Design Methodology and Analysis of Five-Level LLC Resonant Converter for Battery Chargers

Abstract

This paper presents proposal of a five-level LLC resonant DC–DC converter design procedure for battery chargers. The five-level inverter side of the proposed converter is connected to a transform-less LLC resonant tank to ensure operating at high frequency and achieve soft switching. The proposed converter has less weight, size, and cost. It is also much simpler in terms of implementation, and has smooth energy conversion to the load. The proposed converter is designed to work within the range close to the resonant frequency, to ensure higher power density and efficiency. Thus, the range of operating frequency is set to be (91 kHz < fsw < 110 kHz), while the LLC parameters is designed to achieve resonant frequency fr = 100 kHz. Therefore, it is designed to achieve zero voltage switching (ZVS) for all switches, which enhances the efficiency as well. The theoretical analysis outcomes were confirmed by simulation studies conducted using MATLAB/SIMULINK. An experimental model was also developed and validated with 100 VDC input voltage, which delivered output power of 100 W, 48 V, with efficiency around 96.9%. Selected findings are presented to confirm the effectiveness of the suggested converter.

Modelling a five‐level LLC resonant converter for bidirectional battery application

“…Despite the possibility of reducing the stress of voltage on the switches in the 5L-NPC to half that of the converter's input voltage, the NPC requires a greater number of diodes at higher levels, potentially rendering the system infeasible. Some scholars have evaluated the possibility of combining MLIs and LLC resonant converters [47][48][49][50][51][52] ; for example, a modular design for a multiphase, multilevel LLC RC that can attain ZCS for the rectifier diodes and ZVS for the primary switches under different operating conditions has been proposed. 48 Additionally, the voltage stress is reduced by this design to a tenth of the value of the input voltage.…”

“…Some scholars have evaluated the possibility of combining MLIs and LLC resonant converters 47–52 ; for example, a modular design for a multiphase, multilevel LLC RC that can attain ZCS for the rectifier diodes and ZVS for the primary switches under different operating conditions has been proposed 48 . Additionally, the voltage stress is reduced by this design to a tenth of the value of the input voltage.…”

“…Notably, not much is understood with respect to the effect of the switching frequency on the performance of modular multilevel resonant converters, requiring more investigation. A five‐level LLC RC was specifically proposed by Alatai et al 51 for usage in battery charging devices. However, the behavior and performance of an LLC circuit that comprises a five‐level inverter is yet to be evaluated or compared with the performance of a full‐bridge LLC RC under varying input voltage and conditions of load.…”

Design Considerations and Performance Investigation of a Five-Level Cascaded Multilevel LLC Boost DC–DC Converter

“…MLIs are employed on the input side of the converter to further reduce the voltage stress between the switching devices and improve the power range of LLC RCs, making them an appealing alternative for high power and high voltage applications [41]. The pairing of MLIs and LLC RCs has been discussed in some studies [42], [43], [44], [45], [46]. For instance, the study by [43] presented a ''multiphase multi-level LLC RC with a modular design that can achieve ZVS and ZCS for the primary switches and rectifier diodes respectively, under a wide range of load and input voltage; the system can also minimize voltage stress to onenth of the'' input voltage.…”

“…The impact of switching frequency on MMRC, however, has not been thoroughly examined in the investigations so far. In [46], a 5-level LLC resonant DC-DC converter was developed for use in battery charging systems. However, the available studies have not exhaustively explored and tested the performance and behaviour of the LLC circuit with a five-level inverter under varied input voltage and load conditions or compared its behaviour to that of the full-bridge LLC converter.…”