Yuki Itoh

Downsizing Effects of Integrated Magnetic Components in High Power Density DC–DC Converters for EV and HEV Applications

The interleaved DC-DC converters with integrated magnetic components that achieve high power density have recently gained attention in automotive market for eco-friendly cars such as electric vehicles (EV) and hybrid electric vehicles (HEV). Interleaved converters with close-coupled inductors and loose-coupled inductors are well known as the converters capable to achieve high efficiency with low volume and weight. As a new approach, an interleaved converter with integrated winding coupled inductors is proposed. This paper proposes a novel inductor size calculation model. By using this model, the downsizing effects of the integrated magnetic components are discussed at 1 kW output. As a result, interleaved converter with integrated winding coupled inductors is effective for downsizing of the magnetic components with the condition that duty ratio is higher compared to interleaved converters with loose-coupled inductors and close-coupled inductors. In contrast, it is also found that interleaved converter with loose-coupled inductors achieves downsizing of the magnetic component when duty ratio is close to 50 %. The validity of the calculation model is estimated from the experimental viewpoints.

Analysis of coupled-inductor configuration for an interleaved high step-up converter

High step-up converters are widely used in sustainable energy systems and recently used in automotive applications due to their high voltage gain capability. Nevertheless, with the purpose of obtaining a higher voltage gain, in comparison with conventional boost converters, current high step-up converters often employ additional multiplier cells, which may lead to significant cost-up and low power density. Therefore, a novel two-phase interleaved high step-up converter is proposed in order to minimize additional circuit volume used to achieve large voltage gain. The proposed converter addresses the purpose by a particular coupled inductor where three windings are installed in one or two cores. As a result, the proposed converter can achieve higher voltage gain than the conventional topologies by adding a winding and two diodes to the interleaved two phase boost chopper, besides the coupled-inductor configuration. This paper evaluates two arrangements of the coupled-inductor configuration of the proposed high step-up converter: 1. Three windings integrated in only one core and 2. Two independent inductors with a shared winding. The result revealed that the proposed converter shows higher voltage gain than the normal boost converter and the magnetic integration in the coupled-inductor configuration further increases the voltage gain by 20%.

Inductor loss analysis of various materials in interleaved boost converters

High power density DC/DC converters have gained attention in automotive applications for Electric and Hybrid Vehicles. Inductors often appear as the largest component in DC/DC converters. DC/DC converters using a coupled inductor are well-known as one of the topologies which can achieve miniaturization of a magnetic component. Temperature of an inductor tends to be higher in high power density DC/DC converters. Thus, an optimal magnetic property selection is necessary for magnetic designs. In this paper, we have analyzed the relationship between inductor losses that affects the heat and inductor volume as the previous stage of the thermal analysis in the inductor. In addition, this paper presents analytical comparisons of various magnetic materials used in practical designs. This study is focused on interleaved boost converter of integrated winding coupled inductors, loose-coupled inductors and non-coupled inductors. The study is discussed from the view point of inductor losses and inductor volume.

A novel high step-down interleaved converter with coupled inductor

Nowadays, high power density has become essential in networking, telecommunications and computing applications. Additionally, the electronic equipment used in these applications requires a very-low voltage feeding even when its power supply has a much higher voltage rating. Therefore, high step-down converters with high power density performance are required for these applications. Consequently, a novel two-phase interleaved high step-down converter is proposed in order to fulfill the requirements of high power density and high step-down conversion ratio of these applications. The proposed converter addresses the objective by a particular coupled inductor where three windings are only installed in one core. As a result, the proposed converter can achieve higher step-down ratio than the conventional topologies by adding a winding and two switches to the interleaved two phase buck converter, besides the coupled-inductor configuration. In this paper, the novel topology is introduced and analyzed in order to find its conversion ratio operation. Then, the proposed topology is compared to conventional topologies and some improved high step-down converters recently proposed. Finally, the proposed converter is experimentally validated and the results revealed that the proposed converter shows higher step-down conversion ratio than the conventional buck converter with a further increment of 40% in the conversion ratio when the converter is operating at a duty cycle of 30% and ratio of turns of 2.

Design method considering magnetic saturation issue of coupled inductor in interleaved CCM boost PFC converter

The demand of high power Continuous Conduction Mode (CCM) Power Factor Correction (PFC) converter installed in charging devices for Electric and Hybrid Vehicles has grown in the recent years. In these converters, the inductor often appears as the largest component, consequently, the CCM boost PFC converter using coupled inductors is well-known as one of the topologies that can achieve miniaturization and weight reduction of the inductors. However, the change of the magnetic flux during a half cycle of the input AC voltage has not yet been analyzed in detail. Therefore, the cause of the difference of the magnetic saturation is not known. In the case of non-coupled inductor, the magnetic saturation occurs at a point of the peak inductor current. In contrast, in the case of the coupled inductor, the magnetic saturation occurs at a different point than the inductor current peak. In this paper, the change of the magnetic flux in a half cycle of the input AC voltage is analyzed. Additionally, the novel design method of the coupled inductor considering the maximum magnetic flux is proposed. Finally, the validity of the novel design method is confirmed by experimental tests.

Feasible evaluations of coupled multilayer chip inductor for POL converter

Point of load (POL) converters are required smaller size and high efficiency performance in IT industrial applications, etc. Interleaved technique, magnetic integration techniques and application of GaNFETs are well known as good approaches to satisfy these demands. Although coupled inductors for POL converters have been proposed in several studies, a coupled multilayer chip inductor has not examined because of the difficulty of its construction. In this paper, a novel coupled multilayer chip inductor for interleaved POL converters is proposed. This novel coupled inductor has a winding pair with inversely coupled in the magnetic core. Further, magnetic material of the coupled inductor is Fe-based metal composite powder (Fe-Si-Cr). In addition, Fe-based powder in the magnetic core has been processed electrical insulation by highly crystallized oxide nano-layer in order to reduce eddy-current losses. Its high efficiency performance is evaluated by interleaved step down chopper circuit prototype using normally off typed GaNFETs with 1MHz switching frequency.

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.

A detection method of DC magnetization utilizing local inhomogeneity of flux distribution in power transformer core

The DC magnetization is one of the common causes of operational faults in forward DC-DC converters because it may promote magnetic saturation in the transformers. A useful remedy is to detect the DC magnetization using a sensor and eliminate it by a controller. The purpose of this paper is to propose a simple but reliable sensor. Although a number of sensors have been proposed in prior works, they often suffer from complicated implementation or from influence of the load current on the sensor output. The proposed method, on the other hand, can be implemented only by a search coil equipped on the power transformer without adding any special physical structure except a through-hole on the core. Despite of the simple implementation, the method is not affected by the load current and can detect the DC magnetization before apparent magnetic saturation occurs. This paper also presents an experiment, which verified that the load current does not affect the sensor output and that the DC magnetization can be detected even under the flux density below the saturation level. These results support usefulness of the proposed sensor in practical applications.

Inductor loss calculation of coupled inductors for high power density boost converter

The interleaved boost converter with coupled inductors which achieves high power density has gained great attention in automotive applications. However, the temperature of the inductor tends to be high because loss density is increased by the high power density. Therefore, it is important to calculate the inductor losses when the inductors in high power density converters are designed. In this paper, firstly, a core loss calculation method for the coupled inductor is proposed. Then, accuracy of the core loss calculation method is confirmed by experimental validation. Finally, magnetic properties of the used cores are shown and then the usefulness of the coupled inductors is discussed from different viewpoints of inductor losses and volume comparing single-phase, two-phase and two-phase converter with coupled inductors methods by using the imaginary inductors theory. As a result, inductor loss of the coupled inductors can be reduced compared to conventional methods, and a superior core material is suggested.