Control Methods in DC-DC Power Conversion -- A Comparative Study

Several control techniques for dc-dc power conversion and regulation have been studied in this paper. Analog approaches have briefly been described since the focus is the newly developed digital techniques. Principles of operation, advantages, and disadvantages of each control method have been described. Simulation results have been used to compare the performance and accuracy of digital control techniques

Reducing Computational Time Delay in Digital Current-Mode Controllers for Dc-dc Converters

A new method to improve the performance of digital current-mode controllers used in dc-dc power conversion is introduced. The proposed scheme is based on a simple prediction method which offers more time for DSP calculations than its conventional counterparts. Therefore, there will be less DSP computational time delay, which results in faster dynamic response and more accuracy and stability in power electronic converters. Principles of operation of the proposed prediction method as well as its application to several digital control techniques are presented

P/N In(Al) GaAs multijunction laser power converters

Eight In(AI)GaAs PN junctions grown epitaxially on the semi-insulating wafer were monolithically integrated in series to boost the approximately 0.4V photovoltage per typical In(Al)GaAs junction to over 3 volts for the 1 sq cm laser power converted (LPC) chip. Advantages of multijunction LCP designs include the need for less circuitry for power reconditioning and the potential for lower I(sup 2)R power loss. As an example, these LPC's have a responsivity of approximately 1 amp/watt. With a single junction LPC, 100 watts/sq cm incident power would lead to about 100 A/sq cm short-circuit current at approximately 0.4V open-cicuit voltage. One disadvantage is the large current would lead to a large I(sup 2)R loss which would lower the fill factor so that 40 watts/sq cm output would not be obtained. Another is that few circuits are designed to work at 0.4 volts, so DC-DC power conversion circuitry would be necessary to raise the voltage to a reasonable level. The multijunction LPC being developed in this program is a step toward solving these problems. In the above example, an eight-junction LPC would have eight times the voltage, approximately 3V, so that DC-DC power conversion may not be needed in many instances. In addition, the multijunction LPC would have 1/8 the current of a single-junction LPC, for only 1/64 the I(sup 2)R loss if the series resistance is the same. Working monolithic multijunction laser power converters (LPC's) were made in two different compositions of the In(x)Al(y)Ga(1-x-y)As semiconductor alloy, In(0.53)Ga(0.47)As (0.74 eV) and In(0.5)Al(0.1)Ga(0.4)As (0.87 eV). The final 0.8 sq cm LPC's had output voltages of about 3 volts and output currents up to about one-half amp. Maximum 1.3 micron power conversion efficiencies were approximately 22 percent. One key advantage of multijunction LPC's is that they have higher output voltages, so that less DC-DC power conversion circuitry is needed in applications

UHF power conversion with GaN HEMT class-E2 topologies

This paper reviews the use of UHF double class-E (class-E2) topologies for dc/dc power conversion. After introducing this attractive resonant converter in the context of the time-reversal duality principle, two different lumped-element networks are described for appropriately terminating the drain of the switching devices. Recent implementation examples, taking advantage of GaN HEMT processes, are then presented. The potential for a fast dynamic response is validated (with a slew rate over 2 V/nS), while also the feasibility for an appropriate operation without requiring external RF gate driving signals. A solution for approximating a load-insensitive operation is finally exposed

Wide Range DC-DC Power Conversion Systems - Architectures, Circuits and Components

Wide Range DC-DC power conversion find their application in a wide variety of power conditioning environments, ranging from automotive LED drivers -- to bus converters used in data centers -- to integration of renewable energy with the utility grid. While it has been well established that fixed conversion ratio DC-DC converters are capable of operating with extremely high efficiency and power density, addressing wide variation in input voltage or output power still remains unexplored. This thesis identifies several application examples where wide range operation is prevalent and offers solutions capable of operating efficiently over the system's entire operating range. One such application example where wide input voltage, output voltage and output current operation is required is an automotive LED driver. First, using a 2 MHz immittance resonant converter as an automotive LED driver, driven from a fixed 12V input voltage and supplying regulated 0.5A current, a peak efficiency of 93% is achieved with &gt;86% efficiency maintained across an output voltage range of 3V to 36V. Thereafter, problems associated with simple immittance networks when operated with wide input voltage and output current variation are identified and a novel wide range resonant network derived from the basic immittance resonant tank is proposed to circumvent the identified deficiencies. With a control technique devised to minimize the circulating currents in the resonant tank while maintaining soft switching, the proposed converter achieves a peak power stage efficiency of 92.4% and operates with &gt;85% efficiency across the entire input voltage range of 8V to 18V and output voltage range of 10V to 40V using similar active and passive area as the basic LCL-T immittance-network converter. Next, a multiple output two stage automotive LED driver architecture is proposed using a multi-phase non-inverting buck-boost front end stage and LCL-T immittance-network based output current regulation stages. This approach addresses the input voltage variation by using the front-end to provide a regulated input voltage to the resonant networks. For a four-output 120W prototype with 250kHz front-end and 2MHz resonant stages, the measured power stage efficiency is above 88% over wide input (8-18,V) and output (3-50V) voltage ranges, with a peak efficiency of 92.1% at the nominal battery voltage of 13V. Further, a new design methodology is proposed to enhance efficiency of higher-order immittance-network based resonant converters based on the principle of minimizing inductive energy storage. This design methodology is experimentally demonstrated for a 20V input to 5V, 9V and 15V output USB-C battery charger delivering 6$A output current while switching at 1MHz. The proposed design methodology achieves a peak efficiency of 92% and has more than 10% lower losses compared to a conventionally designed prototype. Next, a transformerless composite converter architecture is proposed and applied for a wide input voltage range intermediate bus converter in an AC to low voltage DC power conversion architecture, providing greater than 4-to-1 step down ratio. While driven from 48V to 65V input and delivering a regulated 12V, 10A output, this architecture is shown to achieve a peak efficiency of 97.9% and to maintain greater than 96% efficiency across the entire input voltage and output power range. The remainder of the thesis focuses on design techniques for high-frequency planar magnetic components, which are critical in all aforementioned applications. First, a simple orthogonal-gap technique is proposed to reduce effects of fringing magnetic fields on ac winding losses in high-frequency inductors. As a case study, a planar inductor is designed for an 8kW SiC-based buck converter operating at 250kHz. 3D FEM simulations along with experimental results are provided to compare the proposed air-gap arrangement with the existing solutions. It is shown that approximately 50% reduction in ac winding losses is achieved using the orthogonal air gaps compared to a conventional design. This approach is then extended to converters deploying coupled inductors to achieve several system level advantages. An application of orthogonal airgaps in an AC coupled inductor demonstrated 13% overall loss reduction compared to a system using conventionally gapped coupled inductors. In the final chapter of the thesis, the design of a high-frequency planar transformer suitable for direct low-voltage to medium-voltage (MV) is presented. The transformer is expected to withstand medium voltage (10's of KV) isolation between its primary and secondary terminals. Using a Hipot tester, it is shown how a 14-layer, 30:30 turn, 2oz planar transformer withstands 26kV between the primary and the secondary and between the windings and the grounded core segments. The high-frequency operation of the transformer is experimentally demonstrated in a prototype dc to three-phase ac module processing 7.5kW power with 97% efficiency.</p

High Frequency DC-DC Power Conversion for Automotive LED Driver Applications

This thesis studies high frequency dc-dc power converters for automotive LED driver applications. A high-frequency zero voltage switching (ZVS) integrated-magnetics Ćuk converter is well-suited for automotive LED-driver applications. In this converter, the input and output filter inductors and the transformer are realized on a single magnetic structure, resulting in very low input and output current ripples, thus reducing electromagnetic interference (EMI) and minimizing the required input and output filter capacitances. Active-clamp snubbers are used to mitigate the effects of the transformer leakage inductance. A prototype 1.8~MHz Ćuk converter with integrated magnetics is designed, built and tested. The prototype converter supplies 0.5 A output current to a string of 1-10 LEDs, and achieves 89.6% peak power-stage efficiency. The use of active-clamp snubbers introduces additional conduction and gate-drive losses. This thesis introduces a planar integrated magnetics structure that is designed to minimize the transformer leakage inductance and therefore eliminates the need for snubbers. The planar integrated magnetics structure is optimized using 3D finite element modeling (FEM) tools. Two 1.8 MHz-to-2.4 MHz Ćuk converter prototypes are constructed: one using Silicon MOSFETs and the other using GaN transistors. The former achieves a peak efficiency of 92.9%, while the latter achieves a peak efficiency of 93.5% and a wider ZVS range. Both prototypes maintain greater than 90% efficiency across their wide output voltage range. A new control architecture for the ZVS integrated magnetics Ćuk converter is presented. A Spice-based averaged circuit model is employed to model the converter dynamics. The duty-cycle-to-output-inductor-current transfer function is obtained and an integral compensator is designed to precisely regulate the output inductor current (LED current) over the entire output voltage range of the converter (3 V-to-50 V). To achieve high-resolution PWM dimming, new turn-off and turn-on strategies are proposed. The proposed turn-off strategy reduces the fall time of the LED current by up to 83%, and the turn-on strategy reduces the rise time by up to 43%. The controller is implemented digitally and experimental results are presented. This work also investigates resonant dc-dc converters as an alternative approach for automotive LED driver applications. The LLC resonant dc-dc converter is studied and is found that this converter suffers from high circulating currents, when designed to operate over a wide input and output voltage range. An LC3L resonant dc-dc converter is proposed. The converter exhibits minimal circulating currents. Furthermore, it is shown that when appropriately designed, the converter behaves like a current source, with its output current being independent of the output voltage. This property is particularly favorable for automotive LED driver applications. A 10 MHz LC3L resonant dc-dc converter is designed and simulated. This converter is predicted to achieve greater than 86% efficiency, and be 60% smaller in size compared to the planar integrated magnetics Ćuk converter. Further increase in the switching frequency of automotive LED drivers demands exploring new design techniques and the use of high performance semiconductor devices. This thesis presents high efficiency dc-dc converters operating at very high frequencies using custom monolithic GaN-based half-bridge power stages with integrated gate drivers. A new gate driver circuitry is introduced, which enables efficient converter operation at very high switching frequencies, while maintaining very low quiescent power consumption. While using only n-type transistors in the GaN process, the proposed gate driver emulates complementary operation commonly employed in CMOS processes. A family of monolithic GaN chips is designed to operate over switching frequencies in the range of 20-400 MHz,</p

Design Of Class-E Rectifier With DC-DC Boost Converter

This paper presents the design of Class-E rectifier with dc-to-dc boost converter. In this paper, Class E synchronous rectifier that regulates the output voltage at a fixed switching frequency of 1 MHz is presented by a dc-dc power conversion. The experimental prototype has been built and evaluated. The converter achieved 83.33 percent efficiency with less than 5 percent of ripple percentage of the rectifier. This integrated power converter with class E rectifier provides a low loss operation suitable for Very High Frequency (VHF) applications

Design of a Class-E Rectifier with DC-DC Boost Converter

This paper presents the design of Class-E rectifier with dc-to-dc boost converter. In this paper, Class E synchronous rectifier that regulates the output voltage at a fixed switching frequency of 1 MHz is presented by a dc-dc power conversion. The experimental prototype has been built and evaluated. The converter achieved 83.33 percent efficiency with less than 5 percent of ripple percentage of the rectifier. This integrated power converter with class E rectifier provides a low loss operation suitable for Very High Frequency (VHF) applications

Design of a direct connection scheme of supercapacitors to the grid-tied photovoltaic system

A maximum power-point tracking (MPPT) technique needs to be applied to the photovoltaic (PV) system in order to extract maximum possible power output under those varying conditions. The development of supercapacitor (SC) as high power storage device in recent years has created opportunity to replace electrolytic capacitor by SC as dc-link capacitor to provide power during fault ride-through (FRT) condition. However, due to its much bigger capacitance, the voltage dynamics of SC is much slower compared to electrolytic capacitor. Therefore, in this paper, a MPPT technique using a string of supercapacitors which is directly connected to the DC-link of a PV generation system is proposed. The direct connection is proposed to avoid one stage DC-DC power conversion to implement MPPT, so that the efficiency of the system is increased. The proposed direct connection of supercapacitors string configuration along with MPPT strategy is verified by simulation analysis using MATLAB/Simulink where real solar irradiance data is used

An Overview of Fully Integrated Switching Power Converters Based on Switched-Capacitor versus Inductive Approach and Their Advanced Control Aspects

This paper reviews and discusses the state of the art of integrated switched-capacitor and integrated inductive power converters and provides a perspective on progress towards the realization of efficient and fully integrated DC–DC power conversion. A comparative assessment has been presented to review the salient features in the utilization of transistor technology between the switched-capacitor and switched inductor converter-based approaches. First, applications that drive the need for integrated switching power converters are introduced, and further implementation issues to be addressed also are discussed. Second, different control and modulation strategies applied to integrated switched-capacitor (voltage conversion ratio control, duty cycle control, switching frequency modulation, Ron modulation, and series low drop out) and inductive converters (pulse width modulation and pulse frequency modulation) are then discussed. Finally, a complete set of integrated power converters are related in terms of their conditions and operation metrics, thereby allowing a categorization to provide the suitability of converter technologies