This paper aims to reasonably demonstrate the role of the rotor-side converter (RSC) in subsynchronous oscillation (SSO) and investigates the influence and relationships of all control parameters. Thus, the equivalent circuit of a doubly fed induction generator (DFIG) that considers the RSC is imperative. First, the pertinent equivalent model of a DFIG with RSC control is established. Compared with previous works, this paper innovatively merges the RSC and induction generator with flux and voltage, obtains a complete analytical expression for the equivalent power supply and impedance containing all parameters of both the inner and outer loops of the RSC and then constructs a reasonable equivalent model. The action of the RSC is successfully demonstrated and reflects how the control loops and parameters of the RSC affect the circuit structures and properties of the equivalent model. Then, based on this proposed model, the influence mechanism of the RSC on the SSO of the grid-connected system is carefully analyzed.
This paper presents a study of dynamic equivalence for doubly fed wind farms (DFWFs) in large power systems. The core idea is to find an attribute representing the critical characteristics of a doubly fed induction generator (DFIG) and use it for clustering in the equivalent modeling process. Using the voltage and flux linkage equations of DFIGs, we derived an electromagnetic power expression. Similar to the power angle concept for synchronous generators, an equivalent power angle (EPA) is proposed and shown to represent the dynamic characteristics of a DFIG in the test system. We introduce the similarity degree of the EPA based on similarity theory and construct a similarity index of the EPA for clustering a DFWF. A practical algorithm was developed for parameter aggregation of the equivalent model. In addition, a simulation of DFWFs in Yunnan, China, was conducted to show the feasibility and high precision of the proposed method. INDEX TERMS Doubly fed induction generator, equivalent power angle, dynamic equivalent, similarity degree.
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