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。     

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.     

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.     

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。     

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.     

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.     

A Novel Power Injection Model of IPFC for Power Flow Analysis Inclusive of Practical Constraints

This paper describes a novel power injection model (PIM) of interline power flow controller (IPFC) for power flow analysis. In this model, the impedance of the series coupling transformer and the line charging susceptance are all included. In this situation, it is proved that the original structure and symmetry of the admittance matrix can still be kept, and thus, the Jacobian matrix can keep the block-diagonal properties, and sparsity technique can be applied. The IPFC state variables are adjusted simultaneously with the network state variables in order to achieve the specified control targets. Furthermore, the model can take into account the practical constraints of IPFC in Newton power flow. Numerical results based on the IEEE 57-bus and IEEE 300-bus systems are used to demonstrate the effectiveness and performance of the IPFC model     

Optimal IPFC signal selection and damping controller design using a novel current injection model in a multi-machine power system

This paper develops a novel approach to model the Interline Power Flow Controller (IPFC) with the purpose of enhancing the power system dynamic stability. The dynamic behavior of the IPFC is modeled using a new and detailed current injection model. On the basis of designing a supplementary damping controller, the effectiveness of the proposed model in robust damping of the oscillations is evaluated. Thus, the problem of attaining the damping controller parameters transmitted into an optimization process which is solved using Particle Swarm Optimization algorithm (PSO). The PSO has a strong and reliable capability to find out the optimistic solution. The optimization procedure is performed in a multi-machine power system and under various operating conditions. Assessment the derived results from the nonlinear time domain simulation and through some performance indices with considering to a severe transient disturbance clearly indicates the major performance of the proposed model and the model based designed controller in improvement the system stability margins. Moreover, to identify the most suitable IPFC control signal, a precise evaluation of the employed indices is accomplished. Numerical results verify the superior stabilization effect of the m₁ (one of the IPFC control signals) in the wide range of operating conditions.     

ATC enhancement in electricity markets with GUPFC and IPFC – A comparison

Available transfer capability (ATC) needs to be declared well in advance by the system operator to reserve transactions and avoid any congestion in the network. In this paper, an optimal power flow based approach has been utilized for bilateral/multi-transactions deregulated environment to obtain the ATC. The ATC has been obtained with generalized unified power flow controller (GUPFC) and interline power flow controller (IPFC) for intact and line contingency cases. The impact of ZIP load model has been evaluated on the ATC with both the devices. The main contribution of the paper is the comparison of the ATC obtained with. GUPFC and IPFC for intact and contingency cases with constant P,Q load model and ZIP load model. The results have been determined for intact and line contingency cases taking simultaneous as well as single transaction cases. The results obtained are also compared with DC/AC and PTDFs. The proposed method have been applied for IEEE 24 bus RTS.     

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.     

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.     

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.     

线间潮流控制器应用评估策略研究

随着社会负荷不断增长、网架结构日益复杂,骨干网络潮流分布不均、电压支撑能力不足等问题已成为制约系统输送能力的重要因素。线间潮流控制器(Interline Power Flow Controller, IPFC)是一种潮流控制能力强大的新型FACTS装置,可应用于多条通道的潮流控制和暂态稳定控制,提升稀缺廊道资源的输电效率。考虑到目前缺乏对IPFC应用效果评估的理论研究和指导规划,本文提出了一种基于模糊层次分析的综合评判方法。首先,从静态、暂态、动态等方面定义了电网柔性评估指标,建立评估层次结构,并给出各指标的权重赋值方法。进一步地,在大系统中选取关键输电断面,通过多组算例获取各指标的标度,评估IPFC在典型应用场景下的控制潜力、安全指标及投资价值。最后结合模糊分析给出IPFC方案的综合分值和整体评价,量化装置对系统的作用,为IPFC的规划应用工程提供一定理论依据和技术支撑。     

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。     

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。     

新型同相牵引供电系统方案

针对电气化铁道牵引供电系统存在大量的负序、谐波、无功,以及相邻供电区段分相绝缘器引起的列车速度和牵引力损失等问题,将YN,vd平衡变压器和综合潮流控制器(IPFC)有机结合,构成新型同相牵引供电系统。该系统基本消除了三相不平衡,并使谐波含量尽可能好,从根本上解决了铁道部门与电力部门的主要矛盾。取消电分相环节,顺应了客运高速化、货运重载化的时代趋势。讨论了同相供电系统的结构、平衡变压器的性能,并分析了IPFC的结构、平衡变换原理以及控制策略。仿真结果验证了该方案的可行性。     

同相牵引供电系统满意优化补偿策略研究

针对新型同相牵引供电系统中综合潮流控制器的容量优化配置问题,提出了一种满意优化补偿策略.它能实时检测出负载电流的基波正序有功分量、基波正序无功分量、基波负序分量以及谐波分量.通过给定电能质量期望参数,实时调整负序、无功以及谐波补偿度,使得综合潮流控制器容量在各电能质量补偿参数之间得到实时优化配置.在给定补偿电流参考信号...     

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.     

Comparative performance analysis of teaching learning based optimization for automatic load frequency control of multi-source power systems

This paper presents a new population based parameter free optimization algorithm as teaching learning based optimization (TLBO) and its application to automatic load frequency control (ALFC) of multi-source power system having thermal, hydro and gas power plants. The proposed method is based on the effect of the influence of teacher on the output of learners and the learners can enhance their knowledge by interactions among themselves in a class. In this extensive study, the algorithm is applied in multi area and multi-source realistic power system without and with DC link between two areas in order to tune the PID controller which is used for automatic generation control (AGC). The potential and effectiveness of the proposed algorithm is compared with that of differential evolution algorithm (DE) and optimal output feedback controller tuning performance for the same power systems. The dynamic performance of proposed controller is investigated by different cost functions like integral of absolute error (IAE), integral of squared error (ISE), integral of time weighted squared error (ITSE) and integral of time multiplied absolute error (ITAE) and the robustness of the optimized controller is verified by its response toward changing in load and system parameters. It is found that the dynamic performance of the proposed controller is better than that of recently published DE optimized controller and optimal output feedback controller and also the proposed system is more robust and stable to wide changes in system loading, parameters, size and locations of step load perturbation and different cost functions.