Determination of IPFC operating constraints in power flow analysis

In recent years, the Flexible AC Transmission System (FACTS) controllers have been widely used to enhance the controllability, security and flexibility in power transmission networks. Interline power flow controller (IPFC) is a versatile member of FACTS devices that can be used to control the power flow in multiple lines in network. Modeling of IPFC with handling its operating constraints is an important issue to determine the practical capabilities of this device. This paper presents a simple modeling with strategies for handling all operating constrains of IPFC in Newton–Raphson (NR) load flow algorithm. The various operating constraints such as; the injected series voltages, injected line currents passing through the converters and exchanged powers among the series converters are investigated. The developed IPFC model with these constraints is validated using standard IEEE 30-bus and IEEE 118-bus test systems.     

A Novel Location Method for Interline Power Flow Controllers Based on Entropy Theory

As one of the new generation flexible AC transmission systems (FACTS) devices, the interline power flow controller (IPFC) has the significant advantage of simultaneously regulating the power flow of multiple lines. Nevertheless, how to choose the appropriate location for the IPFC converters has not been discussed thoroughly. To solve this problem, this paper proposes a novel location method for IPFC using entropy theory. To clarify IPFC''s impact on system power flow, its operation mechanism and control strategies of different types of serial converters are discussed. Subsequently, to clarify the system power flow characteristic suitable for device location analysis, the entropy concept is introduced. In this process, the power flow distribution entropy index is used as an optimization index. Using this index as a foundation, the power flow transfer entropy index is also generated and proposed for the IPFC location determination study. Finally, electromechanical electromagnetic hybrid simulations based on ADPSS are implemented for validation. These are tested in a practical power grid with over 800 nodes. A modular multilevel converter (MMC)-based IPFC electromagnetic model is also established for precise verification. The results show that the proposed method can quickly and efficiently complete optimized IPFC location and support IPFC to determine an optimal adjustment in the N-1 fault cases.     

线间潮流控制器建模及潮流优化方法

线间潮流控制器(interline power flow controller,IPFC)作为第3代柔性交流输电系统(flexible AC transmission system,FACTS)的代表性设备,具有强大的潮流调控能力。而IPFC的引入,会增加潮流优化(optimal power flow,OPF)问题的非凸性,导致其难以被准确、快速求解。为解决传统IPFC模型中等效电压源相角对应约束难以被凸化的问题,该文基于注入功率变量重新构造了IPFC的等效约束,并进一步利用数学变形、近似处理、二进制展开技术,对该模型进行凸化处理,将含IPFC的OPF问题从高度非凸的优化问题转化为混合整数二阶锥规划(mixed integer second-order cone programming,MISOCP)问题。最终,在仿真算例中完成近似误差分析,并利用Matlab/Gurobi求解MISOCP模型。结果表明,所提优化方法计算精度高,求解速度快,显著降低了系统发电成本,可为综合型FACTS的在线优化调控提供理论和技术支撑。     

Robust modeling of the interline power flow controller and the generalized unified power flow controller with small impedances in power flow analysis

The interline power flow controller (IPFC) and the generalized unified power flow controller (GUPFC) are two innovative configurations of the convertible static compensator (CSC) of FACTS. In this paper, direct modeling of the practical series or/and shunt operating inequality constraints of the IPFC and the GUPFC in power flow calculations are presented. Special initialization of a solution with the IPFC and GUPFC is also derived. Furthermore, an impedance compensation technique is proposed to deal with the numerical instability or the numerical difficulty of the IPFC and GUPFC models when either their coupling transformer impedances are too small or they are transformer-less controllers. Condition number analysis of the Newton power flow equations is given to get insights of the numerical instability of the voltage sourced models of the IPFC and GUPFC with small impedances. Numerical examples are given based on the IEEE 118-bus system, IEEE 300-bus system and a large scale system with 1000-buses.     

计及FACTS装置的可用输电能力计算

利用功率注入法,建立广义统一潮流控制器(generalized unified power flow controller,GUPFC)和线间潮流控制器(interline power flow controller,IPFC)的数学模型。将GUPFC和IPFC的目标控制约束及运行约束即内部功率平衡约束和考虑等效功率注入模型的潮流约束嵌入到最优潮流计算模型中,得到计及GUPFC和IPFC的可用输电能力(available transfer capability,ATC)计算模型,并利用跟踪中心轨迹内点法对模型进行求解。IEEE-30节点系统的仿真计算显示GUPFC对节点电压和多条线路甚至某一子网络潮流的灵活控制能力及IPFC对线间潮流的合理分配能力;同时验证模型和算法的有效性和可行性。     

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.     

线间潮流控制器在改善电能质量中的应用

介绍了线间潮流控制器(IPFC)的基本工作原理,建立了数学模型.提出了应用IPFC装置的有功无功线间综合控制提高电力系统暂态稳定性的两层控制模型并进行了试验仿真.仿真结果表明:IPFC装置比传统的FACTS装置更能有效地提高系统的暂态稳定性和电能质量.     

Wavelet entropy based algorithm for fault detection and classification in FACTS compensated transmission line

Distance protection of transmission lines including advanced flexible AC transmission system (FACTS) devices has been a very challenging task. FACTS devices of interest in this paper are static synchronous series compensators (SSSC) and unified power flow controller (UPFC). In this paper, a new algorithm is proposed to detect and classify the fault and identify the fault position in a transmission line with respect to a FACTS device placed in the midpoint of the transmission line. Discrete wavelet transformation and wavelet entropy calculations are used to analyze during fault current and voltage signals of the compensated transmission line. The proposed algorithm is very simple and accurate in fault detection and classification. A variety of fault cases and simulation results are introduced to show the effectiveness of such algorithm.     

含线间潮流控制器的电力系统联合潮流计算

线间潮流控制器(IPFC)能实现线路间的潮流转移和分配,可用于解决电力系统中潮流不均引起的一系列问题,具有较大的应用潜力和价值。为评估IPFC工程应用价值,需实现含IPFC的大系统潮流计算,但目前我国多用于电网规划设计的大型电力系统分析软件中没有开发IPFC模型。为解决上述问题,提出了一种基于Matlab与PSD-BPA的含IPFC电力系统的联合潮流计算方法。首先推导了IPFC功率注入模型的数学表达式,并设计了Matlab与BPA联合潮流计算的计算框架,由Matlab进行IPFC求解计算,BPA进行大电网潮流计算,通过数据交换接口完成两种仿真软件的交互与交替求解。进一步对IPFC功率注入模型进行改进,提出了一种基于PI控制器的变步长潮流迭代策略提高了计算方法的收敛性。以南通西北片电网为例,对提出方法进行了仿真验证,计算结果表明了提出方法的正确性和有效性。     

Use of IPFC Detailed Dynamic Model for Analysis of Power Flow Control and Small-Signal Stability Enhancement

This paper presents a study of the power flow control capability of the interline power flow controller (IPFC) and its effect on small-signal stability enhancement. A detailed dynamic model of IPFC suitable for power system electromechanical stability analysis is developed in this paper. The power flow control capability of the proportional-integral (PI) controllers and their effect on power oscillation damping are evaluated first, and modal analysis of the power system is carried out to demonstrate their effectiveness in small-signal stability enhancement. Then the eigenvalue sensitivity based parameter optimization technique is adopted to optimize the control parameters of PI controllers in order to stabilize the oscillatory modes having insufficient damping ratios. Numerical simulation results demonstrate that the IPFC with the proposed control is an effective tool for power flow control and small-signal stability enhancement, and the optimized PI controllers also have a positive effect on improving the performance of IPFC in power flow control. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Grasshopper optimization algorithm optimized multistage controller for automatic generation control of a power system with FACTS devices

This paper uses a Grasshopper Optimization Algorithm (GOA) optimized PDF plus (1+ PI) controller for Automatic generation control (AGC) of a power system with Flexible AC Transmission system (FACTS) devices. Three differently rated reheat turbine operated thermal units with appropriate generation rate constraint (GRC) are considered along with different FACTS devices. A new multistage controller design structure of a PDF plus (1 + PI) is introduced in the FACTS empowered power system for AGC while the controller gains are tuned by the GOA. The superiority of the proposed algorithm over the Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) algorithms is demonstrated. The dynamic responses of GOA optimized PDF plus (1+ PI) are compared with PIDF, PID and PI controllers on the same system. It is demonstrated that GOA optimized PDF plus (1+ PI) controller provides optimum responses in terms of settling time and peak deviations compared to other controllers. In addition, a GOA-tuned PDF plus (1 + PI) controller with Interline Power Flow Controller (IPFC) exhibits optimal results compared to other FACTS devices. The sturdiness of the projected controller is validated using sensitivity analysis with numerous load patterns and a wide variation of parameterization. To further validate the real-time feasibility of the proposed method, experiments using OPAL-RT OP5700 RCP/HIL and FPGA based real-time simulations are carried out.     

Comparison of performances of several FACTS devices using Cuckoo search algorithm optimized 2DOF controllers in multi-area AGC

This paper presents automatic generation control (AGC) of three unequal area thermal systems with single reheat turbine and appropriate generation rate constraints (GRC) in each area. A two degree of freedom (2DOF) controller called 2DOF-integral plus double derivative (2DOF-IDD) is proposed for the first time in AGC as secondary controller. Secondary controller gains and other parameters are optimized simultaneously using a more recent evolutionary computational technique called Cuckoo Search algorithm (CS). The system dynamic responses for various 2DOF controllers such as 2DOF-PI, 2DOF-PID, and 2DOF-DD are compared. Investigations reveal that responses with 2DOF-IDD are better than others. Performance of several FACTS devices such as Static synchronous series compensator (SSSC), Thyristor controlled series capacitor (TCSC), Thyristor controlled phase shifter (TCPS), and Interline power flow controller (IPFC) in presence of 2DOF-IDD controller are compared and found that the dynamic responses with IPFC are better than others. For the first time in AGC, a case study is performed with placement of IPFC and observed that IPFC present in all three areas of the system performs better. Sensitivity analysis reveals that the CS optimized 2DOF-IDD controller parameters obtained in presence of IPFC in all three areas at nominal condition of loading and size of step load perturbation (SLP) are robust and need not be reset with wide changes in system loading and SLP. Also, the comparison of convergence curve of various algorithms reveals that CS algorithm converges much faster than others.     

基于YNvd平衡变压器和模拟负载的同相供电试验系统

为了更深入开展同相供电系统的研究,提出了一种由新型YNvd平衡牵引变压器、模拟负载以及综合潮流控制器(IPFC)构成的同相供电试验系统方案。分别介绍了YNvd平衡变压器、IPFC和模拟负载的结构和工作原理,通过对IPFC与模拟负载制定相应的控制策略,以实现对同相供电系统的仿真模拟。研究结果表明,该试验系统能够模拟牵引负荷特性,实现能量循环利用,模拟同相供电系统,消除了系统负序电流,实现了谐波和无功的动态补偿,验证了同相供电系统的可行性。     

Impact of communication time delays on combined LFC and AVR of a multi-area hybrid system with IPFC-RFBs coordinated control strategy

In this paper, the impact of communication time delays (CTDs) on combined load frequency control (LFC) and automatic voltage regulation (AVR) of a multi-area system with hybrid generation units is addressed. Investigation reveals that CTDs have significant effect on system performance. A classical PID controller is employed as a secondary regulator and its parametric gains are optimized with a differential evolution - artificial electric field algorithm (DE-AEFA). The superior performance of the presented algorithm is established by comparing with various optimization algorithms reported in the literature. The investigation is further extended to integration of redox flow batteries (RFBs) and interline power flow controller (IPFC) with tie-lines. Analysis reveals that IPFC and RFBs coordinated control enhances system dynamic performance. Finally, the robustness of the proposed control methodology is validated by sensitivity analysis during wide variations of system parameters and load.     

A Lyapunov theory based UPFC controller for power flow control

Unified power flow controller (UPFC) is the most comprehensive multivariable device among the FACTS controllers. Capability of power flow control is the most important responsibility of UPFC. According to high importance of power flow control in transmission lines, the proper controller should be robust against uncertainty and disturbance and also have suitable settling time. For this purpose, a new controller is designed based on the Lyapunov theory and its stability is also evaluated. The Main goal of this paper is to design a controller which enables a power system to track reference signals precisely and to be robust in the presence of uncertainty of system parameters and disturbances. The performance of the proposed controller is simulated on a two bus test system and compared with a conventional PI controller. The simulation results show the power and accuracy of the proposed controller.     

Damping forced oscillations in power system via interline power flow controller with additional repetitive control

With the continuous expansion of power systems and the application of power electronic equipment, forced oscillation has become one of the key problems in terms of system safety and stability. In this paper, an interline power flow controller (IPFC) is used as a power suppression carrier and its mechanism is analyzed using the linearized state-space method to improve the system damping ratio. It is shown that although the IPFC can suppress forced oscillation with well-designed parameters, its capability of improving the system damping ratio is limited. Thus, combined with the repetitive control method, an additional repetitive controller (ARC) is proposed to further dampen the forced power oscillation. The ARC control scheme is characterized by outstanding tracking performance to a system steady reference value, and the main IPFC controller with the ARC can provide higher damping, and further reduce the amplitude of oscillations to zero compared with a supplementary damping controller (SDC). Simulation results show that the IPFC with an ARC can not only greatly reduce the oscillation amplitude, but also actively output the compensation power according to the reference value of the ARC tracking system.     

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.     

A new multi-objective fuzzy-GA formulation for optimal placement and sizing of shunt FACTS controller

The location and sizing of FACTS controllers for voltage stability enhancement is an important consideration for practical power systems. In this paper, a strategy for placement and sizing of shunt FACTS controller using Fuzzy logic and Real Coded Genetic Algorithm is proposed. A fuzzy performance index based on distance to saddle node bifurcation, voltage profile and capacity of shunt FACTS controller is proposed. The proposed technique can be used to find the most effective location and optimal size of the shunt FACTS devices. The proposed approach has been applied on IEEE 14-bus and IEEE 57-bus test systems. The application results are promising.     

An Advanced IPFC Model to Reuse Newton Power Flow Codes

Complexities of computer program codes for Newton-Raphson load flow (NRLF) analysis are usually enhanced during power flow modeling of an interline power flow controller (IPFC). This is due to the fact that the contributions of the series converters of the IPFC are needed to be accounted for while computing bus power injections and Jacobian matrix elements. Also, the IPFC real power injection term along with its associated Jacobian matrix call for new codes to be written. In this paper an advanced IPFC model is proposed to address this issue, wherein an existing power system installed with IPFC(s) is transformed into an augmented equivalent network without any IPFC. To obtain the solution of the original network containing IPFC(s), the augmented network can easily be solved by reusing the existing NRLF codes, as this network is now devoid of any IPFC. Consequently, the complexities of the computer program codes are reduced substantially. Various practical device limit constraints of the IPFC can also be taken into account by the proposed model.     

基于统一潮流控制器对电力系统暂态稳定控制的研究

作为灵活交流输电系统(FACTS)重要内容之一的统一潮流控制器(UPFC)可以实现分 别或同时 地对电力系统参数——电压、输电线路阻抗及两端间相角的控制。文中以一简单系统为例， 探 讨了统一潮流控制器若干特例形式之一的分接头切换开关对于提高电力系统暂态稳定性的作 用，并且给出了仿真结果。