An Improved Quantitative Analysis Method of Oscillation Mode for DFIG-Based Wind Power Base With LCC-HVDC Transmission Considering Frequency Coupling Characteristic

The line-commutated converter-based high-voltage direct-current (LCC-HVDC) transmission has become one of the main forms to deliver wind power in China. However, due to the connections of a large number of power electronic devices (PEDs), there emerges a risk of sub/super-synchronous oscillations in the DFIG-based wind power base with LCC-HVDC transmission. The existing multi-node system analysis methods have ignored the frequency coupling characteristic (FCC) of PEDs, unable to obtain accurate oscillation characteristics. Besides, the relationship between the oscillation and multi-level factors has not been revealed yet. Therefore, this paper proposes an improved quantitative analysis method of oscillation mode which considers the FCC on the basis of the system admittance network model. Firstly, the impedance model of the system considering the FCC is established. Then, the improved quantitative analysis method of the oscillation mode considering the FCC is proposed and its steps are as follows. 1) To establish the system transfer function matrix considering the FCC, and determine the system stability accurately by the dominant oscillation mode; 2) To define the node oscillation participation factor, considering the effect of the coupling frequency, and quantify the participation degree of each node and identify the origin and weak point of oscillation; 3) To carry out multi-level oscillation mode sensitivity analysis. Finally, the oscillation characteristics and laws of the DFIG-based wind power base with LCC-HVDC transmission are studied, and the time-domain simulations in MATLAB/Simulink validate the analytical results.