基于PSS/E的特高压交流系统等值方法

在对特高压交流系统进行电磁暂态仿真时,为了简化系统通常需要在保证待保留系统边界节点短路容量恒定的条件下对外部网络进行等值。传统等值方法要对边界节点进行逐一短路,获得与边界节点数目相同的节点电压方程,根据节点电压方程组联立求解得到节点导纳矩阵。当边界节点较多时,方程组维数较大,计算过程繁琐。利用PSS/E软件中SCEQ模块,对特高压浙北—福州工程投产后的华东电网进行等值,将特高压系统作为研究系统,将500kV系统等值为接入特高压中压侧母线的发电机及其互阻抗。通过等值前后无功调压灵敏度和边界母线短路电流对比,验证了等值方法的正确性。     

电力系统中负负荷等值对暂态稳定仿真的影响

随着分布式能源的迅速发展,低压配电网中电源的含量不断升高,配电网电源在满足配电网自身需要的同时还往往通过联变向主网倒送电力,此类节点在仿真中通常被等值为负负荷。为研究负负荷等值对仿真准确度的影响,以EPRI-36节点系统为例,对负负荷等值前后两系统的潮流结果、暂态功角、暂态电压进行了比较。结果表明负负荷的等值对潮流影响很小,但是对暂态稳定仿真影响巨大,甚至与仿真结论完全相反,因此要想得出准确的仿真结果必须对负负荷节点进行详细建模。     

考虑分布式能源集群暂态过电压抑制的交直流混联电网无功优化方法

针对直流故障下高比例新能源交直流混联电网无功盈余而导致的暂态过电压问题,文章提出基于分布式能源集群暂态过电压抑制的交直流混联电网无功优化方法。首先,研究交直流混联电网换流站交流母线处等值交流电网、等值分布式能源集群、等值无功调节设备和换流站的功率平衡特性,考虑直流闭锁故障,研究暂态过程中无功盈余引起的交直流混联电网过电压机理。其次,分别建立包含分布式风电集群、分布式光伏集群和分布式储能集群的交直流混联电网分布式能源集群无功电压响应模型。再次,以最大限度保留动态无功设备的无功回降裕度和减少无功补偿设备投入量为目标,以功率平衡和并网点暂态过电压限值为约束,提出协调分布式能源集群的交直流混联电网无功优化模型。最后,利用修改的IEEE39节点系统以及南方某交直流混联电网实际运行数据进行算例分析,结果表明文章所提方法能够有效抑制交直流混联电网暂态过电压。     

地区电网动态等值模型和等值方法的改进

近年来为简化对大规模特高压互联地区电网的分析,提出了一系列电网等值方法,然而不合理的等值将造成分析电网数据的精度下降。基于上述问题,通过对常用等值方法的等值过程进行分析,找出误差来源,提出了新的改进方案,即在保证等值前后静态边界潮流不变情况下,在等值边界悬挂接地电阻和等值调节功率负荷,以此保证动态情况下外网对内网注入的功率不变。最后,将该方法应用在PSASP软件中的一个8机36节点系统,通过仿真,验证了该方法的简化性和实用性。     

风电交直流通道互联电力系统暂态稳定线性变参数鲁棒反馈控制

针对交直流系统中影响暂态稳定电磁转矩和机械转矩平衡控制问题变参数特性,结合大规模风电功率的不确定性,提出了将直流通道功率控制与互联系统内机械功率作为控制目标的互联系统暂态稳定的线性变参数鲁棒反馈控制方法,以提高经交直流风电通道互联的系统的暂态稳定性。针对互联系统暂态过程的强非线性特性,建立了线性变参数模型;根据暂态过程系统出现的功率差额和风电出力不确定度,将系统暂态过程设计为变参数的线性化模型。对线性变参数模型设计H∞鲁棒输出反馈控制器及其在线求解算法。根据线性变参数设计点和鲁棒控制器,提出了互联系统暂态稳定控制策略拓扑及传递函数。应用交直流联络线互联形成的4个等值电网互联系统进行数字仿真,结果表明,文章所提出线性变参数鲁棒反馈控制模型,具有较好的响应特性和暂态稳定控制效果。     

大型风电场失速型机组等值建模的研究

对于风电场中失速型机组的多机等值,采用异步发电机的机电暂态模型求解发电机组的等值电气参数,利用基于传递函数概念的参数辨识方法及最小二乘法求解发电机组的动态等值参数。利用系统等值得结果对一实例进行仿真,结果表明了等值方法的有效性和正确性,为今后研究风电场与电网之间的相互影响提供了良好的模型基础。     

综合能源交直流混联外送系统暂态过电压分析与快速估算

针对大容量直流和高比例新能源集中接入的交直流送端系统中，由于故障扰动引起的暂态过电压难以快速准确计算导致系统安全稳定运行的问题，提出综合能源交直流混联外送系统暂态过电压分析与快速估算方法。首先，建立风火打捆的送端系统等效模型，考虑储能系统接入后的交直流综合能源的调节特性，对故障后的暂态过电压进行修正。分析故障扰动下风电机组的有功功率和无功功率动态变化特性，给出暂态过电压的计算流程。然后，分析暂态过电压时变参数辨识方法，提出交直流系统暂态过电压快速估计方法。最后，以某地交直流送端系统数据建立仿真模型，仿真结果验证了所提方法在交直流送端系统暂态过电压的计算精度和收敛速度方面具有优越性。     

基于内网常规Ward等值电路的外网静态等值法

在外网信息完全未知的情况下,提出了基于内网Ward等值电路的外网静态等值方法.现有的基于内网信息估计外网等值参数的方法仅依赖于边界节点处的功率方程约束关系,没有充分利用内网其他相关的量测信息.首先基于内网的实测信息得到其常规Ward等值电路,然后建立外网等值参数的量测方程,以此求解外网等值模型参数.通过引进内网常规Ward等值电路,增加了对外网等值参数的约束,使参数估计值更加准确合理.IEEE-39节点系统的仿真结果验证了该方法的有效性.     

多机互联系统下的PSS性能分析

利用PSS稳定器提高电力系统稳定性是一种被普遍采用的有效方法,工程中一般基于单机无穷大系统采用相位补偿方法对其进行现场参数试验计算。但系统理论自振频率和实际电网运行存在差异,考虑实际网侧运行来研究励磁系统特性将会更加准确。在Phillip-Heffron模型基础上,讨论了多机系统下发电机模型的建立,并结合了双端供电、交直流输电2个典型多机系统下暂态扰动的仿真测试,通过比对等效PSS系统和实际工程中的PSS系统,分析了其在多机互联场景下的动态效果,对于PSS的性能改善具有积极意义。     

考虑暂态电压稳定约束的最优潮流计算

根据电压稳定研究的成果,提出了一种适合工程应用要求的暂态电压稳定判据形式.同时,提出了基于最优控制原理的求解暂态电压约束梯度的方法,该算法能有效提高计算速度,并将其作为暂态电压稳定约束加入OTS模型.由于该算法大幅降低了暂态稳定约束的维数,不但减少了计算量,并且能够处理多个预想事故.采用IEEE3机9节点系统对该算法方法进行了仿真分析,结果表明,提出的电压稳定判据有效可行,并且经OTS求解后的系统能够维持暂态电压稳定,从而验证了该算法的有效性和正确性.     

AC/DC power conversion interface for self-excited induction generator

A new AC/DC power conversion interface for the self-excited induction generator (SEIG) is proposed here. The proposed AC/DC conversion interface includes an excitation systemand a diode rectifier connected in parallel.The variable frequency AC power generated by the SEIG is converted into DC power by the diode rectifier.The DC power of the diode rectifier can charge a battery set and supply DC loads or be further converted into fixed-frequency AC power by an inverter for AC loads.The DC voltage is expected to be regulated in the above applications.The excitation system supplies an exciting reactive current to maintain the amplitude of the SEIG output voltage to be a constant value. Moreover, it can also serve as an active power filter to suppress the harmonic current generated by the diode rectifier. The excitation system is composed of an AC power capacitor and a power converter connected in series. The AC power capacitor is adapted to provide a basic reactive power, and it can also reduce the voltage rating and the capacity of the power converter. The salient point of the proposed AC/DC power conversion interface is that the capacity of the power converter in the AC/DC power conversion interface can be minimised, and the power loss of the AC/DC power conversion interface can also be reduced. A prototype is developed and tested to verify the performance of the proposed AC/DC power conversion interface.     

直流调制技术在西北电网应用的可行性研究

对直流调制技术在西北电网应用的可行性进行了研究。仿真结果表明,利用直流调制技术可以改善严重故障后西北电网的频率稳定性和暂态稳定性,消除交流电网过载,提高电网的输电能力。     

考虑风电不确定性的交直流混联系统同质化能量函数模型

交直流混联电网是电网发展的新形态,如何有效保障交直流混联系统安稳运行是重大而紧迫的国家需求。文章针对含大规模风电的交直流混联系统稳定性问题,提出考虑风电波动不确定性的交直流混联弱送端系统同质化能量函数模型。首先,研究含大规模风电的交直流混联弱送端系统潮流方程;其次,建立含风电的交直流混联系统支路暂态势能函数模型,研究交直流混联系统功角稳定机理,建立基于同质化能量函数模型;在此基础上,提出基于同质化能量函数的电力系统稳定性评估模型,并推导交直流混联系统稳定性判据;最后,以北方某区域交直流混联系统为仿真算例,验证所提模型的有效性,为含大规模新能源的交直流混联系统的稳定性控制提供理论依据。     

交直流混合电力系统快速潮流计算

针对交直流混合电力系统潮流算法计算量大、计算速度慢的缺点,提出一种基于广义特勒根定理的交直流混合电力系统快速潮流计算方法。该方法将修正方程的注入功率改为注入电流,得到基于统一迭代法的电流注入型潮流计算模型,该潮流模型既保留了统一迭代法的强收敛性,又降低了模型计算量。在此基础上,应用广义特勒根定理求解所建潮流模型,既减少修正方程求解量又提高了潮流求解速度。对22节点交直流混合电力系统进行仿真计算,仿真结果验证了该方法的正确性和快速性。     

Planning and analysis of the demonstration project of the MVDC distribution network in Zhuhai

The DC distribution system is an important development direction of the distribution system, which can improve the reliability and the quality of the power supply, and support the new energy, the energy storage, the electric vehicles, and the flexible access of AC and DC loads to grid. To realize the demonstration application of the DC distribution technology, China’s first demonstration project of the medium voltage DC distribution network will be built in Zhuhai, Guangdong Province to support the construction of the city energy internet. First, this paper analyzes the demand of the DC distribution network project, and puts forward the construction content and construction target. Then, it designs and analyzes the electrical connection mode, system operation mode, and startup and shutdown mode of the DC distribution network, and proposes the overall project construction plan. Finally, it conducts the specific project design and analysis, which mainly include the selection of equipment such as inverters, DC transformers and DC circuit breakers, the design and analysis of the DC control and protection system, the design and analysis of the over-voltage protection and the configuration scheme of the lightning arrester, and analysis of the system transient characteristics. The design and analysis of the engineering program is a combination of China’s distribution network engineering practice and technical characteristics, which lays a solid foundation for the advancement of the DC power distribution technology in China, and has reference value and demonstration effect for the design and construction of other projects.     

特高压直流输电二次系统雷电电磁暂态影响

研究二次系统的电磁干扰导致的换相失败及双极闭锁等故障产生的机理对确保直流系统的安全可靠运行具有重要意义。通过研究交直流互联系统雷电电磁暂态及电磁能量交互机理、交直流互联网络雷电电磁干扰,揭示了交直流互联系统的雷电电磁暂态传播机理、形成及行为规律,为防止交直流换流站的雷电电磁暂态的交互影响提供了分析手段、理论依据及技术措施。     

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.     

A new method for dynamic performance improvement of a hybrid power system by coordination of converter's controller

In this paper, a new strategy for modeling and controlling a hybrid power generation system that contains a fuel cell (FC) and super capacitor (SC) system is proposed. The main drawback of FC systems is its slow dynamic because the FC current slope must be limited in order to prevent fuel starvation problems and to improve its efficiency and lifetime. To overcome this slow dynamic and to improve dynamic performance, a new control strategy is proposed to combine FC system with SC system. The proposed control strategy can be also used for cold starting and different types of FC systems with different dynamics. The control strategy is capable of determining the desired FC power to prolong FC system lifetime and keeps the AC and DC voltages around its nominal value in transient event by supplying propulsion power and recuperating FC energy. The minimum SC system is computed in new method and used to meet the load demand to constraint the DC bus voltage and enhances power regulation under various active and reactive load conditions. Two different case studies are used to obtain the simulation results using MATLAB/SIMULINK to verify the validity of the proposed control strategy.     

基于序列运算的风光储混合微电网可信容量评估

以含风光储的交直流混合微电网为研究对象,通过聚类分析方法对气象条件进行分类,搭建风光储出力概率模型并进行序列化。提出一种序列运算方法计算交直流混合微电网用电不足期望值,从而迭代求得可信容量,针对风光装机容量配比以及直流负荷敏感度对可信容量的影响进行了分析,并将计算结果与蒙特卡洛法进行了对比,验证该文所提方法的正确性与有效性。     

Impact of selection of DC base values and DC link control strategies on sequential AC-DC power-flow convergence

This paper demonstrates the convergence of the integrated AC-DC power-flow algorithm as affected by the selection of different base values for the DC quantities and adoption of different control strategies for the DC link. For power-flow modeling of integrated AC-DC systems, the base values of the various DC quantities can be defined in several ways, giving rise to different sets of per-unit system equations. It is observed that different per-unit system models affect the convergence of the power-flow algorithm differently. In a similar manner, the control strategy adopted for the DC link also affects the power-flow convergence. The sequential method is used to solve the DC variables in the Newton Raphson (NR) power flow model, where AC and DC systems are solved separately and are coupled by injecting an equivalent amount of real and reactive power at the terminal AC buses. Now, for a majority of the possible control strategies, the equivalent real and reactive power injections at the concerned buses can be computed a-priori and are independent of the NR iterative loop. However, for a few of the control strategies, the equivalent reactive power injections cannot be computed a-priori and need to be computed in every NR iteration. This affects the performance of the iterative process. Two different per-unit system models and six typical control strategies are taken into consideration. This is validated by numerous case studies conducted on the IEEE 118-bus and 300-bus test systems.