Abstract
In an electric power grid that has a high penetration level of wind, the power fluctuation of a large-scale wind power plant (WPP) caused by varying wind speeds deteriorates the system frequency regulation. This paper proposes a power-smoothing scheme of a doubly-fed induction generator (DFIG) that significantly mitigates the system frequency fluctuation while preventing over-deceleration of the rotor speed. The proposed scheme employs an additional control loop relying on the system frequency deviation that operates in combination with the maximum power point tracking control loop. To improve the power-smoothing capability while preventing over-deceleration of the rotor speed, the gain of the additional loop is modified with the rotor speed and frequency deviation. The gain is set to be high if the rotor speed and/or frequency deviation is large. The simulation results based on the IEEE 14-bus system clearly demonstrate that the proposed scheme significantly lessens the output power fluctuation of a WPP under various scenarios by modifying the gain with the rotor speed and frequency deviation, and thereby it can regulate the frequency deviation within a narrow range.
Highlights
For an electric power grid that has a high penetration level of wind, the high fluctuation of wind causes difficulties in regulating the system frequency within a narrow range [1,2,3,4,5,6]. This is because variable-speed wind turbine generators (WTGs), such as doubly-fed induction generators (DFIGs) and fully-rated converter-based WTGs, perform maximum power point tracking (MPPT) control, which is unable to mitigate the fluctuating output power of the WTGs caused by the continuously varying wind speeds
This paper proposes a power-smoothing scheme of a DFIG relying on the frequency deviation
This paper proposes a power-smoothing scheme of a DFIG relying on the frequency deviation loop, the gain of which is modified depending on the rotor speed and frequency deviation
Summary
For an electric power grid that has a high penetration level of wind, the high fluctuation of wind causes difficulties in regulating the system frequency within a narrow range [1,2,3,4,5,6] This is because variable-speed wind turbine generators (WTGs), such as doubly-fed induction generators (DFIGs) and fully-rated converter-based WTGs, perform maximum power point tracking (MPPT) control, which is unable to mitigate the fluctuating output power of the WTGs caused by the continuously varying wind speeds. To avoid or reduce the additional cost for the ESS, power-smoothing schemes have been suggested that release or absorb the kinetic energy stored in the rotating masses of a WTG These schemes use additional control loops operating in conjunction with the MPPT control loop: the rate-of-change-of-frequency (ROCOF) loop and/or frequency deviation loop [11,12]. The performance of the proposed scheme is investigated under various scenarios, including continuously varying wind conditions for two wind power penetration levels in the IEEE 14-bus system using an EMTP-RV simulator
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