IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 38, NO. 3, SEPTEMBER 2023 2075 Coordinated Control for Seamless Integration of Wind Energy Conversion System With Small Hydrogenerator Through Modified Notch Filters Shalvi Tyagi , Member, IEEE, Souvik Das , Member, IEEE, and Bhim Singh , Fellow, IEEE Abstract—This paper deals with the seamless integration of dou- bly fed induction generator (DFIG) based wind energy conversion system (WECS) with local grid constituted by a permanent magnet based small hydrogenerator (PMHG). The seamless integration is carried out using a solid state static transfer switch (SSSTS). The WECS-PMHG system is operated using a coordinated con- trol strategy based on modified notch filters. The modified notch filters are adopted for the computation of (a) sensorless speed and position of the DFIG rotor, (b) fundamental constituents of unbalanced/nonlinear load current and (c) filtered DFIG stator voltages and phase angle. Moreover, the notch filters are also used for mitigating the effects of unbalance/nonlinearity in load currents on the stator and rotor currents of DFIG as well as PMHG currents. Additionally, the control methodology ensures no power interaction between the WECS and the PMHG during the synchronization process. This enables transient-free WECS and PMHG currents. Further, the coordinated control regulates the amplitude and fre- quency of system voltages even amidst wide variations in wind speed and load. The DFIG stator and wind currents are injected at unity power factor with the system voltages, while the excitation requirement of the DFIG is met by its machine side converter. The validness of the control is demonstrated experimentally through a developed laboratory-scale test bench. Index Terms—Batteries, DFIG, microgrid, PMHG, small hydro, seamless, wind energy conversion system. I. INTRODUCTION E LEVATION in generation of electricity has driven the renewables to participate in the generation by 30% in 2021. The expansion in the installation of clean energy distributed sources (DSE) such as wind and hydro has led to the percentage increment of 17% and 6%, respectively as reported in [1]. With a modest growth in the generation of hydropower and offshore wind farms, the consolidation of DSE can improve the resiliency Manuscript received 3 October 2022; revised 12 February 2023; accepted 10 April 2023. Date of publication 21 April 2023; date of current version 22 August 2023. This work was supported by the DST, Govt. of India through SERB NSC Fellowship, under Grants FIST RP03391 and RP03357. Paper no. TEC-01020- 2022. (Corresponding author: Shalvi Tyagi.) The authors are with Electrical Engineering, Indian Institute of Tech- nology Delhi, New Delhi 110016, India (e-mail: tyagi.shalvi@gmail.com; souvik.das.926@gmail.com; bsingh@ee.iitd.ac.in). Color versions of one or more figures in this article are available at https://doi.org/10.1109/TEC.2023.3269079. Digital Object Identifier 10.1109/TEC.2023.3269079 of the grid. Intermittency of wind energy conversion system (WECS) can be mitigated with the integration of hydrogener- ators inculcating the benefits of constant power available from them. Mostly, these sources are operated as standalone entities [2], [3]. In standalone microgrids, due to the unavailability of the utility grid, the voltage and frequency at the AC link tend to vary due to the fluctuations in the local loads. Hydrogenerators have long been used to regulate the frequency of the microgrid during any abnormality in the system [4]. When combined with the wind energy conversion systems, the variation in the wind speed causes fluctuations in the frequency and nominal voltage at the point of common coupling (PCC). This can be eliminated by using energy storage system at the DC bus of wind generators [5]. These energy storage devices act as low pass filters to smoothen the wind power. Considering, separate energy storage unit can reduce the size of the battery and can provide economical solution [6]. During outage of the grid or any other unplanned event, the voltage and frequency of the system are affected, which needs to be stabilized [7]. Saeed et al. [8] have demonstrated a number of microgrid configurations based on the renewables, which can be instru- mental to provide reliable and continuous supply of power depending upon the location and availability. Wind and hydro based microgrid configuration is used in [9], where SyRG based hydrogenerator modulates the voltage and frequency of the AC link and wind generator is tied to DC link. Yet another microgrid configuration based on wind and pumped hydro storage is uti- lized in [10] to capture the complimentary nature of wind-hydro. During larger production of power from the wind, the excess power is harnessed to pump water from a lower reservoir and stored in upper reservoir. During wind fluctuations, this energy can be discharged to match the load demand and also reduces the frequency variations. Not to mention that the water stored in the upper reservoir acts as an energy storage and can be used for the blackstart purpose of the microgrid. In [11], Goel et al., have used squirrel cage induction machine-based wind and hydro generators. These generators are directly connected at the AC link, which might cause transients in currents and power transferred when both the sources are active in the system. Moreover, the system is not validated experimentally. To all intent and approaches, considering a mix of renewables greatly impacts the PCC voltages and frequency. Specifically, while integrating the AC sources, frequency and voltage deviations are 0885-8969 © 2023 IEEE. 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