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.     

Multiple Contingency Selection for Transmission Reliability and Transfer Capability Studies

ABSTRACT

This paper develops a multiple contingency selection procedure that can identify the single contingencies that cause thermal stress on the same branch or branches and, thereby, produce critical multiple contingencies. This multiple contingency selection procedure is required if enumerative transmission reliability [4] is to be successfully applied since all critical single and multiple contingencies can be identified without excessive computation or false alarm or misclassification problems. The multiple contingency selection is accomplished by determining a list of contingencies for each branch that have: (a) apparent power flows that exceed αxl00% of the thermal limit and (b) apparent power flow changes that exceed βxl00% of the thermal limit. A branch contingency measure is used to rank these single contingencies. Combination of the single contingencies taken from any branch's list of contingencies would produce multiple critical contingencies with thermal overloads on that branch assuming superposition holds.

The BOUNSM computer program that provides the information for the enumerati ve transmission reliability program [4] also provides the information required to perform a transfer capability study [3]. A monitored branch measure, which is the sum of the branch contingency measures for a particular branch, would identify the branches, paths, and interfaces that are most insecure for an anticipated transfer and must be specified to run a transfer capability study. The combination of branch's list of contingencies for each of these branches, paths, and interfaces would be the list of contingencies that needs to be specified to perform a transfer capability study.

The monitored branch and branch contingency measures are computed using a BOUNSM program for the contingencies simulated using a matrix compensation method by a Multiple Contingency Load Fow. The combination of the BOUNSM and Multiple Contingency Load Flow is very efficient. The programs are tested on a 1689 bus, 3127 branch system.     

Calculation of weighting factors of static security indices used in contingency ranking of power systems based on fuzzy logic and analytical hierarchy process

Contingency screening and ranking is one of the most important issues for security assessment in the field of power system operation. The objective of contingency ranking is to quickly and accurately select a short list of critical contingencies from a large list of potential contingencies and rank them according to their severity. Then suitable preventive actions can be implemented considering these contingencies that are likely to affect the power system performance. In this paper a novel approach is presented for contingency ranking based on static security assessment. This method employs weighted performance index with the application of fuzzy logic based analytical hierarchy process in order to select appropriate weighting factors to be imposed. The proposed method is applied to IEEE 30 bus system and the results are presented.     

Assessment of oscillatory stability constrained available transfer capability

This paper utilizes a bifurcation approach to compute oscillatory stability constrained available transfer capability (ATC) in an electricity market having bilateral as well as multilateral transactions. Oscillatory instability in non-linear systems can be related to Hopf bifurcation. At the Hopf bifurcation, one pair of the critical eigenvalues of the system Jacobian reaches imaginary axis. A new optimization formulation, including Hopf bifurcation conditions, has been developed in this paper to obtain the dynamic ATC. An oscillatory stability based contingency screening index, which takes into account the impact of transactions on severity of contingency, has been utilized to identify critical contingencies to be considered in determining ATC. The proposed method has been applied for dynamic ATC determination on a 39-bus New England system and a practical 75-bus Indian system considering composite static load as well as dynamic load models.     

Evaluation of available transfer capability using fuzzy multi-objective contingency-constrained optimal power flow

In trying to determine the available transfer capability (ATC), this paper primarily sets out to develop a fuzzy logic approach to parallelizing contingency-constrained optimal power flow (CCOPF). This algorithm may be used by utilities to optimize economy interchange for severe contingencies analyzed without disclosing details of their operating costs to competitors. In fact, the ultimate objective of fuzzy multi-objective CCOPF (FMCCOPF) is to carry out the minimization of both the base case (pre-contingency) operating cost and the post-contingency correction times as conflicting but fuzzy goals. Besides, the Benders decomposition is applied to partition the fuzzy formulation with contingency constraints, which allows for post-contingency corrective rescheduling, motivated by the improvement of computational efficiency using parallel processing. The feasibility of the proposed method is comprehensively realized by a comparison with the conventional optimal power flow (OPF) and the CCOPF with respect to the same array of transactions, base case, and generator/line outages for the IEEE-30 bus system and the IEEE-118 bus system.     

Determination of available transfer capability using multi-objective contingency constrained optimal power flow with post-contingency corrective rescheduling

In a new competitive electricity market, accurate information should be shared to provide nondiscriminatory access to all participants. Key information to determine how much power can be shipped through the network is dubbed available transfer capability (ATC). This paper presents a methodology for the calculation of ATC, which is performed through a fuzzy logic approach to parallelizing contingency constrained optimal power flow (CCOPF). This algorithm may be used by utilities to optimize economy interchange for severe contingencies analyzed without disclosing details of their operating cost to competitors. In fact, the main objective of fuzzy multi-objective CCOPF is to determine the minimization of both the base-case (pre-contingency) operating cost and the post-contingency correction times as conflicting but fuzzy goals. Also, Benders decomposition is adopted to partition the fuzzy formulation with contingency constraints, which allows for post-contingency corrective rescheduling, motivated by the improvement of the computational efficiency using parallel processing. The IEEE-30 bus system is employed to test the proposed algorithm and the results are comprehensively demonstrated by a distinct comparison between the conventional optimal power flow and the CCOPF with respect to the same array of transactions, base-case, and generation/line outages.     

Total transfer capability computation for multi-area power systems

This paper presents a method for multi-area power system total transfer capability (TTC) computation. This computation takes into account the limits on the line flows, bus voltage magnitude, generator reactive power, voltage stability, as well as the loss of line contingencies. The multi-area TTC problem is solved by using a network decomposition approach based on REI-type network equivalents. Each area uses REI equivalents of external areas to compute its TTC via the continuation power flow (CPF). The choice and updating procedure for the continuation parameter employed by the CPF is implemented in a distributed but coordinated manner. The proposed method leads to potential gains in the computational efficiency with limited data exchanges between areas. The developed procedure is successfully applied to the three-area IEEE 118-bus test system. Numerical comparisons between the integrated and the proposed multi-area solutions are presented for validation.     

Pre-screening of single contingencies causing network topologychanges

A multilevel contingency screening method is introduced to process large sets of candidate power system contingencies. The idea is to apply a series of increasingly more accurate and time-consuming algorithms so that each higher screening level processes a reduced set of candidates. A practical implementation of the method uses a fast prescreening step whose algorithm is based upon the local network solution concept. The method is designed to process contingencies whose effects can be localized, e.g. branch outages and bus section faults. The accuracy of the new algorithm is controlled via an automatically calculated small network adequacy ratio while its reliability is enhanced by the use of different contingency severity measures     

Optimal location and parameter setting of UPFC for enhancing power system security based on Differential Evolution algorithm

This paper presents a new approach based on Differential Evolution (DE) technique to find out the optimal placement and parameter setting of Unified Power Flow Controller (UPFC) for enhancing power system security under single line contingencies. Firstly, we perform a contingency analysis and ranking process to determine the most severe line outage contingencies considering line overloads and bus voltage limit violations as a Performance Index. Secondly, we apply DE technique to find out the optimal location and parameter setting of UPFC under the determined contingency scenarios. To verify our proposed approach, we perform simulations on an IEEE 14-bus and an IEEE 30-bus power systems. The results we have obtained indicate that installing UPFC in the location optimized by DE can significantly enhance the security of power system by eliminating or minimizing the overloaded lines and the bus voltage limit violations.     

有FACTS装置的电力系统在市场环境下的最优调度

随着电力工业重构的不断深入,转运业务需求的增加要求系统提供更高的输送能力。FACTS技术的应用能够提高系统的输民能力、降低网损、改善系统的稳定性、降低电能成本,促使电能交易顺利完成。依据有功性能指标,文中提出了FACTS装置的优化配置方法,并通过解最优潮流问题得到FACTS装置的可控参数值,同时讨论了FACTS装置对系统实时电价的影响。用IEEE－14节点算例验证了所提算法的有效性。     

基于统计学习的模糊暂态稳定事故筛选与排序

暂态稳定事故筛选与排序的目的是针对一组预想事故集合挑选出严重事故或滤除掉无害事故,以减少待分析的预想事故数目,满足在线动态安全分析的需要.文中提出一种基于统计学习的模糊暂态稳定事故筛选与排序方法,该方法采用了反映事故严重程度的10个性能指标,并通过样本学习,在每个指标集合上具体定义了系统稳定性的模糊隶属度函数;然后综合运用这10个性能指标的稳定性模糊隶属度得到的平均稳定性模糊隶属度,对预想事故集合按严重性进行了排序;接着根据排序结果,结合所设定的稳定阈值,将无害事故过滤掉.最后,用新英格兰10机39节点网络验证了该方法的有效性.     

Correctability of voltage violations in on-line contingencyanalysis

This paper focuses on determining the correctability of bus voltage violations during the contingency selection process. The present day strategy in the contingency selection function consists of flagging the worst contingency cases for further detailed analysis, when preventive and/or corrective actions are obtained. The worst contingency cases are the ones which bear a large severity or performance index (PI). However, one must take into account that contingencies with a large PI may be easily correctable, whereas contingencies with small PI, that had not even been flagged, may be noncorrectable. Thus, the selection process should flag not only those contingencies with large PI but also those that are not easily correctable. In a previous paper, it was shown that correctability of line overloads can be determined using a first order sensitivity approach with an acceptable increase in contingency selection time. In this paper, the correctability of voltage violations is addressed. Because of the nonlinearities, the algorithm used requires more calculations than the correctability of real power violations, but the additional time needed for the selection process is still quite acceptable for on-line purposes. The paper describes the algorithm, and provides test and timing results     

Fast contingency screening and evaluation for voltage securityanalysis

The authors describe a fast security-analysis technique for voltage security assessment in an energy-management system. The proposed method identifies the location of buses with potential voltage problems and thereby defines a voltage-sensitive subnetwork for contingency screening. This allows the evaluation of a large number of contingencies. The efficiency of this method is derived from the use of a voltage subnetwork to drastically reduce the number of bus voltages to be solved; and subsequently from the use of compensation techniques and sparse-vector methods (including adaptive reduction) for screening and final solution of contingencies. Results demonstrating the effectiveness of the method on a small and a large power system are presented     

A method for parametrized contingency‐constrained optimal power flow (PCCOPF)

This paper presents a method for Parametrized Contingency Constrained Optimal Power Flow (PCCOPF) whose formulation can discriminate unpreventable contingencies, determine the existence of feasible solutions for postcontingencies, and analyze the feasible solution for the contingencies in terms of static sense. The proposed formulation is based on parametrized contingency constraints in which each contingency parameter represents the achievement ratio of each selected contingency. In the formulation, not only parametrized contingency constraints are given by a set of equality constraints which is modified power flow equations, but also the objective is maximization of the sum of the achievement ratios of selected contingencies. Since contingency parameters are treated as decision variables in the proposed method, the information on unsolvability with respect to each contingency can be efficiently obtained. The feasibility and effectiveness of the proposed method are demonstrated on test problems with 4‐bus and 71‐bus systems. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(1): 21–31, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10182     

基于统一灵敏度法的静态电压稳定预防控制

针对低电压校正控制和电压稳定裕度提高的预防控制采用不同的灵敏度指标和控制程序问题,提出了新的静态稳定预防控制方法。该法基于电压稳定灵敏度的等效分析,对电压校正和提高稳定裕度的控制措施进行综合排序,对不同类型的严重故障加入相应的控制约束,建立基于灵敏度的优化控制子问题实现对两方面的安全控制。在算法实现中,采用曲线拟合方法快速计算故障后的稳定裕度,并分析了提高算法效率的方法。该算法不需要计算零特征根的左特征向量,节省了计算量,且在临界点处能够提供相同的控制灵敏度排序。通过对实际的703节点系统仿真,结果验证了所提出的方法是有效的。     

牛顿法和内点罚函数法相结合的概率可用功率交换能力计算

区域间可用功率交换能力(ATC)是所有电力市场的参与者进行交易活动所必需的重要信息。文中运用改进牛顿法和内点罚函数法相结合进行最优潮流计算，取得相应的单点．ATC值；在负荷预测和故障选择的基础上，作概率上的统计分析，得到未来时刻的可能的ATC概率分布情况。根据概率上的要求，将可得到未来时刻所要安全概率对应的ATC值。在模型中，考虑了发电机发电极限，电压水平，线路和设备过负荷等安全性约束条件。IEEE-30节点系统的计算结果表明了用该方法计算ATC的有效性和实用性。     

N-2组合故障集的暂态功角稳定在线快速评估

大电网中N-2组合故障数目巨大,若对每个组合故障分别进行暂态功角稳定评估,难以满足在线评估的时间要求。基于N-2组合故障中第一个元件故障的暂态功角稳定在线评估结果(裕度和主导群发电机的参与因子),结合第一个元件故障的暂态功角稳定主导群中发电机的有功功率对第二个开断元件有功功率的灵敏度,计算出N-2组合故障的暂态功角稳定严重程度排序指标。通过优先对排序在前位的组合故障进行基于详细模型时域仿真的暂态功角稳定量化评估,直至排序号连续的多个组合故障的暂态功角稳定裕度都大于0,则直接判定排序在其后的所有组合故障均是暂态功角稳定的,从而满足N-2组合故障集暂态功角稳定在线评估对计算速度的要求。实际电网算例验证了该方法的有效性。     

基于最优潮流的含VSC-HVDC交直流系统最大输电能力计算

已有的交直流系统最大输电能力计算模型无法直接应用于含电压源换流器型高压直流(VSC-HVDC)的交直流系统的最大输电能力计算问题。文中提出了一种基于最优潮流的最大输电能力计算方法,通过将最优潮流模型拓展到系统的多种运行状态,从而能够准确反映N-1安全约束及N-1故障后VSC-HVDC的控制约束。为解决因考虑N-1安全约束导致的模型求解规模过大的问题,针对含VSC-HVDC的交直流系统的特点,进一步提出一种同时考虑故障对静态电压稳定性及支路传输容量越限影响的N-1故障筛选方法。为保证解的性能,在优化软件AMPL中调用COUENNE求解器对以上模型进行求解,能够同时给出最大输电能力和相应的VSCHVDC控制方式及参数整定值。通过修改的4节点系统、IEEE 118节点系统及辽宁省鞍山电网,验证了所提方法的有效性。     

Fast real power contingency ranking using counter propagation network: feature selection by neuro-fuzzy model

In deregulated operating regime power system security is an issue that needs due consideration from researchers in view of unbundling of generation and transmission. Real power contingency ranking is an integral part of security assessment. The objective of contingency screening and ranking is to quickly and accurately shortlist critical contingencies from a large list of credible contingencies and rank them according to their severity for further rigorous analysis. In the present work, modified counter propagation network (CPN) with neuro-fuzzy (NF) feature selector is used for real power contingency ranking of the transmission system. The CPN is trained to estimate the severity of a series of contingencies for given pre-contingencies line-flows. But for larger size system it becomes rather difficult to cope with the increased size of input pattern and network as well. And it adversely affected the performance of the network and computational overhead. The proposed NF feature selector prunes the size of input pattern by exploring the individual power of features to characterize/discriminate different clusters. The reduced set of discriminating inputs not only ensures saving in training time but also improves estimation accuracy and execution time and these are the deciding parameters in evaluating the performance of particular contingency ranking technique. The effectiveness of proposed approach is demonstrated on IEEE 30-bus test system and practical 75-bus Indian system.     

Improved contingency measures for operation and planningapplications

Three new contingency measures are proposed and tested based on a large power system peak load base case. The Type II contingency measure is zero for all noncritical contingencies, has no misclassification or false alarm problems, and ranks contingencies according to their largest thermal limit violation. It should be used when operating conditions are known exactly. The Type III contingency measure has very small or zero contingency measure for noncritical contingencies, has no perceptible misclassification or false alarm problems, and appears to rank contingencies by their worst thermal limit violation. The Type III contingency measure is very useful for selecting contingencies where the precise operating conditions are unknown. A Type IV contingency measure sets branch weights to zero on all branches that do not experience thermal overloads for a set of contingencies. The Type IV contingency measure is useful for selecting single contingencies that when taken in combination could produce critical multiple contingencies