Puvan Arumugam

Modeling of Different Winding Configurations for Fault-Tolerant Permanent Magnet Machines to Restrain Interturn Short-Circuit Current

This paper describes an analytical model to evaluate the short-circuit (SC) current resulting from an interturn fault by computing the self and mutual inductances under SC fault condition. Two different concentrated winding configurations, i.e., horizontally and vertically placed conductors in the slot of a fault-tolerant permanent magnet synchronous machine are considered. By computing the associated slot-leakage and air-gap fluxes, the self inductance of both healthy and faulty windings as well as the mutual inductance between them, the SC current can be determined for any position and number of shorted turns. The proposed model is verified with finite-element analysis and validated experimentally. It will be shown that the magnitude of an interturn SC current depends on both the number of shorted turns and their position in the slot. The measured SC inductance shows that a new proposed concentrated vertical winding configuration can inherently limit the SC current and reduce its dependence on the position within the slot.

Estimation of Eddy Current Loss in Semi-Closed Slot Vertical Conductor Permanent Magnet Synchronous Machines Considering Eddy Current Reaction Effect

This paper presents an analytical methodology based on subdomain field model to calculate eddy current loss in vertical conductor windings (VCWs) of surface mounted, radial flux, permanent magnet (PM) machines considering the current penetration effect. The proposed model can be used with any slot-pole combination including fractional slot machines having VCW. Initially, the model solves the two-dimensional problem based on the Laplaces and Poissons equations using the separation of variables technique for each of the subdomains: PM, airgap, slot opening, and slot. Then, based on that obtained solution, the eddy current reaction field in the slot is calculated by solving complex Helmholtzs equation. The validity and accuracy of the model is verified using finite-element (FE) analysis. The limitations of analytical method are discussed.

Comparative design analysis of Permanent Magnet rotor topologies for an aircraft starter-generator

This paper presents a comparative design study on Permanent Magnet (PM) rotor topologies for high speed aircraft starter-generators. The application requirements associated with the aircraft starter and generator operation is highlighted. Different rotor design concepts are investigated whilst keeping both the stator and the rotor diameter consistent. In addition, the core material, the electrical and magnetic constraints and the thermal and structural limitations are also kept consistent as the basis for comparison of different rotor topologies in this study. The performance of different optimal rotor designs is evaluated with Finite Element (FE) simulations and the results are presented in this paper. A Surface mounted PM (SPM) machine and a Spoke type PM machine designs are manufactured to demonstrate its ability to produce the required performance.

Analytical modeling of a vertically distributed winding configuration for Fault Tolerant Permanent Magnet Machines to suppress inter-turn short circuit current limiting

This paper presents an analytical model to evaluate the inter-turn short-circuit current in a Fault Tolerant Permanent Magnet Synchronous Machine (FT-PMSM) for different winding configurations. By evaluating slot-leakage and air-gap fluxes, the inductance of both healthy and faulty parts of the phase winding, as well as the mutual inductance between them, can be determined for any position and number of the shorted turns. Using these inductances, the short-circuit current is determined. The proposed model is verified with finite-element analysis and validated experimentally. It will be shown that the magnitude of an inter-turn short-circuit current depends on both the number of shorted turns and their position in the slot. A new concentrated winding configuration with vertical plate conductors in the slot is proposed. The measured short-circuit inductance shows that this winding can inherently limit the short-circuit current and reduce its dependence on the position within the slot.

High-Speed Solid Rotor Permanent Magnet Machines: Concept and Design

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 that are a high torque at start and a high speed at cruise. Conventional IPM topologies that 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 semimagnetic 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 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 while satisfying the structural, thermal, and magnetic limitations.

Impact of Slot/Pole Combination on Inter-Turn Short-Circuit Current in Fault-Tolerant Permanent Magnet Machines

This paper investigates the influence of the slot/pole (S/P) combination on inter-turn short-circuit (SC) current in fault-tolerant permanent magnet (FT-PM) machines. A 2-D sub-domain field computational model with multi-objective genetic algorithm is used for the design and performance prediction of the considered FT-PM machines. The electromagnetic losses of machines, including iron, magnet, and winding losses are systematically computed using analytical tools. During the postprocessing stage, a 1-D analysis is employed for turn-turn fault analysis. The method calculates self- and mutual inductances of both the faulty and healthy turns under an SC fault condition with respect to the fault locations, and thus SC fault current, considering its location. Eight FT-PM machines with different S/P combinations are analyzed. Both the performance of the machine during normal operation and induced currents during a turn-turn SC fault are investigated. To evaluate the thermal impact of each S/P combination under an inter-turn fault condition, a thermal analysis is performed using finite element computation. It is shown that low-rotor-pole-number machines have a better fault tolerance capability, while high-rotor-pole-number machines are lighter and provide higher efficiency. Results show that the influence of the S/P selection on inter-turn fault SC current needs to be considered during the design process to balance the efficiency and power density against fault-tolerant criteria of the application at hand.

Winding concepts for ultra reliable electrical machines

This paper investigates two winding concepts for Permanent Magnet (PM) machines used for more electric aircraft systems where reliability is a concern. Analysis is carried out using two different surface mounted PM machines designed for low and high speed applications: a 12 slot, 10 pole machine with concentrated windings for rotorcraft swashplate actuation and a 36-slot 6-pole machine with distributed winding arrangement for an aircraft starter-generator. The impact of the winding arrangement for the low speed machine is investigated with a focus on turn-turn Short-Circuit (SC) faults. Implications of the SC fault and methods to restrain the resulting SC current are discussed. A prognostics method for potential turn-turn SC faults for the high speed application is then investigated. It is shown that potential winding faults can be detected at an early stage of fault inception and thus measures can be taken to limit propagation.

Selection of slot-pole combination of permanent magnet machines for aircraft actuation

This paper investigates the influence of the slot/pole (S/P) combination on inter-turn short circuit (SC) current in fault tolerant permanent magnet (FT-PM) machines. Eight different S/P combinations are studied. For the investigation, methods based both on 1D and 2D analytical models were adopted. The 2D analytical model is used in combination with genetic algorithm (GA) optimisation to design the FT-PM machine, then a 1D analysis is used to estimate the SC current. It is shown that S/P combination has a significant influence on inter-turn SC fault current and needs to be considered during the design to balance the performance and fault tolerant criteria of the application.

Solid rotor interior permanent magnet machines for high speed applications

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.