At CastNX, our commitment to innovation drives us to develop cutting-edge High-Speed Variable Frequency Drives (VFDs) and motors. While conventional low-speed motors and VFDs typically operate at controlled RPMs up to 6,000, the High-Speed Motor and VFD systems push the boundaries, reaching speeds of up to 120,000 RPM. But why the need for such high speeds? Let’s explore the pivotal role of High-Speed Motors coupled with High-Speed VFDs across various industries.
Enhancing Efficiency in Machine Tools:
The pursuit of increased power density propels the adoption of High-Speed Motors. By exploiting the quasi-linear relation between rotational speed and shaft power, elevating the rated speed becomes a catalyst for boosting power density and operational efficiency. This approach allows for enhanced performance without altering the size of the machine, crucial in industries like machine tool applications. Smaller spindles and machine tools exhibit improved dynamic behaviour, leading to reduced weight and enhanced productivity. Moreover, accelerated rotational speeds facilitate faster tool movements, minimizing production cycle times and optimizing efficiency in high-speed cutting operations.
Transforming Compressor Industry:
In compressor manufacturing, the shift towards electric high-speed motors heralds a new era of efficiency and environmental sustainability. Electric high-speed motors offer superior efficiency, oil-free operation, and emission reduction, making them the preferred choice for environmentally friendly compressor drives. By replacing conventional gearbox setups with VFDs comprising high-speed motors and VFDs, overall efficiency is heightened, and maintenance demands are significantly reduced, aligning with the industry’s imperatives.
Advancing Energy Storage and Cryogenic Applications:
High-speed motor technology revolutionizes energy storage solutions and cryogenic applications alike. Integrated with high-speed generators, energy storage systems utilizing high-speed flywheels offer superior efficiency and environmental benefits by mitigating the need for fossil fuel-based generators. Similarly, in cryogenic applications, the adoption of directly driven motor elements leads to efficiency gains, space optimization, and reduced maintenance overheads, paving the way for sustainable and efficient operations.
The challenges in achieving the high speed
Now, the technicalities! The mentioned advantage of high-speed motors can only be achieved by using high-quality motor elements and advanced drives to adjust the control algorithm up to 120kRPM. Both motor and VFDs have their own challenges. The reason for this is that due to the high rotational speeds, the centrifugal forces on the rotating motor part (rotor) can be very high, leading the materials to the brink of mechanical stress resistance. Failures in motor elements can result in crashes affecting the environment or at least damaging the spindle where the motor is built-in. To prevent this, various physical aspects need to be calculated in a challenging development process, taking into account electromagnetic, thermal, mechanical stress, and structural dynamic aspects. The applied computational methods need to be combined with extensive experience to extend actual operational limitations while prioritizing safety as the highest priority.
Furthermore, the interaction of the VFD and the high-speed motor needs to be understood, as the VFD has a profound impact on heating, noise, clogging, and power consumption of the machine. Especially the interaction of various converter systems with a high-speed motor element demands very specific knowledge and experience. Hence, tests of the above-described applications are crucial for success. They require an intense collaboration between power electronics and high-speed motor specialists. Additionally, the infrastructure enabling performance tests is highly complex and usually not available on the market. Very often, the related costs far exceed the costs incurred during the entire development process of a new motor element product line.
Impact of Power Inverters on High-Speed Motors
Typical inverters operate based on the pulse width modulation method, where continuous switching of voltage or current regulates the output waveform. This method serves as the foundation for controlling motor operations, ensuring precision and efficiency in various industrial applications.
With the need for faster high-speed motors, the switching frequency of inverters experiences a corresponding increase. Modern inverters predominantly employ Insulated Gate Bipolar Transistors (IGBTs) to meet these demands. However, the quest for higher switching speeds drives the exploration of alternative materials such as Silicon Carbide (SiC) or Gallium Nitride (GaN), promising enhanced performance and efficiency.
While an increase in switching frequency enhances noise reduction and efficiency, it also introduces certain drawbacks. Fast switching transients, inherent to high-speed operations, become a significant source of stray losses, impacting overall system efficiency. Additionally, time harmonics generated by switching mode inverters disrupt the distribution of air gap flux, leading to additional eddy current losses in motor elements, particularly in the rotor.
The switching frequency of inverters directly impacts the insulation of high-speed motors. Particularly when IGBTs are utilized, the rapid voltage rise, typically from 0 to 650 V in less than 0.1 microseconds, leads to approximately 10,000 V/microsecond. This phenomenon poses challenges, resulting in an uneven distribution of voltages within the motor, especially during switching transitions, and potentially compromising the integrity of the insulation.
Addressing Challenges and Ensuring Reliability:
Navigating the complexities of inverter technology requires a deep understanding of motor insulation systems and inverter operation. Meticulous design considerations, combined with rigorous testing protocols, are essential to mitigate risks and ensure the reliability and durability of high-speed motors in demanding industrial environments.
Innovations at CastNX
At CastNX, we are developing High-Speed VFDs and motors for various applications. Here, we can affirm that asynchronous and synchronous high-speed motors offer several advantages, such as decreased installation space for higher power and elimination of unnecessary gearboxes. These advantages apply across several fields and are extensively utilized in industries such as machine tools, compressors, cryogenics, and energy generation, for example. Designing and producing these asynchronous and synchronous high-speed motors is an exciting task, where the utilization of the most modern computational methods for the development process is as important as possessing a wide range of experience and expertise to extend actual operational limitations safely. Not only is knowledge of high-speed motors necessary, but also a deep understanding of inverter technology, the partial discharge phenomenon, and so-called stray or additional losses.