Abstract
A sub-/super-synchronous interaction (sub-/super-SCI) can occur between a voltage source converter-based high-voltage direct current (VSC-HVDC) and the permanent magnet synchronous generator (PMSG)-based wind farms with long AC transmission lines. However, the influencing factors have not been properly analyzed. In this paper, these are deconstructed and mathematically analyzed from detailed small-signal impedance equations in the dq-frame and the corresponding Bode stability criterion. Distinguishing conclusions from existing papers are obtained by studying the controllers’ bandwidths instead of their coefficients. The impacts of AC line impedance on system stability are also investigated. From the analysis of their compositions in impedance structure, the VSC-HVDC bandwidths and the wind farm phase-locked loop (PLL) bandwidth and power ratio, and the AC line impedance have various influences on the system stability. Meanwhile, the wind farm outer DC voltage and inner current control bandwidths have little impact on system stability. The results of these studies show that the magnitude in the axes q-axes impedance interaction is the essential factor for system instability. Our studies also show system stability is more sensitive to the HVDC bandwidths than the wind converter PLL bandwidth. The simulation results verify our theory conclusions.
Highlights
In response to the development of large-scale onshore and offshore wind farms, permanent magnet synchronous generator (PMSG) wind turbines have been gaining popularity for their ease of maintenance and dynamic performance in grid voltage fault ride through [1]
Due to the requirement for HVDC as a voltage source mode in the HVDC-based wind farm dedicated transmission line system, VSC-HVDC plays a prominent role in this application scenario
This paper presented an analysis of sub/super-SCI in a VSC-HVDC and PMSG-based wind farm system with AC transmission line
Summary
In response to the development of large-scale onshore and offshore wind farms, PMSG wind turbines have been gaining popularity for their ease of maintenance and dynamic performance in grid voltage fault ride through [1]. Paper [17] built a dqframe-based impedance models These papers indicate that the mechanism of sup/sub-SCI is the interaction between the controls of the VSC-HVDC and controls of the wind farm. All these papers lack a study of system stability influencing factors. Detailed analytical expressions of d-axes and q-axes impedance of PMSG wind farm and VSC-HVDC are present These expressions contain all possible influencing factors on system stability, such as wind farm power ratios (current), AC line impedance, and controllers’ parameters. The rest of this paper is organized as follows: Section 2 gives a small signal impedance model of the system controllers in the dq-frame, including the PMSG-based wind farm and VSC-HVDC sending terminal.
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