Effective turn fault mitigation by creating zero sequence current path for a triple redundant 3x3-phase PMA SynRM

Effective mitigation of excessive stator turn fault current is crucial for fault tolerant machine drives. In this paper, a simple and effective method is proposed for a triple redundant 3x3-phase permanent magnet assisted synchronous reluctance machine (PMA SynRM) by using 3-phase 4-leg inverters. The fourth leg creates a zero sequence current path when a terminal short circuit (TSC) is applied in an event of a turn fault in a 3-phase winding set. Consequently, the zero sequence flux linkages are reduced by the resultant zero sequence current. This leads to lower residual flux linkage and decreased fault current. The machine drive can therefore have larger safety margin or can be designed for improved torque density and efficiency. The proposed approach is verified by both FE simulations and experimental tests in a wide operation range. It shows the fault current is reduced by ~40% and the output torque is not affected

A turn fault mitigation strategy based on current injection technique for a triple 3-phase PMA SynRM

A turn-to-turn short circuit fault usually causes excessive fault current because of very low impedance associated with a few fault turns. It should be dealt with promptly to avoid further damages to the machine, especially for a permanent magnet (PM) machine. In order to limit the turn fault current, a novel turn fault mitigation strategy based on current injection technique is investigated for a triple redundant 3x3-phase PM synchronous reluctance machine (PMA SynRM). First, the flux linkage of the faulty phase where the fault turns are located is estimated considering the influence of PM and currents in the healthy and faulty 3-phase sets. This flux linkage, including that of the fault turns, is subsequently reduced by injecting specific currents to the faulty 3-phase set, leading to much smaller fault current. The proposed current injection method does not affect the operation of the healthy 3-phase sets which continue to produce torque. The effectiveness of the proposed method is validated by extensive finite element (FE) simulation and experimental tests on a prototype 3x3-phase fault tolerant PMA SynRM drive

Enhanced power sharing transient with droop controllers for multithree-phase synchronous electrical machines

This paper presents a droop-based distributed control strategy for multithree-phase machines that provides augmented controllability during power sharing transients. The proposed strategy is able to mitigate the mutual interactions among different sets of windings without controlling any subspace variable, also offering a modular and redundant design. On the contrary, in a centralized configuration, subspaces would be controlled using the vector space decomposition, but fault tolerance and reliability levels required by the stricter regulations and policies expected in future transportation systems would not be satisfied. The proposed method is analytically compared against the state-of-the-art power sharing technique and equivalent models and control design procedures have been derived and considered in the comparison. Uncontrolled power sharing transients and their effects on mutual couplings among isolated sets of windings have been compared against the proposed regulated ones. Experimental results on a 22-kW nine-phase multithree-phase synchronous machine rig validate the design procedures showing good agreement with the expected performances

Fractional slot concentrated winding PM synchronous motors for transport electrification applications

Moving towards electrification of transport including electric vehicles (EV), more electric aircraft (MEA), and electric ships offers a crucial way in dealing with global carbon emissions and climate change. Electric motors are a key enabling technique in these applications, but their increased use is associated with requirements of extreme power/torque density, excellent fault-tolerance, high efficiency, and good manufacturability. The main goal of this thesis is to study permanent magnet electric machine winding theory to determine the suitable electric machine winding topologies for different applications. Two separate vehicle transport applications are investigated, including an EV traction motor and a novel modular electromechanical actuator (EMA) for MEA. The study of the EV traction motor involves the investigation of methods for reducing the significant stator MMF harmonics in fractional slot concentrated winding (FSCW) electric machines, and the development of novel FSCW topologies while keeping the benefits of easy manufacturing and the non-overlapping characteristic of concentrated windings. The novel FSCW topologies can be extended to multi-phase FSCW motors. A traction motor equipped with a novel 24 slots, 14 poles FSCW topology and interior PM (IPM) rotor is developed for evaluation. The performance under normal and fault conditions is fully explored and validated with simulation and experimental results, which demonstrates the applicability and strong potential of the proposed 24 slots, 14 poles IPM motor in fault-tolerant traction motor applications. The second topic focuses on modular fault-tolerant EMAs for aircraft actuation systems which can meet a diverse range of requirements. The architecture and design considerations of the actuator system are firstly determined considering reliability, fault-tolerance, and weight. The modular EMA scheme consisting of a direct-drive rotary motor and mechanical screw is identified. A dual 3-phase 24 slots, 22 poles FSCW motor with a surface-mounted permanent magnet (SPM) rotor is developed and evaluated in terms of electromagnetics, thermal management, and fault-tolerance. Experimental results of the modular EMA motor prototypes agree well with predicted results. All this confirms the applicability and satisfactory implementation of the modular EMA motor for aircraft actuation system applications

Fractional slot concentrated winding PM synchronous motors for transport electrification applications

Moving towards electrification of transport including electric vehicles (EV), more electric aircraft (MEA), and electric ships offers a crucial way in dealing with global carbon emissions and climate change. Electric motors are a key enabling technique in these applications, but their increased use is associated with requirements of extreme power/torque density, excellent fault-tolerance, high efficiency, and good manufacturability. The main goal of this thesis is to study permanent magnet electric machine winding theory to determine the suitable electric machine winding topologies for different applications. Two separate vehicle transport applications are investigated, including an EV traction motor and a novel modular electromechanical actuator (EMA) for MEA. The study of the EV traction motor involves the investigation of methods for reducing the significant stator MMF harmonics in fractional slot concentrated winding (FSCW) electric machines, and the development of novel FSCW topologies while keeping the benefits of easy manufacturing and the non-overlapping characteristic of concentrated windings. The novel FSCW topologies can be extended to multi-phase FSCW motors. A traction motor equipped with a novel 24 slots, 14 poles FSCW topology and interior PM (IPM) rotor is developed for evaluation. The performance under normal and fault conditions is fully explored and validated with simulation and experimental results, which demonstrates the applicability and strong potential of the proposed 24 slots, 14 poles IPM motor in fault-tolerant traction motor applications. The second topic focuses on modular fault-tolerant EMAs for aircraft actuation systems which can meet a diverse range of requirements. The architecture and design considerations of the actuator system are firstly determined considering reliability, fault-tolerance, and weight. The modular EMA scheme consisting of a direct-drive rotary motor and mechanical screw is identified. A dual 3-phase 24 slots, 22 poles FSCW motor with a surface-mounted permanent magnet (SPM) rotor is developed and evaluated in terms of electromagnetics, thermal management, and fault-tolerance. Experimental results of the modular EMA motor prototypes agree well with predicted results. All this confirms the applicability and satisfactory implementation of the modular EMA motor for aircraft actuation system applications

Advanced Fault Detection Methods for Permanent Magnets Synchronous Machines

The trend in recent years of transport electrification has significantly increased the demand for reliability and availability of electric drives, particularly in those employing Permanent Magnet Synchronous Machines (PMSM), often selected due to their high efficiency and energy density. Fault detection has been identified as one of the key aspects to cover such demand. Stator winding faults are known to be the second most common type of fault, after bearing fault. An extensive literature review has shown that, although a number of methods has been proposed to address this type of fault, no tool of general application, capable of dealing effectively with fault detection under transient conditions unrelated to the fault, has been proposed up to date. This thesis has made contributions to modelling, real-time emulation and stator winding fault detection of PMSM. Fault detection has been carried out through model-based and signal-based methods with a specific aim at operation during transient conditions. Furthermore, fault classification methods already available have been implemented with features computed by proposed signal-based fault detection methods. The main conclusion drawn from this thesis is that model-based fault detection methods, particularly those based on residuals, appear to be better suited for transient conditions analysis, as opposed to signal-based fault detection methods. However, it is expected that a combination of the two (model/signal) would yield the best results

Modular Power Sharing Control for Bearingless Multi-Three Phase Permanent Magnet Synchronous Machine

This paper proposes a modular approach to the power sharing control of permanent magnet synchronous bearingless machine. The selected machine topology features a winding layout with phases distributed into non-overlapping three phase groups, a solution whose twofold aim is to increase the fault tolerance and to allow for the radial force generation. The three phase sub-windings are supplied by standard three-phase inverter, leading to a modular system architecture. A throughout explanation of the methodology used to develop the control algorithm is presented considering the torque and force control in combination with the power sharing management of the machine. Special emphasis is also placed on validating the modelling hypotheses based on a finite element characterisation of the machine electro-mechanical behaviour. The proposed control strategy is also extended to cater the possibility of one or more inverters failure, thus validating the intrinsic advantage of the redundancy obtained by the modularity of the system. An extensive experimental test campaign is finally carried out on a prototyped multi-three phase permanent magnet synchronous drive. The obtained results validate the bearingless power sharing operation in healthy and faulty scenarios, both at steady state and under extreme transient condition

Power quality improvement of electrical power systems within more electric aircraft

The application of more-electric aircraft concept will see a significant increase of electrical power demands with newly developed electrical loads. This will make it essential to extract electrical power from both high-pressure and low-pressure shafts of an aircraft engine for future aircraft. With each shaft driving one electrical generation subsystem, an advanced dual-channel power generation system can be formed. The dual-generation architecture can significantly reduce the fuel assumption of aircraft engines through power transfer between different engine shafts. In such a system, two permanent magnet synchronisation generators (PMSGs) will supply a common DC bus through their dedicated AC-DC converters. On the load side, a significant penetration of power electronics is foreseen as they are essential elements to interface load and the DC bus. With an increased number of power electronic converters, harmonics from these converters will impose significant power quality challenges to the electric grid. A capacitor is required to filter the switching harmonics in the DC bus to ensure that its voltage is within the required range. However, due to a high current rating, this capacitor will be bulky and heavy. This thesis aims to address the power quality issues for the common DC bus electrical power system architecture considering a dual-channel power generation system. To improve the power quality on the DC bus, switching harmonic component cancellation schemes are proposed for different cases. In the first case, two PMSGs are considered to supply the DC bus through AC/DC converters. In this case, the modulation scheme (either SPWM or SVPWM) of one AC-DC converter is controlled to actively cancel one specific harmonic component on the DC bus. After the first case study, the use of a bidirectional buck-boost DC-DC converter as a harmonic absorber with the proposed equal-gate-width (EGW) modulation scheme is considered. The proposed method allows for the active control of the magnitude and phase angle of some specific harmonic component and thus can be used to suppress the required harmonic component on the DC bus. Simulation and experimental results have demonstrated the high robustness and effectiveness of the proposed methods

Power quality improvement of electrical power systems within more electric aircraft

The application of more-electric aircraft concept will see a significant increase of electrical power demands with newly developed electrical loads. This will make it essential to extract electrical power from both high-pressure and low-pressure shafts of an aircraft engine for future aircraft. With each shaft driving one electrical generation subsystem, an advanced dual-channel power generation system can be formed. The dual-generation architecture can significantly reduce the fuel assumption of aircraft engines through power transfer between different engine shafts. In such a system, two permanent magnet synchronisation generators (PMSGs) will supply a common DC bus through their dedicated AC-DC converters. On the load side, a significant penetration of power electronics is foreseen as they are essential elements to interface load and the DC bus. With an increased number of power electronic converters, harmonics from these converters will impose significant power quality challenges to the electric grid. A capacitor is required to filter the switching harmonics in the DC bus to ensure that its voltage is within the required range. However, due to a high current rating, this capacitor will be bulky and heavy. This thesis aims to address the power quality issues for the common DC bus electrical power system architecture considering a dual-channel power generation system. To improve the power quality on the DC bus, switching harmonic component cancellation schemes are proposed for different cases. In the first case, two PMSGs are considered to supply the DC bus through AC/DC converters. In this case, the modulation scheme (either SPWM or SVPWM) of one AC-DC converter is controlled to actively cancel one specific harmonic component on the DC bus. After the first case study, the use of a bidirectional buck-boost DC-DC converter as a harmonic absorber with the proposed equal-gate-width (EGW) modulation scheme is considered. The proposed method allows for the active control of the magnitude and phase angle of some specific harmonic component and thus can be used to suppress the required harmonic component on the DC bus. Simulation and experimental results have demonstrated the high robustness and effectiveness of the proposed methods