计及风电场的发输配电系统可靠性评估

考虑风速时序性和自相关性的特点,建立了风速的自回归移动平均(auto-regressive and moving average,ARMA)模型,并结合常规机组、线路和变压器等状态模型,建立了基于蒙特卡罗仿真方法的风电场可靠性模型,对含风电场的发输电组合系统进行可靠性评估,同时建立了发输电组合系统的多状态机组等值模型,将该等值模型与配电系统相结合,计算了平均停电频率和停电电量损失等配电网可靠性指标,通过分析和比较可靠性指标研究了风电场对配电系统可靠性的影响,结果表明风电机组的接入对提高电力系统可靠性具有一定的作用。     

A novel method for maintenance scheduling of generating units considering the demand side

This paper proposes a novel competitive mechanism for maintenance scheduling of generating units in the deregulated environment. In restructured power systems, the objective function of power producers is to maximize their benefits, and the aim of the Independent System Operator (ISO) is to increase the reliability throughout the year as much as possible. Therefore, there are two objective functions for finding an optimal maintenance schedule in the deregulated environment. The main contribution of this paper is considering the condition of demand side in the maintenance scheduling of generating units. In this scheme, authority of the maintenance scheduling has been granted to the ISO. The proposed method schedules the outage windows of generating units to attain maximum producers’ benefits and maximum annual social welfare. This method is tested in a bilateral energy market, and the IEEE-RTS system is used to demonstrate the effectiveness of the proposed method.     

Nodal price volatility reduction and reliability enhancement of restructured power systems considering demand–price elasticity

With the development of restructured power systems, the conventional “same for all customers” electricity price is getting replaced by nodal prices. Electricity prices will fluctuate with time and nodes. In restructured power systems, electricity demands will interact mutually with prices. Customers may shift some of their electricity consumption from time slots of high electricity prices to those of low electricity prices if there is a commensurate price incentive. The demand side load shift will influence nodal prices in return. This interaction between demand and price can be depicted using demand–price elasticity. This paper proposes an evaluation technique incorporating the impact of the demand–price elasticity on nodal prices, system reliability and nodal reliabilities of restructured power systems. In this technique, demand and price correlations are represented using the demand–price elasticity matrix which consists of self/cross-elasticity coefficients. Nodal prices are determined using optimal power flow (OPF). The OPF and customer damage functions (CDFs) are combined in the proposed reliability evaluation technique to assess the reliability enhancement of restructured power systems considering demand–price elasticity. The IEEE reliability test system (RTS) is simulated to illustrate the developed techniques. The simulation results show that demand–price elasticity reduces the nodal price volatility and improves both the system reliability and nodal reliabilities of restructured power systems. Demand–price elasticity can therefore be utilized as a possible efficient tool to reduce price volatility and to enhance the reliability of restructured power systems.     

Reliability and price risk assessment of a restructured power system with hybrid market structure

In a restructured power system with hybrid market structure, generation companies and customers trade electricity and reserve either through a centralized power pool or by bilateral contracts based on their price and reliability offers and requirements. This results in difficulty in price and reliability management of such power systems. This paper presents techniques to evaluate both reliabilities and prices for the pool and bilateral customers in a hybrid power market. In these techniques, reliability and price models for the power pool and bilateral suppliers have been developed using reliability network equivalents to easily include various agreements among market participants. Customer responses to prices are modeled using customer damage functions. The reliability and price problems with and without considering agreements are formulated using improved optimal power flow techniques based on these models. The correlation between reliabilities and prices has been considered in the techniques. The modified IEEE Reliability Test System has been analyzed to illustrate the proposed techniques.     

含光伏发电的电力系统随机生产模拟

光伏发电规模越来越大,其并网对系统的影响不容忽视,研究含光伏发电的电力系统随机生产模拟具有重要意义。在空间上以一个光伏逆变器组为单位,建立了考虑光照与元件故障双重因素的光伏逆变器组多状态模型。在时间上以一天为一个时段,各时段采用不同的多状态模型。将多状态模型加入随机生产模拟,采用等效电量函数法进行计算,得到了发电量、可靠性及经济性等指标。评估了光伏发电容量效益和电量效益。算例分析验证了本文所提方法的合理性。     

The impact of random failures on nodal price and nodal reliability in restructured power systems

Power system deregulation provides customers choices on electricity regarding price and reliability. This paper investigates the impact of random failures on the nodal price and the nodal reliability in a restructured power system. The expected nodal price and the associated standard deviation are introduced to incorporate the effect of random failures on the nodal price. Nodal reliability indices rather than conventional reliability indices used in vertically-integrated power systems are used in this paper to represent customer load point reliability in a restructured power market. A probabilistic technique, which combines the reliability assessment approach and the optimal power flow (OPF) method, is developed to determine the expected nodal price and the associated expected nodal risk. The price fluctuation and the corresponding probability for each system state are also presented. The relationship between the nodal price and nodal reliability are also investigated and discussed in this paper.     

Evaluation of electric power procurement strategies by stochastic dynamic programming

In deregulated electricity markets, the role of a distribution company is to purchase electricity from the wholesale electricity market at randomly fluctuating prices and to provide it to its customers at a given fixed price. Therefore, the company has to take risk stemming from the uncertainties of electricity prices and/or demand fluctuation instead of the customers. The way to avoid the risk is to make a bilateral contract with generating companies or install its own power generation facility. This entails the necessity to develop a certain method to make an optimal strategy for electric power procurement. In such a circumstance, this research proposes a mathematical method based on stochastic dynamic programming and considers the characteristics of the start‐up cost of an electric power generation facility to evaluate strategies of combination of the bilateral contract and power auto‐generation with its own facility for procuring electric power in a deregulated electricity market. In the beginning we proposed two approaches to solve the stochastic dynamic programming, and they are a Monte Carlo simulation method and a finite difference method to derive the solution of a partial differential equation of the total procurement cost of electric power. Finally we discussed the influences of the prime uncertainty on optimal strategies of power procurement. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(2): 20–29, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20296     

电力系统元件可靠性基础数据统计分析

采用国际通用方法,对中国电力企业联合会可靠性管理中心所发布的电力系统元件可靠性统计数据进行了统计与分析,给出了中国电力系统元件2001～2005年的平均可靠性指标(包括发电机组、输变电设备、直流输电系统、直流系统主要可靠性指标)以及6个在运直流系统的平均可靠性指标;并针对交直流互联系统可靠性评估的特殊性,对我国当前直流系统可靠性数据的统计内容和方法中存在的一些不足进行了探讨.     

计及中长期合同电量分解和风电不确定性的电-气综合能源系统日前优化调度

将中长期合同电量分解模型引入电-气综合能源系统日前调度决策过程中,实现了合同电量分解和调度计划制定的嵌套优化。针对合同电量分解结果可能在实际调度计划中不可执行的情况,提出了一种基于拉格朗日乘子的机组日分解电量越限因素定位方法,并通过中长期合同电量分解模型与日前调度模型的协调迭代消除越限电量,保证了中长期交易的有效性。此外,在模型中考虑了天然气网络约束和风电随机性对中长期交易计划的影响,并利用机会约束规划理论构建含风电不确定性的优化调度随机模型。基于风电等效随机输出样本矩阵和随机模拟技术实现机会约束向确定性表达式转化。通过仿真算例验证了所提方法的有效性。     

Cascade controller based modeling of a four area thermal: gas AGC system with dependency of wind turbine generator and PEVs under restructured environment

This paper investigates automatic generation control (AGC) of a realistic hybrid four-control area system with a distinct arrangement of thermal units, gas units and additional power generation. A proportional-integral-double derivative cascaded with proportional-integral (PIDD-PI) controller is employed as secondary controller in each control area for robust restructured AGC considering bilateral transactions and contract violations. The Harris Hawks algorithm is used to determine the optimal controller gains and system parameters under several scenarios. Electric vehicle (EV) aggregators are employed in each area to participate fully along with thermal and gas units to compensate for the unscheduled system demand in the local area. A comparison of non-cascaded controllers such as PI-PD, PD-PID and the proposed PIDD-PI proves the superiority of the last. The effect of the decline in inertia is closely examined because of the sudden outage of a generating unit while at the same time considering the change in area frequency response characteristics and area control error. EV fleets make significant contributions to improving the system dynamics during system inertia loss. The use of EVs in the presence of a wind energy-supported grid can provide a stable efficacy to the power grid. Numerous simulations with higher load demands, stochastic communication delays in presence of the WTG plant, and violations in system loadings and changes in gas turbine time constants in the absence of WTG demonstrate the robustness of the proposed control approach.     

Reliability assessment of restructured power systems using reliability network equivalent and pseudo-sequential simulation techniques

This paper presents a technique to evaluate reliability of a restructured power system with a bilateral market. The proposed technique is based on the combination of the reliability network equivalent and pseudo-sequential simulation approaches. The reliability network equivalent techniques have been implemented in the Monte Carlo simulation procedure to reduce the computational burden of the analysis. Pseudo-sequential simulation has been used to increase the computational efficiency of the non-sequential simulation method and to model the chronological aspects of market trading and system operation. Multi-state Markov models for generation and transmission systems are proposed and implemented in the simulation. A new load shedding scheme is proposed during generation inadequacy and network congestion to minimize the load curtailment. The IEEE reliability test system (RTS) is used to illustrate the technique.     

Fuzzy logic-based direct load control of air conditioning loads considering nodal reliability characteristics in restructured power systems

A fuzzy logic-based direct load control (DLC) scheme of large air conditioning loads (ACL), which considers the reliability characteristics of nodes where the ACL are connected, is proposed for restructured power systems. Transmission system reliability is integrated into the determination procedure of the DLC scheme of ACL using nodal reliability indices. Fuzzy dynamic programming (FDP) is utilized to determine the optimal DLC scheme of ACL which can achieve a good tradeoff among peak load shaving, system operating cost reduction and system reliability improvement. The IEEE reliability test system (RTS) is used to illustrate the proposed technique.     

热电联产系统的随机生产模拟

随机生产模拟是电力市场中进行电价预测和发电管理的有力工具,但传统的随机生产模拟方法对于热电联产系统并不适用。文中对传统的随机生产模拟和目前的联产系统的生产模拟进行了改进,提出了一套针对热电联产进行随机生产模拟的新方法。对机组模型、热电联合等效概率密度函数进行简要介绍,给出了运行指标、系统可靠性指标的计算方法,以及处理机组最小技术出力即机组分段运行情况的方法和如何确定机组带负荷顺序的方法。最后通过一个算例对上述方法进行了验证。     

Development of an analytical model for generation expansion planning as a tool to provide guidelines for preventing instability in the long‐term electricity market

This paper considers the problem of deciding multiperiod investments for generation expansion planning (GEP) in restructured power systems. This problem has presented a challenge for both market managers and suppliers regarding the stability in the electricity market and minimum income for suppliers over the planning period. In this paper, an analytical model for studying the GEP problem from the viewpoint of a central management entity is presented. The aim of this method is to establish a dynamic balance between energy supply and demand by adjustment of GEP over the horizon of planning so that not only the expected profit is provided for all new generating plants but the long‐term stability in the electricity market is also improved. This analytical model can be utilized by regulatory bodies to obtain some guidelines and thereby to set their policies for improving GEP and preventing instability in the long‐term electricity market. To do so, in this study, the uncertainties of demand and supply have been modeled through two stochastic processes. Furthermore, the market price dynamics and their mutual effects on the GEP's results have been considered. Finally, this nonlinear dynamic optimization problem is solved using a modified genetic algorithm (GA). The efficiency and ability of the proposed method are examined on a test power system. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Service-oriented architectural model for generating system adequacy evaluation

A service-oriented architectural (SOA) model is proposed for power system reliability analysis especially for generating capacity adequacy evaluation. Generating system adequacy evaluation is performed to evaluate the ability of the system generating capacity to meet the total system demand. The proposed SOA model is composed of generation system reliability (GSR) service provider, power system service registry and service requester. The data pertaining to power system reliability analysis are represented in extensible markup language (XML) for exchanging the reliability data among the users and service providers. The GSR service provider describes the reliability evaluation services and publishes them to the power system service registry. The calling sequences of reliability evaluation services along with required data are configured as SOAP (Simple Object Access Protocol) messages and the proposed SOA model communicates between the service provider and the service requester with formally defined messages. The proposed model for generating system reliability analysis is highly distributed and has inherent features such as scalability and flexibility and provides a loosely coupled environment for power system reliability analysis.     

考虑可控负荷功率调整的电力服务商分段式补偿定价决策

鉴于分布式电源出力和终端用户负荷需求的随机性,电力服务商实际购买电量与电力市场竞标电量存在偏差,这种偏差会带来惩罚成本。为此,考虑将需求侧可控负荷作为可调度资源,基于可控负荷用户增/减负荷成本函数,提出了一种分段式价格形式的多选项可控负荷功率调整补偿合同。为实现电力服务商与可控负荷用户双赢,建立了兼顾电力服务商经济效益和可控负荷用户需求响应效益的 型stackelberg主从博弈模型,并采用基于遗传算法的逆向归纳法求解。最后,通过算例对比了分段式补偿电价和固定补偿电价下电力服务商运营收益和可控负荷用户功率调整量之间的变化情况。仿真结果表明,所提出的分段式补偿定价方法能够明显降低惩罚成本,有效提高用户需求响应的参与度,实现需求响应资源的优化配置。     

Distributed generation modeling for power flow studies and a three-phase unbalanced power flow solution for radial distribution systems considering distributed generation

Distributed generations (DGs) are generally modeled as PV or PQ nodes in power flow studies (PFSs) for distribution system. Determining a suitable model for each DG unit requires knowing the DG operation and the type of its connection to the grid (direct or indirect). In this respect, this paper offers a helpful list of DG models for PFSs. Moreover, an unbalanced three-phase power flow algorithm for radial distribution networks considering DG is presented based on the power summation method in backward/forward sweep technique. The proposed algorithm is simple and fast and can handle DG units in both PV and PQ mode. In comparison with the current analysis methods, handling of PV nodes in the proposed method is very simple since it uses active and reactive powers as flow variables rather than the complex currents and then checks the limits of reactive power of the generator of PV node straightforwardly. IEEE four-node test feeder is used to validate the proposed method. IEEE 13-node test feeder without regulator and with different DG models is analyzed and the results are presented. Moreover, the results are compared with and without considering system losses.     

Reliability evaluation of electrical power systems including multi-state considerations

A new approach is introduced for calculating the electrical network reliability indices, such as multi-state stationary availability, expected multi-state capacity, expected unsupplied demand, loss of load probability and total failed system probability. The universal moment generating function approach (UMGF) is used to evaluate the different reliability indices of the power system. In this paper we present a survey of recent work which treats the more sophisticated and realistic models in which components and systems may comprise many states ranging from perfect-working to complete failure. Such systems are multi-state (MSS) as they can have different levels of output performance. The objective is to determine the power structure which minimizes costs and satisfies reliability levels. A computer program has been developed to implement the UMGF technique, and an illustrative example is presented.     

New secure bilateral transaction determination and study of pattern under contingencies and UPFC in competitive hybrid electricity markets

In the competitive electricity environment, the flexibility of power transactions is expected to drastically increase among the trading partners and can compromise the system security and reliability. These transactions are to be evaluated ahead of their scheduling in a day-ahead and hour-ahead market to avoid congestion and ensure their feasibility with respect to the system operating conditions. The security of the transactions has become essential in the new environment for better planning and management of competitive electricity markets. This paper proposes a new method of secure bilateral transaction determination using AC distribution factors based on the full Jacobian sensitivity and considering the impact of slack bus for pool and bilateral coordinated markets. The secure bilateral transactions have also been determined considering critical line outage contingencies cases. The bilateral transaction matrix pattern has also been determined in the presence of unified power flow controller (UPFC). The optimal location of UPFC has been determined using mixed integer non-linear programming approach. The proposed technique has been applied on IEEE 24-bus reliability test system (RTS).     

Hybrid Fault Diagnosis Scheme Implementation for Power Distribution Systems Automation

Power distribution automation and control are important tools in the current restructured electricity markets. Unfortunately, due to its stochastic nature, distribution systems faults are hardly avoidable. This paper proposes a novel fault diagnosis scheme for power distribution systems, composed by three different processes: fault detection and classification, fault location, and fault section determination. The fault detection and classification technique is wavelet based. The fault-location technique is impedance based and uses local voltage and current fundamental phasors. The fault section determination method is artificial neural network based and uses the local current and voltage signals to estimate the faulted section. The proposed hybrid scheme was validated through Alternate Transient Program/Electromagnetic Transients Program simulations and was implemented as embedded software. It is currently used as a fault diagnosis tool in a Southern Brazilian power distribution company.