Impedance Model of Turbo-Generator Considering Torsional Characteristics of Shafting
Li Jialong1, Lu Xinyu1, Du Xiong1, Liu Junliang1, Fan Lijuan2
1. State Key Laboratory of Power Transmission Equipment and System Security and New Technology Chongqing University Shapingba District Chongqing 400044 China;
2. System Research Institute, CSG Electric Power Research Institute Guangzhou 510663 China
Due to the increasing number of power electronic devices in power systems, the structure of power systems becomes furtherer more complex, and the difficulty of analyzing the stability of power systems containing power electronic devices and turbo-generators increases. In this case, impedance-based analysis method is a good choice, because it is easy to extend the system topology, and more conducive to the modeling of black box system. In order to make up for the gap that the impedance of turbo-generator can only reflect the characteristics of electrical part and it is difficult to reflect the characteristics of mechanical part, a impedance model of turbo-generator considering the characteristics of shafting is established in this paper, and the mechanical part of turbine, governor and shafting mass spring model is considered. The impedance model established can accurately analyze the stability of the whole frequency band of the turbo-generator.
The turbo-generator is divided into electrical part and mechanical part, and modeled respectively. For the modeling of the electrical part, it is assumed to run in an ideal state and is standardized to get the small signal equation of synchronous motor. For the modeling of the mechanical part, the small signal model is established for the shafting part, the steam turbine and the speed regulator respectively. Further calculation results show that the impedance model of turbo-generator in d-q coordinate system is a 2th-order matrix. Finally, the impedance model of turbo-generator considering shafting can be obtained by converting it into sequence impedance model and considering frequency coupling effect.
In the experimental part, for the impedance model established in this paper: Firstly, the theoretical model is verified by the frequency scanning method. The experimental results show that the frequency scanning points are in good agreement with the theoretical model, which verifies the correctness of the impedance model established. Secondly, taking the wind-thermal bundling delivery system as the research object, the results of oscillation analysis based on the RL equivalent impedance model and the impedance model established in this paper are compared. The experimental results show that the impedance model established can identify the sub-/super-synchronous oscillation risk, while the equivalent impedance model based on the RL cannot accurately identify the risk. The applicability and accuracy of the model for stability analysis in power systems containing new energy and power electronic equipment are verified. Finally, the classical method of turbo-generator stability analysis, complex torque coefficient method, is used to analyze the oscillation of the wind-thermal bundled system again. The comparison results show that the impedance-based analysis method has certain advantages in the accuracy of the modern power system containing a large number of power electronic devices.
This study draws the following conclusions: 1) Compared with the equivalent circuit impedance of synchronous motor, the impedance model established in this research is more accurate near the natural torsional vibration frequency of turbo-generator shafting, which improves the accuracy of the model; 2) The turbo-generator impedance model established can perform stability analysis well in complex power systems containing new energy system and power electronic equipment, and is more accurate than the traditional turbo-generator impedance model in the sub-/super-synchronous frequency band; 3) Compared with the complex torque coefficient method, impedance analysis has certain advantages in accuracy in multi-machine systems containing power electronic devices.
李佳龙, 卢新宇, 杜雄, 刘俊良, 樊丽娟. 考虑轴系特性的汽轮发电机阻抗模型[J]. 电工技术学报, 0, (): 9029-29.
Li Jialong, Lu Xinyu, Du Xiong, Liu Junliang, Fan Lijuan. Impedance Model of Turbo-Generator Considering Torsional Characteristics of Shafting. Transactions of China Electrotechnical Society, 0, (): 9029-29.
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