With the rapid development of wind power, the effects of doubly fed induction generators (DFIGs) on the transient stability of power system have attracted more attention. However, the effects are still not clear due to the lack of deep and theoretical analysis. A control method for enhancing system rotor angle stability enhancement is proposed with considering the power constraints of DFIG. The rotor angle oscillation of the synchronous generator (SG) can be reduced and overspeed and the overcurrent of DFIG can be avoided. In this paper, the effects of the DFIG on the rotor angle characteristics of SG are analyzed. The change law of system rotor angle varying with transient power of the DFIG is obtained. Then, the power equation in the emergency pitch control process is explored. The reactive power constraints of the stator and grid-side converter are deduced. Finally, the system rotor angle stability enhancement control method is proposed based on the power constraints of DFIG. The effectiveness of proposed method is proven by simulations.
With a high proportion of wind power being transmitted through ac and dc lines, a new power grid pattern has gradually emerged. A dc inverter is prone to commutation failure, which may lead to cascading trip of ac lines for overload, resulting in serious consequences. However, existing control methods have problems of over-or under-shedding and are unsuitable for high-proportion wind power transmission systems. Accordingly, a new fault overload control method based on emergency acceleration of doubly fed induction generator (DFIG) is proposed. The fast power control capability of DFIG is fully utilized; the active power of power grid could be rapidly balanced. First, the fault characteristics of a wind power ac/dc transmission system under the fault of dc receiving-end grid are analyzed, and the power flow transfer after self-recovery from the dc commutation failure is derived. Second, by analyzing the power characteristics of DFIG, a fault overload control idea of the wind power transmission system is proposed based on emergency acceleration of DFIG. At last, the maximum controllable capacity of a wind farm is analyzed, and a fault overload control strategy of the wind power transmission system is proposed. The simulation results prove that the proposed method can rapidly reduce the output of wind farms and prevent the overload of ac lines. INDEX TERMS AC/DC system, DFIG-based wind farm, power flow transfer, cascading trip, emergency power control. I. INTRODUCTION Wind energy resources and load centers are reversely distributed. Wind power development generally adopts the mode of large-scale centralized development and long-distance high-voltage transmission [1]. Wind power transmission through line-commutated converter based highvoltage direct current (LCC-HVDC) has become the main method of cross-zone allocation for wind energy resources because LCC-HVDC transmission system has a large transmission capacity and long transmission distance. The associate editor coordinating the review of this manuscript and approving it for publication was Datong Liu.
This paper is focused on the characterization of a fiber Bragg grating (FBG) sensor interrogation system based on a fiber ring laser with a semiconductor optical amplifier as the gain medium, and an in-loop electro-optical modulator. This system operates as a switchable active (pulsed) mode-locked laser. The operation principle of the system is explained theoretically and validated experimentally. The ability of the system to interrogate an array of different FBGs in wavelength and spatial domain is demonstrated. Simultaneously, the influence of several important parameters on the performance of the interrogation technique has been investigated. Specifically, the effects of the bandwidth and the reflectivity of the FBGs, the SOA gain, and the depth of the intensity modulation have been addressed.
The dynamic processes of a power system during grid fault are being changed by the large‐scale applications of wind generation. The transient characteristics of a single doubly fed induction generator (DFIG) have been widely researched. However, the overall characteristics of a wind farm have not been obtained because the existing models of a wind farm cannot cover the differences caused by normal instruction values, controller responses, and protections of the DFIGs. The equivalent model of a doubly fed wind farm used for the electromagnetic transient analysis is studied. The feature information of the stator short‐circuit current (SCC) of a DFIG was excavated based on transient behaviour analysis. The structure similarity indices are established to evaluate the envelope curves of the SCCs. A clustering method based on transient physical process is then proposed to distinguish coherent DFIGs. The equivalent model represented by a small number of DFIGs is obtained by aggregating coherent groups. The simulations indicate that the method effectively recognises transient state differences of the DFIGs. Thus, the model meets the requirements of the transient analysis.
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