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 Chongqing 400044 China; 2. System Research Institute CSG Electric Power Research Institute Guangzhou 510663 China
Abstract：Due to the increasing number of electronic power devices in power systems, power system structures have become complicated, and analyzing power system stability containing power electronic devices and turbo-generators is difficult. The impedance-based analysis method is a good choice because extending the system topology and establishing the black box system model is easy. However, the impedance of the turbo-generator only reflects electrical characteristics. This paper establishes an impedance model of the turbo-generator considering the mechanical part of the turbine, governor, and shafting mass-spring. The turbo-generator is divided into electrical and mechanical parts. For the electrical part modeling, an ideal state is assumed, and the small signal equation of the synchronous motor is standardized. For the mechanical part modeling, a small signal model is established for the shafting part, steam turbine, and speed regulator. Calculation results show that the impedance model of the turbo-generator in the d-q coordinate system is a 2nd-order matrix. Finally, the impedance model of the turbo-generator considering the shafting part is obtained by converting it into a sequence impedance model and considering the frequency coupling effect. The theoretical model is verified by the frequency scanning method. The experimental results of frequency scanning points agree with the theoretical model, which verifies the correctness of the impedance model. Taking the wind-thermal bundling delivery system as the research object, compared with the oscillation analysis based on the RL equivalent impedance model, the proposed impedance model can identify the sub-/super-synchronous oscillation risk. The proposed model for stability analysis in power systems containing new energy and power electronic equipment is verified. Finally, the classical turbo-generator stability analysis, i.e., the complex torque coefficient method, is used to analyze the oscillation of the wind-thermal bundled system. This study draws the following conclusions. (1) Compared with the equivalent circuit impedance of the synchronous motor, the proposed impedance model is more accurate near the natural torsional vibration frequency of the turbo-generator shafting, improving the model’s accuracy. (2) The turbo-generator impedance model can perform stability analysis well in complex power systems containing new energy systems and power electronic equipment. It 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, the impedance-based analysis has advantages in accuracy in multi-machine systems containing electronic power 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, 2024, 39(15): 4767-4781.
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, 2024, 39(15): 4767-4781.
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