Study On Novel Hybrid Excitation Brushless Claw Pole Alterlnator

Automobile alternator is the main power supply of the vehicle electrical equipment, it is not only to provide power to the ignition system and other electrical equipment, but also to charge the battery.By now, the electric excitation claw-pole alternator has been widely used in vehicles due to its simple structure and low cost. However, the high leakage flux, low efficiency, and the existence of brushes and slip rings significantly restrict its further development.With the continuous development of China’s socio-economic, urban car ownership increases gradually, the city’s traffic is congested. The output voltage and output power of the automobile alternator are less than the rating, so the alternator can not charge the battery, or neither can not supply power to the ignition system and the other vehicle equipment. At the same time, the auto ancillary equipment increases gradually, so that the electricity consumption of the car increases significantly. The alternator is often in overload operation, which made the alternator is overheated. In order to overcome all these disadvantages, the alternator with higher power could be used. However, the automobile interior structure is compact, the space leaving for the alternator is very small. For the above reasons, how to reduce the alternator’s volume, or increase the power in the original volume is becoming more and more necessary.The permanent magnet alternator eliminates the field winding, brushes and slip rings, and thus is simpler and more reliable. The efficiency and power density is improved. However, the regulation of magnetic field is difficult to be realized.To improve the capacity of magnetic field regulation of permanent magnet alternators, hybrid excitation has been proposed. The hybrid excitation claw pole alternator has both permanent magnets (PMs) and field winding, which takes the advantages of both the electric excitation claw pole alternator and the permanent magnet alternator. Compared with traditional electric excitation claw pole alternator, the hybrid excitation claw pole alternator has higher efficiency and power density, which makes it a very promising technique in recent years.To overcome all the drawbacks of the present hybrid claw pole alternators, a novel hybrid excitation brushless claw pole alternator is developed in this paper. This alternator combines the constant excitation source by PMs with the variable magnetic flux produced by the toroidal field winding located in the excitation bracket. The permanent magnet magnetic flux and electric excitation flux are parallel connected. This alternator eliminates the brushes and slip rings, so the reliability is greatly improved.The main contents of the paper are as follows:1. In chapter2, a novel hybrid excitation brushless claw pole alternator was proposed to overcome the disadvantages of the present hybrid excitation claw pole alternators. The novel hybrid excitation brushless claw pole alternator includes stator core, armature windings, claw poles, excitation bracket, DC excitation winding and permanent magnets. The rotor is composed of two claws, and the two claws are welded together with magnetic impermeable material. One claw is fixed on the shaft and the other one has a bore in the claw palm. The excitation bracket is fixed on the end closure, and the excitation winding wraps around the excitation bracket, then the excitation winding and excitation bracket insert into the claw through the bore in the claw palm. There are two additional air gaps between the bracket and the claws. The excitation winding is stationary, thus the brush and slip ring can be eliminated. Compared with the ordinary electric excitation claw-pole alternator, this hybrid excitation brushless claw-pole alternator reduces the excitation loss, increases the alternator’s power density, and improves the alternator’s low speed power characteristic. Furthermore, its excitation winding is stationary, thus the brush and slip ring can be eliminated. So it has good reliability.2. Like the other kinds of claw pole alternators, the distribution of magnetic field of the proposed alternator is3-dimensional, so3-D magnetic field analysis is necessary. The no-load magnetic field distributions and the capability of flux control are obtained based on three dimensional finite element analysis.3.3-D finite element analysis can be directly applied to the analysis of magnetic field. However,3-D finite element analysis takes long computation time. In chapter4, an improved equivalent magnetic circuit network model considering three dimensional magnetic field distributions is set up. The analytical expressions of permeability in the claw pole, air gap and the other stricture are deduced. The work of this part provides a powerful tool for the electromagnetic calculation of the novel hybrid excitation brushless claw-pole alternator.4. In chapter5, a12kW,28V prototype was designed and manufactured. The test results showed that the prototype has good performance.5. Two hybrid excitation brushless claw pole alternators with the field windings on the stator were proposed. Compared with the hybrid excitation brushless claw pole alternator with the field winding in the claw, the hybrid excitation brushless claw pole alternators with the field windings on the stator are simpler.