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This article is focused on the thermal design and three-dimensional (3-D) package optimization of planar magnetic components (PMCs), including transformers and inductors for application in an electric vehicle composite boost dc–dc converter. Each PMC comprises electrical windings in printed circuit board (PCB) form in combination with a ferrite core. Multiple features of each PMC package are thermally optimized for the proposed device configurations with given core size, core loss distribution, number of turns in the PCB winding, winding copper thickness, and winding loss distribution. These heuristically optimized features include a lower level cold plate structure with a conformal base for enhanced convective heat transfer, an upper level PMC cap structure for doubled-sided cooling through conductive heat flow to the cold plate, the implementation of functionally distributed copper thermal and electrothermal vias in the PCB winding for improved cross-plane thermal conductance, and judicious implementation of select materials at various locations and interfaces within the package. Detailed numerical modeling reveals the combined effect of this 3-D packaging strategy with a 79.3 °C and 48.5 °C maximum temperature reduction in the core and PCB winding, respectively, relative to a baseline device configuration. Select PMC experimental validation confirms the expected thermal performance of an optimized PCB design. The thermal design approach is relevant for a range of high-power-density electronics PMC packaging applications.

In a composite dc-dc converter, regulation and dual active bridge (DAB)-based fixed-ratio (DCX) modules are arranged to minimize stresses and losses over wide ranges of input and output voltages. The system relies on smooth mode transitions in which a DCX must be quickly powered up from zero output to its nominal fixed-ratio operation. In the case a DCX precedes a regulation stage, the DCX is exposed to a high input voltage, leading to a large inrush current during startup. In the case a DCX follows a regulation stage, the DCX needs to charge the output dc capacitor while simultaneously supplying a high load current. To address these challenges, a generalized DCX modulation scheme is proposed in this paper to maximize the average DCX output current and to enable soft startup transitions in the two configurations considered. The approach is verified by simulations and by experimental results on a 350 V, 25 kW SiC-based prototype.

A decentralized hierarchical control architecture is proposed for composite systems. Automatic mode transitions are performed in a high-level main controller using a state machine that commands references for each partial-power converter module. Local converter module controllers perform gain-scheduled average current control. It is observed during mode transitions, that when the boost module and the dual active bridge (DAB) module change their output voltage simultaneously, there are unwanted transients in the system that induce instabilities. These transients occur because the boost converter is unable to handle the required voltage step up during the turn on of the DAB converter. To mitigate these transients, a boost voltage reference dynamic alteration and DAB reference ramp offset strategy has been proposed in the paper. Mathematical evaluation of the state machine, condition for transient occurrence and mitigation strategies have been presented. Validation of the theoretical hypothesis is provided by simulations and controller-hardware-in-loop (CHIL) test bed results.

This paper presents analysis and modeling of differential-mode (DM) resonances due to interactions between inductances and parasitic winding capacitances in high frequency planar transformers, which may result in undesirable current ringing. These DM phenomena are fundamentally different compared to well-recognized and better understood common-mode (CM) issues. A simplified half-circuit model is developed based on the classical six-capacitor network model, and an analytical expression is derived for evaluation of the worst-case differential-mode current ringing. A direct relationship is found between the electric field energy storage and the DM current ringing. The modeling insights lead to improved design approaches for planar transformer and tank inductor windings in transformer isolated converters. The results are verified by experiments on a SiC-based dual-active-bridge converter prototype operating at 9 kW and 210 kHz.

This paper presents an online optimization strategy for a silicon-carbide (SiC) based Boost converter where the converter switching frequency and dead times are adjusted to set the peak synchronous-rectifier (SR) turn-off current so that zero-voltage switching quasi-square-wave (ZVS-QSW) operation is achieved at any given operating point while minimizing inductor current ripple. The optimal converter switching frequency and dead times are determined based on sensed converter input/output voltages and inductor current using multidimensional parametric curve fit. These timing parameters are applied to the converter in a low-bandwidth feed-forward path operating in conjunction with closed-loop regulation of the converter output voltage. Experimental validation of the online optimization strategy is carried out on a 10kW, 600V converter prototype, demonstrating a close match between analytically computed and curve-fit based switching frequency and dead times over wide ranges of operating points. The proposed approach enables operation of the converter with efficiencies greater than 97.5% for input voltages ranging from 200V to 400V, conversion ratios up to 2.5, and power levels between 2kW and 8kW.

This paper presents state-of-charge (SOC) control between battery modules in an active battery management system (BMS) with series output connected DC-DC modules. To increase both the pack and system-level modularity, the BMS regulates the battery pack average SOC by controlling a common input current from all series-connected modules. A balancing loop introduces input current offsets to regulate all module SOCs. The BMS functions are divided between a central controller for battery pack SOC regulation and individual module SOC control; a module level controller regulates the input current. Experimental results are presented on a 1.5 kW prototype consisting of five series modules that are formed by 15 DC/DC series and parallel connected converters in an active BMS.

This paper presents a modular control architecture for a composite dc-dc converter topology. A composite converter comprises multiple dissimilar partial-power converter modules arranged and operated to minimize stresses and improve system efficiency over a wide range of operating points. This requires transitioning to different operating modes for different operating conditions. A control strategy is required to determine the optimal mode, and to achieve smooth mode transitions and fast closed-loop system dynamic responses. A modular control architecture capable of meeting these objectives is described. In this architecture, low-level module controls are decoupled from system-level operations. The resulting hierarchical control strategy is relatively simple, and highly scalable in nature. The approach is developed and validated on a controller hardware-inthe-loop (CHIL) platform. A frequency scaling strategy is applied to allow validations of high-switching frequency converters on bandwidth-limited CHIL platforms.

This paper presents a relatively simple technique to reduce winding losses due to fringing fields in high-frequency inductors. In high-frequency power electronics, ac inductor winding losses are affected by skin and proximity effects, including uneven current distribution due to fringing magnetic fields around airgaps. It is well known how fringing effects can be mitigated using distributed airgaps, at the expense of non-standard core or winding geometry. The orthogonal-airgap approach proposed in this paper combines airgaps in core segments parallel with the windings with airgaps in segments perpendicular to the windings. The approach is developed using a 1D analytical framework and validated by 2D finite-element simulations. Analytical guidelines are presented to optimize the airgaps to achieve minimum ac resistance. As a case study, a planar inductor is designed for an 8 kW SiC-based buck converter operating at 250 kHz. It is shown how the orthogonal airgaps result in more than 45% reduction in ac resistance and substantially reduced inductor losses compared to the design using standard airgaps. The results are verified by loss measurements on an experimental converter prototype.