Wound Rotor Synchronous Machine Research Articles

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.

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.

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.

Performance Evaluation of Harmonic Reduced Non-Overlap Winding Wound Rotor Synchronous Machine

The analysis and performance evaluation of a harmonic reduction strategy of a non-overlap winding wound rotor synchronous machine is conducted in this paper. The harmonic reduction strategy utilizes phase-shifts between coil currents to reduce sub- and higher-order harmonics. The design is performed on a 3 MW wound rotor synchronous machine with a 16/18 pole/slot combination. The application results in a lowered torque ripple and an increased efficiency of the designed machine. The manufacturing and testing of a 3 kW prototype to ascertain the effectiveness of the design is also presented. The practical measurements correlate successfully with the theoretical 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.

Magnetic Model Identification of Wound Rotor Synchronous Machine Using a Novel Flux Estimator

In this article, an online method is proposed to find the magnetic model of a wound rotor synchronous machine (WRSM). To identify the magnetic model, the stator flux is first estimated by considering two auxiliary variables and using a partially known model of the WRSM. Using this model, the stator flux is estimated at the dq reference frame. Then, to identify the magnetic model or in other words to find the relationship between the machine flux linkage and the machine currents, the stator flux is mapped in terms of stator and rotor excitation currents. To validate the proposed method, simulations and experimental tests are carried out on a WRSM.

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.

Current Sensorless Control for WRSM Using Model-Free Adaptive Control

Sensorless control theory is considered as one of the most important keys to reduce the cost of manufacturing and maintenance in automotive applications. This article presents a current sensorless control algorithm of a wound rotor synchronous machine using a model-free-adaptive control (MFAC). The only controlled variable in this method is the rotor speed, and no observation or estimation will be performed on the phase currents. The presented controller is also compared with a current sensorless control method that uses a Lyapunov-based observation of phase currents in the control algorithm. The developed control algorithm is first tested in simulation under several operating conditions, such as starting, tracking, parameter variation, and load step. Then, experimental tests validated the effective performance of MFAC in a current sensorless control algorithm. According to these results, the control of phase currents is guaranteed with a small error but without using any current sensors.

Analytical calculations of electromagnetic quantities for wound rotor salient-pole synchronous machines

PurposeThis paper aims to present an analytical electromagnetic model for wound rotor synchronous machines with a salient-pole rotor structure based on the two-dimensional subdomain technique.Design/methodology/approachThe machine is divided into five active sub-regions: stator slots, stator slot openings, air gap, rotor slots and rotor slot openings. For each sub-region, the governing partial differential equations are derived and solved analytically.FindingsThe magnetic flux density distributions in all active sub-regions are analytically computed and other quantities such as back-emf, inductances, electromagnetic torque and unbalanced magnetic forces are also analytically calculated. The results of the analytical model are compared to those obtained from the finite element analysis to show the accuracy of the proposed model.Originality/valueThe two-dimensional analytical model of a wound rotor salient-pole synchronous machine using the sub-domain technique is the main contribution of the research.

Data-Driven Model-Free Adaptive Current Control of a Wound Rotor Synchronous Machine Drive System

The lack of precise mathematical model of nonlinear systems, such as electric machines, brings certain limits to design a powerful controller for such systems. This article presents a model-free-adaptive-control (MFAC) scheme as a good alternative to the commonly used model-based-control (MBC) methods in order to improve the controller design limitations due to the need for system model information. In this regard, an MFAC is developed in this article for current control of a wound rotor synchronous machine (WRSM) drive system and compared with a proportional-integral (PI) controller as a well-known model-based controller. Since the controller performance can be affected by unexpected phenomena, such as model errors, parameter variations, and changes in operating point, beforehand, the robustness of developed MFAC is first tested under the mentioned conditions in the simulation area. Then, through experimental validation on a specifically designed test bench, a satisfactory performance was obtained for the MFAC scheme.

Dual-Inverter-Controlled Brushless Operation of Wound Rotor Synchronous Machines Based on an Open-Winding Pattern

In an open-winding machine, three-phase stator currents can be controlled such that the input armature currents may contain the third-harmonic current component in addition to the fundamental. Considering this attribute of open-winding patterns, a harmonic current field excitation technique for a wound rotor synchronous machine (WRSM) is proposed in this paper based on the control of time-harmonic magneto-motive force. Two inverters connected to both terminals of the stator winding are controlled so that the input armature current generates an additional third-harmonic current component. This third-harmonic component generates a vibrating magnetic field that induces a current in the specially designed rotor harmonic winding. The current is supplied as DC current to the rotor excitation winding to generate a rotor field by using a full-bridge diode rectifier in order to achieve brushless operation. The proposed dual-inverter-controlled brushless operation for a WRSM is executed in ANSYS Maxwell using 2-D finite element analysis to validate its operation and electromagnetic performance.

Analysis and Design of a PM-Assisted Wound Rotor Synchronous Machine With Reluctance Torque Enhancement

In this article, a novel structure is proposed for a wound rotor synchronous machine with a small ferrite magnet in each rotor pole. The key is to achieve a higher reluctance torque term and also acquire torque-angle approaching that would allow the field torque and reluctance torque to reach maximum values at the closed current phase angle for efficient production of the average total torque. The assisting ferrite magnet in the proposed model helps compensate the q- axis flux while keeping the d- axis flux unchanged as much as possible, for enhancing reluctance torque and power factor. Meanwhile, the assisting ferrite magnet makes an asymmetrical magnetic flux distribution to close the current phase angles between the maximum of the field torque and the reluctance torque. Moreover, the related parameters of the assisting ferrite magnet in the proposed structure were determined by optimal techniques using the Kriging method and genetic algorithm. In addition, the potential for demagnetization of the assisting magnet was analyzed and the results verified that this would not affect the motor output performance. Finally, prototypes are manufactured for the experiments to verify the principle analysis and finite element analysis results.

Macromodeling of Electric Machines From Ab Initio Models

We extract the lumped-parameter model of a wound-rotor synchronous machine from its physics-based magnetic-equivalent circuit model. Model extraction is formulated as a weighted least square optimization with nonlinear constraints in which time-domain trajectories of flux linkages, currents, and the electromagnetic torque are used as input data to obtain the parameters of the $qd0$ model of the machine. The resulting problem is non-convex and cannot be solved using standard methods. The optimization problem is, therefore, convexified using a cone programming relaxation. The solution to the relaxed problem is used as an initial point for the interior-point method, leading to a reliable framework. Accurate estimations on stator resistance, leakage and mutual inductances in stator and rotor, rotor speed, effective turns-ratio between the field and stator windings, and the number of poles are obtained. Estimated parameters are validated against measured and estimated values reported in literature, and are used to develop a behavioral $qd0$ macromodel of the machine.

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.

Cost-Effective Single-Inverter-Controlled Brushless Technique for Wound Rotor Synchronous Machines

This paper proposes a cost-effective brushless technique for wound rotor synchronous machines (WRSMs). The proposed technique involves a traditional current-controlled voltage source inverter that utilizes a simple hysteresis-controller-based current control scheme and supplies three-phase currents to the armature winding of the machine. The supplied armature currents inherently contain fundamental-harmonic and third-harmonic current components. These unique armature current waveforms were previously realized by using dual-inverter-controlled schemes achieved with and without thyristor switches to develop brushless WRSM topologies. The fundamental-harmonic current component is applied to develop the main stator field, whereas the third-harmonic component is employed to realize the harmonic magnetomotive force, which induces a back electromotive force (EMF) in the harmonic winding located at the rotor periphery. The induced harmonic EMF is rectified to deliver a DC current to the rotor field winding through a full-bridge diode rectifier to achieve brushless operation. The proposed cost-effective brushless technique for WRSMs is validated using 2-D finite element analysis employing JMAG-Designer 19.1 to investigate the electromagnetic and electromechanical behaviors of the machine. Furthermore, the proposed technique is employed in machine topologies with different pole/slot combinations for the armature winding to achieve better performance.

Analysis of a Brushless Wound Rotor Synchronous Machine Employing a Stator Harmonic Winding

This study proposes a new topology for brushless operation of a wound rotor synchronous machine (WRSM) employing a stator harmonic winding. It is based on generating an additional six-pole magneto-motive force component without the use of an inverter. In this topology, six thyristor switches are used to create harmonic currents for brushless operation of the machine. The usage of stator harmonic winding has the advantage of configuring the winding for six poles or any other combination based on the output requirement. In the proposed topology, a six-pole winding arrangement is used to generate a six-pole air-gap flux component aimed at rotor excitation for brushless operation. On the rotor side, two windings, namely rotor harmonic winding (to intercept the air-gap harmonic flux) and field winding, along with a diode rectifier are mounted. 2-D finite element analyses and experiments were carried out to analyze the brushless operation of the WRSM.

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.

Novel Rotary Transformer Topology With Improved Power Transfer Capability for High-Speed Applications

This article proposes a new rotary transformer topology enabling reduction of leakage inductances and significant improvement of power transfer capability compared to traditional topologies thanks to its interleaved windings and resonant compensation circuits. The proposed rotary transformer features a nonferrite rotating part made of lightweight strong nonconductive and nonmagnetic composite material and a large air gap, allowing safe operation at high rotational speeds. Hence, this novel rotary transformer can enable the adoption of wound rotor synchronous machines for electric or hybrid vehicle traction. The performance of the proposed new topology was evaluated and compared to the conventional one. Significant performance improvement was confirmed. A 10-kW proof of concept prototypes was built, and the test has validated the power transfer capability with 95.9% efficiency.

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.