Advanced Materials Research Vols. 1070-1072

Abstract: The exiting of wind turbines will cause the adverse effect on the power grid and its assembling unit in network voltage drops. So, direct-drive wind power generation system should meet the requirement of the certain ability of low voltage. This paper introduces the influence of wind power system with different structure by voltage drop as well as the disadvantage and advantage on LVRT. The relate regulations based on LVRT are analyzed. The existing LVRT technologies of direct-drive wind power systems are briefly presented. The characteristics of each scheme from the different LVRT technology are analyzed. Moreover, further study of LVRT for PMSG is pointed out.

Abstract: To analysis the low voltage ride through tests results carried out in Inner Mongolia, the impedance model of low voltage ride through test equipment ability with the wind turbine is established. The grid current variation caused by series or parallel impedance switching is analyzed theoretically. Results show that grid current will become larger while the parallel impedance of low voltage test equipment is smaller. Consequently, suggestion is proposed to take optimal configuration of impedance in the equipment to reduce effect on grid current, which can ensure the smooth running of low voltage ride through test.

Abstract: The influence of power fluctuation from wind power clusters on power system is more and more significant. In order to describe this influence, a key variable set which can perfectly reflect dynamic characteristics of power system under wind power fluctuation is determined based on a pratical power system. Then, drift characteristics of the key variables under typical power fluctuation of wind power cluster are analyzed. The comparison of the drift characteristics between the key variables and the non-key variables verifies the feasibility and validity of the method.

Abstract: Current control strategy of reactive power and voltage for wind power integration is separate control of single wind farm (WF), which cannot achieve the optimal allocation of reactive power and is not beneficial for the optimization of voltage stability and network loss. In this paper, a coordinated control strategy of reactive power and voltage for wind farm cluster is proposed, which takes the voltage stability at point of common coupling (PCC) and economic operation as the optimization goals. The coordinated control strategy is realized through the platform of Cybercontrol industrial configuration, and the application testing verifies the effectiveness of the proposed strategy.

Abstract: With many grid-connected wind farms of Doubly-fed Induction Generator (DFIG) type taking the palce of conventional synchronous generators, the frequency control ability of the system will decrease. But the existing control strategy based on maximum wind power tracking of DFIG can not response to the deviation of the system frequency. This paper proposes a new hybrid frequency control strategy based on the research of the frequency response to the doubly fed induction wind turbine curves switching inertia control loop and the ability for the pitch angle control participating in the system primary frequency modulation. The strategy reduces the initial rate of change and the steady state error of system frequency with the combined action of the curves switching inertial control and pitch frequency control. Finally, the simulation results of the two areas with four generators validate the effectiveness of the strategy.

Abstract: Accurate model of the wind farm is the basis for the analysis of wind power integrating grid. This paper proposed the equivalent P-v(active power-wind speed) model with K-means algorithm based on the measured operating data. An actual wind farm is adopted to verify the effectiveness of the model. The result of error comparative analysis shows that the accuracy of the model is greatly improved with the method proposed in this paper compared with the traditional model.

Abstract: Traditional wind turbine converter uses wind speed sensors to measure wind speed as a control conditioning signal, but it makes the measured wind speed have some delay, which affecting the response speed of motor control.For this purpose this paper presents a new control strategy of synchronous permanent magnet wind generator-side converter.By using the combination of hill-climbing searching algorithm and synchronous motor vector control of decoupling to realize the maximum wind capture and variable speed constant frequency control. The simulation results validate the rapidity and feasibility of the control method. And it shows that the control strategy can be quickly and accurately to achieve control objectives. It also omits wind speed measuring sensor and reduces cost compared with traditional control strategy.

Abstract: The construction of wind power transmission line lagged behind the development of wind power generation, which leaded to the issue of wind curtailed and power rationing. In the wind power concentrated transmission process, using energy storage system(ESS) can relax transmission bottlenecks, and improve capability of wind power accommodation. An optimal method of using large scale ESS for relaxing wind power centralized transmission bottlenecks was presented in this paper. The comprehensive benefit was calculated by studying the relationship between wind power improved and optimization capacity configuration of ESS. Example shows that the proposed method can achieve more benefit of transmission line and more transmitted wind power than the traditional one without ESS in the same transmission line. ESS optimal power configuration is 46MW, and optimal capacity configuration is 421MWh. The decreased amount of wind curtailed is 983.6GWh with configuration ESS, saving 472100 tons of coal-fired power plans.

Abstract: The aim of this paper is to forecast short term variation of the regional wind energy resource based on the data captured from several wind measuring stations. Firstly, the main spatial patterns are extracted by SVD (singular value decomposition) method, and then the time coefficient series corresponding to principal spatial patterns are processed and forecasted by SVM (support vector machine). Furthermore, according to the SVD method, the new forecasted time coefficient series are used to inversely calculate the wind speed in the future. Finally, the validity and performance of this forecasting method is tested in case study.

Abstract: Themicro-grid technology is an effective way to promote renewable energydevelopment and utilization. Low voltage micro-grid can absorb photovoltaic,wind power and other large number of scattered random distributed power supply,and the system may be three-phase asymmetry while operation, randomness of thepower output and load is stronger. Therefore an improved bidirectional power flow algorithm is putforward suitable for low voltage micro-grid. According to the physicalstructure components of the micro-grid and different kinds of micro powersupply, the types of micro-grid in power flow calculation is studied to dealwith complex node in the micro-grid, improved Zbus algorithm is proposed tocalculate the power flow of micro -grid .IEEE-69 is taken as an example for simulation, the resultsshow that the proposed method is better for the biggest error ratio of voltagedrop and calculation time than traditional method. Atthe same time the algorithm is also suitable for island operation state of the microgrid.