An improved power flow for an ill‐conditioned power system with FACTS devices

This paper addresses the issue of the computation techniques for assessing the steady‐state power flows controlled by Flexible AC Transmission Systems (FACTS), which contain variable series compensators (VSC), phase shifters (PS), interphase power controllers (IPC), and unified power flow controllers (UPFC). An improved Newton–Raphson load flow program has been developed based on an analysis of the convergence characteristic of the conventional method. It is shown that the conventional method tends to suffer from ill‐conditioning problem, resulting in shrinkage of the convergence region. Based on examinations of the condition number of the Jacobian, a penalty function method is adopted in order to avoid the ill‐conditioning problem and to guarantee a successful convergence. Although the computational burden is increased about 2 to 3 times, the proposed method considerably extends the region of convergence. The effectiveness of the proposed method is demonstrated through numerical examinations using IEEE 57 and 118 bus systems. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(1): 30–37, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10027     

A distortion-free phase-locked loop system for FACTS and power electronic controllers

This paper presents a single-phase phase-locked loop (PLL) system which is primarily free from the double-frequency ripples from which the conventional PLL system suffers. The proposed PLL is then extended to reject the harmonic components from the input signal and to estimate the phase-angle and frequency of the distorted input signal with no error. Three units of the proposed PLL can be used in three-phase power systems, such as FACTS and HVDC converters, to estimate the phase-angles of the individual phases with no double-frequency ripples and without sensitivity to the presence of harmonics and inter-harmonics. This makes the proposed PLL unique and desirable for applications which demand highly accurate estimation of the phase-angle(s) and frequency.     

通信系统故障对电力系统实时负荷控制影响的量化评价方法

随着广域测量技术的发展,通信系统和电力网络的同步拓展使得两者之间的交互影响更为复杂。首先,提出了通信系统故障影响研究框架,并分析了电力通信业务失效对电网可观性和可控性的影响;然后,针对采用最优负荷减载算法的电力系统实时负荷控制业务,提出了通信中断故障影响的评估方法,该方法采用故障后负荷控制代价评价监控设备和通信链路故障对电网的影响;算例结果表明了所提方法的合理性和有效性。     

A method of damping transient rush voltage fluctuation of power systems due to a wind driven generator via nonlinear state feedback control

Squirrel-cage induction generators are widely used as generators for windmill power systems, because they are inexpensive, have high durability, and are capable of operating asynchronously with power systems. However, induction generators suffer the drawback that they cause transient rush currents that are several times larger than the rated value when connected to power systems. Also since wind energy is influenced by geographic and weather conditions, start/stop operations occur frequently for windmill power systems. Therefore, connecting induction generators to power systems causes undesirable voltage fluctuations in power systems, which is the major obstacle against the practical use of windmill generator systems. This motivates the study of transient rush current/voltage attenuation in windmill generator systems. In this paper, a nonlinear state-feedback controller for windmill power systems is proposed. The proposed controller globally asymptotically stabilizes the plant and effectively attenuates the transient current/voltage of these systems. Computer simulations using parameters for an actual windmill generator system also gave good results. © 1998 Scripta Technica, Electr Eng Jpn, 124(1):17–23, 1998     

Output power control of wind turbine generator by pitch angle control using minimum variance control

Effective utilization of renewable energies such as wind energy as a replacement for fossil fuels is highly desirable. Wind energy is not constant and wind generator output is proportional to the cube of the wind speed, which causes the power output of wind turbine generators (WTGs) to fluctuate. In order to reduce output power fluctuations of wind farms, this paper presents an output power leveling control strategy for wind farms based on both the mean and the standard deviation of wind farm output power, a cooperative control strategy for WTGs, and a pitch angle control method using a generalized predictive controller (GPC) intended for all operating regions of WTGs. Simulation results using an actual detailed model for wind farm systems show the effectiveness of the proposed method. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(2): 10–18, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20247     

SVG控制系统的稳定性研究

根据静止无功发生器SVG(Static Var Generator)的结构特点,建立了相应的微分方程。考虑到实际系统的非线性周期性时变系数的影响,将逆变器的外部电气性能,用直流量与交流量之间的矢量关系进行了线性化处理,并根据劳斯一胡尔维茨稳定性判据得出了电力电子技术应用时的非线性控制参数与系统参数之间的稳定性关系,根据稳定性的表达式得到了静态稳定结果。     

DFIG的SVM-IPC与SVM-DPC比较

为比较间接功率控制(indirect power control,IPC)和直接功率控制(direct power control,DPC)的控制特点,提出了双馈感应发电机(doubly-fed induction generator,DFIG)的间接功率控制(IPC)和直接功率控制(DPC)策略.首先提出采用空间矢量调制(space vector modulation,SVM)的SVM-IPC策略,该策略通过对转子电流的直接控制间接实现对定子有功和无功功率的解耦控制;其次提出基于SVM的SVM-DPC策略,该策略不通过电流控制环节,直接实现定子有功功率和无功功率的解耦控制.分析结果表明,SVM-IPC具有良好的稳态性能,但动态响应能力取决于PI参数的优化程度;SVM-DPC不仅稳态性能好,而且具有快速的动态响应能力.实验结果验证了提出策略的可行性和正确性.     

Damping enhancement of multimachine power system using adaptive generator control system with neural networks

The authors proposed a nonlinear adaptive generator control system with neutral networks for improving damping of power systems, and showed its effectiveness in a one-machine infinite bus test power system in a previous paper. The proposed neurocontrol system adaptively generates appropriate supplementary control signals to the conventional controllers such as the automatic voltage regulator and speed governor so as to enhance transient stability and damping of the power system. In this paper, the applicability of the proposed neurocontrol system to multimachine power systems is discussed. Digital time simulations are carried out for a 4-machine test power system, where one or several synchronous generators is equipped with the neurocontrol system. As a result, also in the multimachine power system, the proposed adaptive neurocontrol systems improve the system damping effectively and they work adaptively against the wide changes of the operating conditions and the network configuration.     

对FACTS应用前景的探讨

从潮流、稳定、经济性、可靠性、FACTS自身的技术问题、运行经验等6个方面论述了FACTS的应用前景。     

双轴励磁发电机功率跟踪励磁控制系统研究

采用传统双通道励磁控制系统的双轴励磁发电机(简称为双励机)动态过程时间长,振荡幅值大,不利于电力系统的稳定运行。为此,在双励机的功率反馈环节增加不完全微分控制,提出了一种具有功率跟踪功能的励磁控制系统。对双励机动态过程中的有功功率、无功功率和励磁电流差值进行不完全微分,进而判断功率的变化趋势,调节d、q轴励磁电流的比例以改变励磁磁动势的方向,进而抑制功率的振荡,最终达到增加系统阻尼的作用。以转矩扰动和无功扰动为例,对比研究了功率跟踪励磁控制系统与双通道励磁控制系统对双励机动态过程振荡幅值和振荡时间的影响,结果表明,采用功率跟踪励磁控制系统可大幅减小系统的振荡幅值和振荡时间,有效提高系统的阻尼,为电力系统的稳定运行提供有力支撑。     

发电机调速附加控制对系统频率稳定的作用

研究了基于复合偏差功率反馈的同步发电机调速系统附加控制方法及其对频率稳定的作用。该方法克服了传统调速控制因转子质量惯性、负荷特性和转速测量死区而造成的控制延时,并且能精确地进行不平衡力矩补偿,从而在扰动初期能进行及时有效的频率稳定控制。对单区域系统的仿真结果表明,汽轮发电机组和水轮发电机组附加调速控制相比传统调速控制而言,减小了频率的偏移幅度,抑制了频率振荡的发生;提前了锅炉燃烧系统对负荷变化的响应时间,从而提高了机组一次调频的持续力;水轮机组的闸门开合次数及频率也都有一定的减小;降低了机械功率的超调和振荡。     

小功率发电机励磁系统的恒功率因数控制

针对单台并网运行的小功率同步发电机恒功率因数控制问题,采用励磁电流和功率因数双闭环PID控制方法,并网前调节励磁电流使机端电压满足并网条件,并网后调节励磁使功率因数恒定形成恒功率因数控制。以TMS320F2812型DSP为核心器件,充分发挥了它运算速度快,外设功能强大的优点,设计出一种简单、实用励磁调节器,并通过了仿真试验和实验室调试。实验证明系统具有投励准确,投励过程震荡小,功率因数稳定性高的特点。     

静止无功发生器(SVG)的模糊变结构控制研究

结合模糊控制理论和变结构控制理论,设计了电力系统静止无功补偿器(SVG)的模糊变结构控制规律。SVG可以在支撑安装点电压的同时提高发电机的功角稳定性。通过对单机一无穷大系统进行计算机仿真表明,SVG模糊变结构控制器能够提高系统的暂态稳定性,保证电压质量。     

New power consolidation-inversion-control system for faraday MHD generator

The authors propose a new power consolidation-inversion-control system for the Faraday MHD generator using the voltage source PWM inverters. The dc output power for each electrodes pair of the MHD generator is at first inverted into three-phase ac power by a voltage source PWM inverter, and then the ac powers are consolidated by transformers. The proposed system does not need such expensive equipment as an ac filter or phase modifier and can independently and simultaneously control the active and reactive powers provided to the electric power system. Numerical simulations of the whole system, including the Faraday MHD generator, the proposed power consolidation-inversion-control system, and the electric power system, show that the proposed system can stably and steadily transmit and control the electric power from the MHD generator to the electric power system. It is also confirmed that the proposed system can independently and simultaneously control the active and reactive powers and can be used as a fast power controller.     

基于Pareto协同进化算法的多个FACTS元件协调控制

针对多个FACTS装置的控制器之间存在的负交互影响,提出一种基于Pareto协同进化算法的协调控制方法.利用协同进化算法对控制器参数进行种群划分,对各种群采用遍历组合法构造新的个体并计算目标函数值.采用多种群合作策略进行非支配排序,取排序后的最优个体进行遗传操作,最后得到一组Pareto最优解集.与常规多目标优化算法相比,避免了一般多目标优化进化算法中难以处理的适应度值的分配问题,且利用协同进化算法的并行性大幅提高了收敛速度.利用该方法对静止同步串联补偿器(SSSC)与静止同步补偿器(STATCOM)2种典型FACTS装置的协调控制器进行了设计,并通过仿真验证了设计的协调控制器的控制效果良好.     

基于模糊控制的开关磁阻风力发电系统最大功率点跟踪控制

研究了基于风速跟踪的开关磁阻风力发电系统最大功率点跟踪二维模糊控制算法,确定了模糊变量的隶属度分布和相应的模糊控制规则,采用MATLAB/Simulink中的PowerSystems建立了开关磁阻风力发电系统最大功率点跟踪模糊控制系统的仿真模型,对风速阶跃变化、负载变化等工况下的开关磁阻风力机组运行情况进行了仿真,仿真结果表明所设计的开关磁阻风力发电机模糊控制器具有良好的鲁棒性,能使开关磁阻风力发电系统以优良的动静态性能实现最大功率点跟踪。     

Optimized placement of multifunctional FACTS devices for power transit control

Contents Load-flow control with multifunctional FACTS devices can maintain the reliable system operation in the event of additionally demanded power transits. For a systematic transit control, the aptitude of possible FACTS locations is assessed by a sensitivity analysis based on the generation shift distribution factors (GSDF) and the power injection model (PIM). Finally a computer-aided identification of favorable FACTS locations in extended transit scenarios is presented. Received: 30 April 2001 / Accepted: 7 June 2001     

Assessment of techno-economic contribution of FACTS devices to power system operation

In contemporary power system studies, the optimal allocation and utilization of Flexible AC Transmission System (FACTS) devices are important issues primarily due to their cost. In this study four types of FACTS devices (Static VAr compensator (SVC), Thyristor-Controlled Series Capacitor (TCSC), Thyristor-Controlled Voltage Regulator (TCVR), and Thyristor-Controlled Phase Shifting Transformer (TCPST)) are optimally placed in a multi-machine power system to reduce the overall costs of power generation. The placement methodology considers simultaneously the cost of generated active and reactive powers and cost of selected FACTS devices for a range of operating conditions. The optimal power flow (OPF) and genetic algorithm (GA) based optimization procedure are employed to solve the allocation task. The net present value (NPV) method is used to assess the economic value of the proposed methodology. In addition to net reduction in generation cost allocated FACTS devices increased power transfer across the network and improved damping of electromechanical oscillations.     

电力系统暂态稳定性闭环控制（四）——切机控制效果的要素分析

研究投入紧急控制后阻止系统失稳的有效性和经济性,为控制方案的制定、实施提供依据。总结了影响紧急控制有效性和经济性的3个要素:控制施加时间、控制量的大小和控制地点选择。以切机控制为例进行分析,结果表明:在超前失稳侧切机控制投入时间越早,控制效果越好;因闭环控制切机量无法一次精确计算,可以一次略微过量控制保障有效性或多次控制兼顾经济性;超前失稳侧切机的地点不同,阻止失稳的效果不同,需要寻找有效、经济的控制地点。     

基于电力系统稳定分析与控制的FACTS技术评述

对FACTS控制器的数学模型、稳定控制及策略等方面进行了评述,总结了当前国内外FACTS研究在稳定方面的最新动态和关键问题。指出需要在电力系统的动态分析及FACTS的控制方案设计中考虑FACTS的内部动态特性,并认为动态相量模型极具优势。