Hamiltonian Theory Based Coordinated Nonlinear Control of Generator Excitation and STATCOMs

A coordinated controller for generator excitation and STATCOMs is studied based on the Hamiltonian function method. The Hamiltonian realization structure for multimachine power systems including STATCOMs is developed leading to a proposed coordinated scheme of excitation control and STATCOM control. Simulation results illustrate the effectiveness of the proposed control strategy

Development of a FACTS Real-Time Hardware-in-the-Loop Simulation

This paper describes an approach to simulate the bulk power transmission system using hardware-in-the-loop (HIL) FACTS devices. The architecture of the HIL simulation is described and a DSP-PC-based UPFC device designed for HIL simulation is presented. The implementation of UPFC hardware, software and basic control are discussed. Experimental results are provided to support the proposed concept

A Novel Real-time Approach to Unified Power Flow Controller Validation

This paper presents the development of a real-time hardware/software laboratory to interface a soft real-time power system simulator with multiple unified power flow controllers (UPFC) via hardware-in-the-loop (HIL) to study their dynamic responses and validate control and placement approaches. This paper describes a unique laboratory facility that enables large-scale, soft real-time power system simulation coupled with the true physical behavior of a UPFC as opposed to the controller response captured by many other real-time simulators. The HIL line includes a synchronous machine, a UPFC, and a programmable load to reproduce the physical dynamics of the UPFC sub-network

PI parameter tuning of converters for sub-synchronous interactions existing in grid-connected DFIG wind turbines

As a clean energy, wind power has been extensively exploited in the past few years. However, oscillations in wind turbines, particularly those from controllers, could severely affect the stability of power systems. Therefore, oscillation suppression is a recent research focus. Based on the small-signal model eigenvalues and participation factors, this paper detects the sub-synchronous interactions (SSI) mainly determined by converters' PI parameters in a grid-connected doubly fed induction generator (DFIG). With the aim of oscillation restraint, a novel optimization model with the reference-point based non-dominated sorting genetic algorithm (NSGA-III) and the t-distributed stochastic neighbour embedding (t-SNE) is developed to explore and visualize optimal ranges of PI parameters, facilitating the selection of the appropriate PI parameters to augment the damping. Additionally, to study the adaptability of the optimal PI parameters, interactions performance of the system that uses optimal parameters is studied with different output levels of the wind turbine. Finally, a time domain simulation and a practical experiment are conducted to demonstrate the effectiveness of the proposed approach. Results illustrate that the SSI of a grid-connected DFIG is suppressed by the optimization model. This study is highly beneficial to power system operators in integrating wind power and maintaining system stability.</p

Parallel Optimal Control for Cooperative Automation of Large-scale Connected Vehicles via ADMM

This paper proposes a parallel optimization algorithm for cooperative automation of large-scale connected vehicles. The task of cooperative automation is formulated as a centralized optimization problem taking the whole decision space of all vehicles into account. Considering the uncertainty of the environment, the problem is solved in a receding horizon fashion. Then, we employ the alternating direction method of multipliers (ADMM) to solve the centralized optimization in a parallel way, which scales more favorably to large-scale instances. Also, Taylor series is used to linearize nonconvex constraints caused by coupling collision avoidance constraints among interactive vehicles. Simulations with two typical traffic scenes for multiple vehicles demonstrate the effectiveness and efficiency of our method

Why do some overweight children remain overweight, whereas others do not?

OBJECTIVE: To study the dynamics of childhood overweight and the influence of dietary intake on tracking of overweight. DESIGN AND SETTING: A follow-up study conducted in China. SUBJECTS: Ninety-five overweight children, 6-13 years old, identified from 1455 children at baseline, were followed over a 2-year period. METHODS: Data on anthropometry and 3-day dietary intake were collected at baseline and during follow-up. Overweight was defined using the International Obesity Task Force reference of body mass index (BMI)-for-age. Differences between groups were tested using analysis of variance and Cochran-Mantel-Haenszel tests. RESULTS: Of the 95 overweight children, 36.8% remained overweight 2 years later ('tracking group'). Urban boys were three times more likely than rural boys to remain overweight (63.2% vs. 21.9%). At baseline, the tracking group had higher BMI, body weight and fat intake (% of energy), and lower carbohydrate intake (% of energy), than the non-tracking group (who shifted from overweight to not overweight); they were more likely to have a high-fat or high-meat diet, but less likely to have a diet high in carbohydrate or vegetables and fruit. During the follow-up, the tracking group increased fat intake and reduced carbohydrate intake while the non-tracking group did not; and they also grew slower in height but faster in weight. Tracking of overweight seemed to be related to tracking of high-meat (relative risk (RR) 2.4, 95% confidence interval (CI) 1.0-5.6, P < 0.05) and high-fat (RR 1.5, 95% CI 0.9-2.5, P < 0.1) diets. CONCLUSION: Considerable changes in children's overweight status during childhood and adolescence were observed in China, a transitional society. Dietary patterns, particularly dietary composition, seemed to influence the tracking patterns of overweight

Uncovering the Electron‐Phonon Interplay and Dynamical Energy‐Dissipation Mechanisms of Hot Carriers in Hybrid Lead Halide Perovskites

The discovery of slow hot carrier cooling in hybrid organic–inorganic lead halide perovskites (HOIPs) has provided exciting prospects for efficient solar cells that can overcome the Shockley–Queisser limit. Questions still loom over how electron‐phonon interactions differ from traditional polar semiconductors. Herein, the electron‐phonon coupling (EPC) strength of common perovskite films (MAPbBr3, MAPbI3, CsPbI3, and FAPbBr3) is obtained using transient absorption spectroscopy by analyzing the hot carrier cooling thermodynamics via a simplified two‐temperature model. Density function theory calculations are numerically performed at relevant electron‐temperatures to confirm experiments. Further, the variation of carrier‐temperature over a large range of carrier‐densities in HOIPs is analyzed, and an “S‐shaped” dependence of the initial carrier‐temperature to carrier‐density is reported. The phenomenon is attributed to the dominance of the large polaron screening and the destabilization effect which causes an increasing‐decreasing fluctuation in temperature at low excitation powers ; and a hot‐phonon bottleneck which effectively increases the carrier temperature at higher carrier‐densities. The turning point in the relationship is indicative of the critical Mott density related to the nonmetal‐metal transition. The EPC analysis provides a novel perspective to quantify the energy transfer in HOIPs, electron‐lattice subsystem, and the complicated screening‐bottleneck interplay is comprehensively described, resolving the existing experimental contradictions

Laboratory implementation of unified power flow controller hardware-in-loop simulation

One of the most promising network controllers for the bulk power system is the family of power electronics-based controllers, known as flexible AC transmission system (FACTS) devices. FACTS devices work by modifying power flow in individual lines of the power grid, maintaining voltage stability, and damping oscillations. The rapid development of the power electronics industry has made FACTS devices increasingly attractive for utility deployment due to their flexibility and ability to effectively control power system dynamics. The primary function of the FACTS is to control the transmission line power flow; the secondary functions of the FACTS can be voltage control, transient stability improvement and oscillation damping. Although considerable FACTS research work has concentrated on developing control strategies via simulation, there is a general lack of experimental verification of many of the proposed controls. In order to fully understand how to effectively incorporate FACTS devices into existing power systems, a hardware prototype for verification is necessary in addition to software simulation. Experimental studies provide valuable data to evaluate models, test proposed control algorithms, and analyze dynamic performance. Furthermore, experimental studies provide the basis with which to predict the device performance in the actual power system operation. Traditional software-based simulation has the disadvantage of being unable to exactly replicate real operational conditions. On the other hand, a small laboratory power system is not capable of fully capturing the depth and breadth of large-scale power system dynamics. One way to bridge the gap between simulation and real conditions is to combine real-time simulation (RTS) and hardware-in-the-loop (HIL). The contribution of this work is the development of the hardware-software co-design process required to successfully implement the FIL The FIL development has been a joint electrical engineering and computer science project funded by the National Science Foundation and Sandia National Laboratories. This dissertation details the FIL-HIL development from the hardware perspective. --Abstract, pages iii-iv