| Summary: | 碩士 === 國立臺灣科技大學 === 電機工程系 === 97 === The grid code for renewable energy currently used in Taiwan is “Grid Code of Renewable Energy of Taiwan Power Company.” There have been many studies on how to properly harmonize the parameters in the grid code so far and the most common parameters are voltage variation, installation capacity, islanding and reverse power flow. The analysis of these parameters is of great importance at the early stage of developing renewable energy. With the rapid increase of installation capacity of renewable energy, the penetration shouldn’t be thought little of anymore, this is especially true when it comes to the wind power generation. The wind turbines used to be tripped off when influenced by the fault in the system to acquire the optimum protection of wind turbines, but with higher penetration the stability of the system could be disturbed or the system could breakdown if the wind turbine were tripped off when the fault take place. Therefore, utilities from every country start drawing up regulation which requires that the wind turbine should remain connected to the grid when a fault takes place in the system to help the system through the fault. Such requirement is known as low voltage ride through (LVRT).
The primary goal of this thesis is to harmonize the parameters of LVRT for the grid code of Taiwan and to make benefit for steady operation of power system and development of renewable energy industry. In order to completely understand the effect that a voltage sag has on wind turbines, the transient responses of directly coupled squirrel cage induction generator(DCSCIG) and doubly-fed induction generator(DFIG) are simulated by using Matlab/Simulink. The voltages sags are classified into three types which are three phase voltage sag, two phase voltage sag and single phase voltage sag, and the voltage sag level will be decreased from 0.9pu to 0.5pu and then to 0.15pu.
From the simulation result, the main problem that the DCSCIG encountered during a voltage sag is the requirement of reactive power for the operation of induction generator and the rapidly increased rotor speed which adds burden on the mechanical structure of the wind turbine. As for DFIG, the over current in the rotor induced by the voltage sag could damage the power electronic device easily for they are vulnerable and can not withstand such high voltage and high current therefore, the thesis proposes a suggested LVRT characteristics according to the time when the dc-link voltage excesses its limit at different voltage sag level after the fault.
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