Wound Rotor Synchronous Machine Research Articles

A Measurement-Based Wide-Frequency Model for Aircraft Wound-Rotor Synchronous Machine

For the safety of the wound-rotor synchronous machine (WRSM) in aircraft applications, the overvoltage at the motor terminals, electromagnetic interference (EMI) performance, and bearing currents as well as the loss analysis are the core areas to be addressed. The high-frequency (HF) modeling method of the WRSM, which has a strong relationship with all these core areas, is a very critical theme. In this paper, a measurement-based wide-frequency (WF) modeling method to characterize the impedance of the WRSM is proposed to build a straightforward correlation between fundamental models and HF parasitic circuit elements. In this paper, the voltage-behind-reactance method is applied to demonstrate the rotor-angle-dependent characters in the low-frequency domain, while the vector fitting method is used to parameterize the HF branch for high-accuracy consideration. By doing this, a WF electrical model with multistage RLC units is formed, which comprehensively considers both the saliency character of the machine and frequency range. The WF model is also compatible with the circuit-based simulation. Finally, the EMI prediction orientated simulation and experimental results are implemented on a 10 kVA WRSM prototype to verify the correctness and advantages of the proposed modeling method.

Finite element analysis of a modular brushless wound rotor synchronous machine

This study presents a comparative study of different modular brushless wound rotor synchronous machines (MB-WRSM) using non-overlapping fractional slot double-layer concentrated windings. The goal of the study is to highlight the structure which offers the best fault-tolerance capability and the highest output performance. The fundamental winding factor is calculated by using the method based on voltage phasors as a significant criterion to select the preferred numbers of phases, stator slots, and poles. With the limited number of poles for a small machine (3.67 kW/7000 rpm), 15 different machines for different phase/slot/pole combinations are analysed using two- dimensional (2D) finite element method and compared according to three criteria: torque density, torque ripple, and machine efficiency. The seven-phase/seven-slot/six-pole machine is chosen with the best compromise of high torque density, small torque ripple (3.89%), and high nominal efficiency (95%). This machine is then compared with a reference design surface-mounted permanent magnet synchronous machine (SM-PMSM). The simulation results are discussed and demonstrate that the MB-WRSM presents interesting performance features, such as extended field weakening range, with overall performance closely matching that of an equivalent SM-PMSM.

Comparison between fmincon and NOMAD optimization codes to design wound rotor synchronous machines

Comparison between fmincon and NOMAD optimization codes to design wound rotor synchronous machines

Variable-speed, sub-harmonically excited BL-WRSM avoiding unbalanced radial force

Different topologies for brushless wound rotor synchronous machines (BL-WRSMs) have been proposed recently. This paper proposes a new model for the existing sub-harmonically excited BL-WRSM to eliminate the unbalanced radial force presented in the initial model. The initial and proposed models are analyzed using a two-dimensional finite element method. Furthermore, a variable-speed analysis for the BL-WRSM is conducted by altering the stator input current. Finally, a prototype of the proposed model is built and tested at the rated speed, to compare its performance with that of the conventional WRSM. Simulation and experimental results validate the proposed BL-WRSM’s operation.

Torque ripple reduction in brushless wound rotor synchronous machine by two-phase excitation winding

Torque ripple reduction in brushless wound rotor synchronous machine by two-phase excitation winding

Design and analysis of a novel hybrid-excited wound-rotor synchronous machine with high electromagnetic performance

Design and analysis of a novel hybrid-excited wound-rotor synchronous machine with high electromagnetic performance

Consequent-Pole Hybrid Brushless Wound-Rotor Synchronous Machine

Several brushless topologies for wound rotor synchronous machines (WRSMs) have been presented in recent years to replace the brushes and slip-ring assembly in conventional WRSMs [1–4]. The brushless operation of the WRSM presents these machines as an alternative to the permanent magnet synchronous machines (PMSMs) because of their low cost and competitive performance as compared to the PMSMs. However, the drawback of the brushless wound rotor synchronous machines (BL-WRSMs) is their low starting torque because of the absence of the excitation source on their rotor. Although, the BL-WRSM achieves the rated torque at the base speed but low starting torque under the base speed makes these machines less suitable for variable speed applications. A PM assisted BL-WRSM was presented in [5] to overcome the problem of the low starting torque and to provide better performance under full-load conditions. However, the presence of the PM on each pole increases the cost of the machine. Moreover, the leakage flux is increased in PM assisted machines. These issues can be resolved by the consequent pole (CP) machines [6]. In this paper, a consequent pole hybrid brushless wound rotor synchronous machine (CPH-BLWRSM) is proposed to overcome the problem of low starting torque, and to reduce the PM usage as compared to the PM assisted machines. A 2-D finite element analysis is performed to validate the proposed CPH-BL-WRSM and its performance is compared with the existing BL-WRSM and PM assisted BL-WRSM.

Design and Characterization of a Single-Phase Main Exciter for Aircraft Wound-Rotor Synchronous Starter–Generator

This paper proposes and analyzes the design philosophies of the single-phase main exciter (ME) for an aircraft wound-rotor synchronous machine and investigates its operating characteristics in both generating and starting modes. The fundamental structure and starting–generating system are discussed. The load features of single-phase ME are summarized. The ME has the characteristics of linear current amplifier and approximately constant current source the generating mode, which can be used in the wide range of working temperature. Detailed waveforms and finite-element analysis verify that excitation current $I_{\mathrm {ef}}$ is almost irrelevant to speed but in direct proportion to frequency in the starting mode. Besides, simulated data indicate that the energy transferring efficiency between ME stator and rotor can reach about 55% by the single-phase ac excitation method. Finally, the experimental verification is carried out, and the simulated and experimental data and waveforms of single-phase ME agree well with each other.

Nonlinear Estimation of Stator Currents in a Wound Rotor Synchronous Machine

Reduction of the manufacturing costs is one of the major concerns in the automotive industries. Removing the current sensors on the electric powertrain is a way to achieve this. In this paper, the current sensors of a stator of a wound rotor synchronous machine have been removed. In order to keep the control of the electric powertrain, the solution proposed here is to estimate the missing currents. To do so, a nonlinear observer based on the convergence of a Lyapunov candidate function has been developed for this application and compared to an extended Kalman filter. Since the parameters of the system may vary according to the operating point and the wear of the system, the robustness of the observers are tested with and without model errors and then validated on an experimental bench with a successful current sensorless control.

An Investigation Into the Coupling of Magnetic and Thermal Analysis for a Wound-Rotor Synchronous Machine

This paper is dealing with magnetic and thermal analysis coupling of a wound-rotor synchronous machine (WRSM) based on the equivalent circuit methods. The main objective of this work is to introduce the principles of both magnetic equivalent circuit (MEC) and thermal equivalent circuit (TEC) models, as well as the importance of their coupling. The results of nonlinear MEC are compared to 2-D finite-element analysis results obtained by the magnetic field analysis software JMAG while the results of TEC coupled with MEC are compared with the experimental thermal test results.

Optimal Design and Experimental Verification of Wound Rotor Synchronous Machine Using Subharmonic Excitation for Brushless Operation

This paper presents an optimal design of a recently introduced brushless wound-rotor synchronous machine (BL-WRSM). The BL-WRSM, with a special stator winding arrangement, utilizes a single three-phase inverter for generating an additional spatial subharmonic component in the stator magnetomotive force (MMF). This subharmonic component of the stator MMF is used for the brushless excitation of the rotor. The pole span and pole shoe height were the optimized parameters, with the goals of improving the quality of output power and reducing torque ripple. Moreover, the average torque of the machine was improved by optimizing the harmonic winding placed on the rotor. The optimized BL-WRSM was further analyzed for the flux weakening operation. Finite element analysis (FEA) was carried out to analyze the performance of the BL-WRSM. Finally, the performance of the optimal BL-WRSM model was verified through an experimental test, which demonstrated good agreement with the simulation results.

A new brushless wound rotor synchronous machine using a special stator winding arrangement

This paper proposes a new topology for a brushless wound rotor synchronous machine (BL-WRSM) using a specially designed stator winding supplied through a single three-phase inverter. In this topology, a special stator winding, which comprises of two sets of series-connected windings with an unequal number of turns, is used to generate an additional spatial sub-harmonic component in the stator magneto-motive force (MMF). This additional sub-harmonic MMF (SH-MMF) component is utilized for exciting the field winding of the BL-WRSM. The advantage of the proposed brushless topology is the use of a single inverter compared to a dual inverter used in the existing dual inverter BL-WRSM. For the rotor, there are two separate windings: (1) harmonic winding and (2) field winding. Both the harmonic and field windings are connected in parallel with each other through a rotating rectifier. The additional SH-MMF component generates a rotating air-gap magnetic field, which induces the voltage in the harmonic winding. This induced voltage is then rectified and used to supply a dc current to the field winding. A 2-D finite element analysis is performed to analyze and verify the operating principle of this new BL-WRSM.

Overview and development of variable frequency AC generators for more electric aircraft generation system

With the development of more electric aircraft (MEA), higher demands for electrical energy are put forward in generation systems. Compared to constant frequency AC (CFAC) generation systems, the constant speed drive (CSD) is eliminated and integrated starter/generator (SG) can be realized in variable frequency AC (VFAC) generation systems. In this paper, an overview of VFAC generators for safety-critical aircraft applications is presented, with a particular focus on the key features and requirements of candidate generators and the starting control strategies. Wound rotor synchronous machines (WRSMs) are typical generators used in VFAC generation systems so far. Meanwhile, hybrid excitation synchronous machines (HESMs) and cage-type induction machines are promising candidates for VFAC generation systems. The generation operation of WRSM is relatively mature, however, the SG technology of WRSM is still full of challenges. As one of the most important issues, the starting excitation methods of WRSM are summarized. An HESM-based VFAC SG system is proposed and developed in this paper. The experimental results show that the starting mode, transition mode and generating mode of the VFAC SG system are realized. The continuous progress of VFAC generation system makes great contributions to the realization of MEA.

Investigation and implementation of a new hybrid excitation synchronous machine drive system

Hybrid excitation synchronous machines (HESMs) inherit the high-torque density of permanent magnet synchronous machines and flux regulation capability of wound rotor synchronous machines. This makes HESMs attractive candidates for vehicle traction applications. To further improve torque density, an optimised HESM with magnet shunting rotor is proposed in this study. This study presents a maximum torque control strategy with zero d-axis current. Furthermore, an optimised control strategy that utilises the coordinated operation between the field current and d-axis current is proposed. The optimised control strategy exhibits advantages of low-speed high-torque, wide constant power range, and high efficiency in flux-weakening (FW) region. A 100 kW drive system based on the optimised HESM with the proposed control strategy is developed, experimentally realised, and validated. The experimental results show that the FW range is 3.5–1, and the efficiency of the drive system is >92% in most operating region, which verify the superiority and effectiveness of the proposed HESM drive system.

Modeling and analysis of a novel dual open-end stator windings wound rotor synchronous machine with dampers

This work presents a novel wound rotor synchronous machine with dampers with dual three-phase open-end stator windings. The aim of the proposed machine is to improve the power segmentation and the availability of the drive system. The mathematical model of this machine is presented in the Park reference frame. This machine is supplied by four 2-level inverters, where each inverter is dimensioned for quarter power of the machine. For comparison purposes, we use a double star synchronous machine fed by two 2-level inverters. Comparative simulation analysis using THD voltage, THD stator current, and torque undulation showed significant advantages of the proposed machine.

Detailed Excitation Control Methods for Two-Phase Brushless Exciter of the Wound-Rotor Synchronous Starter/Generator in the Starting Mode

An integrated starter/generator based on the wound-rotor synchronous machine is becoming increasingly popular in modern aircraft due to the advantages of high safety and low cost in maintenance. Constant field current for the main generator of the wound-rotor synchronous starter/generator (WRSSG) can simplify the start control scheme distinctly in the starting mode. In order to achieve constant field current for the main generator, three detailed excitation control methods for the two-phase brushless exciter of the WRSSG in the starting mode were proposed and compared in this paper. And in these excitation control methods, feedback control for the field currents of the two-phase brushless exciter and speed reference control for the excitation frequency and phase sequence were adopted. Simulation and experimental results verified the feasibility and effectiveness of these three excitation control methods.

PM Assisted, Brushless Wound Rotor Synchronous Machine

This paper presents a new permanent magnet (PM) assisted topology for a recently introduced brushless wound rotor synchronous machine (BL-WRSM). The BL-WRSM had a dual-inverter configuration for generating a composite magneto motive force (MMF) with a fundamental component and a subharmonic component. The subharmonic component of the MMF is used for brushless excitation of the rotor. In this paper, additional PMs were introduced on the rotor of the BL-WRSM, making it a hybrid BL-WRSM. We also discussed the flux weakening operation for the hybrid BL-WRSM. The hybrid BL-WRSM offered advantages for starting the machine and provided better performance under full-load conditions. The finite element method (FEM) was used to analyze the performance of the hybrid BL-WRSM, and we compared its performance with BL-WRSM. Finally, prototypes were built with and without the PM-assistance, and experiments were conducted to demonstrate their performance.

Novel Brushless Wound Rotor Synchronous Machine With Zero-Sequence Third-Harmonic Field Excitation

This paper introduces a novel topology for generating a spatial third-harmonic current component to excite the rotor field winding of a wound rotor synchronous machine to achieve brushless operation. In this topology, each of the three-phase windings on the stator is connected with a switch in parallel. In particular, two antiparallel thyristors are used to switch during positive and negative half cycles. Two windings are mounted on the rotor of the machine: 1) the harmonic winding and 2) the field winding. Zero-sequence currents are generated, when the switches are closed near zero crossing for a short time interval. Consecutive operation of the switches creates an additional spatial third-harmonic current pulsating in the stator winding. The number of poles of the stator winding and the field winding is the same (four-poles in this case) to intercept the torque generation component of the air-gap flux, whereas, the number of poles of the harmonic windings is adjusted (12-poles in this case) to intercept the harmonic component of the air-gap flux and develop voltage across the harmonic windings. Harmonic voltage is rectified through a rotating rectifier to feed dc current to the field windings. Results verify the proposed topology simulated by a 2-D finite-element method.

An Analytical Design Model for Wound Rotor Synchronous Machines

Optimization-based design of electric machinery over a large design space requires the use of computationally efficient models to predict machine behavior. In this research, an analytical design model is developed for wound rotor synchronous machines, a key technology for power generation. The model is designed to be used in a rigorous multi-objective optimization algorithm, providing the trade-off between competing mass and loss objectives. A formalized approach is presented to calculate the field distribution, as well as qd -axis model parameters, terminal quantities, loss, and developed torque from design data containing material properties, stator and rotor geometries, and winding layout. The calculated parameters include resistances, inductances, and the back-EMF of the machine. The model is verified using finite element analysis and hardware experiment.

Design and Analysis of a Novel Brushless Wound Rotor Synchronous Machine

Permanent magnet synchronous machines (PMSMs) utilize permanent magnets to generate the rotor flux needed to produce torque. They are ideal for high-accuracy fixed-speed drives. But rise in the price of rare earth magnet caused by its scarcity is a key consideration while developing such kind of machines. In this situation, wound rotor synchronous machines (WRSMs) have benefits compared to PMSMs as it does not need magnetic material and can be operated in a wide range of speeds [1]. In a WRSMs field windings are used, which is supplied with a DC current that generates the rotor flux. DC current can be applied to the rotor winding either using the brush and slip-ring structure or brushless excitation method. The brushes and slip rings have losses and maintenance issues, so they are used for small synchronous machines. For brushless excitation, additional (auxiliary) stator windings are used to excite the rotor field winding. Several patents are granted according to this excitation method [2]-[4]. The conventional method faces issues, since both the stator windings are located in the same stator core and require a large stator volume for making place for the both windings. Using a single winding in the stator to perform the brushless operation for the WRSMs is presented in [5]. But in that case concentrated windings are used to develop the higher harmonics for the excitation which will result in more losses. Thus a new idea for brushless WRSMs is proposed in which single stator winding is used to excite the rotor as well as generate the fundamental air gap harmonic for electromagnetic torque. A 2D finite element analysis (FEA) have been done to analyze and verify the proposed brushless WRSMs.