The role of induction generators and power electronic converters for energy conversion system is significant. Self-excited induction generator (SEIG) in stand- alone application provides a significant reduction in system operating costs due to fact that wind power is freely available. SEIG also has several advantageous over other generators due to the ruggedness and low maintenance requirements of induction machines, for example the absence of dc commutating brushes in SEIG. Moreover, the self-excitation of the induction generator causes voltage to collapse rapidly when overloaded. This means that the self excited induction generator is self- protected. On the other hand, there are some drawbacks from using SEIG in stand-alone application mainly the inability to control the voltage and frequency. Due to sufficiently large value of capacitance connected to ensure self-excitation of the induction generator, the possibility of over voltages and frequency mismatch might occur. Recently wind power generation has been experiencing a rapid development in a global scale. The size of wind turbines and wind farms are increasing quickly; a large amount of wind power is integrated into the power system. As the wind power penetration into the grid increases quickly, the influence of wind turbines on the power quality is becoming more and more important.
[...] A STATCOM connected in shunt in the system can provide fast and smooth reactive power control, therefore, effectively control the system voltage level and mitigate the flicker during continuous operation of the grid connected wind turbines. The flicker mitigation has been studied in detail by simulation; the results show that the STATCOM is an effective means to improve system voltage quality Three main aspects, in which wind generation differs from conventional generation was in the center of interest of this study. [...]
[...] Using high frequency PWM, the converter will produce smooth current with low harmonic content The growing importance of wind power, which can be observed in many European countries, the USA, Canada and also Australia requires detailed analysis of the impact of wind power on power system stability. Therefore, a number of studies have been carried out recently and are currently carried out for identifying required network reinforcement, reserve requirements and the impact of wind power on power system stability 2. [...]
[...] However, the frequency of operation at steady state is also decreased Power Electronics Converter: The ac output of SEIG can be rectified either using the uncontrolled 6-pulse fullbridge diode rectifier or with half-controlled thyristor bridge rectifier. The halfcontrolled bridge rectifier utilizes 3 thyristors and 3 diodes for the top group and the bottom group respectively as shown in Fig The firing angle for the thyristors can be found using the following expression. The ac output from SEIG is rectified into dc using an uncontrolled 6-pulse full-bridge diode rectifier. [...]
[...] It provides the generator with wide speed range operation, which enables the optimal speed tracking for maximum energy capture from the wind Voltage Compensation: The STATCOM consists of a controllable PWM voltage source converter, which generates a voltage with the amplitude and phase being continuously and rapidly controlled, so as to effectively perform reactive power control. By control of the voltage source converter output voltage in relation to the grid voltage, the voltage source converter will appear as a generator or absorber of reactive power. [...]
[...] With an extended filter also the German “VDEW-Richtlinie“can be fulfilled CONCLUSION Self-excitation of induction generator is commonly used in stand-alone wind turbine application in rural areas where supply grid is not available. However, the unregulated voltage and frequency is inevitable when the SEIG is used in stand-alone mode. The power electronic converters gave an insight of how the unregulated voltage and frequency of the generator can be improved. The output of the inverter shows the fundamental frequency operation of 50 Hz along with high frequency switching harmonics which can be filtered using the conventional low-pass filter. [...]
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