JP2006299809A - Motor-driven compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor-driven compressor superior in reliability capable of avoiding abnormal stopping and reduction in efficiency, by increasing the stability of three-phase sine wave driving by sensorless vector control, by increasing the moment of inertia of a rotor, without requiring arithmetic processing of a high speed, and without requiring an excessive member. <P>SOLUTION: This motor-driven compressor is mounted with a motor composed of the rotor 42 having a permanent magnet 43 and a stator 44 having a plurality of phase winding 46. The rotor 42 is constituted so that angular acceleration by a compression load torque variation in operation becomes 1,000 (rad/s<SP>-2</SP>) or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric compressor driven by a three-phase sine wave by sensorless vector control.

  Conventionally, as an example of an electric compressor provided with a one-cylinder rotary compression mechanism or reciprocating compression mechanism, there is a one-cylinder rotary electric compressor shown in FIG. The one-cylinder rotary electric compressor is generally driven by a three-phase sine wave by sensorless vector control (for example, Patent Document 1).

  The one-cylinder rotary electric compressor is covered with a sealed case 1 as shown in FIG. A suction pipe 2 is attached to the lower part of the sealed case 1, and a discharge pipe 3 and a terminal terminal 4 are provided on the upper part. Inside the sealed case 1, a brushless DC motor 10 is accommodated as an electric motor part, and a compression mechanism part 20 is accommodated.

  The brushless DC motor 10 includes a stator 11 and a rotor 12. A large number of magnetic pole teeth 11a are arranged on the inner peripheral surface of the stator 11, and a plurality of phase windings 13 are concentratedly wound around the magnetic pole teeth 11a. As shown in FIGS. 6 and 7, the rotor 12 is formed by laminating a large number of disk-shaped steel plates in the axial direction, and the shaft 14 passes through the core portion and surrounds the shaft 14. Four permanent magnet pieces 15 are accommodated. By sequentially switching energization to each phase winding 13 of the stator 11 (commutation), a magnetic field is sequentially generated in each phase winding 13, and due to an interaction between the magnetic field created by each permanent magnet piece 5 of the rotor 12. Rotational torque is generated in the rotor 12.

  The compression mechanism 20 has a main bearing 21 and a sub-bearing 22 for supporting the shaft 14, and a cylinder 23 between both the bearings 21 and 22. An eccentric portion 14 a of the shaft 14 is accommodated in the cylinder 23. A roller 24 is mounted on the outer periphery of the eccentric portion 14 a, and a compression chamber 25 is formed around the roller 24. A suction port 26 communicates with the compression chamber 25, and the suction pipe 2 communicates with the suction port 26. In the cylinder 23, a discharge port (not shown) is formed at a position corresponding to the compression chamber 25.

  When the brushless DC motor 10 is driven to rotate the rotor 12 and the shaft 14, the roller 24 of the compression mechanism unit 20 rotates eccentrically, and suction pressure is generated in the compression chamber 25. The refrigerant is sucked into the compression chamber 25 from the suction pipe 2 by this suction pressure. The sucked refrigerant is compressed in the compression chamber 25 and then discharged into the sealed case 1 from the discharge port. The refrigerant discharged into the sealed case 1 is supplied to the refrigeration cycle via the discharge pipe 3.

  Lubricating oil (not shown) is accommodated in the inner bottom of the sealed case 1. The lubricating oil cools the compression mechanism unit 20 while ensuring a mechanical lubricating action of the compression mechanism unit 20.

In order to drive the brushless DC motor 10 of such a one-cylinder rotary electric compressor, a sensorless vector control circuit as shown in FIG. 8 is prepared. The sensorless vector control circuit does not directly detect the rotor position of the brushless DC motor 10 with a sensor, estimates the rotor position from the drive current, and controls the drive voltage for the brushless DC motor according to the estimated rotor position.
JP 2002-291285 A

  In the one-cylinder rotary electric compressor described above, the fluctuation of the compression load torque during one rotation becomes very large as shown in FIG. The fluctuation of the compression load torque causes a mismatch with the generated torque of the motor, and the rotor speed fluctuates during one rotation according to the difference between the generated torque and the load torque.

  In the three-phase sine wave drive by sensorless vector control, the rotor position is estimated by calculation using the drive current value and motor constants (inductance, DC resistance), and the drive voltage is controlled according to the estimated rotor position. In the estimation calculation of the rotor position, if the speed change rate (angular acceleration) of the rotor is large, an error may occur in the estimation, and an appropriate drive voltage may not be generated.

  FIG. 9 shows the relationship between the motor drive current waveform and the rotor position (represented by the no-load induced voltage waveform), and the relationship between the compression load torque and the rotational speed fluctuation. The rotational speed of the rotor varies. The motor drive current pulsates, and the phase between the induced voltage (= no-load induced voltage) and the drive current fluctuates, and the current advances or lags with respect to the induced voltage.

  If the drive current pulsates or the phase of the induced voltage and the drive current fluctuates, the stability will decrease and it will be easy to stop abnormally, and the motor efficiency will be greatly reduced, and the efficiency of the electric compressor will be reduced. descend.

  These problems can be improved to some extent by shortening the control cycle of sensorless vector control and increasing the number of computation outputs during one rotation, but in order to shorten the control cycle, faster computation processing And the control unit becomes expensive.

  In addition, rare earth magnets are used as permanent magnets in order to reduce the size and increase the efficiency of motors. However, since the rotors of motors using rare earth magnets are small, the moment of inertia is small and the fluctuations in rotational speed are large. The above problem becomes remarkable. For this reason, it is difficult to employ rare earth magnets in a one-cylinder rotary electric compressor driven by sensorless vector control.

  In consideration of the above circumstances, the present invention can increase the moment of inertia of the rotor without requiring high-speed arithmetic processing and without requiring extra members, thereby enabling three-phase by sensorless vector control. An object of the present invention is to provide a highly reliable electric compressor capable of increasing the stability of sinusoidal driving and avoiding abnormal stoppages and lowering of efficiency.

An electric compressor according to a first aspect of the present invention includes a motor including a rotor and a stator, and the rotor includes a permanent magnet, and is an angular acceleration due to a change in compression load torque during operation of the electric compressor. The rotor is configured so as to be 1000 (rad / s ⁻² ) or less.

  According to the electric compressor of the present invention, the inertia moment of the rotor can be increased without requiring high-speed arithmetic processing and without requiring an extra member, and thereby, three-phase sine wave drive by sensorless vector control. As a result, it is possible to avoid an abnormal stop and a decrease in efficiency, thereby improving reliability.

An embodiment of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, the one-cylinder rotary electric compressor is covered with a sealed case 31. A suction pipe 32 is attached to the lower part of the sealed case 31 and a discharge pipe 33 is attached to the upper part. Further, a terminal terminal 34 is provided on the top of the sealed case 31. Inside the sealed case 31, a brushless DC motor 40 is accommodated as an electric motor part, and a compression mechanism part 50 is accommodated.

  The brushless DC motor 40 includes a rotor frame 41a, a rotor iron core 41b rotatably provided inside the rotor frame 41a, and four permanent magnets 43 attached to the inner circumferential surface of the rotor iron core 41b along the circumferential direction. The rotor 42 is composed of a stator 44 provided inside the rotor 42, and a shaft 45 passing through the center of the stator 44. The upper portion of the shaft 45 is coupled to the case 41, and the rotation of the rotor 42 is transmitted to the shaft 45 by the coupling.

  As shown in FIG. 2, a plurality of magnetic pole teeth 44a are arranged on the outer peripheral surface of the stator 44, and a plurality of phase windings 46 are concentratedly wound around the magnetic pole teeth 44a. As shown in FIG. 3, the rotor 42 is formed by laminating a large number of annular steel plates. By sequentially switching energization of each phase winding 46 of the stator 44 (commutation), a magnetic field is sequentially generated in each phase winding 46, and due to the interaction between the magnetic field created by each permanent magnet 43 of the rotor 42, A rotational torque is generated in the rotor 42.

  The compression mechanism 50 includes a main bearing 51 and a sub-bearing 52 for supporting the shaft 45, and a cylinder 53 between the bearings 51 and 52. An eccentric portion 45 a of the shaft 45 is accommodated in the cylinder 53. A roller 54 is mounted on the outer periphery of the eccentric portion 45 a, and a compression chamber 55 is formed around the roller 54. A suction port 56 communicates with the compression chamber 55, and the suction pipe 32 communicates with the suction port 56. Further, a discharge port (not shown) is formed in the cylinder 53 at a position corresponding to the compression chamber 55.

  As the brushless DC motor 40 is driven to rotate the rotor 42, the case 41, and the shaft 45, the roller 54 of the compression mechanism 50 rotates eccentrically, and suction pressure is generated in the compression chamber 55. The refrigerant is sucked into the compression chamber 55 from the suction pipe 32 by this suction pressure. The sucked refrigerant is compressed in the compression chamber 55 and then discharged into the sealed case 31 from the discharge port. The refrigerant discharged into the sealed case 31 is supplied to the refrigeration cycle through the discharge pipe 33.

  Lubricating oil (not shown) is accommodated in the inner bottom portion of the sealed case 31. The lubricating oil cools the compression mechanism unit 50 while ensuring the mechanical lubrication action of the compression mechanism unit 50.

  FIG. 4 shows the load torque fluctuation of the one-cylinder rotary electric compressor configured as described above in comparison with the load torque fluctuation of the two-cylinder rotary electric compressor. That is, the 1-cylinder type has a larger fluctuation in load torque than the 2-cylinder type, and has a fluctuation of about 150% with respect to the average during one rotation. The 2-cylinder type has a small fluctuation of about 30% with respect to the average during one rotation.

Inertia moment J of a rotating system including a permanent magnet rotor of a compressor mounted on a home air conditioner is generally 6 × 10 ^{−4 to} 1.2 × 10 ⁻³ (kg) using a ferrite magnet. · M ² ), and those using rare earth magnets are about 2 × 10 ^{−4 to} 5 × 10 ⁻⁴ (kg · m ² ).

Assuming that the motor generated torque during operation is almost constant, in the example of FIG. 4, a torque difference ΔT of about 2.4 (N · m) is generated at the maximum. If a ferrite magnet is used, From the angular acceleration dω / dt = ΔT / J, angular acceleration of about 2000 to 4000 (rad / s ⁻² ) occurs. If a rare earth magnet is used, the angular acceleration is about 4800 to 12000 (rad / s ⁻² ).

  The torque difference ΔT varies depending on the load condition of the compressor, and increases as the load increases and the compression ratio increases. Although the angular acceleration also changes in proportion to the torque difference ΔT, it is desirable to prevent the drive instability from being reduced under all operating conditions.

Therefore, when various tests were conducted focusing on the relationship between the angular acceleration and the driving instability reduction, when the angular acceleration was 1000 (rad / s ⁻² ) or less, the driving instability phenomenon due to the error in position estimation calculation occurred. It was found to occur.

A three-phase sinusoidal voltage for sensor vector control in a one-cylinder rotary electric compressor is adopted by employing a permanent magnet rotor whose angular acceleration due to fluctuations in compression load torque during operation is 1000 (rad / s ⁻² ) or less. In driving, it is possible to prevent the occurrence of unstable driving phenomenon.

However, in order to reduce the angular acceleration to 1000 (rad / s ⁻² ) or less with an inner rotor type motor, it is necessary to employ a very large permanent magnet rotor.

  On the other hand, as shown in FIG. 1, if the rotor 42 is an outer rotor type brushless DC motor 40 arranged outside the stator 44, the outer diameter of the rotor 42 is large, and therefore the mass is biased toward the outer diameter, As a result, the moment of inertia increases.

  In general, the outer rotor type has a moment of inertia that is several to tens of times that of the inner rotor type. When the moment of inertia becomes K times, the rotational speed fluctuation due to the difference between the generated torque and the load torque is theoretically 1 / K times, and the outer rotor type permanent magnet motor has a very small speed change rate (angular acceleration) during one rotation. Become.

As a result, by performing an appropriate design, it is possible to easily suppress the angular acceleration caused by fluctuations in the compression load torque during driving to 1000 (rad / s ⁻² ) or less, and position estimation in sensorless vector control. The calculation error is reduced, thereby suppressing the pulsation of current and the fluctuation of phase, thereby preventing a reduction in motor efficiency.

Further, when a rare earth magnet is employed as the permanent magnet 43 and the size is reduced, the moment of inertia becomes sufficiently large, so that the angular acceleration due to the fluctuation of the compression load torque during operation can be easily increased to 1000 (rad / s ^−2). ) It is possible to make the following, and there is no problem due to an increase in position estimation error.

  With the above configuration, the moment of inertia of the rotor 42 can be increased without requiring high-speed arithmetic processing and without requiring extra members, thereby improving the stability of three-phase sine wave drive by sensorless vector control. In addition, it becomes possible to avoid an abnormal stop and a decrease in efficiency, and the reliability as an electric compressor is greatly improved. In addition, the use of rare earth magnets can reduce the size and increase the efficiency.

  In the above embodiment, the rotary compressor has been described as an example, but the present invention can be similarly applied to a reciprocating compressor. In addition to the one-cylinder compressor, the present invention can be implemented not only in a compressor that can operate in a single cylinder with a plurality of cylinders.

  In addition, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment.

The figure which shows the internal structure of one Embodiment. The figure which looked at the principal part of one embodiment from the upper part. The perspective view which shows the principal part of one Embodiment. The figure which shows the load torque fluctuation | variation of the 1 cylinder type rotary electric compressor in one Embodiment in contrast with the load torque fluctuation | variation of a 2 cylinder type rotary electric compressor. The figure which shows the structure inside the conventional electric compressor. The figure which looked at the principal part of Drawing 5 from the upper part. The perspective view which shows the principal part of FIG. The block diagram which shows a general sensorless vector control circuit. The figure which shows the relationship between the motor drive current waveform of FIG. 5 and a rotor position, and the relationship between compression load torque and rotation speed fluctuation | variation.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 31 ... Sealing case, 32 ... Suction pipe, 33 ... Discharge pipe, 40 ... Brushless DC motor, 50 ... Compression mechanism part, 41a ... Rotor frame, 41b ... Rotor core, 42 ... Rotor, 43 ... Permanent magnet, 44 ... Stator, 44a ... Magnetic pole teeth, 45 ... Shaft, 46 ... Each phase winding, 53 ... Cylinder, 54 ... Roller, 55 ... Compression chamber, 56 ... Suction port

Claims (2)

In an electric compressor equipped with a motor comprising a rotor having a permanent magnet and a stator having a plurality of phase windings,
An electric compressor characterized in that the rotor is configured such that angular acceleration due to fluctuations in compression load torque during operation is 1000 (rad / s- ² ) or less. 2. The electric compressor according to claim 1, wherein the motor is an outer rotor type in which the rotor is disposed outside the stator, and the permanent magnet of the rotor is a rare earth magnet.

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