外文翻譯----4極自起動(dòng)永磁同步電動(dòng)機(jī)設(shè)計(jì) 英文

1、Design of a 4-pole Line Start Permanent Magnet Synchronous Motor F. Libert1, J. Soulard1 and J. Engström2 1 Royal Institute of Technology Department of Electrical Machines and Power Electronics, 100 44 Stockholm

2、, Sweden e-mail: florence@ekc.kth.se e-mail: juliette@ekc.kth.se 2 ITT Flygt AB Box 1309, 171 25 Solna, Sweden e-mail: jorgen.engstrom@flygt.com Abstract — To improve the efficiency of submersible pumps, the solutio

3、n 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. The analytical procedure to design t

4、he 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 analytica

5、l models. As an example, the design of a 75kW four-pole motor is described. List of principal symbols List of used symbols: B Flux density E0 Induced voltage at synchronous speed g Air-gap length idr Rotor d-cu

6、rrent iqr Rotor q-current ids, Id Stator d-current iqs, Iq Stator q-current L Inductance Rs Stator resistance Rrpu Rotor bar resistance in per unit T Synchronous torque u Voltage ?s Synchronous electrical

7、speed xds, Xd Stator reactance in the d-axis xqs, Xq Stator reactance in the q-axis ?? Flux linkage List of subscript: dr Rotor d-axis ds Stator d-axis m Magnet md Mutual d-axis mq Mutual q-axis qr Rotor

8、q-direction qs Stator q-direction r Rotor s Stator 1. Introduction In order to decrease gas emissions, different countries led by the United States imposed classes of efficiency for stand-alone induction motor

9、s through their legislation. Even though it is possible to increase the efficiency of traditional induction motors, this cannot be easily done without oversizing the motor, which is definitely contrary to the idea

10、 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 Synchronous Motor (LSPM) is

11、 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

12、 losses at steady state (harmonics losses only), a better efficiency can be reached. The design procedure, which will be described in this paper, has been used on a 75kW four-pole motor. Different designs were test

13、ed in order to find a good compromise between good steady state performances and a good start and synchronization. 2. Design procedure A: Start and synchronization of the LSPMs The design of this kind of hybrid rotors

14、is tricky. If the performances in steady state define the required volume of magnet, it is the transients that imposes the size of the squirrel cage. At start, a braking torque from the magnets is added to the load t

15、orque [1]. Figure 1 shows the different torques as a function of the speed during the transients. 2) Finite element simulation The finite element simulations allow at first to confirm the analytical results for the

16、no-load voltage. The direct and quadrature reactances that are needed to compute the performances can then be obtained. The analytical calculation of the inductances is not accurate enough because it is difficult to

17、define an analytical model of the saturation between the magnets and the bars. Different methods can be used to analyse the simulations, depending on the size of the finite element problem. Time-step FEM simulations

18、 with fixed speed can now be conducted in a relative short time depending on the size of the problem (reduced geometry thanks to symmetries). In the case of the 75kW 4 pole LSPM, half the motor needed to be simulated

19、 because of the complex double layer winding. Adapted methods were used to avoid time- consuming simulations. With a static simulation the flux density in the air-gap (figure 4) and the no-load voltage can be plotted

20、 and compared to the expected analytical values. For the 75kW LSPM, the no-load voltage is retrieved from the magnetic vector potentials obtained in the same static simulation [4]. Fig. 4. Flux density in the air-ga

21、p for a test-geometry To compute the d- and q- axis reactances Xd and Xq in the case of the 75kW LSPM, a time-step simulation is run. The rotor keeps the same position while the stator slots are fed with sinusoidal cu

22、rrents. The currents are chosen so that the ratio Id/Iq is constant. When analysing the results of the simulation, the d- and q- axis linkage ?d and ?q are computed from the flux seen by each phase winding with a Par

23、k transformation. The reactances are then found as a function of Id and Iq using: dm d d I f X ? ? ? ? ? 2(2) qq q I f X ? ? ? 2(3) where ?m is the flux created by the magnets. This way, one can get as well the influen

24、ce of the current amplitude on the reactances. Figure 5 represents the curves of Xd and Xq as a function of Id and Iq for the third design present in paragraph 3 of this paper. 3) Performances The next step is to chec

25、k whether the designed motor fulfils the required performances or not. The steady state performances, efficiency, power factor, synchronous torque are computed analytically and compared to the induction motor’s perfor

26、mances. The start and synchronization are then simulated. If the motor does not synchronize, the design procedure has to be run again. The way to simulate the start and synchronization is described in the next par

27、t of the paper. Fig. 5. d- and q axis reactances calculated with finite element simulations as a function of Id and Iq. 2. Problems at start A LSPM, which presents good steady state performances, may have some proble

28、ms to start and synchronize. The start can fail because of a too high magnet braking torque in comparison to the asynchronous torque (see case 1 on figure 6). Problems can also be due to a high inertia or a too

29、 high rotor resistance combining with too thin magnets [5] (Case 2 on figure 6). The figure 6 presents the plot of the speed as a function of time for the three cases at start. In order to simulate the start of the m

30、otor, an analytical dq model has been implemented in Matlab. Finite element time step simulations can also be conducted but are much more time-consuming [6,7]. Fig. 6. Possible behaviour of LSPM at start A. Machine mo