Yukinori Tsuruta

Snubber-Assisted Zero-Voltage and Zero-Current Transition Bilateral Buck and Boost Chopper for EV Drive Application and Test Evaluation at 25 kW

A new high-efficiency and high-power bilateral buck and boost chopper circuit for the electric-vehicle drive application is presented. The operation principle of snubber-assisted zero-voltage and zero-current transition (SAZZ) topology was applied, and a new SAZZ bilateral buck-boost chopper circuit (SAZZ-1) was created by combining two basic SAZZ circuit types. A 50-kHz 25-kW SAZZ-1 was fabricated and tested. An efficiency of 96.6% at 25 kW with boost mode (input: 250 V/output: 390 V) in forward direction and an efficiency of 97.4% at 25 kW with buck mode (input: 420 V/output: 300 V) in forward direction were obtained. The high potentiality of the SAZZ-1 chopper is demonstrated as we expected.

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.

A new zero-voltage-zero-current-transition chopper SAZZ for a FCEV drive

A new snubber assisted zero voltage and zero current transition chopper (SAZZ) is proposed for the fuel cell electric vehicle (FCEV) or the hybrid vehicle. The SAZZ topology provides a simple soft switching technique resulting in the compact and low-loss power converter for the FCEV. Furthermore, the SAZZ operates without voltage spike across the output diode during the reverse recovery. A SAZZ mini-model using IGBT was fabricated and evaluated by a fundamental operational test. The experimental results show the verification of the circuit geometry and the basic operation. In addition, the preliminary SAZZ configuration for the high frequency using the stray capacitance is investigated to minimize the current of the auxiliary resonant stage. Some experimental results are also presented.

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.

Proposal of Bilateral Buck and Boost Chopper Circuit SAZZ-1 for EV Drive Application and the Test Evaluation at 25kW

A new high efficiency and high power bilateral boost and buck chopper circuit for the electric vehicle (EV) drive application is presented. The operation principle of SAZZ (snubber assisted zero voltage and zero current transition) topology was applied and a new SAZZ bilateral buck-boost chopper circuit (SAZZ-1) was created by combining two basic SAZZ circuit types. A 50 kHz-25 kW SAZZ-1 was fabricated and tested. 96.57% efficiency at 25 kW with boost mode (input:250 V/output:390 V) in forward direction and 97.44% efficiency at 25 kW with buck mode (input:420 V/output:300 V) in forward direction were obtained. The high potentiality of SAZZ-1 chopper could be demonstrated as we expected.

A New Circuit Geometry SAZZ for An EV Drive Application

A new circuit geometry SAZZ (snubber assisted zero voltage and zero current transition) is presented. It has the solution to supersede the conventional hard switched DC-DC converter currently in use for an electric vehicle (EV) drive application because of the simplicity and efficiency. Through the discussion of the circuit geometry, the operation principle of SAZZ topology can be applied to the 6 basic DC-DC converters. Moreover, new SAZZ circuit geometry can be created by combining two basic SAZZ circuit types, as shown as the bidirectional converter based on SAZZ topology. A 100kHz-8kW SAZZ mini-model using IGBT was fabricated and evaluated by a fundamental operational test. In addition, the 100kHz-8kW SAZZ bidirectional converter is also presented as a case study of SAZZ geometry for an EV drive application

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.

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.