SOMBUDDHA CHAKRABORTY - Academia.edu (original) (raw)

Papers by SOMBUDDHA CHAKRABORTY

2022 IEEE International Ultrasonics Symposium (IUS), Oct 10, 2022

IEEE Transactions on Power Electronics, 2018

High step-down dc/dc converters are widely utilized in telecom and modern industrial applications... more High step-down dc/dc converters are widely utilized in telecom and modern industrial applications. Due to the high step-down ratio, conventional Buck converter cannot provide satisfactory performance. To solve this problem, quite a few new topologies have been proposed to improve the performance of high step-down dc/dc converters, such as series-capacitor Buck (SC-Buck) converter, 3-level Buck converters, tapped inductor Buck converters, and LLC resonant converters. In this paper, the twice step-down benefit of SC-Buck converter and the zero-voltage switching benefit of series-capacitor tapped Buck (SC-TaB) converter are combined together to propose a new topology: interleaved series-capacitor tapped Buck (ISC-TaB) converter. To analyze the performance of the proposed ISC-TaB converter, the operation principles are discussed and the voltage conversion ratio is derived. In addition, to guide the design procedure and optimization, the current waveforms and voltage waveforms of the proposed ISC-TaB are derived. In order to verify the performance of the proposed ISC-TaB, hardware prototype of the proposed ISC-TaB converter and conventional two-phase series-capacitor tapped Buck converter (2ph-TaB) are designed and tested. The application is targeted at telecom with 48-V input and 3.3 V/20 A output. The test results are compared between these two converters. A peak efficiency of 95.6% is achieved on the proposed ISC-TaB and the efficiency of the ISC-TaB over all load range is at least 1% higher than that of 2ph-TaB.

2019 IEEE Applied Power Electronics Conference and Exposition (APEC)

This paper proposes the design of a dc-dc converter for portable charger applications that uses a... more This paper proposes the design of a dc-dc converter for portable charger applications that uses a Variable-Inverter-Rectifier-Transformer (VIRT) with improved step-down capability. The proposed design leverages an improved rectifier structure to achieve high efficiency (up to 96.2 %) across a wide range of input (120-380 V) and output voltages (5-20 V) at an output power of up to 50 W. The new rectifier configuration incorporates a bypass switch which allows for a full utilization of the effective transformer core area across all modes of operation, improving the core loss of the transformer. Moreover, a hybrid Litz-PCB construction of the VIRT transformer further reduces copper loss by mitigating skin and proximity effects, and enables integration of the LLC converter magnetics into a single component. A hardware prototype of the converter achieves a box power density of 23.2 W/in 3 , and maintains high efficiency and low worst-case power loss across the wide input and output voltage ranges.

IEEE Transactions on Power Electronics, 2022

IEEE 2002 28th Annual Conference of the Industrial Electronics Society. IECON 02, 2002

Purpose: To determine the 1-year changes of mesopic higher order aberrations (HOAs) and contrast ... more Purpose: To determine the 1-year changes of mesopic higher order aberrations (HOAs) and contrast sensitivity (CS) after accelerated corneal cross linking (CXL) in progressive keratoconus. Methods: In this prospective case series, 70 eyes of 62 keratoconic patients underwent accelerated CXL (18 mW/cm 2 , 5 min). HOAs and CS were measured using the OPD Scan III and CSV-1000 CS test charts under mesopic conditions before and 6 and 12 months after CXL. Results: At 1 year, logarithmic mesopic CS in spatial frequencies of 3, 6, 12, and 18 cycles per degree (CPD) had increased by 0.05 ± 0.29 (P ¼ 0.029), 0.04 ± 0.88 (P ¼ 0.012), 0.27 ± 0.46 (P ¼ 0.172), and 0.06 ± 0.22 (P ¼ 0.020), respectively. The decrease in ocular HOAs (0.10 ± 0.69 mm, P ¼ 0.992) [coma (0.08 ± 1.01 mm, P ¼ 0.613), trefoil (0.03 ± 0.37 mm, P ¼ 0.659), and spherical aberration (SA) (0.10 ± 0.59 mm, P ¼ 0.743)] and corneal HOAs (0.40 ± 1.69 mm, P ¼ 0.874) [coma (0.39 ± 1.59 mm, P ¼ 0.401), trefoil (0.33 ± 2.16 mm, P ¼ 0.368), and SA (1.27 ± 1.14 mm, P ¼ 0.354)] were not statistically significant. The correlations between mesopic CS and HOAs were weak before and after CXL. Conclusion: One year after accelerated CXL, CS significantly improved, but changes in HOAs were statistically insignificant. CS changes were independent of HOAs.

2017 IEEE Applied Power Electronics Conference and Exposition (APEC), 2017

This paper demonstrates a two-stage implementation of a power factor preregulator design in which... more This paper demonstrates a two-stage implementation of a power factor preregulator design in which the energy buffer capacitor is placed at the output of the converter. In this implementation, a resonant LLC converter supplies power to a boost converter operating in continuous conduction mode. Here, a variable frequency (VFX) technique is used in the resonant LLC converter stage to achieve a lower variation in the overall efficiency across the universal input voltage range (85 — 265Vrms). The efficiency performance achieved is flatter than other single-stage boost-based power factor correction circuits, whose efficiency tends to drop significantly at low input voltages. The VFX technique not only compresses the effective operating range required of the resonant converter stage, but also allows MOSFETs with lower voltage ratings and better conduction/switching characteristics to be used in both converter stages.

IEEE Open Journal of Vehicular Technology, 2021

A new architecture for electric vehicle (EV) traction system with multiple low voltage battery pa... more A new architecture for electric vehicle (EV) traction system with multiple low voltage battery packs and high conversion ratio DC-DC converters is proposed here. In EV traction systems, higher voltage motors offer improved efficiency and power density. High power DC fast charging also favors charging at high DC voltages to limit the charging cable current to manageable levels. However, the optimum battery voltage is relatively low considering factors such as issues with large number of cells in series and safety. In some designs, a boost DC-DC converter is employed to accommodate large variation in battery voltage and provide a high DC link voltage. However, the DC link cannot go below the battery voltage (for example, 360 V) which limits the benefits of the DC-DC converter. The proposed architecture with multiple 48 V battery packs and integrated, multi-input, high conversion ratio DC-DC converters, can reduce the maximum voltage in the vehicle during emergencies to 48 V, mitigate issues with large number of cells in series, and provide a wide variable DC link voltage. It enables independent charging/discharging control of the different low-voltage battery modules ensuring cell balancing and enhancing reliability. The proposed topology significantly reduces the voltage stress and peak/RMS current stress of the switches. It features seamless bi-directional power flow characteristics, which support regenerative braking and high voltage DC fast charging. Four distinct configurations are analyzed and the configurations with interleaving are shown to improve performance and significantly reduce the filter inductor size. The proposed high conversion ratio converter (HCRC) operation for EV application is verified experimentally through a 4-phase multi-input, 4 kW hardware prototype. With the nominal input fixed to 48 V, the output voltage is controlled to vary between 200 V to 800 V. The converter achieves a peak efficiency of 98.36% and a full-load efficiency of 97.3% at 50 kHz switching frequency for the interleaved configuration.

2018 IEEE 19th Workshop on Control and Modeling for Power Electronics (COMPEL), 2018

This paper introduces a novel single inductor multi-output LED driver. The converter is able to s... more This paper introduces a novel single inductor multi-output LED driver. The converter is able to significantly reduce the area of passive components while maintaining high power processing efficiency by dividing power between a switched capacitor (SC) and a buck-boost converter and taking the output differentially from the two outputs. The volume of the SC converter is reduced by operating the buck-boost converter in DCM and increasing the number of SC switching states from two to three. An experimental setup verifies the effectiveness of the design and indicates an efficiency improvement of 2.5% while reducing passive component area by 63% and increasing the operating range compared to conventional commercial products.

IEEE Open Journal of Power Electronics, 2021

Piezoelectric resonators have shown promise as efficient, power-dense energy storage element alte... more Piezoelectric resonators have shown promise as efficient, power-dense energy storage element alternatives to continue the miniaturization of DC-DC converters. However, practical piezoelectric resonators diverge from their ideal behavior due to spurious modes that cause high loss regions throughout their operating frequency range. Typically, control of piezoelectric resonator DC-DC converters is constrained to unidirectional power flow each resonant cycle for maximum efficiency operation. However, output power depends on the frequency with such control, which means the converter cannot operate at loads corresponding to spurious mode frequencies. This paper presents a fixed-frequency control mode utilizing the high-quality factor of piezoelectric resonators to avoid spurious modes. The fixed-frequency control enables efficient operation spanning the converter's full load range, demonstrated through a prototype DC-DC converter with a custom fabricated lithium niobate resonator. At a conversion ratio of 60 V to 30 V, spurious modes limit the converter's operating range from 33 W to 51 W using unidirectional power-constrained control, yet the fixed-frequency control extends operation from 33 W to 2 W. INDEX TERMS DC-DC power converters, piezoelectric devices.

2021 IEEE Applied Power Electronics Conference and Exposition (APEC), 2021

In this paper, a phase shedding control scheme for extended-duty-ratio (EDR) boost converter is p... more In this paper, a phase shedding control scheme for extended-duty-ratio (EDR) boost converter is proposed to achieve wide input and output voltage range operation of the converter. EDR converters can achieve very high gain, for example above 20 for a 4-phase converter, but have limitations on the lowest allowable gain. The proposed scheme allows operation at gain as low as unity while retaining the main benefits of EDR boost such as low voltage stress across switches. The phase shedding control can be optimized based on the application requirements. In this paper, the phase shedding control is optimized for low device voltage stress over wide input and output voltage range operation. The converter control implementation is discussed in detail. The control scheme is verified with a 4-phase EDR boost converter with input voltage varying between 20 V–40 V and output voltage ranging between 50 V–400 V. Experimental results of closed loop operation with adaptive PI controller are presented and the phase shedding scheme is verified by showing the transition from one configuration to another based on the converters varying gain.

2019 IEEE Energy Conversion Congress and Exposition (ECCE), 2019

This paper presents the design and implementation of an ac-dc converter for portable charger appl... more This paper presents the design and implementation of an ac-dc converter for portable charger applications that uses a new variant of the recently-proposed Variable-Inverter-Rectifier-Transformer (VIRT) technique. This new version of the VIRT technique provides improved efficiency and step-down capability through inclusion of a bypass switch. The proposed design adopts both the Variable Frequency Multiplier (VFX) and the VIRT with bypass technique to maintain high performance across a wide range of input (85 - 265 Vac) and output voltages (5 - 20 Vdc) at an output power of up to 65 W. The VIRT with bypass technique enables full utilization of the transformer core area across all modes of operation and significantly reduces transformer loss. The hardware prototype achieves a displacement power density of 44.6 W/in3 and peak efficiency of 95.1% at the rated power of 65 W.

2020 IEEE Energy Conversion Congress and Exposition (ECCE), 2020

This paper introduces a single-stage universal-input isolated ac-dc converter based on the impeda... more This paper introduces a single-stage universal-input isolated ac-dc converter based on the impedance control network (ICN) architecture. This single-stage converter can perform power factor correction (PFC) and output voltage regulation, while maintaining high efficiency over its entire range of ac input voltage and output power. By using appropriate inverter and rectifier phase-shift control strategies, this converter achieves soft-switching of all inverter transistors with minimal circulating current, throughout the line cycle. The ICN converter also allows all its inductors to be integrated and realized in a single magnetic structure, reducing the number of magnetic components in this converter to two. A design methodology for ICN-based ac-dc converters is also introduced. A universal-input, 20-V output, 400-kHz GaN-based prototype ICN-based ac-dc converter, designed for a maximum output power of 330 W, is built, and tested. The prototype achieves a full-power efficiency of 92%. This paper is the first reported work on the architecture, design, and control of ICN-based ac-dc converters.

IEEE Transactions on Power Electronics, 2021

This article introduces a new single-stage universal-input isolated ac–dc converter based on the ... more This article introduces a new single-stage universal-input isolated ac–dc converter based on the impedance control network (ICN) architecture. This resonant converter performs both power factor correction and output voltage regulation while operating at a constant switching frequency and duty ratio, by modulating the phase-shift between its two half-bridge inverters and the phase-shift between the two legs of its full-bridge rectifier. This phase-shift control strategy along with the ICN architecture also enables the converter to achieve high efficiency by ensuring zero-voltage-switching and near-zero-current-switching of all its inverter transistors throughout the line cycle and across wide ranges of input line voltage and output power. Power density is enhanced by realizing the three ICN inductors using a single magnetic structure with two coupled windings. This coupled inductor and a transformer constitute the two magnetic components of the proposed converter. A systematic methodology to design this ICN ac–dc converter is also introduced. A universal-input (90–265 Vrms), 20-V output, 330-W, 400-kHz ICN ac–dc converter prototype is built and tested. This prototype achieves a power density of 37.9 W/in3 and peak efficiencies of 91.7%, 92.2%, 93.2%, and 93.4% at 90, 120, 230, and 265 Vrms input, respectively.

IEEE Open Journal of Power Electronics, 2021

The performance of inductors at high frequencies and small sizes is one of the largest limiting f... more The performance of inductors at high frequencies and small sizes is one of the largest limiting factors in the continued miniaturization of dc-dc converters. Piezoelectric resonators can have a very high quality factor and provide an inductive impedance between their series and parallel resonant frequencies, making them a promising technology for further miniaturizing dc-dc converters. In this paper we analyze the impact of resonator parameters on the performance of the piezoelectric resonator based dc-dc converter, derive the optimal load impedance and efficiency limits, and analyze the impacts of varying conversion ratio and load impedance. This work is accompanied by a prototype dc-dc converter using a piezoelectric resonator fabricated from lithium niobate. The piezoelectric resonator has a quality factor of 4178 and a coupling coefficient, k 2 t , of 29%. The converter is able to achieve high efficiency zero voltage switching and a continuously variable conversion ratio without the use of any discrete inductors. It achieves a maximum power output of 30.9 W at an efficiency of 95.2% with a power density of 6.76 W cm 3. INDEX TERMS DC-DC power converters, piezoelectric devices.

IEEE Journal of Emerging and Selected Topics in Industrial Electronics, 2021

2019 IEEE Energy Conversion Congress and Exposition (ECCE), 2019

This paper analyzes the fault tolerance of non-isolated, modular, high gain dc-dc boost converter... more This paper analyzes the fault tolerance of non-isolated, modular, high gain dc-dc boost converter under different fault conditions. In the absence of transformer isolation, there are safety concerns in high gain converters in ensuring that high voltage stress is not applied to low voltage ports under any component failure conditions. The main idea is to increase the reliability of converter operation by making minimal modifications to the actual converter and control scheme as well as minimal component addition. Fuses are incorporated in the converter and their control co-ordination with different phase switches is proposed to ensure normal operation under various faults. The proposed method is discussed and implemented to ensure normal operation of converter under different component failures and verified through simulation results. The main faults under consideration are the short circuit fault and open circuit fault of the MOSFETs, diodes and coupling capacitors. The discussed methods are analyzed, tested and validated with a 35V-600V, 500W 4-phase hardware prototype.

2019 IEEE Energy Conversion Congress and Exposition (ECCE), 2019

This paper analyzes the operation of a high gain non-isolated boost converter that is a combinati... more This paper analyzes the operation of a high gain non-isolated boost converter that is a combination of interleaved boost and switched capacitor configuration in critical conduction mode. The converter is able to provide high gain while reducing the current and voltage stresses on semiconductor devices. The converter operation can be divided into different zones based on the duty ratio of operation. In Zone I, which corresponds to the highest gain, the converter possesses inherent current sharing properties among different phases. The inductance value and size are reduced significantly due to interleaving. To further reduce the size, the converter is operated in critical conduction mode. This also results in increased efficiency as turn-on losses of the MOSFETs are zero. A 2kW silicon MOSFET based 4-phase prototype with 42V-52V input and 850V output and operating at varying frequency to maintain critical conduction mode operation at various power levels has been developed to validate the proposed scheme. The total inductor volume is reduced by 48% and the efficiency improves by 0.9% at rated load in CRM operation with the peak efficiency of 97.2% achieved at 1200W.

IEEE Journal of Emerging and Selected Topics in Power Electronics, 2020

Part of the Law Commons This Article is brought to you for free and open access by the University... more Part of the Law Commons This Article is brought to you for free and open access by the University of Minnesota Law School. It has been accepted for inclusion in Minnesota Law Review collection by an authorized administrator of the Scholarship Repository. For more information, please contact

IEEE Transactions on Power Electronics, 2020

The Class Φ 2 /EF 2 amplifier is an attractive topology for high-voltage and high-frequency power... more The Class Φ 2 /EF 2 amplifier is an attractive topology for high-voltage and high-frequency power conversion because of the high efficiency, reduced device voltage stress, simplicity of gate driving, and load-independent ZVS operation. Due to many degrees of freedom for tuning, previous studies can only solve the single-ended Φ 2 circuit using numerical methods. This work focuses on improving the design and operating characteristics of a push-pull Φ 2 amplifier with a T network connected between the switch nodes, or a PPT Φ 2 amplifier. The PPT Φ 2 amplifier has less circulating energy and achieves higher cutoff frequency f T than other Φ 2 /EF 2 circuits. We, then, present a series-stacked input configuration to reduce the switch voltage stress and improve the efficiency and power density. A compact 6.78-MHz, 100-V, 300-W prototype converter is demonstrated that uses low-cost Si devices and achieves 96% peak total efficiency and maintains above 94.5% drain efficiency across a wide range of voltage and power. Together with the advances in wide-bandgap semiconductors and magnetic materials, the PPT Φ 2 circuit opens more possibilities for the state-of-the-art performance of solid-state RF amplifiers in high-frequency, high-power applications, including wireless charging for electric vehicles, plasma RF drives, and nuclear magnetic resonance spectroscopy.

2022 IEEE International Ultrasonics Symposium (IUS), Oct 10, 2022

IEEE Transactions on Power Electronics, 2018

High step-down dc/dc converters are widely utilized in telecom and modern industrial applications... more High step-down dc/dc converters are widely utilized in telecom and modern industrial applications. Due to the high step-down ratio, conventional Buck converter cannot provide satisfactory performance. To solve this problem, quite a few new topologies have been proposed to improve the performance of high step-down dc/dc converters, such as series-capacitor Buck (SC-Buck) converter, 3-level Buck converters, tapped inductor Buck converters, and LLC resonant converters. In this paper, the twice step-down benefit of SC-Buck converter and the zero-voltage switching benefit of series-capacitor tapped Buck (SC-TaB) converter are combined together to propose a new topology: interleaved series-capacitor tapped Buck (ISC-TaB) converter. To analyze the performance of the proposed ISC-TaB converter, the operation principles are discussed and the voltage conversion ratio is derived. In addition, to guide the design procedure and optimization, the current waveforms and voltage waveforms of the proposed ISC-TaB are derived. In order to verify the performance of the proposed ISC-TaB, hardware prototype of the proposed ISC-TaB converter and conventional two-phase series-capacitor tapped Buck converter (2ph-TaB) are designed and tested. The application is targeted at telecom with 48-V input and 3.3 V/20 A output. The test results are compared between these two converters. A peak efficiency of 95.6% is achieved on the proposed ISC-TaB and the efficiency of the ISC-TaB over all load range is at least 1% higher than that of 2ph-TaB.

2019 IEEE Applied Power Electronics Conference and Exposition (APEC)

This paper proposes the design of a dc-dc converter for portable charger applications that uses a... more This paper proposes the design of a dc-dc converter for portable charger applications that uses a Variable-Inverter-Rectifier-Transformer (VIRT) with improved step-down capability. The proposed design leverages an improved rectifier structure to achieve high efficiency (up to 96.2 %) across a wide range of input (120-380 V) and output voltages (5-20 V) at an output power of up to 50 W. The new rectifier configuration incorporates a bypass switch which allows for a full utilization of the effective transformer core area across all modes of operation, improving the core loss of the transformer. Moreover, a hybrid Litz-PCB construction of the VIRT transformer further reduces copper loss by mitigating skin and proximity effects, and enables integration of the LLC converter magnetics into a single component. A hardware prototype of the converter achieves a box power density of 23.2 W/in 3 , and maintains high efficiency and low worst-case power loss across the wide input and output voltage ranges.

IEEE Transactions on Power Electronics, 2022

IEEE 2002 28th Annual Conference of the Industrial Electronics Society. IECON 02, 2002

Purpose: To determine the 1-year changes of mesopic higher order aberrations (HOAs) and contrast ... more Purpose: To determine the 1-year changes of mesopic higher order aberrations (HOAs) and contrast sensitivity (CS) after accelerated corneal cross linking (CXL) in progressive keratoconus. Methods: In this prospective case series, 70 eyes of 62 keratoconic patients underwent accelerated CXL (18 mW/cm 2 , 5 min). HOAs and CS were measured using the OPD Scan III and CSV-1000 CS test charts under mesopic conditions before and 6 and 12 months after CXL. Results: At 1 year, logarithmic mesopic CS in spatial frequencies of 3, 6, 12, and 18 cycles per degree (CPD) had increased by 0.05 ± 0.29 (P ¼ 0.029), 0.04 ± 0.88 (P ¼ 0.012), 0.27 ± 0.46 (P ¼ 0.172), and 0.06 ± 0.22 (P ¼ 0.020), respectively. The decrease in ocular HOAs (0.10 ± 0.69 mm, P ¼ 0.992) [coma (0.08 ± 1.01 mm, P ¼ 0.613), trefoil (0.03 ± 0.37 mm, P ¼ 0.659), and spherical aberration (SA) (0.10 ± 0.59 mm, P ¼ 0.743)] and corneal HOAs (0.40 ± 1.69 mm, P ¼ 0.874) [coma (0.39 ± 1.59 mm, P ¼ 0.401), trefoil (0.33 ± 2.16 mm, P ¼ 0.368), and SA (1.27 ± 1.14 mm, P ¼ 0.354)] were not statistically significant. The correlations between mesopic CS and HOAs were weak before and after CXL. Conclusion: One year after accelerated CXL, CS significantly improved, but changes in HOAs were statistically insignificant. CS changes were independent of HOAs.

2017 IEEE Applied Power Electronics Conference and Exposition (APEC), 2017

This paper demonstrates a two-stage implementation of a power factor preregulator design in which... more This paper demonstrates a two-stage implementation of a power factor preregulator design in which the energy buffer capacitor is placed at the output of the converter. In this implementation, a resonant LLC converter supplies power to a boost converter operating in continuous conduction mode. Here, a variable frequency (VFX) technique is used in the resonant LLC converter stage to achieve a lower variation in the overall efficiency across the universal input voltage range (85 — 265Vrms). The efficiency performance achieved is flatter than other single-stage boost-based power factor correction circuits, whose efficiency tends to drop significantly at low input voltages. The VFX technique not only compresses the effective operating range required of the resonant converter stage, but also allows MOSFETs with lower voltage ratings and better conduction/switching characteristics to be used in both converter stages.

IEEE Open Journal of Vehicular Technology, 2021

A new architecture for electric vehicle (EV) traction system with multiple low voltage battery pa... more A new architecture for electric vehicle (EV) traction system with multiple low voltage battery packs and high conversion ratio DC-DC converters is proposed here. In EV traction systems, higher voltage motors offer improved efficiency and power density. High power DC fast charging also favors charging at high DC voltages to limit the charging cable current to manageable levels. However, the optimum battery voltage is relatively low considering factors such as issues with large number of cells in series and safety. In some designs, a boost DC-DC converter is employed to accommodate large variation in battery voltage and provide a high DC link voltage. However, the DC link cannot go below the battery voltage (for example, 360 V) which limits the benefits of the DC-DC converter. The proposed architecture with multiple 48 V battery packs and integrated, multi-input, high conversion ratio DC-DC converters, can reduce the maximum voltage in the vehicle during emergencies to 48 V, mitigate issues with large number of cells in series, and provide a wide variable DC link voltage. It enables independent charging/discharging control of the different low-voltage battery modules ensuring cell balancing and enhancing reliability. The proposed topology significantly reduces the voltage stress and peak/RMS current stress of the switches. It features seamless bi-directional power flow characteristics, which support regenerative braking and high voltage DC fast charging. Four distinct configurations are analyzed and the configurations with interleaving are shown to improve performance and significantly reduce the filter inductor size. The proposed high conversion ratio converter (HCRC) operation for EV application is verified experimentally through a 4-phase multi-input, 4 kW hardware prototype. With the nominal input fixed to 48 V, the output voltage is controlled to vary between 200 V to 800 V. The converter achieves a peak efficiency of 98.36% and a full-load efficiency of 97.3% at 50 kHz switching frequency for the interleaved configuration.

2018 IEEE 19th Workshop on Control and Modeling for Power Electronics (COMPEL), 2018

This paper introduces a novel single inductor multi-output LED driver. The converter is able to s... more This paper introduces a novel single inductor multi-output LED driver. The converter is able to significantly reduce the area of passive components while maintaining high power processing efficiency by dividing power between a switched capacitor (SC) and a buck-boost converter and taking the output differentially from the two outputs. The volume of the SC converter is reduced by operating the buck-boost converter in DCM and increasing the number of SC switching states from two to three. An experimental setup verifies the effectiveness of the design and indicates an efficiency improvement of 2.5% while reducing passive component area by 63% and increasing the operating range compared to conventional commercial products.

IEEE Open Journal of Power Electronics, 2021

Piezoelectric resonators have shown promise as efficient, power-dense energy storage element alte... more Piezoelectric resonators have shown promise as efficient, power-dense energy storage element alternatives to continue the miniaturization of DC-DC converters. However, practical piezoelectric resonators diverge from their ideal behavior due to spurious modes that cause high loss regions throughout their operating frequency range. Typically, control of piezoelectric resonator DC-DC converters is constrained to unidirectional power flow each resonant cycle for maximum efficiency operation. However, output power depends on the frequency with such control, which means the converter cannot operate at loads corresponding to spurious mode frequencies. This paper presents a fixed-frequency control mode utilizing the high-quality factor of piezoelectric resonators to avoid spurious modes. The fixed-frequency control enables efficient operation spanning the converter's full load range, demonstrated through a prototype DC-DC converter with a custom fabricated lithium niobate resonator. At a conversion ratio of 60 V to 30 V, spurious modes limit the converter's operating range from 33 W to 51 W using unidirectional power-constrained control, yet the fixed-frequency control extends operation from 33 W to 2 W. INDEX TERMS DC-DC power converters, piezoelectric devices.

2021 IEEE Applied Power Electronics Conference and Exposition (APEC), 2021

In this paper, a phase shedding control scheme for extended-duty-ratio (EDR) boost converter is p... more In this paper, a phase shedding control scheme for extended-duty-ratio (EDR) boost converter is proposed to achieve wide input and output voltage range operation of the converter. EDR converters can achieve very high gain, for example above 20 for a 4-phase converter, but have limitations on the lowest allowable gain. The proposed scheme allows operation at gain as low as unity while retaining the main benefits of EDR boost such as low voltage stress across switches. The phase shedding control can be optimized based on the application requirements. In this paper, the phase shedding control is optimized for low device voltage stress over wide input and output voltage range operation. The converter control implementation is discussed in detail. The control scheme is verified with a 4-phase EDR boost converter with input voltage varying between 20 V–40 V and output voltage ranging between 50 V–400 V. Experimental results of closed loop operation with adaptive PI controller are presented and the phase shedding scheme is verified by showing the transition from one configuration to another based on the converters varying gain.

2019 IEEE Energy Conversion Congress and Exposition (ECCE), 2019

This paper presents the design and implementation of an ac-dc converter for portable charger appl... more This paper presents the design and implementation of an ac-dc converter for portable charger applications that uses a new variant of the recently-proposed Variable-Inverter-Rectifier-Transformer (VIRT) technique. This new version of the VIRT technique provides improved efficiency and step-down capability through inclusion of a bypass switch. The proposed design adopts both the Variable Frequency Multiplier (VFX) and the VIRT with bypass technique to maintain high performance across a wide range of input (85 - 265 Vac) and output voltages (5 - 20 Vdc) at an output power of up to 65 W. The VIRT with bypass technique enables full utilization of the transformer core area across all modes of operation and significantly reduces transformer loss. The hardware prototype achieves a displacement power density of 44.6 W/in3 and peak efficiency of 95.1% at the rated power of 65 W.

2020 IEEE Energy Conversion Congress and Exposition (ECCE), 2020

This paper introduces a single-stage universal-input isolated ac-dc converter based on the impeda... more This paper introduces a single-stage universal-input isolated ac-dc converter based on the impedance control network (ICN) architecture. This single-stage converter can perform power factor correction (PFC) and output voltage regulation, while maintaining high efficiency over its entire range of ac input voltage and output power. By using appropriate inverter and rectifier phase-shift control strategies, this converter achieves soft-switching of all inverter transistors with minimal circulating current, throughout the line cycle. The ICN converter also allows all its inductors to be integrated and realized in a single magnetic structure, reducing the number of magnetic components in this converter to two. A design methodology for ICN-based ac-dc converters is also introduced. A universal-input, 20-V output, 400-kHz GaN-based prototype ICN-based ac-dc converter, designed for a maximum output power of 330 W, is built, and tested. The prototype achieves a full-power efficiency of 92%. This paper is the first reported work on the architecture, design, and control of ICN-based ac-dc converters.

IEEE Transactions on Power Electronics, 2021

This article introduces a new single-stage universal-input isolated ac–dc converter based on the ... more This article introduces a new single-stage universal-input isolated ac–dc converter based on the impedance control network (ICN) architecture. This resonant converter performs both power factor correction and output voltage regulation while operating at a constant switching frequency and duty ratio, by modulating the phase-shift between its two half-bridge inverters and the phase-shift between the two legs of its full-bridge rectifier. This phase-shift control strategy along with the ICN architecture also enables the converter to achieve high efficiency by ensuring zero-voltage-switching and near-zero-current-switching of all its inverter transistors throughout the line cycle and across wide ranges of input line voltage and output power. Power density is enhanced by realizing the three ICN inductors using a single magnetic structure with two coupled windings. This coupled inductor and a transformer constitute the two magnetic components of the proposed converter. A systematic methodology to design this ICN ac–dc converter is also introduced. A universal-input (90–265 Vrms), 20-V output, 330-W, 400-kHz ICN ac–dc converter prototype is built and tested. This prototype achieves a power density of 37.9 W/in3 and peak efficiencies of 91.7%, 92.2%, 93.2%, and 93.4% at 90, 120, 230, and 265 Vrms input, respectively.

IEEE Open Journal of Power Electronics, 2021

The performance of inductors at high frequencies and small sizes is one of the largest limiting f... more The performance of inductors at high frequencies and small sizes is one of the largest limiting factors in the continued miniaturization of dc-dc converters. Piezoelectric resonators can have a very high quality factor and provide an inductive impedance between their series and parallel resonant frequencies, making them a promising technology for further miniaturizing dc-dc converters. In this paper we analyze the impact of resonator parameters on the performance of the piezoelectric resonator based dc-dc converter, derive the optimal load impedance and efficiency limits, and analyze the impacts of varying conversion ratio and load impedance. This work is accompanied by a prototype dc-dc converter using a piezoelectric resonator fabricated from lithium niobate. The piezoelectric resonator has a quality factor of 4178 and a coupling coefficient, k 2 t , of 29%. The converter is able to achieve high efficiency zero voltage switching and a continuously variable conversion ratio without the use of any discrete inductors. It achieves a maximum power output of 30.9 W at an efficiency of 95.2% with a power density of 6.76 W cm 3. INDEX TERMS DC-DC power converters, piezoelectric devices.

IEEE Journal of Emerging and Selected Topics in Industrial Electronics, 2021

2019 IEEE Energy Conversion Congress and Exposition (ECCE), 2019

This paper analyzes the fault tolerance of non-isolated, modular, high gain dc-dc boost converter... more This paper analyzes the fault tolerance of non-isolated, modular, high gain dc-dc boost converter under different fault conditions. In the absence of transformer isolation, there are safety concerns in high gain converters in ensuring that high voltage stress is not applied to low voltage ports under any component failure conditions. The main idea is to increase the reliability of converter operation by making minimal modifications to the actual converter and control scheme as well as minimal component addition. Fuses are incorporated in the converter and their control co-ordination with different phase switches is proposed to ensure normal operation under various faults. The proposed method is discussed and implemented to ensure normal operation of converter under different component failures and verified through simulation results. The main faults under consideration are the short circuit fault and open circuit fault of the MOSFETs, diodes and coupling capacitors. The discussed methods are analyzed, tested and validated with a 35V-600V, 500W 4-phase hardware prototype.

2019 IEEE Energy Conversion Congress and Exposition (ECCE), 2019

This paper analyzes the operation of a high gain non-isolated boost converter that is a combinati... more This paper analyzes the operation of a high gain non-isolated boost converter that is a combination of interleaved boost and switched capacitor configuration in critical conduction mode. The converter is able to provide high gain while reducing the current and voltage stresses on semiconductor devices. The converter operation can be divided into different zones based on the duty ratio of operation. In Zone I, which corresponds to the highest gain, the converter possesses inherent current sharing properties among different phases. The inductance value and size are reduced significantly due to interleaving. To further reduce the size, the converter is operated in critical conduction mode. This also results in increased efficiency as turn-on losses of the MOSFETs are zero. A 2kW silicon MOSFET based 4-phase prototype with 42V-52V input and 850V output and operating at varying frequency to maintain critical conduction mode operation at various power levels has been developed to validate the proposed scheme. The total inductor volume is reduced by 48% and the efficiency improves by 0.9% at rated load in CRM operation with the peak efficiency of 97.2% achieved at 1200W.

IEEE Journal of Emerging and Selected Topics in Power Electronics, 2020

Part of the Law Commons This Article is brought to you for free and open access by the University... more Part of the Law Commons This Article is brought to you for free and open access by the University of Minnesota Law School. It has been accepted for inclusion in Minnesota Law Review collection by an authorized administrator of the Scholarship Repository. For more information, please contact

IEEE Transactions on Power Electronics, 2020

The Class Φ 2 /EF 2 amplifier is an attractive topology for high-voltage and high-frequency power... more The Class Φ 2 /EF 2 amplifier is an attractive topology for high-voltage and high-frequency power conversion because of the high efficiency, reduced device voltage stress, simplicity of gate driving, and load-independent ZVS operation. Due to many degrees of freedom for tuning, previous studies can only solve the single-ended Φ 2 circuit using numerical methods. This work focuses on improving the design and operating characteristics of a push-pull Φ 2 amplifier with a T network connected between the switch nodes, or a PPT Φ 2 amplifier. The PPT Φ 2 amplifier has less circulating energy and achieves higher cutoff frequency f T than other Φ 2 /EF 2 circuits. We, then, present a series-stacked input configuration to reduce the switch voltage stress and improve the efficiency and power density. A compact 6.78-MHz, 100-V, 300-W prototype converter is demonstrated that uses low-cost Si devices and achieves 96% peak total efficiency and maintains above 94.5% drain efficiency across a wide range of voltage and power. Together with the advances in wide-bandgap semiconductors and magnetic materials, the PPT Φ 2 circuit opens more possibilities for the state-of-the-art performance of solid-state RF amplifiers in high-frequency, high-power applications, including wireless charging for electric vehicles, plasma RF drives, and nuclear magnetic resonance spectroscopy.