Congestion management with FACTS devices in deregulated electricity markets ensuring loadability limit

This paper addresses an important issue of transmission system congestion management in a pool electricity market environment with the consideration of voltage stability as loadability limit. The optimal generators’ rescheduling has been obtained for three block bid structure submitted to the ISO in a day-a-head market. The base case economic load dispatch has been obtained for generators ensuring the loadability limits and is taken as base case generation output data during the congestion management to obtain new generation scheduling. The generation pattern has been obtained for three bid blocks taking load variation for 24 h considering load scaling factor. The three block bid structure offered to the ISO has been modeled as a linear curve, function of up and down rescheduling within the upper and lower limits offered for congestion management. The impact of third generation FACTS devices has also been studied on the optimal rescheduling of generators’ outputs and thereby the congestion cost. The results have been obtained for IEEE 24 bus and IEEE 57 bus test systems.     

基于可中断负荷拍卖模型电力双边交易阻塞管理

提出了基于可中断负荷拍卖模型的电力双边交易阻塞管理构架,通过市场机制来确定最优的负荷削减程序.在该构架中阻塞调度过程可以分为三个阶段:调度前阶段、无约束调度阶段和考虑可中断负荷拍卖的阻塞调度阶段.在第三阶段,用户可以向调度机构提交各自的可中断负荷服务报价曲线.构建了阻塞调度模型,综合考虑了最小化所中断的负荷量和最小化向用户支付的可中断负荷服务费这两个优化目标.最后用算例对所提出的阻塞调度模型进行了验证.     

Security-constrained transmission expansion planning: A stochastic multi-objective approach

This article presents a stochastic multi-objective optimization framework for transmission expansion planning (TEP) with steady state voltage security management, using AC optimal power flow (AC-OPF). The objectives are to minimize the sum of transmission investment costs (ICs), minimize the Expected Operation Cost (EOC), minimize the Expected Load Shedding Cost (ELSC) and maximize the Expected Loading Factor (ELF). The system load uncertainty has been considered and the corresponding scenarios are generated employing the Monte Carlo (MC) simulations. A scenario reduction technique is applied to reduce the number of scenarios. A multi-objective mathematical programming (MMP) is formulated and the ε-constraint method is used to solve the formulated problem. The N − 1 contingency analysis is also considered for the proposed TEP problem.The proposed TEP model has been applied to the well-known IEEE 24-bus Reliability Test System. The detailed results of the case study are presented and thoroughly analyzed. The obtained TEP results show the efficiency of the proposed algorithm.     

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.     

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.     

An online power system static security assessment module using multi-layer perceptron and radial basis function network

Efficient contingency screening and ranking method has gained importance in modern power systems for its secure operation. This paper proposes two artificial neural networks namely multi-layer feed forward neural network (MFNN) and radial basis function network (RBFN) to realize the online power system static security assessment (PSSSA) module. To assess the severity of the system, two indices have been used, namely active power performance index and voltage performance index, which are computed using Newton–Raphson load flow (NRLF) analysis for variable loading conditions under N − 1 line outage contingencies. The proposed MFNN and RBFN models based PSSSA module, are fed with power system operating states, load conditions and N − 1 line outage contingencies as input features to train the neural network models, to predict the performance indices for unseen network conditions and rank them in descending order based on performance indices for security assessment. The proposed approaches are tested on standard IEEE 30-bus test system, where the simulation results prove its performance and robustness for power system static security assessment. The comparison of severity obtained by the neural network models and the NRLF analysis in terms of time and accuracy, signifies that the proposed model is quick, accurate and robust for power system static security evaluation for unseen network conditions. Thus, the proposed PSSSA module implemented using MFNN and RBFN models are found to be feasible for online implementation.     

A new optimal unified power flow controller placement and load shedding coordination approach using the Hybrid Imperialist Competitive Algorithm-Pattern Search method for voltage collapse prevention in power system

As power systems become more complex and heavily loaded, voltage collapse has become one of the most destructive events in modern power systems leading to blackouts in electric utilities worldwide. Voltage collapse is mainly caused by operating power systems at lower stability margins due to a surge in electric power demand. This paper presents an optimal unified power flow controller (UPFC) placement and load shedding coordination approach for voltage collapse prevention in N − K (K = 1, 2 and 3) contingency condition using Hybrid Imperialist Competitive Algorithm-Pattern Search (HICA-PS). ICA is the main optimizer of the proposed algorithm while pattern search is applied to further fine tune the results of the ICA. To show the effectiveness of the proposed approach in preventing voltage collapse in complex power systems, we implemented it on the New-England 39 bus power system. Its performance was also compared to that of some classical optimization techniques. Decrease in load shedding amounts, continuity of energy supply and voltage collapse prevention is the main positive features of the proposed approach.     

基于可中断负荷的阻塞管理研究

随着电力市场的逐步完善,将可中断负荷引入输电阻塞管理成为缓解阻塞和消除市场力的有效手段。提出通过潮流优化并将可中断负荷引入输电阻塞管理,提出潮流优化与可中断负荷联合调度模型解决输电阻塞问题。对该模型以及IEEE 6节点仿真表明,在电力市场下,采用潮流优化与可中断负荷联合调度模型,可以有效缓解输电阻塞。     

Maclaurin–Newton algorithms in 132 kV subtransmission security simulations

This paper examines how applicable approximate Jacobian inversions are when implemented in the security analysis simulations of 132 kV power subtransmission. The complete Scottish 400/275/132 kV power transmission network was simulated, including the 132 kV subtransmission network with its high r/x ratios. Both the coupled and decoupled Maclaurin–Newton load flow algorithms were tested. It was proved that high r/x ratios found in the 132 kV level, five times higher than in 400/275 kV, have an important influence on convergence and accuracy of the inversion Jacobian load flow algorithms. It was found that the decoupled inversion load flow was applicable for 132 kV, it converged regularly, but had worse convergence and accuracy characteristics, compared to 400/275 kV applications, while the coupled inversion load flow was not applicable at all for 132 kV, it always diverged.     

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.     

Model of distribution system total supply capability considering feeder and substation transformer contingencies

This paper proposes a model for calculating the total supply capability (TSC) for distribution system considering both feeder and substation transformer contingencies. Existing models and methods for TSC only consider substation transformer contingencies and ignore feeder contingencies. However, the feeder contingencies occur much more frequently than substation transformer contingencies in practice. Moreover, some operation state fail the feeder contingencies N − 1 verification even they pass the transformer contingencies N − 1 verification. In this paper, a TSC model is firstly proposed in which feeder and transformer N − 1 contingencies are fully considered. This model is designed in feeder level, which means the topology of interconnection among feeders is accurately modeled. Secondly, a supplementary model for load balancing is set up for a better load distribution solution on feeders and transformers at TSC loading. Finally, the method is tested in a test distribution system and a real partial distribution network and the results are verified by the traditional N − 1 simulation.     

计及可中断负荷影响的阻塞管理定价模型研究

在电力市场环境下,利用可中断负荷参与阻塞管理能有效缓解阻塞和消除市场力,合理的定价是有效利用可中断负荷的关键.作者指出,利用负荷需求的弹性特点并将可中断负荷参与到阻塞管理机制中,通过市场供需关系确定电价可显著减轻阻塞.文中提出了一种定价模型,在此基础上给出了两种定价方法,即节点定价法和分摊定价法,并比较了两种定价方法的特点.最后对两种定价方法进行了仿真,并讨论了电价与负荷弹性的关系,算例结果说明,所提出的定价模型正确合理、简单、实用.     

多时段下计及可中断负荷的电网输电阻塞管理

将可中断电力合同引入多时段下的输电阻塞管理。首先分析了一种实际应用的可中断负荷期权合同,并结合这种合同在多时段条件下建立了输电阻塞管理模型;然后针对该模型利用遗传算法设计了一套多时段最优潮流求解程序;最后通过算例对传统阻塞模型和上述阻塞模型进行了比较。分析结果表明,本文提出的模型实现了可中断负荷在输电阻塞管理中的最优使用,且更有利于实现社会效益的最大化。     

Energy management strategy for fuel cell/battery/ultracapacitor hybrid vehicle based on fuzzy logic

In order to enhance the fuel economy of hybrid vehicle and increase the mileage of continuation of journey, a fuzzy logic control is utilized to design energy management strategies for fuel cell/battery (FC + B) hybrid vehicle and fuel cell/battery/ultra-capacitor (FC + B + UC) hybrid vehicle. The models of hybrid vehicle for FC + B and FC + B + UC structure are developed by electric vehicle simulation software ADVISOR which uses a hybrid backward/forward approach. The results demonstrate that the proposed control strategy can satisfy the power requirement for four standard driving cycles and achieve the power distribution among various power sources. The comprehensive comparisons with the power tracking control strategy which is wide adopted in ADVISOR verify that the proposed control strategy has better rationality and validity in terms of fuel economy and dynamic property in four standard driving cycles. Therefore, the proposed strategy will provide a novel approach for the advanced energy management system of hybrid vehicle.     

LMP机制下可中断负荷用于阻塞管理的最优调度方法

节点边际价格LMP（Locational Marginal Price）在解决交易的公平性和电网阻塞方面具有很大的优势,它从时间和空间两个层面反映电力系统的运行成本。可中断负荷作为需求侧管理的重要手段,可以有效地缓解阻塞。文中对发电出力再调度和可中断负荷量进行了均衡分析,提出了LMP机制下可中断负荷用于阻塞管理的最优调度原则。验证了可中断负荷在降低节点电价、增加社会效益以及解决阻塞方面的优势。文中采用IEEE30节点系统进行仿真,证明了该理论的正确性和合理性。     

计及电压水平的多目标可中断负荷阻塞管理

提出一种可中断负荷参与的阻塞管理多目标模型。以调整发电机出力和裁减负荷为手段,以电压水平、社会效益、可中断负荷量和中断负荷用户数这4种因素为阻塞管理目标,通过这些因素的归一化满意度评估函数来描述模型中的目标函数。结合模型的特点,提出以判断矩阵法为基础,将多目标优化问题转化为单目标问题,并利用遗传算法进行求解。IEEE30节点系统的仿真计算结果表明,所提出的多目标模型比传统模型更具优越性。     

Evaluation of voltage and current profiles and Joule losses for a half-wavelength power transmission line

Half-wavelength lines (HWLLs) have been studied as an option to be applied to power transmission regarding line lengths around 2500 km for a 60 Hz frequency. The main advantage of this type of transmission line, which has not yet been put in commercial operation in any country, is the elimination of reactive compensation, which contributes to cost reduction if compared to a conventional ac transmission. This paper presents a demonstration of voltage and current magnitude profiles along the line, using phasors and graphic calculations. In addition, an algebraic expression for Joule losses is proposed, to be used in economical evaluation of a HWLL solution.     

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.     

An adaptive approach for three zone operation of digital distance relay with Static Var Compensator using PMU

Modern energy transmission systems suffer from great voltage dropping due to enormous loads. Therefore appropriate schemes should be devised to regulate the voltage. FACTS devices such as Static Var Compensator are often used for this purpose. However, SVC at mid-point of transmission line may leads to deteriorate of distance relay operation, resulting in inaccurate estimation of faults locations i.e. over-reach or under reach for different cases. This paper proposed a new algorithm that utilizes synchronized phasors measurement (SPM) to enhance the operation of distance protection zone in many aspects. The proposed method is tested for 230 kV system simulated in EMTDC/PSCAD with Bergeron model of transmission line. The results prevailed for adaptive approach scheme are more accurate, victor and robust in equivalence with usable transmission line distance protection with SVC.     

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。