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The stability issues of cascade systems have been studied for many years. Impedance ratio type criterions in the form of Zo/Zi or Zi/Zo have been proposed to solve these stability issues. However, existing ratio type criterions still have problems in some cascade systems. Terminal characteristic of single module is studied and the different types of cascade system are defined in this paper. It can...
In cascade AC system, the interaction between converters and non-ideal source may cause instability issues, especially when the converters behave as constant power load. From the view of small signal model, the stability issues can be evaluated based on the relationship between the terminal impedance and admittance of sub-modules. Therefore, the stability criterion based on terminal impedance and...
Wind energy is now playing a very important role in the electrical power supply. With growing shares, the focus of the plant control is shifting from maximum power point tracking to also meet grid friendly aspects, like stable output power. This paper analyzed the power flow of wind power generation system equipped with permanent magnet synchronous generator. Wind torque feed-forward control based...
Dynamic voltage restorer (DVR) is a cost effective solution to solve the grid voltage sag problem. Recently DVR is used to fulfill LVRT capability for DFIG wind power systems. The terminal voltage of wind farms usually has large fluctuation and is distorted by voltage harmonics when connected to weak grid. This demands a high requirement for sag detection algorithm, which should detect the voltage...
Wind farms are confronted with increasing demands for power quality and fail-safe operation at grid fault. State-of-art techniques applied to meet low voltage ride-through (LVRT) requirements for fix speed wind farms are blade pitching and dynamic reactive power compensation. Besides, breaking resistor and energy storage unit is also helpful to LVRT performance. However, these approaches have their...
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