Gaurang Vakil

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.

Impact of Soft Magnetic Material on Design of High-Speed Permanent-Magnet Machines

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 analyzed. 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 depends 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 provide insight into the influence of parameters that effect overall power density.

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.

A high-power DC-DC converter based dual active bridge for MVDC grids on offshore wind farms

This paper presents the steady-state analysis of a high power step-up DC-DC converter based three-phase dual active bridge (3DAB) for use as a medium voltage (MV) DC-DC collector of offshore wind farms. An optimization procedure for a high-power medium frequency transformer is explained and moreover, a design of an optimal control phase shift angle is explained and verified through simulation. The comparisons with two scenarios are presented: 4MW converters for power conversion from low dc voltage (LVDC) of the wind turbine output terminal to 40kV MVDC grid of offshore wind farms. The proposed 3DAB DC-DC converter is investigated for the given scenarios in terms of losses of the semi-conductors and the magnetic part as well as the quantity of semi-conductors.

Integrated output filter inductor for permanent magnet motor drives

This paper presents a novel approach to integrate the output filter inductor in permanent magnet synchronous motor (PMSM) drive system. The integrated output filter inductor is based on utilizing the motor magnetics as a filter inductance instead of introducing a separate filter inductor. Thus, eliminating added filter inductor losses and associated weight and volume. The vector controlled model, taking modulation and switching effect in to account, has been developed using MATLAB/Simulink tool for the proposed integrated output filter inductor. The currents obtained from MATLAB/Simulink model are then injected into the Finite Element model to validate the concept. The performance of the proposed and conventional system is analyzed in terms of mean electromagnetic torque, torque ripple, motor losses, inductor losses, weight and volume.

FEA based thermal analysis of various topologies for Integrated Motor Drives (IMD)

Potential benefits of Integrated Motor Drives (IMD) include increase in power density, reliability and efficiency. These benefits are particularly valuable in Aerospace and Automotive applications. However, close physical integration of the drives and the machine may also lead to an increase in component temperature. This requires careful thermal analysis and coupled design of the IMD system. This paper reviews different integration topologies and compares them using FEA based thermal analysis. The effects of the power electronics (PE) position on the IMD system as well as thermal management concepts and cooling systems are also investigated. Thermal models of these IMDs are created using ANSYS and the temperature distributions of these models are analysed.

An analytical modeling and estimating losses of power semiconductors in a three-phase dual active bridge converter for MVDC grids

Due to the increasing installation of renewable and decentralized power sources, Medium-voltage dc (MVDC) grids has been considered for an alternative application to medium-voltage ac (MVAC) application. Three-phase dual active bridge DC-DC (3DAB) converter is proposed as an attractive topology for MVDC grids due to its high power capability, smaller filtering parts, and galvanic isolation. In this paper, a first harmonic approximation (FHA) modeling of 3DAB converter is derived. Using the FHA modeling, a symmetrical modeling of switching devices is introduced and a 4MVA system for 40kV MVDC system has been validated in terms of conduction and switching losses. Experimental implementation of a 10kVA prototype and the results are presented.

Integrated Drives for Transport - A Review of the Enabling Electronics Technology

The space and packaging constraints for various electric transport applications such as for electric and hybrid electric vehicles or mass transit systems ultimately require that electronic and mechanical subsystems become more fully integrated. This paper outlines the current state of art for the power electronic converter technologies which enables greater integration in electric drives. Investigations into the supply options, state of the art devices, switching frequency selection, filtering requirements and system modularity options are explored and future trends are discussed.

Design optimization of integrated rotational inductor for high-speed AC drive applications

In order to make an efficient and power dense overall system, a close physical and functional integration of passive components is required instead of having a separate subsystem for passives. Such power dense system is vital in aerospace and marine applications. This paper presents the design optimization of integrated rotational inductors for high speed AC drive applications. Design degrees of freedom like slot-pole combinations along with different winding configurations such as, single layer (SL), double layer (DL), concentrated winding (CW) and distributed winding (DW) are considered. In this paper, the rotational inductors are optimized for these degrees of freedom and compared with a benchmark EE core inductor in terms of total losses, weight and AC copper resistance at both fundamental frequency (1 kHz) and switching frequency (10, 15 and 20 kHz). The comparative analysis between EE core and rotational inductors has shown a significant reduction in total losses and AC copper resistance at fundamental frequency and all switching frequencies. In comparison with EE core inductor, 12 slots 2 poles rotational inductor with SL DW gives lowest total losses at fundamental frequency whereas 6 slots 2 poles rotational inductor with SL DW offers the lowest AC copper resistance at both fundamental and all switching frequencies.

Sensitivity analysis for performance and power density improvements in salient-pole synchronous generators

Objective of this paper is to provide design recommendations to improve the performance and power density of a 400kVA salient-pole synchronous generator, without exceeding the limitations due to critical parameters such as total harmonic distortion of the no-load voltage. Preliminarily, a finite-element analysis of the considered machine is carried out, aiming at validating the inherent model against experiment measurements. An in-detailed sensitivity analysis of the machines design parameters that mostly affect the performance of the platform under investigation is performed. It has been found that the position and the shape of axial ventilation ducts, as well as the stator slot shape do not affect the electromagnetic performance in a significant way and it can be highly beneficial from a thermal point of view, resulting in reduced rotor temperatures. Additionally, the shape of the salient poles and the damper winding arrangement can produce positive effects on the general performance, particularly allowing for an improved voltage THD and power density of the machine being studied in this paper.