A Bidirectional GaN-Based Flying Capacitor Multilevel Converter for Electric Vehicle Charging

Level II on-board chargers interface the high-voltage batteries of electric vehicles (EVs) with ac grids, providing the ability to charge from widespread residential and commercial ac distribution [1, 2]. Charging power levels range from 1 to 19 kW, and modern EVs typically support charging from both single- and three-phase supplies [1, 3]. Global single-phase services range from 120 to 240 V[[inf]]RMS[[/inf]] at 50 to 60 Hz [4, 5]. For higher charging powers, three-phase 120/208 V[[inf]]RMS[[/inf]]-Y and 240 V[[inf]]RMS[[/inf]]-Delta services are commonly available. Since the charger is carried within the vehicle and can be integrated into the vehicle battery enclosure for manufacturability and modularity, compact and lightweight charger designs are desirable. To reduce losses and consequent demand on cooling harnesses inside the vehicle, the charger must be efficient. Recent work has explored high-efficiency ac-to-dc converters for electric vehicles through innovations in converter topology, control, and packaging. Surveys of the field [6] have indicated a steady increase in EV on-board charger research and development as EV market share continues to increase year-over-year [3, 7]. State-of-the-art work from industry has showcased optimized on-board chargers based on industry-standard power converter topologies such as the LLC resonant converter. The work in [8] achieves 96.5% peak efficiency with a peak power of 6.6 kW corresponding to a 3.8 kW/L power density. The work in [9] achieves a 97.2% peak efficiency with a peak power of 11 kW. Academic investigation of alternative converter topologies and highly optimized designs [10, 11, 12–13] has demonstrated efficiencies greater than 99% and power densities exceeding 7 kW/L [6]. This chapter highlights the work of [14, 15–16], which studies a single-phase bidirectional on-board charger based on the flying capacitor multilevel converter topology achieving a peak efficiency of 99.01% and a peak power of 6.6 kW corresponding to a peak power density of 12.3 kW/L.