Abstract
Doubly-fed induction generators (DFIGs) participate in the system frequency regulation using a fixed-coefficient droop control scheme. Nevertheless, the frequency-supporting capability of this control scheme with fixed gain is limited for different disturbances. This paper suggests an improved droop control scheme for a DFIG that can both alleviate the frequency nadir and maximum rate of change of frequency (ROCOF) during the frequency regulation. To achieve this, an adaptive droop control coefficient based on the ROCOF is suggested. The proposed droop control coefficient is a linear function of the ROCOF. Therefore, the proposed scheme can adjust the control coefficient according to the varying ROCOF. Simulation results clearly demonstrate that the proposed droop control scheme shows better effectiveness in improving the maximum ROCOF and frequency nadir under various sizes of disturbance, even in a varying wind speed.
Highlights
With the increasingly serious problems of energy shortage and environmental pollution, renewable energy power generation represented by wind power has developed rapidly [1]
The frequency quality indexes including the maximum rate of change of frequency (ROCOF, df/dt) and frequency nadir (FN) would be worse, and severe disturbance will lead to large-scale wind power off grid and lead to more serious chain problems [7,8]
This paper aims to design an adaptive droop control coefficient to reduce both the maximum frequency deviation and ROCOF effectively
Summary
With the increasingly serious problems of energy shortage and environmental pollution, renewable energy power generation represented by wind power has developed rapidly [1]. The study in [25] indicated that WTGs can emulate inertia response of TSGs with the ROCOF-based frequency control loop. The authors of [31] suggested a time-varying parameter droop control strategy considering the effective rotational kinetic energy of DFIG, which can effectively enhance the system frequency stability and prevent the stalling of wind turbines under different wind speeds. Based on the droop control scheme with fixed coefficient, this study advances an adaptive droop control strategy for a DFIG that improves the maximum ROCOF and frequency nadir under various disturbances. In this strategy, a novel droop control coefficient based on the ROCOF is suggested. The performances of the enhanced droop control strategy are investigated with various disturbances and wind conditions by EMTP-RV simulator
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