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Analysis of Magnetic Field and Electromagnetic Performance of a New Hybrid Excitation Synchronous Motor with Dual-V Type Magnets

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Analysis of Magnetic Field and Electromagnetic Performance of a New Hybrid Excitation Synchronous Motor with Dual-V Type Magnets energies Article Analysis of Magnetic Field and Electromagnetic Performance of a New Hybrid Excitation Synchronous Motor with dual-V type Magnets Wenjing Hu, Xueyi Zhang *, Hongbin Yin, Huihui Geng, Yufeng Zhang and Liwei Shi School of Transportation and Vehicle Engineering, Shandong University of Technology, Zibo 255049, China; [email protected] (W.H.); [email protected] (H.Y.); [email protected] (H.G.); [email protected] (Y.Z.); [email protected] (L.S.) * Correspondence: [email protected]; Tel.: +86-137-089-41973 Received: 15 February 2020; Accepted: 17 March 2020; Published: 22 March 2020 Abstract: Due to the increasing energy crisis and environmental pollution, the development of drive motors for new energy vehicles (NEVs) has become the focus of popular attention. To improve the sine of the air-gap flux density and flux regulation capacity of drive motors, a new hybrid excitation synchronous motor (HESM) has been proposed. The HESM adopts a salient pole rotor with built-in dual-V permanent magnets (PMs), non-arc pole shoes and excitation windings. The fundamental topology, operating principle and analytical model for a magnetic field are presented. In the analytical model, the rotor magnetomotive force (MMF) is derived based on the minimum reluctance principle, and the permeance function considering a non-uniform air-gap is calculated using the magnetic equivalent circuit (MEC) method. Besides, the electromagnetic performance including the air-gap magnetic field and flux regulation capacity is analyzed by the finite element method (FEM). The simulation results of the air-gap magnetic field are consistent with the analytical results. The experiment and simulation results of the performance show that the flux waveform is sinusoidal-shaped and the air-gap flux can be adjusted effectively by changing the excitation current. This study provides design methods and theoretical analysis references for this type of HESM. Keywords: HESM; analytical model; MMF; permeance function; air-gap flux density; flux regulation capacity 1. Introduction With the rapid development of society, the exhaustion of fossil fuels and environmental pollution have become urgent problems. The development of new energy vehicles (NEVs) is one of the key approaches to solving these problems. Motor design is the key to the development of NEVs. Given this, various topologies of motors have been proposed. The permanent magnet synchronous motor (PMSM) has the advantage of high torque density, high power density, and high efficiency [1–3], but it is difficult to control the magnetic field [4]. The magnetic field of the electrical excitation motor (EEM) can be controlled easily, but the presence of the excitation winding increases the excitation loss, which leads to decreased efficiency. Based on the PMSM with added excitation windings, the hybrid excitation synchronous motor (HESM) with a controllable magnetic field has been proposed, and it has become the focus of increasing attention for scholars around the world [5–7]. In the past decades, many kinds of new HESM topologies have proposed and studied, which are mainly focused on the claw-pole type [8–10], the parallel type [11–13], rotor magnetic shunt type [14,15], and the combined rotor type [16], and most of them are used in generator systems. However, there are two main problems in these types of HSEMs. On the one hand, there is axial flux, which limits Energies 2020, 13, 1501; doi:10.3390/en13061501 www.mdpi.com/journal/energies Energies 2020, 13, 1501 2 of 19 the axial length of the motor. On the other hand, there is an additional air-gap between the magnetic bridge and the rotor core, which reduces the efficiency of the motor, and the structure of the motor is more complex. In the relatively few research works into HESMs without axial flux and additional air-gaps, a hybrid excitation double salient pole motor in which permanent magnets (PMs) and excitation windings are located on the stator is proposed [17,18]. The structure is simple and easily dissipates heat. However, when running as a motor, it causes a large torque ripple. In [19,20], PMs and excitation windings are integrated into one salient pole rotor, and the flux generated by excitation windings passes through PMs, which leads to the high reluctance of the magnetic path and low flux regulation capacity [21]. Based on the salient pole topology, a kind of HESM is researched in which PMs are fixed on the surface of the salient pole and do not cover the salient pole completely, in which the PM and electrical excitation flux are in parallel [22,23]. Since the PMs are “flat-type”, the capacity of magnetic gathering is weakened. An HESM with “spoke-type” PMs is presented in [24,25], in which the PMs are located between two adjacent rotor teeth with excitation coils. Since PMs are of the “spoke-type”, the HESM has high flux regulation capacity, but the top of the air-gap flux density waveform is too flat. Aiming at solving the above-mentioned problems of the poor flux waveform quality and weak flux regulation ability of the existing motors, a new motor topology that considers both the magnetic flux distribution and flux regulation ability can be provided and studied. Furthermore, due to the complexity of the new motor structure, the existing analytical model cannot be used to calculate the magnetic field of the studied motor, so it is necessary to provide an analytical model for the new structure to calculate the magnetic field quickly and accurately. In this paper, a new HESM with salient pole built-in dual-V PMs and non-arc pole shoes is proposed, in which the PMs are entirely devoted to enhancing the air-gap flux and avoiding dips of the middle field, and the role of the pole shoe is to improve the quality of field distribution, simplifying the manufacturing process. In this study, the operating principle, analytical model for magnetic field distribution, electromagnetic performance including the air-gap flux, back electromotive force (back-EMF) and the flux regulation of the motor is analyzed. According to the complicated rotor topology, the magnetomotive force (MMF) model with dual-layer combined PMs is built based on the principle of minimum reluctance, and the permeance function considering non-arc pole shoes and stator slots is derived by the magnetic equivalent circuit (MEC) method. To verify the validity of the analytical model, the calculation results of the magnetic field in the air-gap are compared with those of the finite element method (FEM). Finally, a prototype is manufactured and tested to verify the effectiveness of the topology design and theoretical analysis. 2. Machine Topology and Operating Principle 2.1. Topology Structure Figure1 shows the two-dimensional structure of the motor. V1 PMs are embedded in the middle of the outer side of the salient pole core in such a way that the N poles and S poles are alternately arranged on each salient pole. V2 PMs are sequentially embedded in the outer side of V1 PMs. The outside polarities of V1 PMs and V2 PMs in a single salient pole are the same. The rotor core consists of an even number of non-arc pole shoes. The excitation winding is wound on the salient poles in series. The stator is similar to that of a traditional PMSM and is built in a three-phase distributed armature winding. The permanent magnetic pole on the rotor is regarded as the structure of the embedded double radial magnetic pole. Two V1 PMs together provide air-gap magnetic flux for each pole, which brings about a clear magnetism effect. The V2 PM is designed in the outer middle of the V1 PMs, which can increase the main air-gap magnetic flux and avoid the problem of sinking at the output voltage peaks. Rs and Rr are the radius of the stator core and rotor core, and l1 and l2 are the lengths of the magnetic bridges at the corresponding positions. Energies 2020, 13, x FOR PEER REVIEW 3 of 19 EnergiesEnergies 20202020,, 1313,, 1501x FOR PEER REVIEW 33 ofof 1919 Figure 1. Topology structure of hybrid excitation synchronous motor (HESM). PM: permanent magnet. Figure 1. Topology structure of hybrid excitation synchronous motor (HESM). PM: permanent magnet. Figure 1. Topology structure of hybrid excitation synchronous motor (HESM). PM: permanent 2.2. Characteristics Characteristics of of Magnetic Magnetic Circuit and Operating Principle magnet. There are two MMF sources in the HSEM: PM and electric excitation MMF. MMF. The MMF of PMs is used2.2. Characteristics as the main excitation of Magnetic source Circuit of the and HSEM. Operating For the Principle V-type combined magnetic pole, only its radial flux is considered. Therefore, it is approximately regarded as two “flat-type” combined magnetic poles, flux isThere considered. are two Therefore, MMF sources it is approximatelyin the HSEM: PM regarded and electric as two excitation “flat-type” MMF. combined The MMF magnetic of PMs poles, is which forms the dual radial flux. When the winding is energized, the polarity of the salient poles can whichused as forms the main the dualexcitation radial source flux. Whenof the theHSEM. winding For the is energized,V-type combined the polarity magnetic of the pole, salient only poles its radial can be changed. According to the operating conditions of the HESM, there are two magnetic paths, in which beflux changed. is considered. According Therefore, to the it is operating approximately conditions regarded of the as HESM,two “flat-type” there are combined two magnetic magnetic paths, poles, in a situation is formed that is mainly in parallel and auxiliary in series. whichwhich aforms situation the dual is formed radial thatflux. is When mainly the in winding parallel andis energized, auxiliary the in series.polarity of the salient poles can Figure 2 describes the operating principle of the HESM.
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