1、 毕业设计（外文翻译） 题 目 在电网电压不平衡条件下的动态建模和风力涡轮机的直接功率控制 系 （院） 自动化系 专 业 电气工程与自动化 学生姓名 学 号 2007090124 指导教师 职 称 2011 年 3 月 8 日 1 Dynamic modeling and direct power control of wind turbine driven DFIG under unbalanced network voltage condition Abstract: This paper proposes an analysis and a direct power control (D
2、PC) design of a wind turbine driven doubly-fed induction generator(DFIG)under unbalanced network voltage conditions. A DFIG model described in the positive and negative synchronous reference frames is presented. Variations of the stator output active and reactive powers are fully deduced in the pres
3、ence of negative sequence supply voltage and rotor flux. An enhanced DPC scheme is proposed to eliminate stator active power oscillation during network unbalance. The proposed control scheme removes rotor current regulators and the decomposition processing of positive and negative sequence rotor cur
4、rents. Simulation results using PSCAD/EMTDC are presented on a 2-MW DFIG wind power generation system to validate the feasibility of the proposed control scheme under balanced and unbalanced network conditions. Key words: Doubly-fed induction generator (DFIG) Wind turbine, Direct power control (DPC)
5、, Stator voltage oriented (SVO), Unbalanced network INTRODUCTION,Wind farms based on the doubly-fed induction generators (DFIG) with converters rated at 25%30%of the generator rating for a given rotor speed variation range of25%are becoming increasingly popular. Compared with the wind turbines using
6、 fixed speed induction generators or fully-fed synchronous generators with full-size converters the DFIG-based wind turbines offer not only the advantages of variable speed operation and four-quadrant active and reactive power capabilities, but also lower converter cost and power losses (Pena et al.
7、, 1996).However, both transmission and distribution networks could usually have small steady state and large transient voltage 滨州学院本科毕业设计 (外文翻译 ) 2 unbalance. If voltage unbalance is not considered by the DFIG control system, the stator current could become highly unbalanced even with a small unbala
8、nced stator voltage. The unbalanced currents create unequal heating on the stator windings, and pulsations in the electromagnetic torque and stator output active and reactive powers(Chomatetal.,2002；Jang et al.,2006；Zhou et al.,2007；Pena et al., 2007；Hu et al.,2007；Xu and Wang,2007；Hu and He,2008).C
9、ontrol and operation of DFIG wind turbine systems under unbalanced network conditions is traditionally based on either stator-flux-oriented(SFO)(Xu and Wang,2007)or stator-voltage-oriented(SVO)vector control(Jang et al.,2006；Zhou et al.,2007；Hu et al.,2007；Hu and He,2008).The scheme in(Jang et al.,2
10、006；Zhou et al.,2007；Xu and Wang,2007；Hu et al.,2007)employs dual-PI(proportional integral)current regulators implemented in the positive and negative synchronously rotating reference frames, respectively, which has to decompose the measured rotor current into positive and negative sequence componen
11、ts to control them individually. One main drawback of this approach is that, the time delays introduced by decomposing the sequential components of rotor current can affect the overall system stability and dynamic response. Thus, a current control scheme based on a proportional resonant(PR)regulator
12、 in the stator stationary reference frame was proposed in(Hu and He,2008), which can directly control the rotor current without the need of sequential decomposition. Whereas, the performance of the vector control scheme highly depends on the accurate machine parameters such as stator/rotor inductanc
13、es and resistances used in the control system. Similar to direct torque control (DTC) of induction machines presented a few decades ago, which behaves as an alternative to vector control, direct power control (DPC)of DFIG-based wind turbine systems has been proposed recently(Gokhaleet al.,2002；Xu an
14、d Cartwright,2006；Zhi and Xu,2007). In (Gokh a le et al., 2002), the control scheme was based on the estimated rotor flux. Switching vectors were selected from the optimal switching table using the estimated rotor flux position and the errors of rotor flux and active power. The rotor flux reference was calculated using the reactive power reference. Since the rotor supply frequency, equal to the DFIG slip frequency,
