Advantages and technical difficulties of high-speed permanent magnet motors

permanent magnet motor

In fact, various requirements have led to an increasing demand for high-speed permanent magnet motors and generators. First, there is a constant need to increase power density. Since there is a quasi-linear relationship between the speed of the motor and the shaft power, increasing the rated speed is an effective way to improve the power density and efficiency. Therefore, this method takes advantage of increasing the shaft power without changing the size of the machine. On the other hand, the same performance can be provided in a smaller volume. For example, the latter is crucial in the field of machine tool applications. As a result, the spindle or machine tool as a whole becomes smaller, the weight is reduced and the dynamics are enhanced. Another point in the industry is the cycle time required for a machine tool to complete a specific operation. The faster the tool moves and rotates, the faster it can complete the task. This does not take into account the time when high-speed cutting operations depend on the highest speed to effectively machine individual parts. Other interesting areas of operation for high-speed permanent magnet motors are applications in which a standard gearbox is used to convert the speed of a motor driven at the regular grid frequency (50/60Hz) to a higher speed level.

Replacing this gearbox and the associated regular motor with a variable-speed drive consisting of a high-speed permanent magnet motor and rectifier improves overall efficiency and significantly reduces maintenance costs. An example is the compressor industry, where high efficiency, oil-free operation and no emissions make high-speed permanent magnet motors the most environmentally friendly compressor drivers (for compressor applications, asynchronous motors may also be a good choice due to their ruggedness). In emission-free applications, energy storage systems with high-speed flywheels not only utilize high-speed permanent magnet generators.

As a result, fossil generators that produce harmful emissions can be avoided and maintenance costs can be significantly reduced. The direct drive motor element replaces a set of gearboxes and 50 / 60Hz standard motors. Efficiency can be improved, space required can be reduced, and maintenance costs can be reduced. Thus, energy recovery systems are becoming more and more interesting from a financial and ecological point of view, for example. Therefore, permanent magnet motor components contribute to the continuous development of green energy applications to a certain extent.

Challenging

The above advantages of high-speed permanent magnet motors and generators can only be achieved by using high-quality motor components. The reason for this is that due to the high speed of rotation, the centrifugal force on the rotating motor part (rotor) may be high, so that the material reaches the edge of mechanical stress resistance. A failure of the motor element may result in a crash affecting the environment or at least damaging the system in which the generator or motor is built. To prevent this, various physical aspects need to be calculated during the challenging development process, including electromagnetic, thermal, mechanical stress and structural dynamic aspects. The applied calculation method needs to be combined with long-term experience to extend the practical operational limits into place while putting safety first.

In addition, since the rectifier has a profound impact on the heat generation, noise, blockage and efficiency of the motor, it is necessary to know the interaction between the rectifier and the permanent magnet motor. In particular, the interaction of various frequency converter systems with high-speed motor components requires very specific knowledge and experience.