Power conversion device and method for controlling power conversion circuit

Abstract

This power conversion device is provided with: a power conversion circuit for driving an induction motor by converting DC power into AC power; and a control device that outputs a gate pulse signal to the power conversion circuit and controls the power conversion circuit, the control device obtaining a current command and a magnetic flux command for generating the gate pulse signal. The holding unit is configured to hold a holding value corresponding to a value of the magnetic flux command immediately before a drop of the current command is started, and when the power conversion circuit is turned off, the current command and the magnetic flux command are obtained on the basis of the holding value.

Description

Technical Field

[0001] The present invention relates to a power conversion device and a control method of a power conversion circuit. Background Art

[0002] In the past, a driving method for variable speed driving of an AC motor using a power conversion device has been widely used in railway vehicles. In addition, in most railway vehicles, an induction motor is used to drive the vehicle, and a method for driving multiple induction motors uniformly using one power conversion device has been widely used.

[0003] During the operation of railway vehicles, the operation operation of starting the power conversion device from a stopped state to accelerate, stopping the power conversion device to enter an inertial operation state of inertial running, and restarting the power conversion device from this state to accelerate or decelerate is frequently performed. When the railway vehicle enters the inertial operation state, the voltage is not applied to the induction motor, but the current continues to flow inside the induction motor for a short time after the power conversion device stops. The current is consumed by the internal resistance of the induction motor and gradually decays, but the magnetic flux continues to be generated until the current disappears, so there is residual magnetic flux inside the induction motor. When the power conversion device is restarted in a state where the residual magnetic flux is large, there is a risk of adverse effects such as damage to the power conversion device due to excessive current and deterioration of the ride comfort of the vehicle due to excessive torque.

[0004] As a countermeasure to the above-mentioned problem, for example, the technology described in Patent Document 1 is known. In Patent Document 1, as a control device of a power conversion device having a function of sufficiently attenuating the magnetic flux when stopping the induction motor, a voltage operation unit generating a voltage command based on a current command and a PWM operation unit outputting a gate pulse signal of a power conversion circuit based on the voltage command are disclosed; when the excitation current command drops until it reaches zero, the excitation current command is added with an operation amount calculated according to the time variation of the excitation current command as the excitation current command at the time of cutting off, and the excitation current command at the time of cutting off is used as the current command for the voltage operation unit, thereby attenuating the residual magnetic flux inside the induction motor when the power conversion circuit is stopped.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2017-77079 Summary of the invention

[0008] Problems to be solved by the invention

[0009] The technology described in Patent Document 1 does not consider control in the case where the power conversion device is shut down while the magnetic flux command is being raised. Therefore, in such a case, there is a risk that the residual magnetic flux inside the induction motor cannot be sufficiently attenuated.

[0010] Technical solutions to solve problems

[0011] The power conversion device of the present invention includes: a power conversion circuit that converts DC power into AC power to drive an induction motor; and a control device that outputs a gate pulse signal to the power conversion circuit to control the power conversion circuit, the control device obtains a current command and a flux command for generating the gate pulse signal, and is capable of maintaining a holding value corresponding to the value of the flux command just before the current command begins to decrease, and when the power conversion circuit is cut off, the current command and the flux command are obtained based on the holding value.

[0012] The control method of the power conversion circuit of the present invention is a control method of the power conversion circuit that converts DC power into AC power to drive an induction motor, wherein a current command and a flux command are obtained, a gate pulse signal is generated based on the current command and the flux command, the gate pulse signal is output to the power conversion circuit, a holding value corresponding to the value of the flux command just before the current command starts to decrease is maintained, and when the power conversion circuit is cut off, the current command and the flux command are obtained based on the holding value.

[0013] Effects of the Invention

[0014] According to the present invention, even when the power conversion device is shut down while the magnetic flux command is being raised, the residual magnetic flux inside the induction motor can be sufficiently attenuated. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a diagram showing the structure of a power conversion device according to one embodiment of the present invention.

[0016] Figure 2 It is a functional block diagram showing details of the control device according to the first embodiment of the present invention.

[0017] Figure 3 This is a control block diagram showing details of the pattern generating unit according to the first embodiment of the present invention.

[0018] Figure 4 This is a diagram showing an example of each command and state quantity when the cut-off control is performed after the d-axis magnetic flux command rise is completed.

[0019] Figure 5This is a diagram showing an example of various commands and state quantities when the cut-off control is performed before the d-axis magnetic flux command rise is completed using a conventional control method.

[0020] Figure 6 This is a diagram showing an example of each command and state quantity when the cut-off control is performed before the d-axis magnetic flux command rise is completed in the power conversion device according to the first embodiment of the present invention.

[0021] Figure 7 It is a functional block diagram showing details of a control device according to a second embodiment of the present invention.

[0022] Figure 8 It is a control block diagram showing details of a pattern generating unit according to the second embodiment of the present invention.

[0023] Fig. 9 It is a control block diagram showing details of a pattern generating unit according to the third embodiment of the present invention.

[0024] Fig.10 This is a diagram showing an example of each command and state quantity when the cut-off control is performed before the d-axis magnetic flux command is completed in the power conversion device according to the third embodiment of the present invention. DETAILED DESCRIPTION

[0025] Hereinafter, a power conversion device according to an embodiment of the present invention will be described with reference to the drawings. In the following embodiments, the use in a railway vehicle is described as an example, but the invention can also be applied to other uses such as general industrial use.

[0026] (First Embodiment)

[0027] Figure 1 It is a diagram showing the structure of a power conversion device according to one embodiment of the present invention. Figure 1 The power conversion device shown is connected to the induction motor 3 and includes a power conversion circuit 1 that converts DC power supplied from an external DC power source into AC power and outputs the AC power to the induction motor 3 to drive the induction motor 3 , and a control device 2 that controls the power conversion circuit 1 .

[0028] The power conversion circuit 1 has a U-phase upper arm element 5a, a U-phase lower arm element 5b, a V-phase upper arm element 5c, a V-phase lower arm element 5d, a W-phase upper arm element 5e, and a W-phase lower arm element 5f as semiconductor switching elements. The U-phase upper arm element 5a and the U-phase lower arm element 5b, the V-phase upper arm element 5c and the V-phase lower arm element 5d, and the W-phase upper arm element 5e and the W-phase lower arm element 5f are connected in series in the power conversion circuit 1, respectively, thereby forming upper and lower arm circuits of each phase of the U-phase, V-phase, and W-phase. Power lines connected to the induction motor 3 are connected between the upper arm elements 5a, 5c, 5e and the lower arm elements 5b, 5d, 5f of each upper and lower arm circuit.

[0029] The power conversion circuit 1 converts the DC power supplied from the DC power supply into three-phase AC power by respectively switching the semiconductor switching elements 5a to 5f in accordance with the gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, and Sw2 outputted from the control device 2. The converted three-phase AC power is outputted from the power conversion circuit 1 to the induction motor 3 via the power lines of each phase, thereby performing the drive control of the induction motor 3 by the power conversion device of this embodiment.

[0030] The DC power supplied from the DC power source is smoothed by the smoothing capacitor 4 and input to the power conversion circuit 1. The voltage between the terminals of the smoothing capacitor 4, that is, the voltage Ecf of the DC power input to the power conversion circuit 1 is detected by the DC voltage sensor 6, and the detected value is input to the control device 2.

[0031] In the power lines of each phase provided between the power conversion circuit 1 and the induction motor 3, a U-phase current sensor 7a, a V-phase current sensor 7b, and a W-phase current sensor 7c are provided for respectively detecting the U-phase current iu, the V-phase current iv, and the W-phase current iw flowing in the induction motor 3. The detection results of the currents of each phase obtained by these current sensors 7a to 7c are input to the control device 2.

[0032] The control device 2 generates gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, and Sw2 based on the detection value of the DC voltage Ecf obtained by the DC voltage sensor 6 and the detection values ​​of the U-phase current iu, V-phase current iv, and W-phase current iw obtained by the current sensors 7a~7c, and inputs them to the power conversion circuit 1.

[0033] Figure 21 is a functional block diagram showing the details of the control device 2 of the first embodiment of the present invention. The control device 2 includes a current command generating unit 8, a pattern generating unit 9, a coordinate conversion unit 10, a rotation speed estimation unit 11, a frequency command generating unit 12, a voltage command generating unit 13, and a pulse command generating unit 14. The control device 2 is configured using, for example, a microcomputer having a CPU and a memory, and can realize the same as the control device 2 by executing a predetermined program in the CPU. Figure 2 In addition, a part or all of the functions of the control device 2 may be realized by using a logic circuit such as FPGA (Field Programmable Gate Array).

[0034] The control device 2 receives a control command cmd for operating or stopping the power conversion circuit 1 from the outside. The current command generation unit 8 generates and outputs a d-axis current command Idp1 and a q-axis current command Iqp corresponding to the control command cmd. For example, when the current command generation unit 8 receives a control command cmd for operating the power conversion circuit 1, the d-axis current command Idp1 and the q-axis current command Iqp are generated so that the AC power required to drive the induction motor 3 at a predetermined torque is output from the power conversion device 1.

[0035] The pattern generation unit 9 calculates the excitation current command Idp2 and the d-axis magnetic flux command φdp based on the d-axis current command Idp1 input from the current command generation unit 8, and outputs them to the voltage command generation unit 13. The excitation current command Idp2 is a command value for the current in the direction of the rotating magnetic field of the induction motor 3, that is, the d-axis direction. When the power conversion circuit 1 is normally operated, it is equal to the d-axis current command Idp1. When the power conversion circuit 1 is stopped, it is equivalent to the correction value of the d-axis current command Idp1 corrected to attenuate the magnetic flux of the induction motor 3. In addition, the pattern generation unit 9 switches the calculation method of the excitation current command Idp2 and the d-axis magnetic flux command φdp according to the control state of the induction motor 3. The details of the calculation method of the excitation current command Idp2 and the d-axis magnetic flux command φdp by the pattern generation unit 9 will be described later.

[0036] The coordinate conversion unit 10 obtains the d-axis current detection value Idf and the q-axis current detection value Iqf by performing rotational coordinate conversion on the U-phase current iu, the V-phase current iv, and the W-phase current iw respectively detected by the current sensors 7a to 7c, and outputs these current detection values ​​to the rotation speed estimation unit 11. In addition, in the coordinate conversion unit 10, the direction of the rotating magnetic field of the induction motor 3 is taken as the d-axis direction, and the direction of the current flowing to generate torque is taken as the q-axis direction, and the d-axis current detection value Idf and the q-axis current detection value Iqf are obtained.

[0037] The rotation speed estimation unit 11 estimates the rotor angular frequency of the induction motor 3 based on the excitation current command Idp2 and the q-axis current command Iqp input from the pattern generation unit 9 and the current command generation unit 8, respectively, and the d-axis current detection value Idf and the q-axis current detection value Iqf input from the coordinate transformation unit 10, and outputs the estimation result as the rotor angular frequency estimated value ωre.

[0038] The frequency command generating unit 12 receives the d-axis magnetic flux command φdp obtained by the pattern generating unit 9, the q-axis current command Iqp generated by the current command generating unit 8, and the rotor angular frequency estimated value ωre estimated by the rotation speed estimating unit 11. The frequency command generating unit 12 calculates the angular frequency of the AC voltage applied to the induction motor 3 based on these input information, and outputs it as the primary angular frequency ω1.

[0039] The voltage command generating unit 13 is input with the DC voltage Ecf detected by the DC voltage sensor 6, the excitation current command Idp2 and the d-axis magnetic flux command φdp obtained by the pattern generating unit 9, the q-axis current command Iqp generated by the current command generating unit 8, the rotor angular frequency estimated value ωre obtained by the rotation speed estimating unit 11, and the primary angular frequency ω1 obtained by the frequency command generating unit 12. The voltage command generating unit 13 calculates the modulation factor Vc and the voltage command argument δ of the power conversion circuit 1 based on these input information, and outputs the calculation result as a voltage command for the output voltage from the power conversion circuit 1 to the induction motor 3.

[0040] The pulse command generating unit 14 calculates the gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, and Sw2 for the semiconductor switch elements 5a to 5f of the power conversion circuit 1, respectively, based on the voltage command generated by the voltage command generating unit 13, i.e., the modulation rate Vc and the voltage command angle δ, and the primary angular frequency ω1 obtained by the frequency command generating unit 12. The gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, and Sw2 obtained by the pulse command generating unit 14 are output from the control device 2 to the power conversion circuit 1 as described above, and are used for driving control of each semiconductor switch element 5a to 5f of the power conversion circuit 1.

[0041] in addition, Figure 2 In the functional block diagram of FIG. 1 , an example of a power conversion device that implements speed sensorless control by obtaining the estimated rotor angular frequency ωre of the induction motor 3 using the rotation speed estimation unit 11 is shown. Hereinafter, the present invention will be described using this example, but the present invention can also be applied to speed sensor control in which a speed sensor is provided instead of the rotation speed estimation unit 11 and the rotation speed of the induction motor 3 is detected by the speed sensor. That is, the embodiments described below are not limited to the configuration of the present invention.

[0042] Figure 3 1 is a control block diagram showing details of the pattern generation unit 9 according to the first embodiment of the present invention. Figure 3 As shown, the switching contact 15, adder 16, switching contact 17, lag unit 18, subtractor 19, gain 20, integration unit 21, switching contact 22, gain 23, switching contact 24, lag unit 25, multiplier 26, divider 27, gain 28 and differentiation unit 29 are combined to form the structure.

[0043] In addition, as described above, the pattern generation unit 9 switches the calculation method of the excitation current command Idp2 and the d-axis magnetic flux command φdp according to the control state of the induction motor 3. Specifically, the calculation method of the excitation current command Idp2 and the d-axis magnetic flux command φdp in the pattern generation unit 9 is switched according to the case where the operation of the power conversion circuit 1 is controlled in a manner of outputting AC power from the power conversion circuit 1 to drive the induction motor 3 with a predetermined torque (hereinafter referred to as "normal control") and the case where the operation of the power conversion circuit 1 is controlled in a manner of cutting off the output of AC power from the power conversion circuit 1 to the induction motor 3 (hereinafter referred to as "cut-off control"). The switching of the calculation method can be performed based on the control command cmd input to the control device 2, for example.

[0044] The switching contact 15 switches the excitation current command Idp2 output from the pattern generation unit 9. The pattern generation unit 9 switches the switching contact 15 so that the d-axis current command Idp1 input from the current command generation unit 8 is output as the excitation current command Idp2 in the normal control execution, and the output of the adder 16 is output as the excitation current command Idp2 in the cut-off control execution.

[0045] The adder 16 adds the output of the differentiating means 29 to the d-axis current command Idp1. The added value is outputted from the adder 16 via the switching contact 15 as the field current command Idp2 for the cut-off control as described above.

[0046] The switching contact 17 switches the d-axis current command holding value Idph. The pattern generation unit 9 switches the switching contact 17 so that the d-axis current command Idp1 output from the current command generation unit 8 and input to the pattern generation unit 9 is used as the d-axis current command holding value Idph in the normal control implementation, and the output of the hysteresis unit 18 is used as the d-axis current command holding value Idph in the cut-off control implementation. The hysteresis unit 18 outputs the output of the switching contact 17 with a hysteresis.

[0047] By the operation of the switching contact 17 and the hysteresis unit 18, during the normal control, the d-axis current command holding value Idph is updated successively according to the value of the d-axis current command Idp1 input from the current command generating unit 8 to the pattern generating unit 9. On the other hand, after switching from the normal control to the cut-off control, the value of the d-axis current command Idp1 input from the current command generating unit 8 to the pattern generating unit 9 before the switching is maintained as the d-axis current command holding value Idph.

[0048] The subtractor 19 subtracts the output of the integrating unit 21 from the d-axis current command Idp1 . The subtracted value is output to the gain 20 .

[0049] The gain 20 multiplies the output of the subtractor 19 by the inverse of a preset secondary time constant T2 of the induction motor 3 . The multiplied value is output to the integrating means 21 .

[0050] The integration unit 21 integrates the output of the gain 20. The integrated value is output to the integration unit 21, the switching contact 22, and the switching contact 24.

[0051] The switching contact 22 switches the magnetizing current command I0 input to the gain 23. The pattern generating unit 9 switches the switching contact 22 so that the output of the integrating unit 21 is input as the magnetizing current command I0 to the gain 23 during the normal control and the output of the divider 27 is input as the magnetizing current command I0 to the gain 23 during the cut-off control.

[0052] The gain 23 multiplies the magnetizing current command I0 input from the switching contact 22 by the preset field inductance L of the induction motor 3. The multiplied value is output from the pattern generating unit 9 as the d-axis magnetic flux command φdp.

[0053] The switching contact 24 switches the magnetizing current command holding value I0h. The pattern generation unit 9 switches the switching contact 24 so that the output of the integration unit 21 is used as the magnetizing current command holding value I0h during normal control and the output of the hysteresis unit 25 is used as the magnetizing current command holding value I0h during cut-off control. The hysteresis unit 25 outputs the output of the switching contact 24 with a lag.

[0054] By the operation of the switching contact 24 and the hysteresis unit 25, during the normal control, the magnetizing current command hold value I0h is updated successively according to the value of the magnetizing current command I0 output from the integration unit 21 and input to the gain 23. On the other hand, after the normal control is switched to the cut-off control, the value of the magnetizing current command I0 input to the gain 23 before the switching is held as the magnetizing current command hold value I0h.

[0055] The multiplier 26 multiplies the d-axis current command Idp1 by the magnetizing current command holding value I0h. The multiplied value is output to the divider 27.

[0056] The divider 27 divides the output of the multiplier 26 by the d-axis current command holding value Idph. The divided value is output to the switching contact 22 and the gain 28.

[0057] The gain 28 multiplies the output of the divider 27 by a preset secondary time constant T2 of the induction motor 3 . The multiplied value is output to the differentiation unit 29 .

[0058] The differentiation unit 29 calculates the time variation of the output of the gain 28. The calculated value is output to the adder 16.

[0059] In the pattern generation unit 9 of the present embodiment, the excitation current command Idp2 and the magnetization current command I0 obtained based on the d-axis current command Idp1 can be obtained by the operation of the above-mentioned components, and the d-axis magnetic flux command φdp can be generated based on the magnetization current command I0 and the excitation inductance L preset according to the characteristics of the induction motor 3. Specifically, in the normal control execution, the excitation current command Idp2 can be obtained based on the d-axis current command Idp1, and the magnetization current command I0 can be obtained based on the d-axis current command Idp1 and the secondary time constant T2 preset according to the characteristics of the induction motor 3. In addition, in the shutdown control execution, the magnetization current command I0 can be obtained based on the d-axis current command Idp1, the magnetization current command holding value I0h and the d-axis current command holding value Idph, and the excitation current command Idp2 can be obtained based on the magnetization current command I0 and the secondary time constant T2.

[0060] Next, the operation of the power conversion device of this embodiment will be described with reference to a representative operation example. Figures 4 to 6 This is explained below.

[0061] Figure 4 This is a diagram showing an example of various instructions and state quantities when the cut-off control is performed after the d-axis magnetic flux instruction φdp is completed. Figure 4 As an application example of the present invention, the use of Figure 2 , Figure 3 Although the operation example of the power conversion device in the case of the control device 2 described in the above is an example, the same effect can be obtained in the conventional control method to which the present invention is not applied.

[0062] When the normal command is in the ON state, that is, when the normal control is being executed, in the pattern generating unit 9, the switching contacts 15, 17, 22, and 24 are respectively in the normal switching state as described above. Figure 4In the example, this state continues from the time when the d-axis current command Idp1 rises until it reaches a certain value and is cut off. On the other hand, when the cut-off command is in the ON state, that is, when the cut-off control is being implemented, in the pattern generating unit 9, the switching contacts 15, 17, 22, and 24 are respectively in the switching state when cut off. Figure 4 In the example of , the d-axis current command Idp1 decreases until it reaches zero, and this state continues.

[0063] in addition, Figure 4 In the example of FIG. 1 , the d-axis current command Idp1 is indicated by a solid line, and the magnetizing current command I0 is indicated by a dotted line overlapping the d-axis current command Idp1. The magnetizing current command I0 operates as a first-order lag with a quadratic time constant T2 for the d-axis current command Idp1 through the operation of the subtractor 19, the gain 20, the integrating unit 21, and the switching contact 22 during normal control.

[0064] After the d-axis current command Idp1 has finished rising and reached a certain value, after sufficient time has passed, if Figure 4 As shown, the d-axis current command Idp1 is consistent with the magnetizing current command I0. Therefore, Figure 4 In the example of , during the cut-off control, the d-axis current command Idp1 and the magnetizing current command I0 have the same value due to the operations of the multiplier 26, the divider 27, and the switching contact 22.

[0065] On the other hand, the excitation current command Idp2 becomes the same value as the d-axis current command Idp1 in normal control due to the operation of the switching contact 15, the adder 16, the gain 28 and the differential unit 29, and becomes a value obtained by multiplying the time change rate (dI0 / dt) of the magnetizing current command I0 with respect to the d-axis current command Idp1 by the quadratic time constant T2 and adding them together in the cut-off control.

[0066] The d-axis magnetic flux command φdp is obtained by multiplying the magnetizing current command I0 by the excitation inductance L. Figure 4 In the example, the stable value of the excitation current command Idp2 is defined as Idp0.

[0067] When the d-axis current command Idp1 has completed its rise and reached a certain value in the normal control, the value of the d-axis current command Idp1 coincides with the excitation current command Idp2 and the magnetizing current command I0. The value of the d-axis magnetic flux command φdp at this time is equal to the value obtained by multiplying the stable value Idp0 of the excitation current command Idp2 by the excitation inductance L. When switching from the normal control to the cut-off control is performed in this state, the value of the d-axis magnetic flux command φdp changes continuously from the above-mentioned multiplied value. As a result, during the period from when the d-axis current command Idp1 starts to decrease until it reaches zero, the d-axis magnetic flux φd can be reduced to zero without undershooting the command value obtained based on the d-axis magnetic flux command φdp. As a result, when the power conversion circuit 1 is cut off, the d-axis magnetic flux φd can be attenuated without leaving any residue.

[0068] Next, the problem of the control during the cut-off when the present invention is not applied is discussed below. Figure 5 The following describes an example of the operation. Figure 5 This is a diagram showing an example of various commands and state quantities when the cut-off control is performed before the d-axis magnetic flux command φdp is completely increased by the conventional control method. Figure 5 Zhongyu Figure 4 Differently, an example of an operation waveform is shown in which the d-axis current command Idp1 is decreased after the d-axis magnetic flux command φdp starts to increase and before it reaches a certain value. Figure 5 In the Figure 4 The description of each instruction and state quantity of the same action is omitted below.

[0069] Among the existing control methods, Figure 4 As shown in the figure, when the d-axis magnetic flux command φdp has completed its rise and reached a constant value, the d-axis magnetic flux φd can be sufficiently attenuated when the normal control is switched to the cut-off control. However, when the d-axis magnetic flux command φdp is in the process of rising, the normal control is switched to the cut-off control. Figure 5 As shown, the d-axis flux command φdp is discontinuous, and an excessively large command value is output for the d-axis flux command φdp. As a result, the d-axis flux φd crosses zero and undershoots, so that even after the power conversion device stops, the d-axis flux φd remains inside the induction motor 3. When the power conversion device is restarted in a state where the d-axis flux φd remains inside the induction motor 3, it becomes a cause of excessive current or torque. In order to prevent this, even if the d-axis flux command φdp is shifted from the normal control to the cut-off control during the rise of the d-axis flux command φdp, it is necessary to make the d-axis flux φd decay at a certain rate of change until it reaches zero without making the d-axis flux command φd discontinuous.

[0070] The power conversion device of this embodiment is provided with a means for solving the above-mentioned problem and sufficiently attenuating the magnetic flux of the induction motor 3 when the power conversion device is turned off. Figure 3 As described above, in the pattern generating unit 9 of the control device 2, the d-axis current command Idp1 before switching from the normal control to the shutoff control is held as the d-axis current command holding value Idph by the switching contact 17 and the hysteresis unit 18, and the magnetizing current command I0 before switching from the normal control to the shutoff control is held as the magnetizing current command holding value I0h by the switching contact 24 and the hysteresis unit 25. Then, the magnetizing current command I0 in the execution of the shutoff control is calculated by dividing the value obtained by multiplying the d-axis current command Idp1 by the magnetizing current command holding value I0h by the d-axis current command holding value Idph by the multiplier 26 and the divider 27.

[0071] Thus, even if the d-axis magnetic flux command φdp is transferred to the cut-off control during the rising process, the d-axis current command Idp1 can be corrected according to the ratio of the d-axis current command holding value Idph to the previous magnetizing current command holding value I0h. As a result, the magnetizing current command I0 can be made a continuous value, and the d-axis magnetic flux command φdp that is continuously reduced can be calculated using the magnetizing current command I0. That is, the d-axis magnetic flux φd can be attenuated at a certain change rate until it reaches zero, thereby preventing the d-axis magnetic flux φd from remaining inside the induction motor 3.

[0072] In the power converter of the present embodiment, the d-axis magnetic flux command φdp is calculated based on the corrected value of the d-axis current command Idp1. Therefore, during the falling time of the d-axis current command Idp1 (d-axis current command falling time Td), the d-axis magnetic flux command φdp can be reduced at a constant rate from before the cutoff to zero.

[0073] Figure 6 This is a diagram showing an example of various commands and state quantities when the cut-off control is performed before the d-axis magnetic flux command φdp is completely increased in the power conversion device according to the first embodiment of the present invention. Figure 6 In the Figure 4 The description of each instruction and state quantity of the same action is omitted below.

[0074] Figure 6 Zhongyu Figure 5 Similarly, the control is switched from the normal control to the cut-off control during the rise of the d-axis magnetic flux command φdp. However, in the power conversion device of the present embodiment, the d-axis current command Idp1 is corrected by the ratio of the d-axis current command holding value Idph to the magnetizing current command holding value I0h as described above, and the d-axis magnetic flux command φdp is obtained as the magnetizing current command I0. By this effect, Figure 6As shown, the d-axis magnetic flux command φdp can be continuously changed before and after switching from normal control to cut-off control, so that the d-axis magnetic flux φd decays at a constant rate until it reaches zero. The falling time of the d-axis magnetic flux command φdp at this time coincides with the d-axis current command falling time Td.

[0075] The value of the excitation current command Idp2 in the cut-off control is calculated by multiplying the time change rate (dI0 / dt) of the magnetizing current command I0 by the secondary time constant T2 of the induction motor 3 and adding the result to the d-axis current command Idp1. Since the magnetizing current command I0 decreases at a constant change rate, the value of the excitation current command Idp2 at this time is the value obtained by parallel shifting the d-axis current command Idp1 in the negative direction.

[0076] As described above, in the power conversion device of the present embodiment, even when the d-axis magnetic flux command φdp is shifted from the normal control state to the cut-off control during the rise, the actual d-axis magnetic flux φd in the induction motor 3 can be reduced at a certain rate of change. As a result, the d-axis magnetic flux φd can be attenuated to zero without undershooting. That is, the residual amount of the d-axis magnetic flux φd when the power conversion device is cut off can be made zero. Therefore, the generation of excessive current and torque when the power conversion device is restarted can be suppressed.

[0077] According to the first embodiment of the present invention described above, the following effects can be achieved.

[0078] (1) The power conversion device includes a power conversion circuit 1 that converts DC power into AC power to drive an induction motor 3, and a control device 2 that outputs gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, and Sw2 to the power conversion circuit 1 to control the power conversion circuit 1. The control device 2 obtains a d-axis current command Idp1, an excitation current command Idp2, and a d-axis magnetic flux command φdp for generating the gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, and Sw2, and can hold a magnetizing current command hold value I0h and a d-axis current command hold value Idph corresponding to the value of the d-axis magnetic flux command φdp immediately before the d-axis current command Idp1 starts to decrease, and obtains the d-axis current command Idp1, the excitation current command Idp2, and the d-axis magnetic flux command φdp based on these held values ​​when the power conversion circuit 1 is turned off. Thus, even when the power conversion device is shut down while the d-axis magnetic flux command φdp is being increased, the residual magnetic flux inside the induction motor 3 can be sufficiently attenuated.

[0079] (2) A control command cmd for operating or stopping the power conversion circuit 1 is input to the control device 2. The control device 2 implements either the normal control corresponding to the period before the d-axis current command Idp1 starts to decrease, or the shutoff control corresponding to the period after the d-axis current command Idp1 starts to decrease, according to the control command cmd, and can hold a hold value corresponding to the value of the d-axis magnetic flux command φdp before switching from the normal control to the shutoff control. Specifically, the control device 2 includes a current command generating unit 8 that generates a d-axis current command Idp1 and a q-axis current command Iqp corresponding to the control command cmd, a pattern generating unit 9 that obtains an excitation current command Idp2 and a magnetizing current command I0 based on the d-axis current command Idp1, and generates a d-axis magnetic flux command φdp based on the magnetizing current command I0 and the excitation inductance L preset according to the characteristics of the induction motor 3, a voltage command generating unit 13 that generates a voltage command based on the excitation current command Idp2, the d-axis magnetic flux command φdp, and the q-axis current command Iqp, and a pulse command generating unit 14 that generates gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, and Sw2 based on the voltage command. The pattern generating unit 9 holds the value of the magnetizing current command I0 before switching from the normal control to the cut-off control as a magnetizing current command holding value I0h. Thus, even when the power converter is shut down while the d-axis magnetic flux command φdp is being increased, gate pulse signals Su1 , Su2 , Sv1 , Sv2 , Sw1 , and Sw2 that can sufficiently attenuate the residual magnetic flux in the induction motor 3 can be generated.

[0080] (3) The pattern generating unit 9 obtains the exciting current command Idp2 from the d-axis current command Idp1 using the cutoff contact 15 during the execution of the normal control, and obtains the magnetizing current command I0 based on the d-axis current command Idp1 and the secondary time constant T2 preset according to the characteristics of the induction motor 3 using the subtractor 19, the gain 20, the integrating unit 21, and the switching contact 22. In addition, during the execution of the cutoff control, the magnetizing current command I0 is obtained based on the d-axis current command Idp1, the magnetizing current command holding value I0h, and the d-axis current command holding value Idph using the switching contact 24, the hysteresis unit 25, the multiplier 26, and the divider 27, and the exciting current command Idp2 is obtained based on the magnetizing current command I0 and the secondary time constant T2 using the gain 28, the differentiating unit 29, and the adder 16. Thus, the values ​​of the excitation current command Idp2 and the magnetizing current command I0 required for generating the gate pulse signals Su1 , Su2 , Sv1 , Sv2 , Sw1 , and Sw2 can be appropriately obtained in the normal control and the shutoff control, respectively.

[0081] (4) The pattern generation unit 9 continues to hold the magnetizing current command hold value I0h and the d-axis current command hold value Idph after switching from the normal control to the cut-off control. Specifically, the pattern generation unit 9 holds the value of the magnetizing current command I0 and the value of the excitation current command Idp2 before switching from the normal control to the cut-off control as the magnetizing current command hold value I0h and the d-axis current command hold value Idph, respectively, using the switching contact 24 and the hysteresis unit 25, and the switching contact 17 and the hysteresis unit 18. In addition, the multiplier 26 and the divider 27 calculate the value obtained by dividing the product of the d-axis current command Idp1 and the magnetizing current command hold value I0h by the d-axis current command hold value Idph as the value of the magnetizing current command I0 during the cut-off control. In this way, even if the d-axis magnetic flux command φdp is shifted to the cut-off control during the rise, the value of the magnetizing current command I0 that changes continuously can be calculated. As a result, the d-axis magnetic flux φd can be attenuated at a constant rate of change until it reaches zero, thereby reliably preventing the d-axis magnetic flux φd from remaining inside the induction motor 3 .

[0082] (Second Embodiment)

[0083] Next, a second embodiment of the present invention will be described. In this embodiment, an example in which the calculation method of the magnetizing current command I0 is different from that of the first embodiment will be described. The following description will focus on the differences from the first embodiment.

[0084] The power conversion device of this embodiment has the same structure as that described in the first embodiment. Figure 1 The structure of the power conversion device is the same as that of the power conversion device, but the functional structure of the control device 2 is different.

[0085] Figure 7 is a functional block diagram showing details of the control device 2 according to the second embodiment of the present invention. Figure 2 Compared with the first embodiment described in the above, the pattern generator 9 is replaced by the pattern generator 9A, and the current command generator 8 outputs the d-axis current command fall time Td in addition to the d-axis current command Idp1 to the pattern generator 9A. This is because the d-axis current command fall time Td is used in the calculation of the magnetizing current command I0 and the d-axis magnetic flux command φdp at the time of cutoff in the pattern generator 9A.

[0086] Figure 8 The pattern generation unit 9A of the second embodiment of the present invention is shown in detail in a control block diagram. The pattern generation unit 9A of the present embodiment adds the input of the d-axis current command falling time Td, and is configured to replace the first embodiment described in Figure 3The switching contact 17, the lag unit 18, the switching contact 22, the multiplier 26, the divider 27 and the differentiation unit 29 in the pattern generating unit 9 are provided with a divider 30, a gain 31 and a switching contact 32.

[0087] The divider 30 divides the magnetizing current command hold value I0h by the d-axis current command fall time Td. The divided value is input to the gain 31.

[0088] The gain 31 is obtained by multiplying the output of the divider 30 by −1 to invert the sign, and outputs the gain 28 and the switching contact 32 .

[0089] In the pattern generator 9A of the present embodiment, the differentiating means 29 is not provided on the output side of the gain 28 . Therefore, the gain 28 multiplies the output of the divider 30 after the sign is inverted by the gain 31 by the secondary time constant T2 of the induction motor 3 and outputs the result to the adder 16 .

[0090] The switching contact 31 switches the value input to the integration unit 21. The pattern generation unit 9A switches the switching contact 32 so that the output of the gain 20 is input to the integration unit 21 during normal control execution, and the output of the gain 31 is input to the integration unit 21 during shutdown control execution. Thus, in this embodiment, the d-axis current command fall time Td is used instead of the d-axis current command holding value Idph described in the first embodiment, and the excitation current command Idp2 and the magnetizing current command I0 during shutdown are calculated to obtain the d-axis magnetic flux command φdp.

[0091] In addition, the pattern generation unit 9A inverts the sign of the value obtained by dividing the magnetizing current command holding value I0h by the d-axis current command falling time Td by the gain 31. This process is equivalent to the calculation of the time change rate of the magnetizing current command I0 performed by the differentiating unit 29 in the first embodiment. That is, in this embodiment, the excitation current command Idp2 at the time of disconnection can be obtained without using the differentiating unit 29.

[0092] In addition, the ratio of the d-axis current command drop time Td to the magnetizing current command holding value I0h is integrated by the integrating means 21 during the cut-off control, so that the integrating means 21 can be used in common during the normal and cut-off times. Therefore, the continuity of the d-axis magnetic flux command φdp when the normal control is transferred to the cut-off control can be reliably ensured.

[0093] In the above description, the magnetizing current command I0 that is reduced at a certain rate at the time of disconnection is calculated using the ratio of the d-axis current command falling time Td relative to the magnetizing current command holding value I0h, but the present embodiment does not need to be limited to this structure. For example, a change rate limiter that causes the magnetizing current command I0 at the time of disconnection to decrease at a certain rate of change can also be used to realize the magnetizing current command I0 that is reduced at a certain rate. In this case, the input to the change rate limiter is set to a value obtained by subtracting the magnetizing current command I0 from zero, and the output is limited according to the ratio of the d-axis current command falling time Td relative to the magnetizing current command holding value I0h, thereby realizing the magnetizing current command I0 that is reduced at a certain rate.

[0094] According to the configuration of this embodiment, when the cut-off control is performed before the d-axis magnetic flux command rise is completed, the same control as in the first embodiment can be adopted. Figure 6 The same instructions and status quantities as described in .

[0095] As described above, in this embodiment, when the d-axis magnetic flux command φdp is shifted from the normal control state to the cut-off control during the rise, the d-axis magnetic flux command φdp can be continuously and at a constant rate reduced, so the d-axis magnetic flux φd can be decayed to zero without undershooting. That is, the residual amount of the d-axis magnetic flux φd when the power conversion device is cut off can be made zero. Therefore, the generation of excessive current and torque when the power conversion device is restarted can be suppressed.

[0096] In addition, in this embodiment, the differentiating means 29 described in the first embodiment is not required. Therefore, even when the d-axis current command Idp1 changes suddenly due to disturbances during shutdown, the field current command Idp2 does not diverge, and the power converter can operate stably.

[0097] According to the second embodiment of the present invention described above, the pattern generation unit 9A continues to hold the magnetizing current command holding value I0h after switching from the normal control to the cut-off control. Specifically, the current command generation unit 8 outputs the d-axis current command falling time Td indicating the time from the start of the fall of the d-axis current command Idp1 to the end. The pattern generation unit 9A holds the value of the magnetizing current command I0 before switching from the normal control to the cut-off control as the magnetizing current command holding value I0h using the switching contact 24 and the hysteresis unit 25. In addition, the value obtained by adding the value obtained by dividing the magnetizing current command holding value I0h by the d-axis current command falling time Td with the divider 30, the gain 31 and the integration unit 21 is calculated as the value of the magnetizing current command I0 during the cut-off control. Because of this, even if the d-axis magnetic flux command φdp is transferred to the cut-off control during the rise, the value of the magnetizing current command I0 that changes continuously can be calculated, as in the first embodiment. As a result, the d-axis magnetic flux φd can be attenuated at a constant rate of change until it reaches zero, thereby reliably preventing the d-axis magnetic flux φd from remaining inside the induction motor 3 .

[0098] (Third Embodiment)

[0099] Next, a third embodiment of the present invention will be described. In this embodiment, an example in which the method of holding the magnetizing current command hold value I0h is different from that of the first and second embodiments will be described. The following description will focus on the differences from the first and second embodiments.

[0100] Fig. 9 1 is a control block diagram showing details of a pattern generation unit 9B according to a third embodiment of the present invention. The pattern generation unit 9B of this embodiment is configured to replace the pattern generation unit described in the first embodiment. Figure 3 The pattern generating unit 9 has a switching contact 17, a hysteresis unit 18, a switching contact 22, a switching contact 24, a hysteresis unit 25, a multiplier 26, a divider 27 and a differential unit 29, and has a switching contact 32, a minimum limiter 33 and a gain 34.

[0101] The minimum limiter 33 limits the output from the subtracter 19 to an upper limit value of 0 and outputs the result to the gain 34. That is, if the difference between the magnetizing current command I0 and the d-axis current command Idp1 obtained by the subtracter 19 is a negative value, the difference is directly output to the gain 34, and if it is a positive value, the upper limit value 0 is output to the gain 34.

[0102] The gain 34 multiplies the output of the minimum value limiter 33 by the inverse of the preset primary time constant Tσ of the induction motor 3. The multiplied value is output from the gain 34 to the switching contact 32 and the gain 28.

[0103] In the pattern generator 9B of the present embodiment, similarly to the pattern generator 9A of the second embodiment, the differentiating means 29 is not provided on the output side of the gain 28. Therefore, the gain 28 multiplies the difference between the d-axis current command Idp1 and the magnetizing current command I0, which are limited to a range of less than or equal to the upper limit value 0 by the minimum value limiter 33 and multiplied by the inverse of the primary time constant Tσ by the gain 34, by the secondary time constant T2 of the induction motor 3, and outputs the result to the adder 16.

[0104] In addition, the switching contact 32 switches the value input to the integration unit 21 in the same manner as in the second embodiment. The pattern generation unit 9B switches the switching contact 32 so that the output of the gain 20 is input to the integration unit 21 during normal control execution and the output of the gain 34 is input to the integration unit 21 during shutdown control execution. Thus, in this embodiment, the first-order time constant Tσ is used instead of the d-axis current command holding value Idph described in the first embodiment, and the excitation current command Idp2 and the magnetizing current command I0 during shutdown are calculated to obtain the d-axis magnetic flux command φdp.

[0105] The pattern generating unit 9B of this embodiment operates as a first-order lag with a quadratic time constant T2 as a time constant by using the subtractor 19, the gain 20 and the integrating unit 21 via the switching contact 32 in the normal state as in the first embodiment. On the other hand, at the time of disconnection, the subtractor 19, the minimum value limiter 33, the gain 34 and the integrating unit 21 operate as a first-order lag with an input limiter with a primary time constant Tσ as a time constant by using the subtractor 19, the minimum value limiter 33, the gain 34 and the integrating unit 21 via the switching contact 32. Here, the time constant at the time of disconnection only needs to be sufficiently short relative to the secondary time constant T2, so it is not limited to the primary time constant Tσ of the induction motor 3, and other time constants may be used.

[0106] As described above, in the pattern generation unit 9B of the present embodiment, when switching from the normal control to the cut-off control, the time constant of the first-order lag unit is switched from the quadratic time constant T2 to the first-order time constant Tσ. At this time, since the first-order time constant Tσ is sufficiently short relative to the quadratic time constant T2, the falling rate and falling time of the d-axis flux command φdp at the time of cut-off are almost the same as the d-axis current command Idp1. In addition, the continuity of the d-axis flux command φdp is also maintained by the integration unit 21 constituting the first-order lag unit. Therefore, when the d-axis flux command φdp is transferred from the normal control state to the cut-off control during the rise, the d-axis flux command φdp can also be continuously and at a constant rate.

[0107] Furthermore, in the pattern generating unit 9B of the present embodiment, the output of the gain 34 is multiplied by the quadratic time constant T2 using the gain 28 and the adder 16, and the resultant is added to the d-axis current command Idp1, thereby obtaining the excitation current command Idp2 for the cut-off time. Since the output of the gain 34 is equal to the time change rate of the magnetizing current command I0, the excitation current command Idp2 required for the continuous operation of the d-axis magnetic flux command φdp can be calculated in this way.

[0108] In addition, when switching from normal control to cut-off control after the d-axis magnetic flux command φdp starts to rise but before reaching a certain value, the cut-off control is started when the d-axis current command Idp1 is larger than the magnetizing current command I0. Fig. 9 In the configuration of the pattern generator 9B shown, it is assumed that the minimum value limiter 33 does not exist. Since the subtractor 19, the gain 34, and the integration unit 21 constitute a first-order lag unit, although the d-axis current command Idp1 decreases, the output of the subtractor 19 is positive, and as a result, the magnetizing current command I0 moves in the positive direction, which is the opposite direction to the d-axis current command Idp1. In this way, the excitation current command Idp2 and the d-axis magnetic flux command φdp at the time of cutoff become too large, which causes torque shock or overcurrent. In order to prevent this, it is necessary to make the input of the gain 34 equal to or less than zero. Therefore, in the pattern generator 9B of this embodiment, a minimum value limiter 33 is provided at the front end of the gain 34, which limits the output of the subtractor 19 to a negative value equal to or less than zero and inputs the gain 34.

[0109] Fig.10 This is a diagram showing an example of various commands and state quantities in the case where the cut-off control is performed before the d-axis magnetic flux command φdp is completely increased in the power conversion device according to the third embodiment of the present invention. Fig.10 In the Figure 4 The description of each instruction and state quantity of the same action is omitted below.

[0110] In the power conversion device of this embodiment, by using Fig. 9 The pattern generating unit 9B of the structure shown in FIG. 1 is configured to switch from the normal control to the cut-off control even when the d-axis magnetic flux command φdp is rising. Fig.10 The d-axis magnetic flux command φdp does not become discontinuous. In addition, by switching the time constant of the first-order lag unit from the second-order time constant T2 to the first-order time constant Tσ, it is possible to suppress the increase of the d-axis magnetic flux command φdp during the cutoff.

[0111] In addition, in the cut-off control, the d-axis magnetic flux command φdp is output at a constant value during the period when the d-axis current command Idp1 is greater than the magnetizing current command I0, and the d-axis magnetic flux command φdp is reduced at a constant change rate during the period after the d-axis current command Idp1 coincides with the magnetizing current command I0. Thus, the d-axis magnetic flux command φdp can be reduced until it reaches zero during the d-axis current command drop time Td.

[0112] As described above, in the power conversion device of the present embodiment, when the d-axis magnetic flux command φdp is shifted from the normal control state to the cut-off control during the rise, the actual d-axis magnetic flux φd in the induction motor 3 can be continuously reduced at a certain change rate, so the d-axis magnetic flux φd can be decayed to zero without undershooting. That is, the residual amount of the d-axis magnetic flux φd when the power conversion device is cut off and the drive of the induction motor 3 is stopped can be made zero. Therefore, the generation of excessive current and torque when the power conversion device is restarted can be suppressed.

[0113] According to the third embodiment of the present invention described above, the pattern generation unit 9B uses the integration unit 21 as an integrator to hold a hold value corresponding to the value of the d-axis magnetic flux command φdp immediately before the d-axis current command Idp1 starts to decrease. Specifically, the pattern generation unit 9B uses the subtractor 19 to obtain the difference between the d-axis current command Idp1 and the output of the integration unit 21. Then, in the normal control execution, the output of the integration unit 21 when the product of the difference and the reciprocal of the secondary time constant T2 is input to the integration unit 21 using the gain 20 and the switching contact 32 is obtained as the magnetizing current command I0, and in the cut-off control execution, the output of the integration unit 21 when the product of the difference and the reciprocal of the primary time constant Tσ shorter than the secondary time constant T2 is input to the integration unit 21 using the gain 34 and the switching contact 32 is obtained as the magnetizing current command I0. Furthermore, the pattern generation unit 9B includes a minimum value limiter 33 that limits the input of the integration unit 21 in the cut-off control execution to a range of 0 or less. Because of this, similarly to the first and second embodiments, even when the d-axis magnetic flux command φdp is shifted to the cut-off control during the rising process, the value of the magnetizing current command I0 that changes continuously can be calculated. As a result, the d-axis magnetic flux φd can be attenuated at a constant rate of change until it reaches zero, and the d-axis magnetic flux φd can be reliably prevented from remaining inside the induction motor 3.

[0114] In addition, the present invention is not limited to the above-mentioned embodiments and variations, and can be implemented using any constituent elements within the scope of the main purpose. In addition, each embodiment and variation can be adopted alone, or can be adopted in any combination. That is, in the present invention, by arbitrarily combining the features of each embodiment, the above-mentioned effect can be exerted.

[0115] The above-mentioned embodiment and modification are only examples, and the present invention is not limited to these contents as long as the features of the invention are not damaged. In addition, various embodiments and modification are described above, but the present invention is not limited to these contents. Other modes that can be thought of within the scope of the technical idea of ​​the present invention are also included in the scope of the present invention.

[0116] Description of Reference Numerals

[0117] 1…Power conversion circuit, 2…Control device, 3…Induction motor, 4…Smoothing capacitor, 5a…U-phase upper arm element, 5b…U-phase lower arm element, 5c…V-phase upper arm element, 5d…V-phase lower arm element, 5e…W-phase upper arm element, 5f…W-phase lower arm element, 6…DC voltage sensor, 7a…U-phase current sensor, 7b…V-phase current sensor, 7c…W-phase current sensor, 8…Current command generation unit, 9, 9A, 9B…Pattern generation unit, 10…Coordinate conversion unit, 11…Rotation Speed ​​estimation unit, 12…frequency command generation unit, 13…voltage command generation unit, 14…pulse command generation unit, 15…switching contact, 16…adder, 17…switching contact, 18…hysteresis unit, 19…subtractor, 20…gain, 21…integral unit, 22…switching contact, 23…gain, 24…switching contact, 25…hysteresis unit, 26…multiplier, 27…divider, 28…gain, 29…differential unit, 30…divider, 31…gain, 32…switching contact, 33…maximum Minimum value limiter, 34…Gain, Ecf…DC voltage, Su1…U-phase upper arm gate pulse signal, Su2…U-phase lower arm gate pulse signal, Sv1…V-phase upper arm gate pulse signal, Sv2…V-phase lower arm gate pulse signal, Sw1…W-phase upper arm gate pulse signal, Sw2…W-phase lower arm gate pulse signal, iu…U-phase current, iv…V-phase current, iw…W-phase current, cmd…Control command, Idp1…d-axis current command, Idp2…Excitation current command, Iqp…q-axis Current command, φdp…d-axis flux command, Idf…d-axis current detection value, Iqf…q-axis current detection value, I0…magnetizing current command, Idph…d-axis current command hold value, I0h…magnetizing current command hold value, Idp0…stable value of excitation current command, ωre…rotor angular frequency estimated value, ω1…primary angular frequency, Vc…modulation rate, δ…voltage command angle, L…excitation inductance, Tσ…primary time constant, T2…secondary time constant, Td…d-axis current command fall time.

Claims

1. A power conversion device, characterized in that: include: Power conversion circuitry that converts DC power into AC power to drive an induction motor; and A control device for outputting a gate pulse signal to the power conversion circuit to control the power conversion circuit, The control device obtains a current command and a flux command for generating the gate pulse signal, and is capable of maintaining a holding value corresponding to the value of the flux command just before the current command begins to decrease, and when the power conversion circuit is cut off, the current command and the flux command are obtained based on the holding value.

2. The power conversion device according to claim 1, characterized in that: A control instruction for operating or stopping the power conversion circuit is input into the control device. The control device, According to the control command, either normal control corresponding to a period before the current command starts to decrease or cut-off control corresponding to a period after the current command starts to decrease is performed; The held value corresponding to the value of the flux command immediately before switching from the normal control to the shutoff control can be held.

3. The power conversion device according to claim 2, characterized in that: The control device comprises: a current command generating unit for generating a d-axis current command and a q-axis current command corresponding to the control command; a pattern generating unit that obtains an excitation current command and a magnetizing current command based on the d-axis current command, and generates the magnetic flux command based on the magnetizing current command and an excitation inductance preset according to the characteristics of the induction motor; a voltage command generating unit that generates a voltage command based on the field current command, the magnetic flux command, and the q-axis current command; and a pulse command generating unit for generating the gate pulse signal according to the voltage command; The pattern generation unit holds, as the held value, the value of the magnetizing current command immediately before switching from the normal-time control to the shutoff-time control.

4. The power conversion device according to claim 3, characterized in that: The pattern generating unit, In the process of implementing the normal control, the excitation current command is obtained from the d-axis current command, and the magnetizing current command is obtained based on the d-axis current command and a secondary time constant preset according to the characteristics of the induction motor. During the execution of the cut-off control, the magnetizing current command is obtained based on the d-axis current command and the held value, and the excitation current command is obtained based on the magnetizing current command and the secondary time constant.

5. The power conversion device according to claim 4, characterized in that: The pattern generation unit continues to hold the held value after switching from the normal control to the shutoff control.

6. The power conversion device according to claim 5, characterized in that: The pattern generating unit, respectively holding a value of the magnetizing current command and a value of the excitation current command immediately before switching from the normal control to the cut-off control as a first held value and a second held value, A value obtained by dividing the product of the d-axis current command and the first held value by the second held value is obtained as a value of the magnetizing current command during the execution of the cut-off control.

7. The power conversion device according to claim 5 or 6, characterized in that: The current command generating unit outputs a falling time indicating a time from when the current command starts to fall to when it ends. The pattern generating unit, holding, as the held value, the value of the magnetizing current command immediately before switching from the normal control to the cut-off control, A value obtained by accumulating a value obtained by inverting the sign of a value obtained by dividing the held value by the falling time is obtained as a value of the magnetizing current command during the execution of the cut-off control.

8. The power conversion device according to any one of claims 4 to 7, characterized in that: The pattern generation section holds the held value using an integrator.

9. The power conversion device according to claim 8, characterized in that: The pattern generating unit, Obtaining the difference between the d-axis current command and the output of the integrator, In the process of implementing the normal control, the output of the integrator when the product of the difference and the reciprocal of the quadratic time constant is input to the integrator is obtained as the magnetizing current command, In the process of executing the cut-off control, the output of the integrator when the product of the difference and the reciprocal of the primary time constant shorter than the secondary time constant is input to the integrator is obtained as the magnetizing current command.

10. The power conversion device according to claim 9, characterized in that: The pattern generating unit includes a limiter for limiting the input of the integrator to a range of 0 or less during the execution of the shutoff control.

11. A control method for a power conversion circuit for converting DC power into AC power to drive an induction motor, characterized in that: Obtain current command and flux command, generating a gate pulse signal according to the current instruction and the flux instruction, outputting the gate pulse signal to the power conversion circuit, holding a hold value corresponding to the value of the flux command immediately before the current command starts to decrease, When the power conversion circuit is shut down, the current command and the magnetic flux command are obtained based on the held value.

12. The control method of the power conversion circuit according to claim 11, characterized in that: receiving an input of a control instruction for operating or stopping the power conversion circuit, According to the control command, either normal control corresponding to a period before the current command starts to decrease or cut-off control corresponding to a period after the current command starts to decrease is performed; The held value corresponding to the value of the flux command immediately before switching from the normal control to the shutoff control is held.

13. The control method of the power conversion circuit according to claim 12, characterized in that: generating a d-axis current command and a q-axis current command corresponding to the control command, obtaining an excitation current command and a magnetizing current command based on the d-axis current command, generating the magnetic flux command based on the magnetizing current command and a magnetic inductance preset according to the characteristics of the induction motor, generating a voltage command based on the field current command, the magnetic flux command, and the q-axis current command, generating the gate pulse signal according to the voltage instruction, The value of the magnetizing current command immediately before switching from the normal control to the shutoff control is held as the held value.

14. The control method of the power conversion circuit according to claim 13, characterized in that: In the process of implementing the normal control, the excitation current command is obtained from the d-axis current command, and the magnetizing current command is obtained based on the d-axis current command and a secondary time constant preset according to the characteristics of the induction motor. During the execution of the cut-off control, the magnetizing current command is obtained based on the d-axis current command and the held value, and the excitation current command is obtained based on the magnetizing current command and the secondary time constant.

15. The control method of the power conversion circuit according to claim 14, characterized in that: After switching from the normal control to the shutoff control, the held value continues to be held.

16. The control method of the power conversion circuit according to claim 15, characterized in that: respectively holding a value of the magnetizing current command and a value of the excitation current command immediately before switching from the normal control to the cut-off control as a first held value and a second held value, A value obtained by dividing the product of the d-axis current command and the first held value by the second held value is obtained as a value of the magnetizing current command during the execution of the cut-off control.

17. The control method of the power conversion circuit according to claim 15 or 16, characterized in that: Find the falling time which represents the time from when the current command starts to fall to when it ends, A value obtained by adding a value obtained by dividing the held value by the falling time and inverting the sign thereof to the value of the magnetizing current command when the current command starts to fall is obtained as the value of the magnetizing current command during the execution of the cut-off control.

18. The control method of the power conversion circuit according to any one of claims 14 to 17, characterized in that: An integrator is used to hold the held value.

19. The control method of the power conversion circuit according to claim 18, characterized in that: Obtaining the difference between the d-axis current command and the output of the integrator, In the process of implementing the normal control, the output of the integrator when the product of the difference and the reciprocal of the quadratic time constant is input to the integrator is obtained as the magnetizing current command, In the process of executing the cut-off control, the output of the integrator when the product of the difference and the reciprocal of the primary time constant shorter than the secondary time constant is input to the integrator is obtained as the magnetizing current command.

20. The control method of the power conversion circuit according to claim 19, characterized in that: The input to the integrator during the execution of the shutoff control is limited to a range of zero or less.

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