Abstract
The wind-thermal hybrid power transmission will someday be the main form of transmitting wind power in China but such transmission mode is poor in system stability. In this paper, a coordinated stability control strategy is proposed to improve the system stability. Firstly, the mathematical model of doubly fed wind farms and DC power transmission system is established. The rapid power controllability of large-scale wind farms is discussed based on DFIG model and wide-field optical fiber delay feature. Secondly, low frequency oscillation and power-angle stability are analyzed and discussed under the hybrid transmission mode of a conventional power plant with wind farms. A coordinated control strategy for the wind-thermal hybrid AC/DC power system is proposed and an experimental prototype is made. Finally, real time simulation modeling is set up through Real Time Digital Simulator (RTDS), including wind power system and synchronous generator system and DC power transmission system. The experimental prototype is connected with RTDS for joint debugging. Joint debugging result shows that, under the coordinated control strategy, the experimental prototype is conductive to enhance the grid damping and effectively prevents the grid from occurring low frequency oscillation. It can also increase the transient power-angle stability of a power system.
Highlights
As one of the most efficient new energy sources that have the potential of large-scale development, wind power generation has developed speedily in China
As the analog state variables, the frequency of the common bus of wind farms, the speed of synchronous generator, and the power-angle are the output from GTAO of Real Time Digital Simulator (RTDS), and they are put into the data collection module of the experimental prototype by the signal cable
Compare two figures and it is seen that when low frequency oscillation occurs in the system, DFIG rectifies its active power according to additional controlling signals sent by the experimental device to activate additional damping control
Summary
As one of the most efficient new energy sources that have the potential of large-scale development, wind power generation has developed speedily in China. Given that wind power is not constant and it is not economical to transmit wind power alone, there arises the necessity to “bond” large-scale wind farms with thermal power plant so as to realize transregional transmission. For large-scale wind farms, active power in the whole wind farms can be adjusted randomly and quickly through the communication network, making the wind farms controllable. Controllable power in the wind farms can help increase the damping and prevent low frequency oscillation, and enhance transient angle stability of the power system, which is meaningful for ensuring grid safety. Structural features of hybrid power system of wind farms and thermal power plant are analyzed and problems about stability of the power transmission system are pointed out.
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