@article{awal_montes_teng_wang_bipu_yu_lukic_husain_2023, title={Medium Voltage Solid State Transformer for Extreme Fast Charging Applications}, ISSN={["1048-2334"]}, DOI={10.1109/APEC43580.2023.10131285}, abstractNote={A modular and scalable solid state transformer (SST) with direct medium voltage (MV) AC connectivity is proposed to enable DC extreme fast charging (XFC) of electric vehicles. Single-phase-modules (SPMs), each consisting of an active-front-end (AFE) stage and an isolated DC-DC stage, are connected in input-series-output-parallel (ISOP) configuration. The modular hardware is co-designed with decentralized control of the DC-DC stages where voltage and power balancing are achieved by each SPM using only its local sensor feedback; a centralized controller (CC) regulates the low voltage (LV) DC bus through the AFE stages without any sensor feedback form the SPMs. The controller architecture contrasts sharply with the prior art for MV AC to LV DC SSTs where high-speed bidirectional communication among SPMs and a CC are required for module-level voltage and power balancing, which severely limits the scalability and practical realization of higher voltage and higher power units. Detailed small-signal analysis and controller design guidelines are developed. Furthermore, a soft start-up strategy is presented. The proposed converter and control structure are validated through simulation and experimental results.}, journal={2023 IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION, APEC}, author={Awal, M. A. and Montes, Oscar Andres and Teng, Fei and Wang, Dakai and Bipu, Md Rashed Hasan and Yu, Wensong and Lukic, Srdjan and Husain, Iqbal}, year={2023}, pages={1528–1535} }
 @article{feng_teng_montes_awal_bipu_husain_lukic_2022, title={Passive Capacitor Voltage Balancing of SiC-Based Three-Level Dual-Active-Bridge Converter Using Hybrid NPC-Flying Capacitor Structure}, volume={37}, ISSN={["1941-0107"]}, DOI={10.1109/TPEL.2021.3119210}, abstractNote={Three-level (TL) dual-active-bridge (DAB) converter serves a critical role in the medium-voltage (MV) solid-state-transformers in which high voltage rating and bidirectional power flow are required. The regular neutral-point-clamping (NPC) topology is easily subjected to capacitor voltage unbalance due to nonideal operating conditions. In this article, a hybrid structure incorporating NPC and flying capacitor (FC) is presented to resolve the voltage unbalance issue. The key advantages include minimal additional hardware efforts and no need to resort to active control. The FC behaves as a buffer to leverage the upper and lower capacitor so that passive voltage balance between the two dc-link capacitors can be achieved on a switching cycle basis. Closed-form analysis further reveals the impact of FC value on voltage unbalance. Moreover, the appropriate modulation scheme, switching condition, and commutation loop are evaluated to provide detailed rule of thumb to the implementation of FC circuit. Analysis shows the FC also brings favorable switching loss performance and is friendly to employ upon fast switching of wide bandgap devices such as SiC. Finally, a 1.6 kV input, 400 V output, 8 kW scaled-down hybrid NPC-FC-based DAB converter is built to validate the above analysis.}, number={4}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={Feng, Hao and Teng, Fei and Montes, Oscar Andres and Awal, M. A. and Bipu, Md Rashed Hassan and Husain, Iqbal and Lukic, Srdjan}, year={2022}, month={Apr}, pages={4183–4194} }
 @article{awal_bipu_montes_feng_husain_yu_lukic_2020, title={Capacitor Voltage Balancing for Neutral Point Clamped Dual Active Bridge Converters}, volume={35}, ISSN={["1941-0107"]}, DOI={10.1109/TPEL.2020.2988272}, abstractNote={A capacitor voltage balancing method is proposed for a full-bridge neutral point diode clamped (NPC) dual-active bridge (DAB) converter. In existing literature, capacitor voltage balancing is achieved by actively selecting between the small voltage vectors, i.e., connecting either the upper or the lower capacitor on the dc bus to the transformer winding, on the basis of measured voltage mismatch. These balancing methods are dependent on the direction of power flow through the DAB converter. In this work, we propose a voltage balancing controller, which is independent of power flow direction and does not require adjustments of active voltage vectors through the modulator. Irrespective of the direction of transformer current, by dynamically shifting the switching instants of the inner switch pairs in the two NPC legs during the free-wheeling/zero voltage vector time, either of the two capacitors can be selectively charged without introducing any offsets in the voltage-second seen by the transformer. A simple bidirectional phase-shift modulator is designed to facilitate voltage balancing irrespective of power flow direction or mode of operation. The proposed method is highly and universally effective under any converter operating condition and was verified and demonstrated through analysis, simulation, and hardware experiments using a laboratory prototype.}, number={10}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={Awal, M. A. and Bipu, Md Rashed Hassan and Montes, Oscar Andres and Feng, Hao and Husain, Iqbal and Yu, Wensong and Lukic, Srdjan}, year={2020}, pages={11267–11276} }