Along with the main trends and future challenges of electrical networks embedded in more-electrical aircraft, this article also focuses on optimization efforts in the field of industrial electronics and energy conversion. Optimization can be achieved by the means of expertise or from classical analysis methods, especially those based on simulations. However, novel approaches based on optimization algorithms, so-called integrated design by optimization, are becoming increasingly mature and will become particularly powerful if subsequent efforts are made in terms of modeling for design. In the first part, the current context and new standards of the more-electrical aircraft are summarized. The second part deals with the new trends and challenges of more electrical aircraft, with an emphasis on reversible and hybrid high-voltage dc networks including new storage devices. However, this discussion will mainly focus on systems optimization. Methodological orientations toward integrated optimal design are discussed with representative examples, such as for an environmental conditioning system (ECS).

More Electricity in the Air: Toward Optimized Electrical Networks Embedded in More-Electrical Aircraft

High voltage gain dc-dc converters are required in many industrial applications such as photovoltaic and fuel cell energy systems, high-intensity discharge lamp (HID), dc back-up energy systems, and electric vehicles. This paper presents a novel input-parallel output-series boost converter with dual coupled inductors and a voltage multiplier module. On the one hand, the primary windings of two coupled inductors are connected in parallel to share the input current and reduce the current ripple at the input. On the other hand, the proposed converter inherits the merits of interleaved series-connected output capacitors for high voltage gain, low output voltage ripple, and low switch voltage stress. Moreover, the secondary sides of two coupled inductors are connected in series to a regenerative capacitor by a diode for extending the voltage gain and balancing the primary-parallel currents. In addition, the active switches are turned on at zero current and the reverse recovery problem of diodes is alleviated by reasonable leakage inductances of the coupled inductors. Besides, the energy of leakage inductances can be recycled. A prototype circuit rated 500-W output power is implemented in the laboratory, and the experimental results shows satisfactory agreement with the theoretical analysis.

A High Gain Input-Parallel Output-Series DC/DC Converter With Dual Coupled Inductors

Voltage balancing between series-connected cells of rechargeable lithium-ion batteries is important for battery life, autonomy, and safety. Active balancing is the designated choice for applications that are sensitive to energy losses and maximized autonomy. First, a well-known next-to-next balancing technique is presented and its design and operating limitations are analyzed. Then, the paper focuses on an evolution of the converter's architecture offering better performances while being more compact, requiring fewer and smaller filtering needs and still, being simple to implement. The experimental results of the balancing operation of a pack of eight cells connected in series show demonstrative and satisfactory results.

An Optimized Topology for Next-to-Next Balancing of Series-Connected Lithium-ion Cells

Pulsewidth modulation (PWM) strategies and methods for multilevel converters are usually developed for series converters. One of the aims of this paper is to show that they may be applied to parallel converters using interleaving techniques, given that these converters also have multilevel characteristics. PWM methods based on carriers' disposition and on zero sequence injection are studied for parallel multilevel inverters. Analysis show that the best method in terms of load current ripple (phase disposition (PD) centered space vector PWM) has, nevertheless, a bad influence on the current balancing between commutation cells of the same phase. Another objective is to analyze these problems and to propose a solution to cancel current imbalance when using PD strategy. Experimental results validate the analysis presented in this paper as well as the compensation of band transition of the differential mode current observed when PD strategy is used.

PD Modulation Scheme for Three-Phase Parallel Multilevel Inverters

This paper describes the main trends and future challenges of electrical networks embedded in “more electrical aircraft” especially in the fields of industrial electronics and energy conversion. In the first part, the current context and new standards are put forward, emphasizing the main evolutions on aircraft architectures, from AC fixed frequency networks, variable frequency to “Bleedless” architectures. The main characteristics of more electrical aircraft are discussed, especially in terms of power management rationalization, maintenance, health monitoring capacity, etc. The second part deals with the new trends and challenges of “more and more” electrical aircraft linked with power integration and new architecture with HVDC standard. Recent methodological orientations towards “Integrated Optimal Design” are discussed with representative examples. Finally, new trends towards reversible and hybrid HVDC networks including new storage devices are also emphasized.

New trends and challenges of electrical networks embedded in “more electrical aircraft”

An original converter composed of interleaved flyback is presented. The cells are interconnected through intercell transformers replacing the standard multi-winding inductors used as insulation and storage magnetic device in the flyback. The combination of the interleaving effects and of the intercell transformer characteristics allows eliminating the mains limitations of the standard flyback due to the low performances of multiwindings inductors. In a first part, the different ways to interleave galvanic insulated converters as forward or flyback are briefly recalled. The second part presents the intercell transformers and shows that they can be used to interconnect interleaved converters cells. In the third and last part, this particular magnetic interconnection is applied to interleaved flyback cells and leads to create an ldquointercell transformer flybackrdquo. Its specific properties and advantages are described. Experimental results, obtained on a 2-kW test bench are finally presented.

Multicell Interleaved Flyback Using Intercell Transformers

A low-input voltage high-power realization is presented with the aim to demonstrate the feasibility and the interest of topologies using intercell transformer. They constitute a promising option to interleave converter stages, and therefore, can answer to the specifications considered in this paper. These specifications require a galvanic insulation and the chosen topology is the Intercell Transformer (ICT) flyback converter, previously proposed by the authors. In a first part, the operating principle of the ICT flyback converter is recalled. The second part presents briefly the main features of the intercell transformer design, more precisely described in a previous paper. This part includes a discussion about the choice of the cell number. The last part presents the design and the implementation of the complete flyback converter using eight cells. A preliminary work concerns the choice, the design, and the test of each cell elements, mainly the transformer and the primary switching stage. In the end, the experimental results are presented and discussed. They demonstrate the potential of this original topology that needs only one level of magnetic components. Considering the suitability of the converter interleaving for the high-power-low-voltage applications, the ICT flyback converter constitutes a good candidate in that field.

Design of a 28 V-to-300 V/12 kW Multicell Interleaved Flyback Converter Using Intercell Transformers

Recent uninterruptible power supply (UPS) systems, in the medium power range (a few 100 kW), are based on a three-power stage topology including a rectifier, an inverter, and a dc-dc converter. The dc-dc converter ensures the charger/discharger function necessary for battery management. The monolithic intercell transformer (ICT) described in this paper is dedicated to such a charger/discharger, of which the nominal power is 137 kW. This dc-dc converter is comprised of eight interleaved cells that are interconnected by the ICT. The first part of this paper briefly presents the full UPS system and the topology of the eight-cell charger/discharger arranged around the eight-phase monolithic ICT. The second part suggests a model and emphasizes the design specificities of the monolithic ICT. The final design is provided by an optimization routine, checked in the end by different 2-D and 3-D finite-element simulations, both electromagnetic and thermal. The third part describes the construction of the ICT prototype. It is then placed in a test bench that reproduces the conditions of future operations and provides current balance conditions. Finally, the experimental results obtained for the 137-kW nominal power validate design parameters and confirm the interest of the ICT solution.

Design and Characterization of an Eight-Phase-137-kW Intercell Transformer Dedicated to Multicell DC–DC Stages in a Modular UPS

This paper presents the developments and the results of an analytic method elaborated to design isolated intercell transformers. These particular magnetic components are intended for multicell interleaved flyback converters recently proposed and well-suited to low-voltage, high-power applications. A specific 2-D model to evaluate the winding losses is included in the design process. The results, obtained for standard core shapes, allow defining the ranges of the main parameters, number of cells, and switching frequency, required for future realizations.

Design of Intercell Transformers for High-Power Multicell Interleaved Flyback Converter

The subject of this paper falls under the development of power electronics for more electric aircraft systems. The study concerns the design of a converter whose function is to generate a 300-V dc bus from a standard 28-V dc avionic network. Various systems, such as motor drives, need to be connected to the 28-V dc network. Their design could be simplified significantly, and standardized, by introducing this intermediate 28–300-V stage. The step-up converter in the proposed configuration is integrated as a part of the system. The power specification is 10 kW, which leads to very high-current values on the 28-V side. The choice of the converter topology, therefore, needs to match this central constraint. The proposed converter uses six boost cells, associated to constitute a series–parallel architecture. This arrangement leads to significantly more optimal sizing for high step-up ratios than conventional boost-cell configurations. Cell interconnection is implemented by means of a monolithic InterCell transformer to reduce the weight of the magnetic part. This paper describes the topology, design, and construction of the lab prototype, as well as experimental results obtained during testing.

Jean-Jacques Huselstein

Papers

Multicell Interleaved Flyback Using Intercell Transformers

Design of a 28 V-to-300 V/12 kW Multicell Interleaved Flyback Converter Using Intercell Transformers

Design and Characterization of an Eight-Phase-137-kW Intercell Transformer Dedicated to Multicell DC–DC Stages in a Modular UPS

Design of Intercell Transformers for High-Power Multicell Interleaved Flyback Converter

A Nonreversible 10-kW High Step-Up Converter Using a Multicell Boost Topology