Mariesa L. Crow

STATCOM control for power system voltage control applications

A static compensator (STATCOM) is a device that can provide reactive support to a bus. It consists of voltage sourced converters connected to an energy storage device on one side and to the power system on the other. In this paper the conventional method of PI control is compared and contrasted with various feedback control strategies. A linear optimal control based on LQR control is shown to be superior in terms of response profile and control effort required. These methodologies are applied to an example power system.

Battery Energy Storage System (BESS) and Battery Management System (BMS) for Grid-Scale Applications

The current electric grid is an inefficient system that wastes significant amounts of the electricity it produces because there is a disconnect between the amount of energy consumers require and the amount of energy produced from generation sources. Power plants typically produce more power than necessary to ensure adequate power quality. By taking advantage of energy storage within the grid, many of these inefficiencies can be removed. When using battery energy storage systems (BESS) for grid storage, advanced modeling is required to accurately monitor and control the storage system. A battery management system (BMS) controls how the storage system will be used and a BMS that utilizes advanced physics-based models will offer for much more robust operation of the storage system. The paper outlines the current state of the art for modeling in BMS and the advanced models required to fully utilize BMS for both lithium-ion batteries and vanadium redox-flow batteries. In addition, system architecture and how it can be useful in monitoring and control is discussed. A pathway for advancing BMS to better utilize BESS for grid-scale applications is outlined.

Fault Detection and Mitigation in Multilevel Converter STATCOMs

Many static synchronous compensators (STATCOMs) utilize multilevel converters due to the following: 1) lower harmonic injection into the power system; 2) decreased stress on the electronic components due to decreased voltages; and 3) lower switching losses. One disadvantage, however, is the increased likelihood of a switch failure due to the increased number of switches in a multilevel converter. A single switch failure, however, does not necessarily force an (2n + 1)-level STATCOM offline. Even with a reduced number of switches, a STATCOM can still provide a significant range of control by removing the module of the faulted switch and continuing with (2n - 1) levels. This paper introduces an approach to detect the existence of the faulted switch, identify which switch is faulty, and reconfigure the STATCOM. This approach is illustrated on an eleven-level STATCOM and the effect on the dynamic performance and the total harmonic distortion (THD) is analyzed.

The matrix pencil for power system modal extraction

This work introduces the matrix pencil modal extraction method through the use of several illustrative examples. This method is used to estimate the eigenvalues of reduced-order models of large nonlinear systems based on their dynamic responses.

Decentralized Dynamic Surface Control of Large-Scale Interconnected Systems in Strict-Feedback Form Using Neural Networks With Asymptotic Stabilization

A novel neural network (NN)-based nonlinear decentralized adaptive controller is proposed for a class of large-scale, uncertain, interconnected nonlinear systems in strict-feedback form by using the dynamic surface control (DSC) principle, thus, the “explosion of complexity” problem which is observed in the conventional backstepping approach is relaxed in both state and output feedback control designs. The matching condition is not assumed when considering the interconnection terms. Then, NNs are utilized to approximate the uncertainties in both subsystem and interconnected terms. By using novel NN weight update laws with quadratic error terms as well as proposed control inputs, it is demonstrated using Lyapunov stability that the system states errors converge to zero asymptotically with both state and output feedback controllers, even in the presence of NN approximation errors in contrast with the uniform ultimate boundedness result, which is common in the literature with NN-based DSC and backstepping schemes. Simulation results show the effectiveness of the approach.

Power System Voltage Regulation via STATCOM Internal Nonlinear Control

A new internal STATCOM control based on feedback linearization is proposed. The feedback linearization controller is developed without any simplifying assumptions to the STATCOM model. The proposed control is validated on the IEEE 118-bus system with full-order generator and network models as opposed to a small test system. Furthermore, the proposed control is benchmarked against published results. Lastly controllability issues associated with a singularity in the feedback linearization control (FBLC) coordinate transformation is identified, and a solution is provided to avoid instability.

Power System Stabilization Using Adaptive Neural Network-Based Dynamic Surface Control

In this paper, the power system with an excitation controller is represented as a class of large-scale, uncertain, interconnected nonlinear continuous-time system in strict-feedback form. Subsequently, dynamic surface control (DSC)-based adaptive neural network (NN) controller is designed to overcome the repeated differentiation of the control input that is observed in the conventional backstepping approach. The NNs are utilized to approximate the unknown subsystem and the interconnection dynamics. By using novel online NN weight update laws with quadratic error terms, the closed-loop signals are shown to be locally asymptotically stable via Lyapunov stability analysis, even in the presence of NN approximation errors in contrast with other NN techniques where a bounded stability is normally assured. Simulation results on the IEEE 14-bus power system with generator excitation control are provided to show the effectiveness of the approach in damping oscillations that occur after disturbances are removed. The end result is a nonlinear decentralized adaptive state-feedback excitation controller for damping power systems oscillations in the presence of uncertain interconnection terms.

Structure-Preserved Power System Transient Stability Using Stochastic Energy Functions

With the increasing penetration of renewable energy systems such as plug-in hybrid electric vehicles, wind and solar power into the power grid, the stochastic disturbances resulting from changes in operational scenarios, uncertainties in schedules, new demands and other mitigating factors become crucial in power system stability studies. This paper presents a new method for analyzing stochastic transient stability using the structure-preserving transient energy function. A method to integrate the transient energy function and recloser probability distribution functions is presented to provide a quantitative measure of probability of stability. The impact of geographical distribution and signal-to-noise ratio on stability is also presented.

Performance Indices for the Dynamic Performance of FACTS and FACTS with Energy Storage

The integration of energy storage into flexible AC transmission systems (FACTS) devices leads to increased controller flexibility by providing decentralized active power capabilities. Combined FACTS/energy storage systems (ESS) can improve power flow control, oscillation damping, and voltage control. This article presents performance indices that have been developed for quantifying the active power, reactive power, and voltage performance enhancement of different FACTS combinations. The dynamic responses of a shunt (StatCom), a StatCom/battery energy storage system (BESS), a synchronous series compensator (SSSC), a SSSC/BESS, and a unified power flow controller (UPFC) are presented to support the validity of the developed indices.

An Improved Nonlinear STATCOM Control for Electric Arc Furnace Voltage Flicker Mitigation

Electric arc furnaces (EAF) are prevalent in the steel industry to melt iron and scrap steel. EAFs frequently cause large amplitude fluctuations of active and reactive power and are the source of significant power quality disturbances. Static Synchronous Compensators (STATCOMs) provide a power electronic-based means of embedded control for reactive power support and power quality improvement. This paper introduces a new nonlinear control for the STATCOM that provides significant reduction in EAF-induced aperiodic oscillations on the power system. This method is compared with traditional PI controls and shown to have improved performance.