基于瞬时功率理论的新型功率方向元件

基于瞬时无功功率理论及故障附加网络,提出了一种新型功率方向元件。该功率方向元件由突变量及负序无功方向元件组成,在故障附加网络中,突变量无功元件计算对称三相故障时线路两侧等效无源系统的无功损耗,负序无功元件计算不对称故障的无功损耗,由两侧的无功计算结果可判断区内、区外故障。该功率方向元件基于系统阻抗呈感性这一显著特征,物理意义明确,具有工频故障分量保护原理的优点,且无需设计专门的工频滤波器。而且该继电器的动作速度快于常规的基于工频电气量的方向保护,其可靠性优于行波方向保护,具有较高的灵敏度。理论分析及仿真结果都验证了算法的灵敏性、可靠性及快速性。     

大规模风光互补发电系统建模与运行特性研究

建立了大规模并网风光互补发电系统动态分析模型,提出了基于功率变化率改进扰动观察最大功率跟踪算法。风电及光伏系统均采用有功、无功解耦双环电流控制策略。应用静止同步补偿器分析模型的暂态故障电压。含风电、光伏及风光互补运行的电力系统仿真计算验证了该模型的有效性及其功率波动特性和母线电压的暂态影响。仿真结果表明,该风光互补发电系统模型有效降低了输出功率波动,实现了风光系统低电压穿越,确保故障情况下风光系统不脱网运行以及电网安全稳定运行。     

光储联合发电系统的功率振荡特性分析与控制

高渗透光储并网发电系统功率振荡将因缺乏阻尼能力而威胁系统的动态稳定。首先分析通过调节光储系统的有功、无功增加系统阻尼的原理,并在光储联合系统并网功率控制的基础上,提出光储系统基于有功、无功控制的附加阻尼控制策略。该控制策略通过检测光伏侧直流电压变化,实现功率振荡过程中光伏并网逆变器和蓄电池储能系统的控制模式切换,使联合系统具备持续调节注入系统有功、无功功率的能力,并改善电网的阻尼特性。最后,基于渗透率约为30%的光储并网发电仿真系统,验证在系统出现振荡后,光储系统在所提控制策略下,具备通过快速功率调节抑制功率振荡的能力,从而实现多电源协调改善发电系统阻尼的控制目标。     

潮流转移过负荷识别新方案

为了解决现阶段保护减载的潮流转移过负荷识别环节在系统振荡时发生误判的问题,详细研究了系统振荡对潮流转移过负荷识别的影响,分析了过负荷、系统振荡和故障的特点,根据三者之间测量阻抗角、测量阻抗变化率、电流序分量及保护动作情况的差异,提出了潮流转移过负荷识别新方案。即在后备保护启动后,先根据电流序分量的特征和保护II段动作情况区分出故障,再利用测量阻抗变化率的特征,区分过负荷和系统振荡;或者先根据测量阻抗变化率的特征区分出系统振荡,再利用测量阻抗角的特征,区分过负荷和故障。算例分析结果表明,潮流转移过负荷识别新方案能够有效识别出过负荷,并可以防止系统振荡时的误判,证明了该方案的正确性和有效性。     

基于功角轨迹灵敏度的交直流电网振荡抑制优化

高压直流线路稳态功率影响交直流互联系统功角稳定性。为抑制同步发电机功角振荡,基于功角轨迹灵敏度,提出对故障前直流功率的优化方法。建立交直流系统轨迹灵敏度解析表达,引入中间变量确定功角和稳态直流功率关系。推导潮流解对稳态直流功率的灵敏度,计算轨迹灵敏度初值。基于时域仿真中网络约束方程,推导含直流变量的不平衡项。以功角差最小为目标,提出稳态直流功率优化模型,采用内点法求解。仿真结果验证了所提算法对功角振荡的抑制效果。     

永磁直驱风电机组对系统功率振荡的阻尼控制

风电机组若具备常规发电机组对系统功率振荡的阻尼作用,有利于提高风电渗透率较高的区域电网的稳定性。本文首先分析了电网扰动时引起永磁直驱风电机组全功率变流器直流侧电压波动的原因,并提出了抑制直流电压波动的解决方案,以保证风电机组在稳定运行的前提下能快速对电网提供功率支持。其次,分别分析了永磁直驱风电机组通过有功、无功调节增加系统阻尼的原理,并进一步提出了风电机组基于有功、无功附加控制的阻尼控制策略。最后,通过对含30%风电装机容量的三机系统的仿真分析,验证了系统发生扰动后在所提控制策略的协调控制下,不仅能够提高永磁直驱风电机组的故障穿越能力,并可使系统功率振荡迅速衰减,改善系统的阻尼特性。     

GG-11功率方向继电器在功率交换运行中的动作情况

继电保护中的GG-11功率方向继电器,其电流电压线圈按同名端子接入二次电流、电压回路中,如装在线路开关上的功率方向继电器,当有功、无功同时由母线指向线路(输出)时,该继电器动作(即接点闭合),反之,当有功、无功同时由线路指向母线(输入)时,继电器不动作(即接点断开)。但当有功、无功有不同指向时,继电器将如何动作?下面加以浅析。     

负荷虚拟同步机及其低电压故障穿越控制

负荷虚拟同步机(LVSM)是一种电网友好型负荷并网接口,但其本身不具备低电压穿越能力。为此,文中提出一种适应电网对称与不对称故障的LVSM低电压穿越控制方法。首先,提出LVSM的统一拓扑及其基本控制策略。在基本控制策略的基础上增加电网电压正序分量提取、低电压穿越检测、功率指令变更策略、故障期间使能的负序电流抑制、故障期间电流环输入限幅5个环节,实现电网故障短时间内LVSM不脱网、负荷稳定运行,并最大限度地为电网提供无功支撑。由于LVSM在故障期间保持惯性功率控制,故障结束后功率振荡平滑且有惯性,可有效减轻对电网的暂态冲击。硬件在环实验验证了所提低电压穿越控制方法的有效性。     

限幅环节对DFIG故障中输出特性的影响研究

研究了不同严重程度的三相对称故障下,限幅环节对双馈感应电机(DFIG)输出特性的影响。仿真获得不触发Crowbar动作的不同故障下,DFIG故障中稳态有功输出与稳态电压的关系;给出DFIG功率控制模块中有功功率限幅和转子电流限幅的数学模型,仿真分析了限幅环节对故障期间Crowbar动作次数、暂态有功及无功输出特性的影响。通过理论推导结果与仿真的对比,表明了故障中稳态有功输出特性由有功限幅、转子电流限幅及额定有功输出限制决定,且在严重程度不同的故障下,DFIG故障中功率输出由不同限幅环节决定。     

环形直流微电网故障分析与保护

直流微电网故障的快速检测与切除是提高其运行可靠性的关键。电流差动保护可快速有选择地切除故障,但受短路阻抗影响较大,在高阻抗短路时可能拒动。针对环形直流微电网,文中提出基于母线功率变化率的差动保护,由母线两侧功率变化率作为差动量,在区内故障时,母线功率变化率差动值大于动作值,保护动作切除故障线路。功率变化率差动值与短路电流平方及短路阻抗成正比,相比电流量保护,具有更快的故障识别速度和更高的保护灵敏度。仿真结果验证了所提保护方案具有更好的速动性、灵敏性,提高了环形直流微电网的可靠性和稳定性。     

A Novel Scheme to Identify Symmetrical Faults Occurring During Power Swings

A novel, fast unblocking scheme for distance protection to identify symmetrical faults occurring during power swings has been proposed in this paper. First of all, the change rate of three-phase active power and reactive power being the cosine function and the sine function with respect to the phase difference between the two power systems during power swings has been demonstrated. In this case, they cannot be lower than the threshold of 0.7 after they are normalized. However, they will level off to 0 when a three-phase fault occurs during power swings. Thereafter, the cross-blocking scheme is conceived on the basis of this analysis. By virtue of the algorithm based on instantaneous electrical quantities, the calculation of the active and reactive power is immune to the variation of the system power frequency. As the integration-based criterion, it has high stability. Finally, simulation results show that this scheme is of high reliability and fast time response. The longest time delay is up to 30 ms.     

Performance of Power Differential Relay With Adaptive Setting for Line Protection

In this paper, proposed setting and response evaluations of power differential relay scheme for line protection are presented. Mathematical expressions describing the adaptive features of both active and reactive power settings are given. The union action of these two detectors is adopted to provide sensitive detection for high impedance internal faults and avoid maloperation for all power swings and external fault conditions. Response is computed for both active and reactive power detectors under different operation and fault conditions. The results corroborate the applicability and the immunity of the proposed relay scheme against the sampling misalignment and practical frequency drift. High sensitivity for high impedance internal faults is verified     

输电线路虚拟有功功率差动保护

有功功率差动保护在消除线路分布电容影响、应对高阻故障等方面独具优势,但近处金属性故障时的性能缺陷限制了其实际应用。为解决此问题,文中依据叠加原理,提出了虚拟有功功率的概念,并对内、外部故障时线路两端虚拟有功功率的特征进行了分析。以此为基础,提出了分相虚拟有功功率差动保护动作判据,并对其动作特性进行了定性分析。借助PSCAD搭建500kV输电线路模型,全面仿真和评估了不同故障位置、故障类型、过渡电阻、无功元件调整、非同步数据等多种因素对保护方案的影响。理论分析及仿真结果表明,该保护方案可准确辨别故障区间且近处金属性故障无死区,耐过渡电阻能力较强,数据交换量少,同步要求低,无需电容补偿措施。     

三相电压型PWM整流器功率控制方法

针对三相电压型PWM整流器,提出了一种改进的功率控制方法.以三相整流器在d-q同步旋转坐标系中的数学模型为基础,建立了系统功率关系模型,并通过对系统功率关系的分析,提出了改进的功率控制方法.分别控制瞬时有功功率跟踪动态参考有功功率和控制瞬时无功功率收敛于零,实现了输出电压稳定和高功率因数的目标.根据整流器交直流两侧功率关系,基于系统稳定性分析,设计负载电流补偿,构造出了动态参考有功功率.理论分析表明改进的功率控制方法能够消除直接功率控制策略中构造参考有功功率方法所引入的稳态误差.仿真结果验证了所提出的方法的有效性和实用性.     

三相应急电源和并联型有源滤波器复合系统

提出了一种集三相应急电源(EPS)和并联型有源滤波器(APF)一体的复合系统.该系统应用双向PWM变换器,采用DSP数字控制技术,可以实现两方面的功能,即对负载的应急供电和对来自非线性负载的谐波和无功电流补偿.分别阐述了电路结构和控制策略两方面,计算机仿真初步证实了该系统的可行性.     

High performance decoupled active and reactive power control for three-phase grid-tied inverters using model predictive control

Finite control set-model predictive control (FCS-MPC) is employed in this paper to control the operation of a three-phase grid-connected string inverter based on a direct PQ control scheme. The main objective is to achieve high-performance decoupled control of the active and reactive powers injected to the grid from distributed energy resources (DER). The FCS-MPC scheme instantaneously searches for and applies the optimum inverter switching state that can achieve certain goals, such as minimum deviation between reference and actual power; so that both power components (P and Q) are well controlled to their reference values. In addition, an effective method to attenuate undesired cross coupling between the P and Q control loops, which occurs only during transient operation, is investigated. The proposed method is based on the variation of the weight factors of the terms of the FCS-MPC cost function, so a higher weight factor is assigned to the cost function term that is exposed to greater disturbance. Empirical formulae of optimum weight factors as functions of the reference active and reactive power signals are proposed and mathematically derived. The investigated FCS-MPC control scheme is incorporated with the LVRT function to support the grid voltage in fulfilling and accomplishing the up-to-date grid codes. The LVRT algorithm is based on a modification of the references of active and reactive powers as functions of the instantaneous grid voltage such that suitable values of P and Q are injected to the grid during voltage sag. The performance of the elaborated FCS-MPC PQ scheme is studied under various operating scenarios, including steady-state and transient conditions. Results demonstrate the validity and effectiveness of the proposed scheme with regard to the achievement of high-performance operation and quick response of grid-tied inverters during normal and fault modes.     

基于故障分量的有功功率极性比较式纵联保护

根据故障附加网络中有功功率的极性特征,提出了基于故障分量的有功功率极性比较式纵联保护原理。其主要思想是:发生内部故障时,附加网络中线路两端有功功率的极性相同;外部故障时两端有功功率的极性相反;正、反向出口处故障时不存在死区问题。借助PSCAD/EMTDC电磁暂态仿真软件,搭建500 k V输电线路模型,对所提方案的动作性能进行了仿真和验证。在此基础上,进一步对比分析了分相保护方案和三相保护方案,并提出了基于故障分量有功功率幅值特征的选相方法。理论分析和仿真结果表明,所提方案能够正确判别区内、外不同类型的故障,抗过渡电阻能力较强,出口故障无死区,两端数据无需严格同步,且不受无功因素影响。     

Detection of Symmetrical Faults by Distance Relays During Power Swings

For maintaining security of distance relays, power swing blocking is necessary to prevent unintended operation under power swings. To be dependable, distance relays must operate whenever a fault occurs. Therefore, detecting faults during power swings is an important issue since the relay should be able to differentiate the fault condition and not be blocked during that time. This paper presents a new method for detecting a symmetrical fault during a power swing, based on extracting components of the current waveform using the Prony method. The merit of the method is demonstrated by simulating different faults during power swing conditions using the Alternate Transients Program version of the Electromagnetic Transients Program.     

一种基于功率损耗突变的变压器匝间保护

在分析了现有的变压器保护的基础上,建立了变压器的电磁暂态模型,对匝间短路故障的暂态过程进行了仿真.针对差动保护在反映匝间故障时灵敏度不足的问题,结合对已有的基于电流电压的变压器保护理论的分析,提出了一种基于损耗功率突变的变压器匝间保护方案.通过实时计算有功损耗与无功损耗之间的比值,故障时该比值将发生较大的突变,从而可测量到轻微匝间故障,可有效的补充差动保护在反映轻微匝间故障的灵敏度不足的缺陷.     

一种电力电子电路故障诊断方法

提出了一种基于参考模型的电力电子电路故障诊断方法。该法通过研究实际系统与参考模型特征输出量之间的残差来进行故障诊断,具有输入量少且判据简单的特点,特别适用于复杂电力电子电路的故障诊断。通过以晶闸管三相变流装置主电路故障诊断为例进行仿真和实验研究验证了应用参考模型法进行电力电子电路故障诊断的可行性和有效性。