Induction motor control device

Abstract

To reduce unnecessary torque caused by including an error in a rotation number of an induction machine in a case where the rotation number of the induction machine is relatively small.SOLUTION: A control device 1 is configured by including an inverter circuit 2 which drives an induction machine M and a control circuit 3 by which, in a case where a rotation number ω of the induction machine is larger than a rotation number threshold ωth1, the operation of the inverter circuit 2 is controlled by making an excitation current command value Id* into an excitation current command value Id*1 and making a torque current command value Iq* into a torque current command value Iq*1 and in a case where the rotation number ω is equal to or smaller than the rotation number threshold ωth1, the operation of the inverter circuit 2 is controlled in accordance with an excitation current command value Id*2, which is smaller than the excitation current command value Id1*, and the torque current command value Iq*1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control device for an induction machine. [Background technology]

[0002] As a control device for an induction machine, there is a device that calculates the rotation speed of the induction machine from the period from the rising timing to the falling timing of a pulse signal corresponding to the edge of each tooth of a gear in a rotation sensor installed in the induction machine, and controls the operation of an inverter circuit that drives the induction machine based on the calculated rotation speed.

[0003] However, if there is an error in the period from the rising timing to the falling timing of the pulse signal due to manufacturing variations in the gears, the calculated rotation speed will also contain an error. For example, if the target torque current command value is zero and the rotation speed contains an error, a phase difference will occur between the vector of the excitation current command value calculated based on the rotation speed containing the error and the vector of the excitation current flowing through the induction machine, causing a torque current that should not be generated to flow through the induction machine, generating unnecessary torque in the induction machine.

[0004] Therefore, there is another control device for an induction machine that corrects the rotation speed using a correction value at the rising and falling timings of a pulse signal.

[0005] However, with the other control devices described above, the rotation speed cannot be corrected at timings other than the rising and falling timings of the pulse signal, and there is a risk that the calculated rotation speed will contain errors. In particular, the lower the rotation speed, the more timings at which the rotation speed cannot be corrected, making it more likely that the calculated rotation speed will contain errors. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-78707 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of one aspect of the present invention is to provide an induction machine control device that can reduce unnecessary torque generated due to an error in the rotation speed of the induction machine when the rotation speed of the induction machine is relatively low. [Means for solving the problem]

[0008] One embodiment of the present invention relates to a control device for an induction machine, and includes an inverter circuit that drives an induction machine, and a control circuit that adjusts a torque command value so that a rotation speed deviation calculated from an externally input rotation speed command value and a rotation speed based on a detection value of a rotation sensor converges to zero, and uses the torque command value to obtain an excitation current command value and a torque current command value to control the operation of the inverter circuit.

[0009] When the rotation speed of the induction machine is greater than a first rotation speed threshold, the control circuit controls the operation of the inverter circuit by setting the excitation current command value to a first excitation current command value and the torque current command value to a first torque current command value, and when the rotation speed is equal to or less than the first rotation speed threshold, controls the operation of the inverter circuit by using a second excitation current command value that is smaller than the first excitation current command value and a second torque current command value that is greater than the first torque current command value or the first torque current command value.

[0010] As a result, when the rotation speed of the induction machine is relatively small and the rotation speed is likely to contain errors, the vector of the excitation current command value and the vector of the excitation current can be made relatively small, thereby reducing the torque current generated by the phase difference between the vector of the excitation current command value and the vector of the excitation current, and reducing unnecessary torque generated in the induction machine.

[0011] Furthermore, the control circuit may be configured to control operation of the inverter circuit by setting the excitation current command value to a first excitation current command value and the torque current command value to a first torque current command value when the rotation speed is greater than the first rotation speed threshold, or when the rotation speed is equal to or less than the first rotation speed threshold and the output of the induction machine is greater than a first output threshold, and to control operation of the inverter circuit by using the second excitation current command value and the first torque current command value when the rotation speed is equal to or less than the first rotation speed threshold and the output of the induction machine is equal to or less than the first output threshold.

[0012] This makes it possible to reduce unnecessary torque generated in the induction machine when the rotation speed or output of the induction machine is relatively small.

[0013] Furthermore, when the rotation speed is greater than the first rotation speed threshold, or when the rotation speed is equal to or less than the first rotation speed threshold and the output of the induction machine is greater than a first output threshold, the control circuit controls the operation of the inverter circuit by setting the excitation current command value to a first excitation current command value and the torque current command value to a first torque current command value; when the rotation speed is smaller than a second rotation speed threshold that is smaller than the first rotation speed threshold and the output of the induction machine is smaller than a second output threshold that is smaller than the first output threshold, the control circuit controls the operation of the inverter circuit by a second excitation current command value that is smaller than the first excitation current command value and the first torque current command value; and when the rotation speed is smaller than the second rotation speed threshold and the output of the induction machine is within a range from the second output threshold to the first output threshold, the control circuit controls the operation of the inverter circuit by a third excitation current command value and the first torque current command value that correspond to an output of the induction machine that is within a range from the second excitation current command value to the first excitation current command value.

[0014] Furthermore, the control circuit may be configured to control the operation of the inverter circuit using a fourth excitation current command value and the first torque current command value corresponding to the rotational speed within the range from the second excitation current command value to the first excitation current command value when the rotational speed is within the range from the second rotational speed threshold to the first rotational speed threshold and the output of the induction machine is smaller than the second output threshold, and to control the operation of the inverter circuit using a fifth excitation current command value and the first torque current command value corresponding to the output of the induction machine within the range from the fourth excitation current command value to the first excitation current command value when the rotational speed is within the range from the second rotational speed threshold to the first rotational speed threshold and the output of the induction machine is within the range from the second output threshold to the first output threshold.

[0015] This makes it possible to prevent the excitation current command value from decreasing sharply when the rotation speed or output of the induction machine is relatively small, thereby alleviating the discomfort felt by the user by a sharp decrease in the excitation current command value. [Effects of the Invention]

[0016] According to the present invention, when the rotation speed of the induction machine is relatively low, it is possible to reduce unnecessary torque that occurs due to an error in the rotation speed of the induction machine. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a diagram illustrating an example of a control device for an induction machine according to an embodiment. [Figure 2] 4A and 4B are diagrams illustrating an example of an excitation current command value and a current flowing through an induction machine. [Figure 3] 4 is a flowchart illustrating an operation of a current command value output unit in the first embodiment. [Figure 4] 10 is a flowchart showing the operation of a current command value output unit in the second embodiment. [Figure 5] 11 is a flowchart illustrating an operation of a current command value output unit in the third embodiment. [Figure 6]10 is a diagram for explaining the operation of a current command value output unit in the fourth embodiment. FIG. [Figure 7] FIG. 10 is a diagram showing the relationship between the rotation speed of the induction machine, the output of the induction machine, and the excitation current threshold value. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0019] FIG. 1 is a diagram illustrating an example of a control device for an induction machine according to an embodiment.

[0020] 1 controls the operation of an induction machine M mounted on a vehicle such as an electric forklift or an electric automobile, and includes an inverter circuit 2 and a control circuit 3. The induction machine M is, for example, a wound-type three-phase induction motor.

[0021] The inverter circuit 2 drives the induction machine M using power supplied from a power source P and includes a capacitor C, switching elements SW1 to SW6 (e.g., IGBTs (Insulated Gate Bipolar Transistors)), and current sensors Se1 and Se2. One terminal of the capacitor C is connected to the positive terminal of the power source P and the collector terminals of the switching elements SW1, SW3, and SW5, and the other terminal of the capacitor C is connected to the negative terminal of the power source P and the emitter terminals of the switching elements SW2, SW4, and SW6. A connection point between the emitter terminal of the switching element SW1 and the collector terminal of the switching element SW2 is connected to a U-phase input terminal of the induction machine M via the current sensor Se1. A connection point between the emitter terminal of the switching element SW3 and the collector terminal of the switching element SW4 is connected to a V-phase input terminal of the induction machine M via the current sensor Se2. A connection point between the emitter terminal of the switching element SW5 and the collector terminal of the switching element SW6 is connected to a W-phase input terminal of the induction machine M.

[0022] The capacitor C smoothes the voltage output from the power supply P and input to the inverter circuit 2.

[0023] Switching element SW1 is turned on or off based on drive signal S1 output from control circuit 3. Switching element SW2 is turned on or off based on drive signal S2 output from control circuit 3. Switching element SW3 is turned on or off based on drive signal S3 output from control circuit 3. Switching element SW4 is turned on or off based on drive signal S4 output from control circuit 3. Switching element SW5 is turned on or off based on drive signal S5 output from control circuit 3. Switching element SW6 is turned on or off based on drive signal S6 output from control circuit 3. By switching elements SW1 to SW6 on or off, the DC voltage output from power supply P is converted into three AC voltages that are 120 degrees out of phase with each other, and these AC voltages are applied to the U-, V-, and W-phase input terminals of induction machine M, causing the rotor of induction machine M to rotate. In other words, inverter circuit 2 rotates the rotor of induction machine M by turning switching elements SW1 to SW6 on or off.

[0024] The current sensor Se1 is configured with a Hall element, a shunt resistor, etc., and detects a U-phase current Iu flowing through the U-phase of the induction machine M and outputs the detected current to the control circuit 3. The current sensor Se2 is configured with a Hall element, a shunt resistor, etc., and detects a V-phase current Iv flowing through the V-phase of the induction machine M and outputs the detected current to the control circuit 3.

[0025] The control circuit 3 includes a storage unit 4, a drive circuit 5, and a calculation unit 6.

[0026] The storage unit 4 is configured by a RAM (Random Access Memory) or a ROM (Read Only Memory).

[0027] The drive circuit 5 is configured with an IC (Integrated Circuit) or the like, and compares the voltage value of the carrier wave (triangular wave, sawtooth wave, inverse sawtooth wave, etc.) with the U-phase voltage command value Vu*, V-phase voltage command value Vv*, and W-phase voltage command value Vw* output from the calculation unit 6, and outputs drive signals S1 to S6 according to the comparison results to the gate terminals of the switching elements SW1 to SW6, respectively.

[0028] For example, when the U-phase voltage command value Vu* is equal to or greater than the voltage value of the carrier wave, the drive circuit 5 outputs a high-level drive signal S1 and a low-level drive signal S2; when the U-phase voltage command value Vu* is smaller than the voltage value of the carrier wave, the drive circuit 5 outputs a low-level drive signal S1 and a high-level drive signal S2. When the V-phase voltage command value Vv* is equal to or greater than the voltage value of the carrier wave, the drive circuit 5 outputs a high-level drive signal S3 and a low-level drive signal S4; when the V-phase voltage command value Vv* is smaller than the voltage value of the carrier wave, the drive circuit 5 outputs a low-level drive signal S3 and a high-level drive signal S4. When the W-phase voltage command value Vw* is equal to or greater than the voltage value of the carrier wave, the drive circuit 5 outputs a high-level drive signal S5 and a low-level drive signal S6; when the W-phase voltage command value Vw* is smaller than the voltage value of the carrier wave, the drive circuit 5 outputs a low-level drive signal S5 and a high-level drive signal S6.

[0029] The calculation unit 6 is configured by a microcomputer or the like, and includes a rotation speed calculation unit 7, a position calculation unit 8, a current conversion unit 9, a subtraction unit 10, a torque command value calculation unit 11, a current command value output unit 12, a subtraction unit 13, a subtraction unit 14, a voltage command value calculation unit 15, and a voltage command value conversion unit 16. For example, the microcomputer executes a program stored in the storage unit 4, thereby configuring the rotation speed calculation unit 7, the position calculation unit 8, the current conversion unit 9, the subtraction unit 10, the torque command value calculation unit 11, the current command value output unit 12, the subtraction unit 13, the subtraction unit 14, the voltage command value calculation unit 15, and the voltage command value conversion unit 16.

[0030] The rotation speed calculation unit 7 calculates the rotation speed ω of the induction machine M based on the rising and falling timings of the pulse signal Sp output from a rotation sensor En such as an encoder provided in the induction machine M. For example, the rotation speed calculation unit 7 counts the number of pulses of the pulse signal Sp input per second, multiplies the number of pulses by 2π, and divides the result by the number of gear teeth in the rotation sensor En to obtain the rotation speed (angular velocity) ω.

[0031] Based on the rotation speed ω, the position calculation unit 8 calculates the position (phase angle) θ of the rotor of the induction machine M. For example, the position calculation unit 8 multiplies the rotation speed ω by a unit time (for example, 1 second) and sets the result as the position θ.

[0032] The current converter 9 obtains a W-phase current Iw flowing through the W-phase of the induction machine M using the U-phase current Iu detected by the current sensor Se1 and the V-phase current Iv detected by the current sensor Se2.

[0033] In addition, the current conversion unit 9 converts the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw into an excitation current Id (a current component for generating a weakened field in the induction machine M) and a torque current Iq (a current component for generating torque in the induction machine M) using the position θ calculated by the position calculation unit 8.

[0034] For example, the current converter 9 converts the U-phase current Iu, the V-phase current Iv, and the W-phase current Iw into the excitation current Id and the torque current Iq using the position θ and a transformation matrix for converting from three phases to two phases.

[0035] The currents detected by the current sensors Se1 and Se2 are not limited to the combination of the U-phase current Iu and the V-phase current Iv, but may be the combination of the V-phase current Iv and the W-phase current Iw, or the combination of the U-phase current Iu and the W-phase current Iw. When the current sensors Se1 and Se2 detect the V-phase current Iv and the W-phase current Iw, the current converter 9 determines the U-phase current Iu using the V-phase current Iv and the W-phase current Iw. When the current sensors Se1 and Se2 detect the U-phase current Iu and the W-phase current Iw, the current converter 9 determines the V-phase current Iv using the U-phase current Iu and the W-phase current Iw.

[0036] Furthermore, if the inverter circuit 2 further includes, in addition to the current sensors Se1 and Se2, a current sensor Se3 that detects the current flowing through the W phase of the induction machine M, the current conversion unit 9 may be configured to convert the U-phase current Iu, V-phase current Iv, and W-phase current Iw detected by the current sensors Se1 to Se3 into an excitation current Id and a torque current Iq using the position θ calculated by the position calculation unit 8.

[0037] The subtraction unit 10 calculates the rotation speed deviation Δω between the rotation speed command value ω* input from the outside and the rotation speed ω calculated by the rotation speed calculation unit 7 .

[0038] The torque command value calculation unit 11 calculates the torque command value T* using the rotation speed deviation Δω output from the subtraction unit 10. For example, the torque command value calculation unit 11 refers to information (not shown) stored in the storage unit 4, in which the rotation speed of the induction machine M and the torque of the induction machine M are associated with each other, and determines the torque corresponding to the rotation speed equivalent to the rotation speed deviation Δω as the torque command value T*.

[0039] Furthermore, the torque command value calculation unit 11 calculates the output Po of the induction machine M based on the rotation speed deviation Δω. The output Po of the induction machine M is the ratio of the torque currently being output according to the rotation speed deviation Δω to the maximum torque. For example, the torque command value calculation unit 11 calculates the output Po by calculating the following formula 1. The possible range of the output Po is set to -100[%] to +100[%].

[0040] Output Po = Proportional gain × Rotation speed deviation Δω + Integral gain × ∫ Rotation speed deviation Δωdt Formula 1

[0041] The current command value output unit 12 uses the torque command value T* to determine the excitation current command value Id* and the torque current command value Iq*. For example, the current command value output unit 12 refers to information (not shown) stored in the storage unit 4, in which the torque of the induction machine M is associated with the excitation current command value Id* and the torque current command value Iq*, to determine the excitation current command value Id* and the torque current command value Iq* corresponding to the torque equivalent to the torque command value T*.

[0042] The current command value output unit 12 outputs the excitation current command value Id* calculated from the torque command value T* based on the rotation speed ω and the output power Po, either as is or after reducing the value. The current command value output unit 12 outputs the torque current command value Iq* calculated from the torque command value T* based on the rotation speed ω and the output power Po, either as is or after increasing the value.

[0043] The subtraction unit 13 calculates the difference ΔId between the excitation current command value Id* output from the current command value output unit 12 and the excitation current Id output from the current conversion unit 9 .

[0044] The subtraction unit 14 calculates the difference ΔIq between the torque current command value Iq* output from the current command value output unit 12 and the torque current Iq output from the current conversion unit 9 .

[0045] The voltage command value calculation unit 15 calculates the excitation voltage command value Vd* and the torque voltage command value Vq* by PI control using the difference ΔId output from the subtraction unit 13 and the difference ΔIq output from the subtraction unit 14. For example, the voltage command value calculation unit 15 calculates the excitation voltage command value Vd* by calculating the following equation 2, and calculates the torque voltage command value Vq* by calculating the following equation 3. Note that Kp is a constant for the proportional term of the PI control, Ki is a constant for the integral term of the PI control, Lq is the torque inductance of the induction machine M, Ld is the excitation inductance of the induction machine M, ω is the rotation speed ω calculated by the rotation speed calculation unit 7, and Ψ is the induced voltage.

[0046] Excitation voltage command value Vd* = Kp × difference ΔId + ∫(Ki × difference ΔId) - ωLqIq Equation 2 Torque voltage command value Vq* = Kp × difference ΔIq + ∫(Ki × difference ΔIq) + ωLdId + ωΨ Equation 3

[0047] The voltage command value conversion unit 16 converts the excitation voltage command value Vd* and the torque voltage command value Vq* into a U-phase voltage command value Vu*, a V-phase voltage command value Vv*, and a W-phase voltage command value Vw* using the position θ calculated by the position calculation unit 8. For example, the voltage command value conversion unit 16 converts the excitation voltage command value Vd* and the torque voltage command value Vq* into the U-phase voltage command value Vu*, the V-phase voltage command value Vv*, and the W-phase voltage command value Vw* using the position θ and a conversion matrix for converting from two phases to three phases.

[0048] That is, the control circuit 3 adjusts the torque command value T* so that the rotation speed deviation Δω calculated from the rotation speed command value ω* input from outside and the rotation speed ω based on the detection value of the rotation sensor En converges to zero, and uses the torque command value T* to obtain the excitation current command value Id* and the torque current command value Iq* to control the operation of the inverter circuit 2.

[0049] 2(a) is a diagram showing an example of the excitation current command value Id* and the current flowing through the induction machine M when the rotation speed ω does not contain any error. The solid line shown on the d-axis of the d-axis and q-axis rotating coordinate system represents the ideal excitation current command value Id* that does not contain any error, and the dashed line shown on the d-axis of the d-axis and q-axis rotating coordinate system represents the excitation current Id that flows through the induction machine M. In addition, the torque current command value Iq* is set to zero.

[0050] When the rotation speed ω does not contain an error, as shown in Fig. 2(a), no phase difference occurs between the vector of the excitation current command value Id* and the vector of the excitation current Id, and an unstable torque current does not flow to the induction machine M. Therefore, no unnecessary torque is generated in the induction machine M, and the vehicle equipped with the induction machine M can be kept stopped.

[0051] 2(b) and 2(c) are diagrams showing an example of the excitation current command value Id* and the current flowing through the induction machine M when the rotation speed ω contains an error. The solid line shown on the γ-axis of the γ- and δ-axis rotating coordinate system, which is out of phase with the d- and q-axis rotating coordinate system, represents the excitation current command value Id* containing an error. The dashed line shown on the d-axis of the d- and q-axis rotating coordinate system represents the excitation current Id flowing through the induction machine M. The dashed line shown on the q-axis of the d- and q-axis rotating coordinate system represents the torque current Iq flowing through the induction machine M. The torque current command value Iq* is set to zero. The excitation current command value Id* shown in FIG. 2(c) is smaller than the excitation current command value Id* shown in FIG. 2(b).

[0052] When the rotation speed ω contains an error, as shown in FIG. 2(b), a phase difference occurs between the vector of the excitation current command value Id* and the vector of the excitation current Id, and the vector of the excitation current command value Id* becomes a composite vector of the vector of the excitation current Id and the vector of the torque current Iq. In other words, when the rotation speed ω contains an error, an inconstant torque current Iq flows through the induction machine M even though the torque current command value Iq* is zero. As a result, a torque that should not be generated is generated in the induction machine M, which drives the vehicle equipped with the induction machine M, and this may cause a user driving the vehicle to feel uncomfortable.

[0053] Therefore, in the current command value output unit 12 of the embodiment, when the rotation speed ω is relatively small (when an error is likely to be included in the rotation speed ω), the excitation current command value Id* is set to be smaller than the excitation current command value Id* shown in FIG. 2(b), as shown in FIG. 2(c). In this way, the torque current Iq is reduced by reducing the excitation current command value Id*, which is a composite vector of the vector of the excitation current Id and the vector of the torque current Iq. As a result, even if an error is included in the rotation speed ω and a torque current Iq that is not actually generated flows through the induction machine M, the torque current Iq can be reduced, and the torque generated in the induction machine M can be reduced, thereby suppressing the discomfort felt by the user driving the vehicle.

[0054] Example 1 FIG. 3 is a flowchart showing the operation of the current command value output unit 12 in the first embodiment.

[0055] First, when the rotation speed ω is greater than or equal to the rotation speed threshold ωth1 (first rotation speed threshold) (step S1: No), the current command value output unit 12 outputs the excitation current command value Id*1 (first excitation current command value) as the excitation current command value Id* to the subtraction unit 13, and outputs the torque current command value Iq*1 (first torque current command value) as the torque current command value Iq* to the subtraction unit 14 (step S2). Note that the excitation current command value Id*1 is the excitation current command value Id* calculated from the torque command value T*. Also, the torque current command value Iq*1 is the torque current command value Iq* calculated from the torque command value T*.

[0056] On the other hand, if the rotation speed ω is equal to or less than the rotation speed threshold value ωth1 (step S1: Yes), the current command value output unit 12 outputs an excitation current command value Id*2 (second excitation current command value) smaller than the excitation current command value Id*1 to the subtraction unit 13 and outputs the torque current command value Iq*1 to the subtraction unit 14 (step S3).

[0057] As a result, when the rotation speed ω of the induction machine M is relatively small and the rotation speed ω is prone to contain errors, the vector of the excitation current command value Id* and the vector of the excitation current Id can be made relatively small, thereby reducing the torque current Iq generated by the phase difference between the vector of the excitation current command value Id* and the vector of the excitation current Id, and reducing unnecessary torque generated in the induction machine M.

[0058] <Example 2> FIG. 4 is a flowchart showing the operation of the current command value output unit 12 in the second embodiment.

[0059] First, if the rotation speed ω is greater than the rotation speed threshold ωth1 (step S1: No), the current command value output unit 12 outputs the excitation current command value Id*1 to the subtraction unit 13 as the excitation current command value Id* and outputs the torque current command value Iq*1 to the subtraction unit 14 as the torque current command value Iq* (step S2).

[0060] On the other hand, if the rotation speed ω is equal to or less than the rotation speed threshold ωth1 (step S1: Yes), the current command value output unit 12 outputs the excitation current command value Id*2 to the subtraction unit 13 and outputs a torque current command value Iq*2 (second torque current command value) greater than the torque current command value Iq*1 to the subtraction unit 14 (step S3').

[0061] As a result, when it is desired to make the rotation speed ω of the induction machine M relatively small and the torque of the induction machine M relatively large, unnecessary torque generated in the induction machine M can be reduced.

[0062] Example 3 FIG. 5 is a flowchart showing the operation of the current command value output unit 12 in the third embodiment.

[0063] First, when the rotation speed ω is greater than the rotation speed threshold ωth1 (step S1: No), or when the rotation speed ω is equal to or less than the rotation speed threshold ωth1 (step S1: Yes) and the output Po of the induction machine M is greater than the output threshold Poth1 (first output threshold) (step S4: No), the current command value output unit 12 outputs the excitation current command value Id*1 to the subtraction unit 13 as the excitation current command value Id* and outputs the torque current command value Iq*1 to the subtraction unit 14 as the torque current command value Iq* (step S2).

[0064] On the other hand, if the rotation speed ω is equal to or less than the rotation speed threshold ωth1 (step S1: Yes) and the output Po of the induction machine M is equal to or less than the output threshold Poth1 (step S4: Yes), the current command value output unit 12 outputs the excitation current command value Id*2 to the subtraction unit 13 as the excitation current command value Id* and outputs the torque current command value Iq*1 to the subtraction unit 14 as the torque current command value Iq* (step S3).

[0065] As a result, when the rotation speed ω or the output power Po of the induction machine M is relatively small, unnecessary torque generated in the induction machine M can be reduced.

[0066] In step S3 of the flowchart shown in FIG. 5, the current command value output unit 12 may be configured to output the excitation current command value Id*2 and the torque current command value Iq*2.

[0067] Example 4 FIG. 6 is a diagram for explaining the operation of the current command value output unit 12 in the fourth embodiment.

[0068] The horizontal axis of the two-dimensional coordinate system shown in FIG. 6(a) represents the rotation speed ω, the vertical axis represents the excitation current command value Id*, and the solid line represents a map M1 showing the correspondence relationship between the rotation speed ω and the excitation current command value Id*. The map M1 is assumed to be stored in advance in the storage unit 4. In the map M1, the rotation speed threshold value ωth2 (second rotation speed threshold value) is assumed to be smaller than the rotation speed threshold value ωth1. In the map M1, if the rotation speed ω calculated by the rotation speed calculation unit 7 is larger than the rotation speed threshold value ωth1, the excitation current command value Id* corresponding to the rotation speed ω becomes the excitation current command value Id*1. In the map M1, if the rotation speed ω calculated by the rotation speed calculation unit 7 is smaller than the rotation speed threshold value ωth2, the excitation current command value Id* corresponding to the rotation speed ω becomes the excitation current command value Id*2. Furthermore, in the map M1, when the rotation speed ω calculated by the rotation speed calculation unit 7 is within the range from the rotation speed threshold value ωth2 to the rotation speed threshold value ωth1, the excitation current command value Id* corresponding to the rotation speed ω becomes larger within the range from the excitation current command value Id*2 to the excitation current command value Id*1 as the rotation speed ω increases. In other words, in the map M1, when the rotation speed ω calculated by the rotation speed calculation unit 7 is within the range from the rotation speed threshold value ωth2 to the rotation speed threshold value ωth1, the excitation current command value Id* is proportional to the rotation speed ω.

[0069] 6(b) to 6(d), the horizontal axis represents the output Po, the vertical axis represents the excitation current command value Id*, and the solid line represents map M2 showing the correspondence relationship between the output Po and the excitation current command value Id*. In map M2 shown in FIGS. 6(c) and 6(d), output threshold value Poth2 (second output threshold) is set to a value smaller than output threshold value Poth1. In map M2, the excitation current command value Id* corresponding to an output Po smaller than output threshold value Poth2 and the excitation current command value Id* corresponding to an output Po within the range from output threshold value Poth2 to output threshold value Poth1 change according to the excitation current command value Id* determined by map M1.

[0070] Map M2 shown in Fig. 6(b) shows the correspondence relationship between the output Po and the excitation current command value Id* when the excitation current command value Id* obtained by map M1 is the excitation current command value Id*1 (when the rotation speed ω is greater than the rotation speed threshold ωth1). In map M2 shown in Fig. 6(b), the excitation current command value Id* corresponding to an output Po greater than the output threshold Poth1, the excitation current command value Id* corresponding to an output Po less than the output threshold Poth2, and the excitation current command value Id* corresponding to an output Po within the range from the output threshold Poth2 to the output threshold Poth1 are each set to the excitation current command value Id*1. That is, in map M2 shown in Fig. 6(b), all outputs Po correspond to the excitation current command value Id*1.

[0071] Furthermore, map M2 shown in FIG. 6(c) shows the correspondence relationship between the output Po and the excitation current command value Id* when the excitation current command value Id* obtained by map M1 is the excitation current command value Id*2 (when the rotation speed ω is smaller than the rotation speed threshold value ωth2). Furthermore, in map M2 shown in FIG. 6(c), when the obtained output Po is larger than the output threshold value Poth1, the excitation current command value Id* corresponding to that output Po becomes the excitation current command value Id*1. Furthermore, in map M2 shown in FIG. 6(c), when the obtained output Po is smaller than the output threshold value Poth2, the excitation current command value Id* corresponding to that output Po becomes the excitation current command value Id*2. 6(c), when the determined output Po is within the range from the output threshold Poth2 to the output threshold Poth1, the excitation current command value Id* corresponding to the output Po becomes larger within the range from the excitation current command value Id*2 to the excitation current command value Id*1 as the output Po increases. That is, when the determined output Po is within the range from the output threshold Poth2 to the output threshold Poth1 in the map M2 shown in FIG. 6(c), the excitation current command value Id* is proportional to the output Po.

[0072] Furthermore, map M2 shown in FIG. 6(d) shows the correspondence relationship between the output Po and the excitation current command value Id* when the excitation current command value Id* obtained by map M1 is within the range from the excitation current command value Id*2 to the excitation current command value Id*1 (when the rotation speed ω is within the range from the rotation speed threshold value ωth2 to the rotation speed threshold value ωth1). Furthermore, in map M2 shown in FIG. 6(d), when the obtained output Po is greater than the output threshold value Poth1, the excitation current command value Id* corresponding to the output Po becomes the excitation current command value Id*1. Furthermore, in map M2 shown in FIG. 6(d), when the obtained output Po is smaller than the output threshold value Poth2, the excitation current command value Id* corresponding to the output Po becomes equal to the excitation current command value Id*4 obtained by map M1 and falling within the range from the excitation current command value Id*2 to the excitation current command value Id*1. Furthermore, in the map M2 shown in Fig. 6(d), when the determined output Po is within the range from the output threshold value Poth2 to the output threshold value Poth1, the larger the output Po, the larger the excitation current command value Id* corresponding to that output Po becomes within the range from the excitation current command value Id*4 to the excitation current command value Id*1. That is, in the map M2 shown in Fig. 6(d), when the determined output Po is within the range from the output threshold value Poth2 to the output threshold value Poth1, the excitation current command value Id* is proportional to the output Po.

[0073] The current command value output unit 12 in the fourth embodiment uses the map M1 shown in FIG. 6(a) and one of the maps M2 shown in FIGS. 6(b) to 6(d) to output the excitation current command value Id* and also output the torque current command value Iq*.

[0074] <Excitation current command value Id* output example 1> For example, assume that the rotation speed ω is a rotation speed ωa that is greater than the rotation speed threshold ωth1, and the output Po is an output Poa that is greater than the output threshold Poth1.

[0075] First, the current command value output unit 12 refers to a map M1 shown in FIG. 6(a) to determine an excitation current command value Id*1 corresponding to the rotation speed ωa.

[0076] Next, the current command value output unit 12 creates a map M2 shown in FIG. 6(b) based on the excitation current command value Id*1.

[0077] Then, the current command value output unit 12 refers to the map M2 shown in Figure 6(b) to determine the excitation current command value Id*1 (first excitation current command value) corresponding to the output Poa, and outputs the excitation current command value Id*1 to the subtraction unit 13 as the excitation current command value Id*.

[0078] Similarly, when the rotation speed ω is a rotation speed ωa that is greater than the rotation speed threshold ωth1 and the output Po is an output Pob that is less than the output threshold Poth2, or when the rotation speed ω is a rotation speed ωa that is greater than the rotation speed threshold ωth1 and the output Po is an output Poc that is within the range from the output threshold Poth2 to the output threshold Poth1, the current command value output unit 12 outputs the excitation current command value Id*1 to the subtraction unit 13 as the excitation current command value Id*.

[0079] That is, in Example 4, when the rotation speed ω is greater than the rotation speed threshold value ωth1, the current command value output unit 12 outputs the excitation current command value Id*1 obtained by referring to the map M2 shown in Figure 6(b) to the subtraction unit 13 as the excitation current command value Id*, as shown in Figure 7.

[0080] <Excitation current command value Id* output example 2> For example, assume that the rotation speed ω is a rotation speed ωb that is smaller than the rotation speed threshold value ωth2, and the output Po is an output Poa that is larger than the output threshold value Poth1.

[0081] First, the current command value output unit 12 refers to a map M1 shown in FIG. 6(a) to find an excitation current command value Id*2 corresponding to the rotation speed ωb.

[0082] Next, the current command value output unit 12 creates a map M2 shown in FIG. 6(c) based on the excitation current command value Id*2.

[0083] Then, the current command value output unit 12 refers to the map M2 shown in Figure 6(c) to determine the excitation current command value Id*1 corresponding to the output Poa, and outputs the excitation current command value Id*1 to the subtraction unit 13 as the excitation current command value Id*.

[0084] That is, in the fourth embodiment, when the rotation speed ω is smaller than the rotation speed threshold ωth2 and the output Po is larger than the output threshold Poth1, the current command value output unit 12 outputs the excitation current command value Id*1 obtained by referring to the map M2 shown in FIG. 6(c) to the subtraction unit 13 as the excitation current command value Id*, as shown in FIG. 7.

[0085] <Excitation current command value Id* output example 3> For example, assume that the rotation speed ω is a rotation speed ωc within the range from the rotation speed threshold value ωth2 to the rotation speed threshold value ωth1, and the output Po is an output Poa greater than the output threshold value Poth1.

[0086] First, the current command value output unit 12 refers to a map M1 shown in FIG. 6(a) to determine an excitation current command value Id*4 corresponding to the rotation speed ωc.

[0087] Next, the current command value output unit 12 creates a map M2 shown in FIG. 6(d) based on the excitation current command value Id*4.

[0088] Then, the current command value output unit 12 refers to the map M2 shown in Figure 6(d) to determine the excitation current command value Id*1 corresponding to the output Poa, and outputs the excitation current command value Id*1 to the subtraction unit 13 as the excitation current command value Id*.

[0089] That is, in the fourth embodiment, when the rotation speed ω is within the range from the rotation speed threshold value ωth2 to the rotation speed threshold value ωth1 and the output Po is greater than the output threshold value Poth1, the current command value output unit 12 outputs the excitation current command value Id*1 obtained by referring to the map M2 shown in FIG. 6(d) to the subtraction unit 13 as the excitation current command value Id*, as shown in FIG.

[0090] <Excitation current command value Id*´ output example 4> For example, it is assumed that the rotation speed ω is a rotation speed ωb that is smaller than the rotation speed threshold ωth2, and the output Po is an output Pob that is smaller than the output threshold Poth2.

[0091] First, the current command value output unit 12 refers to a map M1 shown in FIG. 6(a) to find an excitation current command value Id*2 corresponding to the rotation speed ωb.

[0092] Next, the current command value output unit 12 creates a map M2 shown in FIG. 6(c) based on the excitation current command value Id*2.

[0093] Then, the current command value output unit 12 refers to the map M2 shown in Figure 6(c) to determine the excitation current command value Id*2 corresponding to the output Pob, and outputs the excitation current command value Id*2 to the subtraction unit 13 as the excitation current command value Id*.

[0094] That is, in the fourth embodiment, when the rotation speed ω is smaller than the rotation speed threshold ωth2 and the output Po is smaller than the output threshold Poth2, the current command value output unit 12 outputs the excitation current command value Id*2 obtained by referring to the map M2 shown in FIG. 6(c) as the excitation current command value Id* to the subtraction unit 13, as shown in FIG. 7.

[0095] <Excitation current command value Id*´ output example 5> For example, it is assumed that the rotation speed ω is a rotation speed ωb that is smaller than the rotation speed threshold ωth2, and the output Po is an output Poc that is within the range from the output threshold Poth2 to the output threshold Poth1.

[0096] First, the current command value output unit 12 refers to a map M1 shown in FIG. 6(a) to find an excitation current command value Id*2 corresponding to the rotation speed ωb.

[0097] Next, the current command value output unit 12 creates a map M2 shown in FIG. 6(c) based on the excitation current command value Id*2.

[0098] Then, the current command value output unit 12 refers to the map M2 shown in Figure 6(c) to determine the excitation current command value Id*3 (third excitation current command value) corresponding to the output Poc, and outputs the excitation current command value Id*3 to the subtraction unit 13 as the excitation current command value Id*.

[0099] That is, in the fourth embodiment, when the rotation speed ω is smaller than the rotation speed threshold ωth2 and the output Po is within the range from the output threshold Poth2 to the output threshold Poth1, the current command value output unit 12 outputs the excitation current command value Id*3 obtained by referring to the map M2 shown in FIG. 6(c) to the subtraction unit 13 as the excitation current command value Id*, as shown in FIG.

[0100] <Excitation current command value Id*´ output example 6> For example, it is assumed that the rotation speed ω is a rotation speed ωc within the range from the rotation speed threshold value ωth2 to the rotation speed threshold value ωth1, and the output Po is an output Pob that is smaller than the output threshold value Poth2.

[0101] First, the current command value output unit 12 refers to the map M1 shown in FIG. 6(a) to determine the excitation current command value Id*4 (fourth excitation current command value) corresponding to the rotation speed ωc.

[0102] Next, the current command value output unit 12 creates a map M2 shown in FIG. 6(d) based on the excitation current command value Id*4.

[0103] Then, the current command value output unit 12 refers to the map M2 shown in Figure 6(d) to determine the excitation current command value Id*4 corresponding to the output Pob, and outputs the excitation current command value Id*4 to the subtraction unit 13 as the excitation current command value Id*.

[0104] That is, in the fourth embodiment, when the rotation speed ω is within the range from the rotation speed threshold value ωth2 to the rotation speed threshold value ωth1 and the output Po is smaller than the output threshold value Poth2, the current command value output unit 12 outputs the excitation current command value Id*4 obtained by referring to the map M2 shown in FIG. 6(d) to the subtraction unit 13 as the excitation current command value Id*, as shown in FIG.

[0105] <Excitation current command value Id*´ output example 7> For example, it is assumed that the rotation speed ω is a rotation speed ωc within the range from the rotation speed threshold ωth2 to the rotation speed threshold ωth1, and the output power Po is an output power Poc within the range from the output threshold power Poth2 to the output threshold power Poth1.

[0106] First, the current command value output unit 12 refers to a map M1 shown in FIG. 6(a) to determine an excitation current command value Id*4 corresponding to the rotation speed ωc.

[0107] Next, the current command value output unit 12 creates a map M2 shown in FIG. 6(d) based on the excitation current command value Id*4.

[0108] 6(d), the current command value output unit 12 determines an excitation current command value Id*5 (fifth excitation current command value) corresponding to the output Poc, and outputs the excitation current command value Id*5 as the excitation current command value Id* to the subtraction unit 13. Note that the relationship is set as follows: excitation current command value Id*2<excitation current command value Id*4<excitation current command value Id*5<excitation current command value Id*1.

[0109] That is, in the fourth embodiment, when the rotation speed ω is within the range from the rotation speed threshold ωth2 to the rotation speed threshold ωth1 and the output Po is within the range from the output threshold Poth2 to the output threshold Poth1, the current command value output unit 12 outputs the excitation current command value Id*5 obtained by referring to the map M2 shown in FIG. 6(d) to the subtraction unit 13 as the excitation current command value Id*, as shown in FIG.

[0110] In this way, by using maps M1 and M2, the excitation current command value Id*3, the excitation current command value Id*4, or the excitation current command value Id*5 can be obtained as the excitation current command value Id* within the range from the excitation current command value Id*2 to the excitation current command value Id*1.

[0111] Therefore, when the rotation speed ω or the output power Po gradually decreases, the excitation current command value Id* can also be gradually decreased.

[0112] This makes it possible to prevent the excitation current command value Id* from decreasing sharply when the rotation speed ω or output power Po of the induction machine M is relatively small, thereby alleviating the discomfort felt by the user due to a sharp decrease in the excitation current command value.

[0113] In the fourth embodiment, the current command value output unit 12 may be configured to output the torque current command value Iq*2 instead of the torque current command value Iq*1 when the rotation speed ω is equal to or less than the rotation speed threshold value ωth1.

[0114] Furthermore, the present invention is not limited to the above-described embodiments, and various improvements and modifications are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0115] 1. Control device 2. Inverter circuit 3 Control Circuit 4 Storage section 5 Drive Circuit 6 Arithmetic section 7. Rotation speed calculation section 8 Position calculation section 9 Current conversion section 10 Subtraction section 11 Torque command value calculation unit 12 Current command value output section 13 Subtraction section 14 Subtraction section 15 Voltage command value calculation unit 16 Voltage command value conversion unit P power supply C capacitor Se1 Current Sensor Se2 Current Sensor En rotation sensor

Claims

1. an inverter circuit that drives the induction machine; a control circuit that adjusts a torque command value so that a rotation speed deviation calculated from an externally input rotation speed command value and a rotation speed based on a detection value of a rotation sensor converges to zero, and obtains an excitation current command value and a torque current command value using the torque command value to control the operation of the inverter circuit; Equipped with The control circuit when the rotation speed is greater than a first rotation speed threshold, or when the rotation speed is equal to or less than the first rotation speed threshold and the output of the induction machine is greater than a first output threshold, the excitation current command value is set to a first excitation current command value and the torque current command value is set to a first torque current command value to control the operation of the inverter circuit; When the rotation speed is equal to or less than the first rotation speed threshold and the output of the induction machine is equal to or less than the first output threshold, the operation of the inverter circuit is controlled by a second excitation current command value that is smaller than the first excitation current command value and the first torque current command value. A control device for an induction machine characterized by:

2. an inverter circuit that drives the induction machine; a control circuit that adjusts a torque command value so that a rotation speed deviation calculated from an externally input rotation speed command value and a rotation speed based on a detection value of a rotation sensor converges to zero, and obtains an excitation current command value and a torque current command value using the torque command value to control the operation of the inverter circuit; Equipped with The control circuit when the rotation speed is greater than a first rotation speed threshold, or when the rotation speed is equal to or less than the first rotation speed threshold and the output of the induction machine is greater than a first output threshold, the excitation current command value is set to a first excitation current command value and the torque current command value is set to a first torque current command value to control the operation of the inverter circuit; when the rotation speed is smaller than a second rotation speed threshold value that is smaller than the first rotation speed threshold value and the output of the induction machine is smaller than a second output threshold value that is smaller than the first output threshold value, controlling the operation of the inverter circuit using a second excitation current command value that is smaller than the first excitation current command value and the first torque current command value; When the rotation speed is smaller than the second rotation speed threshold value and the output of the induction machine is within a range from the second output threshold value to the first output threshold value, the operation of the inverter circuit is controlled by a third excitation current command value and the first torque current command value corresponding to the output of the induction machine within a range from the second excitation current command value to the first excitation current command value. A control device for an induction machine characterized by:

3. The control device for an induction machine according to claim 2, The control circuit when the rotation speed is within a range from the second rotation speed threshold value to the first rotation speed threshold value and the output of the induction machine is smaller than the second output threshold value, control the operation of the inverter circuit using a fourth excitation current command value and the first torque current command value corresponding to the rotation speed within a range from the second excitation current command value to the first excitation current command value; When the rotation speed is within a range from the second rotation speed threshold value to the first rotation speed threshold value and the output of the induction machine is within a range from the second output threshold value to the first output threshold value, the operation of the inverter circuit is controlled by a fifth excitation current command value and the first torque current command value corresponding to the output of the induction machine within a range from the fourth excitation current command value to the first excitation current command value. A control device for an induction machine characterized by:

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