Abstract

Rapid developments in energy storage and conversion technologies have led to the proliferation of low- and medium-power electric vehicles. Their regular operation typically requires an on-board battery charger that features small dimensions, high efficiency and power quality. This paper analyses an interleaved step-down single-ended primary-inductor converter (SEPIC) operating in the discontinuous conduction mode (DCM) for charging of battery-powered light electric vehicles such as an electric wheelchair. The required characteristics are achieved thanks to favourable arrangement of the inductors in the circuit: the input inductor is used for power factor correction (PFC) without additional elements, while the other inductor is used to provide galvanic isolation and required voltage conversion ratio. A modular interleaved structure of the converter helps to implement low-profile converter design with standard components, distribute the power losses and improve the performance. An optimal number of converter cells was estimated. The converter uses a simple control algorithm for constant current and constant voltage charging modes. To reduce the energy losses, synchronous rectification along with a common regenerative snubber circuit was implemented. The proposed charger concept was verified with a developed 230 VAC to 29.4 VDC experimental prototype that has proved its effectiveness.

Highlights

  • Developments in electronic systems together with improvements in battery technology enable spread of light electric vehicles (LEVs) in a wide range of applications: from electric bicycles, scooters and autonomous package carriers to utility vehicles and electric wheelchairs for disabled or elderly people [1,2,3,4,5]

  • The chargers generally include two-stage ac-dc converters with a power factor pre-regulator (PFP) that is followed by a dc-dc converter [11,12,13]

  • Different solutions based on a variety of single-stage systems without DC-link have been proposed: resonant LLC topology [17,18], boost full bridge converter [19], flyback [20,21], single-ended primary-inductor converter (SEPIC) [22], quasi-resonant bridgeless converter [23], matrix converter [24], and dual active bridge [25]

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Summary

Introduction

Developments in electronic systems together with improvements in battery technology enable spread of light electric vehicles (LEVs) in a wide range of applications: from electric bicycles, scooters and autonomous package carriers to utility vehicles and electric wheelchairs for disabled or elderly people [1,2,3,4,5] Such applications typically employ a low-voltage battery (24–48 V nominal) and are charged from the AC grid with power up to 1 kW [6,7,8,9,10]. The charger with low profile can be realised with standard components in accordance with the design specifications Such configuration can bring benefits in other applications due to the possibility of charging several devices simultaneously.

Analysis of the Modular SEPIC for PFC Application
SEPIC Cell Model
Estimation of the Number of SEPIC Cells Based on Current Quality Parameters
Charger Configuration
Constant Current and Constant Voltage Charging Modes
Boundary Conduction Mode Control
Calculation of Average Power Factor of the Battery Charger
Flyback Regenerative Snubber
Converter Design and Layout
Experimental Results
Verification of Operation in BCM
Verification of Regenerative Flyback Snubber
General Switching Waveforms
Discussion and Conclusions

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