Juncheng Lu

Design consideration of gate driver circuits and PCB parasitic parameters of paralleled E-mode GaN HEMTs in zero-voltage-switching applications

This paper designed the gate driver circuits and optimized the PCB layout in a 7.2kW battery charger using paralleled GaN HEMTs. 650V/60A enhancement mode GaN HEMTs provided by GaN Systems Inc are adopted. To optimize the switching performance of paralleled GaN HEMTs with low loss and high reliability, effects of parasitic inductance and capacitance are modeled and analyzed. Through cancelling the flux in the commutation loop, the power-loop parasitic inductance is reduced to only 0.7nH, which significantly decreases the electrical stress in the switch turn-off process. A diverse-parameter gate driver design has been proposed to achieve the reliable switching off. The Finite-Element-Analysis and Spice simulation show our current design could effectively suppress the voltage overshoot and gate-drive ringing on HEMTs. Experiments were carried out on both double pulse test platform and the 7.2kW charger to verify the proposed design strategy.

A novel energy balanced variable frequency control for input-series-output-parallel modular EV fast charging stations

At present time, the most common electrical vehicle (EV) chargers employ a two-stage design, i.e., a front-end AC/DC stage + an isolated DC/DC converter. In this paper, an isolated dual-active-bridge (DAB) based single-stage AC/DC converter was proposed, which has the power-factor-correction (PFC) and zero-voltage-switching (ZVS) functions over the full-load range. By reducing one power stage and eliminating the large DC link capacitor, a high efficiency and high power density are achieved. Such topology can be used as a modular building block to scale up to 50kW by serial connecting the input terminals and paralleling output terminals. A novel energy-balanced variable switching frequency control for such input-series-output-parallel (ISPO) modular designed is proposed. A single-phase d-q transformation is implemented to achieve zero steady-state error. Simulation analysis and experimental validation are presented.

A novel light load performance enhanced variable-switching-frequency and hybrid single-dual-phase-shift control for single-stage dual-active-bridge based AC/DC converter

Full-bridge power-factor-correction (PFC) front-end + dual-active-bridge (DAB) AC/DC topology is widely used in industry, e.g., electrical vehicle on-board charger. Such two-stage topology limits the system efficiency, and the bulky DC link bus capacitor makes the system power density relatively low. Compared to the two-stage design, the single-stage design, unfolding bridge + DAB, eliminates the bulky DC link bus capacitor and operates the front-end with only 60Hz switching frequency, thereby has the potential to increase the system power density and efficiency. A novel variable-switching-frequency and hybrid single-dual-phase-shift (VSF-SDPS) control strategy is proposed and analyzed for the DAB based single-stage topology. The proposed VSF-SDPF control consists of two phase shifts to guarantee Zero-Voltage-Switching (ZVS) over the full range of the AC line voltage, and frequency modulation to achieve boost PFC. The conventional front-end PFC is simplified to an unfolding bridge by changing DAB control strategy to achieve PFC and ZVS at the same time. Besides, a special ZVS boundary is utilized to solve the grid current distortion problem when the switching frequency saturated, which is especially severe at light load condition. Simulation results and experimental validation are presented under 50Vrms AC line voltage and 200V DC battery voltage test condition.

A model-based buck-type active filter using proportional-resonant controller and GaN HEMTs

To filter the 120Hz output current ripple in our previously designed 7.2kW single-phase EV charger, this paper proposes to equip the charger with a buck-type active filter. 650V/60A enhancement mode GaN HEMTs provided by GaN Systems Inc are adopted to work at hard-switching mode. Experimental results indicated that four such switches could be paralleled to hard switch on/off ∼240A, which is the key for the buck-type active filter. A model-based proportional-resonant controller is adopted to smooth the output current. Such control will enhance the dynamic response of the active filter, compared to the conventional PI controller. The experimental output current ripple and power loss analysis are given.