A Three-Phase Synergetically Controlled Buck–Boost Current DC-Link EV Charger
Daifei Zhang, Jonas Huber, Johann W. Kolar
Abstract
With the ever-increasing share of electric vehicles (EVs) comes a need for highly efficient and compact EV chargers. EV charger modules should provide a wide-output-voltage range (200–1000 V) to ensure compatibility with various EV battery voltages. Thus, buck–boost functionality is needed, which can advantageously be realized by a current DC-link topology; a buck-type current-source rectifier (CSR)-stage and a downstream three-level boost-type DC/DC-stage share the main magnetic component (the DC-link inductor). Furthermore, the two stages can operate collaboratively; for low output voltages, the CSR-stage controls the output voltage and the DC/DC-stage is clamped to avoid switching losses; for high output voltages, the DC/DC-stage shapes the DC-link current such that the CSR-stage operates with 2/3-PWM (switching limited to two out of the three phases) and, hence, with reduced switching losses. This article, thus, introduces a simplified synergetic control concept that ensures this loss-optimum operation of the two-stage system for any output voltage. A compact 10-kW hardware demonstrator with a power density of 6.4 kW/dm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (107.5 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) is then used to verify the control concept and the seamless transitions between operating modes. For the first time, a system-level experimental demonstration of the loss savings achieved by 2/3-PWM is provided, and the precompliance conducted EMI test results meet CISPR 11 Class A. Moreover, a detailed experimental characterization of losses/efficiency over the full range of output voltage and power confirms the loss models and the design procedure presented earlier. Finally, the demonstrator shows quite a flat efficiency characteristic (higher than 98% for most operating points with output voltages above <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$400 \,\mathrm{V}$</tex-math></inline-formula> and more than 25% of rated load) with a peak efficiency of 98.8% at 520 V output voltage and 5 kW. All in all, the presented current DC-link buck–boost PFC rectifier system features a promising solution for future isolated or nonisolated EV charger modules.