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.     

Optimal power flow with expected security costs

This paper discusses the expected-security-cost optimal power flow (ESCOPF) problem. The objective of the problem is to minimize the expected total cost of system operation subject to power system constraints and expected security costs. The probabilities of operating in the pre-contingency operating state and the probabilities of operating in all possible post-contingency states are considered. In addition, the ESCOPF problem includes the cost of interrupting customer load and the cost of generator ramping, which may be necessary when a contingency occurs. The solution to the ESCOPF problem gives information regarding the marginal value of spinning reserve and the marginal value of interruptible load. A graphical tool is used to view the problem solution.     

Multi-objective optimization operation with corrective control actions for meshed AC/DC grids including multi-terminal VSC-HVDC

This paper presents a multi-objective optimal operation of meshed AC/DC power grids including multi-terminal voltage-source-converter-based high-voltage direct current (VSC-MTDC) systems. The proposed approach is modeled as a corrective security-constrained optimal power flow (CSC-OPF) problem, with the minimization of both the operation cost and power loss as the objectives. Moreover, it provides a cost-effective solution to assist in decision-making, and improves the system security during operation. The N − 1 contingency security criterion is enforced for both AC and DC transmission networks, and corrective control is used to eliminate or alleviate post-contingency security violations. The corrective control actions used in this paper include not only secure operation control actions, but also economical post-contingency corrective control of the multi-terminal VSC-HVDC. To increase the computation speed, a contingency screening technique is applied to CSC-OPF by efficiently selecting the most severe case of the N − 1 contingency, as obtained using a voltage security index (VSI). The proposed approach uses the non-dominated sorting genetic algorithm (NSGA-II) to find multi-objective OPF solutions by checking the post-contingency state feasibility while taking into account post-contingency corrective actions. Simulation results confirm the validity and effectiveness of this approach.     

“N-1”预想事故下满足静态电压稳定约束的快速ATC算法

提出了一种“N-1”预想事故下满足静态电压稳定约束的快速可用输电能力(ATC)算法.算法在连续潮流法的基础上,以系统基态“N-1”事故下的运行点和应用灵敏度方法获取的预测点为拟合点,并引入曲线拟合技术来寻找“N-1”预想事故下的近似的“鼻点”,从而确定系统的可用输电能力.以IEEE 30节点测试系统为算例,验证了所提方...     

Assessment of branch outage contingencies using the continuation method

This paper provides a contribution to the contingency analysis of electric power systems under steady state conditions. An alternative methodology is presented for static contingency analyses that only use continuation methods and thus provides an accurate determination of the loading margin. Rather than starting from the base case operating point, the proposed continuation power flow obtains the post-contingency loading margins starting from the maximum loading and using a bus voltage magnitude as a parameter. The branch selected for the contingency evaluation is parameterised using a scaling factor, which allows its gradual removal and assures the continuation power flow convergence for the cases where the method would diverge for the complete transmission line or transformer removal. The applicability and effectiveness of the proposed methodology have been investigated on IEEE test systems (14, 57 and 118 buses) and compared with the continuation power flow, which obtains the post-contingency loading margin starting from the base case solution. In general, for most of the analysed contingencies, few iterations are necessary to determine the post-contingency maximum loading point. Thus, a significant reduction in the global number of iterations is achieved. Therefore, the proposed methodology can be used as an alternative technique to verify and even to obtain the list of critical contingencies supplied by the electric power systems security analysis function.     

Evolutionary programming based security constrained optimal power flow

This paper presents an algorithm for solving security constrained optimal power flow problem through the application of evolutionary programming (EP). The controllable system quantities in the base-case state are optimised to minimize some defined objective function subject to the base-case operating constraints as well as the contingency-case security constraints. An IEEE 30-bus system is taken for investigation. The security constrained optimal power flow results obtained using EP are compared with those obtained using conventional security constrained optimal power flow. The investigations reveal that the proposed algorithm is relatively simple, reliable and efficient and suitable for on-line applications.     

Consideration of multiple uncertainties for evaluation of available transfer capability using fuzzy continuation power flow

In today’s electric power industry, accurate and flexible information is needed to provide nondiscriminatory access to all market participants. This paper primarily purports to determine available transfer capability (ATC) based on the fuzzy set theory for continuation power flow (CPF), thereby capturing uncertainty. Assuming that uncertainties involved in the ATC calculation are estimated or measured, a fuzzy model is formulated in which major uncertainty parameters affecting the ATC are regarded as fuzzy variables subject to their possibility distributions. The purpose of this paper is to elaborate main features of the fuzzy continuation power flow (FCPF) algorithm that can handle uncertainties in load parameters and bus injections as well. As such, the robust solution will assist in providing additional information on the actual ability of the network to a system operator. In other respects, it poses a significant influence on the potential curtailment of power trades from which the reinforcement strategy can be set by the system operator. The viability of the proposed method would be verified through a stark contrast with the ones obtained from the conventional CPF and the fuzzy power flow (FPF) in the IEEE-24 RTS bus system and in the IEEE-118 bus system.     

电网运行状态下的概率优化调度

构建电网运行状态下的有功功率概率优化调度模型,该模型以期望运行效益最大化为目标,采用马尔可夫链对系统未来调度时段的预想事故状态概率进行预测,在满足所有预想事故发生前后状态所对应约束集下获取调度解。其中,在容许时间内,针对预想事故发生后可能出现的系统安全破坏情形,以发电机组允许的输出功率再调整、紧急负荷中断及输电元件短时允许过载量作为有机牵制扩展到约束集中,并考虑相应安全校正措施的费用代价。该模型实现了电网运行状态概率预测与有功调度决策的紧密结合,可得到系统期望最大运行收益的时序变化曲线及各时段下风险收益概率均衡的调度方式。以IEEE-14节点系统为例进行测试分析,论证所提模型的合理性和有效性。     

静态安全约束下基于Benders分解算法的可用传输容量计算

在电力市场环境下，可用传输容量(ATC)是反映输电线路可用于交易的剩余容量的重要指标。文中以最优潮流为基础，采用Benders分解方法将考虑静态安全约束的ATC计算问题分解为一个基态主问题和一系列与各预想事故有关的子问题。主问题用来处理基态潮流和相应约束以及由子问题所返回的Benders割(cut)约束，而各子问题用来处理各预想事故和形成相应的静态安全约束。文章给出了相应的数学模型，并提出了两种改进的求解策略。4节点和IEEE30节点系统的计算结果表明了该方法和求解策略的有效性。     

考虑N-1故障的安全约束机组组合模型及约束削减方法

考虑N-1故障的安全约束机组组合问题规模庞大,对其进行数值求解十分困难.为此,基于直流潮流和线路开断分布因子,建立混合整数线性规划模型并提出约束削减方法.约束削减方法包括两步:根据并联支路潮流之间的关系选出需要监视的支路,以减少并联支路的安全约束;推导故障态潮流的上界,将其与故障态支路容量进行比较,以消除冗余的故障态安...     

改进粒子群优化算法的概率可用输电能力研究

研究了基于改进粒子群优化算法的概率可用输电能力的计算问题。建立了基于最优潮流的区域间可用输电能力模型；构造了适合可用输电能力研究的改进粒子群算法，并提出了自适应调整惯性权重的策略，该策略有效改善了算法的适应性和收敛速度；针对改进粒子群算法的搜索特点，动态调节罚函数。在此基础上对经模态分析方法选出的系统严重故障进行可用输电能力计算，并对各种故障出现概率和相应的可用输电能力进行概率统计分析，得到具有概率性质的可用输电能力。对IEEE-30节点系统的仿真计算验证了文中所提方法的合理性和有效性。     

安全约束最优潮流的实用模型及故障态约束缩减方法

针对大型电力系统安全约束最优潮流(SCOPF)问题具有的计算规模庞大、求解困难的特点,提出了基于潮流转移关系的SCOPF实用模型及故障态约束缩减方法。首先通过预想故障分析建立故障前后的有功潮流转移关系,将故障态支路有功潮流描述为基态支路有功潮流的函数,从而将故障态支路有功潮流约束描述为基态支路有功潮流的线性不等式约束;然后通过对并联线路或并列主变压器进行分组,利用组内支路的有功潮流分布关系减少需监视的支路规模;最后利用设备短时通流能力明显大于其长期通流能力的特征对故障态支路潮流约束进行过滤,以尽可能减小SCOPF问题的计算规模。IEEE 14节点测试系统和华东电网的仿真分析验证了所提模型及约束缩减方法的正确性和有效性。     

静态电压稳定分析的故障筛选和排序方法

提出一种新的故障筛选和排序方法。首先,定义一种负荷裕度阈值,用连续潮流法计算此裕度下的潮流工况,在此工况下,利用最优乘子法依次求解所有的开断潮流,将有解的大部分开断作为安全故障筛选掉,少量无解的则为不安全故障。然后,在基态下利用最优乘子法依次求解不安全故障的开断潮流。有解则为危险故障,并用连续潮流法求解负荷裕度,按裕度给出排序;无解则为失稳故障,结合最小二乘潮流解失配量中隐含的校正控制灵敏度信息,使用序列线性规划法给出使潮流恢复有解的最小切负荷代价,据此代价来排序失稳故障。新英格兰10机39节点系统的仿真结果验证了所提出的方法能快速、可靠、全面地实现电压稳定的故障筛选和排序。     

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.     

A novel control strategy based on a look-up table for optimal operation of MTDC systems in post-contingency conditions

Multi terminal VSC-HVDC systems are a promising solution to the problem of connecting offshore wind farms to AC grids. Optimal power sharing and appropriate control of DC-link voltages are essential and must be maintained during the operation of VSC-MTDC systems, particularly in post-contingency conditions. The traditional droop control methods cannot satisfy these requirements, and accordingly, this paper proposes a novel centralized control strategy based on a look-up table to ensure optimal power sharing and minimum DC voltage deviation immediately during post-contingency conditions by considering converter limits. It also reduces destructive effects (e.g., frequency deviation) on onshore AC grids and guarantees the stable operation of the entire MTDC system. The proposed look-up table is an array of data that relates operating conditions to optimal droop coefficients and is determined according to N-1 contingency analysis and a linearized system model. Stability constraints and contingencies such as wind power changes, converter outage, and DC line disconnection are considered in its formation procedure. Simulations performed on a 4-terminal VSC-MTDC system in the MATLAB-Simulink environment validate the effectiveness and superiority of the proposed control strategy.     

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。     

Contingency severity assessment for voltage security usingnon-parametric regression techniques

This paper proposes a novel approach to power system voltage security assessment exploiting nonparametric regression techniques to extract simple, and at the same time reliable, models of the severity of a contingency, defined as the difference between pre- and post-contingency load power margins. The regression techniques extract information from large sets of possible operating conditions of a power system screened offline via massive random sampling, whose voltage security with respect to contingencies is pre-analyzed using an efficient voltage stability simulation. In particular, regression trees are used to identify the most salient parameters of the pre-contingency topology and electrical state which influence the severity of a given contingency, and to provide a first guess transparent approximation of the contingency severity in terms of these latter parameters. Multilayer perceptrons are exploited to further refine this information. The approach is demonstrated on a realistic model of a large scale voltage stability limited power system, where it shows to provide valuable physical insight and reliable contingency evaluation. Various potential uses in power system planning and operation are discussed     

基于最优乘子潮流估计的故障筛选与排序

提出了一种用于电压稳定安全评估的快速故障筛选和排序方法。该方法从故障前的临界点出发,通过最优乘子潮流法计算得到的故障后边界点来估计故障后临界点,当初始点接近临界点,通过一次迭代即可满足所需的计算精度,从而快速地识别出非严重故障。对于严重故障和某些特殊情况的故障进行了分析并提出了解决办法,保证了对严重故障的估计精度。通过某一实际703节点系统算例验证了该方法的有效性。     

计及风险控制策略的电力系统可用输电容量决策

针对风电装机容量较高的电力系统,在可用输电容量计算时需要合理计及风电机组出力不确定性可能导致的各种风险,文中在可用输电容量决策中引入了风险控制策略,在保证由于风电出力不确定性所引起的系统潮流越限风险不超过给定允许水平的同时,将由于风电机组实际出力不足而导致购电成本超过给定限值的风险控制在一定范围内。首先,将计及风险控制的可用输电容量决策描述为机会约束规划问题;然后,利用半不变量的Gram-Charlier级数展开理论计算相应可用输电容量决策方案下系统的安全风险和经济风险;最后,采用多目标差异进化算法求解所发展的优化模型,并以IEEE 118节点系统为例验证了所提出模型和方法的可行性与有效性。     

基于最优潮流并计及静态电压稳定性约束的区域间可用输电能力计算

可用输电能力(ATC)是衡量电力系统在安全稳定运行的前提下区域间功率交换能力的指标。文中基于最优潮流(OPF)方法，建立起符合电力市场交易机制的ATC计算模型，其中考虑到输电线路故障对系统静态电压稳定性的影响，加入线路N-1故障时广义参数化形式的潮流方程及相应的不等式约束条件，使系统在故障时仍有负荷裕度，以保持电压稳定；以支路功率和系统负荷裕度之间的灵敏度指标进行预想故障选择，并用原对偶内点法计算得到输电线路N-1安全约束下的区域间可用输电能力。IEEE30和IEEE118节点系统算例表明该模型和算法的正确性与有效性。