Michael Terorde

Innovative strategies for protecting power semiconductor switches for phase balancing and feeder balancing in aircraft

An inflexible point-to-point supply of loads is the state-of-the-art technology in aircraft nowadays. Because the wiring is rigid, it is not possible to connect loads to different power feeders when the aircraft is in flight. New technologies are required for handling the increasing demand for electricity on board aircraft. Two concepts - phase balancing and feeder balancing - which lead to an energy-efficient power supply network, are introduced. Both methods use intelligent switching nodes with power semiconductor devices, such as MOSFETs. The power transistors are chosen in such a way that they are slightly above the limits for forward current, blocking voltage and switching frequency. The number of switching operations that produce overvoltages and overcurrents in the electrical grid increases if the concepts that have been presented are used. To ensure that the transistors operate in their safe operating area, snubber circuits are used. Since the switching nodes bring in additional weight, these snubbers have to be designed in such a way that they are sufficiently light. Based on an analytical examination of switching ohmic-inductive and ohmic-capacitive loads, different switching strategies for reducing the negative switching effects have been introduced. Computer simulation results have been presented and evaluated.

Phase balancing for aircraft electrical distribution systems

The aircraft of the future will use several new concepts to improve its electrical power supply system, transforming it into a small smart distribution grid. Among these concepts, power management systems, increase in the main bus voltage, integration of high-voltage direct current grids, phase balancing, and power feeder balancing have been suggested. All these methods aim to reduce the overall weight of the aircraft. In order to analyze the weight-saving potential of aircraft through the phase-balancing method, simulations have been built based on the electrical load analysis of an actual passenger aircraft. The simulations reproduce the electrical power supply grid of an aircraft and the asymmetric utilization of the phases of the power feeders. Within the simulations, phase balancing is tested with different objective functions in order to achieve a more symmetric load of the feeder main line and the feeder branches and to minimize the return current. The new proposed concept suggests that loads be shifted depending on the ground/flight phases based on a fixed switching scheme, which is calculated before the first flight of the aircraft. As a result, only the nonflight-relevant commercial loads have been made switchable. Additionally, based on former publications, the local distribution of the loads and the load power factor have thereby been taken into account. Based on the simulation results, the weight benefit for the actual aircraft has been calculated. To validate the new concept, a switching box containing several multiplex switches has been built, and experimental results are presented.

Implementation of a Solid-State Power Controller for High-Voltage DC Grids in Aircraft

Conventional electrical distribution systems onboard aircraft use a three-phase system with a typical voltage of 115 VAC or 230 VAC to supply electrical loads. Future aircraft demand more electric power due to the replacement of hydraulic and pneumatic systems by electrical ones and the increased use of multimedia entertainment systems. However, the aircraft weight can be decreased if a high-voltage direct current (HVDC) grid with a voltage level of ±270 VDC or 540 VDC is implemented to supply the electrical loads. These higher voltages reduce cable weight, but are a new challenge for solid-state power controllers (SSPC), which are used as protection devices for cables and loads. Currently available SSPCs are limited to lower voltages and currents mainly because of the available power semiconductors. A SSPC for aircraft applications with a nominal voltage of 540 VDC and a nominal load current of 10 A has been developed at the Helmut Schmidt University in Hamburg in cooperation with Airbus Group Innovation using SiC-MOSFETs and has been tested. In this paper the design and experimental results are presented. The SSPC is able to supply itself from the high voltage autarkic and can accomplish various functions.

Implementation of multiplex-switches for power feeder balancing in aircraft

Multiple approaches are available for designing more flexible and energy-efficient electrical grids on board aircraft in order to lower the weight of aeroplanes. Here, two novel concepts in aviation, dealing with intelligent switching nodes based on power semiconductors, are introduced. The balancing concepts (phase balancing and power feeder balancing) reduce the return currents and allow reduction of the power feeder diameter by symmetrising the load of all phases of the power feeders. The focus of this paper is examination of the feasibility and practical realization of multiplex-switches for implementing the two concepts. That is why a prototype multiplex-switch has been developed and tested. The implementation of the multiplex-switch, which is usable for phase and feeder balancing, is explained in detail in this paper. Different transistor types, possible realisations of bidirectional switches and the suitability of Flexible AC Transmission System (FACTS) for load balancing have been discussed. Additionally, experimental results of the prototype multiplex-switch are shown and discussed. Different switching strategies for shifting loads between different feeders have been implemented in the multiplex-switches and have been tested with different load types on a test bench.

Integration scenarios to improve fuel cell dynamics for modern aircraft application

An approach to achieve a high efficiency for energy transfer in modern aircraft could be the More Electric Aircraft concept. According to this, the replacement of the conventional auxiliary power unit by a multi functional fuel cell system reduces the emission of carbondioxide significantly and can increase the efficiency. However, requirements on the electrical system dynamics are higher than currently available fuel cell systems can provide. To improve the electrical dynamics of the fuel cell especially during high peak power demands different methods are considered. This paper compares four possible integration scenarios to improve the system dynamic. Special characteristics as the additional system weight, the stored available energy, the complexity as well as the feasibility under the required conditions are considered. For supplementing the theoretical concepts, a prototype of a super capacitor short-time energy storage was built and integrated into an existing fuel cell test bench. Therefore, a voltage balancing as well as an overvoltage protection is implemented. Measurements show the improved dynamic of the hybrid fuel cell system.

Smart load balancing for large civil aircraft

The electrical power distribution network in the aircrafts cabin and cargo area has typically a tree topology with a three-phase electrical power supply. This paper presents a new optimization concept for this distribution network using dynamic load balancing to reduce the peak currents of the power feeder and to minimize the return current. This technique will reduce the wiring weight and the network configuration effort. To solve the load balancing problem different algorithms based on optimum approximation and mixed-integer linear programming have been applied. In order to validate the concept a simulation model and a lab demonstrator have been built.

Self-testing Solid-State Power Controller for High-Voltage-DC Aircraft Applications

Nowadays solid-state power controllers (SSPC) are widely used in aircraft secondary power supply, because of a higher count of switching cycles, small weight, flexible trip behavior, and a fieldbus connection. Typically, they protect loads and their connection lines. One drawback of these solid-state switches is the typical 28V secondary power supply for the control elements. This paper shows an effective supply arrangement to use the onboard power supply as energy source. Parallel MOSFETs represent the switching unit. This can be used for a self-test without supply interruption of connected loads. A self-test method is shown in this paper.

Integration of a superconducting magnetic energy storage into a control reserve

To ensure the stability of the power system, the transmission system operators (TSOs) keep a control reserve in readiness. This standby capacity is activated when the power system comes under strain and is typically provided by conventional fossil fuel-fired power plants. With the transition from fossil fuel-based energy production to sustainable renewable energy, the process of maintaining the stability of the grid is becoming more complex. A superconducting magnetic energy storage (SMES) is an efficient and highly dynamic system, which can be integrated into a control reserve. The use of a 40 MW/25 MWh SMES in primary control is simulated, its functionality shown, and the results discussed in this paper. The reserve market is analysed for estimating the cost-effectiveness of the approach. The grid frequency indicates the requirements for the SMES. In order to meet the demands for the prequalification of the TSO, such a storage system has to be pooled together with other providers of balancing energy or has to be collateralized by technical units which are already prequalified. High requirements are made on the power converter. To control the thyristors, a sequence control is used to decrease the reactive power.