SE1500527A1 - Electrical machine with two stators - Google Patents

Description

15 20 25 are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description.

According to embodiments presented herein, a dual-cage rotor is provided.

Fig 1A shows a cross sectional view of a section of single cage double stator induction machine geometry and its ?ux distribution; Fig 1B shows a cross sectional view of a section of dual cage double stator induction machine geometry and its ?ux distribution. Windings of the same pattern relate to the same phase. The double stator induction machines referred to herein can operate as a motor, a generator, or both.

In the examples of this description, it is shown a 150 kW induction machine with 12 poles, 54 stator slots and 42 rotor slots. The cross-sectional copper bar area in single cage double stator machine is equal to the sum of the two rotor cages in dual cage double stator machine. The supply voltage is kept constant.

Machine designs with high pole numbers suits this concept better because the thinner stator yoke allows larger stator inner air gap diameter for the two machines.

The dual cage double-stator induction machine enables the possibility to operate inner and outer machine individually, thus enhancing the reliability of the machine.

The relative radial positions of two rotor cages can be adjusted to reduce the rotor core saturation level when operating each individual machine only.

The phase RMS (Root Mean Square) current of the inner and outer stator, rotor bar current and torque of the single cage and dual cage double stator induction machines are compared in Figs 2A-D. Fig 2A shows the outer stator 10 15 20 25 30 current versus slip. F ig 2B shows the inner stator current versus slip. F ig 2C shows rotor bar current versus slip. Fig 2D shows torque versus slip.

As seen in Fig 2D, dual cage double stator machine produces higher torque than single cage machine. The rotor bar current, shown in Fig 2C, in the single cage design is very close to the sum of the current from dual cage design. It is noticeable that close to synchronous speed, the inner stator current shown in Fig 2B of dual cage machine is higher than in single cage design. On the other hand, the outer stator current shown in Fig 2A is lower from dual stator machine. As slip increases, the difference of the inner stator current between the single cage and dual cage designs becomes smaller and smaller.

There are certain ?exibilities in the dual cage double stator induction machines which differ from conventional induction machines and the single cage induction machines. The symmetry of the two stator coils, and the radial alignment of the two sets of rotor cages are investigated and presented in Figs 3A-D, Figs 4A-D and Fig 5.

Fig 3A is the dual cage induction machine with both stator windings symmetrical, i.e. radially aligned between the inner stator and the outer stator, and rotor cages perfectly radially aligned. In this design, the rotor yoke thickness is very limited due to the depth of the rotor bars. This results in over-saturation in individual machine operation, i.e. when only one of the stators is active. A new topology is proposed in Fig 3B where two cages are shifted apart by a certain angle, while the stator windings from inner and outer stator remain symmetrical. Hence, Fig 3B illustrates an embodiment where no bars of ?rst cage are radially aligned with any bar of the second cage. The ?ux distribution of these two designs is presented in F ig 4A and 4B corresponding to the embodiments of Figs 3A and 3B, respectively. Although the stator windings for the phases are placed perfectly symmetrical (radially aligned), the equi-?ux lines from two stators are not in phase. To improve this situation, the inner stator is rotated forward by 6 slots. Depending on the rotor cage alignment, two new topologies are shown in Fig 3C and 3D. Fig 3C 10 15 illustrates an embodiment where the bars of ?rst cage are radially aligned with the bars of the second cage and where the phases are radially unaligned between the inner stator and the outer stator. Fig 3D illustrates an embodiment where no bars of ?rst cage are radially aligned with any bar of the second cage and where the phases are radially unaligned between the inner stator and the outer stator.

The ?ux distribution of these two designs is presented in F ig 4C and 4D, corresponding to the embodiments of Figs 3C and 3D, respectively.

It is evident to conclude that stator coil shift plays more signi?cant role in increasing the torque. Introducing dual-cage radial position divergence brings down the double stator machine torque. However, this reduction is paid by the increasing reliability of the machine when one of the machines is on fault and the other machine is possible to operate.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as de?ned by the appended patent claims.

Claims (3)

10 CLAIMS

1. An electrical machine comprising: an inner stator; an outer stator; and a rotor provided radially between inner stator and the outer stator, wherein the rotor is a dual cage rotor comprising a ?rst cage and a second cage, wherein the ?rst cage is provided radially outside the second cage.

2. The electrical machine according to claim 1, wherein no bars of ?rst cage are radially aligned with any bar of the second cage.

3. The electrical machine according to claim 1 or 2, wherein the phases are radially unaligned between the inner stator and the outer stator.