Power flow control approach to power systems with embedded FACTS devices

This paper focuses on developing an approach to steady-state power flow control of flexible AC transmission systems (FACTS) device-equipped power systems. Based on a power-injection model of FACTS devices and an optimal power flow model, a novel versatile power flow control approach is formulated, which is capable of implementing power flow control incorporating any FACTS device flexibly. Different from existing FACTS device control approaches, the active and (or) reactive power injections are taken as independent control variables. Therefore, using this method, Jacobian matrix need not be changed, although various FACTS devices possess different physical models and different control parameters. Furthermore, it enables the integration of FACTS devices into the existing power system analysis and control programs efficiently. Physical limits of the FACTS devices are also considered in the model. Numerical results on a reduced practical system and a 1500-bus practical system with various FACTS devices are presented to illustrate the vigorousness of the proposed approach.     

含风电场电力系统的潮流计算

潮流计算是分析风电对电网影响的基础,在异步发电机稳态等效电路的基础上,通过动态改变风电场的无功功率、考虑风速、有功功率,机端电压和滑差率,提出了计算含风电场的电力系统潮流的一种简单可行的方法,并通过一含风电的配电网系统验证了该算法的可行性。     

Power flow model/calculation for power systems with multiple FACTS controllers

This paper presents a new procedure for steady state power flow calculation of power systems with multiple flexible AC transmission system (FACTS) controllers. The focus of this paper is to show how the conventional power flow calculation method can systematically be modified to include multiple FACTS controllers. Newton–Raphson method of iterative solution is used for power flow equations in polar coordinate. The impacts of FACTS controllers on power flow is accommodated by adding new entries and modifying some existing entries in the linearized Jacobian equation of the same system with no FACTS controllers. Three major FACTS controllers (STATic synchronous COMpensator (STATCOM), static synchronous series compensator (SSSC), and unified power flow controller (UPFC)) are studied in this paper. STATCOM is modeled in voltage control mode. SSSC controls the active power of the link to which it is connected. The UPFC controls the active and the reactive power flow of the link while maintaining a constant voltage at one of the buses. The modeling approach presented in this paper is tested on the 9-bus western system coordinating council (WSCC) power system and implemented using MATLAB software package. The numerical results show the robust convergence of the presented procedure.     

Power injection modeling and optimal multiplier power flow algorithm for steady-state studies of unified power flow controllers

This paper presents an optimal multiplier based Newton-Raphson power flow algorithm for reliably and efficiently handling power systems with embedded flexible AC transmission systems (FACTS) devices such as unified power flow controllers (UPFCs). A power injection transformation of a two voltage source UPFC model is derived in rectangular form. After detailed analyses of issues in implementation of UPFCs in power flow programmes by various power flow algorithms, the optimal multiplier power flow method for ill-conditioned systems is adopted. The proposed UPFC model and power flow algorithm have been programmed and vigorously tested in a number of systems. The results on the IEEE 30-bus test system and a 306-bus practical system are reported and compared with conventional user defined model type programmes, which clearly illustrate the effectiveness of the proposed algorithm.     

Power flow constrained harmonic analysis in AC-DC power systems

When calculating noncharacteristic harmonics generated by an HVDC converter, unbalance in the AC system at fundamental frequency and all harmonics must be taken into account. This entails that a full three-phase load flow be part of the solution, as there is considerable distortion interaction between the load flow and the converter. To date, this has been achieved by iterating sequentially between the load flow and a harmonic converter model, in a type of decoupled method which is likely to suffer poor convergence. The decoupled method is implemented here, and convergence compared with a unified Newton solution of the load flow and converter models. Finally, the effect of not modelling the distortion interaction between the two systems is investigated     

Distributed generation modeling for power flow studies and a three-phase unbalanced power flow solution for radial distribution systems considering distributed generation

Distributed generations (DGs) are generally modeled as PV or PQ nodes in power flow studies (PFSs) for distribution system. Determining a suitable model for each DG unit requires knowing the DG operation and the type of its connection to the grid (direct or indirect). In this respect, this paper offers a helpful list of DG models for PFSs. Moreover, an unbalanced three-phase power flow algorithm for radial distribution networks considering DG is presented based on the power summation method in backward/forward sweep technique. The proposed algorithm is simple and fast and can handle DG units in both PV and PQ mode. In comparison with the current analysis methods, handling of PV nodes in the proposed method is very simple since it uses active and reactive powers as flow variables rather than the complex currents and then checks the limits of reactive power of the generator of PV node straightforwardly. IEEE four-node test feeder is used to validate the proposed method. IEEE 13-node test feeder without regulator and with different DG models is analyzed and the results are presented. Moreover, the results are compared with and without considering system losses.     

Power injection model of STATCOM with control and operating limit for power flow and voltage stability analysis

This paper presents a power injection model (PIM) of STATCOM for power flow and voltage stability analysis. In this model, PWM control and phase control strategies of STATCOM are handled, and the operating limit is enforced. The NR formulation has the same structure before and after the limit enforcement, and the Jacobian matrix adds only one dimension. This model can also take into account the steady-state losses of STATCOM if desired, and hence more accurately predict the active and reactive power injections. The singular value decomposition (SVD) based method is then extended to study the effect of STATCOM on power systems voltage stability. IEEE 300-bus and 30-bus systems are used to verify the effectiveness and performance of this model and the effect of load changes at all the buses simultaneously on voltage stability has also been studied with the STATCOM.     

基于PSS/E潮流数据的电力系统潮流图生成系统

介绍了电力系统潮流图自动绘制系统.该系统基于已经收敛的PSS/E潮流数据文件,根据用户选择要画的母线和摆放的位置,系统自动根据网络拓扑结构画出潮流图.图形采用矢量形式输出,解决了PSS/E程序本身潮流图输出不理想的缺点.     

基于统一潮流控制器(UPFC)的电力系统潮流控制

统一潮流控制器(UPFC)作为一种典型的FACTS装置,综合了FACTS元件的多种灵活控制手段.基于UPFC的基本原理、数学模型,介绍具有UPFC的电力系统的潮流计算方法.算例表明,UPFC可以控制线路的潮流分布,有效地提高电力系统的稳定性.     

Load flow tracing in power systems with circulating power

Power flow tracing is very important to open access for loss allocation, congestion analysis and reactive power pricing, etc. In a previous paper, power flow tracing of power systems without circulating power has been implemented. In this paper, two lemmas have been proved first which show the reasons for circulating power. Then graph theory is applied to detect the existence of circulating power. After that optimal power flow (OPF) approach is suggested to eliminate circulating power. The sequential quadratic programming is used for OPF solution. The computer tests on a 6-bus system and the IEEE 30-bus power system yield satisfactory results. The suggested method is suitable for both active and reactive power flow tracings of power systems with circulating active and reactive power.     

Performing detailed power system studies for designing and analyzing electrical distribution systems - Power system studies for cement plants

The power system studies for designing and analyzing the electrical distribution system for cement plants is detailed. The analysis consists of a short circuit, load flow, motor starting over-current coordination, and arc flash hazard study. There are several load flow solution algorithms used in industry such as Gauss-Seidel, Newton-Raphson, and current injection. It is good engineering practice to have an up-to-date load flow study for every installation.     

计及多端口直流潮流控制器的直流电网潮流计算

基于含模块化多电平换流器的多端口直流潮流控制器(MDCPFC)的工作原理,提出了一种计及MDCPFC的直流电网潮流计算方法。该方法将加装的MDCPFC用安装支路端点的节点注入功率的修正量来表示,使得运算简便,从而提高了运算效率。以舟山五端柔性直流工程为例,通过对比加装MDCPFC直流电网的潮流计算结果与PSAT软件计算结果以及加装2个直流潮流控制器的计算结果,验证MDCPFC的控制效果更好。     

含VSC-HVDC的交直流混合系统潮流统一迭代求解算法

介绍基于电压源换流器(VSC)的新一代高压直流输电(VSC-HVDC)技术,具有可向无源网络供电、不会出现换相失败等众多优点。分析VSC-HVDC输电系统的原理及其中VSC的控制方式。针对不同控制方式下的VSC,分别推导其交流母线及直流系统相应的潮流修正方程式。提出VSC-HVDC交直流混合系统潮流的统一迭代求解算法,并以修改后的WSCC-9节点交直流混合系统的潮流计算为例,验证统一迭代求解算法的有效性。通过该潮流算法分析VSC-HVDC输电系统的稳态特性和有功功率损耗特性。     

A laboratory for power systems control with static converters

The 4th year course `Power Systems Control' at the University of Toronto includes a laboratory familiarizing the student with the function and use of static converters for the control of power systems. This paper describes the concept of the laboratory and the required equipment. The experiments are discussed in detail to demonstrate the possibility to teach the different aspects of power systems control with static converters     

Adaptive power flow method for distribution systems with dispersed generation

There has been great interest in the integration of dispersed generation units at the distribution level. This requires new analysis tools for understanding system performance. This paper presents an adaptive distributed power flow solution method based on the compensation-based method. The comprehensive distributed system model includes 3-phase nonlinear loads, lines, capacitors, transformers, and dispersed generation units. The numerical properties of the compensation-based power flow method are compared and analyzed under different situations, such as load unbalance, sudden increase of 1-phase loads, degree of meshed loops, number of generator nodes, and so on. Based on these analyses, an adaptive compensation-based power flow method is proposed that is fast and reliable while maintaining necessary accuracy. It is shown that this adaptive method is especially appropriate for simulation of slow dynamics.     

Excitation control for multimachine power systems

The control of power systems on the basis of energy analysis offers many advantages. An essential condition to achieve this control is the measurement of the angles of the major generator groups, which are available using satellite Global Positioning Systems.This paper develop two strategies based on energy function higher order derivatives to design nonlinear excitation controllers for multimachine power systems taking into consideration field flux decay effects.The design is based on maximum reduction of energy and can be successfully implemented with as many controllers as major modes, when few controllers are available control on the basis of energy function higher order derivatives produce good results.The first strategy is based on energy function higher order derivatives design where one controller is required to control one mode of oscillation.The second strategy capable of suppressing the oscillation modes with only one controller is based on a linear optimal control design where a linear quadratic regulator (LQR) control component added to energy function higher order derivatives design.     

Fast power flow for radial power systems using parallel processing

Power flow calculation is a basic tool for power system planning and control which includes power flow analysis, voltage control, service restoration, network reconfiguration, and other operation functions for control centers. In these applications, it is very important to solve the power flow problem as efficiently as possible. This paper presents a fast power flow using parallel processing for radial power systems. This method can be applied to secondary systems and distribution systems. Since it uses as state variables only active and reactive power injection to main lines and laterals, reduction of the number of state variables can be realized. Radical networks are mapped to the tree structure of parallel processor systems in the proposed method. The forward/backward sweep approach is realized by communication from a root processor to leaf processors and vice versa. Using the mapping scheme of the proposed method, each processor has to communicate with only neighboring processors. The proposed method is evaluated on various radial systems with promising results.     

基于联络线功率等值约束条件的潮流算法研究

针对互联电网区域间限制联络线传输功率的要求,提出了一种系统扰动后维持联络线功率为设定值的新算法。该算法设定联络线的交换功率,分区域潮流计算,可以实现通过改变受端系统侧的运行方式,维持联络线功率为设定值的目的。该算法物理意义清晰,容易实现,收敛性好,给出的算例验证了提出算法的可行性。     

基于联络线功率等值约束条件的潮流算法研究

针对互联电网区域间限制联络线传输功率的要求,提出了一种系统扰动后维持联络线功率为设定值的新算法.该算法设定联络线的交换功率,分区域潮流计算,可以实现通过改变受端系统侧的运行方式,维持联络线功率为设定值的目的.该算法物理意义清晰,容易实现,收敛性好,给出的算例验证了提出算法的可行性.     

适合风电接入的VSC-MTDC系统协调控制策略

对于具有小集中、大分散特点的内陆风电,交流并网存在电能质量下降、经济性差等诸多问题,两端柔直并网也无法满足要求。使用多端柔直是未来风电并网的发展方向,文中提出一种适合风电接入的多端柔直系统协调控制策略。该策略综合考虑直流电压改变的方向、电压改变的大小以及换流站功率裕度等因素,自适应实时调节下垂系数,优化换流站之间功率分配,避免不当下垂系数造成的系统损耗增加、部分换流站功率过载。引入附加频率控制与自适应下垂控制协调,可充分利用系统调频容量,改善系统频率稳定性。控制器参数易于整定,结构简单。在PSCAD/EMTDC电磁暂态仿真软件中搭建了嵌入多端柔直系统的四机两区域模型,验证了所提策略的有效性和可行性。