Frequency Control of Power System with Solar and Wind Power Stations by Using Frequency Band Control and Deadband Control of HVDC Interconnection Line

In recent years, environmental problems are becoming serious and renewable energy has attracted attention as their solutions. However, the electricity generation using the renewable energy has a demerit that the output becomes unstable because of intermittent characteristics, such as variations of wind speed or solar radiation intensity. Frequency fluctuations due to the installation of large scale wind farm (WF) and photovoltaics (PV) into the power system is a major concern. In order to solve the problem, this paper proposes two control methods using High Voltage Direct Current (HVDC) interconnection line to suppress the frequency fluctuations due to large scale of WF and PV. Comparative analysis between these two control methods is presented in this paper. One proposed method is a frequency control using a notch filter, and the other is using a deadband. Validity of the proposed methods is verified through simulation analyses, which is performed on a multi-machine power system model.

Frequency Control of Power System with Renewable Power Sources by HVDC Interconnection Line and Battery Considering Energy Balancing

Recently, introduction of renewable energy sources like wind power generation and photovoltaic power generation has been increasing from the viewpoint of environmental problems. However, renewable energy power supplies have unstable output due to the influence of weather conditions such as wind speed variations, which may cause fluctuations of voltage and frequency in the power system. This paper proposes fuzzy PD based virtual inertia control system to decrease frequency fluctuations in power system caused by fluctuating output of renewable energy sources. The proposed new method is based on the coordinated control of HVDC interconnection line and battery, and energy balancing control is also incorporated in it. Finally, it is concluded that the proposed system is very effective for suppressing the frequency fluctuations of the power system due to the large-scale wind power generation and solar power generation and also for keeping the energy balancing in the HVDC transmission line.

Novel Adaptive Neural Controller Design Based on HVDC Transmission System to Damp Low Frequency Oscillations and Sub Synchronous Resonance

This paper presents the effect of the high voltage direct current (HVDC) transmission system based on voltage source converter (VSC) on the sub synchronous resonance (SSR) and low frequency oscillations (LFO) in power system. Also, a novel adaptive neural controller based on neural identifier is proposed for the HVDC which is capable of damping out LFO and sub synchronous oscillations (SSO). For comparison purposes, results of system based damping neural controller are compared with a lead-lag controller based on quantum particle swarm optimization (QPSO). It is shown that implementing adaptive damping controller not only improves the stability of power system but also can overcome drawbacks of conventional compensators with fixed parameters. In order to determine the most effective input of HVDC system to apply supplementary controller signal, analysis based on singular value decomposition is performed. To evaluate the performance of the proposed controller, transient simulations of detailed nonlinear system are considered.

Damping Controller Based Quantum Particle Swarm Optimization for VSC HVDC to Improve Power System Stability

The use of the supplementary controllers of a High Voltage Direct Current (HVDC) based on Voltage Source Converter (VSC) to damp low Frequency oscillations in a weakly connected system is surveyed. Also, singular value decomposition (SVD)-based approach is used to analyze and assess the controllability of the poorly damped electromechanical modes by VSC-HVDC different control channels. The problem of supplementary damping controller based VSC-HVDC system is formulated as an optimization problem according to the time domain-based objective function which is solved using quantum-behaved particle swarm optimization (QPSO). Individual designs of the HVDC controllers using QPSO method are evaluated. The effectiveness of the proposed controllers on damping low frequency oscillations is checked through eigenvalue analysis and non-linear time simulation under various disturbance conditions over a wide range of loading.

Technology and engineering application of cross area HVDC interconnection system high-precision simulation modeling based on ADPSS

In recent years, a large number of high voltage direct current(HVDC) transmission projects have been connected to AC systems. This has started to have an impact on AC/DC hybrid power grids, particularly receiving terminal power grids. An HVDC system is a large-scale power electronic integrated nonlinear system, and it includes a primary system and a control and protection system. Hence, the precision and degree of detail of HVDC systems directly affect the actual effect of simulation. In recent years, in the case of the normal operation and failure of AC power grids, the abnormal fluctuation and even locking of HVDC systems caused by the inappropriate strategies of the control and protection system component have strongly affected power grids. This has significantly affected the safety and stability of receiving power grids and normal operation. In this study, the actual engineering HVDC control logic provided by a manufacturer is analyzed and simulated based on the user defined component library of the ADPSS electromagnetic transient calculation program, and an HVDC control model based on an actual system is established. The accuracy of the DC control custom model based on ADPSS is verified through the simulation of an actual power grid.

PCHD-Based Passivity Control of VSC-HVDC Connected Large Wind Farm

Concentrated integration of large scale wind power demands stronger robustness of VSC-HVDC transmission. Based on PCHD (Port Controled Hamiltonian with Dissipation) equation, the PCHD model of voltage source converter (VSC) in abc frame and d-q rotating frame are built and the strict passivity of VSC is proved. Desired energy function is constructed and used as Lyapunov function by assigning link matrix and damping matrix. Impact from VSC equivalent dc resistance is eliminated by additional damping matrix. The IDA-PB (Interconnection and Damping Assignment Passivity-based) controller is designed based on desired equilibrium point and state variable. With different operation conditions, VSC-HVDC and its control system are simulated by software PSCAD/EMTDC, the results show the proposed control strategy has good performance and strong robustness.

基于VSC-HVDC的海上风电柔性直流输电系统并网控制

由于现有的控制方法并网点处的直流和交流电压较低,控制效果不佳,为此基于VSC-HVDC,针对海上风电柔性直流输电系统并网控制方法展开研究。首先,根据VSC-HVDC系统结构建立海上风电柔性并网模型,在换流侧通过换流设备将交流电源转换为直流电,并将转换后的直流电能输送到直流输电线路上;然后,运用PI控制器根据电流偏差进行调节,调整换流器的输出电流与实际电流误差,限制幅度环节输出控制系统并网有功功率信息,实现内环网并网控制;最后,运用PI控制器对交流电进行跟踪,调整无功分量来改变交流电压,实现外环网并网控制,完成针对海上风电柔性直流输电系统并网控制方法的设计。实验结果表明,经该方法控制后,交流电压维持在约0.7 p.u.的水平,直流电压被成功地限制在0.5~1 p.u.以内,控制效果较好。

VSC-HVDC系统控制体系框架

控制系统是VSC-HVDC系统的核心之一。目前虽已有许多研究者在该领域做了大量的工作,但多数成果集中在VSC-HVDC控制器的设计和控制方法的研究上,对整个VSC-HVDC系统控制体系框架的研究并不多见。本文在介绍VSC-HVDC系统结构的基础上,阐述了VSC-HVDC控制系统的基本功能,指出采用多重化配置和分层控制结构设计的必要性,具体提出建立四层结构的VSC-HVDC系统控制体系框架的观点,即直流系统控制层、换流器控制层、阀组控制层和独立控制层。文章在讲述各层配置原则的基础上,详细阐述了每个控制层次的控制功能和范围以及各层次之间的相互关系,并进一步介绍了控制系统和保护功能的协调配合问题,为VSC-HVDC控制系统的开发奠定了基础。

一种VSC-HVDC控制系统的PI参数整定方法

由于VSC-HVDC大多采用的是直接电流控制策略,其采用的电流内环和电压、功率外环控制均通过PI调节器进行串联校正。因此采用合适的方法设计PI调节器的参数,对于控制系统的性能起着至关重要的作用。本文提出一种参数整定方法,综合考虑控制系统的稳态误差、上升时间、抗干扰性能3个指标,将电流内环、功率外环、直流电压外环分别设计为典型的I型环节,典型的一阶环节和典型的II型环节,使得控制系统具有良好的稳态和动态性能,最后在PSCAD/EMTDC中仿真验证所建立模型的有效性。

基于Simplex算法的VSC-HVDC控制参数优化

以电压源换流器高压直流输电(VSC-HVDC)的稳态模型为基础,根据VSC功率传输方程的直角坐标形式,采用逆系统方法和PI控制相结合的方法设计了VSC的有功功率和无功功率独立调节的VSC-HVDC控制系统。基于非线性单纯形Simplex算法,对PI控制参数进行优化。PSCAD/EMTDC下的仿真结果表明,通过参数优化,VSC-HVDC控制目标的最大误差百分比低于1.5%;同时也证明所设计的控制系统能独立控制有功功率和无功功率。

HVDC送端孤岛运行方式的附加控制策略

直流工程用于远离主干网架的水电站或火电厂的电力送出时,送端交流系统形成相对独立的“孤岛”。在这种运行方式下,在交流系统有扰动时常规定功率或定电流控制方式有可能引起系统功率的持续不平衡,进而导致交、直流系统稳定运行的破坏。提出了一种附加控制策略,该附加控制策略根据系统频率的变化改变直流系统的功率或电流指令,从而实现系统功率的平衡。采用实时数字仿真器对该附加控制策略进行了验证,仿真结果表明,该附加控制策略可以明显增强系统的稳定性。

抑制HVDC送端交流暂态过电压的控制系统优化

为抑制直流输电(HVDC)换相失败恢复过程中的送端交流暂态过电压,通过电磁暂态仿真分析了换相失败过程中HVDC主要状态量的变化特性,分析了相关控制环节的参数与换相失败发生时整流侧交流母线过电压和低电压的灵敏度关系,发现电流控制环节的比例系数、积分时间常数以及换相失败预测功能环节的最小电流限制量和直流电压下降测量时间常数等变量对整流侧交流电压特性有明显影响。通过以上参数的优化,可以在保证直流系统性能的前提下实现换相失败故障后送端交流过电压的抑制。研究结果表明:整流侧电流控制环节、低压限流环节、换相失败预测功能环节是影响换相失败恢复过程的主要控制环节。低压限流环节中的直流电压下降测量时间常数对过电压幅值限制作用明显,对系统动态性能影响较小,可以在控制系统优化时重点考虑。

多落点HVDC附加阻尼控制的最优控制点研究

四川电网是典型直流多落点系统,如何选择最适合的直流线路来阻尼区域间振荡需要研究。在对系统线性化处理的基础上,通过理论推导得出了可以衡量直流阻尼控制器安装地点优劣的指标——控制敏感因子。该指标综合考虑了直流阻尼控制器对目标振荡模式的阻尼效果和对其余振荡模式的影响,其值越大表明控制点对区域间振荡模式可控性越好,且对其余振荡模式的影响越小。进一步给出了控制敏感因子的实用化计算步骤。通过对四川实际电网多种运行方式下的BPA数据模型仿真计算,验证了所提指标的正确性,为直流附加阻尼控制器最优安装地点的选择提供了实用化计算指标和一定程度的理论解释。

改善交直流混合系统阻尼特性的HVDC模糊控制

设计了一个用于改善交直流混合系统阻尼特性的HVDC模糊控制器,该模糊控制器既能根据运行条件修改增益,提高其控制性能;同时该模糊控制器的附加控制量ΔU能提高交流系统的稳定性,增强系统的阻尼,抑制系统的振荡。分别用传统控制与模糊控制方法对三机交直流系统的模型用NETOMAC软件进行了仿真,结果显示:在系统受到大干扰时,模糊控制器较传统的P-I控制器能更好地抑制交直流混合系统中交流系统的振荡、增强系统的阻尼,提高交流系统的稳定性。

考虑直流控制系统影响的HVDC输电线路后备保护研究

在考虑直流控制系统影响的情况下,详细分析了HVDC输电线路区内、区外的故障特征以及直流控制系统的动作特性和控制状态。引入并分析了基于开关函数的交直流系统二次谐波计算等值模型。通过分析故障期间换流器触发角和直流侧二次谐波量的变化特征,提出了一种新的以换流器触发角为保护动作量,利用二次谐波分量闭锁的直流线路后备保护方案,给出了保护整定的理论计算方法。与直流线路纵联差动保护相比,该保护不因直流电流波动影响而被闭锁,保护动作时间较快;与微分欠压保护相比,具有更高的抗过渡电阻能力。通过PSCAD/EMTDC大量仿真计算,验证了该保护能可靠区分直流线路区内、区外故障,与直流线路纵联差动保护和微分欠压保护相比具有明显的优越性。

基于EMTDC的HVDC极控制的建模与仿真

为了配合高压直流输电系统在我国的发展,介绍了高压直流输电极控制系统的基本结构和工作原理,运用PSCAD/EMTDC仿真软件对极控系统中的最主要功能,如定电流控制、定电压控制、定熄弧角控制以及限幅环节进行了数字建模,并应用于Cigre的HVDC标准测试系统,对4种工况进行仿真计算,仿真结果表明该极控系统具有良好的跟踪设定参考值变化的能力;当交、直流系统发生故障时,控制系统调节快速,能迅速抑制故障,并使故障恢复后直流输电系统能平稳过渡到稳定工况,说明所建仿真模型的正确性。

改善暂态稳定性的HVDC非线性控制策略

提出了一种新的高压直流输电系统的非线性紧急控制策略。首先建立包括 HVDC联络线在内的交、直流互联电网的观测解耦状态空间模型 ,根据该模型 ,只需要当地信号实施控制 ,驱动子系统到达局部平衡点 ,就能使全系统达到稳定 ,然后应用非线性最优变目标控制策略推导出HVDC系统的控制规律。用 3机系统进行数字仿真的结果表明 ,该方法能够在大干扰和紧急状态下充分利用 HVDC的快速响应和短时过载能力 ,提高交、直流互联系统的暂态稳定性和对功率突然严重缺额的地区进行紧急功率支援。

基于详细模型的HVDC系统非线性输出跟踪控制器

以往的 HVDC系统控制研究采用的模型不够详尽 ,为了更真实地考察 HVDC系统的控制特性 ,文中采用详细模型模拟了直流线路动态及触发延迟。采用此详细模型后微分几何方法及逆系统方法不便应用 ,为此提出了非线性输出跟踪控制器设计的关联度方法 ,这种方法物理意义明确 ,数学推导简单 ,适用范围广。应用此方法设计了详细模型下 HVDC系统的非线性输出跟踪控制器 ,数字仿真表明所设计的这种 HVDC系统控制器效果良好 ,关联度方法是有效的。

基于逆系统理论的VSC-HVDC新型控制

在讨论电压源型高压直流输电(VSC-HVDC)的控制策略中,根据所给出的拓扑结构,建立三相静止系统下的数学模型;再根据控制需要,通过派克矩阵,将VSC-HVDC转换为dq0旋转坐标下的数学模型;通过逆系统理论,将非线性VSC-HVDC系统强制线性化。同时,为了实现直流输电系统有功和无功的解耦控制,选择直流电流和换流站交流输入输出电流作为反馈来设计相应的控制器,并采用李亚普诺夫间接法证明了所提出的控制策略下VSC-HVDC闭环非线性系统的稳定性。计算机数值仿真显示,大扰动下的系统动态响应特性较好,可实现无功、有功的解耦控制,且具有一定的鲁棒性。