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The three-phase dual active bridge (3p-DAB) converter is widely addressed in emerging power systems applications such as solid-state transformer and dc microgrids. Its successful integration requires accurate modeling of its small-signal characteristics. Due to its dc–ac–dc structure, the DAB converter brings many challenges to small-signal modeling. The state-space averaging (SSA) has been the first proposed methodology to approximate the control-to-output and line-to-output transfer functions of the 3p-DAB. However, as shown in this paper, SSA is not precise for the stability analysis of 3p-DAB converters. A generalized state-space averaging (GSSA) model based on the dynamic phasor concept is developed in this paper for the Y-Δ 3p-DAB. A hybrid SSA and GSSA model representation is then proposed for the evaluation of all the converter transfer functions. The developed models are validated with detailed time-domain switch-level simulations in an electromagnetic transient-type (EMT-type) program. They are also used for the accelerated stability prediction in an EMT-type program. [ABSTRACT FROM PUBLISHER]

The direct current (DC) technology has gained significant momentum in modern distribution systems due to the high penetration levels of dc loads and dc-based distributed generators (DGs). Unlike conventional ac distribution systems, dc distribution systems have the following distinct features that challenge the system stability. 1) The high penetration level of tightly regulated converters used to interface both DGs and loads yields a destabilizing constant power load (CPL) effect in a considerable range of frequencies. 2) The filtering inductors and capacitors form poorly damped LC networks that interact negatively with the CPLs leading to further deterioration of the system stability. 3) Because islanding in a dc system can be hardly detected with passive methods due the absence of the frequency and reactive power terms, DGs are usually equipped with active islanding detection methods to detect the grid disconnection state; however, the islanding detection schemes could negatively impact the distribution system stability. The analysis and mitigation of undesirable interaction dynamics in a dc distribution system considering the aforementioned practical characteristics are not reported in the current literature. In this paper, the interaction dynamics of a dc distribution system characterized by a high penetration level of CPLs, and DGs equipped with positive feedback islanding detection scheme are investigated. The factors affecting the system stability with a single and multiple DGs are thoroughly addressed. Further, a stabilizing compensation loop is proposed to mitigate the stability problems and poor damping capability. Detailed time-domain nonlinear simulations and experimental results validate the analytical results. [ABSTRACT FROM PUBLISHER]

This paper proposes a proportional-integral (inertial) multiresonant (PIMR) type repetitive control (PIMR-type RC) scheme for a grid-tied inverter. The proposed control scheme is composed of a repetitive controller in parallel with a proportional gain for the purpose of replacing lots of parameters of the conventional proportional multiresonant controller, and therefore, only a few parameters need to be designed. The proportional gain not only improves the dynamic response, but also enables repetitive controller (RC) to accommodate a larger RC gain, and hence a faster convergence rate. Theoretical analysis and stability analysis of PIMR-type RC are given, and then a practical step-by-step design tutorial is also provided. The experimental results validate the feasibility and outstanding performance of the proposed control scheme. [ABSTRACT FROM PUBLISHER]

Faced with increasingly bulk power transfer by voltage source converter (VSC)-based HVDC systems, the stability of VSC stations is of interest. Two widely adopted control schemes, that is, to control the VSC as a current source (e.g., the current vector control) or to control the VSC as a voltage source (e.g., the virtual synchronous machine-based control), are analyzed near the power limit. Bottlenecks of the first control scheme are pointed out and a novel quasi-steady-state method to seek the corresponding critical short-circuit ratio is proposed. Distinctive impacts of the short-circuit ratio on the second control scheme are also analyzed. According to the analysis and relevant comparison, supplementary compensators are proposed to provide extra damping for the two control schemes so that they are able to cope with a wider range of grid strengths. The analytical results and enhancement strategies are validated by time-domain simulations. Suggestions on dividing strong and weak systems with respect to VSCs are finally put forward and which control scheme is preferred under different conditions is discussed. [ABSTRACT FROM AUTHOR]

The ITER pulsed power electrical network (PPEN) supplies the superconducting magnets and the heating and current drive systems. During the experimental pulses, about several hundreds of seconds long, active power consumption of 500 MW and reactive one of 950 Mvar are expected. The ITER power supply system is very large and complex, and a careful design is required to assure a safe operation. Stability of ITER PPEN has been already investigated in recent studies by numerical simulation and analytical methods. Now, a new dynamic analytical model of the ITER power supply system is being developed, based on the state-space theoretical approach, which allows the application of the linear control theory to study the stability of the whole system. For each subsystem of the ITER power supply, a state-space model was developed, and in this paper, the ac/dc converter model is presented and validated for six and twelve pulse operation, and circulating current mode. [ABSTRACT FROM AUTHOR]

A nonlinear excitation controller for the uncertain parameters and external disturbances is designed by using the backstepping method and sliding mode control theory. In the design process, nonlinear features are retained completely with no linear technique used here. Compared with the excitation controllers designed via conventional linearization, the newly designed one has superiorities in strong robustness to external disturbances, good adaptive ability to variation of system parameters, super transient performance, and the ability to assure preset constraints. Simulation results prove the validity and stability of the controller. [ABSTRACT FROM AUTHOR]

An eigen-based transformation called Channel Components Transform (CCT) has been recently proposed for decoupling power networks. CCT has revealed many unique features in power system studies especially voltage stability analysis and monitoring. However, this method may face some difficulties in certain situations. The difficulties including the non-existence difficulty and the robustness difficulty are discussed in this paper. This paper will then show that by using the singular value decomposition instead of the eigen-decomposition, the difficulties can be effectively overcome. Therefore, a new transformation based on singular value decomposition is proposed. An algorithm is also presented which shows how the proposed transformation can be applied to voltage stability analysis. The proposed algorithm is verified by using several standard systems as case studies. [ABSTRACT FROM AUTHOR]

In this study, a two-hierarchical decentralised coordinated control scheme based on the multi-agent system (MAS) is proposed to improve the security and the stability of the microgrid. The coordinated switching control strategies are constructed in upper level agent to ensure the microgrid security. The making process of the coordinated switching control strategies is regarded as searching the optimal switching operation mode by means of designing constraint violation function and colour Petri-net, so that the operation mode of the microgrid can be switched during larger power unbalance. The decentralised continuous control is designed by integrating the outer loop droop controller with the inner loop prescribed performance controller in the lower level unit agents to guarantee its unit system stability. Finally, the simulation results demonstrate the effectiveness of the decentralised coordination control based on MAS. [ABSTRACT FROM AUTHOR]

In this paper, we present the results of an economic feasibility study and propose a system structure to test and maintain electrical stability. In addition, we present real operation results after constructing a remote microgrid on an island in South Korea. To perform the economic feasibility study, a commercial tool called HOMER was used. The developed remote microgrid consists of a 400 kW wind turbine (WT) generator, 314 kW photovoltaic (PV) generator, 500 kVA × 2 grid forming inverter, 3 MWh lithium ion battery, and an energy management system (EMS). The predicted renewable energy fraction was 91% and real operation result was 82%. The frequency maintaining rate of the diesel power plants was 57% but the remote microgrid was 100%. To improve the operating efficiency of the remote microgrid, we investigated the output range of a diesel generator. [ABSTRACT FROM AUTHOR]

The article discusses a study which examines the feasibility of a rollover detection and emergency notification system for farm tractors. Tractor rollover tests on a field track were conducted to determine the effectiveness of the system. Findings show that the technology successfully monitored tractor's stability in all tests.

This paper deals with the design of a speed-adaptive full-order observer for sensorless induction motor (IM) drives. A general stabilizing observer gain matrix, having three free design parameters, is used as a design framework. A gain-scheduled selection of the free design parameters is proposed. Furthermore, the full-order observer is augmented with the stator-resistance adaptation, and the local stability of the augmented observer is analyzed. The performance of the proposed full-order observer design is experimentally compared with a reduced-order observer using a 2.2-kW IM drive. [ABSTRACT FROM AUTHOR]

Open-loop constant voltage/frequency (v/f) adjustable speed drives (ASDs) can often experience undesirablesustained oscillations. Factors affecting these oscillation states include induction machine (IM) parameters, dead time,dc-link capacitor size, IM saturation, output voltage, carrier frequency, and IM speed. Many literatures have discussedthe instabilities in light-load or low-frequency operating conditions. Quite a few methods have been proposed forstabilizing such a system. However, the instability problems, at different power levels, have not been completelydescribed. This paper analyzes the causes of this instability for constant v/f drives as power levels change. The 2.2-and 15-kW low-voltage IMs and the 746-kW medium-voltage IM are evaluated to illustrate how the motor parameters affectthe system stability. Additionally, a new oscillation mitigation method is introduced to demonstrate its effectivenessin solving the instability problems. It is based on the synchronous reference frame dynamic current feedback through itsmagnetic flux current component bandpass filtering and proportional control. In a theoretical stability analysis beforeand after the current feedback compensation, simulation studies are presented and verified through a 15-kW 380-V 50-HzIM ASD experimental system. [ABSTRACT FROM AUTHOR]

Power-electronics-based dc power distribution systems, consisting of several interconnected feedback-controlled switching converters, suffer from potential degradation of stability and dynamic performance caused by negative incremental impedances due to the presence of constant power loads. For this reason, the stability analysis of these systems is a significant design consideration. This paper reviews all the major stability criteria for dc distribution systems that have been developed so far: the Middlebrook Criterion, the Gain Margin and Phase Margin Criterion, the Opposing Argument Criterion, the Energy Source Analysis Consortium (ESAC) Criterion, and the Three-Step Impedance Criterion. In particular, the paper discusses, for each criterion, the artificial conservativeness characteristics in the design of dc distribution systems, and the formulation of design specifications that ensure system stability. Moreover, the Passivity-Based Stability Criterion is discussed, which has been recently proposed as an alternative stability criterion. While all prior stability criteria are based on forbidden regions for the polar plot of the so-called minor loop gain, which is an impedance ratio, the proposed criterion is based on imposing passivity of the overall bus impedance. A meaningful simulation example is presented to illustrate the main characteristics of the reviewed stability criteria. [ABSTRACT FROM AUTHOR]

The effect of Hf addition on the electrical performance and bias stability of ZnO-based thin-film transistors (TFTs) has been investigated. All channel layers were deposited by atomic layer deposition with various Hf contents. In addition, multilayer oxide channel TFTs consisting of two or three Hf-doped ZnO (HZO) and ZnO layers were developed for the realization of adequate channel mobility and electrical stability. The subthreshold swing and bias stability were improved by the deposition of the thin-HZO layers with amorphous phase as the first and final channel layers. The use of a conductive ZnO layer enhanced the device mobility. The oxide TFTs with a multilayer channel of a-HZO/ZnO/a-HZO exhibited relatively good stability and mobility due to the reduced interface trap density between the channel and dielectric layers, and the suppressed adsorption of negatively charged oxygen on the back channel. The origin of the stability issues and novel channel design are proposed on the basis of the electrical performance of various TFT structures. [ABSTRACT FROM PUBLISHER]

An accelerometer for electronic stability control utilizes a two-mass mechanical sensor element to implement a fully-differential signal path, achieving robustness against electromagnetic interference (EMI) without the need for external shielding in the package. The EMI rejection is augmented further with a pseudo-random chopping scheme, which spreads the interference over a wide bandwidth, reducing its in-band portion to the level of the noise floor. The chopping function maintains zero-mean voltage waveforms across the sensor electrodes, which is also beneficial for the long-term offset stability of the device. A charge-balanced capacitance-to-voltage converter provides linear transduction for displacements of the proof-mass up to 70% of the gap and minimizes the residual electrostatic forces. A dual-axis design occupies 1.1 mm^2 in 0.18-\mum CMOS and consumes 820 \muA from an internally regulated 1.9-V supply. The system achieves 380 \mu g/ \surd Hz noise floor and 84-dB dynamic range. The offset variation in the automotive temperature range of -40 to +140 ^\circC has a 3 \sigma range of \pm 11 mg. [ABSTRACT FROM PUBLISHER]

A 3-D finite-difference time-domain (FDTD) scheme with controllable stability beyond the stability limit of FDTD is presented. The key to controlling the FDTD stability limit is a spatial filter applied to the electromagnetic field vectors in order to ensure that unstable spatial harmonics are eliminated. A significant advantage of this approach is the simplicity of its incorporation into existing FDTD codes. Moreover, this method is employed as a means to implement a late-time stable 3-D sub-gridding scheme. Applications include waveguide filters and the analysis of screens for near-field sub-wavelength focusing at microwave frequencies. [ABSTRACT FROM PUBLISHER]

The growth of electricity market led to increase utilization and higher loading of the electric transmission grids worldwide. This situation made power system operate close to steady-state stability limit (SSSL). It could trigger voltage instability or voltage collapse phenomenon. An assessment approach on steady state stability analysis was provided using Extreme Learning Machine taking the Modal Analysis as an assessment index. The nonlinear problem between voltage, power flow and participation factor in power system could be solved by Extreme Learning Machine. The method was tested on the IEEE 14 bus and Java-Bali system. The simulation results showed that the proposed method could accurately predict the weakest bus in power system. [ABSTRACT FROM AUTHOR]