Congestion management solution under secure bilateral transactions in hybrid electricity market for hydro-thermal combination

The deregulation of power system has created an environment of competitiveness among different market players and the transmission lines are forced to operate near to their thermal or stability limits. It is a challenge with System Operators (SO) to ensure a secure and reliable transmission of power under these conditions. This paper proposes a rescheduling based congestion management strategy in hybrid (pool + bilateral) electricity market structure for a combination of hydro and thermal units. The proposed congestion management problem has been formulated as mixed integer nonlinear programming (MINLP) problem with an objective to minimize the congestion management cost by suitably rescheduling the hydro and thermal units based on their up and down generation cost bids. The hydro units having lowest operational cost and fast startup time have been used to alleviate the congestion by considering non-concave piecewise linear performance curves for them. The secure bilateral transactions have been ensured while rescheduling of the generators for alleviating the congestion. The performance of the proposed model has been demonstrated by solving the congestion management problem on modified IEEE-24 bus system.     

Transmission congestion management in bilateral markets: An interruptible load auction solution

This paper demonstrates that appropriate invocation of interruptible loads by the independent system operator (ISO) can aid in relieving transmission congestion in power systems. An auction model is proposed, for an ISO operating in a bilateral contract dominated market, for real-time selection of interruptible load offers while satisfying the congestion management objective. The proposed congestion management scheme using interruptible loads can specifically identify load buses where corrective measures are needed for relieving congestion on a particular transmission corridor. The N − 1 contingency criterion has been taken into account to simulate various cases, and hence, examine the effectiveness of the proposed method. It has been shown that the method can assist the ISO to remove the overload from lines in both normal and contingency conditions in an optimal manner.     

基于可中断负荷的阻塞调度方法研究

当系统发生输电阻塞时,仅通过调节发电机的出力来消除输电阻塞不是经济的调节方式。提出在电力市场环境下通过调节发电机组出力和中断可中断负荷共同消除输电阻塞的优化调度方法,即在日前市场中以发电成本最小为目标函数,在实时平衡市场中将可中断负荷应用于阻塞管理,并与发电机组出力再调度共同作为阻塞管理的手段,使阻塞管理费用最小;该优化方法采用基于跟踪中心轨迹的内点法来求解。用IEEE30节点系统验证的结果表明所提方法具有经济性。     

Comparison of Sen Transformer and UPFC for congestion management in hybrid electricity markets

Congestion management (CM) is one of the most important and challenging tasks of the Independent System Operator (ISO) in the deregulated environment. Recently, Sen Transformer (ST) has emerged as an important power flow control device which has the capability of power flow control over a wide range like UPFC. This device with a conventional transformer and tap changers has the capability of bidirectional control of active and reactive power and can play a very important role in future markets for mitigating the congestion problems. In this paper, the capability of ST has been utilized to manage transmission line congestion for hybrid based electricity market model. The main contribution of the paper is: (i) to develop an optimal rescheduling of generators strategy for real time congestion management and impact of ST for congestion management, (ii) the comparison of ST with unified power flow controller (UPFC) for congestion management, (iii) the secure bilateral transactions determination in a hybrid market model and congestion management with both power flow controllers in combined pool and bilateral market model. The optimal location of ST and UPFC has been obtained solving mixed integer non-linear programming model of congestion management. The proposed model has been applied for results on IEEE 24-bus RTS test system.     

Congestion Management Considering Wind Energy Sources Using Evolutionary Algorithm

It is necessary to maintain power system security within a reasonable limit without harming the electric power supply in an emerging electricity market. Power systems are said to be congested when power transmission reaches beyond its limits. Therefore, in a deregulated power system environment, the system operator must look after the power transactions made by market parties. In this article, a novel congestion management method considering wind energy sources is introduced. The proposed congestion management technique is constructed considering the calculation of bus sensitivity factor and generator sensitivity factor. The bus sensitivity factor is used for finding the optimal location of a wind farm. The most sensitive generators are identified to reschedule their output by using the generator sensitivity factor. The artificial bee colony algorithm and particle swarm optimization techniques are applied to compare the generator rescheduling with earlier literature for congestion management. The proposed method has been tested on the 39-bus New-England test system to investigate the effectiveness of the proposed approach of wind farm integration for congestion management.     

主动配电网与输电网协调调度与阻塞管理

针对主动配电网优化调度的研究局限于配电网内部而未考虑与输电网关系的问题,提出了一种计及阻塞管理的输配电网协调优化调度策略。定义了主动配电网的广义投标函数和对外调节裕度作为输、配电网间协调媒介,对系统进行优化调度,通过潮流计算判断输电网的阻塞支路,在阻塞优化中考虑主动配电网中分布式电源的可调度性,利用节点对线路的灵敏度系数进行阻塞管理,消除线路阻塞。上述问题采用改进的粒子群优化算法解决。利用改编的IEEE30节点系统进行仿真实验,验证了所提输配电网协调优化策略与阻塞管理方法的有效性。     

考虑消除阻塞的分段竞价电力市场出清算法

研究了在发电侧开放的电力市场下,作为电网公司,在保证电网运行的安全性及电能质量的前提下,如何购买各发电厂的电力,使得既满足用户的需要又实现安全性和经济性。提出了一种用灵敏度方法消除阻塞的分段竞价电力市场的出清算法,先在不考虑支路过载的情况下,按各发电机的报价进行竞价,依次安排基荷、腰荷和峰荷段的出力;再选取负荷最大时刻对网络进行阻塞管理,以阻塞调整的费用最小为目标,根据各发电机相对阻塞支路的灵敏度调整各发电机的功率,根据此阻塞管理结果对整体竞价过程进行调整并考虑爬坡约束,通过优化腰、峰荷的分界点,得到考虑消除阻塞的分段竞价电力市场的各发电机出力。这种考虑消除阻塞的分段竞价电力市场的出清算法不仅满足电能生产的连续性,区分了电能质量,体现了市场公平性,而且消除了阻塞,因此其结果更具有实用价值。以IEEE 30节点系统为例,证明了算法的可行性。     

Improved multilevel bipartitioning for controlled power system islanding

Nowadays interconnected power systems work close to their limits because of increased economic benefits. If a severe disturbance occurs in any part of the interconnected power system, it can be propagated through it. If no intelligent supervisory action is taken, a power system may be driven into an emergency state which could either cause system collapse by natural islanding or total system blackout. One possible measure to be put in effect in an emergency state is controlled power system islanding. In this paper, our previously proposed multilevel approach for controlled islanding is improved by using slow coherency grouping of generators in the aggregation phase. The approach has been applied to the IEEE 118 bus power system. The results indicate that the best partitioning of the power system is obtained with minimum generation/load imbalance in the islands, and with the coherent groups of generators maintained in each island making the restoration easy. A comparison of the computational complexities involved in the spectral, multilevel kernel k‐means and the improved multilevel approaches is made by applying these methods to the IEEE 9 bus, the IEEE 30 bus, the IEEE 39 bus, the IEEE 57 bus, the IEEE 118 bus, the IEEE 300 bus, the 2383 bus Polish and the 2746 bus Polish power systems to show the suitability of the proposed approach for controlled islanding of large‐scale power systems. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Congestion Management Considering Optimal Placement of Distributed Generator in Deregulated Power System Networks

This article presents an effective methodology for congestion management in deregulated power system networks considering optimal placement of a distributed generator. The novelty of this method is that the optimal placement of a distributed generator in a deregulated power system is decided on the basis of bus impedance matrix (Z_bus ) based contribution factors. The Z_bus -based contribution factors are independent of slack bus location, which complies with the prevailing competitive environment. The congestion management problem formulation comprises the maximization of social welfare function subject to power balance and transmission congestion constraints. The maximization of the social welfare function causes maximization of consumer benefits and minimization of supplier generation cost and distributed generators. The proposed methodology has been simulated on an IEEE 30-bus system, and comparisons of results are presented with and without distributed generators. The results show that the proposed approach gives significant improvement in social welfare and decreases congestion rent with distributed generator placement.     

Security-based multi-objective congestion management for emission reduction in power system

Power system operation in the era of post-restructuring faces several challenges: transmission congestion frequently occurs, security is deterred more than in the past, emission reduction is becoming a matter of importance and intermittent renewable power generation resources (RPGR) have been widely promoted. This paper intends to solve these challenges in a multi-objective optimisation framework. The proposed procedure comprises two stages: in the a priori stage, transmission congestion management cost (TCMC) and emission are traded-off via a proposed stochastic augmented ε-constraint technique which yields a set of non-dominated solutions. In the a posteriori stage, a solution is selected by considering power system security. For this purpose, two strategies are proposed: in the first strategy, based on a proposed managerial vision, a combination of data envelopment analysis introduced by Charnes, Cooper, and Rhodes (CCR-DEA), cross-efficiency technique and robustness analysis is deployed to select the most robust super-efficient solution. The advantage of the proposed a posteriori approach is that selecting the final solution is not subjected to assigning weights to the objective functions and/or providing higher-level information. In the second strategy, first the effective scenarios due to outage of transmission components are identified using CCR-DEA and next, each scenarios’ degree of severity (DOS) is obtained using the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). The sums of the DOS of non-dominated solutions’ effective scenarios are evaluated for final decision making. The proposed approach is applied to IEEE 24 bus test system and the results are analysed.     

Optimal Rescheduling of Generators for Congestion Management Based on Particle Swarm Optimization

Power system congestion is a major problem that the system operator (SO) would face in the post-deregulated era. Therefore, investigation of techniques for congestion-free wheeling of power is of paramount interest. One of the most practiced and an obvious technique of congestion management is rescheduling the power outputs of generators in the system. However, all generators in the system need not take part in congestion management. Development of sound formulation and appropriate solution technique for this problem is aimed in this paper. Contributions made in the present paper are twofold. Firstly a technique for optimum selection of participating generators has been introduced using generator sensitivities to the power flow on congested lines. Secondly this paper proposes an algorithm based on particle swarm optimization (PSO) which minimizes the deviations of rescheduled values of generator power outputs from scheduled levels. The PSO algorithm, reported in this paper, handles the binding constraints by a technique different from the traditional penalty function method. The effectiveness of the proposed methodology has been analyzed on IEEE 30-bus and 118-bus systems and the 39-bus New England system.      

基于FVSI线稳定指标计算母线最大承载负荷确定电力系统弱母线的方法

介绍了使用线稳定指标作为快速电压稳定指标（FVSI）确定电力系统母线的最大承载负荷的方法。该方法根据电压崩溃前各负荷母线能够承载负荷量的大小排序，把能承载负荷量最小的母线排为最高级并把它作为最薄弱母线。基于负荷变量进行线稳定指标计算和电压稳定分析。对于每条负荷母线，如果其电压稳定指标的值越接近于1，说明该母线承载了最大可能的负荷。最后使用IEEE系统对其检验，结果证明所提出的方法能够快速估算各负荷母线的最大承载能力，找到电力系统中薄弱母线。     

日发电计划安全校核及最优调整的研究与应用

由于国内电网网架结构比较薄弱的特点以及当前日发电计划的安全校核和校正的需求,决定了对发电计划的安全校核及优化调整和阻塞调度等问题研究的必要性。基于此,本文开发了一套日发电计划安全校核及最优调整系统的应用软件,这套系统是由EMS数据接口、数据交互平台、应用服务程序、Web页面4大部分组成。文中利用降阶基方程线性规划法实现发电计划的最优调整,具有自动网络等值、母线负荷预测、实时网络状态读取、分区滚动发电及潮流变化曲线显示、系统图形生成等功能。此系统的开发软件已经在安徽省调度中心投入运行,并由运行结果表明此系统可以有效地实现发电计划安全校核和校正。     

Particle swarm optimization algorithm for capacitor allocation problem in distribution systems with wind turbine generators

This paper aims at adopting the Particle Swarm Optimization (PSO) technique to find the near-optimal solutions for the capacitor allocation problem in distribution systems for the modified IEEE 16-bus distribution system connected to wind energy generation based on a cost function. The proper allocation and the optimized number of capacitors have led to adequate power losses reduction and voltage profile enhancement. Because of the wind power generation variations due to the nature of wind speed intermittency and the lack of reactive power compensation, the problem under study have been presented involving a nonlinear fitness function. In order to solve it, the corresponding mathematical tools have to be used. The formulated fitness cost function has consisted of four terms: cost of real power loss, capacitor installation cost, voltage constraint penalty, and capacitor constraint penalty. PSO technique has been used to obtain the near-optimum solution to the proposed problem. Simulation results demonstrate the efficiency of the proposed fitness cost function when applied to the system under study. Furthermore, the application of PSO to the modified IEEE 16-bus system has shown better results in terms of power losses cost and voltage profile enhancement compared to Genetic Algorithm (GA). In order to verify the successful adaptation of PSO toward attaining adequate near-optimal capacitor allocations in distribution systems, this metaheuristic technique has been employed to the large-scale IEEE 30-bus system. The proposed PSO technique has provided adequate results while modifying the objective function and constraints to include the power factor and transmission line capacities for normal and contingency (N-1) operating conditions.     

电能期货合同市场的输电拥堵定价及其输电网的开放

该文提出了一个输电拥堵管理的新方法，这个方法能确保对所有的输电网使用者公平开放电网，并且对输电价格进行公平定价。首先，输电网使用者对使用区域电网之间的输电线路进行容量投标。然后，电网调度机构(ISO)按照输电网使用者对容量投标的价格来分配输电线路的可用容量，使得输电可用容量的总价值最大化。在一条拥堵的线路上得到输电容量调度计划的用户按照边际成本价格为使用这条线路输电而付费。在ISO为缓解区域之间的输电线路拥堵而调整输电计划时，它要对每个发电商和它们的相应用户之间的输电量分别进行平衡。通过将每对发电商，用户组合的输电业务量分离出来，ISO就可以只组织管理输电市场，而不介入发电商和用户之间双边合同形式的电能交易。     

A comprehensive strategy for transmission switching action in simultaneous clearing of energy and spinning reserve markets

There is a great resolution calling for smart grids in recent years. Introduction of new technologies, that make the network flexible and controllable, is a main part of smart grid concept and a key factor to its success. Transmission network as a part of system network has drawn less attention. Transmission switching as a new transmission service can release us from load shedding and remove the constraints’ violations.Transmission switching can provide economic benefits compared to other control methods such as generation unit rescheduling or load shedding for contingency management.Utilizing a stochastic mix-integer nonlinear programming (SMINLP) model, transmission switching is used during contingencies and steady state to determine optimal required energy and reserve values.Stochastic joint energy and reserve markets with transmission switching considering dynamic constraints has been proposed to minimize the cost of supplying load, security expenses.Considering dynamic constraints in proposed model avoid the occurrence of transient instability when opening the line in transmission switching action.A network reduction method based on modified Jacobean AC Newton–Raphson technique power flow considering switchable line in technique is used for speeding up the calculation, efficiency and simplicity.To investigate the efficiency of the proposed strategy IEEE 14 bus test and IEEE 57 bus test system are studied. According to the obtained results, this strategy decreases energy and reserve marginal prices, as well as security cost.     

负荷增长方式不确定条件下有功出力方式优化

优化有功出力方式是提升功率传输极限的有效方法之一。为在优化中考虑负荷增长方式的不确定性,提出了一种具有对立结构的双层优化模型。该模型的上层结构是以负荷裕度最大为目标函数的有功出力方式优化模型;下层结构是以负荷裕度最小为目标函数的最危险负荷增长方式求解模型。通过对上、下2层模型交替进行优化,并将所得的优化解作为参数在2个层间相互传递,快速地求出了最佳的有功出力方式,使系统在最危险负荷增长方式下的负荷裕度最大。最后通过IEEE30、118节点系统和一个实际系统的算例验证了所提方法的有效性。     

Congestion management with distributed generation and its impact on electricity market

Congestion management became more complicated with the increase of complexity in the system. The complexity arose due to restructuring of the utilities alongside the penetration of alternative sources of energy. This paper presents a sensitivity method for allocating distributed generators (DGs) considering congestion relief and voltage security simultaneously. The sensitivities of the overloaded lines with respect to bus injections are considered for ranking the load buses. The new generation capacities for DGs connected at these load buses are then computed by genetic algorithm (GA) with an objective of enhancing the system performance by reducing the system losses and maintaining the voltage profile of the various buses nearest to its nominal value. The N-1 contingency criterion has been taken into account in this work. The expected cost consists of operating cost under normal and contingency states along with their related probabilities to occur. Maximizing social welfare is the objective for normal state while minimizing compensations for generations re-scheduling and load side operation as well as in case of contingency also. Though installation cost of DGs is required, they are useful as cost effective, which can reduce in fact the annual costs for generations re-scheduling and load shedding. It has been shown that the method can assist the ISO to remove the overload from lines in both normal and contingency conditions in an optimal manner. The improvement is measured in terms of available transfer capability (ATC), congestion cost and reliability risk indices of Loss of Load Expectation (LOLE) have also been studied.     

Transmission access and pricing with multiple separate energyforward markets

California's congestion management protocols provide comparable access and prices to all users of the transmission system (power exchange and bilateral contract parties). The users implicitly bid for capacity on major transmission paths between zones. The independent system operator (ISO) allocates the available transmission capacity on these paths so that it maximizes the value of this capacity as measured by the users' bids. Everyone scheduling flow on a congested path is charged the marginal-cost-based price for using the path. The ISO keeps each party's portfolio of generation and load individually in balance when adjusting schedules to relieve congestion on interzonal paths. By keeping the portfolios of the different parties separate, the ISO clears its transmission market without arranging energy trades between parties. Parties are responsible for arranging their own trades. The ISO does not become involved in the energy forward markets     

A generation rescheduling method to increase the dynamic securityof power systems

In this paper, a new method is proposed for dynamic security dispatch. The idea of coherent behavior of generators is used to find a new generation configuration with better transient stability behavior. Rescheduling the generation in the power system improves system security by increasing the critical clearing time or the transient energy margin without changing total generation. The calculation in the proposed method is simple and direct; the generation rescheduling depends only on the original generation and inertia constants of the machines, and their rotor speeds at the fault clearing time. In this work, the transient energy function (TEF) method is used to check the dynamic security of the system by analyzing all credible three phase faults with single line outages. If the worst energy margin is not acceptable, the proposed rescheduling is done, and the security is checked again. The method has been tested on the Ontario Hydro 55-bus 11-generator system, the IEEE 145-bus 50-generator system and the IEEE 162-bus 17-generator system. Results on several loading levels of the 162-bus 17-generator system are also shown