Study and Design of Improved Synchronverter Control Schemes for Distributed Energy Resources

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Name of the Speaker: Hariharan R (EE17D009)
Name of the Guide: Dr. Mahesh Kumar
Date/Time: 28th October 2022, 2.30pm

Recently, there has been an increasing focus on control techniques for distributed energy resources (DERs) that emulate the behavior of a synchronous generator (SG). This type of control is known as synchronverter (SV) or virtual synchronous generator (VSG), which has the advantage of better stability. This research involves different improvements to the SV control of DERs under various conditions and configurations, which are briefly given as follows and the same will be presented in the talk. Initially, a simple gradient descent-based pre-synchronization control for SV scheme is proposed, which does not disturb local load connection to DER during the synchronization. The parameters of the proposed method are designed using steady state and transient response analysis, as compared to trial and error parameters tuning in previous virtual current-based methods. Experimental validations are presented for the proposed pre-synchronization control under all initial conditions, transient response analysis, local load changes, and grid integration. For an unbalanced grid condition, a simple integrated control combining the enhanced-PLL (EPLL) structure with the standard SV scheme is proposed, which allows DER to inject active and reactive power without double-frequency ripples. The proposed integrated control has a simple structure when compared to existing SV or VSG-based methods for an unbalanced grid. The effectiveness of the proposed integrated control is demonstrated by simulation and experimental results. Also, the effect of SV with virtual impedance or inductance during grid voltage variations is analyzed using a small-signal model. Due to the drawbacks inferred from analysis, the reactive power loop (RPL) of the SV scheme is improved to effectively suppress current transients, which is shown through small-signal analysis and simulations. The study of an isolated microgrid configuration with SV-controlled DERs is also discussed and complete small modeling is presented. For improving transient power sharing, virtual inductance is implemented and it is tuned using analysis from the microgrid model. These analysis are validated through experimental results of a microgrid.