In this paper, an Enhancement-mode GaN HEMT based 7.2kW single-phase charger was firstly built. Connecting three such single-phase modules to the three-phase grid respectively generates a three-phase ~22kW charger with the >97% efficiency and >3.3kW/L power density, superior to present Si devices based chargers. In addition to GaN HEMTs with fast switching transitions thereby a high efficiency, the proposed charger employs the DC/DC stage to take care of the power factor correction and power delivery simultaneously, yielding little DC-bus capacitance thereby a high power density. To secure the soft switching for all switches within all voltage and power ranges, a variable switching frequency control with dual phase shifts is adopted at the high power, and a triple phase shift is employed to improve the power factor at the low power. Both of which accommodate the wide input range (80VAC~260VAC) and output range (200V~450VDC). A closed-loop control for the three-phase charger is realized to minimize the output current ripple and balance the power among three single-phase modules. Experimental results validated such design.

An AC/DC + Dual-active-bridge (DAB) circuit was found as one solution for the high-efficiency and high-power-density electric vehicle charger. One control option is to let the AC/DC part only convert the grid voltage to a double-line-frequency folded sine wave and let the DAB stage handle both the power factor and power delivery. While conventional single-phase-shift (SPS) tends to lose zero voltage switching (ZVS) at light load and the variable-switching-frequency dual-phase-shift (DPS) sacrifices the light-load performance, this paper proposes a multiple-phase-shift (MPS) control, which allows for a fixed-switching-frequency triple-phase-shift (TPS) control at the light load to enhance the grid power quality. At medium- and heavy-load conditions, a phase-shift jump from TPS to DPS is performed to reduce the circulating current and improve efficiency. The proposed control strategy secures ZVS, realizes unity PF accurately and minimizes the control complexity. Experimental results on a SiC-based 7.2 kW charger validated its effectiveness and the smooth transition between the heavy load and light load.

An ac/dc + dual-active-bridge (DAB) circuit was found as one solution for the high-efficiency and high-power-density electric vehicle charger. One control option is to let ac/dc part only convert the grid voltage to a double-line-frequency folded sine wave, yielding near-zero switching loss of the ac/dc part and leaving the DAB stage to control both power factor and power delivery. Such a zero-to-peak input voltage and wide-range output voltage can obstruct the zero-voltage switching (ZVS) for the DAB stage, which is a must for high-efficiency applications even with SiC devices. While the conventional single-phase shift loses ZVS at light load, and the variable-switching-frequency dual phase shift (DPS) creates the grid-current distortion at the light load, this paper employs multiple-phase-shifts (MPS) control, which essentially is a fixed-switching-frequency triple-phase-shift (TPS) control at light-load conditions and jumping to DPS at medium- and heavy-load conditions. While the TPS control will sacrifice the system efficiency by introducing the circulating current, a multiobjective optimization is employed to optimize the current stress and efficiency simultaneously, using the database of the double-pulse-test result. Experimental results on a SiC-based charger validated the effectiveness of the proposed control algorithm, that is: 1) high efficiency(>97%) at heavy load (7.2 kW); 2) smooth sinusoidal current without bumps at zero-crossing points from the whole-load range; and 3) the smooth transition between the heavy load and light load.

As part of the recent electrification of the transportation industry, internal combustion engines are being coupled with or replaced by electric motors. This movement towards an electrified drivetrain poses new noise, vibration, and harshness (NVH) challenges related to electric motors. In this paper, the acoustic signature of an electric motor was analyzed to obtain a better understanding of the sound generated by these motors. This work provides an insight into an acoustic measurement technique that can be used to identify certain frequency bands that significantly contribute to the perceived sound. In the first part, the structural response of the motor was correlated with its acoustic spectra. Furthermore, data from acoustic and structural measurements were used to analyze the order content of the signal and identify critical contributors to the overall perceived sound. The differences between data captured by microphones in different positions around the motor helped to localize components of the overall sound. The results provide some discussion about techniques to decrease the overall sound. The technique described in this paper can be extended to fan-cooled motors that are used in vehicles such as golf carts or as auxiliary motors in electric/hybrid vehicles, as well as across a wide range of industrial applications.