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 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.     

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.     

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.     

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.     

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.     

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.     

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.     

计及系统级控制的柔性直流牵引供电系统潮流计算方法

柔性直流牵引供电系统是城轨交通牵引供电技术的重要发展方向,而潮流计算是对其进行分析和设计的重要依据.柔直牵引供电系统的潮流分布直接受到系统级控制的影响,因此需要在潮流计算中计及系统级控制.本文基于高斯迭代法,研究了柔直牵引供电系统的建模问题,设计了能可靠收敛的潮流算法,解决了在柔直牵引供电系统潮流计算中考虑系统级控制问...     

Distribution load flow methods for shipboard power systems

With the recent initiatives to modernize large ship power systems, ship builders are integrating technologies with the aim of an all-electric energy system. New control strategies utilizing distribution automation and network reconfiguration provide greater flexibility, reliability, and quality of service. These automated controls require efficient and accurate load flow solutions. A critique of classical and distribution power-flow methods is conducted for shipboard distribution automation. Three classical radial-network power-flow methods are reviewed. A modification of the forward-backward sweep method is presented, which enhances the computation time and solution convergence. Comparative tests are conducted on a new benchmark test system of a ship's distribution network. The results demonstrate that the modified forward-backward sweep method succeeds in being the fastest method with good convergence on networks with low X/R ratios.     

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     

Electricity market equilibrium of nonlinear power systems with reactive power control

The impact of reactive power control on the electricity market equilibrium is investigated. The effects of limitations on the reactive power generation and absorption, and load power factor adjustments, are examined using a novel electricity market equilibrium model that solves large-scale nonlinear power systems with asymmetric strategic firms. The algorithm implemented employs the linear supply function theory for bid-based pool markets. AC power flow analysis is used to represent the electricity network, incorporating variable price-responsive active and reactive load demands. The significance of the reactive power modeling in the electricity market equilibrium is demonstrated using the IEEE 14-bus and IEEE 118-bus systems. It is shown that variations on the reactive power in the system result in different market outcomes, as incentives are given to the strategic generating firms to alter their bidding strategies. The convergence characteristics of the IEEE 118-bus system are graphically presented and discussed to demonstrate the superior computational performance of the proposed algorithm in producing results under strict binding constraints and heavy transmission congestion conditions.     

Control schemes and transient characteristics of a high‐speed phase shifter for power flow control in power transmission systems

In recent years, attention has been paid to the concept of FACTS (Flexible AC Transmission Systems), along with significant progress in power electronic technology. A high‐speed phase shifter, which is one of the most promising devices in the FACTS concept, has the potential of power flow control and/or voltage stability in power transmission systems. In this paper, theory and experiment reveal that conventional high‐speed phase shifters may cause power swings in a transient state as a result of coupling between instantaneous active and reactive power control loops. Thus, two new control schemes for a high‐speed phase shifter are proposed to achieve both power flow control and power swing damping. The second proposed control scheme is based on the control scheme of an already proposed series active filter. Simulated and experimental results agree well with analytical results, not only in steady states but also in transient states. © 1999 Scripta Technica, Electr Eng Jpn, 128(2): 74–82, 1999