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Detailed interpretation of magnetic levitation motor technology

Date:2023-09-05   Author:XINDA MOTOR

Principle of Maglev Air Conditioning

Magnetic levitation technology - magnetic bearings and positioning sensors use radial bearings and axial bearings composed of permanent magnets and electromagnets to form a CNC magnetic bearing system to realize frictionless movement of the moving parts of the compressor suspended on the magnetic lining. Positioning sensors on the bearings provide ultra-high-speed real-time repositioning of the motor rotor to ensure precise positioning.

Magnetic levitation air conditioner is a high-efficiency energy-saving central air conditioner with magnetic levitation centrifugal compressor as the core technology.

The CNC magnetic bearing system is composed of radial bearings and axial bearings composed of permanent magnets and electromagnets to realize the frictionless movement of the moving parts of the compressor suspended on the magnetic lining. The positioning sensor on the magnetic bearing provides the motor rotor with Ultra-high speed real-time repositioning to ensure precise positioning of the entire air conditioning system without lubricating oil.

Magnetic levitation technology has a long history, and maglev trains have been in operation for many years. This technology eliminates friction, improves mechanical efficiency, and reduces mechanical failures. With the development and maturity of this technology, the air-conditioning industry has also ushered in a wave of maglev.

The magnetic levitation system consists of four parts: a rotor, a sensor, a controller and an actuator. The actuator includes an electromagnet and a power amplifier. Magnetic bearings use a magnetic field to levitate the rotor, so that there is no mechanical contact or mechanical friction during rotation, and there is no need for mechanical bearings and the lubrication system necessary for mechanical bearings. Using magnetic suspension bearings in refrigeration compressors, all the troubles caused by lubricating oil no longer exist. The magnetic levitation refrigeration compressor is the application of the magnetic levitation bearing technology.

Maglev origin and history

In 1842, the British physicist Earnshaw proposed the concept of magnetic levitation. In the early 1900s, experts from the United States, France and other countries proposed several conjectures about objects being able to escape the resistance of their own gravity and operate efficiently - that is, the early model of magnetic levitation.
In 1966, American scientists James Powell and Gordon Denby proposed the first practical magnetic levitation transportation system. In the 1970s and 1980s, maglev trains were tested in Thyssen-Henschel, Germany, and Germany began to name this maglev system "maglev".
Magnetic levitation uses levitation magnetic force to keep objects in a frictionless and contactless suspended equilibrium state. This characteristic has attracted special attention from the scientific community around the world.

After 2003, the advent of magnetic levitation centrifugal compressors meant that the refrigeration and air conditioning equipment industry began to enter a new era of magnetic levitation.

It is discharged from the air conditioning compressor through high-temperature and high-pressure refrigerant, enters the condenser, releases heat to the cooling water of the copper tube, condenses into a medium-temperature and high-pressure refrigerant liquid, and then decompresses it through the shut-off valve into a low-temperature and low-pressure liquid and enters the evaporator. The chilled water flowing through the copper pipe absorbs heat, vaporizes into low-temperature and low-pressure gas, and is then sucked into the compressor. It undergoes secondary compression in the compressor to become high-temperature and high-pressure gas and is discharged. Through this cycle, the purpose of cooling is finally achieved.

In the ten years after 2003, the market capacity of magnetic levitation central air-conditioning was relatively small, but the companies involved in it gradually made clear their development direction. Under their promotion, magnetic levitation central air-conditioning products gradually took steps in the Chinese market.

As the country's "Thirteenth Five-Year Plan" energy conservation and emission reduction policy continues to increase, the market demand for maglev air conditioners has exploded, attracting major maglev manufacturers in the world to increase investment in the Chinese market, and the maglev air conditioner industry has thus formed. A situation where heroes compete for hegemony.

Magnetic Levitation Chiller Features

1. Energy saving and high efficiency

The oil-free system of the magnetic levitation cooler does not mix lubricating oil into the refrigerant, which improves the heat exchange efficiency of the condenser and evaporator. Compared with traditional bearings, the friction loss of magnetic levitation bearings is only about 2% of the former. This improves mechanical efficiency; the magnetic levitation chiller uses digital frequency conversion control technology to improve the part-load efficiency of the chiller.

50% less operating cost than traditional chillers. Taking the data center in Beijing as an example, the air conditioning chilled water in the data center uses 12°C water supply and 18°C return water. The approximation of the plate heat exchanger is 2°C, and the approximation of the cooling tower and wet bulb temperature is 4°C. According to the "Special Meteorological Data Set for China Building Thermal Environment Analysis", the data center air conditioning system operated in a partial natural cooling state for a total of 1,785 hours throughout the year (a total of 8,760 hours throughout the year). As shown in the figure below, the magnetic levitation chiller has greater energy saving space when part of the data center is naturally cooled.

2. Low starting current

The starting current of ordinary large-scale cooling machines can reach 200A-600A, which has a great impact on the power grid. The magnetic levitation chiller adopts variable frequency soft start, and the starting current is very small. When the power supply is restored after the data center is powered off, multiple chillers can be started at the same time.

3. Compact structure

The rotation speed of the magnetic levitation chiller can reach 48,000 rpm, while the rotation speed of the ordinary centrifugal chiller is generally 3,000 rpm. Therefore, the magnetic levitation chiller is smaller and lighter than the ordinary chiller.

4. Quiet operation

The magnetic levitation chiller has no mechanical friction, and the noise and vibration generated by the unit are extremely low. The compressor noise is less than 77dB, and the bare metal noise of ordinary centrifugal compressors is more than 100 dB.

5. High system sustainability

In traditional refrigeration compressors, mechanical bearings are necessary components, and a lubricating oil system is required to ensure the operation of the mechanical bearings. According to statistics, 90% of all burned compressors are caused by lubrication failure. The magnetic levitation cooling machine does not require an oil lubrication system and has no mechanical friction, making it more sustainable than traditional cooling machines. Advantages of service life: The magnetic bearings have no wear and the service life of the air conditioner is as long as thirty years.

6. Low daily maintenance costs
The magnetic levitation unit has few moving parts and no complicated oil circuit system or oil cooling system, which reduces the maintenance content of the cold machine. The air-conditioning system of the data center operates continuously throughout the year, and equipment maintenance is the daily work of the center's operation and maintenance personnel. The use of magnetic levitation chillers can effectively reduce the maintenance content of the chillers, reduce the workload of operation and maintenance personnel, and effectively reduce daily maintenance costs. There are currently magnetic levitation chillers available with a cooling capacity ranging from 100 to 1,500 refrigeration tons.

7. Environmentally friendly refrigerant

The environmentally friendly magnetic levitation air conditioner can use environmentally friendly R134a refrigerant, which has zero harm to the ozone layer. New alternative refrigerants are still under development.

8. The initial investment in equipment is high.

Since the magnetic levitation chiller integrates magnetic levitation bearings and digital frequency conversion control system, the initial investment in equipment is greatly increased compared with ordinary chillers.

When the air conditioner is not used for heating in winter, it is still necessary to energize the unit to prevent freezing; there are many accessories, such as water replenishment valves, exhaust valves, etc., and some models also need to install expansion water tanks to increase leakage points. The outdoor unit is larger in size and heavier in weight.

Maglev compressor

The main components of the magnetic levitation compressor include an aluminum alloy precision-cast compressor body, a two-stage compression centrifugal impeller, an integrated motor rotor and drive shaft made of permanent magnet materials, a permanent magnet synchronous motor, electromagnetic bearings, and an adjustable inlet guide. Flow blades, AC/DC power conversion system, electromagnetic bearing control system and soft start control system, etc.

The magnetic levitation frequency conversion centrifuge is discharged from the air conditioner compressor through high-temperature and high-pressure Freon, enters the condenser, releases heat to the cooling water of the copper tube, condenses into a medium-temperature and high-pressure Freon liquid, and then depressurizes through the throttle valve into a low-temperature and low-pressure liquid and enters the evaporator. In the shell of the evaporator, heat is absorbed from the frozen water flowing through the copper tube, gasified into a low-temperature and low-pressure gas, then sucked into the compressor, and then compressed into a high-temperature and high-pressure gas in the compressor to be discharged. Through this cycle, the cooling effect is finally achieved. Purpose.

Magnetic levitation compressor features:

1. High operating efficiency:

  Especially under partial load conditions, the compressor saves 48% more energy than the same model from other brands. This special feature enables on-site or remote monitoring through a network-based monitoring and diagnostic system.

2. No lubricating oil is required, and maintenance costs are 50% lower than oil-containing compressors:

  Oil-free is achieved after decades of struggle in the industry. The oil-free design not only eliminates the possibility of reducing efficiency due to oil pollution, but also eliminates oil management accessories: oil heaters, oil pumps, oil separators, oil filters, etc.

3. Ultra-light body design:

  A 120-ton compressor weighs only 295 pounds, about 1/5 the weight of some conventional machines.

4. Ultra-quiet operation process:

  The operating sound is less than 70 decibels, and the compressor is so quiet that you can't tell it is running over the background noise of typical equipment.

5. Redefined soft start:

  The compressor redefines the soft start, only needs 2 amps of starting current, while the traditional compressor needs 500~600 amps. 

Comparison of Traditional Refrigeration Compressor and Maglev Refrigeration Compressor

1. Principle

  For traditional refrigeration compressors, mechanical bearings are necessary components, and a lubricating oil circulation system is required to ensure the mechanical bearings work.

  The magnetic levitation refrigeration compressor is a kind of magnetic levitation bearing that uses a magnetic field to suspend the rotor in the air without mechanical contact and mechanical friction during rotation. Therefore, the magnetic levitation bearing no longer needs mechanical bearings and the necessary lubrication system for mechanical bearings.

2. The redundancy function of the cooling system;

  The redundant function of the cooling system is very important, but often due to the limitation of space and cost, traditional refrigeration compressors cannot install multiple compressors in one machine to realize the redundant function of the cooling system.

  The volume of the magnetic levitation refrigeration compressor enables multiple magnetic levitation compressors to be installed in a common unit to achieve redundant functions. If a single compressor fails, the other compressors can still operate normally for cooling.

3. In terms of operating efficiency:

  The cooling capacity of traditional refrigeration compressors requires at least 500-600A starting current. Maglev refrigeration compressors are 30% more efficient than traditional compressors. The adaptive control logic in the automatic control system allows a 450-ton chiller to provide a minimum cooling capacity of 0.33 kW/ton, and the cooling time is as long as 40-50 hours. This super-adaptive control logic can meet cooling needs throughout the day and requires no special settings.

Magnetic bearings, motors, blowers

Magnetic bearings
Since the 1990s, magnetic levitation technology has been applied to bearings, bringing special advantages such as no contact, no friction, long life, no lubrication and high precision. Scholars and business people at home and abroad have devoted great efforts to it. Interest and enthusiasm for research.

Compared with traditional rolling bearings, sliding bearings and oil film bearings, magnetic suspension bearings have no mechanical contact, and the rotor can run to a high speed, with small wear, low energy consumption, low noise, long life, no lubrication, no oil pollution, etc. advantage.Especially suitable for high-speed, vacuum, ultra-clean and other environments.
In fact, magnetic levitation is only an auxiliary function of bearings, not a form of bearings. Specific applications also need to cooperate with other bearing forms, such as magnetic levitation + ball bearings, magnetic levitation + oil bearings, magnetic levitation + vaporization bearings, etc.
High speed magnetic levitation motor
It is a popular new research direction in recent years. It integrates magnetic suspension bearings and motors, has self-suspension and driving capabilities , does not require any independent bearing support, has the characteristics of small size and high critical speed, and is more suitable for ultra-high-speed operation occasions. , also suitable for small and even ultra-small structures.

Since the mid-1990s, researches have been carried out abroad, and various types of permanent magnet synchronous magnetic levitation motors, switched reluctance magnetic levitation motors, and induction magnetic levitation motors have appeared one after another.

Magnetic levitation high-speed motors are mainly used in centrifugal compressors. This is because centrifugal compressors require a high speed. In order to achieve high speeds, traditional centrifuges not only require huge high-precision gear transmissions, but also require complex oil lubrication systems, Oil sealing system and so on.
The use of magnetic levitation high-speed motors perfectly avoids these unfavorable factors. Through the magnetic levitation technology combined with permanent magnets and electromagnetics, the centrifuge shaft can be in a relatively perfect six-sided volley state.
Magnetic refrigeration centrifugal compressors were first developed. In 2003, the world's first magnetic levitation compressor was born. In 2006, China's first magnetic levitation centrifugal compressor central air conditioner was launched.
At present, domestic magnetic levitation centrifugal compressor application technology is not very mature, and most of the core components of magnetic levitation refrigeration centrifugal compressors come from foreign companies, such as Danfoss.

Magnetic Levitation Centrifuge - Radial Bearing

Magnetic Levitation Centrifuge - Axial Bearing

Magnetic Levitation Centrifuge - Positioning Sensor

Magnetic levitation centrifuge - motor and drive shaft

Oil-free magnetic levitation centrifugal compressors and oil-free magnetic levitation blowers are the main application directions of magnetic levitation in air compressors.
There are currently very few domestic companies involved in oil-free centrifugal compressors with common pressures, mainly because there is still a technical gap.
Foreign brands are leading the way in this regard, such as the magnetic levitation variable frequency centrifuge Quantima launched by Compair in 2010, with a flow and pressure range covering 3~8bar and 28~70m³/min.

At present, air compressor companies in the domestic market, including Atlas, have launched magnetic levitation single-stage centrifugal blowers , targeting the market that replaces a large number of Roots blowers.
The design of the impeller and other units of the single-stage centrifugal blower is very mature in China and is relatively difficult. The core of the technology is the magnetic suspension bearing. Most of the magnetic levitation centrifugal blowers launched by domestic air compressor companies are only OEM or assembled, and most of the technology sources come from South Korea's Shia.
Interestingly, the localization of magnetic levitation bearings does not come from within the air compressor industry, but from outside the industry. The well-known domestic independent magnetic levitation bearing technologies include: Tianjin Yisheng, Zhejiang Feixuan, Nanjing Magnetic Valley, etc. The technology sources include Tsinghua University and Southwest Jiaotong University.

But to be honest, fans and pumps are traditionally in the same industry segment, and the sales channels and models are quite different from those of air compressors.

In the final analysis, magnetic levitation centrifugal blowers are still in the category of fans. When air compressor companies develop this market, they are not only faced with the problem of explaining new products, but also facing unfamiliar channels, unfamiliar user markets, unfamiliar models, as well as fans and Serious .