An Improved Droop Control Scheme of a Doubly-Fed Induction Generator for Various Disturbances

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.

Recent Trends in Wind Energy Conversion System with Grid Integration Based on Soft Computing Methods: Comprehensive Review, Comparisons and Insights

“…It enhanced the frequency nadir by minimum 18% as compared to the conventional frequency control approaches. In [136], Xu et al proposed an enhanced droop control method for a DFIG which can reduce the maximum frequency change rate and frequency nadir during the frequency regulation. The proposed droop control coefficient is a linear function of the frequency change rate.…”

New Synthetic Inertia Control for Wind Energy Conversion System

“…Where PDroop is the power generated from the Δf-dependent control loop; Δf is the frequency deviation; Kd is the Δfdependent control constant gain. Remark 2:  According to [12], the typical natural inertia Δfdependent control of the VSWTGs primarily influences the system's frequency nadir of the power system frequency response; it also has a limited impact on the system's ROCOF.  Regarding [7], the standard structure of Δf-dependent control with a fixed control gain is not capable of providing sufficient frequency regulation with different disturbances.…”

“…In power systems, during any disturbance, the system's inertial response is an inherent process in which the stored kinetic energy in the rotating masses is released and transmitted to the power system to resist the frequency drop. Due to the decrease in total system inertia with increasing penetration of renewable energy sources and under severe disturbance conditions, the frequency performance indicators could deteriorate [12]. Also, the power system's global rate of change of frequency (ROCOF) could be sufficient to activate under the frequency load-shedding protection scheme [13].…”

“…In [26], the typical natural inertial ∆f-dependent control, which mimics power-frequency droop characteristics for conventional synchronous generators, is studied. In [23,27], the performances of typical natural inertia ROCOFdependent and typical natural inertia ∆f-dependent control schemes for the VSWTs were analyzed using various fixed control gains; it was demonstrated that using conventional natural inertia controllers, which have large control coefficients with VSWTGs, delivers an appropriate frequency response, but wind turbine rotation stalling is highly probable because a large amount of the stored kinetic energy is released regardless of the available wind speed; on the other hand, lower control coefficients can prevent the wind turbine rotation stalling but contribute less to improving the system's frequency indices [12,23]. Moreover, the conventional natural inertia ∆f-dependent control scheme of the VSWTGs primarily influences the system's frequency nadir; however, it has a limited impact on the system's ROCOF.…”

Power System Stability Analysis of the Sicilian Network in the 2050 OSMOSE Project Scenario

“…Academic and industrial research studies have been (and are) extensively active in proposing methods and technologies able to transform RESs and loads into sources of flexibility by modifying their control procedures and/or combining them with Battery Energy Storage Systems (BESSs). More specifically: in [2][3][4] the authors propose control strategies to enable wind generators to provide Synthetic Inertia (SI); in [5] wind generators are made capable to provide primary droop frequency regulation; in [6,7] converter-interfaced generators are designed to provide SI; in [8][9][10] aggregates of thermal loads are controlled Energies 2022, 15, 3517 2 of 33 to provide primary and secondary frequency regulation services; in [11] a control strategy for a building air cooling system that provides secondary frequency regulation is experimentally validated; in [12] multiple BESSs are controlled to provide frequency regulation; in [13] BESSs are coupled with wind generators to provide frequency regulation services; in [14] a BESS is coupled with a large scale photovoltaic (PV) generator to provide primary frequency regulation; in [15] a decentralized control strategy is proposed to allow wind generators to provide primary voltage regulation; in [16] primary voltage regulation is realized by multiple BESSs via broadcast control at subtransmission level, while [17] generalizes this technique for any type of RES, applies it at distribution network level, upgrades it with an additional coordination level and compares it against centralized optimal reactive power control; in [18,19] voltage regulation is realized through DSR considering residential loads; in [20] voltage regulation performance form Distributed Energy Resources (DERs) are validated by Hardware-in-the-Loop simulations; in [21,22] voltage regulation is realized by PV generators; in [23] a chance-constrained optimization method is proposed to provide voltage regulation by DERs; in [24] voltage regulation is provided by distributed BESSs via reinforcement learning.…”