Brushless Wound Rotor Synchronous Machine Research Articles

A Novel Rotor Harmonic Winding Configuration for the Brushless Wound Rotor Synchronous Machine

In the last decade, permanent magnet (PM)-free or hybrid PM machines have been extensively researched to find an alternative for high cost rare-earth PM machines. Brushless wound rotor synchronous machines (BL-WRSMs) are one of the alternatives to these PM machines. BL-WRSMs have a lower torque density compared to PM machines. In this paper, a new topology is introduced to improve the torque producing capability of the existing BL-WRSM by utilizing the vacant spaces in the rotor slots. The new topology has two harmonic windings placed on the rotor which induce separate currents. A capacitor is used between the two harmonic windings to bring the currents in phase with each other. The harmonic winding currents are fed to the rectifier which is also placed on the rotor. Due to additional harmonic winding, the overall field current fed to the rotor field winding has been increased and hence the average torque has also increased. Finite element analysis (FEA)-based simulations are performed using ANSYS Maxwell to validate the proposed topology. The results show that the average torque of the machine has been significantly increased compared to the reference model. The detailed comparison results are provided in this paper.

Sub-harmonic-based Cost-effective Brushless Wound Rotor Synchronous Machine Topology

This paper proposes a sub-harmonic-based brushless wound rotor synchronous machine (WRSM) topology. The proposed topology involves two three-phase stator windings with a different number of turns. Both windings are linked in parallel and are provided with current from a single inverter. One of these windings is a four-pole winding while the second winding is a two-pole winding. This arrangement generates a magneto-motive force (MMF) in the air-gap of the machine comprising of two components: a regular fundamental MMF and a sub-harmonic MMF. The fundamental component produces the main stator field whereas the sub-harmonic component generates a sub-harmonic field that is utilized to produce a harmonic current in a two-pole rotor harmonic winding. The induced harmonic current is rectified to inject direct current (DC) to the field winding and produce a four-pole rotor magnetic field. The four-pole rotor magnetic field when magnetically interacts with the same number of the main stator field poles producing torque. Finite element analysis (FEA) is carried out to confirm the operation and achieve the electromagnetic behavior of theproposed topology.

Novel Double Mode Dual-Stator Wound Rotor Synchronous Machine for Variable Speed Applications

This paper offers a novel dual-mode double stator wound rotor synchronous machine for variable speed applications. The proposed motor integrates the benefits of both the traditional wound rotor synchronous machine (WRSM) and brushless wound rotor synchronous machine (BL-WRSM). A constant torque can be attained in the maximum torque per ampere region by operating the proposed machine as a traditional WRSM in Mode I, and a constant power can be attained in the field-weakening region by operating it as a BL-WRSM in Mode II. Moreover, due to the dual-stator structure, the proposed machine exhibits improved performance in terms of high torque density as compared to the existing single stator BL-WRSM. By using a special stator winding arrangement to achieve the sub-harmonic component of the stator magnetomotive force, the brushless operation of the proposed machine is achieved. The additional sub-harmonic component induces a voltage in the harmonic winding placed on the rotor, which is then rectified and provided a DC current to field winding for brushless excitation. In order to validate the effectiveness of the proposed machine, a two-dimensional finite element analysis (FEA) is carried out.

Brushless Wound Rotor Synchronous Machine Based on a Consequent-Pole Rotor Structure with Better Torque Attributes

This paper presents a subharmonic-based brushless wound rotor synchronous machine (BL-WRSM) topology with permanent magnet-assisted (PMA) and consequent-pole (CP) rotor structures to achieve better torque characteristics as compared to the conventional subharmonic-based brushless WRSM. The proposed topologies use the conventional high-efficient subharmonic field excitation technique to achieve a brushless operation and a lower volume of permanent magnet (PM) to achieve better average, starting, maximum, and minimum torques and lower torque ripple. A four-pole, twenty-four-slot (4-pole/24-slot) machine with conventional, PM-assisted (PMA), and consequent-pole (CP) rotor structures are developed in a JMAG-Designer 20.1 environment to carry out two-dimensional finite element analysis (2D-FEA). The developed machines are used to validate the operation and achieve electromagnetic and electromechanical performances of the proposed subharmonic-based BL-WRSM topologies with better torque attributes.

Dual-Mode Brushless Wound Rotor Synchronous Machine for High Starting Torque

This paper proposes a dual-mode brushless wound rotor synchronous machine (DBL-WRSM) for high starting torque. The proposed DBL-WRSM consists of two modes: induction and brushless (BL)-synchronous modes. First, the induction mode operates as a wound rotor induction machine (WRIM) to achieve a high starting torque. Second, the BL-synchronous mode operates as a brushless wound rotor synchronous machine (BL-WRSM) using the subharmonic of the stator magnetomotive force (MMF) in the steady state. To realize the dual-mode topology of the proposed machine, the stator is composed of two divided armature windings and two inverters that can produce subharmonics. The rotor has five switches that convert the rotor winding configuration between the two modes. To verify the proposed topology of DBL-WRSM, finite element analysis (FEA) was performed. Through the FEA results of the transient electromagnetic torque for the voltage source, it was confirmed that the proposed DBL-WRSM not only operates as a BL-WRSM in a steady state but also has a sufficiently high starting torque even under a full-load condition.

Novel Hybrid Consequent-Pole Brushless Wound Rotor Synchronous Machine for Improving Torque Characteristics

This article introduces a hybrid consequent-pole brushless wound rotor synchronous machine (CP-BL-WRSM). The CP-BL-WRSM installs permanent magnets (PMs) on the alternative rotor poles. Compared with the conventional BL-WRSM and permanent magnet-assisted brushless WRSM (PM-BL-WRSM), the proposed machine provides advantages of high average output torque, high maximum torque, and high starting torque. In addition, the proposed CP-BL-WRSM’s torque ripple is also lower than the conventional brushless WRSM. The volume of PM in the CP-BL-WRSM machine is lower than the conventional permanent magnet synchronous machines (PMSMs) and PM-BL-WRSM. In this brushless topology, the machine uses three-phase stator windings powered by a single inverter, which provides a unique armature current to the stator windings that comprises of fundamental and third-harmonic components. The fundamental current component is used to generate the main stator field, and the third-harmonic current component is used to induce a harmonic current in the harmonic winding. A diode rectifier installed on the rotor is used to rectify the harmonic current. After the rectification, a direct current (DC) is injected into the field winding of the rotor to form a rotor magnetic field and achieve brushless operation. In order to verify the operation of the proposed CP-BL-WRSM topology and analyze its performance, 2-D finite element analysis (FEA) was used in JMAG-Designer. Finally, the performance of the proposed CP-BL-WRSM topology was compared with the conventional BL-WRSM topology and PM-BL-WRSM topology to verify its higher starting torque, higher average torque, and higher maximum torque and higher minimum torque. The proposed topology can replace the existing highly expensive PM synchronous machines (PMSMs) due to its less PM volume and conventional BL-WRSMs due to its better performance.

Novel Sub-Harmonic-Based Self-Excited Brushless Wound Rotor Synchronous Machine

This article aims to realize a self-excited wound rotor synchronous machine (WRSM) topology established while considering the subharmonic field excitation scheme. Unlike the conventional subharmonic-based brushless WRSMs that require a dual-inverter configuration, the proposed topology uses a single inverter and a dual-armature winding pattern. The employed dual-armature winding configuration involves a four-pole main armature winding (ABC) and a two-pole open winding (X). The ABC winding is supplied with a three-phase current from a single customary current source inverter (CSI), whereas the X winding carries no current due to its open winding pattern and is responsible for generating subharmonic magnetomotive force (MMF) in the air gap along with the fundamental-harmonic MMF. The fundamental-harmonic MMF is utilized to create a four-pole stator field, while the subharmonic MMF is used to induce the harmonic current in the two-pole harmonic winding of the rotor. The generated harmonic current is rectified to energize the rotor field winding and develop a four-pole rotor field. The electromagnetic interaction of the four-pole stator and rotor fields generates torque. As the proposed subharmonic-based self-excited brushless WRSM employs a single inverter for its brushless operation, this makes it cost-effective compared to the conventional dual-inverter subharmonic-based brushless WRSM topologies. The proposed self-excited brushless WRSM topology is validated through the finite-element analysis (FEA). JMAG-Designer tool is employed to carry out FEA for a four-pole, 24-slot (4p24s) machine. The quantitative relative performance evaluation of the proposed self-excited WRSM topology with the recently developed dual-inverter-controlled subharmonic-based brushless WRSM topology is presented to show its better performance in terms of average, maximum, and minimum torques and torque ripple.

Optimization, 3D-Numerical Validations and Preliminary Experimental Tests of a Wound Rotor Synchronous Machine

In this paper, a complete methodology to design a modular brushless wound rotor synchronous machine is proposed. From a schedule of conditions and a chosen structure (with 7 phases, 7 slots and 6 poles), a non-linear and non-convex optimization problem is defined and solved using NOMAD (a derivative free local optimization code): the external volume is minimized under some constraints, which are the average torque equal to 5 Nm, the torque ripple less than 5%, the efficiency greater than 94%, and the surface temperature less than 85 °C. The constraints have to be computed using 2D-finite element simulations in order to reduce the CPU-time consumption for each NOMAD iteration. Moreover, a relaxation of this optimization problem makes it possible to provide an efficient starting point for NOMAD. Thus, a good optimal design is obtained, and it is then validated by using 3D electromagnetic and thermic numerical methods. These numerical verifications show that, inside the end-winding, the leakage flux is high. This yields a lot of iron losses in this machine. Moreover, the surface and coil temperature differences between the 2D and 3D numerical approaches are discussed. Finally, the machine prototype is built following the optimal dimensions and a POKI-POKITM assembly technology. Preliminary experimental tests are carried out, and the results are devoted to the comparison of measured and predicted 3D numerical results.

Cost-Effective Scheme for a Brushless Wound Rotor Synchronous Machine

This paper proposes a new scheme for a brushless wound rotor synchronous machine (WRSM) by generating an additional, two-pole component of magneto-motive force (MMF) with a series-connected additional three-phase winding with the armature three-phase winding. Unlike existing brushless excitation schemes, which use the inverter to inject harmonic currents in the stator windings, the proposed scheme uses series-connected additional winding on the stator with the armature winding in a two-pole configuration. Consequently, as the current flows in the armature winding, it creates a fundamental rotating air gap flux to interact with the field flux. At the same time, additional rotating flux is created from the additional three-phase winding, which cannot synchronize with the field winding. This additional flux can cause the induction of a voltage in a winding with exactly the same number of poles. For this purpose, a harmonic winding is installed in the rotor along with the field winding connected through a diode bridge rectifier, in order to feed the direct current (DC) to the field winding for rotor excitation without an input current from the brush-slip-ring assembly. The 2D finite-element analysis (FEA) was performed to validate the brushless operation of the proposed machine system.

High-Efficient Brushless Wound Rotor Synchronous Machine Topology Based on Sub-Harmonic Field-Excitation Technique

This paper presents a new high-efficient three-phase brushless wound rotor synchronous machine (BL-WRSM) based on a sub-harmonic field excitation technique. In the proposed machine topology, the stator is equipped with two different three-phase windings: (1) main armature winding, and (2) additional armature winding. The main armature winding is based on a 4-pole winding configuration, whereas the additional armature winding is based on a 2-pole winding configuration. Both windings are supplied current from two different inverters, i.e., inverter-1, inverter-2, and simultaneously. Inverter-1 provides the regular input current to the main armature winding, whereas inverter-2 provides a three-phase current of low magnitude to the 2-pole additional armature winding. This generates an additional sub-harmonic component of MMF in the airgap beside the fundamental MMF. On the other side, the rotor is equipped with (1) harmonic, and (2) field windings. These windings are electrically coupled via a rectifier. The fundamental component of MMF produces the main rotating magnetic field, whereas the sub-harmonic MMF gets induced in the harmonic winding to produce harmonic current. This current is rectified to give DC to the rotor field winding to attain brushless operation. To authenticate the operation and analyze its performance, the proposed BL-WRSM topology is supported using 2-D finite element analysis (FEA) in JMAG-Designer. Later on, the performance of the proposed brushless topology is compared with the customary BL-WRSM topology to verify its high efficiency, high output torque, low torque ripple, and low unbalanced radial force on the rotor.

Dual-Mode Wound Rotor Synchronous Machine for Variable Speed Applications

This paper presents a novel dual-mode wound rotor synchronous machine (DWRSM) for variable speed applications. The proposed machine combines the advantages of both the conventional wound rotor synchronous machine (CWRSM) and the brushless wound rotor synchronous machine (BWRSM). Unlike the existing BWRSM, through the dual-mode operation of the proposed machine, constant torque is achieved in the constant torque region by operating the machine in mode-I, i.e., as a CWRSM, and constant power is achieved in the field weakening region by operating the machine in mode-II, i.e., as a BWRSM. The mode change is performed through an additional thyristor drive circuit. The airgap magnetomotive force (MMF) in both modes is derived analytically. To verify this principle, finite element analysis (FEA) and an experiment on a 1- horsepower prototype machine was performed, and key influential factors were verified. The transients in the stator currents and torque during the mode change was analyzed. The test results validated the correctness of the theory and the FEA results.

Design and analysis of a PM-assisted brushless WRSM for improving torque characteristics

This paper proposes a permanent magnet assisted brushless wound rotor synchronous machine (PMa–BL–WRSM) design. The proposed machine has the advantage of a high starting torque compared to existing BL–WRSM topologies. Additionally, the average torque increases and the torque ripple is reduced when the permanent magnet assisted machine structure is used. PMa–BL–WRSM operates on the principle of brushless excitation using zero-sequence, third-harmonic current generation in the stator windings. The third harmonic component is harnessed to induce a voltage in the harmonic winding which is mounted on the rotor. As there is no flux generated from filed winding in the starting, the starting torque of the machine is also zero. To overcome the problem, permanent magnets (PMs) are inserted in each field tooth to provide the initial source of flux on the rotor. Finite element analysis is performed with the PM–BL–WRSM, and the elicited results are compared with the basic machine structure. The proposed machine operation is verified using 2-D finite element analyses using the ANSYS Maxwell analysis tool.

Brushless wound rotor synchronous machine with third-harmonic field excitation

This manuscript discusses a novel harmonic current excitation technique for a wound rotor synchronous machine based on control of the time harmonic magneto-motive force (MMF) for brushless operation. Two inverters are used to feed the armature winding in such a way that at a time, one inverter supplies the current to armature winding. The two inverters are 180° phase-shifted. The inverter assignment is based on time-division multiplexing technique to generate continuous armature currents containing reasonable third-harmonic component beside fundamental component. This third-harmonic current component generates pulsating MMF and is induced in the rotor harmonic winding; the induced current is rectified and applied to rotor field winding to generate rotor field. The rotor field interacts with armature fundamental current component for torque generation. Finite element analysis is performed to verify the idea.

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.

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

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.

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.

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.