JP6993558B2 - How to drive the motor, how to start the compressor, compressor - Google Patents

Description

The present invention relates to a method of driving an electric motor, for example, the electric motor drives a compressor that compresses a refrigerant.

The torque required to start a compressor, for example, a compressor that compresses a refrigerant (hereinafter referred to as "starting torque") is the torque required for the compressor during normal operation (hereinafter referred to as "normal operating torque"). In comparison, it may be larger. This is because compression by the compressor overcomes the differential pressure between the suction side and the discharge side, but the differential pressure is large depending on the state of the refrigerant before startup (or the refrigerant system using the refrigerant). Because there is.

When the starting torque is large, the starting of the compressor is likely to fail. If the startup fails, it is necessary to wait for the startup until the differential pressure becomes small. In such an operation, not only the power required for the failed start-up is wasted and is not desirable from the viewpoint of power saving, but also the comfort is caused by the substantial delay in the operation of the electric appliance using the refrigerant, for example, the air conditioner. May be damaged.

In Patent Document 1 below, the crank portion is connected to the rotor of the motor via the rotating shaft, and the crank portion is connected to the piston of the compressor. Then, in order to easily activate the compressor, a technique for initial alignment of the rotor to the bottom dead center of the piston before forcibly aligning the rotor to a predetermined activation position in the suction process is disclosed.

Patent Document 2 below discloses a technique for eliminating a start-up failure by utilizing the torque due to the inertia of a reciprocating compressor. Specifically, a rotation command for rotating the synchronous motor for driving the reciprocating compressor in the reverse direction is given for a predetermined time, and then a rotation command for rotating the synchronous motor in the forward direction is adopted.

Japanese Patent No. 4515432 Japanese Unexamined Patent Publication No. 2007-267451

Patent Document 1 is a technique for a compressor using a piston. It also teaches that the rotor is generally near bottom dead center due to the influence of inertial force. Therefore, it is considered that the compressor that requires the load torque for the motor and the motor that outputs the output torque are required to be connected in a positional relationship that makes it easy to start. Such a requirement is not desirable from the viewpoint of man-hours in the assembly process. Moreover, depending on the differential pressure and the position of the rotor, it becomes difficult to move the rotor to the starting position where the rotor is forcibly aligned, and if the positioning is performed again, the starting time may be lost.

In Patent Document 2, the start-up of the compressor is improved by changing the rotation direction. It teaches that the rotor rotates in the direction in which the load torque decreases by rotating in the reverse direction and stopping once without overcoming the load torque and then rotating in the forward direction. Such a stop from the reverse rotation of the rotor is premised on the moment of inertia of the rotor, and compression of a non-reciprocal compressor, for example, a rotary type or scroll type compressor, which has a small inertia. It is considered difficult to apply to the aircraft. Further, in order for the reverse rotation itself to occur, it is considered that the position of the rotor is required to be within a predetermined range of width π / 2 (3π / 2 to 2π in the embodiment of Patent Document 2).

Therefore, an object of the present invention is to easily start a compressor having a small inertia even if the differential pressure is large.

The method for driving an electric motor according to the present invention is a method for driving a compressor that compresses a refrigerant by a rotary motion or a swivel motion of a compression member. The method includes a first step (S103) of generating a first rotational magnetic flux (φa0, φa1) for rotating the motor in the first rotation direction from the state where the compressor is stopped, and the first step (S103). After the first step, a second step (S105) for generating a second rotational magnetic flux (φa2) for rotating the electric motor in the second rotation direction is provided in the electric motor. Here, the first rotation direction is the direction opposite to the second rotation direction, and the second rotation direction is the rotation direction of the electric motor that causes the compressor to compress the refrigerant.

The method for starting the compressor according to the present invention is to start the compressor by the first step and the second step.

The compressor according to the present invention is activated by the first step and the second step.

Even if the differential pressure is large, a compressor with a small inertia can be easily started.

It is a block diagram which shows the compression system to which the driving method of the electric motor which concerns on embodiment is applied. It is a schematic diagram which illustrates the structure of the electric motor which concerns on embodiment. It is a vector figure which shows the driving method of the electric motor which concerns on embodiment. It is a vector figure which shows the driving method of the electric motor which concerns on embodiment. It is a vector figure which shows the driving method of the electric motor which concerns on embodiment. It is a vector figure which shows the driving method of the electric motor which concerns on embodiment. It is a vector figure which shows the driving method of the electric motor which concerns on embodiment. It is a vector figure which shows the driving method of the electric motor which concerns on embodiment. It is a figure which shows the current waveform which shows the driving method of the electric motor which concerns on embodiment. It is a flowchart which shows the driving method of the electric motor which concerns on embodiment. It is a flowchart which partially shows the driving method of the electric motor which concerns on embodiment.

{Outline of configuration}
FIG. 1 is a block diagram showing a compression system to which the motor driving method according to this embodiment is applied.

The compressor 4 is driven by the electric motor 3 to compress the refrigerant. For the compressor 4, for example, a rotary type, a turbo type, a screw type or a scroll type compressor is adopted. Since it is well known that such a type of compressor compresses the refrigerant by the rotational movement or the swirling motion of the compression member, the illustration of the compression member is omitted. Inertia is generally small in these formats. It is also well known that a rotary piston, a swing piston, a swivel scroll, a screw rotor, and a turbo impeller can be adopted as the compression member.

The electric motor 3 is driven by the inverter 2. Specifically, for example, the electric motor 3 is a three-phase electric motor, and the three-phase currents Iu, Iv, and Iw output from the inverter 2 are input and driven. The electric machine 3 is driven by the interaction between the armature magnetic flux and the field magnetic flux generated by the three-phase currents Iu, Iv, and Iw.

FIG. 2 is a schematic diagram illustrating the configuration of the electric motor 3. The electric machine 3 includes an armature winding 3a through which three-phase currents Iu, Iv, and Iw flow to generate an armature magnetic flux, and a field magnet 3b that generates a field magnetic flux. Since the armature winding 3a and the field magnet 3b are known to be normally provided in the electric motor 3, detailed description of the structure of the electric motor 3 is omitted here. Hereinafter, for the sake of simplicity, a case where the magnitude of the field magnetic flux is constant and the field 3b functions as a rotor will be described.

The inverter 2 inputs a command signal J, generates three-phase currents Iu, Iv, and Iw based on the command signal J, and outputs the three-phase currents Iu, Iv, and Iw to the electric machine 3 (more specifically, the armature winding 3a). The command signal J determines the pattern of switching performed for the operation of the inverter 2, for example, DC / AC conversion.

Since a technique for generating three-phase currents Iu, Iv, and Iw that generate armature magnetic flux in the motor 3 from such a command signal J is known, detailed description thereof will be omitted.

The control unit 1 inputs an operation command K and generates a command signal J based on the operation command K. The control unit 1 also inputs a position signal Q, and generates a command signal J based on the position signal Q. For the operation command K, for example, a command value of the rotation speed of the electric motor 3, a command value of torque, or both can be adopted. The position signal Q is a signal indicating the rotational position of the rotor of the electric motor 3. The position signal Q can be obtained from the position sensor by providing a position sensor (not shown) in the motor 3. Alternatively, the three-phase currents Iu, Iv, and Iw can be measured directly or indirectly, and the rotation position estimated based on the measurement can be adopted. Since the method of generating the position signal Q in any case is known, detailed description thereof will be omitted.

However, the position signal Q is not indispensable when it comes to the activation method according to the present embodiment described later. The position signal Q can be adopted in the normal operation after the start-up.

{Explanation of issues according to the embodiment}
3 to 8 are vector diagrams showing a driving method of the electric motor according to this embodiment. In these figures, the phase is represented by the electrical angle. The fixed coordinate system αβ of the motor 3 is set. The β-axis is 90 degrees ahead of the α-axis.

The term armature magnetic flux φa is used as a general term for the armature magnetic flux φa0 (FIG. 3, FIG. 4), φa1 (FIG. 5, FIG. 6, FIG. 7), and φa2 (FIG. 8). The phase of the armature magnetic flux φa is represented by the M axis. The three-phase currents Iu, Iv, and Iw generally generate a rotating magnetic field as an armature magnetic flux φa, except in the case of DC excitation described later. Therefore, the phase of the M axis fluctuates with respect to the α axis (and therefore also with respect to the β axis).

The phase of the field magnetic flux φr is represented by the R axis. The field magnetic flux φr is generated by the field magnet 3b, and the positional relationship between the field magnet 3b and the armature winding 3a fluctuates (rotates) relatively, so that the R axis is relative to the α axis (hence the β axis). However, the phase fluctuates.

As a technical common sense, if the absolute values of the field magnetic flux φr and the armature magnetic flux φa do not fluctuate, the smaller the phase difference between the two, the torque generated between the armature winding 3a and the field magnet 3b. (That is, the torque generated in the electric machine 3) is large.

First, with reference to FIG. 3, the problem to be solved will be described according to this embodiment. The situation (i) shown in FIG. 3 is a situation immediately after the start of driving of the motor 3, and the armature magnetic flux φa0 is generated. In the situation (i), the phase difference between the field magnetic flux φr and the armature magnetic flux φa0 (that is, the phase difference between the M axis and the R axis) is large, and the torque generated in the motor 3 is small. Therefore, when the differential pressure in the compressor 4 is large and therefore the starting torque is large, if the driving of the motor 3 is started with such a phase difference, it is easy to fail.

Indeed, by increasing the absolute value of the armature magnetic flux φa0, it is theoretically possible to generate a torque larger than the starting torque in the motor 3 while maintaining the phase difference. However, in view of the fact that it is usual to set an upper limit on the absolute values of the three-phase currents Iu, Iv, and Iw that generate the armature magnetic flux φa, increasing the absolute value of the armature magnetic flux φa0 is not practically controlled. do not have.

In the techniques disclosed in Patent Documents 1 and 2, according to FIG. 3, the phase difference between the M axis and the R axis is reduced by moving the R axis closer to the M axis in the fixed coordinate system αβ. However, as mentioned above, it may be difficult for such a technique to easily start a compressor having a small inertia. Therefore, in the present embodiment, the phase difference between the two at the time of activation is reduced by moving the M axis closer to the R axis in the fixed coordinate system αβ.

{Behavior of armature magnetic flux φa in this embodiment}
FIG. 4 shows a situation (ii) following the situation (i). The situation (ii) is a situation in which the absolute value of the armature magnetic flux φa0 is increased without changing the phase of the M axis with respect to the α axis. In other words, the situations (i) and (ii) are the situations where the electric motor 3 is DC-excited, and the armature magnetic flux φa0 is the non-rotating armature magnetic flux φa. In FIG. 4, the rotation direction Rb of the armature magnetic flux φa is added to indicate the direction thereof, and does not indicate that the armature magnetic flux φa0 is rotating in the situation (ii).

The situation (ii) is not for generating a torque larger than the starting torque in the motor 3. Normally, the three-phase currents Iu, Iv, and Iw are not output stepwise, but are output as absolute values that increase like a lamp. This is a natural phenomenon because the armature winding 3a of the motor 3 usually forms a coil, and the motor 3 has an inductive load. Such a gradual increase in the absolute values of the three-phase currents Iu, Iv, and Iw causes a transition from the situation (i) to the situation (ii). However, the three-phase currents Iu, Iv, and Iw may be output stepwise.

FIG. 9 shows the current waveforms of the three-phase currents Iu, Iv, and Iw in the present embodiment. The Roman numeral indicating the timing in FIG. 9 corresponds to the Roman numeral indicating the situation in FIGS. 3 to 8. With the passage of time, the situation (i) shifts to the situation (ii), and the absolute values of the three-phase currents Iu, Iv, and Iw gradually increase. In the transition from situation (i) to situation (ii), it is not always essential that the phase difference between the three-phase currents Iu, Iv, and Iw is maintained. In other words, DC excitation is not always essential in situations (i) and (ii).

After the situation (ii) occurs, the armature magnetic flux φa is changed from the armature magnetic flux φa0 that performs DC excitation to the armature magnetic flux φa1 that rotates in the rotation direction Rb (denoted as “reverse rotation” in FIG. 9). .. Specifically, the three-phase currents Iu, Iv, and Iw are alternating currents.

FIG. 5 shows a situation (iii) following the situation (ii). Situation (iii) indicates a situation in which the M axis rotates in the rotation direction Rb after the situation (ii). Specifically, the phases of the three-phase currents Iu, Iv, and Iw fluctuate while maintaining the absolute values of the three-phase currents Iu, Iv, and Iw. The rotation direction Rb is the direction opposite to the rotation direction Rf. The rotation direction Rf corresponds to the direction in which the motor 3 rotates in the operation of compressing the refrigerant in the compressor 4 (hereinafter referred to as “compression operation”). More specifically, it is the direction in which the field magnetic flux φr rotates in the compression operation.

In FIGS. 5 to 8, the phase of the armature magnetic flux φa1 (currently) is set to the M'axis with the position of the M axis (that is, indicating the phase of the armature magnetic flux φa0) in the situations (i) and (ii) as the M'axis. It is also described with the M axis showing.

In FIGS. 3 and 4, in the situations (i) and (ii), the case where the M axis is separated from the R axis by less than 180 degrees when viewed along the rotation direction Rb is shown. Therefore, as the armature magnetic flux φa1 rotates in the rotation direction Rb, the phase difference between the M axis and the R axis becomes smaller. FIG. 5, however, illustrates the case where the generated torque is still small and the R axis is maintained.

FIG. 6 shows the situation (iv) following the situation (iii). The situation (iv) shows a situation in which the M axis further rotates in the rotation direction Rb after the situation (iii), and the M axis coincides with the R axis while the R axis is maintained. The absolute value of the armature magnetic flux φa1 is set large enough to generate at least a torque equal to or greater than the torque required for the motor 3 to rotate in the reverse direction when the M axis coincides with the R axis (hereinafter referred to as “reverse torque”). do. The reverse torque is smaller than the starting torque due to the differential pressure of the compressor 4.

After the situation (iv), the armature magnetic flux φa1 rotates in the rotation direction Rb, so that the field magnetic flux φr also rotates in the rotation direction Rb. As a result, the R axis also rotates in the rotation direction Rb in line with the M axis.

FIG. 7 shows the situation (v) following the situation (iv). The situation (v) shows a situation in which the armature magnetic flux φa1 further rotates in the rotation direction Rb after the situation (iv), and rotates in the rotation direction Rb while the R axis and the M axis coincide with each other. In FIGS. 7 to 8, the position of the R axis in the situations (i) to (iv) (that is, before the field magnetic flux φr rotates in the rotation direction Rb) is set as the R'axis, and the field magnetism (at present). It is also described with the R axis showing the phase of the magnetic flux φr.

FIG. 7 particularly shows a situation in which the M axis and the M'axis form a phase angle π (= 180 degrees). That is, it shows a situation where the phase angle at which the armature magnetic flux φa1 moves in the rotation direction Rb is π. If the armature magnetic flux φa1 rotates in the rotation direction Rb at a phase angle π in this way, the R axis and the M axis always coincide with each other during that time. Therefore, by rotating the armature magnetic flux φa1 in the rotation direction Rb at least with a phase angle π (that is, rotating at 180 degrees or more), the position of the R axis (phase difference with respect to the α axis) is not known, in other words. The position of the R axis is moved along the rotation direction Rb without requiring the position signal Q, and the motor 3 is rotated in the direction opposite to the compression operation.

FIG. 9 illustrates a case where the armature magnetic flux φa1 moves in the rotation direction Rb larger than the phase angle π.

Assuming that the position of the R axis is unknown, the absolute value of the armature magnetic flux φa1 is set large enough to generate a torque equal to or larger than the reverse torque when the M axis coincides with the R axis from the beginning. Is desirable. Specifically, in the situation (ii), the three-phase currents Iu, Iv, and Iw are increased in advance in order to increase the armature magnetic flux φa0 in advance.

FIG. 8 shows a situation (vi) in which the armature magnetic flux φa is rotated in the rotation direction Rf (denoted as “normal rotation” in FIG. 9) after the R axis and the M axis are aligned. Since the phase difference between the M axis and the R axis becomes substantially zero, a large torque is generated even if the absolute values of the three-phase currents Iu, Iv, and Iw are small. Therefore, even if the differential pressure is large, the compressor 4 having a small inertia can be easily started.

In FIG. 9, a situation is provided in which a period of DC excitation in which the armature magnetic flux φa does not rotate is provided from the time when the armature magnetic flux φa1 finishes rotating in the rotation direction Rb to the time when the armature magnetic flux φa2 starts rotating in the rotation direction Rf ( vii) is illustrated. This situation (vii) is provided for the convenience of measuring the three-phase currents Iu, Iv, and Iw, and is not an essential situation for easily starting the driving of the motor 3.

{Explanation of steps to drive the motor}
FIG. 9 is a flowchart showing a driving method of the electric motor 3 for activating the compressor 4 in the present embodiment. However, the situation (vii) will be briefly explained using a separate flowchart. It can be said that the compressor 4 is activated by the driving method of the electric motor 3.

Each step constituting the flowchart of FIG. 9 is executed by the control unit 1 itself or by the inverter 2 under the control thereof.

In step S101, the armature magnetic flux φa0 is generated and increased. Following step S101, it is determined in step S102 whether or not the absolute value of the armature magnetic flux φa0 has reached a predetermined value. Step S101 is repeatedly executed until the determination result becomes affirmative (see the "No" route from step S102 to step S101). Situations (i) and (ii) are realized by repeatedly executing step S101. The period during which step S101 is repeatedly executed is indicated as "| φa | increasing" in FIG.

If the determination result of step S102 is affirmative, step S103 is executed (see the "Yes" route from step S102 to step S103). In step S103, an armature magnetic flux Φa1 that rotates in the rotation direction Rb is generated. This realizes situation (iii). Following step S103, it is determined in step S104 whether or not the armature magnetic flux φa1 has rotated 180 degrees (π in radians) or more in the rotation direction Rb. Step S103 is repeatedly executed until the determination result becomes affirmative (see the "No" route from step S104 to step S103). Situations (iv) and (v) are realized by repeatedly executing step S103.

Until the situation (iv), the compressor 4 is in a stopped state. Therefore, in step S103, the first step of generating the armature magnetic flux Φa1 which is the first rotating magnetic flux for rotating the motor 3 in the direction opposite to the compression operation from the state where the compressor 4 is stopped is generated in the motor 3. Can be seen as.

If the situation (v) is realized, the determination result of step S104 becomes affirmative, and step S105 is executed (see the "Yes" route from step S104 to step S105).

Therefore, it can be said that the situations (iv) and (v) are realized at least at the end of the period for executing the first step described above. In the situations (iv) and (v), it can be said that the M axis, which is the direction of the magnetic pole of the armature magnetic flux Φa1, coincides with the R axis, which is the direction of the field magnetic flux φr when the motor 3 is stopped.

In step S105, an armature magnetic flux Φa2 that rotates in the rotation direction Rf is generated. This realizes the situation (vi).

Therefore, it can be seen that step S105 is a second step of generating a second rotating magnetic flux in the motor 3 for rotating the motor 3 in the direction of the compression operation after the first step described above.

After step S105, the determination in step S106 is performed. Step S106 is a process for setting the starting position of the compressor 4 to a desired position. Specifically, in step S106, it is determined whether or not the field magnetic flux φr is in a desired phase in the fixed coordinate system αβ. Such a determination can be made based on, for example, the position signal Q.

Step S105 is repeatedly executed until the determination result becomes affirmative (see the "No" route from step S106 to step S105). If the determination result is positive, the field magnetic flux φr is in the desired phase at that time. In that case, step S107 is executed to generate an armature magnetic flux that rotates in the rotation direction Rf (see the “Yes” path from step S106 to step S107).

{Transformation}
In step S107, the electric motor 3 for causing the compressor 4 to perform the compression operation can be driven. Therefore, strictly speaking, this step S107 may be excluded from the "startup" of the compressor 4.

Step S106 can be omitted without setting the starting position of the compressor 4 to a desired position. In this case, step S107 is also combined by step S105.

As described above, the three-phase currents Iu, Iv, and Iw may be output stepwise. In this case, steps S101 and S102 can be omitted. In other words, it can be said that step S101 is a third step of generating a DC magnetic flux in the motor 3 prior to the above-mentioned first step.

In order to realize the above situation (vii), DC excitation may be performed between step S104 and step 105. FIG. 11 partially shows a flowchart in the case of performing such DC excitation. Since steps S101 to S103 are the same as the flowchart shown in FIG. 10, they are omitted in FIG.

When the determination result in step S104 is affirmative, DC excitation and current measurement are performed in step S108 prior to the execution of step S105. As shown in FIG. 9, the DC excitation has fixed values of the three-phase currents Iu, Iv, and Iw. Such DC excitation can be seen as a fourth step performed after the first step described above and before the second step.

Further, in the current measurement, the direct current flowing through the inverter 2 is detected by a known method, and the value Id is given to the control unit 1 (see FIG. 1). The control unit 1 can estimate the three-phase currents Iu, Iv, and Iw based on the DC current value Id and the command signal J generated by the control unit 1.

Since the technique itself for performing such estimation is well known, detailed description thereof will be omitted here. It is known that it is desirable that a non-zero current flows in any phase of the motor 3 from the viewpoint of easily enhancing the above estimation. According to the present embodiment, it is desirable that the absolute values of the three-phase currents Iu, Iv, and Iw are all positive.

The above-mentioned third step (corresponding to step S101) and the fourth step (corresponding to DC excitation in step S108) are not essential as a driving method of the electric motor 3 for starting the compressor 4, and the driving driving method is described above. It can be said that it is sufficient if the first step (corresponding to step S103) and the second step (corresponding to step S105) are provided.

In the situations (i) and (ii), the M axis may be separated from the R axis by 180 degrees or more along the rotation direction Rb. In this case, with the help of the differential pressure, at the beginning of step S103, the field magnetic flux φr quickly rotates toward the rotation direction Rb, and the R axis coincides with the M axis.

S101 (3rd) step S103 (1st) step S105 (2nd) step S108 (4th) step φa1 armature magnetic flux (first rotating magnetic flux)
φa2 armature magnetic flux (second rotating magnetic flux)

Claims (7)

It is a method of driving a compressor that compresses a refrigerant by a rotary motion or a swivel motion of a compression member by an electric motor.
The first step (S103) of generating the first rotational magnetic flux (φa1) for rotating the electric motor in the first rotation direction from the state where the compressor is stopped, and the first step (S103).
After the first step, a second step (S105) of generating a second rotating magnetic flux (φa2) for rotating the motor in the second rotation direction in the motor ,
Prior to the first step, with the third step (S101) of generating a DC magnetic flux in the motor.
Equipped with
The first rotation direction is opposite to the second rotation direction.
The second rotation direction is the rotation direction of the electric motor that causes the compressor to compress the refrigerant, which is a method of driving the electric motor. The first aspect of claim 1, wherein the direction of the magnetic pole of the first rotational magnetic flux coincides with the direction of the field magnetic flux of the motor in the state where the motor is stopped, at least at the end of the period in which the first step is executed. How to drive the motor. The method for driving an electric motor according to claim 1 or 2 , wherein in the first step, the first rotating magnetic flux (φa1) rotates 180 degrees or more in the first rotation direction (S103, S104). After the first step (S103) and before the second step (S105), a fourth step (S108) in which DC excitation is performed on the motor.
The method for driving an electric motor according to any one of claims 1 to 3 , further comprising. The method for driving a motor according to claim 4 , wherein in the fourth step, a non-zero current flows in any phase of the motor. The method for starting a compressor according to any one of claims 1 to 5 , wherein the compressor is started by the first step and the second step. A compressor activated by the first step and the second step of the method for driving an electric motor according to any one of claims 1 to 5 .

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