基于灵敏度计算的发电机无功资源价值分析

无功对电力系统的经济、安全和可靠运行具有重要的作用,因此必须对无功的成本和价值进行分析,才能科学解决无功定价问题。鉴于有大量的文献对无功生产成本做了分析,该文从系统侧阐述了不同节点发电机发出或吸收的无功对系统电压和网损的影响,从而提出了基于网损灵敏度和无功灵敏度的分析方法,合理地说明了发电机无功对系统价值,并以算例进行说明。     

Impact of FACTS controllers on the stability of power systems connected with doubly fed induction generators

The increasing power demand has led to the growth of new technologies that play an integral role in shaping the future energy market. Keeping in view of the environmental constraints, grid connected wind turbines are promising in increasing system reliability. This paper presents the impact of FACTS controllers on the stability of power systems connected with wind energy conversion systems. The wind generator model considered is a variable speed doubly fed induction generator model. The stability assessment is made first for a three phase short circuit without FACTS controllers in the power network and then with the FACTS controllers. The dynamic simulation results yield information on (i) the impact of faults on the performance of induction generators/wind turbines, (ii) transient rating of the FACTS controllers for enhancement of rotor speed stability of induction generators and angle stability of synchronous generators. EUROSTAG is used for executing the dynamic simulations.     

A unified approach for the solution of power flows in electric power systems including wind farms

This paper proposes a solution approach of the power flow problem to assess the steady-state condition of power systems with wind farms in a single frame of reference, in which the state variables of the wind generators are combined with the nodal voltage magnitudes and angles of the entire network for a unified iterative solution through the Newton-Raphson method. Different wind energy conversion systems (WECS) are mathematically derived from the steady-state representation of the induction generator. Suitable strategies for initializing the state variables of the wind generators are also proposed in this paper. Lastly, three numerical examples are presented to numerically illustrate the applicability of the proposed approach.     

金风S50／750型风力发电机组的失速特性分析

根据定浆距风力发电机的设计特点和能量传榆特性及机组在不同空气密度及风速下的运行状况。分析机组的失速特性及有效失速保护,并通过改变桨距角来调整叶轮的能量捕获,改善风力发电机组失速性能,使机组运行在可靠的安全范围之内。     

Modeling real-time balancing power demands in wind power systems using stochastic differential equations

The inclusion of wind power into power systems has a significant impact on the demand for real-time balancing power due to the stochastic nature of wind power production. The overall aim of this paper is to present probabilistic models of the impact of large-scale integration of wind power on the continuous demand in MW for real-time balancing power. This is important not only for system operators, but also for producers and consumers since they in most systems through various market solutions provide balancing power.     

Reliability sensitivity of wind power system considering correlation of forecast errors based on multivariate NSTPNT method

The impact of wind power forecast errors (WPFEs) on power system reliability can be quantified by a sensitivity model, which helps to determine the importance of different wind farms. However, the unknown distribution and correlation of WPFEs make it difficult to calculate the reliability sensitivity. The existing univariate non-standard third-order polynomial normal transformation (NSTPNT) expresses the reliability sensitivity of WPFEs by a normal random variable with explicit distribution, and is not suitable for multiple wind farms with correlated forecast errors. In this paper, the univariate NSTPNT method is extended to the multivariate by deriving the analytical expression of the correlation coefficients before and after the transformation, to establish the transformation between the WPFEs and a normal random vector (RV) with the specific correlation. A reliability sensitivity model to the WPFEs expressed to the normal RV is then proposed. The numerical results validate the accuracy of the proposed multivariate NSTP NT and the sensitivity model. The maximum relative error for using the sensitivity to approximate the change of reliability with distribution parameters of the WPFEs is less than 2.42%. The necessity of considering the correlation of WPFEs is analyzed. The maximum relative error of the sensitivity reaches 83% when the correlation is ignored.     

Small signal stability enhancement of DFIG based wind power system using optimized controllers parameters

This paper presents the state space modelling of doubly fed induction generator (DFIG) for small signal stability assessment. The gains of PI controller in torque and voltage control loop of rotor-side converter (RSC) are optimized by particle swarm optimization (PSO) to improve the dynamic performance of DFIG. These optimized parameters results in improved damping of DFIG and minimizes the oscillations in rotor currents and electromagnetic torque. The nature of modes of oscillations for DFIG integrated to infinite bus are analysed under different operating conditions such as varying wind speed and grid strength. The transient analysis with optimized parameters shows the enhancement in LVRT capability during voltage sag and three phase fault as desired by grid codes.     

Wind Parks equivalent ARX models for the simulation of power systems with large wind power penetration, using system-identification theory

In this paper models of Wind Parks (WPs) appropriate for simulation purposes of large power systems with high wind power penetration are developed. The proposed models of the WPs are developed using system identification theory. Data obtained from the simulation of detailed WP models are used for system identification. The obtained models are general and they can be applied to different configurations of WPs as only system's input/output data are used and not any internal states of the model. Simulation results confirm the accuracy and the advantages of the proposed WP equivalent models.     

A meteorological information mining-based wind speed model for adequacy assessment of power systems with wind power

Accurate wind speed simulation is an essential prerequisite to analyze the power systems with wind power. A wind speed model considering meteorological conditions and seasonal variations is proposed in this paper. Firstly, using the path analysis method, the influence weights of meteorological factors are calculated. Secondly, the meteorological data are classified into several states using an improved Fuzzy C-means (FCM) algorithm. Then the Markov chain is used to model the chronological characteristics of meteorological states and wind speed. The proposed model was proved to be more accurate in capturing the characteristics of probability distribution, auto-correlation and seasonal variations of wind speed compared with the traditional Markov chain Monte Carlo (MCMC) and autoregressive moving average (ARMA) model. Furthermore, the proposed model was applied to adequacy assessment of generation systems with wind power. The assessment results of the modified IEEE-RTS79 and IEEE-RTS96 demonstrated the effectiveness and accuracy of the proposed model.     

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.     

Optimal reactive power control of DGs for voltage regulation of MV distribution systems using sensitivity analysis method and PSO algorithm

This paper addresses the problem of reactive power control of distributed generation (DG) units in the medium voltage (MV) distribution systems to maintain the system voltages within the predefined limits. An efficient approach for the load flow calculation is used here which is based on the topological structure of the network. It has been formulated for the radial distribution systems. A direct voltage sensitivity analysis method is developed in this paper which is also based on the topological structure of the network and independent of the network operating points. Thus, the sensitivity matrix is calculated once with the load flow program and it is used in all the system working conditions. The problem of DGs reactive power control is formulated as an optimization problem which uses the sensitivity analysis for linearizing the system around its operating points. The objective of the optimization problem is to return the system voltages inside the permitted range by using the reactive power of DGs in an optimal way. The optimal solutions are obtained by implementing particle swarm optimization (PSO) algorithm. Then, the results are verified by running a load flow considering new values of DGs reactive power. The procedure is repeated as long as a voltage violation is observed. Simulation results reveal that the proposed algorithm is capable of keeping the system voltages within the permitted limits.     

用神经网络对风力发电中电力电子故障分析

随着风能资源的利用水平不断提高,风力发电系统中的电力电子装置使用也越来越多,其工作可靠性要求也越来越高。风力发电装置多位于野外,为减轻检修人员的工作负担,对风机运行中远方检测到的大量数据进行快速而有效的可视化分类及故障状态粗略判断,引入了一种用单层前向神经网络来对数据进行快速分类绘制故障非故障分界线的方法。通过该方法能够很好地根据实时数据判断风机电力电子装置的故障。     

Reactive power control of wind farm made up with doubly fed induction generators in distribution system

In recent years, the number of small size wind farm made up with doubly fed induction generators (DFIG) located within the distribution system is rapidly increasing. DFIG can be utilized as the continuous reactive power source to support system voltage control by taking advantage of their reactive power control capability. In this paper, considering both reactive power control and distribution network reconfiguration can be used to reduce power losses and improve voltage profile, a joint optimization algorithm of combining reactive power control of wind farm and network reconfiguration is proposed to obtain the optimal reactive power output of wind farm and network structure simultaneously. The proposed algorithm has been successfully implemented on the 16 bus distribution network and the results obtained demonstrate the efficiency of the algorithm.     

地区电网采用高效变压器的节电潜力分析

对配电变压器的运行损耗进行了深入的分析,并根据3种变压器损耗算法建立了3种节电潜力评估模型。以广东电网公司某供电局的电网侧和该地区的用户侧配电变压器为例,分析了该地区电网更换低压配电变压器的节电潜力,结果表明,该地区电网低压配电变压器节电潜力巨大,若进行更换,可获得可观的效益。     

Impact of hybrid wind and hydroelectric power generation on the operational performance of isolated power systems

In recent years, electric power systems are adopting new technologies in their structure in order to achieve better performance and efficiency in the electricity production, transmission and distribution. This fact together with additional financial incentives being developed in many countries have increased considerably the number of power generating units using renewable energy sources. However, a major drawback of these units is their dependency on unexpected weather conditions such as the wind speed and the rainfalls in the respective hydrologic areas. The purpose of this paper is to investigate the impact of wind parks and hydroelectric power plants on the reliability and operational performance of isolated power systems. A probabilistic methodology has been developed for simulating more efficiently and realistically the reliability and operational performance of these power systems. This is an effective computational methodology that is based on the Monte-Carlo sequential simulation approach and it evaluates the reliability and operational indices of the conventional thermal and hydroelectric power plants, the wind parks and the overall indices of the system. An appropriate model based on the power system of a Greek island is used and the obtained results are presented for a number of case studies representing various planning and operating schemes in order to deduce the optimal one.     

Output power leveling of wind turbine generators using pitch angle control for all operating regions in wind farm

Effective utilization of renewable energies such as wind energy instead of fossil fuels is desirable. Wind energy is not constant and windmill output is proportional to the cube of the wind speed, which causes the generated power of wind turbine generators (WTGs) to fluctuate. In order to reduce the output power fluctuation of wind farms, this paper presents an output power leveling control strategy for a wind farm based on both the average wind farm output power and the standard deviation of the wind farm output power, a cooperative control strategy for WTGs, and pitch angle control using a generalized predictive controller (GPC) in all WTG operating regions. Simulation results using an actual detailed model for wind farm systems show the effectiveness of the proposed method. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 31– 41, 2007; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20448     

Improvement of transient stability of power systems with STATCOM-controller using trajectory sensitivity

This paper discusses the use of trajectory sensitivity analysis (TSA) in determining the transient stability margin of a power system compensated by a shunt FACTS device. The shunt device used is static synchronous compensator (STATCOM). It is shown that TSA can be used for the design of controller for the STATCOM. The preferable locations for the placement of the STATCOM for different fault conditions are also identified. The effects of STATCOM in maintaining different bus voltages in the post-fault condition are studied. The STATCOM is modeled by a voltage source connected to the system through a transformer. The systems used for the study are the WSCC 3-machine 9-bus system and the IEEE 16-machine 68-bus system.     

电力变压器绕组电气参数对绕组变形的全局灵敏度分析

目前已有利用变压器绕组电气参数检测绕组变形的方法,但对电气参数变化与绕组变形之间的联系的研究还不够深入。为此,提出一种分析绕组电气参数对不同种类变形的全局灵敏度方法。该方法首先采用响应面法,建立显式化的绕组电感电容参数响应面模型。然后基于蒙特卡罗的Sobol’全局灵敏度分析法计算各电气参数对不同变形种类的全局灵敏度,分析各电气参数反映不同类型绕组变形的灵敏度。进一步分析其变异系数,以比较不同电气参数针对同一类型绕组形变的灵敏度。以某型号变压器为例进行了分析,分析结果表明利用本方法可以揭示各电气参数与绕组变形种类的内在联系。依据结果可将灵敏度较高的参数信息引入变形判据,为基于电气参数的绕组变形检测提供了理论基础和新的思路。     

Day-ahead price forecasting in restructured power systems using artificial neural networks

Over the past 15 years most electricity supply companies around the world have been restructured from monopoly utilities to deregulated competitive electricity markets. Market participants in the restructured electricity markets find short-term electricity price forecasting (STPF) crucial in formulating their risk management strategies. They need to know future electricity prices as their profitability depends on them. This research project classifies and compares different techniques of electricity price forecasting in the literature and selects artificial neural networks (ANN) as a suitable method for price forecasting. To perform this task, market knowledge should be used to optimize the selection of input data for an electricity price forecasting tool. Then sensitivity analysis is used in this research to aid in the selection of the optimum inputs of the ANN and fuzzy c-mean (FCM) algorithm is used for daily load pattern clustering. Finally, ANN with a modified Levenberg–Marquardt (LM) learning algorithm are implemented for forecasting prices in Pennsylvania–New Jersey–Maryland (PJM) market. The forecasting results were compared with the previous works and showed that the results are reasonable and accurate.     

考虑负荷容量的改进型二阶灵敏度分析SV系数在城乡配电网无功选址中应用

在考虑负荷容量的前提下,针对灵敏度优选补偿集合存在的四个问题,在二阶无功灵敏度分析的基础上进一步探讨二阶无功灵敏度对线路总网损的影响,并通过极限与微分的公式推导得出了当二阶无功灵敏度与线路负荷相乘可以作为二阶无功灵敏度选址的依据,将其定义为SV系数,选取SV系数较大的节点作为无功补偿节点,并通过改进粒子群算法加以定容验证,以PGE69节点进行验证实验,验证了该方法的可行性和可靠性。