基于UPFC对微电网不平衡电压的治理

针对微电网公共连接点（PCC）三相电压不平衡的问题,本文提出一种在公共连接点接入统一潮流控制器(unified power flow controller,UPFC),通过向输电线路中注入负序电压来治理微电网PCC三相不平衡电压的控制策略。首先,分析了UPFC的工作原理。其次,提出了功率解耦控制方法,建立了UPFC在正、负序同步旋转坐标系下的换流器控制模型,分别设计了串、并联侧换流器的控制策略,实现输电线路中有功功率和无功功率的独立控制,同时,在微电网三相不平衡情况下,获得输电线路中的负序电压并进行补偿。最后,在MATLAB/Simulink中建立了仿真模型,对提出的补偿控制策略进行了仿真分析。仿真结果证明：所提出的补偿控制能有效地治理输电线路的三相不平衡,实现微电网PCC的三相电压平衡。     

Unified power flow controller models for three-phase power flow analysis

In this paper, three models of the unified power flow controller (UPFC) suitable for three-phase power flow analysis in polar coordinates are presented. The symmetrical components control model can be used to control the positive-sequence voltage of the shunt bus and the total three-phase active and reactive power flows of the transmission line while the injected shunt voltages and the series voltages are balanced, respectively; the general three-phase control model can be used to control the three shunt phase voltages and the six independent active and reactive power flows of the transmission line; the hybrid control model can be used to control the positive-sequence voltage of the shunt bus and the six independent active and reactive power flows of the transmission line. The proposed UPFC models were successfully implemented in a three-phase Newton power flow algorithm in polar coordinates. In the implementation of these UPFC models, transformers of some common connection types, which connect the UPFC with the network, are explicitly represented. Numerical results based on a five-bus system and the modified IEEE 118-bus system are given to illustrate the UPFC control models and demonstrate the computational performance of the three-phase Newton power flow algorithm.     

含UPFC元件三相电力系统潮流模型和算法的研究

基于附加节点注入功率法,建立了统一潮流控制器( UPFC)在给定控制方式下的三相附加节点注入功率模型.在研究了UPFC 三相附加节点注入功率模型的基础上,运用三相解耦-补偿理论,对三相系统进行潮流计算.通过网络分析,说明了UPFC元件在改善系统的三相不平衡的作用.经算例仿真,验证了建立的UPFC三相潮流模型及运用算法的...     

基于断面负载均衡度的统一潮流控制器潮流优化控制方法

区域间断面的输电能力主要受限于重载通道的热稳极限,同时关键输电断面对于电网的安全稳定运行具有重要意义。文中提出一种针对断面输电能力受限和潮流分布不均的统一潮流控制器(UPFC)控制方法。定义了断面负载均衡度这一指标,为评估UPFC的潮流控制效果、UPFC对断面潮流分布的优化作用提供了可量化的指标。以江苏省苏州市500 kV UPFC科技示范工程为例,从三相永久性N-1故障、稳态运行和锦苏直流闭锁3种工况提出了相应的UPFC控制方法。仿真结果表明,基于所提指标的UPFC控制方法可以达到改善断面输电能力和潮流分布的目的,同时提高电网的安全稳定性。     

基于PSCAD/EMTDC的统一潮流控制器动态仿真模型

设计了组成统一潮流控制器(UPFC)的动态仿真模型的各个模块,包括正弦脉宽调制(SPWM)信号产生模块、电压源变换器(VSC)控制模块和UPFC控制器的比例积分(PI)控制电路.首先采用三相桥式全控电路组成VSC,VSC的开关器件采用绝缘栅双极性晶体管(IGBT),门极信号按SPWM的方式产生.然后通过分析线路传输功率方程设计了一个简单的PI控制器,并构成完整的UPFC仿真模型.还基于该动态模型对UPFC在功率调节、电压控制和抑制振荡等方面的功能进行了仿真分析.仿真结果表明该UPFC仿真模型在线路功率发生较大变动时能使线路快速恢复;在系统发生三相短路时能有效减少系统的功率损失和减小母线电压的暂降幅度;在系统发生功率波动时还能大幅度减小振幅.     

新型直流电网潮流控制器及其控制方法

直流潮流控制器能够有效提升环网式直流电网的潮流控制自由度,解决直流电网部分线路潮流不可控问题。针对现有直流潮流控制器应用场合的局限性,基于电容线间能量交换的思路,提出一种新型直流潮流控制器拓扑,并对其工作原理和运行特性进行了深入研究。基于新型潮流控制器的多种运行状态,设计了基于脉宽调制(PWM)的控制策略,并以其中一种运行状态为例,研究了各状态变量之间的关系。最后,在电磁暂态仿真软件中搭建等效三端直流环网模型,验证了所提出的直流电网潮流控制器拓扑方案与控制策略的可行性与有效性。     

Nonlinear Adaptive Backstepping Controller Design for Three-Phase Grid-Connected Solar Photovoltaic Systems

A cascaded control structure is proposed in this paper for injecting active and reactive power in a three-phase grid-connected solar photovoltaic (PV) system by considering external disturbances. In the proposed cascaded control structure, there are two control loops—the outer loop voltage controller is used to ensure a continuous balance in power flow between the PV arrays and electrical power grid whereas the inner loop current controller controls the output current of the inverter. Moreover, the DC-DC boost converter is controlled to achieve a constant voltage at the input of the inverter. In order to obtain the power balance and extract maximum power, an incremental conductance (IC) based maximum power point tracking (MPPT) method is used in this paper. The current controller is designed using a nonlinear adaptive backstepping technique to regulate the active and reactive components of the grid current. The regulation of these currents towards desired values which in turn control the active and reactive power delivered into the grid. The overall stability analysis of the system is performed based on the formulation of control Lyapunov functions (CLFs). Finally, the performance of the designed controller is tested on three-phase grid-connected PV systems with single as well as multiple PV units under different environmental conditions and compared with an existing sliding mode controller. Simulation results confirm the effectiveness of the proposed adaptive backstepping control scheme and demonstrate the superior performance over the sliding mode controller.     

Static VAR compensator using recurrent neural network

In this paper, an internal model control recurrent neural network method is used to control the switching of thyristor-controlled reactor in a static VAR compensator (SVC) system for regulating the voltage. The novel controller scheme contains several feedback loops instead of only a feed-forward loop as in the conventional recurrent neural network (RNN). In the proposed controller model, the RNN identifier creates a sample of the connected system and its output generates a part of inputs for the RNN controller which then sends the control signal to the SVC system. Three types of non-linear conditions are chosen to test the operational capability of the new control system to perform the voltage regulation satisfying the IEEE Std 519-1992. The test cases contain a three-phase fault power system, opening of one of the transmission lines in a double line transmission system and sudden changes in the load demand. Results show that the proposed control model is capable of regulating the voltage of the system in a desired range.     

Power flow control schemes for series-connected FACTS controllers

Unified power flow controller (UPFC) and interline power flow controller (IPFC) are FACTS devices that can control the power flow in transmission lines by injecting active and reactive voltage components in series with the lines, using power converter modules, based on an externally regulated dc-link voltage. One key issue, in this application, is to find a relationship between the injected voltage and the resulting power flow in the line. In this paper, this relationship is derived analytically, and used to design two power flow control schemes. The proposed control schemes are applicable to any series-connected FACTS controller with the capability of producing a controllable voltage. In this paper, the proposed power flow control schemes are applied to a voltage-sourced converter-based IPFC, and the resulting control performances are examined using PSCAD/EMTDC simulation package. The simulation results show the effectiveness of the proposed power flow control schemes.     

Transmission series power flow control

This paper presents the characteristics of two gate turn-off (GTO) thyristor voltage-sourced inverter-based series power flow control devices, namely the series power flow controller (SPFC) and the unified power flow controller (UPFC). These devices represent series extensions of the STATCON, an inverter-based shunt device developed under a tailored collaboration by EPRI, TVA and the Westinghouse Science and Technology Center, which will soon be placed in service on the TVA 161 kV transmission system for transmission voltage control. Operation of the SPFC and UPFC is illustrated through the use of easily-constructed circle diagrams on the P-Q plane. The circle diagrams provide the transmission planning engineer with a simple means to assess the performance of these devices on the transmission system. A concluding example illustrates that the UPFC provides a level of power flow control which is unattainable with more conventional devices     

电网不平衡电压下基于PCHD模型的MMC-HVDC无源控制策略

文中针对模块化多电平变流器(Modular Multilevel Converter,MMC)的高压直流输电(High-voltage direct current)系统的变流站级控制,提出一种电网不平衡电压下基于端口受控耗散哈密尔顿(Port-controlled Hamiltonian with Dissipation,PCHD)模型的无源策略(Passivity-based Control,PBC)。文中针对系统的数学模型,通过功率表达式,得出三种控制目标,针对每种控制目标得出相应的电流参考量;通过基于PCHD模型的无源控制理论,推导出系统能量函数和相应的无源控制器;针对三相不平衡电网中产生的负序分量的情况,文中系统加入正负序分离思想,进一步提高了系统的控制精度;通过Matlab/Simulink仿真平台,搭建了不平衡电网电压下的MMC-HVDC系统,并在三种控制目标下验证了所提控制策略的有效性和优越性。     

潮流和最优潮流分析中FACTS控制器的建模

综述了最近FACTS控制器的数学模型在电力系统潮流和最优潮流分析中的新进展.不仅讨论了单换流器FACTS控制器,如静止同步并联补偿器(STATCOM)和静止同步串联补偿器(SSSC);而且也讨论了多换流器FACTS控制器,如统一潮流控制器(UPFC)、相间功率控制器(IPFC)、通用统一潮流控制器(GUPFC)和电压源型直流输电(VSC HVDC).此外还讨论了基于电压源换流器技术的HVDC的数学模型.不仅涵盖FACTS控制器的单相数学模型,而且也涉及FACTS控制器的三相数学模型.此外,还探讨了多换流器FACTS控制器的电流、电压以及功率等不等约束在潮流计算中的数学模型及计算机实现.     

Design of an ANN tuned adaptive UPFC supplementary damping controller for power system dynamic performance enhancement

A supplementary damping controller for a unified power flow controller (UPFC) is designed for power system dynamic performance enhancement. To maintain a good damping characteristic over a wide range of operating conditions, the gains of the UPFC supplementary damping controller are adapted in real time, based on online measured transmission line loadings (active and reactive power flows). To speed up the online gain adaptation process, an artificial neural network is designed. A major feature for the proposed adaptive UPFC supplementary damping controller is that only physically measurable variables (active and reactive power flows over the transmission line) are employed as inputs to the adaptive controller. To demonstrate the effectiveness of the proposed adaptive UPFC supplementary damping controller, computer simulations are performed on a power system subject to a three-phase fault. It is concluded from the simulation results that the proposed adaptive UPFC supplementary damping controller can yield satisfactory dynamic responses over a wide range conditions. The electromechanical mode with an oscillation frequency around 0.78 Hz has been effectively damped by the proposed damping compensators.     

考虑暂稳约束下含TCSC联络线的传输能力

可控串补(TCSC)通过改变线路电抗值即改变网络结构来实现对系统的控制.随着现代电力系统的发展,系统规模越来越大、电压等级越来越高,电网输送能力赶不上负荷的需求、而电力市场化运营又需要系统采用更多的控制手段,在输电电网中应用TCSC来增加输电能力、控制系统潮流、提高系统稳定性显得尤为迫切.文中研究输电线路安装了TCSC...     

Immersion and Invariance-based Non-linear Coordinated Control for Generator Excitation and Static Synchronous Compensator of Power Systems

In this article, a non-linear coordinated control of generator excitation and a static synchronous compensator is proposed to enhance the transient stability of an electrical power system. The coordinated controller proposed is designed via immersion and invariance methodology. In particular, a non-linear model of the power system and immersion and invariance design method are used to achieve not only power angle stability but also frequency and voltage regulations following a large disturbance (a symmetrical three-phase short-circuit fault) on one transmission line or a small perturbation to mechanical power input to synchronous generators in the system. The controller design is validated using a simulation study on a single-machine infinite bus. Simulation results show that the proposed controller can not only keep the system transiently stable but also simultaneously achieve power angle stability and frequency and voltage regulation.     

一种新颖的三相四桥臂逆变器解耦控制的建模与仿真

三相四桥臂逆变器是针对三相不平衡或非线性负载的供电提出来的。该文提出了1种采用内环空间矢量电流调节器和外环同步坐标比例积分控制器相级联的三相四桥臂逆变器的控制方案，实现了对三相四桥臂逆变器的解耦控制。建立了三相四桥臂逆变器在αβγ空间的电路模型，分析了其在αβγ空间的三维电压矢量分布并由此提出了1种采用2个三电平滞环比较器和1个两电平滞环比较器相结合的内环电流调节方案。外环采用了同步坐标电压控制器，使用1个简单的比例调节器就可实现输出电压跟踪的零稳态误差，保证了良好的稳态性能。建立了整个系统在dqo坐标系下的控制模型，实现了对d,q,o3个分量的独立解耦控制。仿真结果验证了该控制方案的正确性与可行性。     

三相有源PFC拓扑及其控制策略

论述了PFC技术在电力电子装置中的重要性，讨论了典型的三相PFC拓扑及其控制策略，介绍了最新研究进展和发展趋势。本文主要涉及软开关技术、SVM控制策略和单周控制器等在三相PFC中的应用。通过单周控制器在VIENNA整流器拓扑中的应用验证结果，展示了单片三相PFC控制芯片集成的可行性。     

电感共用式线间直流潮流控制器及其控制

在多端柔性直流输电中,存在换流站不能完全控制各线路潮流的问题。为了实现潮流的灵活控制,提出一种电感共用式线间直流潮流控制器。该潮流控制器通过在两条输电线路中各串入一个电容,利用共用电感进行功率交换,实现潮流控制,其拓扑结构和控制都较为简单,可模块化,适用于多端直流电网。首先分析了该潮流控制器的工作原理及控制策略,然后在PLECS仿真软件中搭建三端直流输电系统进行验证。仿真结果表明,电感共用式线间直流潮流控制器在正常供电、换流站功率缺失等多种工况下,对直流输电系统潮流进行了灵活和准确的控制。     

VSC-HVDC统一电磁暂态模型及其控制策略

为了更好的应用基于电压源换流器(VSC)的新型高压直流输电系统,发挥其技术优势,提出了VSC-HVDC统一电磁暂态模型并进行了其控制策略的研究。交流侧电磁暂态模型是基于d-q同步旋转坐标系下建立的;利用交流侧与直流侧瞬时有功功率相等的原理建立了直流侧电磁暂态模型,且该模型考虑了换流电抗器损耗等因素。利用前馈补偿法设计了解耦控制器以达到分别通过电流d轴和q轴分量来独立调节有功功率和无功功率的目的。利用PSCAD/EMTDC对利用VSC-HVDC连接两端的有源网络以及对无源网络的供电进行仿真试验的结果证明,提出的计算模型及控制策略准确、可靠,对于各种干扰有较好的响应速度和较高的精度。     

UPFC运行点变化对电力系统稳定和控制性能的影响

统一潮流控制器(UPFC)的主要控制功能是潮流控制和电压控制,控制的水平由控制器的设定参考值决定。它们也是文中所指的UPFC的控制运行点,即UPFC安装线路上由UPFC调节达到的输送的有功和无功水平,以及安装母线上由UPFC控制达到的电压水平。文中讨论了UPFC控制运行点变化对电力系统稳定性的影响。同时还发现,控制运行点在较大程度上决定了控制器的控制性能和2个UPFC之间的交互影响。通过2个装有UPFC的电力系统的仿真结果证实了文中的讨论。