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WIDE INPUT RANGE FULL-BRIDGE RESONANT CONVERTER

IP.com Disclosure Number: IPCOM000248447D
Publication Date: 2016-Nov-30
Document File: 7 page(s) / 409K

Publishing Venue

The IP.com Prior Art Database

Related People

Francisco Canales: AUTHOR [+3]

Abstract

LLC resonant converter is getting more popular because of its simple structure and soft switching characteristics for both switch and rectifier. Particularly, in high power high voltage application, the resonant converter concept becomes essential because of a large leakage inductance of the transformer caused by high insulation voltage requirement. However, as the input voltage range gets wider, the switching frequency, fsw, variation range also gets wider, which increases the passive component size. In order to relieve this drawback, this disclosure presents a wide input range LLC resonant converter based on full-bridge inverter. By suitably changing the switching pattern of the full-bridge inverter, the LLC resonant converter can operate over a wide input voltage range with a narrow fsw variation.

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WIDE INPUT RANGE FULL-BRIDGE RESONANT CONVERTER

The disclosure relates to a wide input range LLC resonant converter based on a full- bridge inverter.

1 Background

The resonant converter becomes more and more popular in high power applications such as power electronic transformer (PET), traction auxiliary power supply, DC fast car charger, etc, because of its simple structure and soft switching characteristics for both switch and diode. Particularly in the applications where high primary-secondary insulation voltage is required, a large leakage inductance of the transformer naturally lead to the resonant converter concept.

LC resonant converter

Among resonant converters, the LC resonant converter shown in Fig. 1(a) is one of the most popular basic topologies for its simple structure. In this configuration, the output voltage is controlled by the frequency modulation. In general, the resonant converter shows the best performance around the resonant frequency, fres, where the input-output gain is 1. Since the input-output gain is always equal or less than 1, as shown in Fig. 2(a), it does not make the LC resonant converter suitable for wide input voltage range applications. Moreover, as the load condition decreases, fsw should also be increased to maintain the input-output gain. This wide fsw variation is the main drawback of the LC resonant converter, which makes the magnetic component design and the filter design difficult.

Figure 1. An example of a resonant converter. (a) LC series resonant converter. (b) LLC resonant converter.

© Copyright [2016] ABB. All rights reserved.

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FI-1411001


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Figure 2. Examples of input-output gain characteristics of (a) LC series resonant converter and (b) LLC resonant converter.

LLC resonant converter

In order to overcome the abovementioned limitations of the LC resonant converter, the LLC resonant converter shown in Fig. 1(b) has been investigated and widely adopted in these days [1-3]. By inserting an additional inductor in parallel with the load, the LLC converter has a step-up capability when fsw is smaller than fres, as shown in Fig. 2(b). Owing to this gain characteristic, the LLC converter can be used for wider input voltage and load range applications than the LC resonant converter. Moreover, in the case of isolated converters, the leakage and magnetizing inductances of the transformer can be utilized as resonant inductor and parallel inductor, respectively.


2 Prior Art

Conventional approach for wide input range applications

If the input range gets even wider, however, it is very challenging for the conventional LLC resonant to maintain narrow fsw variation range while achieving both high efficiency and high power density. In order to operate LLC resonant converter very wide input range, the following approach have been developed:

© Copyright [2016] ABB. All rights reserved.



FI-1411001


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· Two-stage power converte...