Abstract
A multi-scale transients model of a doubly fed induction generator (DFIG)-based wind energy conversion system (WECS) is developed, implemented, and validated. All ac circuit and control quantities of the electrical part are modeled by analytic signals rather than just real signals. In addition to the real parts, the analytic signals also comprise orthogonal imaginary parts. While measured Fourier spectra of real ac quantities involve positive and negative frequency components, they only involve positive frequency components when extended and represented as analytic signals. With the introduced shift frequency operator, the analytic signal can now be shifted in the frequency domain to reduce its maximum frequency contents and thus allow for a larger time-step size in accordance with the Nyquist criterion. If the shift frequency is set equal to the ac fundamental frequency, then the affiliated ac voltages and currents become dynamic phasors. At a zero shift, however, instantaneous signals can be tracked as in an electromagnetic transients program (EMTP). This is illustrated here for the voltage sourced converters (VSC) of the WECS. By appropriate selection of the shift frequency, both electromagnetic and electromechanical transients are simulated efficiently. Studies involving wind power fluctuations, three-phase-to-ground fault and single-phase-to-ground fault confirm these claims.
Highlights
W IND power is widely distributed and renewable, and produces no greenhouse gases during operation [1]
The present paper addresses the multi-scale modeling of doubly fed induction generator (DFIG)-based wind energy conversion system (WECS)
This paper addresses DFIGbased WECS multi-scale modeling
Summary
W IND power is widely distributed and renewable, and produces no greenhouse gases during operation [1]. The present paper addresses the multi-scale modeling of doubly fed induction generator (DFIG)-based WECS. This type is the most widely used by the wind turbine industry [5]. Only the envelopes of ac voltages and currents are tracked This makes phasor-based simulation efficient for emulating low-frequency transients as for example electromechanical transients. In frequency-adaptive simulation of transients (FAST) [19], [20], this is achieved by introducing a variable shift frequency and representing all ac voltages and currents through analytic signals, which are complex. To ensure the numerical accuracy and stability of the proposed DFIG-based WECS model, a new interface which links real and analytic signals used in different parts is developed.
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