Improving high-speed electrical machines by amorphous metals
- Date: 2019
This dissertation is about the application of an amorphous magnetic material (AMM) to a sleeve-free interior permanent-magnet (PM) rotor of high-speed synchronous motors. Currently, surface-mounted PM rotors are commonly used in the high-speed motors. In order to protect the high-speed rotors from centrifugal forces, high-strength non-ferromagnetic sleeves are required. This results in a reduced torque density, lowered flux-weakening ability, and highen losses of the motor caused by pulse-width-modulation (PWM) voltage. Hence, a sleeve-free rotor structure is beneficial.
AMM has been used for transformers and inductors for decades. It is well-known due to its low core losses. However, because of its high hardness and brittleness, slotting becomes a key obstacle to its application in electrical machines. Hence, this material has not been widely applied in the electrical machines yet. An important property, the high mechanical strength of the AMM has been ignored eagerly. In this work, an interior PM rotor made from AMM for high-speed operation is studied. The high mechanical strength and the low core losses of the AMM are fully taken use of. Because of the difficulty in slotting of the AMM, this material is not used for the stator and a conventional silicon steel will be used.
In order to fulfill the proposed high-speed rotor, the properties of the AMM in terms of electromagnetics and mechanics are experimentally studied. The influences of the mechanical stress and temperature on the electromagnetic properties of the AMM cores are well studied. Based on the measured data, a prototype is designed and optimized in terms of electromagnetics, mechanics and thermal behaviors. To ensure the success of the prototype, the slotting methods are also investigated and wire electrical discharge machining method is selected for manufacturing of the AMM rotor core. In order to show the advantages and disadvantages of the proposed high-speed AMM rotor, a surface-mounted PM rotor covered by a carbon-fiber sleeve is designed as a comparison. Since the influences of the PWM inverter on the losses of the high-speed motors are significant and this problem has not been thoroughly investigated before, the dissertation goes into a further research on it to fill the gap in this field.
Finally, two prototypes are built and tested. The design results are verified through experiments. It is verified that by applying the AMM to the proposed rotor, the performance of the high-speed PM motor is significantly improved, such as better flux weaking ability, higher torque and power densities and higher efficiency. Based on the tested data of the prototypes, it is confirmed that the AMM has high potential in the application of high-speed high-power-density PM motors.