Selection of objectives in minimum loss power flow in hydrothermal electric power systems

Two formulations of the optimal minimum loss hydrothermal power flow problem in electric power systems are discussed. The formulations — one based on Kron's loss objective function and the other a network-based loss formulation — are treated in detail and the results of the two approaches are compared using two standard test systems. For the systems investigated, Kron's loss minimization schedules higher thermal generation than that required by the network loss minimization during lower demand. Kron's loss minimization involves lower active power transmission losses than those involved by the network-based loss minimization during low demand, and higher active power transmission losses than those required by the network-based loss minimization during higher demand. The total energy loss involved in the outcome of the Kron's loss minimization results is higher than that due to the network-based loss minimization schedule. There is a negligible difference in voltage magnitudes. Reactive power generation results favour the network-based loss approach. On the basis of the experiments, it is concluded that a network-based loss model is preferable in this application.     

Interruptible load management using optimal power flow analysis

An interruptible load management (ILM) scheme is proposed using dynamic optimal power flow analysis. It enables real-time selection of interruptible loads incorporating power network constraints and dynamic restriction on generation, viz. ramp-rate limits. The model provides an analytical framework for addressing several important issues associated with optimal selection of load curtailment, e.g. advance notification for load curtailment, short-term price discounts and long-term discounts on demand-charges, power factor of the load and customer-cost associated with the load to be curtailed, and power system security. A six-bus example illustrates the proposed methodology     

考虑网络损耗的碳排放流理论改进与完善

考虑实际电力系统中的网络损耗,通过计算线路等效传输功率和负荷节点等效负荷需求,将网络损耗分摊到各负荷,将有损网络转换成无损网络,实现碳排放流理论的补充和完善,使其能够应用于实际有损电力系统。IEEE 30节点系统仿真结果验证了所提的考虑网络损耗的碳排放流理论的有效性和实用性,其能够清晰追踪电力系统中碳排放流的具体流向,可以对负荷的碳流进行来源分析,也为碳交易市场下负荷侧应缴纳的碳配额计算提供了参考依据。     

Power injection modeling and optimal multiplier power flow algorithm for steady-state studies of unified power flow controllers

This paper presents an optimal multiplier based Newton-Raphson power flow algorithm for reliably and efficiently handling power systems with embedded flexible AC transmission systems (FACTS) devices such as unified power flow controllers (UPFCs). A power injection transformation of a two voltage source UPFC model is derived in rectangular form. After detailed analyses of issues in implementation of UPFCs in power flow programmes by various power flow algorithms, the optimal multiplier power flow method for ill-conditioned systems is adopted. The proposed UPFC model and power flow algorithm have been programmed and vigorously tested in a number of systems. The results on the IEEE 30-bus test system and a 306-bus practical system are reported and compared with conventional user defined model type programmes, which clearly illustrate the effectiveness of the proposed algorithm.     

松弛节点电压对优化潮流及电力市场经济性的影响

用优化潮流（OPF）寻求发电总成本最低的运行方案是电力公司追求的主要目标之一。在网络拓扑和负荷水平一定的情况下，松弛节点电压的改变对优化程序和电力市场的经济性指标，如程序收敛性、系统发电总成本、有功网损和无功网损均会产生直接影响。文中运用优化工具对这一问题进行研究，并对IEEE－11、14和30节点系统进行仿真，仿真结果表明：采用优化技术可显著降低系统的发电总成本；维持恰当的松弛节点电压幅值也有助于节省发电费用和降低网损，带来理想的经济效益。对无功网损为负的网络，要对电压稳定和系统安全予以更多关注。     

Prediction of critical load levels for AC optimal power flow dispatch model

Critical Load Levels (CLLs) are load levels at which a new binding or non-binding constraint occurs. Successful prediction of CLLs is very useful for identifying congestion and price change patterns. This paper extends the existing work to completely solve the problem of predicting the Previous CLL and Next CLL around the present operating point for an AC Optimal Power Flow (ACOPF) framework. First, quadratic variation patterns of system statuses such as generator dispatches, line flows, and Lagrange multipliers associated with binding constraints with respect to load changes are revealed through a numerical study of polynomial curve-fitting. Second, in order to reduce the intensive computation with the quadratic curve-fitting approach in calculating the coefficients of the quadratic pattern, an algorithm based on three-point quadratic extrapolation is presented to get the coefficients. A heuristic algorithm is introduced to seek three load levels needed by the quadratic extrapolation approach. The proposed approach can predict not only the CLLs, but also the important changes in system statuses such as new congestion and congestion relief. The high efficiency and accuracy of the proposed approach is demonstrated on a PJM 5-bus system and the IEEE 118-bus system.     

The minimum cost optimal power flow problem solved via the restarthomotopy continuation method

The potential of the continuation method to solve the minimum-cost optimal power flow (OPF) problem is assessed. Initially, the complete OPF problem is simplified by creating a subproblem in which limits on functional variables are ignored. A restart homotopy continuation algorithm is developed that solves the sub-problem by manipulating the control variables to satisfy the optimality conditions of a family of relaxed subproblems which converge to the desired solution. Particular features of this minimum-cost problem are exploited to make the algorithm very efficient. Numerous examples are tested using the algorithm on systems up to 118 buses, 179 transmission lines, 68 controls, and 62 generation units. The commercial code MINOS (Version 4.0) is used to evaluate the performance of the algorithm and verify the results. The algorithm appears to be faster and more reliable     

最优潮流的发展

最优潮流是在保证系统安全运行的前提下 ,实现系统经济运行的问题。由于其安全约束众多、数学模型复杂 ,而难以实现。此文将回顾近二十年来最优潮流的逐步发展的过程 ,对主要的优化方法列出几篇具有代表性的文章 ,列出几种简单的数学模型并对各种方法的优化效果做出比较。并对最优潮流的进一步发展做出深入的探讨。     

A complete decomposition and coordination algorithm for large‐scale hydrothermal optimal power flow problems

This paper presents a complete decomposition and coordination algorithm to solve large‐scale hydrothermal optimal power flow (HTOPF) problems. Based on the approximate Newton directions method, which decouples the first‐order Karush–Kuhn–Tucker conditions of the original problem, an HTOPF problem with cascaded hydro plants is decomposed into a thermal plant subproblem with independent optimal power flow solutions for each time period and a hydro plant subproblem combined with fixed and variable heads and cascaded plants issues. In order to verify the effectiveness of the proposed algorithm, numerical tests are performed on three large‐scale test systems with up to 3120 buses and 7 531 915 primal–dual variables over 168 time periods. Test results show that the proposed algorithm gives excellent performances in convergence and stability. It not only reduces memory usage significantly but also decreases CPU time by about 65–75%. With parallel computing, it is capable of achieving 10–20 times or even 1000 times speed without loss of optimality. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

最优潮流的发展

最优潮流是在保证系统安全运行的前提下,实现系统经济运行的问题.由于其安全约束众多、数学模型复杂,而难以实现.此文将回顾近二十年来最优潮流的逐步发展的过程,对主要的优化方法列出几篇具有代表性的文章,列出几种简单的数学模型并对各种方法的优化效果做出比较.并对最优潮流的进一步发展做出深入的探讨.     

计及发电机无功约束的最优乘子潮流计算方法比较

基于牛顿—拉夫逊法的最优乘子法已经广泛用于电力系统潮流计算中。其中比较突出的是S.Iwamoto等人提出的直角坐标最优乘子法、H.W.Dommel等人提出的极坐标下阻尼牛顿法以及王宪荣等提出的极坐标准最优乘子法。采用上述三种方法对IEEE57、118标准算例以及北美3 199、6 739节点实际系统进行了大量计算,比较了它们在计算速度、鲁棒性和适应性等方面的差别,探讨了潮流计算迭代中发电机PV-PQ节点类型转换对最优乘子法计算过程和结果的影响。数值结果表明,阻尼牛顿法与发电机PV-PQ节点类型转换之间的适应性差,极坐标准最优乘子法计算速度相对较快、受节点类型转换影响小、鲁棒性好。     

计及发电机无功约束的最优乘子潮流计算方法比较

基于牛顿-拉夫逊法的最优乘子法已经广泛用于电力系统潮流计算中.其中比较突出的是S.Iwamoto等人提出的直角坐标最优乘子法、H.W.Dommel等人提出的极坐标下阻尼牛顿法以及王宪荣等提出的极坐标准最优乘子法.采用上述三种方法对IEEE57、118标准算例以及北美3 199、6 739节点实际系统进行了大量计算,比较了它们在计算速度、鲁棒性和适应性等方面的差别,探讨了潮流计算迭代中发电机PV-PQ节点类型转换对最优乘子法计算过程和结果的影响.数值结果表明,阻尼牛顿法与发电机PV-PQ节点类型转换之间的适应性差,极坐标准最优乘子法计算速度相对较快、受节点类型转换影响小、鲁棒性好.     

基于碳排放流理论的电力系统源-荷协调低碳优化调度

在低碳电力的背景下,需求侧资源逐渐参与电力系统调度,为降低电力系统碳排放提供了新思路.建立了一种考虑碳排放流理论和以碳价为价格信号的需求响应电力系统两阶段低碳优化调度模型.首先,以电力系统经济调度为一阶段优化模型.其次,基于Shapley值碳责任分摊方法,计算出各负荷侧碳责任合理范围并由此提出阶梯碳价定制方法,然后基于...     

以最小削减及最少启停为特征的空调负荷双层优化调度策略

为了维持电网稳定运行、节约调度成本、改善用户的舒适度,在空调负荷的优化调度中提出了以最小削减及最少启停为特征的双层调度策略。沿着负荷最优削减方向,以最小空调削减量为目标,实现空调削减在空间上的优化组合;对于各调控节点下的多台空调,以空调启停数量最少为目标,通过安全开关和调温控制策略的优化组合,满足调控精度的要求。所提双层优化策略在保证电网稳定的同时,有效地降低了空调的削减量,并且在保证调控精度的同时,最大限度地保证了用户的舒适度,降低了调度成本。IEEE 33节点配电网算例的仿真结果验证了所提调度策略的可行性和准确性。     

基于最优潮流的无功定价方法探讨

电力市场环境下精确可行的无功服务定价是近年来研究的热点问题.将无功发电机会成本和无功补偿设备的投资加入到最优潮流的目标函数中,并考虑旋转备用的重要性,加入旋转备用约束条件,提出了新的基于最优潮流的无功功率实时定价模型.并对IEEE4-57节点系统进行了测试,所得的无功电价既能涵盖大部分的无功生产费用,又能提供足够的经济信息.     

基于最优潮流的无功定价方法探讨

电力市场环境下精确可行的无功服务定价是近年来研究的热点问题。将无功发电机会成本和无功补偿设备的投资加入到最优潮流的目标函数中,并考虑旋转备用的重要性,加入旋转备用约束条件,提出了新的基于最优潮流的无功功率实时定价模型。并对IEEE4-57节点系统进行了测试,所得的无功电价既能涵盖大部分的无功生产费用,又能提供足够的经济信息。     

基于无迹变换随机潮流建模的主动配电网优化调度

为了解决风电和电动汽车大量接入主动配电网所引发的随机优化调度问题,利用基于无迹变换的随机潮流计算方法处理风电出力的波动性、电动汽车充电的随机性以及电网负荷的随机波动。进而建立了以电动汽车充电功率和分布式电源出力为优化变量,以配电网运行费用最小、有功网损最小和负荷方差最小为优化目标的主动配电网随机优化模型。同时,采用多目标粒子群算法对模型进行求解,并以改进的IEEE 33节点测试系统为例对该模型进行仿真。仿真结果表明:考虑不确定性和电动汽车有序充电的优化调度模型,可以有效地减少配电网运行的成本、降低网损和缩小峰谷差,验证了所提模型的正确性和有效性。     

LNG调峰电厂负荷优化分配的应用探讨

对于多机组的燃气-蒸汽联合循环调峰电厂,机组间负荷的合理分配直接关系到电厂运行的经济性.通过对惠州天然气电厂3×390 MW机组DCS运行数据进行分析,拟合构建了各机组燃耗特性函数,提出了在AGC指令下结合等微增率法进行机组负荷优化分配方法.计算结果表明,在机组非额定工况下采用该方法分配负荷的燃耗较单纯采用AGC指令分配有一定降低,可得出更经济的运行组合方式.     

优化潮流的数值计算

通过对电力系统运行状态的分析，就潮流计算的数学模型进行了合理的简化并针对其解的稳定性提出了延拓法确定初值。利用此优化潮流的计算方法，可以迅速且有效地对系统潮流进行适当的调整和控制，以满足安全可靠或经济性的要求。     

最优潮流算法综述

最优潮流是一个典型的非线性优化问题,且由于约束的复杂性使得其计算复杂,难度较大.虽然人们已经提出了许多种方法,并且在部分场合有所应用,但是要大规模实用化,满足电力系统的运行要求还有不少问题要解决.此文总结了现今有关最优潮流的几个方面,从优化方法和所遇到的新问题出发,对主要的优化方进行了介绍和简要的分析,以供从事无功优化的人员参考,同时还对最优潮流的进一步发展做了一些探讨.