The droop control method is usually employed in the DC microgrids to share the load current demand among multiple sources due to its advantage of being independent of a communication network. However, the performance of the droop control method is affected by the mismatched transmission line resistance and the offset in the nominal voltage reference. This paper presents the design and optimization of the droop coefficient of converters, using the genetic algorithm to enhance the current sharing and the DC bus voltage regulation performance. The proposed approach is tested on the single bus multi-source electrical power system (EPS) for the more electric aircraft (MEA) applications. The effectiveness of the proposed approach is validated using a detailed simulation model of the MEA EPS developed in MATLAB Simulink.

A Half-bridge-active-clamp (HBAC) converter is used as an alternative to replace Dual active bridge (DAB) converter for 540V/28V on-board grid in more electric aircraft applications. The HBAC converter provides an opportunity to reduce the turn-ratio of the high frequency transformer compared to DAB converter with reduced current stress on the low voltage side benefit from a current-fed LV bridge. HBAC converter shows a much better performance both on efficiency and volume compared to conventional DAB converter. In addition, a Model Predictive Control (MPC) method for LV output current regulation is proposed based on HBAC converter with the aim of achieving fast dynamic performance.

Most of the existing methods used to estimate the cable resistance require the use of many hardware devices and the injection of perturbations to the system. Therefore, they are time-consuming, costly and prone to errors. In addition, the injection of perturbations has the potential of degrading the power quality of the system. In this paper, a new artificial neural network (ANN) aided cable resistance estimation approach is proposed. The ANN model is trained by simulation data. The trained ANN model can quickly and effectively map the current sharing ratios between the converters to the droop coefficients of the converters. In this way, the optimal droop coefficient combination that will yield the desired accurate current sharing ratio between the converters can be predicted by the trained ANN model. Subsequently, the optimal droop coefficient combination can be used in the estimation of the corresponding subsystem cable resistance by solving an equation set. The estimated cable resistance is compared with the simulated cable resistance and an excellent match is observed.

The idea of electric propulsion for transportation is not new; indeed, the first cars, nearly 200 years ago, were electric. However, our dependence on fossil fuels over the last 100 years is now being questioned, and as a global society, we are moving toward more-electric transportation solutions. Electric propulsion of aircraft is part of this trend, either all-electric or through a large variety of the proposed hybrid propulsion systems. This article considers some of these systems, their technological requirements, and the ongoing research and development in motors and drives necessary to make this technological change a feasible option for the future of passenger flight.

This paper presents the design and implementation of multicellular isolated bidirectional dual-active-bridge (DAB) DC/DC converters which are the core equipment of the European CleanSkyII Project ASPIRE. Both the primary and the secondary H-bridge circuits use gallium nitride (GaN) devices which enable high frequency operation. Between two H-bridge circuits is a planner transformer which is customized for the frequency range from 100kHz to 300kHz, saving the volume and weight. Three proportional integral controllers in parallel are also proposed to control the power transfer and compensate the DC offset values to the transformer, providing efficient operation in both buck and boost modes, allowing on-fly turn-on, turn-off and fast power reversal. Experiment results validate that the converters satisfy the requirements of the Project ASPIRE for the use in more electric aircrafts.

This paper explores the possibility of a semiconductor-based over-current bypass circuit for high current solid-state power controllers (SSPCs). Therefore, two different topologies of the bidirectional DC SSPCs: a. without over-current bypass circuit b. with an over-current bypass circuit are presented for the same power ratings. The first SSPC consists of a parallel matrix connection of the discrete MOSFET devices (conducts during nominal and over-current conditions) and the second one is designed with fewer MOSFET loops (conducts during nominal condition) and additional IGBT modules matrices to bypass the over-current. The thermal performances of both the SSPCs are evaluated analytically and compared during the nominal and over-current situations. Later, the PLECS simulation models of the SSPCs are developed and the junction temperature of the devices are estimated. The overall weight, power density, and cost of these two SSPCs are approximated for the comparison. It is found that the SSPC topology with bypass circuit exhibits better power density and lower cost. Therefore, it can be employed to replace the tradition circuit breakers for the more electric aircraft (MEA) in the near future.

Mechanically-driven actuators, compressors and pumps are being replaced by the aircraft manufacturers that shift the trend towards “More Electric Aircraft” and hence reducing the mechanical linkages within the aircraft system. This elevates the dependence of the electrical power on the main engine, deicing and cabin environmental system which originates from the starter-generator. This paper presents a trade-off study for the design of high-performance starter-generator, surface-mounted permanent magnet machines, considering slot-pole combination, winding configuration and geometrical layout as degrees of freedom while satisfying the output power and strict volume requirements. 18S/12P combination seems a promising candidate for starter generator application which satisfy all the given requirements, giving the output power of 32kW at 14kRPM within the volume of 1407cm3.

Multi-source DC power systems have been widely used in electric transportations, including more-electric aircraft, electric ship and electric vehicles. These systems normally involve in power electronic converters whose switching actions may cause current fluctuation on DC-bus capacitors. Eliminating certain order harmonics can help the system potentially reduce the volume and weight of the capacitor. In this paper, a simplified model to estimate 2nd carrier harmonic of DC current in two-level converters is proposed. In derived model, magnitude of the harmonic is only determined by the DC-bus current and modulation index of the converter. Meanwhile, the phase angle of it is determined by angle of carrier signals. Based on this model, a new harmonic cancellation method is proposed. The method has high robustness and can work under any fundamental frequency and power sharing ratio. Simulation results are presented in this paper to verify the validation of proposed harmonic model and the enhanced cancellation method.

When designing an electric power system (EPS) architecture for a more electric aircraft (MEA), the total weight of the system is treated as one of the most important criteria. For the weight saving purpose, this paper proposes an optimal power flow (OPF) based architecture design method to minimise the redundancy of the EPS of MEA, which includes reducing the generator overloading requirements for lighter generator design, and cutting down the excessive harness and number of contactors to lighten the wiring system. Based on the formulized mixed-integer linear programming (MILP) model, the addressed optimal architecture design (OAD) problem can be solved by optimising the power routing with minimum transmission losses in different flight stages simultaneously to minimise generator sizing and number of connections. The model contains both decision variables indicating the system architecture (e.g. cables existences and generator capacity) and the ones indicating the power flows with regards to the flight stages. In addition, the total transmission losses in the system are considered by formulizing the non-linear transmission losses of the DC/DC converters and cables losses in model constraints. By minimising the transmission losses, the generator overload capacity, as well as the cable needed for the connections, an optimised architecture with less redundancy and having optimal power routing in different flight stages can be realized, leading to lighter generator and wiring system for EPS.

In the More Electric Aircraft framework, the objective is to increase the efficiency and the reliability of the aircraft by gradually substituting the existing subsystems with electrical ones. Newer aircrafts already incorporate a great share of electric power, making the on-board electrical power distribution system (EPDS) a complex structure composed of generators, actuators and storage. Because of the importance of power electronics in this scenario, the control system is critical to ensure the stability of the EPDS. This paper analyzes the sensitivity to the control parameters of the EPDS stabiltiy. A state-space model is derived and the root loci are used to show in a graphical way the effects of the design parameters.

As the electrical network of future aircraft become more and more complex, safety issues related with electrification need to be addressed. This paper shows that this can be achieved by developing an advanced control strategy and then applying it, through a smart controller, to initiate fast and automatic actions to protect the vital operations of such an electrical power system (EPS). The case study presented in this paper demonstrates how a smart controller can be used to ensure uninterrupted power supply to the high priority loads in the event of single, or multiple, power electronic converter failures. The control logic is implemented using a finite state machine (FSM) and applied to a DC based EPS which is representative of future aircraft. The results are verified and validated in the Simulink environment.

This paper proposes a semi-flooded cooling concept for a high speed machine design. The electrical machine considered is for an aircraft starter-generator system where power density and efficiency are crucial. In order to achieve the high power density permanent magnet machine, a direct oil cooling strategy for the machine stator is adopted. A stator oil sleeve is designed to separate the machine into an oil-flooded stator chamber and an oil-free rotor chamber to avoid windage loss due to the high rotor speed. Different materials, Carbon Fiber (CF) and E-glass fiber (GF) are considered for the oil-sleeve design. Implications of the aforementioned materials on the structural design are investigated and optimized accordingly using finite element methods. It is shown that the oil sleeve made of CF provides structural capability with a minimum sleeve thickness. However the sleeve made from GF has the benefit of having no electrical conductivity. Both oil sleeves are made and the GF sleeve is successfully applied to the machine and tested.

This paper proposes solid rotor Interior Permanent Magnet (IPM) machine for an aircraft starter-generator. The key challenge in the design is to satisfy two operating conditions which are high starting torque and high speed continuous operation. A Surface mounted PM machine designed for such an application is used as a benchmark. Then, the IPM machine is designed adopting a solid rotor to have a maximum mechanical stress level well below the material Ultimate Tension Strength (UTS) and minimal rotor eddy current losses. A detailed design is carried out through Finite Element (FE) electromagnetic and structural analysis. The static and dynamic structural analyses are presented. Several novel approaches to minimize the rotor eddy current losses are investigated. It is shown that the proposed solid rotor concept for IPM fulfils both high torque and high speed design requirements whilst satisfying the structural and magnetic limitations.

Stability margins of the switch-mode DC/DC power conversion systems are very sensitive to variations in load and system parameters. In aerospace applications these systems can be exposed to considerable variations in temperature that can cause large changes in system parameters from their nominal values and can lead to stability problems if this issue is not properly taken into account during the design phase. In this study robust stability margins are calculated for a system that consists of a DC/DC closed loop buck converter and an input LC filter considering extreme variations in temperature. For the prototype system, the paper details a modelling approach to developing an uncertain system model which is used to assess robust stability based on the principle of Structural Singular Value. The approach is verified through simulations in MATLAB and through experimental tests.

Droop control methods are widely used in dc microgrids due to its simplicity and easy implementation. However, DC bus voltage deviation increases as the droop gain increases although accuracy of power sharing is improved. In order to overcome this paper proposes an improved voltage regulation method under high droop gain circumstance with consideration of cable impedance. It allows accurate power sharing and the low voltage-regulation simultaneously. The reduced-order model is developed neglecting fast converter dynamics. The effect of this proposed method on stability is also studied by eigenvalues method. Time domain simulation in Matlab/Simulink validates all the analysis.

This paper deals with the control design for an aircraft electric starter-generator system that utilizes recent advances in modern power electronics allowing the use of novel machine types together with the introduction of controlled power electronics into the main path of energy flow. The paper describes the developed system and focuses on control design including flux weakening control of high-speed permanent magnet machine and droop control of the system output dc-link current. The analytical design results and the expected system performance are confirmed by time-domain simulations.