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Temporary Frequency Support of a DFIG for High Wind Power Penetration
Yang, Dejian,Kim, Jinho,Kang, Yong Cheol,Muljadi, Eduard,Zhang, Ning,Hong, Junhee,Song, Seung-Ho,Zheng, Taiying IEEE 2018 IEEE transactions on power systems Vol.33 No.3
<P>This paper proposes a temporary frequency-support scheme of a doubly fed induction generator (DFIG) that can improve the frequency nadir while ensuring rapid frequency stabilization, particularly for high wind power penetration levels (WPPLs). Upon detecting a disturbance, the power reference is increased by the incremental power and maintained for a preset period. The proposed incremental power varies with the rotor speed and WPPL. Then, to force the rotor speed to converge to a stable operating range, the reference decreases with the rotor speed. During the deceleration period, the proposed scheme releases less kinetic energy, which helps in the rapid recovery of the rotor speed. During the acceleration period, to accelerate the rotor speed recovery, the reference smoothly decreases with time and rotor speed until it reaches the maximum power point tracking curve. The test results, which are based on the IEEE 14-bus system, demonstrate that even though less kinetic energy is released, the proposed scheme can improve the frequency nadir while rapidly recovering the rotor speed under various wind conditions and penetration levels, but it is particularly effective for higher penetration levels. The scheme helps providing a promising solution to the ancillary services of a DFIG in a power system with high WPPLs.</P>
Power Smoothing of a Variable-speed Wind Turbine Generator
Dejian Yang,Yong Cheol Kang,박정욱,Young IL Lee,Seung-Ho Song 제어·로봇·시스템학회 2021 International Journal of Control, Automation, and Vol.19 No.1
This paper presents a power-smoothing scheme of a variable-speed wind turbine generator (VSWTG)that employs separate control gains for the over-frequency section (OFS) and under-frequency section (UFS). Inthe proposed scheme, an additional proportional control loop based on the system frequency deviation operatingin conjunction with maximum power point tracking operation is used. In the OFS, to improve the energy-storingcapability, the scheme suggests the gain of the frequency deviation control loop, which is set to be monotonouslydecreasing with the rotor speed while being significantly larger than that in the UFS. In the UFS, to improve theenergy-releasing capability while preventing over-deceleration, the gain of the frequency deviation control loop isset to be a linear function of the rotor speed. The simulation results under continuously varying wind speeds withdifferent wind patterns and wind speeds clearly demonstrate that the proposed scheme significantly mitigates theoutput power fluctuations of a VSWTG. The proposed scheme keeps the frequency within a narrow range, therebyreducing the required primary frequency control reserve for regulating the frequency under normal operations. This paper presents a power-smoothing scheme of a variable-speed wind turbine generator (VSWTG)that employs separate control gains for the over-frequency section (OFS) and under-frequency section (UFS). Inthe proposed scheme, an additional proportional control loop based on the system frequency deviation operatingin conjunction with maximum power point tracking operation is used. In the OFS, to improve the energy-storingcapability, the scheme suggests the gain of the frequency deviation control loop, which is set to be monotonouslydecreasing with the rotor speed while being significantly larger than that in the UFS. In the UFS, to improve theenergy-releasing capability while preventing over-deceleration, the gain of the frequency deviation control loop isset to be a linear function of the rotor speed. The simulation results under continuously varying wind speeds withdifferent wind patterns and wind speeds clearly demonstrate that the proposed scheme significantly mitigates theoutput power fluctuations of a VSWTG. The proposed scheme keeps the frequency within a narrow range, therebyreducing the required primary frequency control reserve for regulating the frequency under normal operations.
Hybrid Reference Function for Stable Stepwise Inertial Control of a Doubly-Fed Induction Generator
Yang, Dejian,Lee, Jinsik,Hur, Kyeon,Kang, Yong Cheol The Korean Institute of Electrical Engineers 2016 Journal of Electrical Engineering & Technology Vol.11 No.1
Upon detecting a frequency event in a power system, the stepwise inertial control (SIC) of a wind turbine generator (WTG) instantly increases the power output for a preset period so as to arrest the frequency drop. Afterwards, SIC rapidly reduces the WTG output to avert over-deceleration (OD). However, such a rapid output reduction may act as a power deficit in the power system, and thereby cause a second frequency dip. In this paper, a hybrid reference function for the stable SIC of a doubly-fed induction generator is proposed to prevent OD while improving the frequency nadir (FN). To achieve this objective, a reference function is separately defined prior to and after the FN. In order to improve the FN when an event is detected, the reference is instantly increased by a constant and then maintained until the FN. This constant is determined by considering the power margin and available kinetic energy. To prevent OD, the reference decays with the rotor speed after the FN. The performance of the proposed scheme was validated under various wind speed conditions and wind power penetration levels using an EMTP-RV simulator. The results clearly demonstrate that the scheme successfully prevents OD while improving the FN at different wind conditions and wind power penetration levels. Furthermore, the scheme is adaptive to the size of a frequency event.
Hybrid Reference Function for Stable Stepwise Inertial Control of a Doubly-Fed Induction Generator
Dejian Yang,Jinsik Lee,Kyeon Hur,Yong Cheol Kang 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.1
Upon detecting a frequency event in a power system, the stepwise inertial control (SIC) of a wind turbine generator (WTG) instantly increases the power output for a preset period so as to arrest the frequency drop. Afterwards, SIC rapidly reduces the WTG output to avert over-deceleration (OD). However, such a rapid output reduction may act as a power deficit in the power system, and thereby cause a second frequency dip. In this paper, a hybrid reference function for the stable SIC of a doublyfed induction generator is proposed to prevent OD while improving the frequency nadir (FN). To achieve this objective, a reference function is separately defined prior to and after the FN. In order to improve the FN when an event is detected, the reference is instantly increased by a constant and then maintained until the FN. This constant is determined by considering the power margin and available kinetic energy. To prevent OD, the reference decays with the rotor speed after the FN. The performance of the proposed scheme was validated under various wind speed conditions and wind power penetration levels using an EMTP-RV simulator. The results clearly demonstrate that the scheme successfully prevents OD while improving the FN at different wind conditions and wind power penetration levels. Furthermore, the scheme is adaptive to the size of a frequency event.
Improved Frequency Mitigation of a Variable-Speed Wind Turbine
Mingguang Li,Dejian Yang,Yong Cheol Kang(강용철),Junhee Hong(홍준희) 대한전기학회 2018 전기학회논문지 Vol.67 No.6
For a power grid that has a high wind penetration level, when wind speeds are continuously fluctuating, the maximum power point tracking (MPPT) operation of a variable-speed wind turbine (VSWT) causes the significant output power fluctuation of a VSWT, thereby significantly fluctuating the system frequency. In this paper, an improved power-smoothing scheme of a VSWT is presented that significantly mitigates the frequency fluctuation caused by varying wind speeds. The proposed scheme employs an additional control loop based on the frequency deviation that operates in combination with the MPPT control loop. To improve the power-smoothing capability of a VSWT in the over-frequency section (OFS), the control gain of the additional loop, which is set to be inversely proportional to the rotor speed, is proposed. In contrast, the control gain in the under-frequency section is set to be proportional to the rotor speed to improve the power-smoothing capability while avoiding over-deceleration of the rotor speed of a VSWT. The proposed scheme significantly improves the performance of the power-smoothing capability in the OFS, thereby smoothing the frequency fluctuation. The results clearly demonstrate that the proposed scheme significantly mitigates the frequency fluctuation by employing the different control gain for the OFS under various wind penetration scenarios.
Dimensionless Parameter Diagrams for the Active and Passive Stability of a Shallow 3D Tunnel Face
Lianheng Zhao,DeJian Li,Feng Yang,Liang Li,Xiao Cheng 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.2
The methods for calculating the elliptical cone’s geometric parameters of multiple elliptical cone sliders were improved by introducing expression of elliptical path in 3D space. This elliptical path is the intersecting line of a cone and inclined cutting plane. Based on upper-bound limit analysis method and an improved method, Sequential Quadratic Programming (SQP) method was employed to obtain optimal upper bound solutions of failure pressure. The effectiveness of this method was verified by a comparative analysis, and a detailed parametric study on the failure pressure and failure modes was presented. In this study, the stability and failure modes of tunnel face are significantly affected by internal friction angle φ and dimensionless parameter C/D for both active and passive failure; by contrast, dimensionless parameters γD/c and σs/c have small effects. It is also found that dimensionless parameters C/D and σs /c have no effect on the results if the failure region does not reach the ground surface.