In this paper, a three-phase current-fed dual-active-bridge (DAB) bidirectional DC-DC converter is presented. Compared to the voltage source DAB converter, the proposed converter allows low RMS current and maintains zero voltage switching (ZVS) in the whole operating range by keeping the ratio between primary side and secondary side DC-link voltage constant, leading to high efficient energy conversion over a wide input voltage range. In addition, the ZVS conditions can be maintained using small DC inductors and the input current ripple still remains small because of high DC inductor current ripples being alleviated by three-phase interleaving structure. Furthermore, the proposed topology with Y-Y connected transformers is proven to have better current sharing capability compared with other three-phase topologies with different transformer connections. The operation mode analysis, soft switching conditions, and hardware design guidelines are derived in this paper. A 6-kW hardware prototype with input voltage range of 24~48 V and rated 288 V output voltage is developed and tested in the laboratory. The experimental results verified that the proposed converter could maintain high efficiency over a wide input voltage and power range.

A Soft Switching Three-phase Current-fed Bidirectional DC-DC Converter With High Efficiency Over a Wide Input Voltage Range

Electrical power systems in future hybrid and fuel cell vehicles may employ three voltage [14 V, 42 V, and high voltage (HV)] nets. These will be necessary to accommodate existing 14-V loads as well as efficiently handle new heavy loads at the 42-V net and a traction drive on the HV bus. A low-cost DC-DC converter was proposed for connecting the three voltage nets. It minimizes the number of switches and their associated gate driver components by using two half-bridges and a high-frequency transformer. Another salient feature is that the half bridge on the 42-V bus is also utilized to provide the 14-V bus by operating at duty ratios around an atypical value of 1/3. Moreover, it makes use of the parasitic capacitance of the switches and the transformer leakage inductance for soft switching. The use of half bridges makes the topology well suited for interleaved multiphase modular configurations as a means to increase the power level because the capacitor legs can be shared. This paper presents simulation and experimental results on an interleaved two-phase arrangement rated at 4.5 kW. Also discussed are the benefits of operating with an atypical duty ratio on the transformer and a preferred multiphase configuration to minimize capacitor ripple currents.

A Multiphase, Modular, Bidirectional, Triple-Voltage DC–DC Converter for Hybrid and Fuel Cell Vehicle Power Systems

The coupling of the windings can be easily increased by using multiply stacked planar windings connection Interleaving is a well-known technique used to reduce leakage inductance and minimize high-frequency winding losses The paper aims to analyze leakage inductance based on magneto motive force (MMF) and energy distribution in planar transformer and correct the formula of leakage inductance proposed by previous publications The investigation of different winding arrangements shows significant advantages of interleaving structure In this work, a novel half turn structure is proposed to reduce leakage inductance further Some important issues are presented to acquire desired leakage inductance The design and modeling of 1 kW planar transformer is presented In order to verify the analytical method for leakage inductance in this paper, finite element analysis (FEA) and measurement with impedance analyzer are presented Good matching between calculation, FEA 2D simulation and measurement results is achieved

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The analysis and comparison of leakage inductance in different winding arrangements for planar transformer

A review of some of the available technologies for inductor hybrid integration is given in this paper. In accordance with low voltage and high current requirements, low-temperature co-fired ceramics (LTCC) technology is identified to be a suitable candidate for power electronics passives integration. This paper will discuss the various limitations of the current LTCC processing technique and introduce a fabrication technique which will open a new field for chip inductors for hybrid power electronics integration. The design of an LTCC inductor will also be presented. This inductor exhibits an inherent current dependent inductance, leading to high efficiency at low loads as an important systems advantage in portable electronics.

A Class of Ceramic-Based Chip Inductors for Hybrid Integration in Power Supplies

Planar transformers (PTs) are of particular interest in switching mode power supplies and, more generally, in power converter design. They provide enhanced performance, compactness, ruggedness, constant quality, and low cost. Their optimum performance can, however, only be obtained through an accurate design which accounts for both electromagnetic and thermal problems. For that reason, this paper proposes a new combined and accurate electrothermal model for PT design. First, the electrical model based on the eddy current equation is defined. A finite element method is applied to obtain the current density distributions. Second, a 1-D thermal model based on Green's function approach is developed to calculate the temperature distribution in the device. The results obtained using the proposed coupled model are compared with measurements. The comparison indicates a relatively good correlation between the results of our model and experimental data. An excellent agreement is however observed at early times.

A Coupled Electrothermal Model for Planar Transformer Temperature Distribution Computation

Planar transformers provide a distinct advantage over the traditional transformer. However, when the planar transformer is integrated into a power circuit, the interconnect parasitic effects arise that are not shown in a traditional wire-wound transformer. For typical soft-switching converters, a specific leakage inductance is generally needed to charge and discharge the device output capacitances to achieve zero-voltage turn on. This designated leakage inductance value needs to be large enough to extend the zero-voltage switching range. However, it was found that this hard-to-come-by leakage inductance in a planar structure may be overshadowed by the circuit interconnect parasitic inductance. This paper presents a design integration that incorporates the planar transformer and a full-bridge dc/dc converter. Through design calculation, finite element analysis, and experimental verification, it was proven that the role of the parasitic inductance is indeed far exceeding the transformer leakage inductance. Thus, for any design optimization, it is necessary to take into account the parasitic inductance in the integrated structure.

J. Ferrell

Papers

The role of parasitic inductance in high-power planar transformer design and converter integration