Giuseppe Guidi

Assessment of Coupled and Independent Phase Designs of Interleaved Multiphase Buck/Boost DC–DC Converter for EV Power Train

The paper discusses two approaches to multiphase nonisolated dc-dc converter design. An approach based on independent phases is directly compared to an approach using coupled phases. The comparison is performed through theoretical analysis of respective conversion functions, input and output filter requirements, and required input inductor size. Three-dimensional (3-D) high-power-density computer aided design (CAD) models and full-scale 56 kW prototypes based on both approaches were designed, built, and experimentally compared. As expected, the approach with independent phases has a considerable advantage regarding the low-power conversion efficiency where the efficiency can be up to 2% higher than with the coupled approach. On the other hand, the design with coupled inductors can reach power density as high as two times that of the independent phase design (87 kW/L versus 44.2 kW/L). Therefore, the use of coupled inductors may be very beneficial for space critical applications. In case of the electric vehicle power train, both factors may be very important and the suitable approach should be chosen based on system design priorities.

Improvement of light load efficiency of Dual Active Bridge DC-DC converter by using dual leakage transformer and variable frequency

Dual Active Bridge (DAB) topology performs very well for converter output/input ratio close to transformer ratio. However, if a considerable deviation from the transformer ratio is required the conversion efficiency drops significantly. The approach presented in this paper uses variable AC link reactance to improve the DAB performance during operation at light load. The variable reactance is obtained by using a variable frequency in combination with so-called dual leakage transformer. Simple phase-shift control is used, and the switching frequency is varied in order to minimize the peak transformer current. In addition to that, the dual leakage transformer proposed in this paper has a winding configuration yielding a high leakage inductance at low currents and low leakage inductance at high currents. A fully operational prototype was built, demonstrating a power density of 7.1 kW/Liter with forced air cooling, and a peak efficiency at rated 4 kW load equal to 96.6 %. The presented variable reactance approach resulted in more than 10 % efficiency improvement over the conventional DAB design in the most critical point.

Buck/Boost DC–DC Converter Topology With Soft Switching in the Whole Operating Region

This paper proposes a buck/boost dc-dc converter topology based on the principle of auxiliary resonant commutated pole. The used snubber is fairly simple yet effective in reducing the switching losses. All active devices operate with soft switching, and switching noise is suppressed as much as possible. In addition to the conventional active switch loss reduction, the snubber participates in suppression of output diode reverse recovery. Moreover, complete soft switching in the whole operating region is achieved through controlled extended reverse conduction of synchronous rectifier. The topology was implemented in a 14 kW converter prototype operating at 62.5 kHz and tested with complete closed-loop control. Experimental efficiencies in the range of 98.5% show that the proposed circuit is highly capable while remaining sufficiently simple.

Efficiency optimization of high power density Dual Active Bridge DC-DC converter

A DC-DC converter based on the Dual Active Bridge topology is designed, having high power density as main design target. To that aim, a simple structure has been proposed for the transformer with embedded inductor, allowing high frequency operation with low losses and requiring only readily available magnetic core shapes. Simple phase-shift control has been used, and the switching frequency is varied in order to minimize the peak transformer current, thus achieving high conversion efficiency. A fully operational prototype has been built and tested, demonstrating a power density figure of 7.1 kW/Liter with forced air cooling, and a peak efficiency at rated 4 kW load equal to 96.6 %.

Experimental data analysis on total driving performance of series chopper based ev power train

The series chopper type power train for EV is proposed for aiming the increase of one battery charge driving range. A motor-test bench and also actual car were constructed, and the proposed power train with SAZZ (Snubber Assisted Zero voltage and Zero current Transition) chopper was experimentally compared between with and without the chopper.

Driving Performance Experimental Analysis of Series Chopper Based EV Power Train

In this paper, the series chopper based power train for electric vehicle is proposed for aiming the increase of one battery charge driving distance. Both the motor test bench based experiments and the chassis dynamo based experiments are tested and then analyzed for EV driving performance that the proposed power train with SAZZ chopper and Quasi-PAM control scheme is compared with or without the series chopper. It is confirmed through two kinds of experimental analyses that the series chopper power train for EV can be useful to extend the driving distance if the high efficiency and the low weight of chopper are satisfied.

Ultra high efficient battery voltage compensation against decrease in the terminal voltage of electric vehicles

This paper proposes a system and its control method to boost part of the battery voltage for electric vehicle. This system consists of the powertrain of electric vehicles and a bi-directional isolated DC-DC converter called dual active bridge (DAB). The powertrain of electric vehicles in the market has the problem that its performance degrades due to fluctuations in battery voltage. In order to solve this problem, a DC-DC converter is often inserted serially between the battery and the inverter. However, in this solution, the conduction loss of the DC-DC converter always occurs. In this paper, as a solution to the above problems, a voltage boosting system using DAB converter is shown.

Driving range extension by series chopper power train of EV with optimized dc voltage profile

This paper proposes driving range extension by series chopper power train for Electric Vehicles (EV for abbreviation). The proposed method was experimentally verified and compared with the previous publication [1]. Further measurement on motor test bench, to compare this drive with the conventional power train, showed a 2.1 % improvement.

Four quadrant SAZZ-1 chopper for EV and HEV power train

This paper discusses four quadrant SAZZ-1 chopper (Snubber Assisted Zero Voltage and Zero Current Switching) and its direct application to a EV (Electric Vehicle) power train. The performance of SAZZ-1 chopper is demonstrated on several prototypes. The first prototype is a 25 kW, 50 kHz SAZZ-1 with efficiency in the range between 96 % and 97 %. This was further improved by a redesigned SAZZ-1 chopper which reached even higher efficiency in the range of 97 % to over 98 %. Further on, a new mid-power 30 kW water cooled SAZZ-1 chopper was constructed for KAST (Kanagawa Academy of Science and Technology) advanced EV project. This prototype was used and fully tested in an EV prototype named KAST-EV-Kana. As discussed, SAZZ-1 topology proved to be well performing in direct EV application.

Efficient use of Electric Double Layer Capacitor as energy source on board of electric vehicles

Electric Double Layer Capacitors (EDLC) are energy storage devices featuring extremely high power capabilities and superior cycle life, when compared to electrochemical batteries. However, due to the poor energy density, their use in electrical transportation is often limited to the implementation of power buffers for another energy source. After shortly describing this kind of application, the paper focuses on techniques for efficiency improvement and downsizing of such power buffer, based on the use of a split EDLC bank. Two different design methodologies for the proposed power buffer topology are presented and discussed, and their advantage over conventional implementations is shown by means of theoretical analysis and numerical simulation.