Silicon-Carbide (SiC) devices are receiving popularity for high-power converter systems in aircrafts due to many advantages over silicon counterparts. However, the electro-magnetic interference (EMI) problems are more serious with the SiC devices operating at higher switching speed and higher switching frequency. The common-mode (CM) EMI filter design of the high-power SiC converter is especially challenging for high-altitude application due to the harsher requirements of insulation and heat dissipation. The optimization of the CM EMI filter design in a 100-kW SiC generator-rectifier system operating at 50,000 ft is conducted in this paper to obtain the highest power density of the EMI filter and the rectifier system. A PCB-based planar CM choke is designed with the consideration of partial discharge (PD) and heat dissipation at the altitude of 50,000 ft. The structure of the CM choke is optimized with embedded electric-field shielding plates, which controls E-field stress in air below 300 V/mm by considering the Paschen’s effect. The large surface area of PCB windings improves the efficiency of heat dissipation at high altitudes and reduce the profile of the CM choke. A Pareto optimization is conducted to minimize the size of the choke and the volume of the final design is only 155 cm3. The experimental results show that the CM noise is reduced effectively with the CM EMI filter. PD is not observed even at the altitude of 50,000 ft and the thermal performance is excellent with a current of 190 A.

Planar Common-Mode EMI Filter Design and optimization in a 100-kW SiC-based Generator-Rectifier System for High-Altitude Operation

This letter reports characterization of the novel nanocrystalline flake ribbon (NFR) soft magnetic material. The comparative analysis among the ferrite N87, N27, and the NFR is presented at different temperature, frequency, and peak magnetic flux density, respectively. Experimental results prove that the NFR has lower loss density, higher magnetic flux density saturation, and better temperature stability from 85 to 300 kHz. A <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> resonant tank based circuit is employed for large signal characterization. The mass-based stacking factor of the NFR core is adopted to describe the core structure. This letter suggests that the NFR is a good alternative to the ferrite for high power magnetic cores due to its superior performance and flexibility structures. 

Characterization of Nanocrystalline Flake Ribbon for High Frequency Magnetic Cores

This letter reports characterization of the novel nanocrystalline flake ribbon (NFR) soft magnetic material. The comparative analysis among the ferrite N87, N27, and the NFR is presented at different temperature, frequency, and peak magnetic flux density, respectively. Experimental results prove that the NFR has lower loss density, higher magnetic flux density saturation, and better temperature stability from 85 to 300 kHz. A LCL resonant tank based circuit is employed for large signal characterization. The mass-based stacking factor of the NFR core is adopted to describe the core structure. This letter suggests that the NFR is a good alternative to the ferrite for high power magnetic cores due to its superior performance and flexibility structures.

The CLLC converter is widely used in the power electronic applications as a DC transformer, which can provide galvanic isolation, bidirectional power flow and an adjustable output voltage with the use of proper controls. As the most critical component in the CLLC converter, the high frequency (HF) transformer should be optimized according to the design targets, such as efficiency and power density. Starting with the analysis of the CLLC operating characteristics, this paper proposes a formal approach to design the HF transformer of a 100kW CLLC converter for a grid-tied application. The optimization method for the HF transformer is presented and the effect of the resonant inductor is analyzed. The optimized transformer is simulated with the finite element analysis (FEA) and Matlab/Simulink.

Design and Optimization of the High Frequency Transformer for 100kW CLLC Converter

Compared to the traditional aircraft, electrification of power system in aircraft has potential to revolutionise the aviation industry. Typically, more ‐ electric aircraft (MEA), even all ‐ electric aircraft has been developed and delivered to decrease the greenhouse gas emission and increase the energy efficiency. The next generation of MEA will operate at high voltage to facilitate the transfer of significant levels of electrical power in an electrified aircraft. However, the higher voltage inevitably leads to an increased risk to the insulation of the electrical components and power system. This study aims to provide a critical overview of the insulation challenges from the perspective of electrified aircraft, typically MEA application. The development of MEA and the special working conditions are explained at the beginning. Then the insulation challenges of power modules, electric machines, aeronautical cables etc. are discussed in detail. Finally, the existing technical barriers and future prospects of insulation for electrified aircraft are summarised. It provides a reference for the future design and test in power system of next generation MEA and related electrified air transportations.

A review on insulation challenges towards electrification of aircraft

The rapid development of more electric aircraft (MEA) raises the demand of high-power converters with significant weight and volume reduction for onboard power distribution. The isolated DC/DC converter using the medium-frequency transformer (MFT) is a feasible solution. To design an MFT with improved electromagnetic and thermal performance, a matrix core transformer (MCT) architecture is proposed with accurate models in this paper. With superior heat dissipation ability, the high current windings can be effectively cooled with both natural and forced air convection. In addition, an optimization methodology for MCT design is presented. As a result, the prototype of a 100 kW, 50 kHz MCT with an additive manufactured bobbin is built. The results of both finite element analysis (FEA) simulation and experimental study in a full power dual active bridge with the MCT prototype are presented to verify the theoretical design. The power density and efficiency of the MCT reach to 17.7 kW/L and 99.63%, respectively.

Design and Demonstration of a 100 kW High-Frequency Matrix Core Transformer for More Electric Aircraft Power Distribution

The trends toward higher power density and efficiency for the DC/DC converters has posed more strict requirements for inductors. The inductor current in turn affect the operating characteristics of the converters significantly and thus needs to be accurately estimated. In this paper, a new bisection-method-based inductor current estimation approach considering the variation of inductance is proposed. The proposed approach can be adapted and applied for various DC/DC converters, including the widely used buck and boost converters and etc. Comparing to the conventional estimation method using constant inductance, the proposed method can obtain more precise estimations of both the inductor current waveform and the power loss. Experimental results on a buck converter with a ferrite-core inductor are presented to validate the effectiveness of the proposed approach.

An Inductor Current Estimation Approach for DC/DC Converters Based on Bisection Method

In this work, the analytical models and optimization procedure for the design of high-power matrix core transformer (MCT) aiming at isolated DC/DC converter applications, especially for dual active bridge (DAB) converters, are proposed. The loss models, leakage inductance and thermal network models of MCT are presented, and a multi-variable, multi-objective optimization methodology of MCT is proposed. A 100 kW/50 kHz MCT design is selected and prototyped based on the optimization results. An additive manufactured bobbin design is also presented to control the leakage inductance and the path of the airflow. The electrical, magnetic, and thermal performance of the prototype are validated using by experimental studies.

A High-Power, High-Frequency Matrix Core Transformer Design for Medium Voltage Dual Active Bridge

This paper proposes a novel composite DC-DC converter, which consists of a current-fed dual-half-bridge (CF-DHB) module and a conventional boost converter module. With each module delivering partial power to the load, the operations of two converter modules can be optimized individually, which improves system efficiency and reduces the voltage stress across the power devices. Compared with the existing composite converter based on the dual-active-bridge (DAB), the proposed design has simplified topology and control with a less number of switches. Efficiency is much improved in low power range compared to the conventional boost converter. Experimental studies are performed to demonstrate the operation principle and validate the effectiveness of the proposed converter and its control.

A Composite DC-DC Converter using Current-Fed Dual-Half Bridge

Paralleling silicon carbide (SiC) MOSFETs is a practical way to increase the system current carrying capability, though this often leads to current sharing issues. In this paper, a simple close-loop current balancing method is proposed and demonstrated on a three-phase SiC inverter with two SiC modules paralleled in each phase. The paralleled modules are connected to the load through power cables, whose inductance can suppress the steady state current mismatch and simplifies current sensing process. With the sensed differential mode current information, the current sharing regulation is realized in a close-loop form by skewing the edges of the pulse-width module signal in every switching cycle. The proposed method can be easily applied to a three-phase inverter without complicated control algorithm and hardware modifications. Experimental tests results verify that even current sharing between paralleled modules can be achieved effectively by the proposed method.

Nan Lin

Papers

Design and Demonstration of a 100 kW High-Frequency Matrix Core Transformer for More Electric Aircraft Power Distribution

An Inductor Current Estimation Approach for DC/DC Converters Based on Bisection Method

A High-Power, High-Frequency Matrix Core Transformer Design for Medium Voltage Dual Active Bridge

A Composite DC-DC Converter using Current-Fed Dual-Half Bridge

A Close-loop Current Balancing Method for High Power Silicon Carbide Inverter with Paralleled Power Modules