Low cost motor technology in refrigeration compressors
With the complexity of the application scenarios and the enrichment of functional requirements, the refrigeration and compression industry will also change its operating conditions from the previous single operating conditions to the multi-operating conditions. Therefore, permanent magnet synchronous motors have more advantages than asynchronous motors. At the same time, in response to the government's environmental protection requirements for energy conservation and emission reduction, permanent magnet synchronous motors have gradually replaced asynchronous motors in the compression refrigeration industry. However, in recent years, as the prices of rare earth raw materials continue to rise, permanent magnet synchronous motors will face the real pressure of rising prices. Therefore, the first article in our series on advanced motor introductions in the refrigeration and compression industry will focus on reducing motor costs. In fact, the cost reduction has been going on. We have counted the technological changes of compressor motors in the past ten years. It is not difficult to find that there are driving forces for cost reduction.
Early permanent magnet DC compression motors were almost all surface-type magnetic steel structures. For example, Delphi's compression motors in Thermal Systems use surface permanent magnet steel structures.
The surface magnetic steel has a simple structure and is easy to manufacture. However, since it is attached to the outside of the rotor, the tensile strength of the magnetic steel is much lower than the compressive strength. When the centrifugal force generated during high-speed operation approaches or exceeds the tensile strength of the magnetic steel, the magnetic steel is easily damaged, so the surface magnetic Steel is generally suitable for operation at low speeds. However, there are some technologies that can also increase the tensile strength of magnetic steel to increase the rotational speed of the surface magnetic steel structure, such as filling the stator and rotor air gap with epoxy material, and then using a fiberglass or carbon fiber ring outside. Set fixed. However, the disadvantage of this is to increase the thickness of the air gap and increase the amount of magnetic steel. The advantage of the surface magnetic steel structure is that the air gap is uniform, the magnetic leakage is small, and the harmonic content is small. But from an economic point of view, the surface magnetic steel structure is not the most economical solution.
2. Built-in IPM structure
Since the built-in magnetic steel structure is embedded in the rotor, the tensile strength will be greatly improved. The rotor magnetic circuit will no longer be symmetrical, and the direct axis reluctance is greater than the cross-axis reluctance, and reluctance torque will be generated.
According to the torque formula:
Among them, the front is the permanent magnet torque generated by the permanent magnet flux linkage, followed by the reluctance torque. Reluctance torque will increase the motor's overload capability. (Because the magnetic path in the surface magnetic steel structure is symmetrical, Ld=Lq, the reluctance torque term is zero, that is, there is no reluctance torque.)
A drawback of the built-in magnetic steel structure is that it is easy to generate magnetic flux leakage at the ends of the magnetic steel, thereby reducing the strength of the air gap magnetic field. At the same time, the harmonic content of the air gap magnetic field will increase. Therefore, it is necessary to minimize the magnetic flux leakage and reduce harmonics by modifying the internal structure of the rotor to maximize the use of the permanent magnet flux linkage.
3. Permanent magnet-assisted synchronous reluctance motor
The "double U-shaped" built-in magnetic steel structure improves the sinusoidality of the air gap magnetic field, reduces the harmonic content, and reduces the loss of magnetic flux leakage. At the same time, the convex polarization is made larger, and the reluctance torque is utilized to a greater extent. Ferrite is generally used as a magnetic steel material. This is indeed an economical solution. It has been used in large quantities and has two typical characteristics:
One is that the magnetic steel is replaced by expensive NdFeB, which is cheaper ferrite. The latter's unit price is only 1/10~1/5 of the former, so the cost of the motor can be reduced and the cost reduction effect can be achieved.
The second is the torque structure of the motor. The proportion of the reluctance torque exceeds the permanent magnet torque. Because the torque composition changes, the permanent magnet changes from the main angle to the supporting angle, so it is also called the synchronization of the permanent magnet. Reluctance motor.
However, there are also some short plates in the "double U-shaped" structure. One of them is because the nonlinear reluctance of the motor has a large proportion of reluctance torque, which makes the control motor operation more complicated, especially in the vibration noise of the motor. The energy density of the two ferrite structures is smaller than that of NdFeB, so the overall power density and torque density are not the same as the one-word or V-shaped structure of the previous generation. Does not meet the development trend of miniaturization of the home appliance industry.
4. New V-type continuous magnetic pole built-in structure
The CP-IPMSM rotor structure designed by New Widetech reduces the number of magnets in each pair. A separate magnetic circuit is provided by a piece of magnetic steel.
Although the magnetic steel structure of CP-IPMSM can reduce the amount of magnetic steel, the disadvantages are also obvious. The degree of magnetic path is increased, the harmonic content of the air gap magnetic field is increased, the sinusoidality of the back EMF waveform is reduced, and the cogging torque Increase. In order to improve the above problem, in the rotor structure, it is attempted to further modify the rotor structure from the magnetic steel thickness, the magnetic island width, the magnetic steel angle, and the rotor slot width to optimize the magnetic circuit.
The CP-IPMSM motor designed by New Widetech has a running condition of 3,420 rpm and a rated torque of 0.85 Nm. For the "one-shaped" magnetic steel structure under the same working conditions, 33.9% of the magnetic steel consumption can be saved while maintaining the efficiency of the motor and even increasing it. This will bring huge cost reductions.
Reprinted from the network