Compact Integrated Transformer – Grid Inductor Structure for E-Capless Single-Stage EV Charger

This article proposes a planar magnetic integration technique that combines the grid inductors and transformer in the single-stage E-capless electric vehicle charger into one core. The proposed integration technique reduces the number of magnetic components; therefore, the cost, total magnetic core loss, and volume can be significantly reduced. Using the integrated structure, the overall converter power density increases up to 11.1% compared to the nonintegrated one. This article also presents a detailed analysis of the optimal printed circuit board (PCB) winding arrangement considering both ac resistance and winding stray capacitance. Due to the high dc resistance of PCB winding, Litz wire was also considered for the proposed integrated structure. The effectiveness of the proposed structure was validated by implementing it on a 3.7-kW prototype of a single-stage ac–dc converter. Results show that the prototype with the proposed integrated structure achieved higher efficiency with both PCB winding and Litz wire. Peak efficiency of 97.17% and 6.55-kW/L power density were achieved.

I. Introduction

The growing awareness of climate change and global warming has shifted automotive industries and manufacturers from internal combustion engines (ICE) to electric vehicles (EV). Despite being environmentally friendly, and a cheaper solution compared to ICE, the long charging time and range anxiety of EVs remain the major obstacles that slow down their mass adoption [1]. To ensure a short charging time for a large battery capacity, EV chargers are required to handle larger power. Another critical issue in the mass adoption of EVs is the availability of charging infrastructures. One of the solutions to this issue is the installation of an onboard charger (OBC). OBC enables EV users to charge to any utility source without having to rely on the availability of off-board charging stations [2]. However, power density becomes a crucial aspect as OBCs must be installed in a tight space under the hood of the vehicle [3], [4]. The U.S. Department of Energy (DoE) has set a specific target for OBC in terms of power density and reliability for the year 2025 which are 4.6 kW/L and 300 000 miles, respectively [5]. Many approaches to achieving high power density OBC have been proposed, such as increasing the switching frequency and using wide bandgap (WBG) devices [6], [7], introducing the single-stage approach [8], [9], [10], implementing system-level integration such as the integration between OBC and low voltage DC-DC converter (LDC) [11], [12], and applying magnetic integration techniques. [13], [14], [15]. With the two-stage structure [6], the power density improvement is limited even with comparably high switching frequency due to the use of bulky E-cap at the dc-link which occupies more than 30% of the footprint. Moreover, without a proper cooling method, electrolytic capacitors may have a shorter lifetime, resulting in lower system reliability [16].