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Accurate simulations of transient X-ray photoelectron spectra (XPS) provide unique opportunities to bridge the gap between theory and experiment in understanding the photoactivated dynamics in molecules and materials. However, simulating X-ray photoelectron spectra along a photochemical reaction pathway is challenging as it requires accurate description of electronic structure incorporating core-hole screening, orbital relaxation, electron correlation, and spin–orbit coupling in excited states or at nonequilibrium ground-state geometries. In this work, we employ the recently developed multireference algebraic diagrammatic construction theory (MR-ADC) to investigate the core-ionized states and X-ray photoelectron spectra of Fe(CO)5 and its photodissociation products (Fe(CO)4, Fe(CO)3) following excitation with 266 nm light. The simulated transient Fe 3p and CO 3σ XPS spectra incorporating spin–orbit coupling and high-order electron correlation effects are shown to be in a good agreement with the experimental measurements by Leitner et al. [J. Chem. Phys., 2018, 149, 044307]. Our calculations suggest that core-hole screening, spin–orbit coupling, and ligand-field splitting effects are similarly important in reproducing the experimentally observed chemical shifts in transient Fe 3p XPS spectra of iron carbonyl complexes. Our results also demonstrate that the MR-ADC methods can be very useful in interpreting the transient XPS spectra of transition metal compounds. [ABSTRACT FROM AUTHOR]

Control of the converter stations in a multi-terminal DC (MTDC) grid to provide frequency support for the surrounding AC systems is the subject matter of this paper. The standard autonomous power sharing control loop for each converter is modified with a frequency droop control loop. The objective is to minimize the deviation from nominal AC system frequency and share the burden of frequency support among the converter stations of the MTDC grid. The effectiveness of the frequency support is demonstrated through nonlinear simulation of a test system consisting of three isolated AC systems interconnected through an MTDC grid with four converter stations. An averaged model of the MTDC grids is developed to carry out modal analysis of combined multi-machine AC-MTDC systems. Modal analysis is used to characterize and substantiate the time domain behavior in presence of frequency droop control. It is established that appropriate droop control loop for the MTDC grid converters could be effective in reducing the deviation from nominal AC system frequency provided the sensitivity of the system eigen-values to changes in control parameters (e.g., droop coefficients) is accounted for a priori through modal analysis. [ABSTRACT FROM PUBLISHER]

The interconnected electric power grid is the single largest and most complex machine in the world. Power outages, even for a short interval, have a very low probability but an enormous impact. Transmission systems around the world are facing increasing load demands, and system elements are being pushed toward their thermal limits. Wide-area power trading with varying supply and load patterns is contributing to the ever-increasing congestion. The power grid of the future must be secure, cost effective, and environmental friendly yet reliably integrated and built with intelligent solutions and innovative technologies. High-voltage dc (HVdc) transmission systems are a proven tool in tackling these challenges. [ABSTRACT FROM PUBLISHER]

Interaction between multimachine ac systems and a multiterminal dc (MTDC) grid and the impact on the overall stability of the combined ac-MTDC system is studied in this paper. A generic modeling framework for voltage-source converter (VSC)-based MTDC grids, which is compatible with standard multimachine ac system models, is developed to carry out modal analysis and transient simulation. A general asymmetric bipole converter configuration comprising positive and negative pole converters and dc cable network with a positive, negative, and metallic return circuit is considered to enable different types of faults and dc-side unbalance studies. Detailed dynamic representation of the dc cables with distributed pi-section models is used along with the averaged model and decoupled control for the converter stations. An averaged model in Matlab/SIMULINK is validated against the detailed switched model in EMTDC/PSCAD by comparing the responses following small and large disturbances (e.g., faults on the dc side). Modal analysis is performed to identify the nature and root cause of the dynamic responses. Interaction between a multimachine ac system and an MTDC grid is examined following faults on the ac and dc sides and outage of converters. It is shown that the cause of instability in certain cases could only be attributed to the dc-side state variables. An averaged model of the converter along with the dc cable network is shown to be essential to analyze the stability and dynamics of combined ac-MTDC grids. [ABSTRACT FROM AUTHOR]

Latency or delay in remote feedback signals can adversely affect the closed-loop damping performance. Accurate time-stamp information at both (PMU location and control center) ends offers a possibility to continuously compensate for time-varying latency. In this paper, an adaptive phasor power oscillation damping controller (APPOD) is proposed wherein the rotating coordinates for phasor extraction are adjusted to account for the change in phase caused due to the delay. The oscillatory component of the original signal is thus retrieved out of the delayed signal received at the control center. Unlike conventional phasor POD, which uses a fixed phase shift to generate damping control signal, an adaptive phase shift algorithm is used here to suit varying signal locations and operating conditions. Case studies confirm the effectiveness of the proposed technique, both in terms of robustness and handling continuously varying delays. A comparison with a conventional gain scheduled POD (CGPOD) and a Unified Smith Predictor (USP) approach is also presented. [ABSTRACT FROM AUTHOR]

This paper investigates the problem of appropriate load sharing in an autonomous microgrid. High gain angle droop control ensures proper load sharing, especially under weak system conditions. However, it has a negative impact on overall stability. Frequency-domain modeling, eigenvalue analysis, and time-domain simulations are used to demonstrate this conflict. A supplementary loop is proposed around a conventional droop control of each DG converter to stabilize the system while using high angle droop gains. Control loops are based on local power measurement and modulation of the d-axis voltage reference of each converter. Coordinated design of supplementary control loops for each DG is formulated as a parameter optimization problem and solved using an evolutionary technique. The supplementary droop control loop is shown to stabilize the system for a range of operating conditions while ensuring satisfactory load sharing. [ABSTRACT FROM AUTHOR]

An adaptive critic design (ACD)-based damping con- troller is developed for a thyristor-controlled series capacitor (TCSC) installed in a power system with multiple poorly damped interarea modes. The performance of this ACD computational intelligence-based method is compared with two classical techniques, which are observer-based state-feedback (SF) control and linear matrix inequality LMI-H∞ robust control. Remote measurements are used as feedback signals to the wide-area damping controller for modulating the compensation of the TCSC. The classical methods use a linearized model of the system whereas the ACD method is purely measurement-based, leading to a nonlinear controller with fixed parameters. A comparative analysis of the controllers' performances is carried out under different disturbance scenarios. The ACD-based design has shown promising performance with very little knowledge of the system compared to classical model-based controllers This paper also discusses the advantages and disadvantages of ACDs, SF, and LMI-H∞. [ABSTRACT FROM AUTHOR]

Research effort has been given to locate the optimal locations of thyristor-controlled series capacitor (TCSC) and their initial compensation levels using mixed-integer programming (MIP). As a useful technique for combinatorial optimisation over integer and continuous variables, the MIP approach can provide robust performance as well as high computational efficiency while solving complex optimal problems. Previous work using MIP employed dc load flow model ignoring reactive power balance, power loss and transformer tap ratios. In this paper, a new planning method is developed based on recently reported line flow equations and basic linearisation of binary-continuous products. The objectives of the planning strategy are to improve system loadability, voltage profile in the network, as well as to minimise the investment cost by choosing proper locations and settings of devices. Simulation results are presented and discussed for IEEE 9-, 57-, 118-, and 300-bus systems. [ABSTRACT FROM AUTHOR]

An application of a normalized H∞ loop-shaping technique for design and simplification of damping controllers in the liner matrix inequalities (LMI) framework is illustrated in this paper. The solution is sought numerically using LMIs with additional pole-placement constraints. This ensures that the time-domain specifications are met besides robust stabilization. The designed control algorithm is implemented using a rapid prototyping controller. The performance of the controller is validated in real time using a detailed model of the power system implemented using Linux PC-based, multi-processor technology. The coupling between the controller and the power system is through a set of DAC and ADC modules in the analogue domain. [ABSTRACT FROM AUTHOR]

This brief illustrates a control design procedure for handling time delays encountered in transmitting the remote signals in power systems. A unified Smith predictor (USP) approach is used to formulate the control design problem in the standard mixed sensitivity framework. The solution to the problem is sought numerically using linear matrix inequalities (LMIs) with additional pole-placement constraints. The predictor based method is applied for designing a damping controller for a prototype power system. Simulation results show that the controller performs satisfactorily even though the feedback signals arrive at the control site after a finite time delay. [ABSTRACT FROM AUTHOR]

This paper demonstrates an adaptive control strategy for damping interarea oscillations in a large power system model, employing a probabilistic approach to model-based control. The scheme accounts for the uncertain nature of the post-disturbance dynamics of the system for computing the control moves. A number of linearized plant models are considered to represent the system dynamics following the probable contingencies. Conventional observer-based state feedback controllers are designed to achieve the desired performance for each of these models. This strategy has been used to design and test a damping controller for a thyristor controlled series compensator (TCSC) device installed in a 16-ma- chine, 68-bus system model. The control scheme worked satisfactorily following possible disturbances without any prior knowledge about the specific post-disturbance dynamics. [ABSTRACT FROM AUTHOR]

Recent technological advances in the area of wide- area measurement systems (WAMS) has enabled the use of a combination of measured signals from remote locations for centralized control purpose. The transmitted signals can be used for multiple swing mode damping using a single controller. However, there is an unavoidable delay involved before these signals are received at the controller site. To ensure satisfactory performance, this delay needs to be taken into account in the control design stage. This paper focuses on damping control design taking into account a delayed arrival of feedback signals. A predictor-based H∞, control design strategy is discussed for such time-delayed systems. The concept is utilized to design a WAMS-based damping controller for a prototype power system using a static var compensator. The controller performance is evaluated for a range Of operating conditions. [ABSTRACT FROM AUTHOR]

This paper demonstrates the application of multiple-model adaptive control (MMAC) strategy for robust damping of low-frequency electromechanical oscillation in an interconnected power system. The control algorithm uses a model-based approach to account for the variability and uncertainty involved in the postdisturbance dynamics of the system. Conventional proportional-integral-derivative (PID) controllers are tuned to achieve the desired performance for each of these models. Using a Bayesian approach, the probability of each model representing the actual power system response is computed in each iteration. The resultant control action is derived as a probability-weighted average of the individual control moves of the controllers. This strategy has been used to design and test a damping controller for a thyristor controlled series compensator (TCSC) device installed in a prototype power system. The control scheme worked satisfactorily following possible disturbances without any prior knowledge about the specific postdisturbance dynamics. [ABSTRACT FROM AUTHOR]