A robust power flow model for active power flow control via thyristor‐controlled series compensator

In this paper, a new power flow model for active power flow control through a thyristor‐controlled series compensator (TCSC) in an AC network system is proposed. The proposed power flow model is based on the Newton–Raphson method. In this model, TCSC's admittance effect is included as a state variable into the Jacobian matrix to avoid the divergence problem. Unlike similar studies in the literature, TCSC's admittance is ignored in the bus admittance matrix, and the need for rebuilding the bus admittance matrix in each power flow iteration caused by the change of TCSC's admittance is prevented. So, faster convergence for power flow calculation is achieved. For this aim, new power equations are obtained. Also, in the proposed approach, we need not consider each terminal of TCSC as an individual bus in the power flow calculation. Thus, increasing the Jacobian and bus admittance matrixes sizes caused by the total bus number is prevented. The proposed approach is tested on an IEEE 57‐bus test system. The obtained results prove that this approach provides efficient, reliable, and fast convergence. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

给定线路功率的控制潮流求解方法及应用

介绍一种新的控制潮流算法。该算法考虑了发电机有功—频率特性曲线和无功—电压特性曲线的调节特性,避免了常规潮流对PV、PQ及平衡点的假设,有效地解决了电力系统调度运行中通过调整发电机出力使某些重要线路的传输功率维持在给定值的问题。特别是系统受到负荷扰动时,该算法能快速确定各机组的出力。对试验系统的计算表明,该算法是正确有效的。     

双馈感应发电机参与调频的概率最优潮流模型

随着风电并网容量增加,风电机组部分取代同步机组,需要其参与调频以维持电网稳定性。现有电网经济调度研究,在考虑频率时往往忽略风电,或以风电功率代替具体风电机组。提出一种计及双馈感应发电机(DFIG)参与一次调频的概率最优潮流模型。计及风速预测误差概率特性,在优化目标中引入频率偏移,通过权重系数兼顾发电成本和频率偏移。引入DFIG内部约束,提出优化模型中DFIG参数的修正方法,实现DFIG与同步发电机共同参与一次调频。算例分析了DFIG参与调频效果、目标权重系数对优化结果的影响,给出了发电成本和频率偏移的概率特性,验证了所提模型的有效性。     

Charge‐sharing read port with bitline pre‐charging and sensing scheme for low‐power SRAMs

In this paper, we present our decoupled differential read (DDR) port and bitline (BL) pre‐charging scheme. The proposed scheme allows the charge sharing between bitlines during the read operation. DDR port isolates the internal nodes, thus improves the read static noise margin and allows the subthreshold operation. BLs are not pre‐charged to full V_DD. Read port is designed such that for the read ‘1’ operation, BL shares its charge with BLB, and for read ‘0’ operation, BL is charged toward V_DD and BLB is discharged to the ground. The proposed non‐V_DD BL pre‐charging and the charge‐sharing mechanism provide substantial read power savings. Virtual power rail is used to suppress the BL leakages. A dynamic voltage level shifting pre‐amplifier is used that shifts both BLs to the middle voltage and amplifies the voltage difference. Single‐ended write driver is also presented that only conditionally charges the write BL. The proposed 10‐transistor static random access memory cell using DDR provides more than 2 times read static noise margin, ~72% read power savings, and ~40% write power savings compared with the conventional six‐transistor static random access memory. Copyright © 2016 John Wiley & Sons, Ltd.     

Coordinated voltage control of transformer taps with provision for hierarchical structure in power system

Participation of distributed generators (DGs), such as wind turbines, cogeneration systems, etc., is a natural trend from an ecological point of view and will continue to increase. The outputs of these DGs mainly depend on weather conditions but do not correspond to the changes of electrical load demand necessarily. On the other hand, due to deregulation of the electric power market, the power flow in a power system will uncertainly vary with several power transactions. Thus, complex power flow by DGs or transactions will cause voltage deviation. It will be difficult to sustain the voltage quality by using conventional voltage/reactive power control in the near future. In this paper, in order to avoid such voltage deviation and to decrease the frequency of transformer tap operations, the coordinated voltage control scheme of transformer taps on account of hierarchical structure in the power system is proposed. In the proposed scheme, integral of voltage deviation at each layer bus is applied to decide the timing of each transformer tap operation. Numerical simulations confirm that the proposed scheme is able to respond to every condition on voltage deviation. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(4): 48–55, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20531     

Fast evaluation of dynamic changes of electric power systems frequency during primary control

The paper presents the development of a simple method for the fast and sufficiently accurate assessment of dynamic changes of power systems frequency during the time period of primary control. Also, this model gives corresponding values of the total mechanical power of synchronous generators, during the some period. The development of a proposed low-order system frequency response model is based on the main assumption of uniform movement of generators, which enables representation of the power system through an equivalent controlled synchronous machine. The characteristics of the developed method were determined on an example of a real electric power system and a comparison was made with the results of a stricter approach.     

兼顾系统调频需求的分布式风电分散自治调控策略

越来越多的风力发电将分布在配电系统中,它们无法像常规电源一样由输电网调度中心集中调度和控制,通常需要采用分散自治的调控方式。然而,风电机组完全不顾输电系统的运行需求充分自治,会在某些方式下导致系统运行状态恶化。因此,需要研究风电机组新型调控策略,使充分自治转变成能够兼顾系统某些特殊运行需求的有限自治,配合系统渡过难关。针对此问题,提出了能够兼顾系统调频需求的分布式风电机组分散自治调控策略,该策略根据风电机组运行信息和系统频率将风电机组调控区划分为并网控制区、正常调控区、异常调控区、紧急调控区和脱网控制区五类,并给出了异常调控、紧急调控和故障调控三种新的调控模式。算例表明:风电机组能够较好地根据系统调频需求,在最大可用输出功率范围内调整自身输出功率,一定程度上给予系统积极的支持。     

Crosstalk‐noise‐aware bus coding with low‐power ground‐gated repeaters

Crosstalk noise is one of the serious reliability concerns in nanoscale integrated circuits. Repeater insertion together with shielding wires is a typical method to suppress crosstalk noise associated with global data bus. A new crosstalk‐noise‐aware bus coding scheme with ground‐gated repeaters is proposed in this paper to minimize the routing overhead as well as power consumption of data bus systems. A subset of 4‐to‐6 crosstalk‐noise‐aware codes is selected to minimize the number of simultaneous data transitions. The routing overhead is reduced by 12.31% with the new bus coding scheme compared with the conventional data bus with shielding wires. Furthermore, the leakage power and worst‐case active power consumptions are reduced by 12.5% and 18.26%, respectively, with the new crosstalk‐noise‐aware data bus system as compared with the previously published bus coding system in an industrial 40‐nm CMOS technology.     

Disconnection control of wind power generators for the purpose of reducing frequency fluctuation

This paper proposes a new approach for disconnection control of wind power generators to reduce the frequency fluctuation caused by wind power. The approach is based on the correlation between frequency and total output of wind power generators and the turbulence degrees of individual wind power generators. At a control center, frequency and all the outputs of wind power generators are monitored, and the correlation and the turbulence degrees are computed on‐line. If the large variation of frequency is detected, then whether the variation comes from the wind power generators or loads is checked by using the correlation. When the wind power generators cause the frequency variation, the wind power generator with maximum turbulence degree is searched and disconnected from the power systems. This search and disconnection process is repeated until the correlation reaches the level where the frequency variation observed is not caused by the wind power generators. The effectiveness of the proposed approach was confirmed with the simulation studies of a two‐area interconnected power system including many wind power generators. The results show that the correlation and the turbulence degree are useful for the reduction of frequency fluctuation so as not to disconnect too many wind power generators. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(1): 10–18, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20911     

大容量机组投运对湖南电网的安全运行影响研究

2006年湖南电网将新建大容量电源机组,这些新机组的投运,为湖南电网的可靠供电提供强有力的保障,但这些大容量机组的投运却将给湖南电网带来新的问题.文中着重分析大容量机组通过单一500kV上网对湖南电网输送能力及湘中联变输送功率的影响,同时分析大容量机组投运对暂态稳定的影响,对负荷中心大容量机组跳闸对系统稳定性的影响及鄂湘联络线输送功率的影响也进行了详细分析.根据计算结果,提出了协调大容量机组与湖南电网的安全稳定运行的措施.     

CCS参与的火电机组一次调频能力试验研究

火电机纽投入机炉协调方式运行后，数字电液控制系统(DEH)内部实现的一次调频功能被机组的协调控制系统(CCS)作为系统内扰很快克服，在电网发生事故，系统频率持续偏离时，无法达到电力系统一次调频的目的，提出利用CCS与DEH侧一次调频回路在调节特性与作用时序上的互补性，实现快速持久的一次调频。采用选取典型机组进行对比试验的方法，实施并完善了新的一次调频方案，验证了该方案使一次调频功能在保持快速性的同时，能在电网频率偏离的情况下持续作用，并使一次调频的能力得到加强。通过对典型机组现场试验的结果分析，确认新方案下机组的调节品质可满足运行的安全性要求。     

Impacts of load models and power factor control on optimal sizing of photovoltaic distributed generators in a distribution system

This paper studies the impact of optimal sizing of photovoltaic distributed generators (PV‐DGs) on a distribution system using different static load models (i.e., constant power, constant current, and constant impedance) and various power factor (PF) operations. A probabilistic approach with Monte Carlo simulation is proposed to obtain the optimal size of PV‐DG. Monte Carlo simulation is applied to predict the solar radiation, ambient temperatures, and load demands. The objective is to minimize average system real power losses, with the power quality constraints not exceeding the limits, i.e. voltage and total harmonic voltage distortion (THDv) at the point of common coupling (PCC). A modified Newton method and a classical harmonic flow method are employed to calculate the power flow and THDv values, respectively. An actual 51‐bus, medium‐voltage distribution system in Thailand is employed as a test case. Results demonstrate that the proposed method performs well to provide the optimal size of PV‐DG based on technical constraints. Further, the results show that the three static load models do not affect the optimal PV‐DG size but the model has a different impact for various PF operations. PV‐DGs may improve the voltage regulation and decrease the losses in distribution systems practically, but the THDv values could increase. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Investigation of performance of UPFC without DC link capacitor

This paper presents an analysis of the dynamic operation of unified power flow controller without DC link capacitor. In this scheme of UPFC the shunt converter present in the static synchronous compensator is operated as a current source rectifier, which maintains a fixed DC voltage and DC current on the DC link without capacitor. The capacitor in the DC link is replaced by an AC filter on the line side with a very small value to reduce higher order harmonics. The voltage source inverter present in the series compensator is operated with space vector modulation technique. The proposed scheme is fully validated through digital simulation. The simulated results show that the DC link voltage is maintained constant without DC link capacitor; STATCOM provides good voltage regulation and static synchronous series compensator influences power flow over the transmission line. Transient responses of single machine infinite bus power system have also been presented.     

基于分段控制的双馈风电机组有功-频率控制

为缓解大规模风电并网给电力系统频率带来的不利影响,在考虑风力发电经济性的前提下,使风电机组具有类似常规机组的调频特性,以改善含大规模风电的电力系统的频率稳定性,提出一种基于分段控制思想的双馈风电机组有功-频率控制策略,将风电机组有功-频率控制分为4段：卸载运行段、调频段、最大功率运行段及脱网运行段。研究采用该策略的控制模型参数整定问题,进而分析采用该控制策略的双馈风电机组的调频能力,探讨风电渗透率及负荷变化幅度对其调频效果的影响,在此基础上得出双馈风电机组的有功-频率特性。仿真结果验证了所提有功控制策略的可行性与有效性。     

考虑频率波动的孤岛微电网在线三相概率潮流计算方法

为了量化短期源荷功率扰动对频率波动的影响并保证模拟精度,从短期概率潮流问题出发,采用预测分量和随机预测误差分量分别表示风电和负荷的实时扰动功率,同时用一次调频实现扰动功率中随机预测误差分量的平衡,用基于超前控制方式的二次调频实现系统当前功率缺额和扰动功率预测分量的平衡,从而实现了对源荷功率扰动影响的准确量化评估。同时,提出的模型考虑了微电源的三相电压、电流对称控制特性以及可控微电源与负荷的静态频率电压调节特性,精确模拟了孤岛微电网的调频过程以及微电源的三相潮流控制特性,因而大幅提高了三相潮流与频率波动的仿真精度。采用三点估计法实现所建模型的概率评估,并通过IEEE 33节点修正系统的仿真分析验证了所提方法的有效性。     

基于改进转子转速和桨距角协调控制的变速风电机组一次调频策略

风电机组参与一次调频缓解了传统同步机组的调频压力,但其调频性能受功率跟踪方法的影响,不利于系统频率稳定。为此提出了基于改进转子转速和桨距角协调控制的一次调频策略,在全风速范围内预留调频所需功率裕度,在系统频率波动时能够提供快速且持久的有功支撑,实现对风电机组静调差系数的整定。对比分析不同减载控制策略下机组疲劳载荷和损伤等效载荷,结果表明所提策略可有效降低机组的疲劳载荷,延长使用寿命。最后,通过仿真验证了所提一次调频策略的有效性,频率改善效果优于传统一次调频控制,提高了风电场参与系统频率调节服务的一致性和可预测性。     

电力系统频率稳定分析的直接法

根据最近一次潮流计算的雅可比矩阵，提出了频率稳定分析的直接法，该方法不需进行逐步积分，能够一步计算出最近一次系统操作后的稳态频率，从而判断系统频率稳定性。本文在某６８ 节点系统上进行了仿真计算，对所提出的算法的精度和计算速度进行了校验，取得了满意的结果。     

Stochastic optimal power flow incorporating offshore wind farm and electric vehicles

In this paper, an optimal power flow model of a power system, which includes an offshore wind farm and plug-in electric vehicles (PEVs) connected to grid, is presented. The stochastic nature of wind power and the uncertainties in the EV owner’s behavior are suitably modelled by statistical models available in recent literatures. The offshore wind farms are assumed to be composed of doubly fed induction generators (DFIGs) having reactive power control capability and are connected to offshore grid by HVDC link. In order to obtain the optimal active power schedules of different energy sources, an optimization problem is solved by applying recently introduced Gbest guided artificial bee colony algorithm (GABC). The accuracy of proposed approach has been tested by implementing AC–DC optimal power flow on modified IEEE 5-bus, IEEE 9-bus, and IEEE 39-bus systems. The results obtained by GABC algorithm are compared with the results available in literatures. This paper also includes AC–DC optimal power flow model, implemented on modified IEEE-30 bus test system by including wind farm power and V2G source. It has been shown that the uncertainty associated with availability of power from wind farm and PEVs affects the overall cost of operation of system.     

Dynamic Load Flow Technique for Power System Simulators

This paper presents a dynamic load flow technique for power system simulators. The approach presented can be applied to a system when there is a net accelerating or decelerating power in the system. It possesses all the attractive features and basic structure of the normal fast decoupled method, and it does not depend on the selected reference bus. The modifications to the standard fast decoupled power flow algorithm are derived, and power system simulator implementation considerations are discussed. The algorithm has been tested on standard IEEE test cases and on a metropolitan utility 559 bus model. A numerical example of the above algorithm on the 559 test case is presented which demonstrates convergence characteristics and computation requirements of the proposed algorithm. These results are compared with those of normal fast decoupled load flow.