多馈入直流输电系统谐波交互影响分析

多馈入直流输电系统中各换流站交流侧谐波存在交互影响现象。分别给出了多馈入直流输电系统中交流侧谐波吸收、谐波放大的定义,描述了其发生现象,提出了基于谐波阻抗分析方法的双馈入直流输电系统谐波交互影响分析模型,揭示了谐波交互影响的机理。以华东电网为例,利用EMTDC电磁暂态仿真软件,建立多馈入直流输电系统模型。通过各条直流输电工程交流滤波器组合投切、交流侧故障的仿真以及实际录波数据分析,验证了谐波交互影响现象和其发生机理,并分析比较了非特征谐波、特征谐波放大倍数的差异。对各换流站交流侧谐波自阻抗进行了扫描分析,结果表明两换流站交流侧等效谐波自阻抗幅值差值较大或相位差值较大是发生明显谐波吸收、放大现象的必要条件。     

多回直流输电系统稳定性研究

采用BPA数字仿真法,分别研究了三峡一华东多回直流输电系统在直流线路故障(单、双极闭锁)时的暂态稳定性,以及直流功率提升和切机措施对保持三峡电网暂态稳定性的作用。计算结果表明,2回直流输电线路各自单极闭锁以及葛上直流输电线路双极闭锁时,三峡电网都能保持稳定：三常直流输电线路双极闭锁时,三峡电网必须同时进行直流功率提升和切机才能保持稳定．     

New control for HVDC system connected to large windfarm

HVDC consisting of self‐commutated inverters is able to be applied for power transmission connecting from a remote large windfarm to a weak AC system. Most self‐commutated HVDC is applied for connection between two AC systems that have synchronous power sources, but it is not suitable for a windfarm that consists of induction generators without synchronous power source. This paper presents new control for the self‐commutated HVDC system connected to a large windfarm of induction generators. The effect of the proposed control is shown by EMTP simulation. ©2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(4): 31–39, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20539     

连接交流系统的HVDC线路暂态稳定判别及保护机制

随着交/直流混联系统不断推广应用,混联系统的保护动作机制决定着系统的稳定性。提出了一种交直流混联系统稳定性判别原则,根据直流系统故障后的恢复运行极限时间配置保护。分析了交直流混联系统的暂态稳定性模型,推导出了HVDC连接下的电磁功率表达式。以两机交直流混联系统为例,分析了暂态稳定的AC/DC等面积定则,给出了故障前、故障中和故障后的分析。根据两机系统暂态稳定判据,提出了直流系统故障下的恢复运行的极限时间,以此配置保护,提高混联系统的暂态稳定性。通过仿真算例,分析了影响AC/DC系统暂态稳定性的主要参数,同时说明了所提方法的适用性。     

Transient stability of small plant generators connected to a weak utility system-a case study

Small generators connected through a large impedance and operating in synchronism with a weak utility system are more likely to pull out of step on a large perturbation, i.e., a fault in the utility's system. Under an incident impact, which will be distributed unevenly among various machines, every machine will be retarded or accelerated, and undergo damped or divergent oscillations. This paper demonstrates that the small machines are more vulnerable and may fall out of step. This may plunge the entire process plant into a complete power outage on system separation. A case study of two small generating units and the improvements in the transient stability by fast system separation and load shedding is demonstrated.     

A multi-terminal HVDC transmission system for offshore wind farms with induction generators

Voltage source converter, multi-terminal HVDC transmission (MTDC) for the connection of large offshore wind farms to the terrestrial grid is investigated. Induction generators without the need of wind turbine converters are installed in the wind farms due to the supports from the voltage source converters of the HVDC. A control system is designed which incorporates the voltage–current characteristics of the voltage source converters and the power reduction from the wind turbines during a fault. During normal operation, grid side converters control the DC voltage and coordinate the power sharing to the terrestrial grids. During abnormal operation, wind farm side converters take over the DC voltage control and coordinate the power reduction between wind farms. The control system removes the requirement for fast communication between the converters and achieves automatic coordination. The dynamic performance of a MTDC with the control system is tested through simulations using PSCAD/EMTDC.     

直驱型机组风电场并网静态电压稳定性研究

对基于永磁直驱型机组的风电场静态电压稳定性进行了研究.通过单机无穷大系统分析了影响并网风电场电压稳定性的主要因素,以美国西部电网WSCC3机9节点系统为例,分析了风电场接入后对系统电压稳定性的影响,并对不同线路等值阻抗、不同控制方式下的电压稳定性进行了比较分析,得出了P-V曲线.     

600 MW空冷亚临界发电机组空冷岛厂用电系统谐波分析

本文针对首套国产化600MW发电机组空冷岛低压配电系统,风机变频器负载谐波含量及大小进行分析论证,对合理选用滤波设备容量有着比较实用的工程意义。     

适应风电接入的异步联网高压直流输电系统自适应调频控制策略

大规模风电接入高压直流送端系统将导致系统惯量降低,送端系统调频能力不足。为充分挖掘直流和风电协同调频的潜力,提高含风电高压直流送端系统的调频性能,提出一种基于频率轨迹规划的异步联网高压直流输电系统自适应调频控制策略。分析了含风电高压直流送端系统的频率控制特性;综合考虑风电主动频率支撑和直流辅助频率控制,以频率偏差和频率变化率为量化指标,生成参考频率轨迹;在此基础上,对频率轨迹进行区域划分,以参考频率轨迹为基准,实现高压直流输电对送端系统频率的自适应调节。基于MATLAB/Simulink平台搭建改进的两区域4机模型进行仿真分析,验证了所提策略的有效性和优越性。     

Control sensitivity indices for stability analysis of HVDC systems

This paper presents a new concept called the “Control Sensitivity Index” or CSI, for the stability analysis of HVDC converters connected to weak AC systems. The CSI for a particular control mode can be defined as the ratio of incremental changes in the two system variables that are most relevant to that control mode. The index provides valuable information on the stability of the system and, unlike other approaches, aids in the design of the controller. It also plays an important role in defining nonlinear gains for the controller. This paper offers a generalized formulation of CSI and demonstrates its application through an analysis of the CSI for three modes of HVDC control. The conclusions drawn from the analysis are confirmed by a detailed electromagnetic transients simulation of the AC/DC system. The paper concludes that the CSI can be used to improve the controller design and, for an inverter in a weak AC system, the conventional voltage control mode is more stable than the conventional γ control mode     

Impact of FACTS controllers on the stability of power systems connected with doubly fed induction generators

The increasing power demand has led to the growth of new technologies that play an integral role in shaping the future energy market. Keeping in view of the environmental constraints, grid connected wind turbines are promising in increasing system reliability. This paper presents the impact of FACTS controllers on the stability of power systems connected with wind energy conversion systems. The wind generator model considered is a variable speed doubly fed induction generator model. The stability assessment is made first for a three phase short circuit without FACTS controllers in the power network and then with the FACTS controllers. The dynamic simulation results yield information on (i) the impact of faults on the performance of induction generators/wind turbines, (ii) transient rating of the FACTS controllers for enhancement of rotor speed stability of induction generators and angle stability of synchronous generators. EUROSTAG is used for executing the dynamic simulations.     

经柔性直流接入的大规模直驱风电场等效建模与小干扰稳定性分析

含多台风机的大规模风电场经柔性直流接入交流系统的详细模型阶数过高,对小干扰稳定性分析和失稳机理研究提出了挑战.为此,建立了风电场经柔性直流接入交流系统的开环、闭环线性化状态空间模型.基于风电场开环状态空间模型及风电场节点电压电流关系,将全阶风电场模型通过单台风机动态及交流拓扑信息矩阵进行等效,并分析了风机输出功率、风机...     

弱电网下电压源型变换器静态稳定性分析

电压源型变换器(Voltage Source Converter,VSC)作为新能源发电的并网接口广泛地应用于电力系统.以单台VSC经线路阻抗并入无穷大电网为例,推导弱电网下VSC功率输出特性.基于VSC系统阻尼转矩模型得出阻尼系数直接决定系统静态稳定,同步系数通过影响阻尼功率相位间接影响系统稳定.根据阻尼功率与同步功...     

A theory of maximum capacity of distributed generators connected to a distribution system using electric power density model

Recently, the number of distributed generators (DGs) connected to distribution systems has been increasing. System operators should know the maximum capacity of DGs that can be connected without problems to one feeder of the system in order to control the system appropriately. Many studies of the maximum capacity of the DG have been presented, but they have produced limited results calculated by a typical or average‐value model. However, many DGs will access one feeder if deregulation of the electric power industry is accelerated in the near future. In order to deal with this situation, the authors have derived a general formula to calculate the range of the maximum DG capacity per feeder. Copyright © 2004 Wiley Periodicals, Inc. In order to deal with sets of DGs that are dispersed completely on the distribution line, the authors have derived a differential equation for the complex power and one for the voltage drop, which are expressed as functions of distance from the substation. The general formula to calculate the range of the maximum DG capacity connected to the system is determined by solving these equations under the constraints of the line voltage, the line current, and the power factor of the DGs. By a numerical analysis, the authors have calculated the maximum capacity of DGs depending on many parameters, such as the length of the feeder, the DG power factor, and the like. In a short‐length system, the maximum DG capacity is governed by the current constraint, but in a long length system, it is governed by the upper voltage constraint. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(3): 18–28, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20330     

基于Hopf分岔的电力系统HVDC稳定直流分段控制策略

为有效处理电力动态失稳现象,提出基于Hopf分岔的电力系统HVDC稳定直流分段控制策略。首先,基于IEEE 14电力测试系统并利用HVDC整流器进行电力3段系统构建,然后利用代数方程实现系统模型表示;其次,对3段系统利用Hopf雅可比分岔点理论进行灵敏度研究,并选用HVDC工作点进行线路电流参数调整,实现最佳参数的线性可控确定,获得电力系统直流分段的稳态控制效果;最后,实验对比结果显示,所提策略可得到最佳操作点,可实现Hopf分岔过程的阻尼振荡和稳定裕度提升,从而大幅提升系统的稳态控制效果。     

Harmonic cancellation characteristics of specially connected transformers

Specially connected transformers such as V–V, Scott and Le-Blanc transformers are used to convert a three-phase supply into one or two single-phase supplies. These transformers are commonly used in the electro locomotive traction systems. This paper investigates the harmonic cancellation characteristics of such transformers. The results show that when two harmonic-producing loads are connected to each single-phase side of the transformers, the harmonics produced by the loads will cancel out at the primary sides of the transformers. The amount of cancellation is affected by transformer type and harmonic order. The study is performed for seven types of specially connected transformers.     

基于多直流落点系统稳定性的电网静态分区方案选择方法

针对多直流落点系统静态分区方案的选择问题,提出多直流落点相互作用因子、多直流落点有效短路比、频率偏差因子3个评价指标,以及反映上述指标整体性和均衡性的子指标。建立线性加权和模型求解该多目标决策问题,采用综合赋权法计算权重系数,并提出基于多直流落点系统稳定性的电网静态分区方案选择方法。以实际电网为例,对静态分区方案进行评价和选择,得到最优方案。利用PSS/E平台对各方案的系统稳定性能进行仿真,结果表明,各分区方案的系统稳定性优劣排序与静态分区方案选择方法的计算结果排序具有一致性,验证了所提方法的有效性。