To study the torsional vibration characteristics of the doubly fed induction generator (DFIG)-based wind farm,a detailed small signal model for DFIG is established first.Then the small signal model and a simplified equivalent model for a wind farm composed of DFIGs are proposed.Modal analysis is employed to investigate the torsional vibration characteristics of a wind farm with several identical wind turbine generators (WTGs),whose accuracy is demonstrated through the time-domain simulation.The effect of torsional vibration propagation is found,indicating that the shaft torsional oscillation is not only decided by one wind turbine.Finally,the analysis and comparison between the traditional small signal model and the proposed equivalent model have been conducted.This equivalent model not only maintains the torsional vibration characteristics of the original small-signal model,but also reduces the computation complicity.

As large‐scale wind farms (WFs) are integrated with the power grid, the interaction between the WF and the grid may excite torsional vibration of the shaft of the wind turbine. To study the shaft's torsional vibration characteristics of a doubly fed induction generator (DFIG)‐based WF, a detailed small‐signal model of DFIG is established first. Then the small‐signal model for a WF composed of multiple DFIGs is developed on the basis of the single‐machine model. Modal analysis is employed to investigate the torsional vibration characteristics of a WF made up of several identical DFIGs, whose accuracy is also demonstrated through time‐domain simulation. To simplify the torsional vibration analysis for the DFIG‐based WF, a reduced‐order equivalent model is proposed. The results obtained from modal analysis show that the equivalent model not only precisely maintains all the torsional vibration modes of the original small‐signal model but also greatly reduces the computation complexity. With the equivalent model, the ‘curse of dimensionality’ problem is solved in torsional vibration analysis for large WFs, which is of great help in the design of further damping schemes. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Small signal stability of permanent magnet synchronous generator (PMSG)-based wind turbines connected to the power grid should be studied properly in order to facilitate damping strategy design. In this paper, unified small-signal models for different types of PMSGs are developed to study their small-signal stability. The models are composed of mechanical systems, electrical systems and control systems. A two-mass shaft model for the mechanical system is provided to analyze the dynamic and steady-state behaviors of the wind turbine and generator rotor. Meanwhile, PMSG, converter system and transmission line are separately modeled to build unified small-signal models for three PMSG-based wind turbine generator systems (WTGS). Then, based on unified small-signal models, eigenvalue analysis is conducted to determine the relation between different oscillation modes and state variables through calculating participation factors. With modal analysis, the developed small signal models are able to find out all types of oscillation modes for PMSGs connected to the power grid, which are subsynchronous oscillation (SSO), subsynchronous control interaction (SSCI) and low-frequency oscillation, including frequency and damping of each oscillation mode. Different initial values of the small signal models can influence both frequencies and damping ratios of oscillation modes, which lay basis for further damping strategy study.

The combined heat and power (CHP) systems can provide heat and electricity simultaneously. They are promising in the future energy landscape because of high efficiency and low emissions. This paper proposes a new operation optimization model of CHPs in deregulated energy markets. Both CHPs' overall efficiency and heat to electricity ratio are closely linked with the loading level, which are dynamically determined in this paper. A discrete optimization model is then proposed to determine the optimal real-time operation strategies for the CHPs. The optimization problem is solved by the interior point method with discrete time intervals, in which the discrete optimal operation points can be identified effectively. This step projects the potential operation strategies that could produce maximum benefits. Finally, a dynamic programming algorithm is developed to maximize the profits of CHPs through dynamically modifying the operation strategies projected in the previous step considering transient constraints. The proposed new methodology is demonstrated on a 1-MW CHP system with real-time data.

The harmonic/interharmonic emission principle of DFIG is derived theoretically and also verified through simulation and field measurements in this paper. To deal with sample data of variable-speed wind turbines accurately and get current spectrum including harmonic and interharmonic, a rotor speed based sliding window for harmonic analysis is proposed. the proposed method is applied to simulation results and field measurements to verify the effectiveness. Compared with spectral analysis using ELC61000-4-7, the frequency spectnim got from the proposed method is more complete.

Network-connected combined heat and powers (CHPs), owned by a community, can export surplus heat and electricity to corresponding heat and electric networks after community loads are satisfied. This paper proposes a new optimization model for network-connected CHP operation. Both CHPs' overall efficiency and heat to electricity ratio (HTER) are assumed to vary with loading levels. Based on different energy flow scenarios where heat and electricity are exported to the network from the community or imported, four profit models are established accordingly. They reflect the different relationships between CHP energy supply and community load demand across time. A discrete optimization model is then developed to maximize the profit for the community. The models are derived from the intervals determined by the daily operation modes of CHP and real-time buying and selling prices of heat, electricity and natural gas. By demonstrating the proposed models on a 1 MW network-connected CHP, results show that the community profits are maximized in energy markets. Thus, the proposed optimization approach can help customers to devise optimal CHP operating strategies for maximizing benefits.

Data from wind farm monitoring show that torsional vibration poses severe effect on service life of wind turbines (WTs). Torsional vibration mode of onefold wind farms containing the same WTs is remarkably different from that of single wind turbine. Hybrid wind farms containing different types of WTs are often built to realize WTs’ complementary operation, making torsional vibration more complex. Small signal models for fixed speed induction generator (FSIG), doubly fed induction generator (DFIG) and permanent magnet synchronous generators (PMSG) and three corresponding onefold wind farms were established. Also three kinds of hybrid wind farm models were proposed for DFIG-PMSG, FSIG-DFIG and FSIG-PMSG wind farms. Modal analysis and correlation factors were employed to investigate torsional vibration transfer effect among WTs. Finally, torsional vibration characteristics of onefold and hybrid wind farms were concluded.

停电事故后电力系统恢复过程主要包括网架修复和负荷恢复,合理的黑启动方案对加快电力系统的恢复有重要作用。当电网由于故障全停之后,孤岛运行的电动汽车充放储一体化电站作为电网中的一种分布式电源可以参与黑启动。介绍了一体化电站的结构和功率特性,分析了一体化电站作为黑启动电源与传统黑启动方式相比的优越性。基于黑启动的基本原理,建立了一体化电站满足潮流约束和系统安全约束的黑启动模型,制定了一体化电站参与黑启动的具体方案。将建立的模型应用于含有16座一体化电站的区域电网,采用遍历算法对问题进行求解,得到了区域电网的恢复过程,验证了所提出一体化电站黑启动方案的可行性。

根据一体化电站信息流分布情况,通过监控系统对一体化电站及车载终端的详细参数进行采集。利用物联网(IOT)和GPS技术,可对一体化电站内外电池工作状态进行状态监控和故障处理。对一体化电站与电网之间的交换功率和一体化电站的能量水平进行分析及融合。根据上述融合信息,结合一体化电站和电网运行信息,提出一种新型的并网控制策略。实际算例表明,基于信息融合技术的并网控制策略对一体化电站和电网的正常运行有着积极作用。

This paper develops a discrete operation optimization model for combined heat and powers (CHPs) in deregulated energy markets to maximize owners’ profits, where energy price forecasting is included. First, a single input and multi-output (SIMO) model for typical CHPs is established, considering the varying ratio between heat and electricity outputs at different loading levels. Then, the energy prices are forecasted with a gray forecasting model and revised in real-time based on the actual prices by using the least squares method. At last, a discrete optimization model and corresponding dynamic programming algorithm are developed to design the optimal operation strategies for CHPs in real-time. Based on the forecasted prices, the potential operating strategy which may produce the maximum profits is pre-developed. Dynamic modification is then conducted to adjust the pre-developed operating strategy after the actual prices are known. The proposed method is implemented on a 1 MW CHP on a typical day. Results show the optimized profits comply well with those derived from real-time prices after considering dynamic modification process.

The number of wind farms is increasing worldwide and capacity of variable-speed wind turbines has been increased significantly. This has raised wide concern over the power quality, especially harmonic current emissions of variable speed wind turbines. However, the current IEC standard does not have corresponding coping methods, including measurement and analysis. This paper implements a model of doubly fed induction generator (DFIG) whose rotor speed is variable. The origin of harmonics generated by DFIG is derived theoretically and also verified through simulation. To deal with sample data of variable-speed wind turbines accurately and get current spectrum including harmonic and interharmonic, a time-varying window for harmonic analysis is proposed. Compared with results based on IEC61000-4-7, the results of the proposed method is more complete.

Because of the large scale wind farms occupied a larger area,and containing a large number of wind turbines,wake effects and wind delay among wind turbines have a certain impact on wind farms.Based on Weibull distribution function,the stochastic wind model and wind turbine mathematical model of wind farm were established in this paper.The small signal stability model of wind farm was created,and the complex wind farms operation was comprehensively analyzed.The linear-distribution and cross-distribution of three fan system were simulated,and the changing of eigen-values under different distribution methods was analyzed.It was found out that wake effects and the time-delay have little influence to small signal stability.The stability margin of wind farms via reasonable distribution of fans can thus be increased.

With electric power network getting larger and more complex, it is unprecedented vulnerable and modern society is faced with higher blackout risk The stable and reliable operation of a power system is necessary after major emergencies (or blackouts) following a major system event. The intelligent integrated station (IIS), providing energy and changing batteries for EVs, has the ability to separate and isolate itself from the power grid seamlessly with little or no disruption to loads in the station. Then, when the utility grid returns to normal, the IIS resynchronizes and reconnects itself to the grid in an equally seamless manner. According to conventional system restoration after a black-out, the control principles of black-start for intelligent integrated station are put forward. The build-up strategy is used to restore power system with IIS, which includes the process of restoring separated parts (islands) in the power system and interconnecting them afterwards. The control of IIS with energy storage system will deal with building isolated network, forming and operating island, and connecting island and re-synchronization with upstream network or grid system. A model based on the black-start principle proposed above is developed and the model is applied in a regional power grid.

After a blackout, power needs to be restored as quickly and reliably as possible to reduce economic loss, and consequently, detailed restoration plans are necessary. According to the basic black-start method, the control principles of black-start for intelligent integrated station (IIS) are put forward. To speed up the restoration process, the whole system containing intelligent integrated stations is partitioned into several subsystems which are restored in parallel. These independent subsystems will later be synchronized to restore the original power system seamlessly through virtual connection control. A model based on the black-start principle proposed above is developed. At last, a regional power system containing 16 intelligent integrated stations is employed as an example to verify the validity of the proposed approach.