Abstract
Recently, explanations of the sub-synchronous oscillation (SSO) caused by wind farms based on direct-driven wind generators (DDWGs) have been published in the literatures, in which the controller parameters of DDWGs and the system equivalent parameters play an important role. However, more than one set of parameters can cause weakly damped sub-synchronous modes. The most vulnerable and highly possible scenario is still unknown. To find scenarios that have potential oscillation risks, this paper proposes a small disturbance model of wind farms with DDWGs connected to the grid using a state-space modeling technique. Taguchi’s orthogonal array testing is introduced to generate different scenarios. Multiple scenarios with different parameter settings that may lead to SSOs are found. A probabilistic analysis method based on the Gaussian mixture model is employed to evaluate the consistency of these scenarios with the actual accidents. Electromagnetic transient simulations are performed to verify the findings.
Highlights
1.1 MotivationWith the vigorous exploitation of wind power generation, stability problems associated with wind farms have increased [1,2,3,4,5], among which sub-synchronous oscillation (SSO) is a prominent example
This paper focuses on the new type of SSO and provides a methodology for finding a system scenario consistent with the actual accident, considering the stochastic variation in the operating conditions of the wind farms
The dynamics of the direct-driven wind generators (DDWGs) can be described by a set of differential equations, while the constraints of the grid can be described by algebraic equations
Summary
With the vigorous exploitation of wind power generation, stability problems associated with wind farms have increased [1,2,3,4,5], among which sub-synchronous oscillation (SSO) is a prominent example. In July 2015, several thermal generators were tripped off by shaft torsional vibration relay in a thermal power plant in Hami, Xinjiang Uygur Autonomous Region of China. This event led to the emergent power reduction of a nearby highvoltage direct-current (HVDC) transmission line and caused sharp fluctuation in the frequency of the grid. Analysis of the records of the phasor measurement units after the accident revealed that the sub-synchronous current that aroused the torsional vibration came from wind farms north of the region [7]. This paper focuses on the new type of SSO and provides a methodology for finding a system scenario consistent with the actual accident, considering the stochastic variation in the operating conditions of the wind farms
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