1、PDF外文：http:/ B 外文文献 Design of a 4-pole Line Start Permanent Magnet Synchronous Motor F. Libert1, J. Soulard1 and J. Engstrm2 1 Royal Institute of Technology Department of Electrical Machines and Power Electronics, 100 44 Stockholm, Sweden e-mail: florenceekc.kth.se e-mail: julietteekc.kth.se 2
2、 ITT Flygt AB Box 1309, 171 25 Solna, Sweden e-mail: Abstract To improve the efficiency of submersible pumps, the solution described in this article consists in replacing the rotor of the induction motor with a rotor presenting a squirrel cage and buried permanent magnets that can start on the grid
3、. The analytical procedure to design the rotor is presented with magnets placed in U shape and a four-pole motor. The steady state and transient performances of the different designed motors are then studied using finite element calculations and analytical models. As an example, the design of a 75kW
4、 four-pole motor is described. 1. Introduction In order to decrease gas emissions, different countries led by the United States imposed classes of efficiency for stand-alone induction motors through their legislation. Even though it is possible to increase the efficiency of traditional induction mot
5、ors, this cannot be easily done without over sizing the motor, which is definitely contrary to the idea of an integrated motor for products such as pumps. In this case, the solution could be to find another type of motor that reaches higher efficiency levels: the Line Start Permanent Magnet Synchron
6、ous Motor (LSPM) is one of them. By introducing permanent magnets buried beneath the squirrel cage, a hybrid rotor is obtained which combines an asynchronous start with a synchronous steady state operation. With really low copper losses at steady state (harmonics losses only), a better efficiency ca
7、n be reached. The design procedure, which will be described in this paper, has been used on a 75kW four-pole motor. Different designs were tested in order to find a good compromise between good steady state performances and a good start and synchronization. 2. Design procedure A: Start and synchroni
8、zation of the LSPMs. The design of this kind of hybrid rotors is tricky. If the performances in steady state define the required volume of magnet, it is the transient that imposes the size of the squirrel cage. At start, a braking torque from the magnets is added to the load torque 1. Figure 1 shows
9、 the different torques as a function of the speed during the transients. Fig. 1. Example of the evolution of different torques during the transients The expression of the magnet braking torque as a function of the equivalent electrical parameters of the LSPM is: 2 2 2220 2 2 2( 1 )3 ( 1
10、)2 ( 1 ) ( ( 1 ) )s q ssbs s q s d sR X sp R s ETs R X X s （ 1） This torque is proportional to the square of the no-load voltage. If the volume of magnet in the rotor is too high then some problems at start can occur (see paragraph 2). Therefore a compromise has to be found in order to combine
11、 a good start and synchronization, and good steady state performances. Taking into account these considerations, an analytical design procedure has been developed 2 and improved for the design of a 75kW four-pole motor. B. The design procedure For economical reasons, the stator and windings of the L
12、SPM are identical to the induction motor of the same power used at present in the pumps. This means that between the induction motor and the LSPM, only the rotor is changed. The flow chart in figure 2 shows the important steps in the design procedure. 1) Analytical calculation of the geometry At fir
13、st the data concerning the power and the stator of the motor are entered. The user chooses the configuration of the magnets: for each pole either 3 magnets placed in U or two magnets placed in V under the squirrel cage. The squirrel cage is then designed giving the value of the rotor cage resistance, the level of saturation in a rotor tooth and the number of bars (chosen according to the number of stator slots to minimize the oscillations at start).
