U. Badstuebner

Impact of Power Density Maximization on Efficiency of DC–DC Converter Systems

The demand for decreasing costs and volume leads to a constantly increasing power density of industrial converter systems. In order to improve the power density further different aspects, like thermal management and electromagnetic effects must be considered in conjunction with the electrical design. Therefore, a comprehensive optimization procedure based on analytical models for minimizing volume of DC-DC converter systems has been developed at the Power Electronic Systems Laboratory of the ETH Zurich. Based on this procedure three converter topologies - a phase shift converter with current doubler and with capacitive output filter and a series-parallel resonant converter - are optimized with respect to power density for a telecom supply (400V/48V). There, the characteristic of the power density, the efficiency and the volume distribution between the components as function of frequency is discussed. For the operating points with maximal power density also the loss distribution is presented. Further more, the sensitivity of the optimum with respect to junction temperature, cooling and core material is investigated. The highest power density is achieved by the series-parallel resonant converter. For a 5 kW supply a density of approximately 12 kW/ltr. and a switching frequency of ca. 130 kHz results.

Design of a 5-kW, 1-U, 10-kW/dm

The demand for decreasing cost and volume and also for increasing efficiency leads to a constantly increasing power density of converter systems. For maximizing the power density of a 5 kW telecom supply, an optimization procedure that automatically balances the switching frequency, semiconductor and passive losses, and thermal performance has been developed. This procedure and the belonging analytical converter and transformer models are presented in this paper. Moreover, the resulting optimized design, which has a power density of 10 kW/dm 3 and an efficiency of 94.5% at a height of 1 U, is presented.

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The development of new converter systems with higher power density and/or efficiency offers many degrees of freedom for the design parameters as a large number of system component values have to be defined, where all of which are interdependent, to some extent, on another. Therefore, an automated optimization procedure, based on comprehensive analytical models and the resulting optimal design parameters, e.g., switching frequency or transformer design, to achieve the most compact and/or efficient design, is presented in this paper. In addition, the design of a volume-optimized 400/46-56-V phase-shift dc-dc converter with a current doubler rectifier and the underlying analytical models are also introduced. The power density of the converter is increased by integrating the output inductors in the transformers core. A new lossless magnetic snubber circuit is introduced, which damps the intrinsic voltage ringing of the rectifier diodes and feeds the ringing energy to the output. The experimental results prove the analytical models and the design procedure. The 5-kW dc-dc converter prototype has a power density of 147 W/in3 (9 kW/L) and a maximum efficiency of 94.4% at 54-V output voltage and full load.

Resonant DC–DC Converter for Telecom Applications

The electrical determination of power losses by measuring the input and output power can reach sufficient accuracy for DC-DC converter systems, if well calibrated voltage meters and shunt resistors are applied. However, it is difficult to determine the power in AC-systems, especially with harmonics, due to phase-errors in the electric measurement. In addition, the electromagnetic interference (EMI) of switched-mode power supplies can disturb the electric power measurement. In this paper, the calorimetric determination of power converter system losses resulting in a high accuracy and which is almost immune against EMI phase errors, is described. The closed-type calorimeter is realized with a double-jacketed chamber which enables the power loss measurement between 10W and 200W for power converter systems of several kW. The resulting deviation of the implemented measurement system is less than ±0.4W, or ±0.05% at full load conditions (several kW), respectively, over the entire measurement range.

Optimization of a 5-kW Telecom Phase-Shift DC–DC Converter With Magnetically Integrated Current Doubler

The development of new power supply systems is increasingly focused on higher efficiency, while the power density should remain on a high level. This is especially true for data center and telecom application Power Supply Units (PSU). The commonly-used DC-DC converter in telecom and data center PSUs are full-bridge phase-shift PWM converter, which enables a high power and highly efficient conversion, compact design and simple control due to constant switching frequency. The component dimensioning of the converter system has many degrees of freedom, as the design parameters are interdependent from each other to some extend. An automatic optimization procedure based on comprehensive analytical models leads to the optimal design parameters, such as switching frequency and geometry of the magnetic components. In this paper, the development, optimization and design process for an efficiency-optimized 5kW, 400 V to 48..54 V phase-shift PWM DC-DC converter with LC-output filter and synchronous rectification is presented. The proposed optimization algorithm, which considers the part-load-efficiency as well, results directly in the component values for the realized prototype. The design of the converter is explained in detail and measurement results are presented and discussed.

Calorimetric Power Loss Measurement for Highly Efficient Converters

In the last decade power electronic research focused on the power density maximization mainly to reduce initial systems costs [1]. In the field of data centers and telecom applications, the costs for powering and cooling exceed the purchasing cost in less than 2 years [2]. That causes the changing driving forces in the development of new power supplies to efficiency, while the power density should stay on a high level. The commonly used DC-DC converter in the power supply unit (PSU) for data centers and telecom applications are full bridge phase-shift converters since they meet the demands of high power and efficient power conversion, a compact design and the constant operation frequency allows a simple control and EMI design. The development of the converter with respect to high efficiency has a lot of degrees of freedom. An optimization procedure based on comprehensive analytical models leads to the optimal parameters (e.g. switching frequency, switching devices in parallel and transformer design) for the most efficient design. In this paper a 5kW, 400V–48⋖56V phase-shift PWM converter with LC-output filter is designed for highest efficiency (η ≥99%) with a volume limitation and the consideration of the part-load efficiency. The components dependency as well as the optimal design will be explained. The realized prototype design reaches a calculated efficiency of η = 99.2% under full load condition and a power density of ρ = 36W/in3 (2.2 kW/liter).

An optimized, 99% efficient, 5 kW, phase-shift PWM DC-DC converter for data centers and telecom applications

In the last decade there has been a tremendous growth in the number of data centers due to the increasing demand for internet services. At the same time, the cost for energy and materials have increased because of reducing resources and increased demand. That has caused a change in the driving forces for new power supply development, with more consideration on power density and efficiency. The commonly used DC-DC converter in the power supply unit (PSU) for data centers and telecom applications are full bridge phase-shift converters since they meet the demands of high power levels and concurrently efficient power conversion as well as a compact design. The constant operating frequency allows a simple control and EMI design. To develop a new converter with higher power density and/or high efficiency the designer has a lot of degrees of freedom. An optimization procedure, based on comprehensive analytical models, has been developed and leads to the optimal parameters (e.g. switching frequency or transformer design) to achieve the most compact and/or efficient design. In this paper an volume optimized 400V/48V phase-shift DC-DC converter with current doubler rectifier based on analytical models is constructed. The power density of the converter is increased by integrating the output inductors in the transformers core. The intrinsic voltage ringing of the rectifier diodes is damped by a lossless magnetic snubber, which feeds ringing energy to the output. Experimental results prove the theoretical analytical models and the design procedure.

Design of an 99%-efficient, 5kW, phase-shift PWM DC-DC converter for telecom applications

Power density and efficiency are one of the major driving forces in the development of new power supplies for telecommunication and information industry. The phase-shift PWM and the series-parallel resonant DC-DC converter are promising topologies that can meet these demands at high power rates. Based on conventional criteria such as the number of semiconductors/passive components or voltage/current stress it is not possible to identify the topology that offers a higher power density or efficiency. Therefore, an optimization procedure has been developed, which calculates the optimal converter parameters (e.g. switching frequency or transformer design) with respect to the maximal power density and/or efficiency. This procedure is based on detailed analytical models for the converter, semiconductor losses, HF losses in the magnetic components as well thermal and geometrical models of the transformer. With the procedure a 5 kW series-parallel resonant converter and a phase shift converter with capacitive output and with current doubler have been optimized. With the calculated parameters a resonant converter prototype has been constructed and experimental results are presented.

An Optimized 5 kW, 147 W/in 3 Telecom Phase-Shift DC-DC Converter with Magnetically Integrated Current Doubler

Efficient power conversion is one of the fundamental research drivers for modern power supplies. In order to achieve and design on the edge of the system performance space, automatic optimization procedures based on comprehensive analytical converter operation and loss models have to be employed. In this paper, a 5kW, 400V to 46–56V phase-shift dc-dc converter with LC output filter is optimized for the highest possible full-load efficiency. The system performance is discussed and compared for full-load, half-load and part-load optimization. Furthermore, the complexity of the first applied comprehensive analytical models is reduced step by step and the resulting values of the design parameters and the system performance are compared in detail with the reference system optimized with the comprehensive models. The sensitivity of the optimization to the level of detail of the modeling as well as the possibilities of the model-complexity reduction is explained. It is shown that certain complex components of the system model can be omitted without noticeably affecting the resulting efficiency.

Power density and efficiency optimization of resonant and phase-shift telecom DC-DC converters

Over the last decades, the converter systems performance has been substantially improved but the endeavor for highest possible performance, especially with respect to power density, efficiency, and costs remains the most important driver of present and future developments and research. In latest publications, comprehensive analytical models have been applied in optimization procedures to calculate the design parameters of single-phase AC-DC converter systems resulting in the highest performance concerning multiple objectives. In this paper, an experimental validation of this analytical design approach is provided based on four prototype rectifier systems with Power Factor Correction (PFC) which result from the optimization with respect to power density or efficiency of the mature double-boost bridgeless Continuous Conduction Mode (CCM) and the recently published interleaved totem-pole-based Triangular Current Mode (TCM) rectifier topology. All design details, such as power component values and EMIfilter structure as well as volume and losses distributions, are provided and the measurement results regarding efficiency, EMI standards, and input current quality (power factor and total harmonic distortion) allow the direct performance comparison of the investigated rectifier topologies. All four prototype systems comply with the EMI standard CISPR 22 class B and exhibit a high power factor and a low current THD. The recently published TCM-topology is beneficially applied to achieve a higher efficiency compared to the efficiency- and volume-optimized double boost CCM rectifier systems with a similar power density. With the loss-optimized TCM-prototype an extreme efficiency of 99.23 % at nominal input voltage and rated output power has been measured.