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This study uses the Neural Network (NN) technique to optimize design of surface-mounted Permanent Magnet Synchronous Motors (PMSMs) for More-Electric Aircraft (MEA) applications. The key role of NN is to provide dedicated correction factors for the analytical PMSM mass and loss estimation within the entire design space. Based on that, a globally optimal design can be quickly obtained. Matching the analytical estimation with Finite-Element Analysis (FEA) is the main research target of training the NN. Conventional analytical formulae serve as the basis of this study, but they are prone to loss accuracy (especially for a large design space) due to their assumptions and simplifications. With the help of the trained NNs, the analytical motor model can give an estimation as accurate as the FEA but with super less time during the optimization process. The Average Correction Factor (ACF) approach is regarded as the comparison method to demonstrate the excellent performance of the proposed NN model. Furthermore, a NN aided three-stage-seven-step optimization methodology is proposed. Finally, a Pole-10-Slot-12 PMSM case study is given to demonstrate the feasibility and gain of the NN aided multi-objective optimization approach. In this case, the NN aided analytical model can generate one motor design in 0.04 s while it takes more than 1 min for the used FEA model.

This paper proposes a novel application method, Inverse Application of Artificial Intelligence (IAAI) for the control of power electronic converter systems. The proposed method can give the desired control coefficients/references in a simple way because, compared to conventional methods, IAAI only relies on a data-driven process with no need for an optimization process or substantial derivations. Noting that the IAAI approach uses artificial intelligence to provide feasible coefficients/references for the power converter control, rather than building a new controller. After illustrating the IAAI concept, a conventional application method of Artificial Neural Network (ANN) is discussed, an optimization-based design. Then, a two-source-converter microgrid case is studied to choose the best droop coefficients via the optimization-based approach. After that, the proposed IAAI method is employed for the same microgrid case to quickly find good droop coefficients. Furthermore, the IAAI method is applied to a modular multi-level converter (MMC) case, extending the MMC operation region under unbalanced grid faults. In the MMC case, both simulation and experimental online tests validate the operation, feasibility, and practicality of IAAI.

In this paper, a new approach for the design of the droop coefficient in the droop control of power converters using the artificial neural network (ANN) is proposed. In the first instance, a detailed more electric aircraft (MEA) electrical power system (EPS) circuit model is simulated in a loop using different combinations of the converters droop coefficients within a design space. The inaccurate output DC currents sharing of the converters due to the influence of the unequal cable resistance are then obtained from each of the simulations. The data generated is then used to train the NN to be a dedicated surrogate model of the detailed MEA EPS simulation. Thus, for any user-defined desired current sharing among the converters that are within the design space, the proposed NN can provide the optimal droop coefficients. This NN approach has been verified through simulations to ensure accurate current sharing between the converters as desired. Hence, can be used in the design of the droop coefficient to enhance the performance of the conventional droop control method.

In this paper, a dc filter design and optimization problem is studied for dc electrical power distribution systems onboard more-electric aircraft. Component sizing models are built to serve as the basis of the optimization whose objectives are mass and power loss of this filter. A categorization strategy of search and surrogate algorithms are proposed and used for the target multi-objective optimization problem (MOOP). A genetic algorithm is utilized as a search algorithm to identify potential best solutions based on a set of filter sizing functions (subject to constraints). Additionally, two machine learning (ML) algorithms are considered as surrogate algorithms to address the same optimization problem. In the ML training process, a constraint violation model is applied since there are various constraints in optimization and this kind of classification model is relatively difficult to train. A support vector machine is applied for the constraint violation model after which two artificial neural networks are trained as the final surrogate model for mapping design variables to filter performance. To address these issues, a novel category of search and surrogate algorithms are proposed. Both algorithms are explored to solve the filter MOOP and their optimization results are compared at the end.

For the DC electrical power distribution system onboard more electric aircraft, the voltage quality of DC bus is of a great concern since there could be significant harmonics distortions when feeding different power electronics loads. This problem can be potentially addressed by introducing a dc filter to the point-of-load converters regulated by the finite control set model predictive control (FCS-MPC). To optimize this filter, Genetic Algorithm (GA) is utilized for searching the optimal design which guarantees a low mass and low power losses. Different from the conventional filter design methods, the proposed method treats LC as design variables which need to be optimised while ensuring the output power quality. First, relations among variables, operation conditions and constraints are built based on commercial data and circuit simulations. Then, the design and optimization are developed with these relations and a Pareto-front is finally given by GA. After that, the best design is obtained by an index integrating two objectives. Lastly, the design approach is verified by experiment where an FCS-MPC regulated converter was used as a particular example fed by three different LC filters.

The Dynamic Phasor (DP) concept has been widely used in modelling electrical power systems. So far, the DP concept has been restricted to modelling systems with one single electrical source at a fixed fundamental frequency; either one generator or an ideal three-phase AC source. This paper aims to extend the DP modelling methodology to a wider application area. Two major achievements have been introduced: 1. application of DPs for multi-source, multi-frequency systems; 2. modelling of systems with time-varying frequencies. These two techniques enable the use of DPs to study nearly all types of Electrical Power Systems (EPS). The developed theory is validated using a twin-generator system from the More Open Electrical Technologies (MOET) project. The accuracy and effectiveness of the developed models is confirmed by comparing the simulation results of detailed switching models and DP models under both balanced and unbalanced conditions.

This paper presents control analysis and design for an aircraft electric starter-generator system based on a Permanent Magnet Machine (PMM) operated in Flux-Weakening mode (FW). The focus is on detailed stability analysis which helped to discover an intrinsic instability when operating the PMM in FW mode. An adaptive voltage magnitude controller, including a variable current limit, is proposed and shown to guarantee stable operation. The analytical findings are verified by experimental investigation.

This paper presents an overview of technology related to on-board microgrids for the More Electric Aircraft. All aircraft use an isolated system, where security of supply and power density represent the main requirements. Different distribution systems (AC and DC) and voltage levels coexist, and power converters have the central role in connecting them with high reliability and high power density. Ensuring the safety of supply with a limited redundancy is one of the targets of the system design, since it allows increasing the power density. This main challenge is often tackled with proper load management and advanced control strategies, as highlighted in this paper.

More-electric aircraft (MEA) has become a dominant trend for modern aircraft. On-board MEA, many functions, which are conventionally driven by pneumatic and hydraulic power, are replaced with electrical subsystems. Starting aircraft engines with an electrical motor instead of using pneumatic power from the auxiliary power unit (APU) is one of the major characteristics of future aircraft. This paper presents the development of a novel electric starter-generator system for aircraft applications. The paper describes the main achievements of the project within the key areas including electric machines, power electronic converters, thermal management and overall system control design. The developed prototype has been tested successfully and the test results are presented in this paper.

This paper describes a high performance neutral point voltage balancing technique for a Neutral point clamped (NPC) Converter. Conventional neutral point voltage balancing methods do not function well under low power factor, low pulse ratio and near-unity modulation index operation conditions. These conditions are essentially dominant operation conditions for aircraft starter/generator systems. This paper introduces an alternative space vector modulation technique for three-level NPC converters in an aircraft starter generator system. The selection of voltage space vectors is optimized for high modulation index and low power factor operation. Disturbances caused by low pulse ratio is also compensated. The proposed method maintains neutral point voltage balance and ripple minimization over the full range of operating conditions. The paper also provides a detailed analysis into the sources of neutral point voltage imbalances and ripples in high speed drives with deep flux weakening. Simulation results obtained from a Simulink/PLECS model and experimental results obtained from a 45kVA, 32krpm aircraft starter generator test rig proves the proposed method eliminates the neutral point voltage imbalance and significantly reduces the neutral point voltage ripple.

A design procedure for the Dual Active Bridge (DAB) converter is presented, which aims to optimized power density and computational effort. When designing a DAB, the selection of circuit design parameters such as switching frequency, leakage inductance and semiconductor technologies is a complex question when targeting losses and weight minimization of the final design. In this paper, analytical models of the operating waveforms, the losses and the weight of all DAB components are developed. The proposed design algorithm is used for designing a 3kW high frequency DAB for an aircraft DC power system.

The Auto-Transformer Rectifier Unit (ATRU) is one preferred solution for high-power AC/DC power conversion in aircraft. This is mainly due to its simple structure, high reliability and reduced kVA ratings. Indeed, the ATRU has become a preferred AC/DC solution to supply power to the electric environment control system on-board future aircraft. In this paper, a general modelling method for ATRUs is introduced. The developed model is based on the fact that the DC voltage and current are strongly related to the voltage and current vectors at the AC terminals of ATRUs. In this paper, we carry on our research in modelling symmetric 18-pulse ATRUs and develop a generic modelling technique. The developed generic model can study not only symmetric but also asymmetric ATRUs. An 18-pulse asymmetric ATRU is used to demonstrate the accuracy and efficiency of the developed model by comparing with corresponding detailed switching SABER models provided by our industrial partner. The functional models also allow accelerated and accurate simulations and thus enable whole-scale more-electric aircraft electrical power system studies in the future.

This paper introduces a novel modulation technique for the single phase Dual Active Bridge (DAB) in which the switching frequency and transformer flux are modulated to achieve improved power transfer characteristics and reduced converter losses. By analyzing the DAB, it is noticed that in the traditional Single Phase Shift (SPS) modulation, the transformer flux linkage decreases with increasing power. The proposed Flux Control Modulation (FCM) counteracts this decrease and aims to keep the transformer utilization constant on the whole load range by a reduction in switching frequency. This has two effects: First, the reduced frequency substantially lowers switching losses and second, the power transfer characteristic of the DAB is linearized, facilitating the control of this converter. The new modulation technique is validated by simulation

Electrical starter/generator (ESG) system is one of the key innovations of more-electric aircraft initiative. The ESG cranks the engine and accelerates it up to self-sustained speed using electric energy (starter mode) and then runs as a generator to supply onboard loads. Three-level neutral point clamped (NPC) converter have been identified as a preferable choice for ESG applications due to high power quality as well as efficiency. However, the application of three-level NPC converter in the ESG systems has certain challenges. One of which is the low frequency neutral point voltage ripple, especially in generation mode when running at high speeds such that the flux weakening control is required. The paper proposes an advanced modulation scheme which can balance the neutral point voltage for the full range of speeds and loading conditions. Using the proposed technique, zero neutral point voltage deviation within each switching period is achieved by introducing a sharing factor computed in a deadbeat predictive approach. The proposed technique is validated with simulation results.

Due to developments in power electronics, electric machines, energy storage and control, electric propulsion and integrated electrical power systems have become major trends for commercial and naval vessels. This is mainly due to the fact that the use of electric propulsion and integrated power systems can improve efficiency and fuel consumption while reducing noise and vibration when compared to conventional systems. Such advantages are extremely attractive to vessel owners due to increasingly stringent emission requirements, especially in environmental control areas, from the international maritime organization. This paper aims to summarize the recent advancement of marine power systems including propulsion systems, electrical distribution systems and novel loads.

It is known that, when tightly regulated, actively controlled power converters behave as constant power loads (CPLs). These loads can significantly degrade the stability of their feeder system. The loop-cancelation technique has been established as an appropriate methodology to mitigate this issue within dc–dc converters that feed CPLs. However, this has not yet been applied to uncontrolled rectifier based ac–dc converters. This paper therefore details a new methodology that allows the loop-cancelation technique to be applied to uncontrolled rectifier based ac–dc converters in order to mitigate instability when supplying CPLs. This technique could be used in both new applications and easily retrofitted into existing applications. Furthermore, the key contribution of this paper is a novel adaptive stabilization technique, which eliminates the destabilizing effect of CPLs for the studied ac–dc power system. An equation, derived from the average system model, is introduced and utilized to calculate the adaptable gain required by the loop-cancelation technique. As a result, the uncontrolled rectifier based ac–dc feeder system is always stable for any level of CPL. The effectiveness of the proposed adaptive mitigation has been verified by small-signal and large-signal stability analysis, simulation, and experimental results.

Stability studies are a crucial part of the design of power electronic systems, especially for safety critical ap¬plications. Standard methods can guarantee stability under nominal conditions but do not take into account the multiple uncertainties that are inherent in the physical system or in the system model. These uncertainties, if unaccounted for, may lead to highly optimistic or even erroneous stability margins. The structured singular value-based method justifiably takes into account all possible uncertainties in the system. However, the application of the method to power electronic systems with multiple uncertainties is not widely discussed in the literature. This work presents practical approaches to applying the method in the robust stability analysis of such uncertain systems. Further, it reveals the significant impact of various types of parametric uncertainties on the reliability of stability assessments of power electronic systems. This is achieved by examining the robust stability margin of the dc/dc buck converter system, when it is subject to variations in system load, line resistance, operating temperature and uncertainties in the system model. The predictions are supported by time domain simulation and experimental results.

This paper presents a newly developed Power Electronic Inverter library in Modelica. The library utilises a multi-level approach with increasing model complexity at progressively higher levels. All levels are fully interchangeable so as to provide a flexible library able to be utilised for investigation at single or multiple levels of complexity. Within this inter¬changeable multi-level approach, there are two key attributes which are implemented into this new library. The first is the ability to include losses between the input and output of the Power Electronic Inverter. This is implemented so that the losses are included irrespective of the direction of power flow. Secondly, this library also provides the ability to trigger single or multiple open and short circuit faults within the Inverter. The library therefore provides an extremely useful tool able to compare system response under a variety of operational scenarios.

This paper proposes an active switching harmonic current reduction method within the DC-link capacitor of two-level, three-phase, back-to-back converters. The method is based on the derived analytical solution for switching harmonic currents in the DC-link. It is shown that by controlling the PWM carrier waveform’s phase angles, the harmonics in the 2nd carrier band of the rectifier and the inverter can be synchronized such that cancellation occurs in the DC-link capacitor. This synchronization is provided by harmonic phase feedback control. The feasibility of the proposed approach has been verified experimentally and results are presented in the paper

The impedance based stability assessment method has been widely used to assess the stability of interconnected systems in different application areas. This paper deals with the source/load impedance analysis of the droop-controlled multiple sources multiple loads system which is a promising candidate in the future more-electric aircraft (MEA). This paper develops a mathematical model of the PMSG-based variable frequency generation system, derives the output impedance of the source subsystem including converter dynamics and shows the effect of parameters variation on source impedance and load impedance. A dynamic droop controller is proposed to provide the active damping to the system. In addition, the impedance analysis is extended to a generalized single bus-based multiple sources multiple loads system in which power losses are also investigated. The aforementioned analytical result is confirmed by experimental results.

The paper presents control analysis and design for a Permanent Magnet Machine (PMM) operated in Flux-Weakening (FW) mode for an aircraft electric starter-generator application. Previous literature has focused on FW control of PMMs in motoring (starting) mode, however the system stability and control in generating mode has been inadequately studied. The paper reports detailed, rigorous control analysis and design for a PMM based aircraft electric starter-generator operated in flux-weakening mode. It is shown that an unstable area of operation exists. A novel control scheme which eliminates this instability is proposed. The key analytical findings of the paper are verified by experimental investigation. The paper therefore concludes that the presented technique is able to ensure system stability under all modes of operation. Furthermore, it is noted that the findings of this work are also valuable for any two-quadrant PMM drive with frequent change between starting and generating regimes under current-limiting operation.

This paper presents an assessment of different torque ripple minimization techniques for more electric aircraft Switched Reluctance Machine (SRM) starter/generator (S/G). SRM is one of the most popular potential candidates for future aircraft S/G. SRM is a type of electric machine that features simple structure hence it is cheap to manufacture, also it is very robust. However, one of the major disadvantages of SRM is that, due to its structural nature, its highly nonlinear characteristics would result in unwanted torque ripple. In order to eliminate/minimise the torque ripple, some techniques were proposed over the last decades. In this paper, several techniques of Torque ripples minimization (TRM) are introduced and then it focuses on the assessment of two techniques suitable for the proposed 45 kW SRM as S/G, namely torque sharing function (TSF) technique and a newly proposed closed-loop torque control (CLTC) technique. An analytical modelling method is also proposed in order to apply the proposed TRM techniques. Conclusions and future works are presented at the end of this paper.

The future aircraft electrical power system is expected to be more efficient, safer, simpler in servicing and easier in maintenance. As a result, many existing hydraulic and pneumatic power driven systems are being replaced by their electrical counterparts. This trend is known as a move towards the More-Electric Aircraft (MEA). As a result, a large number of new electrical loads have been introduced in order to power many primary functions including actuation, de-icing, cabin airconditioning, and engine start. Therefore electric power generation systems have a key role in supporting this technological trend. Advances in modern power electronics allow the concept of starter/generator (S/G) which enables electrical engine start and power generation using the same electrical machine. This results in substantial improvements in power density and reduced overall weight. One of the potential S/G solutions is to employ a permanent magnet machine (PMM) controlled by active front-end rectifier (AFE). Operation of the PMM as a generator at wide range of speed that is dictated by the engine and electrical loads connected to the aircraft bus require careful design of the controllers. Corresponding plant models are derived and verified with simulations using developed models in Matlab/Simulink. The relevant controllers are designed based on the derived plants and operating points. The controllers are tested with Simulink models and experimentally using a scaled prototype of the investigated generator system.

The paper describes a hybrid control scheme for a permanent magnet machine based starter-generator (S/G) system. There has been increased usage of electric drive systems in the transportation sector for increased efficiency and reduced emissions. One of the advantages of utilising suitable electric drives is the capability to operate as a starter or generator. The control design of such a system should be considered due to the operating requirements and fast load changes. Different control approaches should therefore be considered in order to achieve these goals, which are a current trend in the transportation sector. Model Predictive Control (MPC) is considered due to its very fast dynamic performance. In particular, Modulated Model Predictive Control (M²PC) was recently introduced and showed significantly better performance than the standard MPC. The control scheme used in this paper utilises M²PC for the current inner loop and PI controllers for the outer loop. The use of M²PC allows very fast transient current response for the S/G system. The proposed overall control benefits from reduced current ripple when compared with a full cascaded PI control scheme. Simulation analyses and experimental results show the capability and performance of the designed controller across both starter and generator modes.

This paper focuses on the analysis of a single DC bus multi-generator Electrical Power System (EPS) for future More Electric Aircrafts (MEA). Within such a single bus paradigm, the paper proposes a detailed control design procedure and provides a stability analysis based on the derivation of the output impedance of the source subsystem and input impedance of the load subsystem, including control dynamics. The single bus characteristic is analyzed and the stability properties of the EPS are investigated when supplying constant power loads. In addition, the paper highlights the impact on stability of the number of parallel sources and of the power sharing ratio. The theoretical analysis is instrumental in designing an optimally stable single DC bus EPS. The key findings are validated by experimental results.

Multiple-spool gas turbines are usually utilized for power supply in aircrafts, ships, and terrestrial electric utility plants. As a result, having a reliable model of them can aid with the control design process and stability analysis. Since several interconnected components are coupled both thermodynamically and through shafts, these engines cannot be modeled linearly as single shaft gas turbines. In this paper, intercomponent volume method (ICV) has been implemented for turbine modeling. A switched feedback control system incorporating bump-less transfer and antiwindup functionality is employed as governor for the engine. Validation with test results from a three spool gas turbine highlights high accuracy of turbine-governor model in various maneuvers. Results show that over-speed after load rejection is considerable due to the fact that in this arrangement, the power turbine (PT) is not coupled with the compressor which acts like a damper for single shaft gas turbines. To address this problem, bleed valves (mainly before combustion chamber) are used to arrest the over-speed by 20%. In addition, a switch is employed into the governor system to rapidly shift fuel to permissible minimum flow.

The paper will deal with the problem of establishing a desirable power sharing in multi-feed electric power system for future more-electric aircraft (MEA) platforms. The MEA is one of the major trends in modern aerospace engineering aiming for reduction of the overall aircraft weight, operation cost and environmental impact. Electrical systems are employed to replace existing hydraulic, pneumatic and mechanical loads. Hence the onboard installed electrical power increases significantly and this results in challenges in the design of electrical power systems (EPS). One of the key paradigms for future MEA EPS architectures assumes high-voltage dc distribution with multiple sources, possibly of different physical nature, feeding the same bus(es). In our study we investigate control approaches to guarantee that the total electric load is shared between the sources in a desirable manner. A novel communication channel based secondary control method is proposed in this paper. Stability of the proposed method is investigated and it proves that the system stability margin is upgraded using the compensation method. The analytical results of the study will be supported by both time-domain simulations and experimental results.

The paper presents a conceptual design approach for Energy Storage (ES) devices in advanced hybrid propulsion system for small aircrafts. The study targets operational improvement and reduction of fuel consumption for different flight missions. Power sharing strategies for ES and the engine are proposed for cruise flight phase aiming to maximise the range and/or endurance for the available amount of fuel in the tank. The ES size is designed against the engine performance and the proposed power sharing strategy by optimizing the flight altitude.

The paper presents a novel robust field oriented vector control for induction generators. The proposed controller exploits the concept of indirect field orientation and guarantees asymptotic DC-link voltage regulations when DC-load is constant or slowly varying. An output-feedback linearizing Lyapunov’s based technique is employed for the voltage controller design. Flux subsystem design provides robustness with respect to rotor resistance variations. Decomposition of the voltage and current-flux subsystems, based on the two-time scale separation, allows to use a simple controllers tuning procedure. Results of comparative experimental study with standard indirect field oriented control are presented. It is shown that in contrast to existing solutions designed controller provides system performances stabilization when speed and flux are varying. Experimentally shown that robust field oriented controller ensures robust flux regulation and robust stabilization of the torque current dynamics leading to improved energy efficiency of the electromechanical conversion process. Proposed controller is suitable for energy generation systems with variable speed operation.

A novel maximum torque per Ampere (MTPA) controller for induction motor (IM) drives is presented. It is shown to be highly suited to applications that do not demand an extremely fast dynamic response, for example electric vehicle drives. The proposed MTPA field oriented controller guarantees asymptotic torque (speed) tracking of smooth reference trajectories and maximises the torque per Ampere ratio when the developed torque is constant or slow varying. An output-feedback linearizing concept is employed for the design of torque and flux subsystems to compensate for the torque-dependent flux variations required to satisfy the MTPA condition. As a first step, a linear approximation of the IM magnetic system is considered. Then, based on a standard saturated IM model, the nonlinear static MTPA relationships for the rotor flux are derived as a function of the desired torque, and a modified torque-flux controller for the saturated machine is developed. The flux reference calculation method to achieve simultaneously an asymptotic field orientation, torque-flux decoupling and MTPA optimization in steady state is proposed. The method guarantees singularity-free operation and can be used as means to improve stator current transients. Experimental tests prove the accuracy of the control over a full torque range and show successful compensation of the magnetizing inductance variations caused by saturation. The proposed MTPA control algorithm also demonstrates a decoupling of the torque (speed) and flux dynamics to ensure asymptotic torque tracking. In addition, a higher torque per Ampere ratio is achieved together with an improved efficiency of electromechanical energy conversion.

Aircraft engines, the prime source of on-board power, play a vital role within the electrical power generation system. In literature these are considerably simplified to rudimentary engine speed. In this paper, a nonlinear zero-dimension (0-D) order turbofan engine model has been developed for use with an integrated power center. By analyzing the compressor maps in detail, the results reveal a limit on the amount power off-take from each engine shaft at different altitudes.

The current trend for future aircraft is the adoption of the More Electric Aircraft (MEA) concept. The electrical based starter-generator (S/G) system is one of the core ideas from the MEA concept. The PI based control scheme has been investigated in various papers for the permanent magnet based S/G system. Different control schemes are to be considered to improve the control performance of the S/G system. A type of non-linear control called Model Predictive Control (MPC) is considered for its capability to accomplish fast dynamic control performance. The Modulated Model Predictive Control (variant of MPC with an intrinsic modulator) was presented that showed considerably better control performance than the standard MPC. A control scheme is presented in this paper that utilises PI controllers for the outer loop and Modulated Model Predictive Control for the inner loop that covers operation for both starter and generator modes. Simulation analyses are carried out to compare between the proposed control and a full cascaded PI control scheme. The proposed control is also subjected to parameter variation tests for performance evaluation.

This paper presents an analytical modelling approach for Switched Reluctance Machines (SRMs) with a wide saturation range. There are many existing analytical modelling approaches in literature that give good accuracy, however most do not consider modelling accuracy in the deeply saturated region of operation. The proposed modelling method is suitable for SRMs operating under the entire saturation range. The proposed methodology begins by modelling the inductance profile as a Fourier series in order to take advantage of its approximately sinusoidal variation with respect to rotor position. Improvements are then presented to achieve higher accuracy. Flux linkage and torque models for the SRM can then be derived from the inductance model. An example 60kW 6/4 SRM with a wide saturation operating range is used for analytical modelling. It is shown that high accuracy is obtained by the derived analytical model when evaluated against the measured magnetic characteristics of the machine.

Droop control has been widely applied in DC microgrids (MGs) due to its inherent modularity and ease of implementation. Among the different droop control methods that can be adopted in DC MGs, two options have been considered in this paper; I-V and V-I droop. I-V droop controls the DC current depending on the DC voltage whilst V-I droop regulates the DC voltage based on the output current. The paper proposes a comparative study of V-I/I-V droop control approaches in DC MGs focusing on steady-state power sharing performance and stability. The paper presents the control scheme for current-mode (I-V droop) and voltage-mode (V-I droop) systems, derives the corresponding output impedance of the source subsystem including converters dynamics and analyzes the stability of the power system when supplying constant power loads. The paper investigates first the impact on stability of the key parameters including droop gains, local control loop dynamics and number of sources and then performs a comparison between current-mode and voltage-mode systems in terms of stability. In addition, a generalized analytical impedance model of a multi-source, multi-load power system is presented to investigate stability in a more realistic scenario. For this purpose, the paper proposes the concept of “global droop gain” as an important factor to determine the stability behaviour of a parallel sources based DC system. The theoretical analysis has been validated with experimental results from a laboratory-scale DC MG.

This paper investigates the dynamic stability of a droop-controlled multi-generator system in the more electric aircraft (MEA). Based on the developed state-space model of the potential dc electrical power system (EPS) architecture, the stability boundaries of EPS operation depending on parameter variations including component parameters and operating conditions are investigated. The effect of multiple parametric uncertainties on EPS stability is graphically illustrated by stability regions maps. In addition, the effect of the droop coefficient on the stability is discussed from the impedance point of view. The detailed mathematical models and analytical results of stability assessment are verified by time domain simulation studies.

The paper presents a novel maximum torque per Ampere (MTA) controller for induction motor (IM) drives. The proposed controller exploits the concept of direct (observer based) field orientation and guarantees asymptotic torque tracking of smooth reference trajectories and maximizes the torque per Ampere ratio when the developed torque is constant or slowly varying. A dynamic output-feedback linearizing technique is employed for the torque subsystem design. In order to improve torque tracking accuracy a motor magnetizing curve is taken into account during MTA optimization and controller design. The achieved steady-state system efficiency have been compared experimentally for three types of controllers, namely: standard vector control with constant flux operation, controller based on classic maximization of torque per Ampere ratio for linear magnetic circuit and controller based on MTA strategy for saturated induction motor. It is shown experimentally that the controller designed for saturated induction motor provides not only higher torque per Ampere ratio but also increases power factor and reduces active power consumption hence improving the drive efficiency. Operation with slowly varying torque references has also been analysed. It is shown that the proposed controller is suitable for applications that do not demand an extremely fast dynamic response, for example for electric vehicle drives.

Starting an aircraft engine with an electrical machine has been one of the major trends for future aircraft. This paper studies the stability of a permanent-magnet machine (PMM) based aircraft starter/generator (S/G) system. Using control-to-output transfer functions, the stability analysis of this S/G system is thoroughly studied. The impact of the key parameters including the control parameters is analysed. Simulation and experimental results support the analytical result.

This paper proposes a novel solid rotor topology for an Interior Permanent Magnet (IPM) machine, adopted in this case for an aircraft starter-generator design. The key challenge in the design is to satisfy two operating conditions which are: a high torque at start and a high speed at cruise. Conventional IPM topologies which are highly capable of extended field weakening are found to be limited at high speed due to structural constraints associated with the rotor material. To adopt the IPM concept for high speed operation, it is proposed to adopt a rotor constructed from semi-magnetic stainless steel, which has a higher yield strength than laminated silicon steel. To maintain minimal stress levels and also minimize the resultant eddy current losses due to the lack of laminations, different approaches are considered and studied. Finally, to achieve a better tradeoff between the structural and electromagnetic constraints, a novel slitted approach is implemented on the rotor. The proposed rotor topology is verified using electromagnetic, static structural and dynamic structural Finite Element (FE) analyses. An experiment is performed to confirm the feasibility of the proposed rotor. It is shown that the proposed solid rotor concept for an IPM fulfils the design requirements whilst satisfying the structural, thermal and magnetic limitations.

This paper deals with the modeling and small signal stability analysis of a DC-distribution electrical power system (EPS) sourced by a permanent magnet synchronous generator (PMSG). The topology employed here is one of the main candidates for future more-electric aircraft (MEA). A detailed mathematical model is developed and comprehensive EPS modal analysis is performed. Eigenvalue sensitivity and participation factor are utilized in order to assess the effect of machine and control parameters, as well as system operating conditions, on EPS stability. Furthermore, this paper also presents comparative analysis of system models with and without the inclusion of system cabling. This crucial analysis shows that the tendencies in stability behavior can be significantly different with and without cabling. It is therefore shown that system simplification, by removal of cabling, can deliver remarkably misleading results. Time domain simulations are carried out to support the theoretical analysis. The comprehensive analysis presented in this paper provides EPS designers with an extremely useful methodology for the selection of appropriate EPS parameters at the early design stages.

The paper proposes a method of active switching harmonics current reduction in the DC-link capacitor of a two-level, three-phase, back-to-back converter. Based on the derived analytical solution for switching harmonic currents in the DC-link, it is shown that by specific control over the PWM carriers’ phase angles, the targeted harmonics of the rectifier and the inverter can be synchronized in phase such that their cancellation occurs in the DC-link capacitor. This synchronization is provided by harmonic phase feedback control. The three step procedure to implement the method is detailed in the paper. The effectiveness of the proposed approach is verified experimentally.

This paper investigates the effect of two soft magnetic materials on a high speed machine design, namely 6.5% Silicon Steel and Cobalt-Iron alloy. The effect of design parameters on the machine performance as an aircraft starter-generator is analysed. The material properties which include B-H characteristics and the losses are obtained at different frequencies under an experiment and used to predict the machine performance accurately. In the investigation presented in this paper, it is shown that machines designed with 6.5% Silicon Steel at a high core flux density has lower weight and lower losses than the Cobalt-Iron alloy designs. This is mainly due to the extra weight contributed by the copper content especially in the end-windings. Due to the high operating frequencies, the core-losses in the Cobalt-Iron machine designs are found to outweigh the copper-losses incurred in the Silicon Steel machines. It is also shown that change in stack length/number of turns has a considerable effect on the copper losses at starting, however has no significant advantage on rated efficiency which happens to be in a field-weakening operating point. It is also shown that the performance of the machine designs depend significantly on material selection and the operating point of the core. The implications of the variation of design parameters on the machine performance is discussed and provides insight into the influence of parameters that effect overall power density.

This paper proposes an improved voltage regulation method in multi-source based DC electrical power system in the more electric aircraft. The proposed approach, which can be used in terrestrial DC microgrids as well, effectively improves the load sharing accuracy under high droop gain circumstance with consideration of cable impedance. Since no extra communication line and controllers are required, it is easily implemented and also increases the system modularity and reliability. By using the proposed approach the DC transmission losses can be reduced and system stability is not deteriorated for normal and fault scenarios. In this paper optimal droop gain settings are investigated and the selection of individual droop gains as well as the proportional power sharing ratio has been described. Experimental results validate the effectiveness of the proposed method.

This paper aims to develop a functional model of symmetrical multi-pulse Auto-Transformer Rectifier Units (ATRUs) for More-Electric Aircraft (MEA) applications. The ATRU is seen as the most reliable way readily to be applied in the MEA. Interestingly, there is no model of ATRUs suitable for unbalanced or faulty conditions at the moment. This paper is aimed to fill this gap and develop functional models suitable for both balanced and unbalanced conditions. Using the fact that the DC voltage and current are strongly related to the voltage and current vectors at the AC terminals of ATRUs, a functional model has been developed for the asymmetric ATRUs. The developed functional models are validated through simulation and experiment. The efficiency of the developed model is also demonstrated by comparing with corresponding detailed switching models. The developed functional model shows significant improvement of simulation efficiency, especially under balanced conditions.

In this paper, a functional model for diode-bridge rectifiers is developed based on the dynamic phasor concept. The developed model is suitable for accelerated simulation studies of the electric power systems under normal, unbalanced and line faulty conditions. The high accuracy and efficiency of the developed model have been demonstrated by comparison against three-phase time-domain model and against the model employing synchronous space-vector representations. The experimental verification of the developed model is also reported. In addition, an error analysis shows that the error of the developed model is less than 10% at the most severe unbalanced conditions. The prime purpose of the model is for the simulation studies of more-electric aircraft power architectures at a system level; however it can be directly applied for simulation study of any other electrical power system interfacing with uncontrolled diode bridge rectifiers.

Many issues can degrade the electrical drive performance such as cross-coupling, time delay, external disturbances, and parameter variation. The Synchronous Reference Frame (SRF) PI Current Controller (CC) is the most popular control scheme for the motor drive current control due to its simplicity. However, the PI controller does not have an optimal dynamic response due to the reasonably low transient response of the integral parts. Furthermore, the tuning of the PI controller depends heavily on the machine’s parameters. Recently, alternative control schemes such as Model Predictive Control (MPC) and Active Disturbance Rejection Control (ADRC) are studied due to their dynamic performance and disturbance rejection capability, respectively. This paper presents a comparative study between the conventional PI, ADRC, and MPC control schemes applied for Permanent Magnet Synchronous Motor (PMSM) taking into consideration the operational issues of electrical drives.

Active disturbance-rejection control (ADRC) as a current control (CC) method for ac drive systems has been recently shown to have significant strengths. Its robustness to system uncertainties and its high disturbance-rejection capability render it an attractive control scheme for various mobile applications. Until now, however, all the known tuning methods available in literature are based on a number of assumptions that may lead to the degraded drive performance and even to the loss of stability. This article, thus, provides a rigorous analysis and proposes a new CC design method based on the ADRC technique. The design derives a generic closed-loop transfer function considering system delays and the dynamics of the extended state observer. Based on this analysis, a tuning method able to guarantee a set performance to avoid unstable operation is thus proposed. The effects of model uncertainties on the current loop system stability and robustness are also analyzed and reported. A tuning criterion to enhance system robustness and to improve its dynamic performance is developed and validated experimentally on a case study system.

Synchronous reference frame proportional-integral (PI) current controller (CC) is considered the most well-established solution for the current regulation in electrical drives. However, the gain selection of the PI CC is still regarded to be poorly reported, particularly in relation to the effect of the inevitable execution time taken by the controller and inverter. Mostly, tuning process of PI CC is done by trial and error or using simple rules based on pole zero cancelation and pole placement methods which ignore time delays through the controller and inverter. Hence, PI CC delivers significantly different performance compared to the expected one during the digital implementation, especially if high bandwidth or low ratio between the switching and operational frequency are required. Therefore, this paper firstly addresses and analyses the common tuning rules of PI CC which ignore the existence of time delays followed by a rigorous analysis for PI CCs’ robustness to the influence of computational and modulation delays. Based on this analysis, generic recommendations have been proposed to select the PI CCs’ gains as a function of the electrical drive switching frequency considering the delay effect. A set of simple, generic, and fast tuning rules were derived that guarantee fast dynamic performance with reasonable stability margins. Moreover, the effects of model uncertainties on these developed rules have been analyzed and reported. Comprehensive experimental results are provided to prove the key analytical results of this study and to validate the proposed design recommendations.

In this paper, a flexible switching table (FST) for direct torque control (DTC) of permanent magnet synchronous motors (PMSMs) was proposed to enhance the steady-state and dynamic performances of the drive system. First, the influence of each converter output voltage vectors on the torque and stator flux deviation rates was analyzed to assess the voltage selection strategies of the conventional STs and their impact on the DTC system’s performance. Then, a new flexible ST was proposed which uses a simple algorithm to adaptively select the appropriate voltage vector for two of its states according to the system operating condition. The effectiveness and feasibility of the proposed FST were verified through a comparative evaluation with the conventional STs using experimental results obtained from a 0.75 kW PMSM drive system.

This paper presents an overview of technology related to on-board microgrids for the More Electric Aircraft. All aircraft use an isolated system, where security of supply and power density represent the main requirements. Different distribution systems (AC and DC) and voltage levels coexist, and power converters have the central role in connecting them with high reliability and high power density. Ensuring the safety of supply with a limited redundancy is one of the targets of the system design, since it allows increasing the power density. This main challenge is often tackled with proper load management and advanced control strategies, as highlighted in this paper.

More-electric aircraft (MEA) has become a dominant trend for modern aircraft. On-board MEA, many functions, which are conventionally driven by pneumatic and hydraulic power, are replaced with electrical subsystems. Starting aircraft engines with an electrical motor instead of using pneumatic power from the auxiliary power unit (APU) is one of the major characteristics of future aircraft. This paper presents the development of a novel electric starter-generator system for aircraft applications. The paper describes the main achievements of the project within the key areas including electric machines, power electronic converters, thermal management and overall system control design. The developed prototype has been tested successfully and the test results are presented in this paper.