Abstract
This paper is dedicated to presenting control-tuning methodologies for the rotor-side converter (RSC) and grid-side converter (GSC) of series-compensated DFIG-based wind farms (WF) and to determining the origin of subsynchronous resonance (SSR). Unlike conventional approaches to re-tuning controller gains to achieve desirable performance, these methodologies only consider the mathematical models of the states variables to be controlled. A PI cascade topology is used to control the RSC and GSC. An inner loop is required for current control and an outer loop for voltage control. Special consideration is taken for tuning the RSC because this converter is coupled with the mechanical variables as mechanical rotor speed of the DFIG. Compared with standard tuning, a better system behavior during a resonance condition is achieved with the proposed tuning methodology. Regarding the analysis of the SSR origin, the modal impedance (MI) technique is used as a tool to study SSR issues; its advantages compared to the driving point impedance technique are highlighted. In this context, the small-signal-stability (SSS) analysis is performed to evaluate the overall system. With the combination of MI and SSS, the phenomena of induction generator effect, torque interaction, and torque amplification are analyzed. As a result, the modes involved in the SSR phenomenon are identified and a discrimination procedure is described to determine the origin of the SSR.
Highlights
According to Global Wind Energy Council (GWEC), wind energy is the most promising green power for bulk production due to it becomes more profitable each year and has an increasing global commitment to combat climate change [1]
The proposed methodology to calculate the gains of the GSC controller (GSCC) and RSC controller (RSCC) is compared against the ones reported in the literature; this comparison is conducted with quasistationary changes in the series compensation to produce subsynchronous resonance (SSR)
The evaluation of the system performance with these two sets of gains is conducted by simulating the system with series compensation of 10% as an initial condition, when the system reaches the steady-state at 100 seconds, the series compensation is changed to 70%, and to 71% at 105 seconds
Summary
According to Global Wind Energy Council (GWEC), wind energy is the most promising green power for bulk production due to it becomes more profitable each year and has an increasing global commitment to combat climate change [1]. The merit of this approach is that it only requires the linearization of those state variables to be controlled, instead of the linearization of the entire system as the proposed. The bidirectional switching functions are identified by S and Sfor each phase which can be either on or off (1 or 0, states of the switch), respectively [32]
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