Benjamin Gaussens

A Hybrid-Excited Flux-Switching Machine for High-Speed DC-Alternator Applications

This paper presents a new topology of hybrid-excited flux-switching machine with excitation coils located in stator slots (or inner dc windings). After describing the three-phase structure to be investigated, the working principle is discussed, and the main electromagnetic performances are simulated by finite-element (FE) analysis. It is demonstrated that the air-gap field can be easily controlled, which is interesting for variable-speed applications. Finally, a prototype having 12 stator poles and different rotor tooth numbers (10 or 14) was built. Experiments were performed, validating the FE simulations and the operation principle. Finally, the thermal behavior of the prototype machine is investigated through experiments. It is shown that, up to 12 000 r/min, the thermal stabilization is achieved, making this topology an excellent candidate for high-speed applications.

Analytical Approach for Air-Gap Modeling of Field-Excited Flux-Switching Machine: No-Load Operation

This paper presents a general and accurate approach to determine the no-load flux of field-excited flux-switching (FE-FS) machines. These structures are inherently difficult to model due to their doubly-slotted air gap. This analytical approach is based on magnetomotive force-permeance theory. The analytical model developed is extensively compared to field distribution obtained with 2-D finite element (2-D FE) simulations. The good agreement observed between analytical model and 2-D FE results emphasizes the interest of this general approach regarding the computation time. Hence, this analytical approach is suitable for optimization process in pre-sizing loop. Furthermore, based on the field model, classical electromagnetic performances can be derived, such as flux linkage and back-electromotive force (back-EMF) and also, unbalanced magnetic force. Once again, FE results validate the analytical prediction, allowing investigations on several stator-rotor combinations, or optimization of the back-EMF.

Analytical Armature Reaction Field Prediction in Field-Excited Flux-Switching Machines Using an Exact Relative Permeance Function

In this paper, an analytical approach for the prediction of the armature reaction field of field-excited flux-switching (FE-FS) machines is presented. The analytical method is based on the magnetomotive force (MMF)-permeance theory. The doubly-salient air-gap permeance, developed here, is derived from an exact solution of the slot permeance. Indeed, the relative slot permeance is obtained by solving Maxwells equations in a subdomain model and applying boundary and continuity conditions. In addition, during a no-load study, we found that, regarding the stator-rotor teeth combination, phase distributions were modified. Hence, in this paper, phase MMF distributions, for q phases, several stator-rotor combinations and also phase winding distribution (single- or double-layers) are proposed. We compare extensively magnetic field distributions calculated by the analytical model with those obtained from finite-element analyses. Futhermore, the model is used to predict the machine inductances. Once again, FE results validate the analytical prediction, showing that the developed model can be advantageously used as a design tool of FE-FS machine.

Magnetic Field Solution in Doubly Slotted Airgap of Conventional and Alternate Field-Excited Switched-Flux Topologies

A general solution of the magnetic field in the airgap of conventional and alternate field-excited switched-flux (FE-SF) machines is proposed in this paper. The analytical model is based on the subdomain method. It involves the solution of governing field equations in a doubly slotted airgap using the variable separation method. The complete model is derived and described in a general manner so that it can be easily extended to unconventional FE-SF topologies. By means of example, analytical predictions of airgap field are extensively compared and validated using 2D FE results. FE simulations were performed on a 24-10 classical FE-SF structure and also on a novel 18-11 FE-SF machine with additional spacer teeth.

Improved output power capability of Hybrid Excited Flux-Switching DC-Alternators: Analysis and experiments

In this paper, performance evaluation of a Hybrid Excited Flux-Switching Permanent Magnet (HEFSPM) DC-generator is presented. The application principle of a DC controlled bus over a wide speed range will be firstly detailed. The main idea of such machine topology is that all the active parts are located in the stator so that the air-gap flux can be easily controlled with no need of brushes. This scheme uses a low-cost diode bridge rectifier directly connected to the HEFSPM Generator to transfer active power to the battery and the load. By means of Finite Element Analysis (FEA), a simple methodology was developed to determine the power capability of the proposed structure. The influence of the BH magnetization curve will be also explored. Experimental results on a 3kW - 24-Slot 20-Pole HEFSPM DC Generator were performed and compared to the previous analysis. This relative low time-consuming approach could be useful to predict, with good agreement, the power capability of hybrid excited generator. Finally, an original compensation technique to improve performance of the generator is discussed. An analytical approach to predict the impact of series capacitor on the power capability is proposed and then validated by experiments. It is demonstrated that low speed power capability can be enhanced by 2.5 times using this technique.

Uni- and Bidirectional Flux Variation Loci Method for Analytical Prediction of Iron Losses in Doubly-Salient Field-Excited Switched-Flux Machines

Field-Excited Flux-Switching machines are doubly-salient machines with complex flux-density waveforms in the core. Hence, prediction of iron losses is difficult. In this article, we propose a method to determine flux loci in iron parts in an analytical manner, accounting for bidirectional field in back-irons of stator and rotor. The analytical model for flux-density prediction in the core at no-load was first validated with 2D FE simulations. Then measured iron losses on a prototype machine were used to calibrate an iron loss model. It was shown that in FE-SF machines rotor iron losses are not negligible and represent 28% of total iron losses. This model could be advantageously used in a design optimization procedure.

Proposal to increase the convertible power by an hybrid excitation flux switching synchronous machine associated with an voltage inverter. Application in hybrid or electric vehicle

Synchronous machines associated with their voltage inverter are generally controlled in current mode. In this paper, we are interested in supplying in full-wave voltage. The second part describes the expected performance with this control mode. In the third part, we present a hybrid excitation flux switching synchronous machine (HEFSSM) whose characteristics make it a potential candidate for electric motors of hybrid or electric vehicles. The experimental results of this HEFSSM containing ferrite permanent magnets (Br=0,4T) fed in full-wave voltage to convert the maximal power are presented in the fourth part. In the last section, we present two solutions to increase the maximal convertible power, so the maximal speed in no-load mode.