emissions reduction. High-power electric motors fed by Variable Frequency Drives (VFDs) have replaced gas turbines as drivers for gas compression applications. In Liquefied Natural Gas (LNG) plants, unexpected downturns could be experienced in case of high torsional vibrations of power generations units. These torsional vibrations derive from the interaction among turbine-generator (TG) units and VFDs and are known as Sub-Synchronous Torsional Interactions (SSTIs). SSTIs can lead to instability when the overall electromechanical system lacks sufficient damping. In this scenario, electrical damping assessment is fundamental in order to ensure stability and reliable operation of an LNG plant. Negative electrical damping is strictly related to the negative incremental resistance behavior of the power converters and it is influenced by the converter’s control system. In this paper, a real case study based on Thyristor Variable Frequency Drives (TVFDs) is considered. Ad hoc dynamic models of the power converters and of the TG unit are developed and combined in order to provide an accurate estimation of the electrical damping. It is demonstrated that the electrical damping is affected by variations of the main control system parameters and how the use of a simplified model instead of an ad hoc model can impact the stability evaluation.

Synchronous reference frame (SRF) phase-locked loops (PLLs) represent a commonly used technique for grid synchronization in distributed generation (DG) systems. Since PLLs affect transient dynamics, they are a crucial component for stability studies. In this letter, it is shown that a commonly used small-signal SRF-PLL model can be used for stability analysis in some preconditioned scenarios with a single grid-connected DG unit, but does necessarily require perturbation quantities that are offset free. Otherwise, an incorrect usage may result in unacceptable errors. To overcome this restriction, an improved small-signal PLL model is proposed, which enables to analyze the effects of grid frequency and phase angle changes as well as variations of the input voltage magnitude. Finally, the model accuracy is validated by means of computer simulations. [ABSTRACT FROM PUBLISHER]

Using voltage-source converter high-voltage direct current (VSC-HVDC) to interconnect weak ac power systems has drawn much attention. Under the traditional vector control for the VSC that the response of AC voltage loop cannot match that of the active power loop may limit power transmission capability of the VSCs that interconnect with weak power systems. To enhance the power transmission capability and stability, this paper proposes a power compensation control that is based on the analysis of characteristics of power–voltage (PV) curves. This method can improve the damping control performance of the active power and the ac voltage by adjusting the compensated values adaptively. A small-signal model of the integrated system is established to study the performance of the proposed control method. The impact of the compensation coefficients and steady-state operating points on the system stability is studied. Motivated by an on-going back-to-back project in China, corresponding electromagnetic transient simulation models are constructed in MATLAB/Simulink environment to verify the effectiveness of the proposed method on the performance of operating limits, damping performance, disturbance withstanding capability, and fault ride-through capability. [ABSTRACT FROM AUTHOR]

In a dc microgrid (DC-MG), the dc bus voltage is vulnerable to power fluctuation derived from the intermittent distributed energy or local loads variation. In this paper, a virtual inertia control strategy for DC-MG through bidirectional grid-connected converters (BGCs) analogized with virtual synchronous machine (VSM) is proposed to enhance the inertia of the DC-MG, and to restrain the dc bus voltage fluctuation. The small-signal model of the BGC system is established, and the small-signal transfer function between the dc bus voltage and the dc output current of the BGC is deduced. The dynamic characteristic of the dc bus voltage with power fluctuation in the DC-MG is analyzed in detail. As a result, the dc output current of the BGC is equivalent to a disturbance, which affects the dynamic response of the dc bus voltage. For this reason, a dc output current feedforward disturbance suppressing method for the BGC is introduced to smooth the dynamic response of the dc bus voltage. By analyzing the control system stability, the appropriate virtual inertia control parameters are selected. Finally, simulations and experiments verified the validity of the proposed control strategy. [ABSTRACT FROM PUBLISHER]

The micro-grid is an important part of future Smart Distribution Automation, and the micro-grid technology is a trend of the future distributed power system. Combined with the current hot issue in the field of power system, i.e. , micro-grid stability problem, an experiment course of "stability analysis experiment of micro-grid based on small-signal model" is proposed for the students of electrical engineering and related majors, The course includes theoretical knowledge of MATLAB/Simulink, theoretical knowledge of DC micro-grid and stability analysis, small signal modeling of converter and stability analysis of cascade converters. It also contains choosing topics and the corresponding MATLAB simulation, seminars and so on. Students are required to master the simple DC micro-grid small signal stability analysis within 20 courses. This experiment course focuses on the issues concerned at present and nearly future, combines the control theory analysis with new energy power grid, makes students understand the new development of science and technology and the academic trends, enlightens students’ thought of scientific research, and introduces the research method (small signal analysis) to the experiment teaching activities. [ABSTRACT FROM AUTHOR]

Wind energy is going to be a significant part of electric energy generation in the very near future. However, in addition to its intermittent nature that could lead to major difficulties for power system reliability and stability, the conventional control applied to wind turbines and their generators, usually doubly-fed induction generators (DFIGs), does not allow them to participate in frequency regulation, whether short or long term. Moreover, the use of wind generators for autonomous frequency regulation is becoming an essential objective in power grids with reduced inertia and isolated microgrid operation. While droop-control is suggested by many researchers to solve these problems, detailed analysis of droop-controlled DFIG units in microgrids has not been reported. To fill-out this gap, this paper presents torque- and power-droop implementations in DFIG-based units by some simple modifications in the conventional control and then, by means of small-signal modeling and eigen-value studies, shows how both techniques influence frequency stability. Sensitivity studies, with respect to the presence of turbine- and inverter-based generators in microgrids; and impacts of pitch-angle controller, wind speed variation and isolated mode operation with only wind-generators, are conducted. Time-domain simulation is utilized to verify the analytical results. [ABSTRACT FROM PUBLISHER]

In recent years, the Oil & Gas industry has been subjected to a progressive electrification process aiming to comply with global environmental requirements on CO2 emissions reduction. High-power electric motors fed by Variable Frequency Drives (VFDs) have replaced gas turbines as drivers for gas compression applications. In Liquefied Natural Gas (LNG) plants, unexpected downturns could be experienced in case of high torsional vibrations of power generations units. These torsional vibrations derive from the interaction among turbine-generator (TG) units and VFDs and are known as Sub-Synchronous Torsional Interactions (SSTIs). SSTIs can lead to instability when the overall electromechanical system lacks sufficient damping. In this scenario, electrical damping assessment is fundamental in order to ensure stability and reliable operation of an LNG plant. Negative electrical damping is strictly related to the negative incremental resistance behavior of the power converters and it is influenced by the converter's control system. In this paper, a real case study based on Thyristor Variable Frequency Drives (TVFDs) is considered. Ad hoc dynamic models of the power converters and of the TG unit are developed and combined in order to provide an accurate estimation of the electrical damping. It is demonstrated that the electrical damping is affected by variations of the main control system parameters and how the use of a simplified model instead of an ad hoc model can impact the stability evaluation. [ABSTRACT FROM AUTHOR]