Coordinated nonlinear robust control of TCSC and excitation for multi-machine systems

An advanced nonlinear robust control scheme is proposed for multi-machine power systems equipped with thyristor-controlled series compensation (TCSC). First, a decentralized nonlinear robust control approach based on the feedback linearization and H∞ theory is introduced to eliminate the nonlinearities and interconnections of the studied system, and to attenuate the exogenous disturbances that enter die system. Then, a system model is built up, which has considered all the generators’ and TCSC’s dynamics, and the effects of uncertainties such as disturbances. Next, a decentralized nonlinear robust coordinated control law is developed based on this model. Simulation results on a six-machine power system show that the transient stability of the power system is obviously improved and die power transfer capacity of long distance transmission lines is enhanced regardless of fault locations and system operation points. In addition, the control law has engineering practicality since all the variables in the expression of he control strategy can be measured locally.

Nonlinear and Variable Structure Excitation Controller for Power System Stability

A new nonlinear variable structure excitation controller is proposed. Its design combines the differential geometry theory and the variable structure controlling theory. The mathematical model in the form of ＂an affme nonlinear system＂ is set up for the control of a large-scale power system. The static and dynamic performances of the nonlinear variable structure controller are simulated. The response of system with the controller proposed is compared to that of the nonlinear optimal controller when the system is subjected to a variety of disturbances. Simulation results show that the nonlinear variable structure excitation controller gives more satisfactorily static and dynamic performance and better robustness.

Nonlinear Mixed-Effects Models for Repairable Systems Reliability

Mixed-effects models,also called random-effects models,are a regression type of analysis which enables the analyst to not only describe the trend over time within each subject,but also to describe the variation among different subjects.Nonlinear mixed-effects models provide a powerful and flexible tool for handling the unbalanced count data.In this paper,nonlinear mixed-effects models are used to analyze the failure data from a repairable system with multiple copies.By using this type of models,statistical inferences about the population and all copies can be made when accounting for copy-to-copy variance.Results of fitting nonlinear mixed-effects models to nine failure-data sets show that the nonlinear mixed-effects models provide a useful tool for analyzing the failure data from multi-copy repairable systems.

CHAOTIC OSCILLATION OF ANONLINEAR POWER SYSTEM

For a nonlinear power transmission system, the residue calculus method is introduced and applied to study its heteroclinic bifurcation. There a cone region and a strip region of parameters are obtained, in which the power transmission system displays chaotic oscillation. This gives a theoretic analysis and a computational method for the purpose to control the nonlinear system with deviation stably running.

Analysis of Nonlinear Characteristics of Turbine Governor and Its Impact on Power System Oscillation

In this paper, the model of turbine governor?based on the physical principles is constituted to improve the accuracy of power system dynamic simulation, making the results of simulation consistent with the actual situation. The unit and grid coupling model which reflects the interaction between thermal system of power plant and power system is built using EMTDC/PSCAD. The influence of nonlinear characteristics on the valve opening and the steam turbine mechanical power is also analyzed in this paper. The results of simulation show that the improper setting of parameters reflecting nonlinear characteristics of turbine governor can lead to the cyclical oscillations of the valve opening and the?steam turbine mechanical power, and even can lead to the power oscillation persistently. The research achievements in this paper have a certain reference value on exploring the causes of power oscillation from the prime mover.

Wide-area nonlinear robust voltage control strategy for multi-machine power systems

This paper presented a novel wide-area nonlinear excitation control strategy for multi-machine power systems. A simple and effective model transformation method was proposed for the system's mathematical model in the COI (center of inertia) coordinate system. The system was transformed to an uncertain linear one where deviation of generator terminal voltage became one of the new state variables. Then a wide-area nonlinear robust voltage controller was designed utilizing a LMI (linear matrix inequality) based robust control theory. The proposed controller does not rely on any preselected system operating point, adapts to variations of network parameters and system operation conditions, and assures regulation accuracy of generator terminal voltages. Neither rotor angle nor any variable's differentiation needs to be measured for the proposed controller, and only terminal voltages, rotor speeds, active and reactive power outputs of generators are required. In addition, the proposed controller not only takes into account time delays of remote signals, but also eliminates the effect of wide-area information's incompleteness when not all generators are equipped with PMU (phase measurement unit). Detailed tests were conducted by PSCAD/EMTDC for a three-machine and four-machine power systems respectively, and simulation results illustrate high performance of the proposed controller.

Effect of Tooth Profile Modification on Vibration of Power Split Gear Transmission System

Based on Newton ' s second law,the bend-torsion-shaft coupling nonlinear dynamic model and equations of power split gear transmission system are established.According to the principle of tooth profile modification,the tooth profile modification is considered as time-varying gear backlash function acting along the line of action.Then the dynamic functions are solved by using Runge-Kutta numerical method.After analyzing the effect of tooth profile modification quantity( TPMQ) and relative tooth profile modification length( TPML) to the nonlinear dynamic characteristics of power split gear transmission,the following conclusions are drawn:1 The TPMQ of a certain stage transmission affects the vibration of its own stage more significantly than the other stage,and the coupling effect between two stages can be ignored usually in the modification design;2 If the first stage TPMLs are less than 0.3,the influence of the first stage TPMLs to the first stage transmission vibration is much more greatly than the influence of the second stage TPMLs to the first stage transmission vibration,or else both the first and second stage TPMLs affect the first stage transmission vibration largely.The same is true for the second stage TPMLs,and the cutoff value is 0.2;3 The TPMQ affects the vibration of power split gear transmission system more principally than the TPML,and should be top-priority in the modification design.

Transient Stability Analysis of Power System Based on an Improved Neural Network

A new type of ANN (Artificial Neural Network) structure is introduced, and a nonlinear transformation of the original features is proposed so as to improve the learning covergence of the neural network. This kind of improved ANN is then used to analyse the transient stability of two real power systems. The results show that this method possesses better effectiveness and high convergence speed.

Switching Excitation Controller for Enhancement of Transient Stability of Multi-machine Power Systems

This paper proposes a switching structure excitation controller(SSEC)to enhance the transient stability of multimachine power systems.The SSEC switches between a bangbang funnel excitation controller(BFEC)and a conventional excitation controller(CEC),based on an appropriately designed state-dependent switching strategy.Only the tracking error of rotor angle is required to realize the BFEC in a bang-bang manner with two control values.If the feasibility assumptions of the BFEC are satisfied,the tracking error of rotor angle can be regulated within the predefined error funnels.The power system having the SSEC installed can achieve faster convergence performance compared to that having the CEC implemented only.Simulation studies are carried out in the New England 10-generator 39-bus power system.The control performance of the SSEC is evaluated in the cases that three-phase-to-ground fault and transmission line outage occur in the power system,respectively.

Robust excitation control of multi-machine multi-load power systems using Hamiltonian function method

Using an energy-based Hamiltonian function method,this paper investigates the robust excitation control of multi-machine multi-load power systems described by a set of uncertain differential algebraic equations.First,we complete the dissipative Hamiltonian realization of the power system and adjust its operating point by the means of pre-feedback control.Then,based on the obtained Hamiltonian realization,we discuss the robust excitation control of the power system and put forward an H1 excitation control strategy.Simulation results demonstrate the effectiveness of the control scheme.

Adaptive Excitation Control with L_2 Disturbance Attenuation for Multi-Machine Power Systems

Generator excitation control plays an important role in improving the dynamic performance and stability of power systems. This paper is concerned with nonlinear decentralized adaptive excitation control for multi-machine power systems. Based on a recursive design method, an adaptive excitation control law with L2 disturbance attenuation is constructed. Furthermore, it is verified that the proposed control scheme possesses the property of decentralization and the robustness in the sense of L2-gain. As a consequence, transient stability of a multi-machine power system is guaranteed, regardless of system parameters variation and faults.

Coordinated Frequency Control for Isolated Power Systems with High Penetration of DFIG-Based Wind Power

This paper proposes a coordinated frequency control scheme for emergency frequency regulation of isolated power systems with a high penetration of wind power.The proposed frequency control strategy is based on the novel nonlinear regulator theory,which takes advantage of nonlinearity of doubly fed induction generators(DFIGs)and generators to regulate the frequency of the power system.Frequency deviations and power imbalances are used to design nonlinear feedback controllers that achieve the reserve power distribution between generators and DFIGs,in various wind speed scenarios.The effectiveness and dynamic performance of the proposed nonlinear coordinated frequency control method are validated through simulations in an actual isolated power grid.

Switching Power System Stabilizer and Its Coordination for Enhancement of Multi-machine Power System Stability

This paper proposes a coordinated switching power system stabilizer(SPSS)to enhance the stability of multimachine power systems.The SPSS switches between a bang-bang power system stabilizer(BPSS)and a conventional power system stabilizer(CPSS)based on a state-dependent switching strategy.The BPSS is designed as a bang-bang constant funnel controller(BCFC).It is able to provide fast damping of rotor speed oscillations in a bang-bang manner.The closed-loop stability of the power system controlled by the SPSSs and the CPSSs is analyzed.To verify the control performance of the SPSS,simulation studies are carried out in a 4-generator 11-bus power system and the IEEE 16-generator 68-bus power system.The damping ability of the SPSS is evaluated in aspects of small-signal oscillation damping and transient stability enhancement,respectively.Meanwhile,the coordination between different SPSSs and the coordination between the SPSS and the CPSS are investigated therein.

A new adaptive backstepping method for nonlinear control of turbine main steam valve

A new approach for nonlinear adaptive control of turbine main steam valve is developed. In comparison with the existing controller based on ＂classical＂ adaptive backstepping, this method does not follow the classical certaintyequivalence principle in the design of adaptive control law. We introduce this approach, for the first time, to power systems and present a novel parameter estimator and dynamic feedback controller for a single machine infinite bus （SMIB） system with steam valve control. This system contains unknown parameters such as reactance of transmission lines. Besides preserving useful nonlinearities and the real-time estimation of uncertain parameters, the proposed approach possesses better performances with respect to the response of the system and the speed of adaptation. The simulation results demonstrate that the proposed approach is better than the design based on ＂classical＂ adaptive backstepping in terms of properties of stability and parameter estimation, and recovers the performance of the ＂full-information＂ controller. Hence, the proposed method provides an alternative for engineers in applications.

Nonlinear excitation controller design for power systems:an I&I approach

The Immersion and Invariance （I＆I） methodology provides a novel approach for nonlinear system control, which is distinct from the traditional feedback linearization and backstepping method. In this paper, a new excitation controller is designed for single machine infinite bus system （SMIBS） based on the I＆I approach. Firstly the dynamic model of SMIBS is homeomorphously transformed to a specific form for which a stable lower-order target system is selected. Then the I＆I excitation controller is designed by immersing the transformed system into the target system. Simulation results from PSCAD/EMTDC demonstrate that the proposed controller guarantees transient stability of the system after large disturbances.

Koopman原理内嵌MLP神经网络模型驱动的电力系统非线性振荡特征分析方法

针对电力系统非线性动态特性表征与物理机理融合不清晰、精度低的问题,提出了一种Koopman原理内嵌多层感知机(MLP)神经网络模型驱动的电力系统非线性特性表征与分析方法。阐明了Koopman算子的基本原理,分析了Koopman算子在非线性系统时序演化中的作用。采用MLP神经网络构建编码、解码映射,进而形成Koopman原理内嵌的神经网络深度学习模型,通过深度学习实现非线性系统“编码映射-线性演化-解码映射”3种结构的演化逼近。分析了将所提方法应用于电力系统动态特性分析的物理机理,建立了所提方法的求解与应用流程。通过单机与4机系统算例对所提方法进行对比验证,结果表明所提方法可以精确表征平衡点稳定域内的系统动态过程,可用于电力系统非线性振荡动态特性解析。

高空风电系统的优化控制研究进展与挑战

为了实现“碳达峰,碳中和”的战略目标,我国将持续推动可再生能源的高比例发展,构建以新能源为主的新型电力系统.作为可再生的清洁源,风能的开发和利用已成为研究的重要方向.研究表明远离地面的高空中风速更加强劲并且更均匀,风向也更稳定,因此,风力发电的进一步突破可以通过用风筝捕获高空风能来实现.为了确保高空风能系统安全、经济、高效地运行,对其控制系统设计的要求极高.本文阐述了国际上几种主流高空风电技术的发电原理、发展进程以及现状.通过对典型的Yo-Yo式结构进行动力学建模,分析了各类非线性控制技术的原理和特点,具体描述了非线性模型预测控制原理和轨迹跟踪控制的仿真结果.总结了未来高空风能控制技术面临的控制算法计算量大,控制系统可靠性研究缺乏以及智能化水平不高等关键问题.

基于多尺度法的多机非线性强迫振荡机理研究

随着高比例新能源电网的发展,电力系统呈现出更明显的非线性特征,可以采用多尺度法展示二次非线性对多机系统强迫振荡的影响。首先,建立多机系统强迫振荡模型,将系统数学模型进行多次恒等变换并进行简化,与单机系统相比,多机系统有着更广泛的适用性。然后,利用多尺度法导出了非线性强迫振动稳态响应的幅频特性曲线和动态响应的近似一阶解析表达式,并分析关键参数对非线性强迫荡的影响。最后,以三机系统为例,验证了所提方法的准确性,并对由非线性引起的频率偏移和跳跃的现象做出了解释。