**8. Conclusions**

A complete controller design method for AC current injection to a battery is developed in this manuscript. This method includes the passive component selection, controller gain selection, and controller architecture. The controller was able to operate for both synchronous buck and H-bridge converters. The proposed versatile controller successfully controlled the AC battery current for offline and online modes (while charging/discharging) over a range of frequencies and magnitudes as expected from the bode plot of the simulation. The proposed controller and design method will be useful for internal impedance measurement, advanced charging, and preheating applications. The advantage of the proposed technique is that it does not require any changes in the control architecture for different mode of operation for various topologies over a range of frequencies. The disadvantage of the proposed controller is that it requires voltage feedback for optimized operation. The performance of this controller with AC/DC/DC grid tied application is not verified yet and will be investigated in the future.

**Author Contributions:** All the authors contributed substantially to the manuscript. Contributions of each author are as follows: conceptualization, S.M.R.I.; methodology, S.M.R.I.; software, S.M.R.I.; validation, S.M.R.I. and S.-Y.P.; formal analysis, S.M.R.I.; investigation, S.M.R.I.; resources, S.M.R.I. and S.-Y.P.; data curation, S.M.R.I.; writing—original draft preparation, S.M.R.I.; writing—review

and editing, S.M.R.I. and S.-Y.P.; visualization, S.M.R.I.; supervision, S.-Y.P.; project administration, S.-Y.P.; funding acquisition, S.-Y.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Science Foundation of under Grant No. 1454578.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** This work was supported by the National Science Foundation under grant no. 1454578. However, any opinions, findings, conclusions, or recommendations expressed herein are those of the authors and do not necessarily reflect the views of the National Science Foundation.

**Conflicts of Interest:** The authors declare no conflict of interest.The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
