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This paper introduces a new approach for output voltage regulation in impedance control network (ICN) resonant dc–dc converters, in which the rectifier of the ICN converter alternates between full-bridge and half-bridge topologies. This approach, termed topology morphing control, allows the ICN converter to maintain soft switching across power levels while substantially reducing the output capacitance requirement and improving partial-power efficiencies compared to the conventional burst mode (on/off) control. A closed-loop control architecture for the ICN converter is also introduced, which regulates the converter's output voltage under input voltage and load variations while ensuring smooth transitions between the multiple operating modes of the proposed topology morphing control. A prototype 1-MHz, 120-W step-down ICN resonant converter designed for an input voltage range of 18–36 V, an output voltage of 12 V, and a 10:1 output power range has been built and tested with both burst mode control and the proposed topology morphing control. The topology morphing control reduces the output capacitance requirement in the prototype ICN converter by 57% and reduces converter losses at partial power levels by up to 46.5%. The prototype ICN converter is also tested under closed-loop control and is shown to successfully regulate its output voltage in the face of input voltage and load variations. [ABSTRACT FROM AUTHOR]

This paper presents the design and implementation of a large-step-down soft-switched dc–dc converter based on the active bridge technique, which overcomes some of the limitations of the conventional dual active bridge converter. The topology comprises a double-stacked bridge inverter coupled to a reconfigurable rectifier through a special three-winding leakage transformer. This particular combination of stages enables the converter to run in an additional low-power mode that greatly increases light-load efficiency by reducing core loss and extending the zero-voltage switching range. The converter is implemented with a single compact magnetic component, providing power combining, isolation, voltage transformation, and energy transfer inductance. A 175 kHz, 300 W, 380–12 V GaN-based prototype converter achieves 95.9% efficiency at full load, a peak efficiency of 97.0%, an efficiency above 92.7% down to 10% load, and an efficiency above 79.8% down to 3.3% load. [ABSTRACT FROM AUTHOR]

This paper introduces an isolated step-down impedance control network (ICN) resonant dc–dc converter that utilizes enhanced inverter and rectifier phase-shifts to achieve both soft switching and output voltage regulation. Compared to previously presented ICN converters, which utilize burst-mode control to achieve output voltage regulation, this ICN converter with the proposed enhanced phase-shift control has dramatically reduced output capacitance requirement. The avoidance of burst-mode control also simplifies the design of the converter's input electromagnetic interference filter, reduces switch stresses due to overshoots during repeated startup transitions, and improves converter efficiency by eliminating startup and shutdown losses as well as by reducing conduction losses when backing off in power. A closed-loop control architecture for the ICN converter operated under enhanced phase-shift control is also proposed, wherein state-feedback control is incorporated to guarantee stability and achieve good dynamic performance across wide variations in input voltage and output power. A prototype 1-MHz, 120-W step-down ICN converter designed for an input voltage range of 18–75 V, an output voltage of 12 V, and a 10:1 output power range is built and tested with both burst-mode control and the proposed enhanced phase-shift control. When operated with enhanced phase-shift control, the prototype ICN converter achieves a peak efficiency of 95.7% and maintains full-power efficiency above 91.7% across its 4:1 input voltage range. Compared to when operated under burst-mode control, the ICN converter with enhanced phase-shift control reduces converter losses by up to 30% and reduces the output capacitance requirement by two orders of magnitude. The prototype ICN converter is also operated under closed-loop control using a digitally implemented controller based on the proposed architecture, and is shown to successfully regulate its output voltage in the face of input voltage and load variations. [ABSTRACT FROM AUTHOR]

This paper introduces a new analysis approach to modeling resonant converters that can be used to determine closed-form expressions for the exact resonant network waveforms. This approach, based on superposition of step responses to inverter and rectifier imposed steps, can easily be applied to resonant converters with high-order resonant networks, multiple inverters, and/or rectifiers. The usefulness of the proposed analysis approach is demonstrated first by applying it to a series-resonant converter, wherein it is used to determine accurate closed-form expressions for its tank current in different operating modes. These expressions are utilized to draw insights that help identify the converter's operating mode, and determine associated expressions for its output voltage and the switching frequency required to achieve a desired output power. The proposed approach is also applied to the multi-inverter multi-element impedance control network (ICN) resonant converter, wherein it is used to derive closed-form expressions for the converter's currents. These expressions are utilized to evaluate the behavior and optimize the design of an ICN resonant converter. A prototype 200-W 500-kHz ICN resonant converter optimized using the proposed approach is used to validate the modeling results. It is shown that there is an excellent agreement between the experimental and modeled waveforms during steady-state operation as well as during startup transients. [ABSTRACT FROM AUTHOR]

This paper presents an improved efficiency impedance control network (ICN) resonant dc–dc converter that maintains zero-voltage switching (ZVS) and near-zero-current switching (ZCS) across wide ranges in input and output voltages and output power. The improvement in efficiency in this burst mode operated converter is achieved through an optimized startup control that minimizes its startup transient and helps the converter maintain ZVS and near-ZCS operation, even during the startup for each burst cycle. This optimization of startup is made possible by a new accurate time domain model for the ICN converter waveforms that helps reduce the number of non-ZVS transitions by 75%. A prototype 200 W, 500 kHz ICN resonant converter designed to operate over an input voltage range of 25–40 V and output voltage range of 250–400 V is built and tested. The prototype ICN converter achieves a peak efficiency of 97.2% and maintains greater than 96.2% full power efficiency at 250 V output voltage across the nearly 2:1 input voltage range, and maintains full power efficiency above 94.6% across its full input and output voltage range. The converter also maintains efficiency above 93.6% over a 10:1 output power range across its full input and output voltage range. [ABSTRACT FROM AUTHOR]

This paper introduces a new resonant converter architecture that utilizes multiple inverters and a lossless impedance control network (ICN) to maintain zero-voltage switching and near zero-current switching across wide operating ranges. Hence, the ICN converter is able to operate at fixed frequency and maintain high efficiency across wide ranges in input and output voltages and output power. The ICN converter architecture enables increase in switching frequency (hence reducing size and mass), while achieving very high efficiency. Three prototype 200-W 500-kHz ICN resonant converters, one with low-Q, one with medium-Q, and one with high-Q resonant tanks, designed to operate over an input voltage range of 25 to 40 V and an output voltage range of 250 to 400 V are built and tested. The low-Q prototype ICN converter achieves a peak efficiency of 97.1%, maintains greater than 96.4% full power efficiency at 250 V output voltage across the nearly 2:1 input voltage range, and maintains full power efficiency above 95% across its full input and output voltage range. It also maintains efficiency above 94.6% over a 10:1 output power range across its full input and output voltage range owing to the use of burst-mode control. [ABSTRACT FROM AUTHOR]

Microinverters operating into the single-phase grid from solar photovoltaic (PV) panels or other low-voltage sources must buffer the twice-line-frequency variations between the energy sourced by the PV panel and that required for the grid. Moreover, in addition to operating over wide average power ranges, they inherently operate over a wide range of voltage conversion ratios as the line voltage traverses a cycle. These factors make the design of microinverters challenging. This paper presents a multilevel energy buffer and voltage modulator (MEB) that significantly reduces the range of voltage conversion ratios that the dc-ac converter portion of the microinverter must operate over by stepping its effective input voltage in pace with the line voltage. The MEB partially replaces the original bulk input capacitor, and functions as an active energy buffer to reduce the total size of the twice-line-frequency energy buffering capacitance. The small additional loss of the MEB can be compensated by the improved efficiency of the dc-ac converter stage, leading to a higher overall system efficiency. The MEB architecture can be implemented in a variety of manners, allowing different design tradeoffs to be made. A prototype microinverter incorporating an MEB, designed for 27 to 38 V dc input voltage, 230-V rms ac output voltage, and rated for a line cycle average power of 70 W, has been built and tested in a grid-connected mode. It is shown that the MEB can successfully enhance the performance of a single-phase grid-interfaced microinverter by increasing its efficiency and reducing the total size of the twice-line-frequency energy buffering capacitance. [ABSTRACT FROM AUTHOR]