LLC Resonant Converter for Fast Electric Vehicle Charging Module With a Reconfigurable Bi-Directional Switch

This article presents a new reconfigurable LLC converter in fast electric vehicle (EV) charger applications. By using a reconfigurable bi-directional switch, the proposed converter restructures the secondary side windings of the transformers of two LLC converters in series or parallel, providing an adjustable effective turns ratio. The most powerful advantage of the proposed converter is the simple structure for reconfiguration. Also, the proposed converter does not contain capacitors in series with the resonant current path, which is appropriate for a large charging current in a fast EV charger. Furthermore, the proposed converter maintains identical switching frequency range for both 400 and 800 V batteries, due to the same quality factors in both cases. To verify the effectiveness of the proposed converter as a fast EV charger module, a prototype converter with a 150–1000 V and 25 kW/62.5 A output was constructed.

I. Introduction

Due to the growing severity of climate change, the significance of electric vehicles (EVs) and their charging infrastructure is rapidly increasing. Modern EV batteries can be either 400 or 800 V, depending on the manufacturer. The 400 V batteries have a voltage range of 150–500 V, while 800 V batteries have a range of 300–1000 V. In order to accommodate both 400 and 800 V batteries, the dc/dc converter in universal EV chargers must cover an extremely wide output voltage range, such as 150–1000 V. Furthermore, high charging power is becoming a trend in EV chargers to minimize charging time. Achieving a broad output voltage range with high power capability is a significant challenge in today’s EV charging applications. Fig. 1 represents a typical structure of a fast EV charger with paralleled power modules. Fast chargers with power racks contain multiple ac/dc power modules in parallel. This structure enables easier maintenance due to easy module-level replacement in the case of malfunction. To support larger than 200 kW charging power, each module nowadays supports larger than 25 kW. A power module contains ac/dc power factor correction (PFC) and dc/dc stages. ac/dc PFC converts three-phase ac input voltage to dc link voltage with high-quality input current. The dc link voltage is usually variable in the 700–800 V range, to partially cover the wide output voltage range. The dc/dc converter provides 150–1000 V output voltage from the dc link voltage. Fig. 1.

Fast EV charger with power rack and modules.