Hyeokjin Kim

Design of EMI Filters Having Low Harmonic Distortion in High-Power-Factor Converters

This paper studies how electromagnetic interference (EMI) filters affect the harmonic distortion in high-power-factor converters. The EMI filter presents a tradeoff: higher noise attenuation results in higher harmonic distortion. In many modern converters, the EMI filter is designed to meet certain noise requirements. However, when tested in practice, the filter, while attenuating the EMI noise well, is found to generate high harmonic distortion, and should be redesigned. The cause of this distortion is a nonlinear interaction of the filter and the bridge rectifier. The current understanding of this process is incomplete, especially in modern converters that use high-order LC filters, and modern low-cost inverters. As a result, harmonic distortion is typically tuned by repeated trial-and-errors. In this paper, we provide a simple model for evaluating the harmonic distortion. The harmonic distortion is shown to be dominated by a single parameter: the filter total capacitance. The total harmonic distortion and capacitance are shown to be to be related by a simple power-law function. This relation is proved to be accurate if the total filter inductance is smaller than a given threshold. Experimental results show that total harmonic distortion can be estimated by the capacitance, with a normalized error of 0.09%.

A 98.7% Efficient Composite Converter Architecture With Application-Tailored Efficiency Characteristic

A DC-DC boost composite converter architecture is introduced that can lead to optimized efficiency over a range of operating points dictated by the application requirements. The composite converter system employs dissimilar modules to minimize the ac power losses in the indirect power conversion paths. It is composed of three converter modules: buck converter, boost converter, and a dual active bridge converter that operates as a DC Transformer (DCX). Each module processes partial power, with reduced voltage rating. With the same semiconductor area and same magnetics volume, substantial efficiency improvements and reductions in capacitor size are achieved relative to a conventional boost architecture. It is possible to design each module to optimize efficiency over a wide operating range, including passthrough modes that exhibit very low loss. A 10 kW boost composite converter is experimentally demonstrated having 98.7% efficiency at a critical partial power point, with similar very high efficiencies achieved over a wide operating range.

A high power density single-phase inverter using stacked switched capacitor energy buffer

This paper presents a high power density 2 kW single-phase inverter, with greater than 50 W/in3 power density and 90% line-cycle average efficiency. This performance is achieved through innovations in twice-line-frequency (120 Hz) energy buffering and high frequency dc-ac power conversion. The energy buffering function is performed using an advanced implementation of the recently proposed stacked switched capacitor (SSC) energy buffer architecture, and the dc-ac power conversion is performed using a soft-switching SiC-FET based converter, with a digital implementation of variable frequency constant peak current control.

Design of a high efficiency 30 kW boost composite converter

An experimental 30 kW boost composite converter is described in this paper. The composite converter architecture, which consists of a buck module, a boost module, and a dual active bridge module that operates as a DC transformer (DCX), leads to substantial reductions in losses at partial power points, and to significant improvements in weighted efficiency in applications that require wide variations in power and conversion ratio. A comprehensive loss model is developed, accounting for semiconductor conduction and switching losses, capacitor losses, as well as dc and ac losses in magnetic components. Based on the developed loss model, the module and system designs are optimized to maximize efficiency at a 50% power point. Experimental results for the 30 kW prototype demonstrate 98.5% peak efficiency, very high efficiency over wide ranges of power and voltage conversion ratios, as well as excellent agreements between model predictions and measured efficiency curves.

Electrified Automotive Powertrain Architecture Using Composite DC–DC Converters

In a hybrid or electric vehicle powertrain, a boost dc-dc converter enables reduction of the size of the electric machine and optimization of the battery system. Design of the powertrain boost converter is challenging because the converter must be rated at high peak power, while efficiency at medium-to-light load is critical for the vehicle system performance. By addressing only some of the loss mechanisms, previously proposed efficiency improvement approaches offer limited improvements in size, cost, and efficiency tradeoffs. This paper shows how all dominant loss mechanisms in automotive powertrain applications can be mitigated using a new boost composite converter approach. In the composite dc-dc architecture, the loss mechanisms associated with indirect power conversion are addressed explicitly, resulting in fundamental efficiency improvements over wide ranges of operating conditions. Several composite converter topologies are presented and compared to state-of-the-art boost converter technologies. It is found that the selected boost composite converter results in a decrease in the total loss by a factor of 2-4 for typical drive cycles. Furthermore, the total system capacitor power rating and energy rating are substantially reduced, which implies potentials for significant reductions in system size and cost.

SiC-MOSFET composite boost converter with 22 kW/L power density for electric vehicle application

A SiC-MOSFET composite boost converter for an electric vehicle power train application exhibits a volumetric power density of 22 kW/L and gravimetric power density of 20 kW/kg. The composite converter architecture, which is composed of partial-power boost, buck, and dual active bridge modules, leads to a 60% reduction in CAFE average losses, to a 280% improvement in power density, and to a 76% reduction in magnetics volume compared to the conventional Si-IGBT boost converter. These gains were achieved with the help of optimization based on a comprehensive loss model including SiC-MOSFET switching loss and magnetic losses based on the FEM method simulated in FEMM. Experimental results for the 22 kW/L SiC-MOSFET composite converter project 97.5% average efficiency on US06 driving cycle and a CAFE average efficiency of 97.8%.

A high power density drivetrain-integrated electric vehicle charger

This paper presents a new architecture for an isolated level 2 on-board electric vehicle (EV) battery charger which is integrated with the EVs drivetrain dc-dc boost converter. The proposed charger leverages many of the existing stages of a highly efficient and power-dense composite-architecture-based drivetrain boost converter. This composite boost converter comprises a buck, a boost and a dc transformer (DCX) stage. In selecting the proposed charging architecture, four alternative approaches to drivetrain integration are identified, explored and compared quantitatively in terms of added weight and charging losses. Out of the considered approaches, the proposed charging architecture provides an effective tradeoff between additional weight and charging losses. This drivetrain-integrated charger adds only a bridgeless-boost-based power factor correction (PFC) ac-dc stage, plus an H-bridge and a single winding to the composite boost converter, to achieve high-power on-board charging functionality without substantial additional weight. A 6.6 kW prototype of the proposed charger has been designed and its PFC stage built and tested. The PFC stage uses a digital implementation of a current sensor-less control strategy and employs effective ways of mitigating zero crossing distortion. The proposed charger architecture reduces the additional weight required for the onboard charging functionality, while achieving greater than 97% peak efficiency for the added charger module PFC stage.

Boost composite converter design based on drive cycle weighted losses in electric vehicle powertrain applications

A weighted design optimization is introduced to minimize total loss of electric vehicle drivetrain power electronics over EPA standard drive cycles. It is shown that the net loss of the conventional boost converter can be reduced by a factor of 1.5 with this approach, while computational effort is reduced by three orders of magnitude. Even larger efficiency improvements are achieved by optimized boost composite converters: losses are reduced by factors of 4.5, 2.9, and 4.3 for US06, UDDS, and HWFET driving cycles, respectively. These design optimization results are experimentally verified with a 30 kW laboratory prototype boost composite converter, which demonstrates 98.4% average efficiency over the US06 driving cycle.