MULTI-POLE MAGNETIC CIRCUIT COMPARISONS
Permanent magnets can be magnetized with two or more (4, 6, 8, etc.) poles, using permanent or pulse magnetic flux. Pulse magnetization allows achievement of larger magnetic fields necessary for Nd-Fe-B or Sm-Co magnets. Multi-pole magnetization requires special magnetization heads with preformed windings which allow achievement of required distribution of magnetic field. Magnetic circuits in hitherto manufactured heads are executed in electrotechnic sheets or are of air. The paper describes construction of head with core of magnetically soft iron powder bonded with dielectric – dielectromagnetic used in eight-pole magnetization of ring magnets. Timelines for magnetization current and magnetization circuit voltage, a photograph of configuration of magnetic poles obtained were recorded, and magnetic induction values on magnet surface were measured.
Development and Analysis of the Magnetic Circuit on Double-Radial Permanent Magnet and Salient-Pole Electromagnetic Hybrid Excitation Generator for Vehicles
With the improvement of vehicles electrical equipment, the existing silicon rectification generator and permanent magnet generator cannot meet the requirement of the electric power consumption of the modern vehicles electrical equipment. It is difficult to adjust the air gap magnetic field of the permanent magnet generator. Consequently, the output voltage is not stable. The silicon rectifying generator has the problems of low efficiency and high failure rate. In order to solve these problems, a new type of hybrid excitation generator is developed in this paper. The developed hybrid excitation generator has a double-radial permanent magnet, a salient-pole electromagnetic combined rotor, and a fractional slot winding stator, where each rotor pole corresponds to 4.5 stator teeth. The equivalent magnetic circuit diagram of permanent magnet rotor and magnetic rotor is established. Magnetic field finite element analysis (FEA) software is used to conduct the modeling and simulation analysis on double-radial permanent magnet magnetic field, salient-pole electro-magnetic magnetic field and hybrid magnetic field. The magnetic flux density mold value diagram and vector diagram are obtained. The diagrams are used to verify the feasibility of this design. The designed electromagnetic coupling regulator controller can ensure the stable voltage export by changing the magnitude and direction of the excitation current to adjust the size of the air gap magnetic field. Therefore, the problem of output voltage instability in the wide speed range and wide load range of the hybrid excitation generator is solved. MULTI-POLE MAGNETIC CIRCUIT COMPARISONS
Generator is a key component of vehicle power system. At present, the main generator used in the vehicle is the silicon rectification generator and permanent magnet generator. The magnetic field of silicon rectification generator is created by electric excitation winding. Most of electric energy through the electric excitation winding is consumed in the form of heat, and only small part of electric energy is converted into magnetic energy for power generation, which causes the low efficiency of the generator. Permanent magnet generator’s magnetic field is created by permanent magnet without any electrical excitation winding, which has advantages of simple structure and reliable operation. However, limited to the current development level of permanent magnet generator, it is difficult to adjust the magnetic characteristics of the generator and maintain the output voltage stable [1, 2]. Permanent magnet generator is mainly used on the vehicle whose generator power is relatively small. While the generator power is too large, costs will be greatly increased and its popularization and application will be affected.
Hybrid excitation generator is a combination of permanent magnets generator and electromagnetic generator [3,4,5,6,7,8]. The hybrid excitation generator using Nd–Fe–B permanent-magnet materials to excite the magnetic field, which makes the specific power of generator increased, field winding current and excitation loss decreased, and efficiency of generator improved. Furthermore, the generator’s idle speed performance is better. According to the relationship between the permanent magnetic potential and the electric field potential, the hybrid excitation generator can be divided into two types: series hybrid excitation generator and parallel hybrid excitation generator. In the series hybrid excitation generator, electric field winding is arranged below the permanent magnet of the rotor to form a series structure. Due to the presence of the brush and slip ring structure, the reliability of the generator is reduced . In order to improve the structure of the brush generator, Leonardi et al.  put forward a kind of permanent magnet and excitation winding are located on the stator of the series hybrid excitation generator. Cancelled the brush and slip ring, the structure is more simple. But the electric excitation magnetic potential direct affects the permanent magnet and it is prone to irreversible demagnetization. Therefore, scholars have less research on this kind of generator. At present, the research of hybrid excitation generator is mainly concentrated in the parallel hybrid excitation generator. Hoange  proposed a hybrid excitation flux-switching generator based on the structure of flux-switching permanent magnet generator. Many scholars have shown a strong interest in the structure of the motor, and launched a related research [12, 13]. According to the different combinations of permanent magnet and electric field winding, the electromagnetic performance and magnetic field regulation ability of the hybrid excitation flux-switching generator with different topologies were compared and analyzed [14, 15]. The generator has no permanent magnet or electric field winding on its rotor, and has many advantages of high power density and high efficiency. But the magnetic circuit of the generator is easily saturated, and the cogging torque is larger. A hybrid excitation claw-pole generator was proposed by Professor Qunjing Wang in HeFei University of Technology [16, 17]. Because the electrical excitation part of the generator adopts the claw-pole structure, the additional air gap is large, the magnetic flux leakage is bigger, and the power density is low. Professor Surong Huang  in Shanghai University proposed a hybrid excitation bypass flux generator. The generator is easy to manufacture. However, the electric field winding is installed on the stator side, which results in a larger the electric excitation magnetic circuit reluctance affecting the efficiency of the generator.
In this paper, the double-radial permanent magnet and salient-pole electromagnetic hybrid excitation generator is developed adopting a combined rotor structure. The permanent magnet part is designed as a double radial permanent magnet structure, which can increase the air gap flux in the case of a certain volume of the generator, and increase the power density of the generator. The electric exciting part is designed as a salient electromagnetic structure, which is simpler than that of the traditional claw-pole electromagnetic and is easy to be processed. Consequently, the axial length of the generator is reduced. The double-radial permanent magnet field and the salient-pole electromagnetic magnetic field are used as the main generating part and the auxiliary generating part of the generator, respectively. The salient-pole electromagnetic magnetic field plays the role of increasing or weakening the main magnetic circuit magnetic flux in the hybrid magnetic field. The generator not only has good adjustment characteristic, but also has advantages of high power density, high efficiency and high reliability. It has important application value in the vehicle power system.