| MS Seminar

Name of the Speaker: Mr. Avinash V S N Bhamidipati (EE21S136)
Guide: Dr. Krishna Vasudevan
Venue: ESB-244 (Seminar Hall)
Date/Time: 2nd April 2025 (Wednesday), 3.30 PM
Title: Study of current control strategies for grid-tied inverter.

Abstract :

The recent advancements in modern technology and our goal of achieving net-zero carbon emissions have led to the transition to self-reliant electrical networks called microgrids that can operate independently of the main grid and generate power locally. In this modern era of microgrid technology, grid-tied inverters and their control strategies play a vital role in integrating various distributed energy resources (DERs) into the grid and injecting power.

For the past several decades, a grid-tied inverter connected through an L filter has been very popular due to its simplicity and ease of implementation in the control strategy. In recent years, LCL filters have gained popularity over L filters due to their compact design and cost-effectiveness for similar output power requirements. The main drawback of an LCL filter when implementing a control strategy is its resonant frequency, which must be suppressed using various passive or active damping strategies widely discussed in the literature.

However, the most crucial challenging factor for the various control techniques is the presence of computational delays and dead time involved in real-world systems, which can potentially impact the stability and performance of controllers. Some of the commonly used control strategies for grid-tied inverters are first studied. Then the need for an alternative control strategy suitable for grid-tied inverters is discussed. The formulation of a dual-loop current control (DLCC) strategy in a synchronous reference frame for grid-tied inverters equipped with an LCL filter is presented. It highlights the significance of feedforward and decoupling terms in obtaining proper plant models and the capacitor voltage buildup for smooth synchronisation of a voltage source inverter with the grid. The impact of inverter delay on DLCC controller design is validated through MATLAB results. The influence of dead time for grid-tied inverter applications is studied, and its impact on the controller dynamics is presented. The methods to compensate for the lower-order harmonics resulting in voltage source inverters due to dead time have also been brought out. Finally, the simulation results of the dual-loop current control strategy with dead-time harmonic compensation are presented and validated on a 12 kW SiC-based solar PV inverter.

While the applications of solar PV systems have been the motivator, a technology demonstrator for the conversion of the work potential of steam into a grid-injectable output power has also been studied for future implementation of the proposed dual-loop current control strategy.