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摘要
With the continuous increase of the transmission capacity of the line commutated converter based high voltage direct current (LCC-HVDC) system in the power grid, the coupling strength of AC and DC continues to deepen, and the strength of the AC system continues to weaken. The problems of small disturbance oscillation instability in the LCC-HVDC system are becoming increasingly prominent. Due to the clear physical concepts, impedance analysis method has been widely applied in the resonance analysis of LCC-HVDC systems, and the key to this method is to establish an impedance model. The accuracy of the impedance model directly affects the small disturbance stability analysis of the system. To improve the impedance modeling accuracy of LCC-HVDC, this article proposes a DC side impedance modeling method based on single-side modulated mapping function, which significantly improves the accuracy of the DC side impedance model. Firstly, starting from the principle of synchronous triggering, a mapping function based on single-side modulation is introduced, which contains control and commutation information, and thus accurately establishes the mapping relationship between the AC and DC sides during commutation/non commutation. Then, by combining the mapping function with the DC side voltage and converter transformer valve side current under different conduction states of the converter valve, the detailed commutation dynamics are considered and the complete frequency domain small signal dynamic models of DC side voltage and AC side current are obtained through harmonic linearization and Fourier transform. Furthermore, considering the damping circuit of the control and converter valve, establish analytical models for the DC impedance of the rectifier and inverter sides. Finally, taking the CIGRE high-voltage DC standard test model as an example, the accuracy of the DC side impedance model and its effectiveness in small disturbance stability analysis were verified based on the PSCAD/EMTDC platform. The following conclusions can be drawn from the simulation analysis: (1) Considering synchronous triggering and accurate commutation dynamics, a mapping function based on single-side modulation is proposed, which can accurately reflect the AC/DC modulation relationship during commutation/non commutation of LCC converters. (2) Analyzed the influence of commutation dynamics and RC circuit on the DC side impedance. The influence of commutation dynamics on the DC side impedance is mainly reflected in the lower frequency range, while the influence of RC circuit on it is mainly reflected in the higher frequency range. (3) Establish an accurate DC side impedance model that takes into account factors such as detailed commutation dynamics, control links, and RC circuit of the converter valve. Compared with existing switch function based modeling methods, this modeling method has higher accuracy. ? 2024 China Machine Press.
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