Faculty Publications

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Author: search.filters.author.Gaonkar, D.N.Subject: search.filters.subject.Phase locked loops

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    Seamless transfer of microturbine generation system operation between grid-connected and islanding modes
    (2009) Gaonkar, D.N.; Pillai, G.N.; Patel, R.N.
    The intentional islanding operation of grid-connected distributed generation systems can greatly improve the reliability and quality of the power supply. The existing control techniques for distributed generation systems are designed to operate either in the grid-connected or islanding modes of operation, thus, not allowing for both modes to be implemented and transitioned between. In this article, a novel scheme for automatic mode switching of a microturbine-based distributed generation system between the grid-connected and islanding modes of operation is proposed. The presented scheme is based on the phase angle estimated by the phase-locked loop. The developed phase-locked loop provides an accurate estimation of the phase angle even under unbalanced conditions. The presented scheme does not negatively affect the distributed generation system or utility operations and can work even under matching distributed generation and load power ratings. In this work, back-to-back converters are used to interface the microturbine-based distributed generation system to the grid. Converter control strategies developed for both modes of distributed generation operation is also presented. The simulation results show good accuracy of the proposed scheme.
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    Operation of the Microgrid with Improved Droop Control Strategy and an Effective Islanding Detection Technique for Automatic Mode Switching
    (Taylor and Francis Ltd., 2021) Kulkarni, S.V.; Gaonkar, D.N.; Guerrero, J.M.
    This paper presents the islanding detection and automatic mode switching for inverter-based distributed generation sources (DGs) in the microgrid with an improved droop controlled scheme. The modification in the conventional droop among the DGs is contrived to share the load proportionate to their power capacity. And to reduce the circulating currents and to improve reactive power-sharing the virtual impedance is implemented for the microgrid in the stand-alone mode operation. Also, the modified Park synchronous reference frame based phase-locked loop (PSRF-PLL) is implemented for the operation of the microgrid in the grid-connected mode. The islanding detection and automatic mode switching depend on the PSRF-PLL, which uses the input obtained from the stationary reference frame. The proposed PLL implemented in this work is simple in construction and keeps the phase locking error to near zero, thus leading to proper locking with reduced complexity. The control scheme's performance in the microgrid is validated using the real time hardware in the loop platform. The performance of PSRF-PLL based islanding detection scheme is analyzed considering the various grid disturbances, and the comparative study with the other PLL based scheme is also presented in this paper to show the improved performance of the proposed PSRF-PLL scheme. © 2021 Taylor & Francis Group, LLC.
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    HIL implementation of an islanding detection and an automatic mode switching for droop-based microgrid
    (Inderscience Publishers, 2022) Kulkarni, S.V.; Gaonkar, D.N.
    This paper presents the control schemes and performance study of parallel connected inverter based distributed generation sources (DGs) in microgrid for grid-connected and stand-alone modes of operation. This standalone mode of operation of inverter based DG system is mainly based on droop control scheme with the virtual complex impedance in the outer voltage loop. The microgrid load power is proportionally shared by the DGs according to their power ratings which features a good reliability and efficiency. Both the modes are switched automatically based on the Phase Locked Loop (PLL) phase error sin(γ – θ). This phase error is used to detect the islanding during disturbances in the system and also helps in seamless transfer between the modes. The PLL phase error response, islanding detection and mode switching are presented for various fault conditions. The hardware-in-the-loop (HIL) based platform is used to evaluate the performance of the microgrid in both the modes with islanding detection and automatic mode switching operation. © © 2022 Inderscience Enterprises Ltd.
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    A Novel Islanding Detection Technique Based on Piezoelectric Sensors for Grid-Integrated DG Systems
    (Taylor and Francis Ltd., 2023) Kulkarni, S.V.; Hegde, V.; Gaonkar, D.N.
    This paper presents the novel islanding detection technique that depends on the piezoelectric sensors for distributed generation sources (DGs) in the grid-integrated operation mode. The islanding detection method employs a piezoelectric sensor for the detection of the frequency variations during grid disruptions. The designed diaphragm-based sensor has a natural frequency as that of the fundamental frequency of the system frequency signal. Any further deviations from the natural frequency due to the disturbances will be sensed by the sensor and a control signal is being sent to the associated circuit breaker for suitable action. The sensor structure is modeled using the finite element method and implemented in the Phase-Locked Loop (PLL) of the grid-integrated DGs. The proposed circular diaphragm-based sensor structure will have the bandwidth in the range of natural frequency with the tolerance rate of ±1% and uses the input signal received from the PLL controller outer loop. The proposed islanding detection technique’s performance and reliability for grid-integrated DG are validated using the real-time hardware in the loop test-bed platform. The HIL virtual simulated responses show that the method can be proposed effectively for islanding detection in the event of frequency variations in the grid-integrated DG systems. © 2023 IETE.
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    A Fast and Robust PLL Design with a Combination of Frequency-Adaptive Alpha-Beta-CDSC and SOGI
    (Institute of Electrical and Electronics Engineers Inc., 2025) Mondal, S.; Gayen, P.K.; Gaonkar, D.N.
    Recent research has focused on the enhancement of the prefiltering capability of phase-locked loops (PLL). The cascaded delayed signal cancellation (CDSC) PLL removes the low-order selective harmonic frequencies near the fundamental frequency. Here, a frequency-adaptive time delay unit is used to cope with frequency and phase variations of voltage. The high-frequency signal arising due to the frequency-adaptive loop cannot be mitigated. In effect, the transient response of adaptive CDSC-PLL shows a significant irregular pattern. Therefore, this article suggests the use of a second-order generalized integrator (SOGI) after the adaptive CDSC unit to improve the transient profile of frequency response. In the design, the high gain (K = 5.4) of SOGI is chosen to quickly settle the response of PLL at the expense of its ignorance of lower-order harmonics near the fundamental frequency. However, the lower-order harmonics are selectively eliminated by the CDSC unit. So, both prefilters complement each other's filtering capabilities. Additionally, the suggested prefilter provides improved noise immunity and eliminates DC offset via the SOGI unit. The linearized model and tuning procedure for the different control parameters of the proposed PLL are described. The real-time hardware-in-loop tests are executed to justify the optimum performance of the proposed PLL. © 2024 IEEE.