Overview of the requirements and implementations of bidirectional isolated AC-DC converters for automotive battery charging applications

Abstract

This paper is divided into three main parts. In the first part, i.e. Section II, a general outline of the system level aspects regarding battery chargers (power converters) for plug-in electric vehicles (PEVs) is given. Thereby, the different charging modes of the converters, the corresponding power levels, and the infrastructural facilities are discussed. Moreover, Vehicle-to-Grid (V2G) operation by means of grid-forming, grid-feeding, and gridsupporting converter functionality is briefly explained, and the input power quality and electromagnetic compatibility requirements are summarized. In the second part, i.e. Section III, the mutually coupled indices that determine the overall performance of the system, such as power losses (efficiency), volume (power density), weight (specific power), failure rate (reliability), and costs (relative cost), are outlined. In this context, the role that wide band-gap power semiconductors (e.g. SiC, GaN) can play in order to further improve the system performance is highlighted. In the third part, i.e. Section IV, a concise overview of the possible topological implementations for the mentioned power converters is provided. The focus is on conductive, isolated AC-DC converter topologies with high AC input power quality in terms of power factor correction (PFC) and harmonic distortion, and with bidirectional power flow capability in order to facilitate V2G operation.

Comparison of SiC-based DC-DC modular converters for EV fast DC chargers

“…increasing the switching frequency results in increasing the switching losses. However, designers tend to use high frequency to reduce the size of the passive components [12], [13]. Hence, soft-switching techniques are normally employed aiming to reduce the switching losses with high switching frequency operation.…”

“…Auxiliary losses defined as the total losses of the power supply of the cooling system, the digital control, and the power semiconductor drivers. A lower weight, volume and cost are achieved by reducing the cooling requirements and the number of semiconductor devices [13], [15].…”

“…Multiple advantages result from a low converter volume and weight such as simple handling, installation and maintenance of the converter [15]. Lower weight and consequently lower cost converter can be achieved by increasing the switching frequency which results in reducing the size of passive components [13].…”

“…However, this results in higher weight and cost of the system. Hence, a trade-off analysis is required [13].…”

“…The lower the number of components the lower is the system cost. A qualitative measure to determine the overall system cost can be expressed by the 'relative cost' as follows [13]:…”