Subsynchronous control interaction (SSCI) associated with wind farms has become one of the major challenges for maintaining the stability and reliability of modern power systems. SSCI is mainly caused by the active participation of fast-acting wind turbine converter (WTC) controls in the phenomenon. It can damage the system equipment, reduce the amount of power generation, and degrade the power quality. Thus, it is urgent to develop practical mitigation techniques for the SSCI in order to achieve a smooth and reliable operation of grid interfaced wind farms. This study presents an overview of potential SSCI mitigation techniques at various stages of the power system, including system planning, operation, control, and protection phases at both network and generation sides. In particular, this paper reviews the active damping controls utilizing flexible ac transmission systems (FACTS) and WTC controls. Finally, it outlines the challenges and future work in studying SSCI mitigation techniques in practical wind power systems.

Mitigating subsynchronous control interaction in wind power systems: Existing techniques and open challenges

This paper is part II of a two-paper series that reviews, analyzes, and explores mitigation methods for sub-synchronous resonance (SSR) in series compensated doubly-fed induction generator (DFIG) based wind farms. The paper studies three different possibilities for the addition of controllers that perform SSR damping to eliminate induction generator effect SSO (SSIGE): controllers can be added to (1) thyristor-controlled series capacitor (TCSC) (2) gate-controlled series capacitor (GCSC), or (3) DFIG grid-side converter (GSC) controller. The first and second cases are related to the series flexible AC transmission systems (FACTS) family, and the third case uses the DFIG converters themselves to damp the SSR. In order to better understand this part II, it is highly recommended that part I of the two-paper series be studied first.

Sub-Synchronous Resonance Analysis in DFIG-Based Wind Farms: Mitigation Methods - TCSC, GCSC, and DFIG Controllers - Part II (Power-Point Presentation)

This paper presented an accurate analysis of the instability in DFIG-based wind farms due to the use of series compensation and provided maximum power extraction from these farms using the high compensation without the unstable sub-synchronous oscillation occurrence. For this purpose, using modal analysis, it is first shown that the main cause of this instability is low wind speed in the high compensation. This issue causes the series compensated DFIG-based wind farms is unstable due to a sub-synchronous mode. In order to prevent the unstable sub-synchronous oscillation occurrence, a supplementary controller called SSRIPC and DFIG controllers are used. Also, for good dynamic response and proper use of the SSRIPC, an objective function considered based on three factors of minimum damping ratio, overshoot, and settling time of the oscillations. By accurate optimization of the proposed controller using root-locus and PSO algorithm, it is prevented the instability caused by sub-synchronous resonance and sub-synchronous control interaction that are classes of the sub-synchronous oscillations. IEEE SSR first benchmark model and MATLAB/Simulink software are used to validate the performance of the proposed method.

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Safe Sub Synchronous Oscillations Response for Large DFIG-Based Wind Farms

Recently, a new type of subsynchronous oscillation (SSO) has occurred in doubly-fed induction generator (DFIG)-based wind farms. This oscillation is also called the subsynchronous control interaction (SSCI), which is mainly caused by the interaction between the transmission series compensation and the DFIG controller. Therefore, the oscillation frequency of the SSCI is susceptibly impacted by DFIG operating conditions, which presents major challenges to conventional mitigation strategies. To solve this problem, a grid-connected series-compensated DFIG-based wind farm is established, and the formation process of the SSCI is analysed. The strategy of active disturbance rejection control (ADRC), which can automatically estimate and compensate for the total disturbance of the system in real-time, is introduced into the rotor-side converter to mitigate the SSCI in the DFIG. ADRC is designed based on dynamic parameter tuning and chaos optimization. Finally, a detailed model-based time-domain simulation is conducted to evaluate the performance of the proposed optimized ADRC (O-ADRC) compared to conventional virtual impedance and ADRC. The simulation results show that O-ADRC can effectively mitigate the SSCI under different operating conditions and provide sufficient damping for the DFIG-based wind farms.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/gtd2.12228

Mitigation of subsynchronous control interaction in DFIGs using active disturbance rejection control

In this paper, subsynchronous resonance (SSR) instability was accurately analyzed in doubly fed induction generator (DFIG)-based wind farms by the linearization of equations and modal analysis. In addition, the possibility of high compensation for the transmission lines connected to DFIG-based wind farms was provided using a SSR prevention controller (SSRPC). For this purpose, an SSRPC was connected to the output voltage of the grid side converter (GSC) of the DFIG. The GSC output voltage was selected as the connection point of the SSRPC because it directly affects the induction generator effect (IGE) and can be an inhibitor factor in its occurrence. Furthermore, using system dynamic equations and the participation factor, it was shown that the effective factor on subsynchronous mode was the capacitor series voltage of the line, considered an input signal to the SSRPC. To validate the performance of the proposed method, a simulation was performed based on the IEEE SSR first benchmark model using the software MATLAB/Simulink.

https://journals.tubitak.gov.tr/elektrik/issues/elk-20-28-5/elk-28-5-20-1912-177.pdf

A subsynchronous resonance prevention for DFIG-based wind farms

Subsynchronous oscillations (SSO), especially, subsynchronous resonance are potential problems in series compensated power system. A fixed speed wind farm employing single cage induction generator (IG) and double cage IG connected to series compensated line are prone to SSR problem. This paper presents some investigations on SSO resulting from induction generator effect (IGE) with the wind turbine generator (WTG) modelled either as single cage IG or double cage IG. Eigenvalue analysis is carried out for various levels of series compensation for different sizes of wind farm with varying power outputs. Eigenvalue analysis is validated by the electromagnetic transient simulations using PSCAD/EMTDC software. The possibility of steady state SSR (IGE) and transient SSR is investigated in depth using PSCAD/EMTDC for the modified IEEE first bench mark (MFBM) model. SVC is employed for mitigating SSR. A new voltage regulator (VR) model of SVC is proposed and linear state space model of SVC is developed. Eigenvalue analysis conducted with the proposed voltage regulator reveals that the proposed VR model is more effective in mitigating SSR compared to VR models that are reported in the literature.

V. P. Boopathi

Papers

Analysis and mitigation of subsynchronous oscillations in a radially-connected wind farm