50MVA STATCOM的链节及其背靠背额定工况运行试验

上海西郊变电站的50MVA 新型静止无功发生器(Static var Compensator, STATCOM)装置采用基于IGCT器件的链式逆变器,每相由10个IGCT单相逆变器(链节)串联而成并输出10kV线电压,IGCT器件容量为4500V/4000A.为了有效地验证链节在额定工况下运行时IGCT压装及连接工艺、控制电源、控制、保护、冷却、电磁兼容等方面的设计是否达到了技术标准的要求,需要对链接进行额定工况运行试验.试验时两个被试验链节输出通过一个连接电抗相连,通过控制两个链节输出电压相位角来控制链节间交换的无功功率方向和大小,损耗由连接到其中一个链节的直流电容的外接直流电源提供.文中给出了链节原理及其设计、背靠背试验原理以及试验结果.试验结果表明链节设计达到了链式STATCOM技术标准的要求.     

应用于STATCOM链节背靠背试验的闭环控制策略

某换流站百兆乏静止同步补偿器(STATCOM)链节采用IGBT作为主要功率器件,每相桥臂由40个链节构成。为验证链节在额定及过载工况下的性能,通常采用背靠背试验方法,试验时将两个被试验链节的输出通过一个连接电抗器相连,其中链节1的直流电容由外接直流电源供电,链节2的直流电容悬浮,设定其中一个链节输出感性无功,另一链节输出同容量的容性无功。针对该方法提出了一种闭环控制策略,将试验拓扑等价为通过电抗器连接的单相逆变器与单相整流器,在整流器侧采用单相虚拟成三相方式并进行d-q解耦控制,通过该闭环控制策略可有效实现悬浮侧电容电压的稳定控制,并可精确设定试验电流的幅值与方向。给出了该闭环控制策略的原理,通过百兆乏STATCOM链节的试验结果证明了该控制策略的正确性及实用性。     

采用IGCT链式逆变器的50 MVA STATCOM

基于链式逆变器的静止无功发生器（STATCOM）具有比基于变压器多重化逆变器的STATCOM更多的优点。文中介绍了50 MVA STATCOM的主要作用及技术指标，给出了基于集成门木及换相晶闸管（IGCT）链式逆变器的主电路50 MVA STATCOM的构成、基于谐波优化的脉宽调制（PWM）控制策略。装置的满载出厂试验采用等价额定工况运行试验。文中给出了等价额定工况运行试验的原理以及试验结果。试验结果表明，链节设计达到了链式STATCOM技术标准的要求。     

不平衡工况下链式STATCOM的运行极限分析

在并网电压不平衡或补偿无功电流不平衡的工况下,需采用控制策略以保证链式静止同步补偿器(STATCOM)各个链节单元的直流电压基本恒定。常用的方法是将三角形接线的STATCOM叠加零序电流或星形接线的STATCOM叠加零序电压。基于零序分量叠加的方法,分析了在不平衡工况下保证链式STATCOM正常运行的条件。综合考虑并网电压不平衡与补偿无功电流不平衡的情况,分析了并网电压不平衡度、补偿无功电流不平衡度与装置额定电流、额定电压之间的关系。据此定量给出了三角形接线与星形接线的STATCOM装置不平衡运行的极限。通过比较发现,三角形接线的STATCOM更适用于补偿无功电流不平衡度较高的场合,而星形接线的STATCOM更适用于并网电压不平衡度较高的场合。最后在MATLAB/Simulink环境中搭建了仿真系统,仿真结果验证了上述分析的正确性和有效性。     

电网谐波对级联STATCOM运行影响分析及抑制

采用移相载波调制算法的链式静止同步补偿器(STATCOM)每相各链节之间交流输出电压中同频次谐波分量存在相位差,当电网中存在相应频次的电压谐波并使得STATCOM产生谐波电流时,会造成各链节与系统之间交换幅值不同的谐波有功。当STATCOM在低载输出工况时,由于链节直流电压均衡控制策略效果的弱化,使得谐波有功对链节直流电压的影响增大,这时差异化的谐波有功会使得链节间直流电压逐渐发散,并使得设备失稳。这里分析了采用移相载波调制算法的链式STATCOM在系统电压存在谐波情况下各链节谐波有功的差异,指出了链节直流电压均衡策略对此问题的缺陷,提出对应的解决策略,在PSCAD/EMTDC环境中进行了仿真验证,并在实际工程应用中有效解决了相关问题。     

电网不平衡下链式STATCOM补偿与控制策略

针对电网电压不平衡工况下的链式STATCOM的运行特性与控制策略问题,通过对比研究三角形与星形两种链式STATCOM的补偿特性,提出一种基于等效电纳变换法的星形链式STATCOM的零序电压计算方法,并在两相静止坐标系下完成不平衡电流跟踪控制。仿真与实验结果表明,在电网不平衡时,所提出方法不但能使星形链式STATCOM正常运行,而且能够补偿无功负载,减轻电网电流不平衡度,最终扩展了星形链式STATCOM的运行范围。     

不对称故障STATCOM过流抑制技术的研究

此处以广东电网500 kV水乡变电站静止无功补偿器(STATCOM)在电网发生不对称故障时易出现过流的问题为研究背景,通过深入分析网侧不对称电压对STATCOM输出电压影响,提出一种基于分相瞬时电流控制策略的过流抑制方案,从而有效避免因负序电压导致的持续过流,确保STATCOM安全运行,并在两套并联三角形连接的35 kV±100 Mvar链式STATCOM装置上进行过流抑制试验验证。试验结果表明此处提出的链式STATCOM过流抑制控制方法是正确可行的,具有较好的工程应用价值。     

系统电压不平衡下链式静止同步补偿器控制研究

针对三角形连接的链式静止同步补偿器(static synchronous compensator,STATCOM)系统电压不平衡下的控制问题,提出分相瞬时电流控制策略,在此基础上研究了链式STATCOM在不平衡电压下的补偿模式,提出无功补偿和电压控制2种改进裂补偿模式,并设计了其离散化电流环控制器.通过分相瞬时电流控制能够维持链式STATCOM在不平衡电压下的正常工作,2种改进型补偿模式使链式STATCOM能够有效的对不平衡系统进行补偿,仿真验证了所提控制策略及补偿模式.研制了一台三相36个链节的物理样机,并在样机上进行实验,证明了所提方法的正确性和有效性.     

一种链式换流器子单元全工况试验方法

目前,对链式换流器子单元进行功率试验均需要通过外部电路包括不控整流电路或可控整流电路提供直流电源,以上2种方法均存在主电路元件繁多、试验接线复杂、功能单一等问题。为此,对链式换流器子单元全工况试验方法进行研究后,简化了链式换流器子单元试验电路。试验主电路由试验电源、连接电抗器及被试换流器子单元组成。给出了试验主电路及其闭环控制策略,研制了链式换流器子单元全工况试验平台。实验结果表明,所提主电路结构及控制方法是有效的,试验平台实现了链式换流器子单元的全工况试验,能够在试验电源下实现额定直流电压输出额定无功电流。     

电气化铁路用单相链式STATCOM控制策略

为了研究单相链式STATCOM(static synchronous compensator)对电气化铁路电能质量问题的治理情况,在建立单相链式静止同步补偿器的数学模型基础上,得出单相链式结构中链节悬浮电容的充放电规律,从而提出一种基于占空比调节的悬浮电容电压平衡控制策略。针对单相链式STATCOM的电流控制问题,基于内模原理,采用准PR调节器对交流正弦电流信号进行跟踪,最后结合悬浮电容电压平衡控制策略及电流控制方法,给出了链式STATCOM的电压外环,电流内环的双闭环整体控制策略,并在6MVA STATCOM仿真模型上进行了仿真研究。同时,构建了基于DSP+FPGA的STATCOM原理样机,并进行了相关实验。仿真及实验结果验证了所提控制策略的有效性及可行性。     

Adaptive overcurrent protection scheme coordination in presence of distributed generation using radial basis neural network

The operational performance of conventional overcurrent protection relay coordination connected to a distribution network is adversely afected by the penetration of distributed generators (DG) at diferent buses in the network. To address this problem, this paper proposes a novel adaptive protection coordination scheme using a radial basis function neural network (RBFNN), which automatically adjusts the overcurrent relay settings, i.e., time setting multiplier (TSM) and plug setting multiplier (PSM) based on the penetration of DGs. Short circuit currents and voltages measured at diferent buses are acquired using the remote terminal units (RTU) connected to diferent buses within the terminal network. Communication between the various remotes and local end station RTUs is through hybrid communication systems of fber optic and power line communication system modules. The new adaptive overcurrent protection scheme is applied to the IEEE 33-bus distribution network with and without DGs, for single and multi-DG penetration using both the ETAP and MATLAB software. The simulation results show the proposed scheme signifcantly improves the protection coordination.     

Numerical inverse definite minimum time overcurrent relay for microgrid power system protection

Access of distributed generation gets complicated at the distribution level, and hence managing these systems effectively becomes highly challenging. Microgrids have been proposed as a way of integrating a large number of distributed renewable energy sources with a distribution system. They are low to medium voltage networks of small load clusters with distributed generation sources and storages. Microgrids can be operated in the islanded mode or the grid‐connected mode. If a microgrid is connected to the system, it is seen as a single aggregate load. One of the potential advantages of a microgrid is that it could provide more reliable supply to customers by islanding itself from the system in the event of a major disturbance. However, a major problem with microgrid implementation in islanded operation is designing a proper protection scheme. The fault currents for grid‐connected and islanded microgrids are significantly different. Additionally, high penetration of inverter‐connected distributed generation sources leads to conditions where no standard overcurrent protection method will work. Overcurrent protection is considered as the backbone of any protection strategy, especially in distribution systems. Distribution systems constitute the largest portion of the power system network, and therefore the diagnosis of faults in this system is a challenging task. Faults occurring in distribution systems will affect the reliability, security, and quality of a power system. Field‐processable gate array (FPGA) Xilinx Zynq‐based numerical overcurrent relay protection is provided to the microgrid that is operated in islanded mode. This results in faster discrimination and quicker isolation of the faulty section from the microgrid. This improves the reliability of the microgrid because the fault is rapidly diagnosed and isolated from the healthy part, thanks to the high‐speed operation of the 800‐MHz FPGA Xilinx Zynq‐based numerical overcurrent relay. This system is simulated using MATLAB Simulink SimPower system tool box and LabView software. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

一种新型的微网自适应过流保护方法

微网灵活的运行模式给保护带来了严峻的挑战,对此提出了一种新型的微网自适应过流保护方法。以微网三处典型的故障为案例,从并网和离网角度剖析了微网自适应保护应具备的功能。以此为基础,给出了微网自适应保护方案并阐述了集中式微网保护的主从工作机制;提出了三段式自适应保护的过电流整定算法,设计了故障识别流程;基于分析传统过电流保护时限配合在微网保护中存在的弊端,提出了微网自适应保护在并网和孤岛时的动作时限优化方案,结合案例分析了其优点。理论和案例分析表明,所提自适应保护方法能够快速可靠地识别故障区域,满足微网对保护的要求。     

位移过电压抑制转接地故障消弧的柔性电源控制方法

柔性电源具备中性点位移过电压抑制和接地故障消弧功能,对配电网安全稳定运行至关重要,但是位移过电压抑制在线切换到故障消弧时,存在柔性电源输出过流问题.针对切换瞬间的过流问题,提出了一种幅值差分越限主动闭锁的控制方法,实现柔性电源运行模式的可靠切换.首先,介绍柔性电源运行机理,提出一种共用电流内环的闭环控制方法.其次,建立2种运行模式下的等效电路模型,分析切换过程中的过电流原理,通过位移过电压抑制模式下电压突变量是否越限来判定切换状态,进而闭锁交流输出直至收到上层故障消弧指令,柔性电源转为接地故障消弧模式.然后,仿真分析了2种运行模式及其切换控制方法的合理性.最后,研制样机并在中国某66 kV电网得到应用,现场实测结果验证了该方法的可靠性和先进性.     

高压电动机负序过电流保护整定计算

分析、计算了各种运行情况下电动机的负序电流,分析了各种运行方式下出现负序电流对电动机的危害,粗略估算了各种运行方式下出现负序电流的允许时间,并分析了各种运行方式下正序电流与负序电流、负序功率方向的关系,指出无负序功率方向闭锁负序过电流时常用整定值存在的问题,在区外不对称短路时易引起误动。对不同负序过电流保护动作判据、不...     

含分布式电源配电网保护方案

分布式电源（DG）接入配电网会对传统的配电线路电流保护产生影响,可能导致保护不正确动作。针对这一问题,文中提出一种新的保护方案,对传统的配电线路保护配置进行了改进。该保护方案根据DG接入点的位置,对被保护馈线进行了分区,在DG的上游区域配置了方向纵联保护,而整条馈线则保留了过电流保护。为了能方便整定工作以及更快地切除故障,根据DG接入位置的不同,馈线的过电流保护分别采用定时限或反时限形式。采用该保护方案后,无论DG的输出功率如何变化,故障都能被可靠切除。最后,对一个10 kV配电系统进行了仿真,验证了保护方案的有效性。     

DG容量及接入方式对变电站继电保护定值的影响

为探讨分布式发电(DG)的并网运行将可能对原变电站的继电保护带来哪些影响,以生物质能发电厂接入110 kV终端变电站为例,从故障点是否出现在系统电源进线入手,通过分析DG接入对变电站线路短路电流增量的影响以及线路故障尚未切除时DG能够满足暂态稳定运行时间的长短,进而研究分布式电源的不同容量、不同接入方式对所接入变电站原有三段式电流继电保护的影响,并通过EMTDC/PSCAD仿真加以验证.研究结果表明,在不考虑孤岛运行的前提下,分布式电源可能会对所接入的变电站出线三段式电流保护产生影响;对电流保护的动作电流定值的影响主要取决于DG容量的大小,会对哪些段的动作电流定值产生影响取决于故障时DG失稳时间的长短.     

Control and protection of a microgrid connected to utility through back-to-back converters

This paper discusses the control and protection of a microgrid that is connected to utility through back-to-back converters. The back-to-back converter connection facilitates bidirectional power flow between the utility and the microgrid. These converters can operate in two different modes-one in which a fixed amount of power is drawn from the utility and the other in which the microgrid power shortfall is supplied by the utility. In the case of a fault in the utility or microgrid side, the protection system should act not only to clear the fault but also to block the back-to-back converters such that its dc bus voltage does not fall during fault. Furthermore, a converter internal mechanism prevents it from supplying high current during a fault and this complicates the operation of a protection system. To overcome this, an admittance based relay scheme is proposed, which has an inverse time characteristic based on measured admittance of the line. The proposed protection and control schemes are able to ensure reliable operation of the microgrid.     

Development of self-commutated SVC for power system

A 50-MVA self-commutated Static Var Compernsator (SVC) using the worlds's largest GTO thyristors rated 6 kV-2500 A has been developed for voltage control of electric power systems. The rated dc voltage is 16.8 kV which is four times higher than the highest one manufactured so far. To achieve the high dc voltage, eight GTO thyristors are connected in series. Voltage unbalance between GTOs during switching transient was investigated. A new overcurrent limiting method is proposed, since conventional fuse protection cannot be applied due to such high voltage. Newly developed technologies for this large and high-voltage self-commutated SVC are described. Although simple star-delta connection transformers are used, harmonics generated from SVC are almost equivalent to the 24-pulse converter by shifting the pulse timing appropriately. The PWM control based on 150 Hz is applied and the SVC is designed to continue operation during system faults. The performance of the controller is tested successfully by a simulator, and typical rest results are introduced.     

分布式能源功率倒送引发变压器过电流保护误动场景及对策

分布式能源的大规模并网可能引发系统发生功率倒送,从而给变压器过电流保护的性能带来影响。首先对分布式能源发生功率倒送的场景及其可能引发变压器过电流保护误动作的风险进行分析,然后根据分布式能源发生功率倒送时电气量的特征,将变压器的运行功率引入变压器过电流保护的整定计算中,构造一种基于变压器功率的自适应过电流保护方案,以识别上述工况。仿真结果表明,所提方案能够有效防止上述工况引发的变压器过电流保护误动作。