The pursuit of "higher, faster, stronger" ultra-high-speed motor drive

"Higher, faster, stronger", just as Olympic Motto, the same Olympic spirit also exists in the field of motor drive: higher motor speed, faster dynamic response and stronger load capacity. In the racing competition of motor speed, high-speed motor and ultra-high-speed motor tracks are subdivided. Today, editor together with all come closer to the ultra-high-speed motor drive and its corresponding key technologies.

01 What is ultra-high-speed motor drive

Motor-drive racing is not simply distinguished by high-speed motors and ultra-high-speed motors according to the speed of rotation, but according to the difficulty of control. At present, experts at home and abroad of the same opinion that the difficulty of motor control is on the rise with the product of power and speed, called high speed index. Therefore, we use the square root of the motor power multiplied by the speed to judge the degree of high speed of the motor. For the convenience of description, we will multiply the motor power by the rotation speed as the high-speed index. Motors with a speed of more than 10,000rpm can be called high-speed motors. Generally speaking, in the high-speed motor drive, only the motors, the high-speed index of wihcu is greater than 70,000, can be called ultra-high-speed motor drive.

Let's look at a few examples:

• An ultra-high-speed drive for dicing machine, the power is 1.8kw, the speed of the drive motor is 60,000rpm, and the high-speed index is 80,498.

• An ultra-high-speed drive for PCB drilling and high finish milling  machines, with a power of 0.75kw, a drive motor speed of 300,000rpm and a high-speed index of 259,807.

• An ultra-high-speed drive for high-speed blowers or compressors, with a power of 300kw, a motor speed of 36,000rpm and a high-speed index of 19,718,012?????.

02 Advantages of high-speed motor drive

Just like the pursuit of "higher" Olympic spirit, the motor drive control is also running fast at high speed on the track, pursuing steadily "higher speed". Development from ordinary motors to high-speed motors, and from high-speed motors to ultra-high-speed motors, there may be "ultra-ultra-high-speed motors" in the future. But what is the relentless pursuit of "higher"?

After the motor and the drive are developed to high-speed one, due to the small moment of inertia of the motor and the high power density of the system, the material cost can be effectively saved. Secondly, high-speed transmission also has the advantages of high efficiency, low noise and fast dynamic response and so on. In recent years, high-speed machining technology has attracted more and more attention, because it can not only achieve higher machining quality, but also achieve higher production efficiency and reduce production costs. Therefore, ultra-high-speed motor drive technology is considered to be one of the most promising advanced manufacturing technologies in the 21st century.

03 Application areas of ultra-high-speed drives

Ultra-high-speed motor drives are widely used in national strategic fields such as semiconductors, high-precision machining, and green dual-carbon after combining with electric spindles or fluid turbines.

Industry application case 1 - wafer dicing

Wafer dicing (dicing) is a key process in the semiconductor chip manufacturing process, cutting the entire wafer into a single chip. The miniaturization of semiconductor devices requires optimization of the mechanical dicing process to reduce the frontside and backside chipping during wafer dicing. The spindle of a wafer dicing machine requires high load stiffness and low operating vibration, while taking into account the requirements of high speed and small size, so it requires the use of ultra-high-speed drives with excellent performance.

Excellent ultra-high-speed drive, its control performance ensures low heat generation and low vibration when the motor is running, reducing the frontside and backside chipping during cutting, and significantly improving the cutting quality and efficiency of the dicing machine.

Industry Application Case 2 - Molecular Pump

Molecular pump is a kind of equipment for obtaining ultra-high vacuum, which is widely used in the process of semiconductor industry. For example, the “stranglling" ASML lithography machine uses a high-end molecular pump. The relatively primary molecular pump can use the induction motor solution, while the high-end molecular pump needs to use the permanent magnet motor solution drived by ultra-high-speed drive. If the ultra-high-speed motor drive is synchronously associated  with the magnetic bearing control technology, the speed of the molecular pump can reach 90,000rpm. At present, there are only a handful of matured manufacturers in the world that master the ultra-high-speed motor drive and magnetic bearing control technology at the same time.

Industry Application Case 3 - high-speed PCB drilling machine

High-speed PCB drilling machine is a kind of equipment used in PCB processing and drilling process, which is used to drill through holes of PCB. Due to the popularization of 5G technology and personal wearable electronic technology and the emergence of complex products such as various ultra-thick plates and special-shaped plates, conventional drilling machines can no longer meet the processing needs of various complex ultra-thick plates.

Relevant studies have shown that if a hole of10um is to be drilled, a spindle of the speed at least 1,000,000rpm is required. Existing high-performance PCB drilling spindles, using aerostatic bearings, can run up to 300,000rpm. If the speed does not meet the minimum processing requirements, the machining cannot be performed. Therefore, the ultra-high-speed electro-spindle puts forward extremely strict performance requirements on the drive and the drive must have a higher control frequency.

The ultra-high-speed drive has a strong load-carrying capacity,  can realize high-speed drilling without speed drop under load increase. If the dynamic response of the drive control is slow, it is easy to eccentric and break the tool during processing. Therefore, excellent ultra-high-speed motor drive can reduce the risk of tool breakage and improve the efficiency of continuous production.

Industry Application Case 4 - High Precision Grinder

High-precision grinding occupies a unique position in the field of machine tools, especially internal grinding, which requires a spindle speed of 250,000 rpm. The ultra-high speed puts forward strict requirements on the motor drive. Under the condition of no speed sensor, the drive needs to have the ability of precise speed control. In addition, in order to reduce the influence of processing temperature on sensitive materials and avoid the influence of temperature rise on processing accuracy, the drive also needs to minimize the heat generationof the spindle.

Ultra-high-speed drives are much suitable for grinding applications. The switching frequency of Qingzheng Yuanhua's products can reach 64kHz, which can realize one-cycle control. Associated with the high-speed sensorless control algorithm, it can still control the spindle speed stably at ultra-high speed. At the same time, the extremely low ripple current can improve the machining accuracy of the grinding machine and reduce the heating of the spindle.

Industry Application Case 5 - high-speed compressor

In the field of turbines, higher speeds and direct drive without a gearbox help improve system efficiency and reduce failure rates. Therefore, high-speed motors are gradually replacing traditional low-speed motors. Especially in the field of hydrogen fuel cells, due to the requirements of power density and rotational speed, hydrogen energy air compressors need to be driven by ultra-high-speed drives.

Due to high rotating field frequency and small rotor size, standard frequency converters cannot adequately drive high-speed motors. Even employing expensive add-on components (such as sinusoidal filters etc.), the driving effect is only satisfactory. The ultra-high-speed drive using advanced technology, combined with the unique control algorithm for high-speed motors, can output the high rotation field necessary for the motor，so as to  ensures low motor heat generation of the omotor without the use of sinusoidal filters, significantly improving system efficiency and increasing motor and bearing service life time, increasing energy efficiency, especially for vehicle applications.

Industry Application Case 6 - high-speed turbo blower

In recent years, the application of high-speed turbo blowers has greatly  increased in a very considerable growth in the application fields of oil, natural gas, sewage treatment, chemical industry, textile and shipbuilding. As a green and energy-saving solution, the high-speed turbine blower can greatly reduce the operating power consumption under the condition of the same air supply volume. For example, a textile park used high-speed turbine blowers to replace traditional blade blowers, saving 40% of energy and recovering the investment within 10 months. After the high-speed blower product is realized, in addition to energy saving, it also has other advantages such as high environmental friendliness, low operating noise, and small daily maintenance etc.

04 Technical difficulties of ultra-high-speed drives

Why is ultra-high-speed motor drive a typical “strangling” technology? The main technical difficulties are concentrated in the following three aspects.

Self-Adaptibility to Load Change and Robustness Against Disturbances

When the motor is running, the speed will fluctuate due to the influence of load changes. Due to the small inertia of the high-speed motor, the fluctuation of the rotational speed is more obvious when the load changes, which in turn affects the working characteristics of the driven equipment. For example, when drilling at high speed, the spindle motor speed drops significantly due to load increase, which will lead to poor drilling quality and even tool breakage.

Relying on powerful computing power, the ultra-high-speed drive can calculate the speed of the motor in real time through the algorithm and realize the closed-loop control of the speed of the motor through the speed regulator. When the load changes cause the motor speed to change, the drive uses an adaptive current control algorithm and uses high-speed power semiconductor devices to quickly adjust the motor current, so as to control the output torque of the motor and the load torque to maintain a relative balance so that the motor speed remains stable. The adaptability to load changes and the robustness against disturbances are significantly improved.

Vibration suppression at high speed

When a general-purpose converter is used to drive a high-speed motor, due to the low switching frequency of the converter, the current of the motor during high-speed operation (when the fundamental frequency is high) contains a large number of harmonics. These harmonic currents generate harmonic torque, which causes the motor to vibrate. Due to the higher switching frequency of the power semiconductor devices used in the ultra-high-speed drive, it can ensure that the current waveform of the drive can still maintain a good sinusoidal characteristic when the output fundamental frequency is high, which greatly reduces the current harmonic content and significantly suppresses vibration and noise at high-speed operating conditions.

Countermeasures for motor high temperature rise

The power consumption of the motor during operation mainly includes copper loss in the winding, iron loss in the iron core, mechanical loss and additional loss. The increase of the motor speed will not only increase the mechanical loss, but also increase the frequency of change of the magnetic field in the motor, which will increase the eddy current loss and hysteresis loss. When a motoe is driven by a general-purpose converter, the large number of harmonics contained in the motor current will generate harmonic magnetic fields, which also increase the additional losses. The above losses will be converted into heat, which will significantly increase the temperature of the high-speed motor, thereby affecting the life time of the motor.

When the ultra-high-speed motor drive is used to drive the high-speed motor, due to the fast calculation speed and high switching frequency of the drive, the accuracy of the magnetic field orientation can be effectively improved, thereby improving the torque-to-current ratio, and the required torque can be obtained with a smaller current, effectively reducing copper loss. The ultra-high-speed motor drive has good drive current sinusoidal characteristics, which can effectively reduce additional losses. In addition, the ultra-high-speed motor drive can also use an algorithm to adjust the magnetic field when the motor is under no-load, thereby reducing the iron loss when the motor is under no-load. Through the above measures, the ultra-high-speed motor drive can effectively suppress the temperature rise of the high-speed motor.

05 Summary

As a key core technology serving national strategic fields such as semiconductors, high-precision machining, and green dual-carbon, ultra-high-speed drives have very broad prospects. We firmly believe that the self-controllable domestic ultra-high-speed drive technology can bring better product prices, more reliable service guarantees and faster development cooperation to domestic equipment manufacturers.

An excellent athlete actually has both agile reflexes and powerful muscular explosiveness. Similar to sports, an excellent ultra-high-speed motor controller can not only drive the motor with a "higher" speed, but also need to have a "faster" dynamic response and a "stronger" load capacity. How to drive the motor to achieve "faster" and "stronger" at ultra-high speed? The editor will bring it to you in the introduction of vector control technology.