Research

Project Duration: Sep 2019-Jan 2020 (5 months)

Advisor: Dr Kaushik Basu, Dept. of EE, IISc

Optimal operation of dual active bridge (DAB) converters has been extensively researched in literature. The modulation parameters of the DAB converter are chosen to minimize a given objective function which can be the RMS or the peak of inductor current. This work presents a comparison of the optimal rms current problem and the optimal peak current problem. For medium power operation, a closed-form solution is derived for the modulation parameters which leads to minimum RMS currents. It is observed that the solution is computationally demanding and hence not suitable for real-time implementation.

A hybrid modulation strategy is proposed which achieves both optimal rms and peak currents and is simple to implement in real-time. Simulation and experimental results confirm the theoretical analysis.

Publication resulted from this work: D. Das and K. Basu, "Modulation Strategy to Minimize RMS and Peak Currents in Dual Active Bridge Converter," 2020 IEEE Energy Conversion Congress and Exposition (ECCE), (Accepted for publication).

Project Duration: Oct 2018-Jan 2019 (4 months)

Advisor: Dr Kaushik Basu, Dept. of EE, IISc

The battery chargers in electric vehicles need to have high efficiency and power density. Moreover, bidirectional power flow capability is necessary for vehicle to grid (V2G) applications. This work proposes a bidirectional isolated three phase AC-DC converter based on the dual active bridge (DAB) conversion principle and line frequency unfolding resulting in low switching loss.

Sections of the fundamental components of line currents are generated using DAB modulation and then appropriately combined to produce the actual line currents. The proposed solution can be used for bidirectional power flow and power factor correction. The high efficiency due to reduced switching loss and improved power density makes it a promising solution for battery chargers particularly in vehicle to grid (V2G) applications.

Publication resulted from this work: D. Das and K. Basu, "A Soft-switched isolated Single Stage Bidirectional Three phase AC-DC Converter," 2019 IEEE Energy Conversion Congress and Exposition (ECCE), Baltimore, MD, USA, 2019, pp. 596-601

Project Duration: Feb 2018-Sep 2018 (8 months)

Advisor: Dr Kaushik Basu, Dept. of EE, IISc

In vehicle to grid (V2G) applications, the battery charger of the electric vehicle (EV) needs to have a bidirectional power flow capability. Galvanic isolation is necessary for safety. An AC-DC bidirectional power converter with high-frequency isolation results in high power density, a key requirement for an on-board charger of an EV. Dual active bridge (DAB) converters are preferred in medium power and high voltage isolated DC/DC converters due to high power density and better efficiency. This work presents a DAB based three-phase AC-DC isolated converter with a novel modulation strategy that results in:

1) Single stage power conversion with no electrolytic capacitor, improving the reliability and power density

2) Open loop power factor correction

3) Soft switching of all semi-conductor devices

4) A simple linear relationship between control variable and transferred active power.

A detailed analysis along with simulation results and experimental verification is carried out for verifying the efficacy of the proposed solution.

Publication resulted from this work: D. Das, N. Weise, K. Basu, R. Baranwal and N. Mohan, "A Bidirectional Soft-Switched DAB-Based Single-Stage Three-Phase AC–DC Converter for V2G Application", in IEEE Transactions on Transportation Electrification, vol. 5, no. 1, pp. 186-199, March 2019.

Project Duration: May 2016-Dec 2017 (1 year 8 months)

Advisor: Dr U Jayachandra Shenoy, Dept. of EE, IISc

The popularity of distributed generating (DG) sources have been increasing over the past few years. With the increasing penetration of these DGs, the concept of microgrid is becoming popular. A microgrid is a small power system network with distributed generating sources which can operate seamlessly irrespective of the presence of the utility grid. Operating the microgrid in this manner increases system reliability and reduces power interruptions. However, it introduces several control challenges.

This work aims at analysing the behaviour of a microgrid system during the transition between grid connected mode and islanded mode of operation and address the control challenges through novel schemes. With the presence of grid, the microgrid system variables, such as voltage and frequency, are strictly regulated by the grid. The local sources follow the voltage and frequency reference set by the grid and supply constant power. With the loss of grid, that is when the system is islanded, the network variables need to be regulated by the local sources. The control structures for the inverter-based sources during the two operating modes are detailed in the present work.

With the loss of grid, the system should be able to transfer seamlessly to islanded mode without any transients. Similarly, when the grid supply is restored, the microgrid should seamlessly resynchronize to the grid without any transients. Two novel controller schemes for achieving seamless transfer between grid-connected and islanded mode in microgrids have been proposed. The first scheme uses an output feedback topology to reduce the transitions during mode transfer. The second scheme uses a Linear Quadratic Regulator theory-based compensator to achieve seamless transfer. The performance of the proposed schemes has been validated through simulations on a benchmark microgrid network.