Martin Pavlovsky

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.

Pursuing high power-density and high efficiency in DC-DC converters for automotive application

The paper presents an approach to designing automotive converters with main objectives being high efficiency and high power density. The approach is demonstrated by presenting two case study designs and measurements on converter prototypes. The goals of high efficiency and high power density are reached by an optimal converter design including soft switched SAZZ topology, paralleled mosfets, integrated inductors, interleaved converter modules, advanced thermal management and optimized spatial design. The initial goals of the project were to reach as high efficiency as possible and to exceed power density of 10 kW/litre. The power density goal was exceeded by a large margin reaching the power density of 17.7 kW/litre even for air-cooled system. The measured efficiency of a single converter module operating at 200 kHz is as high as 95.4% and a larger efficiency is still expected from the complete interleaved converter prototype.

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 %.

Recent improvements of efficiency and power density of DC-DC converters for automotive applications

Automotive industry is considered to be one of the main contributors to environmental pollution and global warming. Therefore, many car manufacturers are in near future planning to introduce hybrid electric vehicles (HEV), fuel cell electric vehicles (FCEV) and pure electric vehicles (EV) to make our cars more environmentally friendly. These new vehicles require highly efficient and small power converters. In recent years, considerable improvements were made in designing such converters. In this paper, an approach based on so called Snubber Assisted Zero Voltage and Zero Current Switching topology otherwise also know as SAZZ is presented. This topology has evolved to be one of the leaders in the field of highly efficient converters with high power densities. Evolution and main features of this topology are briefly discussed. Capabilities of the topology are demonstrated on two case study prototypes based on different design approaches. The prototypes are designed to be fully bi-directional for peak power output of 30 kW. Both designs reached efficiencies close to 99 % in wide load range. Power densities over 40 kW/litre are attainable in the same time. Combination of MOSFET technology and SAZZ topology is shown to be very beneficial to converters designed for EV applications.

Bi-directional buck/boost dc-dc converter with ultra high efficiency based on improved SAZZ topology

An improved bi-directional buck/boost SAZZ topology is proposed in this paper. The improvements are aimed at increasing the total conversion efficiency as well as at enlarging the soft switching operating area and hence improving the overall converter performance. The modifications with respect to the conventional SAZZ topology are: configuration of snubber circuits enhanced by saturable inductors and use of synchronous rectification. The proposed topology is implemented in a 60 kW, 50 kHz converter design. The improved topology reaches conversion efficiencies in the 99 % region in a broad range of operating conditions and output power. In the same time, the improved topology together with an advance structural and thermal converter design result in the power density higher than 40 kW/l.

Very high efficiency SAZZ chopper using high speed IGBT

In this paper a study for very high efficiency targeting 99 % range converter is described. We have proposed a new soft switching boost type chopper based on snubber assisted zero voltage and zero current transition (SAZZ) with output diode fabricated “SiC schottky diode”. The output power of 8 kW with the efficiency of 98.96% was obtained. The loss breakdown evaluation of SiC-SAZZ is discussed.

State-of-the-art high power density and high efficiency DC-DC chopper circuits for HEV and FCEV applications

Recent environmental issues have accelerated the use of more efficient and energy saving technologies in any area of our daily life. One of the major energy consumptions is in the transportation area, especially in the automobile field. DC/DC chopper circuits for use in hybrid electric vehicles (HEV), fuel cell electric vehicles (FCEV) and so on will be discussed in this paper from the view point of power density and efficiency. A typical power range of such converters can be in order of kWs up to over 100 kW with a short term overload requirement of often more than 200%. Considering the state of the art, switching frequency of these converters is in the range from 50 kHz with IGBTs to 200 kHz with power MOSFETs, the power density peaks at about 25 kW/l, and the highest efficiency is close to 98 [%] depending on the load conditions. As can be seen from the brief introduction, the design of such converter presents multiple challenges from power density as well as efficiency point of view and these are discussed further in the paper.

Buck/boost Dc-Dc converter with simple auxiliary snubber and complete soft switching in whole operating region

The paper proposes a buck/boost dc-dc converter topology based on a simple auxiliary snubber. The snubber is simple yet effective in reducing the switching losses. In addition to the conventional active switch loss reduction, the snubber can participate in suppression of output diode reverse recovery through synchronous rectifications and it can also be used to provide complete soft switching in the whole operating region through extended conduction of synchronous rectifier. Experimental efficiencies in the range of 98.5 % show that the proposed circuit is highly capable while remaining simple.