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This paper introduces a megahertz-frequency resonant dc–dc converter that inherently achieves a load-independent output current while maintaining high efficiency across a wide output voltage range. These properties make the proposed converter well-suited for automotive light-emitting diode (LED) driver applications, where a varying number of LEDs need to be driven with a constant current. The proposed converter achieves load-independent output current by utilizing an LCL-T resonant network, and achieves high efficiency using a comprehensive design optimization methodology. This LCL-T resonant converter is also capable of regulating its output current at any desired value by utilizing phase-shift control. The performance of the LCL-T resonant converter is theoretically and experimentally compared with an LC3L and an LCLC resonant converter. For the experimental comparison, prototypes LCL-T, LC3L, and LCLC resonant converters are designed to operate at 2 MHz and across an output voltage range of 3.3–49.5 V while supplying a constant 0.5 A output current to the LEDs. The LCL-T resonant converter prototype achieves a peak efficiency of 91.1%, which is 0.6% and 1.8% higher than the peak efficiency of the LC3L and the LCLC converter prototypes, respectively. Furthermore, the LCL-T converter prototype maintains 0.8% and 1.6% higher average efficiency over its 15:1 output voltage range relative to the LC3L and the LCLC converter prototypes, respectively. [ABSTRACT FROM AUTHOR]

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 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]

This paper presents a new topology for a high-efficiency dc/dc resonant power converter that utilizes a resistance compression network (RCN) to provide simultaneous zero-voltage switching and near-zero-current switching across a wide range of input voltage, output voltage, and power levels. The RCN maintains desired current waveforms over a wide range of voltage operating conditions. The use of ON/OFF control in conjunction with narrowband frequency control enables high efficiency to be maintained across a wide range of power levels. The converter implementation provides galvanic isolation and enables large (greater than 1:10) voltage conversion ratios, making the system suitable for large step-up conversion in applications such as distributed photovoltaic converters. Experimental results from a 200-W prototype operating at 500 kHz show that over 95% efficiency is maintained across an input voltage range of 25-40 V with an output voltage of 400 V. It is also shown that the converter operates very efficiently over a wide output voltage range of 250-400 V, and a wide output power range of 20-200 W. These experimental results demonstrate the effectiveness of the proposed design. [ABSTRACT FROM AUTHOR]