Electrically Excited Synchronous Machine Research Articles

Sensorless Control of Electrically Excited Synchronous Machines Considering Magnetic Saturation and Flux Linkage Dynamics for Automotive Applications

For electrically excited synchronous machines (EESMs) used in automotive applications, the flux linkages are non-linear and the magnetic saturation plays an important role. The coupling between d-axis and exciter axis in EESMs introduces a significant fluctuation of the flux linkages due to current changes. To cope with these problems, a novel observer incorporating flux linkage saturation and dynamics caused by the coupling is proposed. The flux is not regarded as linear, but the absolute and differential inductances are used in the observer. Moreover, the current dynamics induced flux variations are compensated for. As the system is nonlinear and time-varying, Lyapunov's method is used to prove the stability of the system and to derive a speed-adaptive algorithm. The experimental results on an EESM test bench confirm the effectiveness of the proposed method.

Model Validation of Synchronous Motors With a New Standstill Measurement Technique

Permanent magnet synchronous machines (PMSM), synchronous reluctance machines (SynRM), and electrically excited synchronous machines (EESM) are widely used in the industry and transportation sectors. Their rotors are often equipped with conducting parts like permanent magnets, thick rotor laminations, damper windings, or a conducting sleeve, or they even have a solid rotor core. Such conducting elements do not allow applying standard AC supply techniques for inductance measurements because of the alternating flux induced by eddy currents. We propose a new technique for inductance measurement at a standstill with a quasi-static voltage supply, which mitigates the eddy current phenomenon. The inductance is measured at several rotor positions over a complete electrical cycle, which allows to proceed with a harmonic spectrum analysis of the inductance variation. With this information, it is possible to estimate motor performance characteristics, such as optimum torque, voltage control, power factor, and torque ripple. The new technique is experimentally validated on a 12 kW axially laminated anisotropic solid-rotor high-speed SynRM. In principle, the method also suits PMSMs, EESMs, and other synchronous machines (not verified in this paper). Experimental validation with a solid-rotor SynRM shows a good correspondence with the simulation. Furthermore, the torque computed using the measured inductance is very similar to the experimental one confirming the effectiveness of the method.

Modelling of the Electrically Excited Synchronous Machine with the Rotary Transformer Design Influence

An electrically excited synchronous machine (EESM) is a promising alternative to the permanent magnets synchronous machines being used in the automotive industry. However, the main disadvantage of the EESM with the conventional excitation system with brushes is the presence of slip rings on the shaft, which need regular maintenance. A promising alternative to the conventional excitation system of the EESM is a wireless power transfer (WPT) system. In this paper, we focused on WPT excitation system based on the rotary transformers. First, the model of the EESM in the d-q reference frame with vector control system has been built (based on the parameters of the real machine) and analyzed using MATLAB/Simulink software. Second, the influence of the rotary transformer design parameters on the dynamic performance of the EESM has been investigated. Finally, different topologies of the rotary transformers found in the literature have been analyzed, modeled and compared using an analytical and numerical approach. Based on the obtained results, the most suitable electrical parameters (i.e., geometry parameters, supply frequency, magnetizing and leakage inductance, winding resistance and efficiency) of the rotary transformer have been identified and implemented into the d-q model of EESM.

A Novel Experimental Method for Identifying the Flux Linkage Map of a High-Power Medium-Voltage Electrically Excited Synchronous Machine with Double Stator Winding

Accurate knowledge of the magnitude and position of the magnetic flux is essential for implementing field-oriented control (FOC) and achieving high-performance behaviour of AC drives. For estimating the flux in a wide range of speeds, so-called hybrid flux estimators, which are a combination of current-model and voltage-model based estimators, are usually used. Since the inductances are used as parameters in the current model, knowledge of the actual flux–current relationship, i.e., of the actual flux linkage map, is inevitable. In this paper, a novel experimental method for identifying the flux linkage map of an electrically excited synchronous machine (EESM) with double stator winding is proposed, which, unlike most existing experimental methods, does not require an additional machine to be used as a load. The flux is determined for different operating points to which the unloaded and sped-up machine is brought to by injecting d- and q-axis stator current components, whereby the current controllers are used to keep them constant for a certain operating point. The proposed method has been used to identify the flux linkage map of a medium-voltage EESM with double stator winding. A more than acceptable accuracy confirmed by comparison with three different analytical methods, together with the fact that it does not require a complex experimental setup, makes the proposed method suitable for the identification of a machine’s flux linkage map in an industrial environment.

A Reduced-Order Model for Wirelessly Excited Machine Based on Linear Approximation

Due to the high cost and shortage of rare earth materials, electrically excited synchronous machines (EESMs) become a potential alternative for electric vehicles. With the help of inductive power transfer (IPT), the EESM would easily realize the brushless excitation to improve its reliability. However, the dependence of IPT and EESM leads to significant control challenge, especially considering the inductive load characteristics. When the traditional modeling approaches are applied to the whole system, a complicated 13th-order model is built, which is unfavorable for dynamic analysis. For simplification, this article proposes a systematic and universal reduced-order model approach based on the local linear approximation of resonant voltage/current. A reduced ninth-order model of system is then obtained based on the approach. The frequency domain characteristic of primary-side control is analyzed, and the reduced-order model has high accuracy compared with the full-order one. Finally, the experimental results are given out to verify the effectiveness of the proposed modeling method.

Investigation of a novel brushless electrically excited synchronous machine with arc-shaped rotor structure

Electrically excited synchronous machines (EESMs) with brushes and slip rings are popular in many application fields. Nevertheless, the brushes and slip rings of EESM would increase maintenance cost and reduce the reliability. Addressing this issue, this paper proposes a novel brushless electrically excited synchronous machine (BEESM) with arc-shaped rotor structure, whose armature and field windings are placed on the stator. Firstly, the special structure and operation principle of the BEESM are illustrated and studied. Then, the electromagnetic performance indexes, including the air-gap flux density, flux linkage, back electromotive force (back-EMF), cogging torque, output torque and losses are fully analyzed by finite element method (FEM). Finally, the proposed BEESM is optimized to suppress the cogging torque. The results indicate that the proposed BEESM could serve as a high reliability and cost-effective candidate for the electricity generation system and industrial drive.

Effect and Inhibition Method of Armature-Reaction Field on Superconducting Coil in Field-Modulation Superconducting Electrical Machine

This paper studies the special effects of the armature reaction field (ARF) on the SC coils in the field-modulation superconducting (SC) machines (FMSCMs). Through comparing with the conventional SC synchronous machines (SCSMs) with similar structure to the electrically-excited synchronous machine (EESM), some special characteristics of the ARF effect of the FMSCMs are found, namely, the ARF will generate abundant moving harmonics with high amplitudes in the airgap, including the fundamental harmonic, all of which are alternating external magnetic field relative to the SC coils. These alternating harmonics will increase the AC loss, and induce high voltages in the SC coils. In order to weaken the ARF effect, some inhibition methods are proposed from the perspective of electrical machine design. Finally, the proposed combined method of simultaneously adding damper-coils and copper shield layer on the double-stator FMSCM (DS-FMSCM) exhibits an excellent inhibition effect, making the harmonic level of the DS-FMSCM match with that of the SCSM, meanwhile, reducing the induced voltages in the SC coils from several hundred volts to several volts.

Operation of an Electrical Excited Synchronous Machine by Contactless Energy Transfer to the Rotor

This paper deals with the design, the setup, and the operation of a rotating contactless energy transfer (CET) system. The system is used to replace the slip rings of an electrical excited synchronous machine and to transfer energy onto the rotor of the machine without mechanical contact. A compensation topology with an autoresonant circuit to generate the high frequency voltage is presented. Furthermore, the required parameters of the CET system are calculated. Based on these calculations, the system consisting of the power electronics, the compensation network, the magnetic path, the control system, and the electrical excited synchronous machine with controller, is set up. Finally, the calculated parameters are verified by measurements.

Simulation and Experimental Analysis of a Brushless Electrically Excited Synchronous Machine With a Hybrid Rotor

Electrically excited synchronous machines with brushes and slip rings are popular but hardly used in inflammable and explosive environments. This paper proposes a new brushless electrically excited synchronous motor with a hybrid rotor. It eliminates the use of brushes and slip rings so as to improve the reliability and cost-effectiveness of the traction drive. The proposed motor is characterized with two sets of stator windings with two different pole numbers to provide excitation and drive torque independently. This paper introduces the structure and operating principle of the machine, followed by the analysis of the air-gap magnetic field using the finite-element method. The influence of the excitation winding’s pole number on the coupling capability is studied and the operating characteristics of the machine are simulated. These are further examined by the experimental tests on a 16 kW prototype motor. The machine is proved to have good static and dynamic performance, which meets the stringent requirements for traction applications.

Thermal Modeling of a Hybrid Excitation Synchronous Generator with Alternated Current Linkages for Stand-Alone Power Supply

This paper presents the thermal modelling and analysis of a hybrid excitation synchronous generator with alternated current linkages (HESG-ACL) for stand-alone power supply. The HESG-ACL belongs to a class of hybrid excitation synchronous machines (HESMs), which combine the merits of electrically excited synchronous machines (EESMs) and permanent magnet synchronous machines (PMSMs). To confirm the performance and thermal behaviour of the HESG-ACL, an experimental prototype (69 kVA apparent power) equipped with thermal sensors was built and tested. A description of the HESG-ACL is given. The thermal analysis of the HESG-ACL is carried out based on the thermal resistance network model. The results obtained from the thermal model are verified by the experimental results.