Current control system

Abstract

To provide a current control system capable of reducing vibration at a lower cost than when the rigidity of a magnetic circuit or a motor is changed.SOLUTION: A control device 20 includes a current table 25 in which a d-axis current command and a q-axis current command corresponding to a torque and a rotation speed are stored. The d-axis current command and the q-axis current command are stored in the current table 25 such that a phase of a current when the torque is within a first range and a rotation speed is within a second range is delayed relative to a phase of the current when the torque is within the first range and the rotation speed is outside the second range, and a magnitude of the current when the torque is within the first range and the rotation speed is within the second range is larger than a magnitude of the current when the torque is within the first range and the rotation speed is outside the second range. The control device 20 refers to the current table 25, derives the d-axis current command and the q-axis current command based on the torque and the rotation speed, and outputs an output command based on the derived d-axis current command and the q-axis current command to a power converter 40.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a current control system for reducing vibration in an electric motor. [Background technology]

[0002] In recent years, there has been a demand for smaller electric motors installed in electric vehicles (hereinafter referred to as EVs). However, when a smaller electric motor is used at high torque, vibration increases. Regarding vibration in electric motors for EVs, it is important to reduce vibration at the 24th and 48th rotational orders. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 4-29583 Summary of the Invention [Problem to be solved by the invention]

[0004] Known methods for reducing vibration in permanent magnet synchronous motors for EVs include modifying the magnetic circuit and the motor's rigidity. However, reducing vibration using these methods requires modifying many parts, such as the rotor, stator, and motor frame, which is time-consuming and expensive.

[0005] Given the above, the challenge is to provide a current control system that can reduce vibration by changing the current supplied to the electric motor at a lower cost than when changing the rigidity of the magnetic circuit or motor. [Means for solving the problem]

[0006] The present invention has been devised in view of the above-mentioned problems of the related art, and one aspect thereof comprises: an electric motor that is driven at a torque and a rotation speed corresponding to a current supplied thereto; a power converter that controls the current supplied to the electric motor based on an output command; and a control device that has a current table in which a d-axis current command and a q-axis current command corresponding to the torque and the rotation speed are stored, refers to the current table to derive the d-axis current command and the q-axis current command based on the torque and the rotation speed, and outputs the output command based on the derived d-axis current command and q-axis current command to the power converter, wherein the current table contains The d-axis current command and the q-axis current command are stored so that the phase of the current supplied to the electric motor when the torque is within a first range and the rotation speed is within a second range is delayed compared to the phase of the current supplied to the electric motor when the torque is within the first range and the rotation speed is outside the second range, and the magnitude of the current supplied to the electric motor when the torque is within the first range and the rotation speed is within the second range is greater than the magnitude of the current supplied to the electric motor when the torque is within the first range and the rotation speed is outside the second range.

[0007] In one aspect, the current table sets the d-axis current command when the torque is within the first range and the rotational speed is within the second range to a value smaller than the d-axis current command when the torque is within the first range and the rotational speed is outside the second range, and sets the q-axis current command when the torque is within the first range and the rotational speed is within the second range to a value larger than the q-axis current command when the torque is within the first range and the rotational speed is outside the second range.

[0008] In one aspect, the electric motor is an interior magnet synchronous motor. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a current control system that can reduce vibrations by changing the current supplied to the electric motor at a lower cost than when changing the rigidity of the magnetic circuit or the motor. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing a current control system according to an embodiment; [Figure 2] FIG. 4 is a diagram showing an example of a current table according to the embodiment. [Figure 3] FIG. 4 is a diagram showing an example of the relationship between the rotation speed and a d-axis current command in the embodiment. [Figure 4] FIG. 4 is a diagram showing an example of the relationship between the rotation speed and a q-axis current command in the embodiment. [Figure 5] 4 is a flowchart showing the procedure of a current control process performed by the control device. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of a current control system according to the present invention will be described in detail with reference to FIGS.

[0012] [Embodiment] <Overall composition> First, the configuration of a current control system 1 according to the embodiment will be described. Fig. 1 is a block diagram showing the configuration of a current control system 1 according to the present embodiment.

[0013] As shown in FIG. 1, the current control system 1 includes an electric motor (rotating machine) 10, a control device 20, a torque command unit 30, a power converter (for example, an inverter, hereinafter referred to as the inverter) 40, and a DC power supply 50.

[0014] The electric motor 10 is, for example, a permanent magnet synchronous motor (PMSM). More specifically, the electric motor 10 is an interior permanent magnet synchronous motor (IPMSM) in which permanent magnets are embedded in the rotor.

[0015] The electric motor 10 is connected to an inverter 40 and is driven at a torque corresponding to the magnitude of the current supplied from the inverter 40 and at a rotation speed corresponding to the frequency of the current. The electric motor 10 has a speed detector 11 that detects the rotation phase and rotation speed. The speed detector 11 is, for example, an encoder such as a resolver.

[0016] The control device 20 includes a current command calculation unit 21 , a current controller 22 , coordinate conversion units 23 and 24 , and a current table 25 .

[0017] The current command calculation unit 21 is connected to the torque command unit 30, the speed detector 11, the current controller 22, and the current table 25. The current command calculation unit 21 refers to the current table 25, and derives a d-axis current command and a q-axis current command based on the rotation speed detected by the speed detector 11 and the torque command output from the torque command unit 30, and outputs the d-axis current command and the q-axis current command to the current controller 22.

[0018] The current table 25 stores d-axis current commands and q-axis current commands corresponding to each torque and each rotation speed. The d-axis current commands and q-axis current commands stored in the current table 25 are values ​​calculated in advance through experiments or the like, and are values ​​that can reduce vibration of the electric motor 10. Details of the current table 25 will be described later in the description of FIG. 2.

[0019] The current controller 22 is connected to the current command calculation unit 21 and the coordinate conversion units 23 and 24. The current controller 22 compares the d-axis current command and q-axis current command output from the current command calculation unit 21 with the d-axis current detection information and q-axis current detection information output from the coordinate conversion unit 24, and outputs to the coordinate conversion unit 23 a d-axis / q-axis output command (for example, a d-axis / q-axis output current command or a d-axis / q-axis output voltage command) that adjusts the current based on the comparison result.

[0020] The coordinate conversion unit 23 is connected to the current controller 22, the speed detector 11, and the inverter 40. The coordinate conversion unit 23 converts the d-axis and q-axis output commands output from the current controller 22 into three-phase (u-phase, v-phase, w-phase) output commands (e.g., output current commands or output voltage commands) based on the rotation phase of the electric motor 10, and outputs them to the inverter 40. The phase of the current supplied to the electric motor 10 is determined based on the d-axis current command and the q-axis current command.

[0021] The coordinate conversion unit 24 converts information on the current supplied from the inverter 40 to the motor 10 (three-phase current detection information) into d-axis current detection information and q-axis current detection information based on the rotation phase of the motor 10, and outputs the information to the current controller 22.

[0022] The DC power supply 50 supplies current to the inverter 40. Based on the three-phase output command output from the coordinate conversion unit 23, the inverter 40 converts the DC current supplied from the DC power supply 50 into AC current, and controls the current supplied to the electric motor 10 to have a desired phase and magnitude.

[0023] <Configuration of Current Table 25> Next, the current table 25 will be described in detail. Fig. 2 is a diagram showing an example of the current table 25. In Fig. 2, the vertical axis represents torque (Nm) and the horizontal axis represents rotation speed (rpm). As shown in Fig. 2, the current table 25 stores a d-axis current command Id and a q-axis current command Iq corresponding to the torque (Nm) and rotation speed (rpm).

[0024] The d-axis current command Id will now be explained. When the torque is within a predetermined first range A1 and the rotation speed is within a predetermined second range A2, the d-axis current command Id is smaller than when the torque is within the first range A1 and the rotation speed is outside the second range A2. The above characteristics can be represented graphically as shown in Figure 3.

[0025] Therefore, for example, the d-axis current command Id in Fig. 2 174 ~Id 178 is the d-axis current command Id 169 ~Id 173 ,Id 179~Id 180 is smaller than.

[0026] The q-axis current command Iq will now be explained. When the torque is within the first range A1 and the rotation speed is within the second range A2, the q-axis current command Iq is larger than when the torque is within the first range A1 and the rotation speed is outside the second range A2. The above characteristics can be represented graphically as shown in Figure 4.

[0027] Therefore, for example, the q-axis current command Iq in Fig. 2 174 ~Iq 178 is the q-axis current command Iq 169 ~Iq 173 ,Iq 179 ~Iq 180 is greater than.

[0028] Here, we will explain how to determine the first torque range A1 and the second rotational speed range A2. Generally, as the torque increases, the vibration of the electric motor 10 increases. Furthermore, when the torque is small, the d-axis current command Id is originally small, and the range in which the d-axis current command Id can be reduced is narrow. Therefore, it is desirable that the first range A1 be a range in which the torque is greater than a predetermined value. In the example of FIG. 2, the first torque range A1 is set to 140 to 190 Nm.

[0029] The second range A2 of rotation speed is preferably set to a rotation speed that is frequently used. Furthermore, when performing field-weakening control, it is difficult to adjust the phase in this range of rotation speed, so the second range A2 is preferably set to a rotation speed that is not affected by field-weakening control. In the example shown in Figure 2, this is set to 2500 to 4500 rpm.

[0030] Here, if the phase of the current output from the inverter 40 to the electric motor 10 is θ, when the torque is within the first range A1 and the rotation speed is within the second range A2, the phase θ of the current lags more than when the torque is within the first range A1 and the rotation speed is outside the second range A2. In other words, since the phase θ of the current is determined based on the d-axis current command Id and the q-axis current command Iq, the d-axis current command Id and the q-axis current command Iq are set so that when the torque is within the first range A1 and the rotation speed is within the second range A2, the phase θ of the current lags more than when the torque is within the first range A1 and the rotation speed is outside the second range A2.

[0031] Furthermore, the magnitude of the three-phase current after converting the d-axis current command Id and the q-axis current command Iq listed in the current table 25 into three phases is larger when the torque is within the first range A1 and the rotation speed is within the second range A2 than when the torque is within the first range A1 and the rotation speed is outside the second range A2. In other words, when the torque is within the first range A1 and the rotation speed is within the second range A2, the d-axis current command Id and the q-axis current command Iq are set so that the current magnitude is large enough to compensate for the reduction in torque caused by the delay in the phase θ.

[0032] <Control procedure> FIG. 5 is a flowchart showing the procedure of the process performed by the control device 20.

[0033] 5, the control device 20 (current command calculation unit 21) acquires a torque command from the torque command unit 30 and a rotation speed from the speed detector 11 (S1, S2). Note that the method for acquiring the rotation speed is not limited to acquiring it from the speed detector 11, and it may be determined from the frequency of the inverter 40.

[0034] Next, the control device 20 (current command calculation unit 21) refers to the current table 25 (S3), and derives a d-axis current command Id and a q-axis current command Iq based on the torque command and the rotation speed (S4). Subsequently, the control device 20 outputs the d-axis current command Id and the q-axis current command Iq to the current controller 22 (S5).

[0035] <Effects> When the phase of the current supplied to the electric motor 10 is delayed, the magnetic force acting on the rotor is reduced, and vibration is reduced. When the current is increased to compensate for the torque shortage caused by the phase delay, the magnetic force acting on the rotor is increased, and vibration increases. In this case, the effect of reducing vibration due to the phase delay is greater than the effect of increasing vibration due to an increase in current.

[0036] In the present embodiment, the control device 20 stores in the current table 25 a d-axis current command Id and a q-axis current command Iq that delay the phase of the current and increase the current when the torque is within the first range A1 and the rotation speed is within the second range A2. Because the control device 20 controls the current supplied to the electric motor 10 based on this current table 25, vibration can be reduced without changing the mechanical configuration of the electric motor 10 (the magnetic circuit or the motor rigidity). This makes it possible to reduce the time and cost required to suppress vibration of the electric motor.

[0037] Generally, the larger the d-axis current, the greater the vibration of the motor. In this embodiment, when the torque is within the first range A1 and the rotation speed is within the second range A2, the d-axis current command is reduced and the q-axis current command is increased, thereby reducing the vibration of the motor. More specifically, the vibration at the 24th and 48th rotation orders can be reduced.

[0038] Furthermore, the method of reducing vibration by reducing the d-axis current, as in this embodiment, is more effective when applied to an interior permanent magnet synchronous motor (IPMSM).

[0039] Although the present invention has been described in detail above only with respect to the specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the technical concept of the present invention, and it is natural that such modifications and variations fall within the scope of the claims. [Explanation of symbols]

[0040] 1...Current control system 10...Electric motor (rotating machine) 20...Control device 30...Torque command unit 40...Power converter (inverter) 50…DC power supply 11...Speed ​​detector 21...Current command calculation section 22...Current controller 23, 24... Coordinate conversion section 25...Current table

Claims

1. an electric motor that is driven at a torque and rotation speed according to the supplied current; a power converter that controls the current supplied to the electric motor based on an output command; a control device that has a current table in which a d-axis current command and a q-axis current command corresponding to the torque and the rotation speed are stored, that derives the d-axis current command and the q-axis current command based on the torque and the rotation speed by referring to the current table, and that outputs the output command based on the derived d-axis current command and q-axis current command to the power converter; Equipped with The current table includes: a d-axis current command and a q-axis current command stored in the memory that delay the phase of the current supplied to the electric motor when the torque is within a first range and the rotational speed is within a second range relative to the phase of the current supplied to the electric motor when the torque is within the first range and the rotational speed is outside the second range, and that increase the magnitude of the current supplied to the electric motor when the torque is within the first range and the rotational speed is within the second range relative to the magnitude of the current supplied to the electric motor when the torque is within the first range and the rotational speed is outside the second range.

2. The current table is the d-axis current command when the torque is within the first range and the rotational speed is within the second range is set to a value smaller than the d-axis current command when the torque is within the first range and the rotational speed is outside the second range, 2. The current control system according to claim 1, wherein the q-axis current command when the torque is within the first range and the rotational speed is within the second range is set to a value greater than the q-axis current command when the torque is within the first range and the rotational speed is outside the second range.

3. 2. The current control system according to claim 1, wherein the electric motor is an interior permanent magnet synchronous motor.

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