Y Yang Tang

Comparison of flux-switching machines and permanent magnet synchronous machines in an in-wheel traction application

Purpose – This paper is aimed at investigating the potential advantages of flux‐switching machines (FSM) compared to permanent magnet synchronous machines (PMSM), particularly for the applications of electric vehicle traction.Design/methodology/approach – A 12‐slot 14‐pole PMSM designed for an in‐wheel traction application is chosen for the comparison. With the same volume constraint, three 12/14 FSM structures are created. Both the PMSM and the three FSM structures are modeled using the software Flux. Based on these models, finite element analyses (FEA) are performed, and the results are compared in terms of open‐circuit back electromotive force (EMF), electrical loading capability, and thermal conditions.Findings – Within the same volume constraint, a 12/14 FSMs can achieve the maximum torque higher than the one of 12/14 PMSM. This conclusion is drawn based on the observed facts that at the same rotor speed, a larger open‐circuit back EMF is induced in the FSM, while a larger electrical loading is also ...

Energy Conversion in DC Excited Flux-Switching Machines

This paper initiates a study on energy conversion in dc excited flux-switching machines (DCEFSMs) to reveal the torque production mechanism of this type of machines. The flux linkage components and self- and mutual inductances of a single-phase two-rotor-tooth DCEFSM are investigated. Based on the understanding of the relation between these variables and the rotor position, two different switching strategies are implemented to the armature current of this machine. Current-flux linkage loops are sketched for each switching strategy, resulting in different torque expressions. These torque expressions, validated using finite element analysis, show that the DCEFSM is a reluctance machine in which torque is generated due to variation of self- and mutual inductances. In addition, the torque component related to the mutual inductance can be dominant with certain current commutation in the armature winding.

Influence of Multiple Air Gaps on the Performance of Electrical Machines With (Semi) Halbach Magnetization

The ever increasing necessity to improve torque density while simultaneously maintaining high efficiency is a constant point of concern for electrical machine designers. This is mainly driven by the need for direct-drive solutions in evermore applications. This paper presents a general mesh-free description of the magnetic field distribution in multiple air-gap electromagnetic machines, although the tool is also useful for single air-gap machines, actuators, and other magnetic devices. The used method is based on transfer relations and Fourier theory, which can provide the magnetic field solution for a wide class of 2-D boundary value problems. This technique is in this paper applied to the rotary multiple air-gap machine with slotless (without slots but with and without rotor back-iron) armature. The presented analysis is compared to finite-element analysis for the multiple-layer winding, which shows the applicability of this method for future optimization. It is shown that multiple air-gap machines make better use of the volume and for short axial lengths where a single-side bearing configuration can be utilized provides a means to improve the achievable torque density.

Automated Design of DC-Excited Flux-Switching In-Wheel Motor Using Magnetic Equivalent Circuits

DC-excited flux-switching motors (DCEFSMs) are increasingly considered as candidate traction motors for electric vehicles due to their robust and magnet-free structure with relatively high torque density and extendable speed range. In this paper, an automated design tool based on nonlinear magnetic equivalent circuits (MEC) is initiated for the preliminary design of a 6-stator-segment 5-rotor-tooth DCEFSM used for the indirect drive in-wheel traction of electric cars. This MEC-based design tool is configured using a versatile manner that reduces the workload involved in constructing elaborate MEC models. Using this design tool, parameter sweeping is performed on the split ratio and back iron height of the motor to maximize the torque production with different constraints of flux density. The accuracy of this design tool is validated using finite element analysis.

Control of DC-excited flux switching machines for traction applications

Electrical traction motors face challenging torque-speed requirements. DC-excited flux switching machine (FSM) offers inherently a good torque capability along with an effective controllability thanks to its DC field windings. These machines have been evaluated mainly over their performance with little consideration on their control. This paper proposes a control strategy, applied on a 3-phase 6/5 DC-excited FSM for traction applications. To obtain the non-linear magnetic behavior of the machine, 2D finite element method (FEM) simulations are performed. The controller regulates the DC field current before reaching base speed to minimize the iron and copper losses. Due to the high armature reaction of the motor the speed range is extended by limiting both the field and armature currents as a function of the speed and inverter supply voltage. Torque control of the machine is performed throughout its complete speed range.

Investigation of winding topologies for permanent magnet in-wheel motors

Purpose – This paper aims to find the optimal winding topology for a 14‐pole permanent magnet synchronous motor (PMSM) to be used as an in‐wheel motor in automotive applications.Design/methodology/approach – Comparison is first performed among lap windings with different combinations of slot numbers and pole numbers. A general method for calculating the winding factors using only these numbers is proposed, thus the preferable slot numbers resulting in relatively large winding factors for this 14‐pole PMSM are found. With these slot numbers, the Joule losses of armature windings are further investigated, where the impacts of different end‐winding lengths are considered. By this means, the optimal slot number that causes the least Joule loss is obtained. On the other hand, as a competitor to lap windings, toroidal windings are also discussed. The thermal performances of these two types of windings are compared by performing a finite element analysis (FEA) on their 2‐D thermal models.Findings – For the 14‐po...

Winding topologies of flux-switching motors for in-wheel traction

Purpose – The purpose of this paper is to investigate winding topologies for flux-switching motors (FSMs) with various segment-tooth combinations and different excitation methods. Design/methodology/approach – For the ac winding of FSM, two winding topologies, namely the concentrated winding and the distributed winding, are compared in terms of the winding factor and efficiency. For the field winding of dc-excited FSM (DCEFSM), another two winding topologies, namely the lap winding and the toroidal winding, are compared in terms of effective coil area, end-winding length, and thermal conditions. Analytical derivation is used for the general winding factor calculation. The calculation results are validated using finite element analysis. Findings – Winding factors can be used as an indication of winding efficiency for FSMs in the same manner as done for synchronous motors. For FSMs with concentrated windings, the winding factor increases when the rotor tooth number approaches a multiple of the stator segmen...

Field weakening performance of flux-switching machines for hybrid/electric vehicles

Flux-switching machines (FSMs) are a viable candidate for electric propulsion of hybrid/electric vehicles. This paper investigates the field weakening performance of FSMs. The investigation starts with general torque and voltage expressions, which reveal the relationships between certain parameters and the produced torque and induced voltage of this machine. Based on the understanding of these relationships, a number of methods for reshaping the torque-speed characteristic of an FSM design are proposed and validated using finite element analysis (FEA).

Analytical Modeling of Flux-Switching In-Wheel Motor Using Variable Magnetic Equivalent Circuits

Flux-switching motors (FSM) are competitive candidates for in-wheel traction systems. However, the analysis of FSMs presents difficulty due to their complex structure and heavy magnetic saturation. This paper presents a methodology to rapidly construct, adapt, and solve a variable magnetic equivalent circuit of 12-stator-slot 10-rotor-tooth (12/10) FSMs. Following this methodology, a global MEC model is constructed and used to investigate correlations between the radial dimensions and the open-circuit phase flux linkage of the 12/10 FSM. The constructed MEC model is validated with finite element analysis and thus proved to be able to assist designers with the preliminary design of flux-switching motors for different in-wheel traction systems.

Topologies of flux-switching machines for in-wheel traction

Flux-switching machines (FSMs) are a strong candidate for in-wheel traction of electric vehicles. However, the winding topology of this type of machines still needs to be investigated. This paper proposes a general method for calculating the winding factor of flux switching machines (FSMs) using the numbers of phases, stator slots and rotor teeth. With this method, winding factors of FSMs with different number combinations of phases, phase slots, and rotor teeth are obtained and compared as an indication of their efficiencies. Based on the obtained winding factors, flux-switching machines with full-pitch distributed windings are proposed and analyzed.