A Buck-Boost Transformerless DC-DC Converter 1 Based on IGBT Modules for Fast Charge of Electric 2 Vehicles 3

: A transformer-less Buck-Boost DC-DC converter in usage for the fast-charge of electric 11 vehicles, based on powerful high-voltage IGBT (Isolated Gate Bipolar Transistor) modules is 12 analyzed, designed and experimentally verified. The main advantages of this topology are: simple 13 structure on the converter’s power stage; a wide range of the output voltage, capable to support 14 nowadays vehicles on-board battery packs; efficiency and power density accepted to be high 15 enough for such class of hard-switched converters. A precise estimation of the loss, dissipated in 16 the converter’s basic modes of operation – Buck, Boost, and Buck-Boost is presented. The analysis 17 shows an approach of loss minimization, based on switching frequency reduction during the 18 Buck-Boost operation mode. Such a technique guarantees stable thermal characteristics during the 19 entire operation, i.e. battery charge cycle. As the Buck-Boost mode takes place when Buck and 20 Boost modes cannot support the output voltage, operating as a combination of them, it can be 21 considered as critically dependent on the characteristics of the semiconductors. With this, the 22 necessary duty cycle and voltage range, determined with respect to the input-output voltages and 23 power losses, require additional study to be conducted. Additionally, the tolerance of the applied 24 switching frequencies for the most versatile silicon-based powerful IGBT modules is analyzed and 25 experimentally verified. Finally, several important characteristics, such as transients during 26 switch-on and switch-off, IGBTs voltage tails, critical duty cycles, etc., are depicted experimentally 27 with oscillograms, obtained by an experimental model.


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The technology of fast charge is an inevitable part of a future transport system based on electric 32 vehicles, had been proven by numerous studies [1][2][3][4]. Fast can be considered a charge cycle of 20 min number of IGBT modules to be analyzed and experimentally verified. Such a solution has the structure, which this type of DC-DC converter usually had. Inherently, their power stages are based 51 on a small number of semiconductors. In this case, an application of the currently available powerful 52 silicon-based IGBTs would allow for only two modules to be used. 57 Figure 1 shows the power part of transformerless fast-chargers based on Buck topology which 58 is widely used today. Such charging stations are powered by a high-voltage distribution system 59 through a low-frequency power transformer in order for their impact over the low-voltage system to 60 be minimized. As a rectifier is usually used a controllable AC-DC converter with PFC (Power Factor proposed models have application in converter design, mode-of-operation analysis, lifespan estimation, analysis and design of the necessary cooling system, etc. implementation of Buck-Boost mode has the potential to decrease the losses and to increase the efficiency can be set at 97-98% for both semiconductors. In the currently available literature, the IGBT operation at Buck-Boost operation mode is not presented in details, considering the relatively low switching frequency (8kHz -16kHz), significant voltage tails for the silicon based 132 IGBTs, and the necessary time rages.

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 The voltage region of the Buck-Boost operation mode is of primary importance for achieving a 134 robust and efficient operation [35,36,37]. Several techniques are applicable mainly used for converters [35], reduction of the passive elements [36], high level of implementation of a digital 137 control system for low power portable electronics. It depends on the semiconductors' 138 parameters, or in this case, currents and voltage tails of the selected IGBT modules, the 139 maximum duty cycle at Buck and Boost modes, and switching frequency, etc. Its importance 140 requires it to be analyzed and verified experimentally.

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The paper is organized as follows: chapter two presents an analysis of the proposed converter,     Table 1 174 Appendix).  Table 1 177 Appendix).

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As Buck and Boost mode of operations have trivial descriptions [42,43], although fundamental 216 for this converter, their basic equations are given in Table 2 without further explanation.

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The Buck-Boost mode of operation can be derived from Buck and Boost modes, as in this mode,

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The total losses of an IGBT are given as a sum of two components -conduction and switching losses, given by the equation [

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The thermal resistance is given as: is the thermal resistance junction to case; is the thermal resistance case to heatsink; is the thermal resistance heatsink to ambient.

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The same data, as a functional dependence of the duty cycle (DC), is presented in figure 8.

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-the efficiency is slightly slower than the expected 98%, but in the range of the acceptable error.

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In this paper, a buck-boost transformer-less DC-DC converter based on high-voltage IGBT 425 modules for usage in battery charger has been proposed, analyzed and experimentally verified.

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The results explicitly showed that a Buck-Boost converter, based on IGBT modules is a possible