Mostafa Noah

Power loss analysis of multi-phase and modular interleaved boost DC-DC converters with coupled inductor for electric vehicles

Efficiency is one of the most important aspects to consider in the design of electric systems for mobility applications. In this study, the interface between the storage system and the inverter is considered. This interface is a step-up DC-DC converter aimed to boost the energy storage voltage to the inverter voltage. This paper introduces the analysis, design, and comparison of four topologies of the interleaved boost DC-DC converter evaluating the effect of magnetic four-phase coupled inductorcoupling in multi-phase and modular circuits. Additionally, a novel idea of a four-phase coupled inductor is presented. These power DC-DC converters are designed in order to find the suitable arrangement with the best efficiency.

A novel three-phase LLC resonant converter with integrated magnetics for lower turn-off losses and higher power density

The aim of this work is to present a novel topology of a three-phase LLC converter with integrated magnetics. The converter operation and the comprehensive theoretical analysis are presented; this analysis follows the first harmonic approximation (FHA) approach to simplify the system model. Usually, LLC converter achieves zero voltage switching (ZVS) as long as it working in the inductive region. Therefore, the turn off losses are considered as the main source of the switching losses in the converter. In this paper the design in optimized to minimize the switching losses. On the other hand, adapting three discrete transformer cores in this topology will definitely increase the size and volume of the converter. As a result, a novel magnetic integration concept is introduced where all magnetic components of the three-phases are advantageously combined into a single magnetic core to increase the converter power density. Finally, the experimental results are presented to verify the optimized design by showing a reduction in the turn-off losses and the effectiveness of adapting the proposed integrated transformer, in which an increment of 56% in the power density of the converter could be attained.

A Magnetic Design Method Considering DC-Biased Magnetization for Integrated Magnetic Components Used in Multiphase Boost Converters

High power density and high efficiency in dc/dc converters are required in various applications such as the automotive application. Interleaved multiphase circuits with integrated magnetic components can fulfill these requirements because passive components occupying significant space in power converters can be downsized without high-switching frequency driving of power devices. However, dc-biased magnetization is a drawback of integrated magnetic components because of unbalanced inductor average currents. This imbalance arises from the tolerance among the phase components. To overcome this problem, inductor average current control is implemented in interleaved multiphase dc/dc converters. Nevertheless, the imbalance cannot be completely eliminated because the current sensors inserted into each phase have gain errors. The purpose of this paper is to present a magnetic design method to improve the immunity to unbalanced currents. A comprehensive analysis is carried out with two main objectives: to prevent magnetic saturation, which may arise due to the current unbalance and to downsize the magnetic components by selecting the optimal coupling coefficient taking into consideration the maximum permissible percentage of unbalanced currents. Simulation case studies are presented to support the analysis. Finally, a 1-kW prototype of the interleaved boost converter is built to validate the accuracy of the design method.

Three-phase LLC resonant converter with integrated magnetics

Recently, Electric Vehicles (EVs) have required high power density and high efficiency systems in order to save energy and costs. Specifically, in the DC-DC converter that feeds the non-propulsive loads in these vehicles, where the output voltage is much lower than the one of the energy storage unit. Therefore, the output current becomes quite high, and the efficiency and power density are reduced due to the high current ratings. Furthermore, magnetic components usually are the biggest contributors to the mass and volume in these converters. This paper proposes a Three-phase LLC resonant converter with one integrated transformer where all the windings of the three independent transformers are installed into only one core. Using this technique, a high reduction in the core size and thereby an increment in the power density and a reduction of the production cost are obtained. In addition, this integrated transformer is intended to be applied in the novel Three-phase LLC resonant converter with Star connection that is expected to offer reduction of the imbalanced output current, which is produced by tolerances between the phase components. Finally, the proposed converter with the novel integrated transformer is discussed and evaluated from the experimental point of view. As a result, a 70% reduction in the mass of the magnetic cores was achieved.

Design of a four-phase interleaved boost circuit with closed-coupled inductors

In this paper, a novel magnetic structure suitable for boost converters is proposed. Multi-phase interleaved method using coupled-inductor has gained attention in electric powertrains for electric, hybrid and fuel cell vehicles in order to achieve high power density. In fact, a four-phase boost converter using coupled inductor is used in the drive system of the Honda CLARITY. In particular, magnetic coupling method is used in coupled inductors, Loosely-Coupled Inductors (LCI) and Closed-Coupled Inductors (CCI). This study is focused on these methods, especially using the CCI. This paper presents a design method of a closed-coupled inductors using generic cores for a four-phase interleaved boost converter. In addition a comparison between the proposed topology with other conventional non-coupled methods is carried out. Furthermore, the evaluation of miniaturization is studied. As a result, the proposed method can achieve a huge reduction in the core volume and mass.

A Current Sharing Method Utilizing Single Balancing Transformer for a Multiphase LLC Resonant Converter With Integrated Magnetics

Integrated magnetics is applied to replace the three-discrete transformers by a single core transformer in a three-phase LLC resonant converter. The magnetic circuit of the integrated transformer is analyzed to derive coupling factors between the phases; these coupling factors are intentionally minimized to realize the magnetic behavior of the three-discrete transformers, with the benefit of eliminating the dead space between them. However, in a practical design, the transformer parameters in a multiphase LLC resonant converter are never exactly identical among the phases, leading to unbalanced current sharing between the paralleled modules. In this regard, a current balancing method is proposed in this paper. The proposed method can improve the current sharing between the paralleled phases relying on a single balancing transformer, and its theory is based on Ampere’s law, by forcing the sum of the three resonant currents to zero. Theoretically, if an ideal balancing transformer has been utilized, it would impose the same effect of connecting the integrated transformer in a solid star connection. However, as the core permeability of the balancing transformer is finite, the unbalanced current cannot be completely suppressed. Nonetheless, utilizing a single balancing transformer has an advantage over the star connection, as it keeps the interleaving structure simple which allows for traditional phase-shedding techniques, and it can be a solution for the other multiphase topologies where realizing a star connection is not feasible. Along with the theoretical discussion, simulation and experimental results are also presented to evaluate the proposed method considering various sources of the unbalance such as a mismatch in: 1) resonant and magnetizing inductances; 2) resonant capacitors; 3) transistor on-resistances of the MOSFETS; and 4) propagation delay of the gate drivers.

Analytical investigation of interleaved DC-DC converter using closed-coupled inductor with phase drive control

Interleaved techniques and magnetic integration in a boost converter have gained attention in electric powertrains system for electric, hybrid and fuel cell vehicles in order to achieve high power density or to improve power conversion efficiency. Furthermore, the proposed multi-phase boost converter is equipped with a phase drive control to improve the efficiency at all load ranges. Furthermore, a design method of a coupled-inductor for an interleaved boost converter with phase drive control is also proposed. However, the interleaved DC-DC converter using coupled method with phase drive control has many problems. In this paper, this problem of interleaved DC-DC converter using coupled inductor with phase drive control (PDC) is analyzed. In addition, defensive method of this method.

Magnetic design and experimental evaluation of Integrated Magnetic Components used in Interleaved Multi-phase DC/DC converter with Phase Drive Control

Interleaved Multi-phase DC/DC Converters (IMDDC) with Integrated Magnetic Components (IMC) are well-known as one of the converter topologies that can achieve high-power-density. However, as one of the drawbacks of IMDDCs, the power conversion efficiency when all phases are driven may decrease between light and middle loads. The main causes of the efficiency reduction are non-load losses caused by parasitic capacitances in power devices and magnetic components. These losses especially increase under higher switching frequency and hard switching condition. To deal with this problem, IMDDCs with Phase Drive Control (PDC) has already been proposed as an attractive control scheme which can improve power conversion efficiency in all load ranges, by changing the number of drive phases. However, employing PDC in IMDDCs with IMC comes with two main drawbacks: 1) Magnetic saturation may occur due to the biased magnetization while driving a single-phase. 2) The circulating current flow in the anti-parallel diode of off-switch reduces the power conversion efficiency. Therefore, to overcome these problems, this paper proposes a novel design method of IMCs used in IMDDCs with PDC. The effectiveness of the proposed design method is discussed from theoretical and experimental viewpoints.

A high-reliable magnetic design method for three-phase coupled inductor used in interleaved multi-phase boost converters

This paper proposes a high-reliable magnetic design method considering DC-biased magnetization for a Loosely Coupled Inductor (LCI) used in interleaved three-phase boost converters. The interleaved multi-phase boost converters with an LCI are well-known as one of the attractive circuit topologies that can achieve high-power-density of the converters. However, when designing and implementing an LCI in the interleaved converter, DC-biased magnetization in the transformer part of LCI must be taken into account because magnetic saturation of the core may easily occur. This phenomenon is caused by unbalanced inductor average currents in each phase. Inserting air-gaps into magnetic paths of the transformer part of a LCI is considered as one of the solutions to prevent the magnetic saturation. Nonetheless, in this case, the volume and weight of LCI increase, and they become a matter of concern because the characteristics of an LCI goes closer to the characteristics of the independent inductors. Therefore, there is a trade-off between handling the DC-biased magnetization and downsizing the magnetic core. To optimize this trade-off, a novel magnetic design method for LCI is proposed by considering the maximum permissible percentage of unbalanced inductor average currents. This paper focuses on the three-phase coupled inductors used in three-phase interleaved boost converters. The accuracy and the effectiveness of the proposed magnetic design method are discussed from both theoretical and experimental points of view.

Magnetic structure of close-coupled inductors to improve the thermal handling capability in interleaved DC-DC converter

Interleaved DC-DC converter employing close-coupled inductors is a popular topology among other power converters topologies. Close-coupled inductors allow the power converter to achieve high power density and high efficiency. This paper proposes a novel magnetic structure of close-coupled inductors suitable for increasing the thermal handling capability. The proposed magnetic structure is combined of different magnetic materials, namely, ferrite and powder cores. The design method of the integrated close-coupled inductors are presented. Furthermore, this design method is considering the DC bias superposition characteristics, and the iron and copper losses as well. A 300W prototype is built to validate the proposed analysis. Finally, excellent heat dissipation of the proposed magnetic structure of the integrated close-coupled inductors is also reported.