C. F. Tong

Design of high power density converter for aircraft applications

This paper presents a design methodology for high power density converter (HPDC) operating as an AC aircraft bus provider, which presents a particular gravimetric power density challenge. High power rating 3-phase AC-DC converter design with weight minimization is elaborated. By considering sizing of major converter parts that contribute to total converter weight, optimal switching frequency to yield highest power density is evaluated. The design evaluation for 50 kW converter with SiC power modules yields overall gravimetric power density of 3.76-5.35 kW/kg at optimal switching frequency of 60 kHz and volumetric power density of 7.04-7.38 kW/l respectively.

A novel gate assisted circuit to reduce switching loss and eliminate shoot-through in SiC half bridge configuration

The trend towards SiC-based high power density converter requires to drive SiC MOSFET with high-speed switching. However, it tends to aggravate dv/dt effect due to the impact of parasitic parameters, resulting in shoot-through and high device stress in the half bridge configuration. In this work, a novel gate assisted circuit is proposed to eliminate shoot-through issue without compromise on switching speed. The mathematical model for the gate assisted circuit is developed. Then the switching test experiment is set up to validate its performance with commercial SiC half bridge module, which shows a high dv/dt up to 20 and 31 V/ns at turn-on and turn-off respectively and a 34% reduction of switching loss without any shoot-through issue.

Gate driver optimization to mitigate shoot-through in high-speed switching SiC half bridge module

The high-speed switching of SiC MOSFET allows power converter to operate with higher frequency and lower switching loss. However, it tends to aggravate dv/dt effect due to the impact of parasitic parameters, resulting in shoot-through and high device stress in the half bridge configuration. In this study, a compact and high-speed gate driver is developed and optimized for SiC half bridge module. The impact of various circuit parameters including Miller capacitance, common source inductance, gate resistance and gate inductance is evaluated. The improved gate drivers with additional features are compared and optimized to eliminate shoot-through.

LCL Filter Design of a 50-kW 60-kHz SiC Inverter with Size and Thermal Considerations for Aerospace Applications

To achieve high power density, increasing the switching frequency of the power converter has become a trend. The LCL filter is a major contributor of the overall weight of a high-power-density converter (HPDC), especially the inverter-side inductor, which requires to suppress higher frequency harmonic contents at the inverter side. This paper describes a comprehensive design flow of the LCL filter for a 50-kW, 60-kHz two-level silicon carbide (SiC) inverter for high-power aerospace applications with space constraint and harsh ambient temperature environment. To meet the space constraint requirement and reduce the inductor size, specific design attention is made on a customized amorphous cored inductor with a comprehensive study on the relationships of inductor weight, core width, and total surface area with respect to air gap length. To overcome the harsh ambient temperature environment, a liquid cooling system of the amorphous cored inductor is also described.

A 99% efficiency SiC three-phase inverter using synchronous rectification

The reactive power in power converter with inductive load (motor drive e.g.) requires a current commutation path for the freewheeling current. Due to the high voltage drop of body diode of SiC MOSFET, a SiC Schottky diode is normally recommended as the anti-parallel freewheeling diode for SiC MOSFET to suppress the conduction of body diode. However, since the MOSFET can work as synchronous rectifier, the freewheeling diode only conducts during the dead time, leading to a low utilization rate of device. In this work, the three-phase SiC inverter using synchronous rectification is investigated. The analytical model for inverter power loss with and without freewheeling diode is built. Based on the switching characterization, the inverter with synchronous rectification permits a surprising higher efficiency than that with freewheeling diode due to the reduced current overshoot at turn-on. And a 5 kW prototype of three-phase inverter is developed, which shows a 99% high efficiency at the switching frequency of 40 kHz. This work confirms the possibility to remove the freewheeling diode in SiC inverter without degrading the efficiency.

Evaluation on filter topologies in high power density converter design for power quality and EMI control

This paper evaluates different passive filter topologies of the grid-connected high power density converter (HPDC) for the purpose power quality control and electromagnetic interference (EMI) reduction. The harmonics generated by the switching circuits in the HPDC affect power quality at lower frequency as well as EMI at higher frequency. Various common passive filter topologies are carefully evaluated in terms of reduction of total harmonic distortion (THD) and EMI.

Heatsink design for high power density converter in aircraft applications: Parameter sensitivity analysis

Cooling systems significantly contribute to the total mass and/or volume of power electronic systems especially for aerospace application where it will directly increase the operating cost of the aircraft. This paper investigates the heat sink parameters that contribute to the thermal resistance as well to weight of the high power density converter. The lowest heat sink thermal resistance for any type of coolant can be achieved by choosing a greater number of flow channels and thicker fin thickness. To minimize the weight, lower number of channels and thinner fins are desirable. The design case of 50kW power converter with 1.16% power loss using the most promising coolant in aircraft application is investigated and presented. Manufacturing constrains of the heat sink have also been taken into account.

Challenges in switching waveforms measurement for a high-speed switching module

As SiC MOSFET is moving towards high current rating through parallel devices in a module, the ability to switch it fast with minimum switching loss becomes a new challenge. Amid this new challenge, power converter designers need to deal with more demanding measurement method to obtain correct switching waveforms. Switching waveforms are an important asset for converter designers because they can reveal vital parasitic information, indicate any potential overshoot or undershoot and estimate the switching loss. This paper shares the experimental work results, its measurement techniques (current and voltage) and test setup use to obtain minimum voltage overshoot of a 5 parallel SiC devices module. The cable length (of voltage probe) is shown to directly affect the switching loss estimation especially when a fast 5Ω gate driver resistance is used.

FEM modelling of three-phase common mode choke for performance evaluation

This paper presents the extraction of common mode (CM) and differential mode (DM) inductances of a common mode choke (CMC) using 3D finite element method (FEM). For optimal performance of the CMC, the effects of CM and DM currents on the magnetic core saturation are investigated. As the parasitic capacitance of a CMC is a critical parameter that affects its high frequency performance, the parasitic capacitances of the turn-to-turn and the turn-to-core capacitances of different winding layouts are also extracted for comparison. Finally, different core structures are modeled and simulated for performance evaluation.

Analysis and design of coupled inductor and output harmonic filter for interleaved three phase VSCs

This paper presents the benefits of interleaving three phase voltage source converters (VSCs) to improve the power density. The output harmonics are also analyzed in frequency domain, then design and optimization of coupled inductor and output filter are given. Verifications are carried out through electrical circiut and electromagnetics FEM simualtions. Finally, the inductor weight are compared with and without interleaving.