Mechanism analysis and suppression method of ultra-low-frequency oscillations caused by hydropower units

Wang, Guoteng; Xu, Zheng; Guo, Xiangyang

doi:10.1016/j.ijepes.2018.05.021

Cited by 43 publications

(11 citation statements)

References 15 publications

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“…Regardless of the type of generator, equations (19) and (20) always hold. ω0 is the rated rotor speed, which is 314rad/s.…”

Section: B the Basic Equaiotns And The Relationship Between δω1 And δω2mentioning

confidence: 99%

“…To reveal the ULFO mechanism in multi-machine system, based on the equivalence model and simulations of the multi-machine system, the large phase lag of hydro unites was regarded as the main cause of ultra-low frequency oscillation [17] [19]. Furthermore, the effect of nonlinear components and the dead zone on ultra-low frequency oscillation were also analyzed [20] [21].…”

Section: Introductionmentioning

confidence: 99%

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The Mechanism of Ultra-Low Frequency Oscillations With the Same Mode Shapes

et al. 2020

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The ultra-low frequency oscillation (ULFO) problem reappears in China recently. Different from the classical low frequency oscillation (LFO), the generators in ULFO have the same mode shapes, namely oscillating in the same pace. To reveal the reason why ULFO generators do not oscillate inversely as classical LFO does, this paper investigates the mechanism of ULFO based on improved Philips-Heffron model of two-machine system. Through this model, the phase angle relationship between different generators is obtained. Based on the bode diagram, it is found that the phase angle difference of the two machines is around zero in ultra-low frequency band however the generator parameters change. On the contrary, the situation is different in classical low frequency band, which reveals the mechanism that generators in ULFO always oscillate in the same pace. Finally, the analysis above is validated through a 2area 4-machine system and a 6-machine system established in PSASP software. INDEX TERMS ultra-low frequency oscillation, mode shape, dynamic mechanism NOMENCLATURE E '' di, E '' Y Complex admittance matrix (p.u.). yij, βij Amplitude of Y, phase angle of Y (p.u.). δij Difference between δi and δj, in rad. Cij,Sij cos(βij-δij), sin(βij-δij) (p.u.).

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“…Regardless of the type of generator, equations (19) and (20) always hold. ω0 is the rated rotor speed, which is 314rad/s.…”

Section: B the Basic Equaiotns And The Relationship Between δω1 And δω2mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Mechanism of Ultra-Low Frequency Oscillations With the Same Mode Shapes

et al. 2020

View full text Add to dashboard Cite

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“…According to (7), the derivation of the new system is consistent with the original system. The state equation of the new system can be described by (8).…”

Section: Decoupling Componentsmentioning

confidence: 99%

“…Generally, the terrible dynamic performances are attributed to turbine factors, electronic devices, and uncertain loads, such as "water hammer effect"and poorly tuned controllers [7]. Frequency-domain approaches like Nyquist Diagram and Routh Criterion are utilized to analyze the effects of the above factors [8], and the too small values of proportional and integral coefficients in the proportional-integral-derivative (PID) governor are evaluated to be the major reasons of ULFO. Reference [9] denotes that the governor would add a new eigenmode with ultra-low frequency.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Mode Interaction in Ultra-low Frequency Oscillation Based on Trajectory Eigenvalue

Xue

Bin

2020

Journal of Modern Power Systems and Clean Energy

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Complex phenomena such as prolongedly undamped ultra-low frequency oscillation (ULFO) and eigenmode re-excitation are observed in the simulations of hydroelectric power systems. Emphases are put on nonlinearities and mode interactions, which cannot be analyzed by traditional eigen-analysis methods. In order to investigate the mechanism of the evolvement of the nonlinear dynamic process in ULFO, this paper proposes a method to analyze the mode interactions quantificationally. First, a disturbed trajectory is decoupled into a set of time-varying components. Second, transfer matrices of eigenmodes are extracted along the trajectory. Third, consecutive sequences of eigenvalues and trajectories of components are formed by a proposed technique. Based on the decoupled components and transfer matrices, the mechanisms of mode interactions and inheritance relationships between eigenmodes are analyzed. The causes and developments of the above complex phenomena are revealed by the proposed method in a test two-machine system. Meanwhile, the accuracy of the eigenmode matching technique is verified in the New England system.

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“…According to [16,17], the accident of the Sayano-Shushenskaya hydropower plant in Russia was caused by operations in the instability zones. In [18,19], authors studied the ultra-low frequency oscillation of hydropower stations with a surge tank and proposed some methods to suppress the oscillation to improve the stability of the hydropower generating system. In [20,21], considering the effect of water hammer in the penstock system, the authors researched the dynamic performance of the hydropower system.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on the Optimal Strategy for Power Regulation of Governing System of Hydropower Station

Wang

Zhang

2021

Water

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Active power instability during the power regulation process is a problem that affects the operation security of hydropower stations and the power grid. This paper focuses on the dynamic response to power regulation of a hydro-turbine governor in the power control mode. Firstly, the mathematical model for the hydro-turbine governing system connected to the power grid is established. Then, considering the effect of water hammer and the guide vane operating speed on power oscillation and reverse power regulation, a novel control strategy based on the S-curve acceleration and deceleration control algorithm (S-curve control algorithm) is proposed to improve power regulation. Furthermore, we carried out field tests in a real hydropower station in order to compare the regulation quality of the novel control strategy based on the S-curve control algorithm with the traditional linear control strategy. Finally, the obtained results show that the proposed optimal control strategy for the hydro-turbine governor improves the stability of power regulation by effectively suppressing reverse power regulation and overshoot. This study provides a good solution for the instability of power and reverse power regulation during the regulation process of the hydro-turbine governor in the power control mode.

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Mechanism analysis and suppression method of ultra-low-frequency oscillations caused by hydropower units

Cited by 43 publications

References 15 publications

The Mechanism of Ultra-Low Frequency Oscillations With the Same Mode Shapes

The Mechanism of Ultra-Low Frequency Oscillations With the Same Mode Shapes

Analysis of Mode Interaction in Ultra-low Frequency Oscillation Based on Trajectory Eigenvalue

Experimental Study on the Optimal Strategy for Power Regulation of Governing System of Hydropower Station

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