Wound Field Synchronous Machine Research Articles

Sensorless Control of Wound Field Synchronous Machine Drive Using Current Source-Based Modular Multilevel Converter

This paper proposes a wound field synchronous machine (WFSM) drive using a double star chopper cell (DSCC) based modular multilevel converter (MMC) for high power medium voltage variable speed applications. A controlled current source delivers power to this DSCC-MMC. This current source is derived using the field winding of WFSM and a 12-pulse full-controlled thyristor rectifier. The 12-pulse rectifier draws power from a three-phase grid and delivers power to the field winding and the DSCC-MMC. Thus, the field current of WFSM becomes the input dc current of the DSCC-MMC, and no separate power supply is required for the field winding of WFSM. The input current to the DSCC-MMC is kept constant at all operating speeds of the WFSM for a given value of torque to keep peak-peak voltage ripple constant across the submodule capacitor of the MMC. The field current is varied proportionately with the average torque to avoid the saturation of the machine at light load torque. This variation of field current is essential for the successful operation of DSCC-MMC. The small current ripple in the field current, caused by the 12-pulse thyristor rectifier, is utilized to extract the rotor speed information for sensorless operation of vector-controlled WFSM drive. Simulation results are presented in this paper to verify the proposed configuration and their control strategy at medium voltage. A hardware prototype has also been built in the laboratory to verify the same results experimentally at low voltage and low power.

Analysis of Efficiency Maps of Synchronous Machines

In this contribution the efficiency maps of synchronous machines are analyzed. The tool developed to draw these efficiency maps allows considering the synchronous machines electromagnetic parameters and related losses. It will be exploited to analyze the effects of the different parameters on the efficiency maps. The developed tool is based on the synchronous machine’s electrical circuit model in the Park’s referential frame. The adopted modeling approach allows considering all types of classical synchronous machines: wound field synchronous machines (WFSM), permanent magnet synchronous machines (PMSM), hybrid excited synchronous machines (HESM) and synchronous reluctance machines (SRM). It can even indirectly consider the effect of magnetic saturation. These analyses will help identify parameters sets allowing optimizing the energy efficiency of synchronous machines for a given application like electrical traction. Particularly, the effect of saliency ratio will be considered and studied.

Novel Dual Inverter Sub-Harmonic Synchronous Machines

Sub-harmonic synchronous machines are a relatively new bread of brushless wound field synchronous machines considered alternatives to many electric machines in transportation electrification applications. This paper presents two dual inverter sub-harmonic synchronous machines having unique two-layer and three-layer stator winding topologies. The two inverters provide the stator windings with two sets of balanced three-phase currents. These two and three-layer windings are arranged in such a way that they can generate both fundamental and sub-harmonic magnetomotive force. Furthermore, the fundamental MMF component of this machine is four times the sub-harmonic MMF component used for the brushless operation. In contrast, the sub-harmonic magnetomotive force is used for field excitation, which leads to brushless operation. Two 8-pole, 48-slot, 2-inverter, 2-layer and 3-layer sub-harmonic machines are designed to validate the concept through a 2-D finite element analysis of these new topologies, showing a better overall torque profile and performance as compared with the other sub-harmonic and brushless wound field synchronous machines.

Detection of Rotor Field Winding, Damper Bar, and Eccentricity Faults in Salient Pole Synchronous Machines With the Pole Drop Test

The pole drop test is the most widely applied means of detecting shorted turns in the rotor field winding of salient pole wound field synchronous machines (WFSM). It is a simple off-line test that relies on detecting the asymmetry between the voltage drop in the windings of each pole with ac voltage applied to the field winding terminals. Although it can provide sensitive detection of shorted field turns, it is also influenced by asymmetries in the motor produced by defects or imperfections in the rotor poles or damper bars. In this work, the feasibility of using the pole drop test for detecting damper bar and eccentricity faults in addition to shorted field windings is investigated for the first time. The change in the impedance of each pole under the fault conditions is analyzed from the electrical equivalent circuit and finite element (FE) simulation. Based on the analysis, it is shown that the 3 faults can be detected and classified from the impedance or voltage distribution with the pole drop test. Experimental tests performed on 4 pole, 30 kVA and 6 pole, 5.5 kVA salient pole WFSMs confirm that the 3 faults can be identified as claimed.

Input Current Source-Based Modular Multilevel Converter for Wound Field Synchronous Machine Drive With Improved Low-Speed Operation

This article proposes a new configuration of modular multilevel converter (MMC)-based wound field synchronous machine drive for high power applications. In this configuration, the MMC incorporates the field winding and delivers power to the three-phase stator windings of the synchronous machine. There is no need for a separate dc power supply for the field winding of the synchronous machine. The proposed control strategy of this drive ensures that the peak–peak ripple voltage of the submodule capacitor does not depend on the operating frequency of the drive. Thus, the problem of high peak–peak ripple voltage of the submodule capacitor at a low frequency of the drive is solved without overloading the machine and the MMC. The article analyses the operation of the drive and proposes a suitable control strategy for this drive. The operation of this drive has been verified using simulation in MATLAB/Simulink platform and a scaled-down proto-model developed in the laboratory.

Exciterless Wound-Field Medium-Power Synchronous Machines: Their History and Future

The excitation system (ES) of the wound-field synchronous machine (WFSM) has remained largely unchanged over the past 50 years. Nonetheless, there has been significant research into exciterless solutions, which, through the integration of the ES with the main machine, aim to offer improved power density, simplified manufacture, and better cooling opportunities.

A Novel Field Current Estimation Method for Brushless Wound-Field Synchronous Machine

Compared with other electric machines, wound-field synchronous machines (WFSMs) have the advantage of having three control variables (stator <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> -axis currents and rotor current). Determining the optimum combination of field and armature currents is necessary for ensuring the high-performance control of the WFSM. Two methods are usually employed to supply the field winding of the WFSM. The first one uses brushes and slip rings, while the second one uses a brushless excitation system. Concerning the WFSM with a brushless excitation system, a dc field current is provided by a rotating diode bridge rectifier fed by an exciter machine. Therefore, direct measurement of the field current is not possible. As a solution, field current needs to be accurately estimated. Previously, field current estimation methods proposed in the literature have been based on modeling the brushless exciter machine and the rotating rectifier. Using the brushless exciter machine model, these methods estimate electric quantities of the exciter rotor (currents and voltages); then, through the rotating rectifier model, the rectified field current is estimated. Accordingly, any inaccuracy in the models leads to estimation errors. The effectiveness of the techniques relying on the brushless excitation system model is not clearly justified, especially because the nonlinearity of the brushless system has been intensified by the existence of the rotating uncontrolled diode bridge rectifier. This article proposes an accurate online field current estimation method for WFSMs without the need neither to estimate exciter rotor voltages or currents nor to use a rotating rectifier model. The accuracy and effectiveness of the proposed field current estimation method are demonstrated by experimental validation tests.

Double Layer Capacitive Power and Heat Transfer in Rotating Machinery

Doubly fed induction machines, wound field synchronous machines and dc homopolar machines all require a brushed slip ring connection to the rotor conductors. This connection inherently limits the performance and/or lifespan of these machines. Noncontact methods, such as brushless exciters and wireless power transfer, have been used to support some of these machine types, but they can be physically large and/or overly reliant on power electronics. Additionally, these methods do not support the cooling of the rotor conductors since their function is purely electrical. This article introduces a rotating electric double layer capacitor concept, or supercapacitor, to form a noncontact, slip-ring-like, ac electrical connection between a stator and rotor that simultaneously provides a cooling platform. An experimental proof-of-concept consists of concentric stainless-steel sleeves separated by a ceramic bearing to facilitate relative rotary motion but maintain constant facing area and gap distance. Electrolyte floods the space between the sleeves to form double layer capacitances and can also serve as a heat transfer mechanism. The sleeves were tested as bare metal and with an activated carbon coating to enhance capacitance further. Measurements demonstrate coupling capacitances up to Farad levels with three to six orders of magnitude improvement in A/Hz over rotary air capacitors, enabling low frequency operation.

Two-Level Surrogate-Assisted Transient Parameters Design Optimization of a Wound-Field Synchronous Machine

The rapid development of ultra-high voltage direct current transmission systems has placed greater demands on the design optimization of transient parameters for large wound-field synchronous machines (WFSMs) in power systems, such as large synchronous condenser for dynamic reactive power compensation. This paper proposes a novel two-level surrogate-assisted multi-objective optimization method for WFSMs that can optimize transient parameters including per-unit reactance and time constants rapidly and accurately. To facilitate the manufacture of a prototype for verification, the proposed method is applied to the optimization of a WFSM for scale-down generator application. This method is employed to deal with the excessive number of design parameters, issues of multi-objective evaluation and strong coupling between objectives that either result in inaccuracy or become time-consuming by using conventional methods. To generate the training set for the surrogate model efficiently by finite element analysis, an improved arbitrary rotor position standstill time response (SSTR) method is employed to identify all transient parameters simultaneously in a single test, while Latin hypercube design is used to capture data features. The optimal WFSM designed by using the proposed method is prototyped and measured. It confirms that the proposed method can achieve high validity and high optimization efficiency simultaneously.

Analysis of Excitation Winding Induced EMF in Non-Overlapped Stator Wound Field Synchronous Machines

Different from the induced electromotive force (EMF) in armature winding, the induced EMF in excitation winding is detrimental to the performance of wound field synchronous machines by causing unstable excitation field and thus extra torque pulsation and losses. Moreover, it also imposes challenges to machine control, particularly for high-speed operation. This article investigates the induced EMF in the excitation winding of 3-phase non-overlapped stator wound field synchronous machines (SWFSMs). It has revealed that the amplitude of the excitation winding induced EMF is largely dependent on the slot-pole combination. Therefore, with suitable slot-pole combinations, the induced EMF issue will be significantly alleviated by eliminating low-order induced EMF harmonics. Although the excitation winding induced EMF can also be reduced by passive techniques, e.g., optimization and shaping of rotor pole arc, the average torque will be greatly degraded as well. Finally, the finite element predictions are validated by measurements on two prototyped non-overlapped SWFSMs.

Hybrid Excited Synchronous Machines

Hybrid excited synchronous machines (HESMs) combine permanent-magnet (PM) excitation and wound field (WF) excitation. The goal of hybrid excitation is to combine the advantages of PM excited machines and WF synchronous machines. HESM have been identified as one of the emerging technologies for modern energy conversion systems. They have been the subject of many review articles. The principle of hybrid excitation allows solving many drawbacks related to PM electric machines operation: flux weakening, energy efficiency, and PMs price fluctuation. It helps to introduce an additional degree of freedom in the design of synchronous machines, and allows therefore an easier adaptation of PM synchronous machines to a wider applications scope. To this additional degree corresponds the possibility of adjusting the contribution of the two magnetic field sources: PM and WF. The use of this technology for electric traction has been the subject of many scientific and technical contributions. In this contribution, the emphasis will be put on the use of these machines as generators in transportation applications and renewable energy applications. The design and operation of three particular structures will be presented. Two of them have been designed as generators for transportation applications, and the third one has been designed as generator for renewable energy conversion. All of them are flux switching hybrid excited synchronous machines (FSHESM).

A Novel Multi-Excitation-Tooth Nonoverlapping Stator Wound Field Synchronous Machine With Salient Rotor

In this paper, based on the conventional nonoverlapping stator wound field synchronous (N-SWFS) machine, a novel multi-excitation-tooth N-SWFS (MN-SWFS) machine is firstly proposed by changing winding configurations and the excitation-teeth shape. The electromagnetic performance of four optimized MN-SWFS machines sharing the same 12-stator-teeth but different rotor-teeth numbers, namely 12/10, 12/11, 12/13, and 12/14, is compared by finite element analysis (FEA). The corresponding simulation results show that 12/10 and 12/14 are the optimal stator-teeth/rotor-teeth combinations due to much smaller back electromotive force (back-EMF) THD and torque ripple (<i>T_rip</i>). Finally, a series of comparative studies are carried out on the proposed MN-SWFS machines and the conventional N-SWFS machines. The comparative results validate that the proposed 12/10 and 12/14 MN-SWFS machines exhibit better electromagnetic performance than the conventional 12/11 and 12/13 N-SWFS machines, such as higher fundamental back-EMF amplitude and greater torque output capability, though their cogging torque (<i>T_cog</i>) and torque ripple are slightly higher, and the torque anti-saturation ability is slightly weaker.

Design of an asymmetric rotor pole for wound field synchronous machines

This study proposes a novel asymmetric rotor pole design for wound field synchronous machines (WFSMs), which can achieve high saliency ratio and also low torque ripple. The key point is the optimal design of the asymmetric rotor pole with the inverse-cosine-shaped (ICS) plus reverse 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic shaping. The asymmetric rotor pole can help to improve the average output torque by enhancing the saliency ratio. The reverse 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic shaping on the rotor pole surface is mainly used to reduce the torque ripple. To certify the effectivity of the proposed design, three-phase 54-slot / 6-pole 4.7kW WFSMs with uniform air gap and with non-uniform air gap shaped by the ICS plus optimum reverse 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic are utilized as the basic model and referenced model for comparison. For the referenced model, the optimum amplitude of reverse 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic is preferred as 1/6. Finally, all electromagnetic characteristics of the investigated machines are predicted by the finite-element method (FEM). The highest saliency ratio and comparatively low torque ripple have been verified.

Spiral vector modeling of brushless doubly-fed induction machines with short-circuited rotor windings

A unified spiral vector model is presented that can be used to assist the finite element method-based performance analysis of brushless doubly-fed induction machines with various short-circuited rotor windings. Specifically, magnet-free brushless doubly-fed induction machines working in doubly-fed or singly-fed synchronous mode are investigated. A dynamic model in spiral vector notation is developed, based on which the torque-angle and power-angle characteristics are derived. It is shown that the investigated brushless machines are equivalent to a traditional non-salient-pole synchronous machine with brushes. By introducing a conversion factor, they can also be analyzed with methods similar to the conventional phasor theory. A comparison is made between the brushless doubly-fed induction machine and non-salient-pole wound-field synchronous machine with brushes, revealing that the performance of the brushless machine degrades faster when the laminated core is saturated. A scaled-down prototype is tested to validate the effectiveness of the theoretical analysis.

High-Harmonic Injection-Based Brushless Wound Field Synchronous Machine Topology

This paper discusses the design and analysis of a high-harmonic injection-based field excitation scheme for the brushless operation of wound field synchronous machines (WFSMs) in order to achieve a higher efficiency. The proposed scheme involves two inverters. One of these inverters provides the three-phase fundamental-harmonic current to the armature winding, whereas the second inverter injects the single-phase high-harmonic i.e., 6th harmonic current in this case, to the neutral-point of the Y-connected armature winding. The injection of the high-harmonic current in the armature winding develops the high-harmonic magnetomotive force (MMF) in the air gap of the machine beside the fundamental. The high-harmonic MMF induces the harmonic current in the excitation winding of the rotor, whereas the fundamental MMF develops the main armature field. The harmonic current is rectified to inject the direct current (DC) into the main rotor field winding. The main armature and rotor fields, when interacting with each other, produce torque. Finite element analysis (FEA) is carried out in order to develop a 4-pole 24-slot machine and investigate it using a 6th harmonic current injection for the rotor field excitation to both attain a brushless operation and analyze its electromagnetic performance. Later on, the performance of the proposed topology is compared with the typical brushless WFSM topology employing the 3rd harmonic current injection-based field excitation scheme.

Magnetic Flux Analysis for the Condition Monitoring of Electric Machines: A Review

Magnetic flux analysis is a condition monitoring technique that is drawing the interest of many researchers and motor manufacturers. The great enhancements and reduction in the costs and dimensions of the required sensors, the development of advanced signal processing techniques that are suitable for flux data analysis, along with other inherent advantages provided by this technology, are relevant aspects that have allowed the proliferation of flux-based techniques. This article reviews the most recent scientific contributions related to the development and application of flux-based methods for the monitoring of rotating electric machines. Particularly, aspects related to the main sensors used to acquire magnetic flux signals as well as the leading signal processing and classification techniques are commented on. The discussion is focused on the diagnosis of different types of faults in the most common rotating electric machines used in industry, namely: squirrel cage induction machines, wound rotor induction machines, permanent magnet machines, and wound field synchronous machines. A critical insight of the techniques developed in the area is provided and several open challenges are also discussed.

Utilization of reluctance torque for improvement of the starting and average torques of a brushless wound field synchronous machine

In this paper, the reluctance torque is utilized for improving the starting and average torques of a conventional brushless wound field synchronous machine (BL-WFSM). The conventional BL-WFSMs have an inherent issue of zero-starting torque. The existing BL topologies use expensive rare-earth permanent magnets (RE-PMs) to improve the starting torque; however, the marker price of RE-PMs fluctuates. Therefore, this paper proposes the use of the reluctance torque for improving the starting and average torques of BL-WFSMs. The winding topology and machine layout are adopted, from recently published work. The suggested approach increases the reluctance effect in BL-WFSM by optimizing the rotor shape. The reluctance effect is optimized, to improve the starting and average torques. The Kriging method and a genetic algorithm are used for the rotor optimization. A two-dimensional finite element analysis confirms the improved starting and average torques based on the increase in the reluctance torque.

Mathematical Model Approach for AC and DC Regulators Excitation Systems (ES)

Balancing equations for excitation system is very basic and fundamental concept and in some cases it becomes more difficult so that a mathematical treatment is needed in order to make it easy for AC and DC Regulators Excitation Systems (ES). This research paper mainly focuses on an excellent application of The power generating units and higher power motors are majority included by wound field synchronous machines because of it has flexible field excitation, flux intrinsic weakening capacity and high efficiency. It can be also used in low to medium power range for high end solutions in a wide range. This paper is analyzing a study of modern methods and technologies of excitation system for AC and DC regulators.

Belt-Driven Integrated Starter and Generator Using Planetary Gears for Micro Hybrid Electric Vehicles

This paper presents a 12 V mechanical torque converting belt-driven integrated starter and generator (BSG) system without a DC-DC converter. A micro hybrid electric vehicle (micro HEV) typically uses a 12 V battery with a 12/48 V bidirectional DC-DC converter to satisfy its high starting torque and wide operating speed for generating the required power. In contrast, the proposed BSG consists of a wound field synchronous machine (WFSM), planetary gears, and a belt-type pulley, which does not require an additional bidirectional DC-DC converter. Owing to the mechanical torque converter, the proposed BSG system produces a high starting torque in starter-mode with a 12:1 gear ratio, and it operates in generator-mode with a 1:2 gear ratio to satisfy the required target specifications. To verify that the proposed BSG system meets the required target design specifications, simulations using MATLAB/Simulink 2018b and ANSYS electromagnetic 19.0 were performed. Additionally, the experimental results verify that this proposed BSG meets the required starter and generator modes specifications. Based on an analysis of the cost and vehicle environment conditions, the proposed BSG provides an efficient solution to the high cost issue incurred by a micro-HEV that requires a DC-DC converter system.

Simplified Brushless Wound Field Synchronous Machine Topology Based on a Three-Phase Rectifier

This paper proposes a novel simplified brushless wound field synchronous machine (BL-WFSM) topology based on an uncontrolled three-phase rectifier. The output of the rectifier is injected into the common point of the star-connected three-phase armature winding. This arrangement develops an armature MMF consisting of two components: the fundamental MMF, which is rotating in nature, and the harmonic pulsating magnetic field, which induces the harmonic current in the specially designed harmonic winding of the rotor. The induced harmonic current is rectified through the full-bridge rectifier, which excites the main rotor field to achieve brushless operation and produce torque while interacting with the main fundamental rotating field of the armature. The proposed brushless topology is simple as it involves a single three-phase rectifier which does not require any complicated control strategy. Furthermore, this topology is a cost-effective solution as compared to the conventional brushless WFSM topologies since it does not require any additional hardware component except for a typical rectifier. In addition, the performance of the proposed brushless topology is better than the existing three-phase rectifier-based brushless scheme in terms of efficiency, output torque, and torque ripple. The proposed simplified BL-WFSM topology is validated through 2-D finite element analysis (FEA) using JMAG-Designer 19.1 to obtain the output torque of the machine.