含风电场的电力系统静态电压稳定性分析翻译

燕 山 大 学 本科毕业设计（论文）英文翻译 课题名称含风电场的电力系统静态电压稳定性探讨 学院（系）电气工程学院 年级专业09级电力四班 学生姓名张建春 指导老师 王珺 完成日期 2013.5.8 一 The interduction of steady-State Characteristics the speed-torque characteristic is quite linear around synchronous speed. If the rotor speed is below synchronous speed，the induction machine is operating as a motor and if the rotor speed is above synchronous speed，the induction machine is running as a generator.the mechanical power and the mechanical torque are given by the slip,rotor resistance and the rotor current.The speed-torque characteristic of the induction machine is quite linear around synchronous speed. the torque is proportional to the inverse of the rotor resistance. This implies that it is possible to have external rotor resistances connected in series with the existing rotor resistances of a wound-rotor induction machine. By changing the value of the external rotor resistance it is possible to change the slope of the speed-torque characteristic. One disadvantage with this is that it is only possible to increase the slip using the external rotor resistances. This implies that if the induction machine is running as a motor, then an increased rotor resistance will decrease the rotor speed. On the other hand, if the induction machine is running as a generator, then if the rotor resistance increases, the rotor speed will also increase. Before semiconductors were available, one way of adjusting the slip was to introduce external rotor resistances. The external rotor resistance will cause additional losses in the rotor circuit. When semiconductors became available it was possible to recover the slip otherwise dissipated in the external rotor resistance.Thus, the slip power can be recovered into mechanical or electrical energy; therefore,this is called slip power recovery. The rotor current must be rectified with a diode rectifier. For motor operation, the rotor circuit will see the diode rectifier as a resistance and therefore this will work approximately in the same way as for the external rotor resistances. Note that the diode rectifier cannot be used in generator operation. The rectified current could be converted to mechanical power using a dc motor coupled to the shaft of the induction motor or fed back into the grid .Since Kramer drive require an extra dc motor it is of no interest, while the Scherbius drive is still in use.The main advantage of this configuration compared to the external rotor resistance is that the losses of the external rotor resistance can be recovered.If both stator voltage and frequency can be adjusted by an inverter, the torque-speed characteristic can be easily changed. When the speed is increased so that the stator voltage reaches maximum voltage, there is need for field weakening, the stator voltage is kept constant while the frequency is still increased.