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Li H.,Chongqing University | Fu B.,Chongqing University | Yang C.,Chongqing University | Zhao B.,Chongqing University | Tang X.,Chongqing KK QIANWEI Wind Power Equipment Co.
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2013

In order to make better use of energy storage system to reduce the fluctuation of active power for large-scale wind farm, this paper proposes the optimization power distribution control strategies of the multistage vanadium redox flow battery (VRB) storage. Firstly, based on the equivalent circuit of a VRB and by using the interface of the DC/AC converter cascade multiple bi-directional DC/DC converter, a vector control strategy of DC/AC converter is presented to keep the stable DC bus voltage, and a double closed loop control strategy of DC/DC converter is established to switch charge-discharge style as a constraint of state of charge (SOC) on a single VRB. Secondly, by taking SOC value of each battery as priority target selection of output power, and by using the limit of external terminal voltage as the constraint conditions for battery safety charging and discharging, an optimization power distribution strategy of the multistage VRB energy storage is proposed. Finally, as an example of two-stage VRB energy storage system with different SOC values, the smoothing results of wind power fluctuation and the operation performances of charge-discharge on every VRB unit are simulated under the wind speed variation, and the simulation results are compared by using the average distribution strategy of active power. the comparative results have shown that the proposed power optimization distribution control strategies for VRB storage system could better smooth wind power fluctuation, but also could further reduce the charging and discharging times of single VRB, and ensure the battery work in the more safe operation region.


Li H.,Chongqing University | Chen H.,Chongqing University | Yang C.,Chongqing University | Zhao B.,Chongqing University | Tang X.,Chongqing KK QIANWEI Wind Power Equipment Co.
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2013

Based on the theory analysis of the transient energy function, this paper proposed a fuzzy additional damping control strategy for a doubly-fed induction generator (DFIG) based wind farms. Firstly, by adjusting the active/reactive output power of the wind farm, a theoretically analysis was carried out to find that, the transient oscillation energy can be continuously reduced to suppress the inter-area low frequency oscillation. Secondly, on the basis of describing a conventional PSS additional damping control of DFIG wind farm, by judging the oscillation stage of the transient energy with the active power variation signal of transmission lines, an additional damping strategy with fuzzy control was proposed. Finally, to compare the three different control straties of fuzzy additional control, traditional PSS control and without any damping controller, the two-area four-machine IEEE power system integrated with a DFIG wind farm is taken as example, and the system dynamic performances were simulated under the operational conditions of 3-phase short-circuit of transmission lines and the small disturbance of active power on the traditional synchronous generator. The simulation results verify the effectiveness of the proposed fuzzy additional damping control strategies on the active/reactive power loop. Furthermore, besides the damping ability of the inter-area low frequency oscillation, the results also show that as with the reactive power loop with fuzzy additional damping control, it can also reduce the shaft torsional torque oscillation of the wind turbine drive train. © 2013 Chin. Soc. for Elec. Eng.


Li H.,Chongqing University | Chen H.,Chongqing University | Yang C.,Chongqing University | Zhao B.,Chongqing University | Tang X.,Chongqing KK QIANWEI Wind Power Equipment Co.
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2013

The grid integration of large scale wind power may increase the risks of inter-area low frequency, local power oscillations and the shaft torsion oscillation of the wind turbine. The paper studied the influence of the integration of doubly fed induction generator (DFIG)-based wind farms integration on the low frequency oscillation characteristics of the power system. In order to do small signal stability analysis, a detailed mathematical model was established by considering the effects of wind turbine drive drain, variable pitch control, dynamic models and control strategy of DFIG. By using modal analysis method low-frequency oscillation modes in an IEEE two-area four-machine power system with DFIG-based wind farm were investigated, and the results of the time-domain simulation demonstrated the validity and effectiveness of the model and the corresponding analysis. In the two cases of the constant and variable power flow, the characteristics of local oscillation modes, inter-area oscillation modes, and shaft torsional vibration modes were respectively analyzed under variable operational conditions, including different operation points, different integrated capacity of wind power and whether wind farm participates in reactive power dispatching. The results show that low-frequency oscillation characteristics are closely related to the variation of the power flow, the control strategy and the capacity of wind farm. A suitable coordinated control scheme of synchronous generators could improve the oscillation damping in the condition of constant power flow.


Li H.,Chongqing University | Fu B.,Chongqing University | Yang C.,Chongqing University | Zhao B.,Chongqing University | Tang X.,Chongqing KK QIANWEI Wind Power Equipment Co.
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2012

In order to satisfy the testing requirements of the low voltage ride through (LVRT) of wind turbine generation system and the need for the electrical model conformance evaluation, a LVRT control strategy of doubly fed induction wind turbine generation system was proposed by considering the reactive current injected into the grid. Based on the description of the LVRT testing requirements and the control principle, the maximum limited reactive current expressions of the stator side of doubly fed induction generator (DFIG) and the grid side converter were derived, respectively. Then the effects of the voltage sag levels, the total output active power of DFIG on the limited reactive current were also investigated. Furthermore, the corresponding reactive current allocation algorithm, the improved control strategies of the active power and the reactive power for the LVRT operation were proposed. Finally, as an example of the factual 2 MW DFIG wind turbine generation system, the simulated comparison and the prototype testing for LVRT operational performances were investigated under the conditions of 5 m/s and 12 m/s wind speed, the grid voltage balancing drop to 20% and 50%, respectively. Compared with the traditional LVRT control method, the results have shown that DFIG can better meet the LVRT testing requirements by using the improved control strategy, the validity of this control strategy and the simulation models is further testified by the prototype testing results. © 2012 Chin. Soc. for Elec. Eng.


Li H.,Chongqing University | Hu Y.,Chongqing University | Li Y.,Chongqing University | Yang D.,Chongqing University | And 3 more authors.
Dianli Zidonghua Shebei/Electric Power Automation Equipment | Year: 2015

A method of gradual deterioration probability analysis based on the temperature characteristic parameters is proposed for the critical components of WTGS (Wind Turbine Generator System) to grasp their deterioration level and tendency. Since the fixed threshold may not be used to accurately determine the degradation degree, the concept of data fitting and turbine grouping based on the temperature characteristic parameters and rotation speeds of the critical components is proposed to set the dynamic thresholds for the upper and lower limits of degradation degree. In order to include the effects of operating condition and duration on the degradation degree, the nonparametric kernel density estimation method is applied to build the probability density function of degradation degree for the critical components and a method of gradual deterioration probability analysis is presented for different monitoring cycles. With the rear bearing of a wind-turbine generator in an actual wind farm as an example, the proposed dynamic threshold method and probability analysis method are verified based on the historical monitoring data of its gradual deterioration. Compared with the fixed threshold method, the proposed dynamic threshold method can more accurately determine the degradation degree of components and more effectively analyze the deterioration tendency of critical components. © 2015, Electric Power Automation Equipment Press. All right reserved.

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