Control method for power conversion device and power conversion circuit

Abstract

This power converter comprises: a power converter circuit that converts direct-current power to alternating-current power to drive an induction motor; and a controller that outputs a gate pulse signal to the power converter circuit to control the power converter circuit. The controller can determine a current command and a magnetic flux command that are used for generating the gate pulse signal, and hold a hold value corresponding to the value of the magnetic flux command immediately before the start of falling of the current command. When interrupting the power converter, the controller determines the current command and the magnetic flux command on the basis of the hold value.

Description

[Technical Field]

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

[0002] Conventionally, in railway vehicles, a driving method that uses a power conversion device to perform variable-speed driving of an alternating-current motor has been widely used. In addition, in many railway vehicles, induction motors are used for driving the vehicles, and a method of collectively driving a plurality of induction motors by one power conversion device is generally widely adopted.

[0003] In the operation of a railway vehicle, after starting the power conversion device from a stopped state and accelerating, the power conversion device is stopped to enter a coasting state where the vehicle travels by inertia. From this state, driving operations of restarting the power conversion device to accelerate or decelerate are frequently performed. When a railway vehicle enters a coasting state, no voltage is applied to the induction motor, but for a while after the power conversion device stops, current continues to flow inside the induction motor. This current is consumed by the internal resistance of the induction motor and gradually attenuates. However, magnetic flux continues to be generated until the current disappears, so residual magnetic flux exists inside the induction motor. Restarting the power conversion device when this residual magnetic flux is large may cause adverse effects such as damage to the power conversion device due to generation of excessive current, and deterioration of the riding comfort of the vehicle due to generation of excessive torque.

[0004] As a countermeasure to the above-mentioned problem, for example, the technology described in Patent Document 1 is known. Patent Document 1 discloses a control device for a power conversion device that has a function to sufficiently attenuate magnetic flux when stopping an induction motor, which has a voltage calculation unit that generates a voltage command based on a current command and a PWM calculation unit that outputs a gate pulse signal of a power conversion circuit based on the voltage command, and when the excitation current command is interrupted from falling edge to zero, an operating amount calculated according to the time change amount of the excitation current command is added to the excitation current command to obtain an interruption-time excitation current command, and this interruption-time excitation current command is used as a current command to the voltage calculation unit, thereby attenuating the residual magnetic flux inside the induction motor when stopping the power conversion circuit. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2017-77079 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The technology described in Patent Document 1 does not consider control when the power conversion device is shut off during the rise of the magnetic flux command. Therefore, in such cases, there is a risk that the residual magnetic flux inside the induction motor may not be sufficiently attenuated. [Means for solving the problem]

[0007] The power conversion device according to the present invention comprises a power conversion circuit that converts DC power to 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, wherein the control device determines a current command and a magnetic flux command used to generate the gate pulse signal, and can hold a holding value corresponding to the value of the magnetic flux command immediately before the falling edge of the current command begins, and when shutting off the power conversion circuit, it determines the current command and the magnetic flux command based on the holding value. The power conversion circuit control method according to the present invention is a control method for a power conversion circuit that converts DC power to AC power to drive an induction motor, and comprises: determining a current command and a magnetic flux command; generating a gate pulse signal based on the current command and the magnetic flux command; outputting the gate pulse signal to the power conversion circuit; holding a value corresponding to the value of the magnetic flux command immediately before the falling edge of the current command begins; and determining the current command and the magnetic flux command based on the held value when shutting off the power conversion circuit. [Effects of the Invention]

[0008] According to the present invention, even when the power conversion device is shut off during the process of raising the magnetic flux command, the residual magnetic flux inside the induction motor can be sufficiently attenuated. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows the configuration of a power converter according to one embodiment of the present invention. [Figure 2] This is a functional block diagram showing details of the control device according to the first embodiment of the present invention. [Figure 3] This is a control block diagram showing details of the pattern generation unit according to the first embodiment of the present invention. [Figure 4] This figure shows an example of the commands and state variables when interruption control is performed after the d-axis magnetic flux command has finished starting up. [Figure 5] This figure shows an example of the commands and state variables when interruption control is performed before the d-axis magnetic flux command has finished rising, using a conventional control method. [Figure 6] This figure shows an example of commands and state variables when interruption control is performed before the d-axis magnetic flux command is fully activated in a power conversion device according to the first embodiment of the present invention. [Figure 7] This is a functional block diagram showing details of a control device according to a second embodiment of the present invention. [Figure 8] This is a control block diagram showing details of the pattern generation unit according to a second embodiment of the present invention. [Figure 9]This is a control block diagram showing details of the pattern generation unit according to the third embodiment of the present invention. [Figure 10] This figure shows an example of commands and state variables when interruption control is performed before the d-axis magnetic flux command is fully activated in a power conversion device according to a third embodiment of the present invention. [Modes for carrying out the invention]

[0010] 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 application to railway vehicles will be described as an example, but it can also be applied to other applications such as general industrial applications.

[0011] (First Embodiment) Figure 1 is a diagram showing the configuration of a power conversion device according to one embodiment of the present invention. The power conversion device shown in Figure 1 is connected to an induction motor 3 and comprises a power conversion circuit 1 that converts DC power supplied from an external DC power source into AC power and outputs it to the induction motor 3 to drive the induction motor 3, and a control device 2 that controls the power conversion circuit 1.

[0012] The power conversion circuit 1 includes semiconductor switching elements: 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. The U-phase upper arm element 5a and U-phase lower arm element 5b, the V-phase upper arm element 5c and V-phase lower arm element 5d, and the W-phase upper arm element 5e and W-phase lower arm element 5f are connected in series in the power conversion circuit 1 to form upper and lower arm circuits for the U-phase, V-phase, and W-phase, respectively. Power lines connected to the induction motor 3 are connected between the upper arm elements 5a, 5c, and 5e and the lower arm elements 5b, 5d, and 5f of each of these upper and lower arm circuits.

[0013] The power conversion circuit 1 converts DC power supplied from a DC power source into three-phase AC power by causing the semiconductor switching elements 5a to 5f to perform switching driving respectively in accordance with gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, Sw2 output from the control device 2. The three-phase AC power after this conversion is output from the power conversion circuit 1 to the induction motor 3 via the power line of each phase, whereby drive control of the induction motor 3 by the power conversion device of the present embodiment is performed.

[0014] DC power supplied from the DC power source is smoothed by the smoothing capacitor 4 and input to the power conversion circuit 1. The inter-terminal voltage 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.

[0015] A U-phase current sensor 7a, a V-phase current sensor 7b, and a W-phase current sensor 7c that respectively detect a U-phase current iu, a V-phase current iv, and a W-phase current iw flowing through the induction motor 3 are installed on the power line of each phase provided between the power conversion circuit 1 and the induction motor 3. The detection results of each phase current obtained by these current sensors 7a to 7c are input to the control device 2.

[0016] The control device 2 generates the gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, 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 to 7c, and outputs the generated signals to the power conversion circuit 1.

[0017] FIG. 2 is a functional block diagram showing details of the control device 2 according to the first embodiment of the present invention. The control device 2 has the following functional blocks: a current command generation unit 8, a pattern generation unit 9, a coordinate conversion unit 10, a rotational speed estimation unit 11, a frequency command generation unit 12, a voltage command generation unit 13, and a pulse command generation unit 14. The control device 2 is configured using, for example, a microcomputer including a CPU, a memory, and the like, and functions corresponding to the respective functional blocks in FIG. 2 can be implemented by executing a predetermined program in the CPU. Note that part or all of the functions of the control device 2 may be implemented using a logic circuit such as an FPGA (Field Programmable Gate Array).

[0018] A control command cmd for operating or stopping the power conversion circuit 1 is input to the control device 2 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 according to the control command cmd. For example, when a control command cmd for operating the power conversion circuit 1 is input, the current command generation unit 8 generates the d-axis current command Idp1 and the q-axis current command Iqp such that AC power necessary for driving the induction motor 3 with a predetermined torque is output from the power conversion circuit 1.

[0019] The pattern generation unit 9 calculates an excitation current command Idp2 and a d-axis magnetic flux command φdp based on the d-axis current command Idp1 input from the current command generation unit 8, and outputs the calculated values to the voltage command generation unit 13. The excitation current command Idp2 is a command value for a current in the d-axis direction, which is the direction of the rotating magnetic field of the induction motor 3. The excitation current command Idp2 is equal to the d-axis current command Idp1 during normal operation of the power conversion circuit 1, and corresponds to a correction value obtained by correcting the d-axis current command Idp1 to attenuate the magnetic flux of the induction motor 3 when stopping the power conversion circuit 1. Note that the pattern generation unit 9 switches the calculation methods for the excitation current command Idp2 and the d-axis magnetic flux command φdp respectively according to the control state of the induction motor 3. Details of the method for calculating the excitation current command Idp2 and the d-axis magnetic flux command φdp by the pattern generation unit 9 will be described later.

[0020] The coordinate transformation unit 10 performs a rotational coordinate transformation on the U-phase current iu, V-phase current iv, and W-phase current iw detected by the current sensors 7a to 7c, respectively, to obtain the d-axis current detection value Idf and the q-axis current detection value Iqf, and outputs these current detection values ​​to the rotational speed estimation unit 11. In the coordinate transformation unit 10, the direction of the rotational magnetic field of the induction motor 3 is defined as the d-axis direction, and the direction of the current flowing to generate torque is defined as the q-axis direction, and the d-axis current detection value Idf and the q-axis current detection value Iqf are determined accordingly.

[0021] The rotational speed estimation unit 11 estimates the rotor angular frequency of the induction motor 3 based on the excitation current command Idp2 and 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 q-axis current detection value Iqf input from the coordinate transformation unit 10, and outputs the estimation result as the rotor angular frequency estimate value ωre.

[0022] The frequency command generation unit 12 receives the d-axis magnetic flux command φdp obtained by the pattern generation unit 9, the q-axis current command Iqp generated by the current command generation unit 8, and the rotor angular frequency estimate ωre estimated by the rotation speed estimation unit 11 as input. Based on this input information, the frequency command generation unit 12 calculates the angular frequency of the AC voltage applied to the induction motor 3 and outputs it as the primary angular frequency ω1.

[0023] The voltage command generation unit 13 receives the DC voltage Ecf detected by the DC voltage sensor 6, the excitation current command Idp2 and d-axis magnetic flux command φdp determined by the pattern generation unit 9, the q-axis current command Iqp generated by the current command generation unit 8, the rotor angular frequency estimate ωre determined by the rotation speed estimation unit 11, and the primary angular frequency ω1 determined by the frequency command generation unit 12 as input. Based on this input information, the voltage command generation unit 13 calculates the modulation rate Vc and voltage command deviation δ of the power conversion circuit 1, and outputs the calculation result as a voltage command for the output voltage from the power conversion circuit 1 to the induction motor 3.

[0024] The pulse command generation unit 14 calculates gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, and Sw2 for the semiconductor switching elements 5a to 5f of the power conversion circuit 1, based on the modulation rate Vc and voltage command deviation angle δ, which are voltage commands generated by the voltage command generation unit 13, and the primary angular frequency ω1, which is determined by the frequency command generation unit 12. The gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, and Sw2 determined by the pulse command generation unit 14 are output from the control device 2 to the power conversion circuit 1 as described above, and are used to drive control each of the semiconductor switching elements 5a to 5f of the power conversion circuit 1.

[0025] Figure 2 shows an example of a power converter that achieves speed sensorless control by determining the rotor angular frequency ωre of the induction motor 3 using the rotational speed estimation unit 11. The present invention will be explained below using this example, but the present invention can also be applied to speed sensor-equipped control in which a speed sensor is provided instead of the rotational speed estimation unit 11, and the rotational speed of the induction motor 3 is detected by this speed sensor. In other words, the embodiments described below do not limit the configuration of the present invention.

[0026] Figure 3 is a control block diagram showing details of the pattern generation unit 9 according to the first embodiment of the present invention. In this embodiment, the pattern generation unit 9 is configured by combining, for example, a switching contact 15, an adder 16, a switching contact 17, a delay element 18, a subtractor 19, a gain 20, an integral element 21, a switching contact 22, a gain 23, a switching contact 24, a delay element 25, a multiplier 26, a divider 27, a gain 28, and a differential element 29, as shown in Figure 3.

[0027] As mentioned above, the pattern generation unit 9 switches the calculation method for the excitation current command Idp2 and the d-axis magnetic flux command φdp depending on the control state of the induction motor 3. Specifically, the pattern generation unit 9 switches the calculation method for the excitation current command Idp2 and the d-axis magnetic flux command φdp depending on whether the operation of the power conversion circuit 1 is controlled to output AC power from the power conversion circuit 1 to drive the induction motor 3 with a predetermined torque (hereinafter referred to as "normal control") or whether the operation of the power conversion circuit 1 is controlled to cut off the output of AC power from the power conversion circuit 1 to the induction motor 3 (hereinafter referred to as "cutoff control"). This switching of the calculation method can be performed, for example, based on the control command cmd input to the control device 2.

[0028] The switching contact 15 switches the excitation current command Idp2 output from the pattern generation unit 9. When normal control is being performed, the pattern generation unit 9 outputs the d-axis current command Idp1 input from the current command generation unit 8 as the excitation current command Idp2, and when interruption control is being performed, the switching contact 15 switches the output of the adder 16 as the excitation current command Idp2.

[0029] The adder 16 adds the output of the differential element 29 to the d-axis current command Idp1. This added value is output from the adder 16 via the switching contact 15 as the excitation current command Idp2 in the interruption control, as described above.

[0030] 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 when normal control is being performed, the d-axis current command Idp1 output from the current command generation unit 8 and input to the pattern generation unit 9 is the d-axis current command holding value Idph, and when interruption control is being performed, the output of the delay element 18 is the d-axis current command holding value Idph. The delay element 18 delays the output of the switching contact 17 before outputting it.

[0031] Due to the operation of the switching contact 17 and delay element 18 described above, during normal control, the d-axis current command retention value Idph is sequentially updated according to the value of the d-axis current command Idp1 input from the current command generation unit 8 to the pattern generation unit 9. On the other hand, after switching from normal control to interruption control, the value of the d-axis current command Idp1 input from the current command generation unit 8 to the pattern generation unit 9 immediately before the switch is retained as the d-axis current command retention value Idph.

[0032] The subtractor 19 subtracts the output of the integral element 21 from the d-axis current command Idp1. This subtracted value is output to the gain 20.

[0033] Gain 20 is obtained by multiplying the output of the subtractor 19 by the reciprocal of the pre-set second-order time constant T2 of the induction motor 3. This multiplied value is output to the integral element 21.

[0034] The integrating element 21 integrates the output of the gain 20. This integrated value is output to the integrating element 21, the switching contact 22, and the switching contact 24.

[0035] The switching contact 22 switches the magnetization current command I0 input to the gain 23. The pattern generation unit 9 switches the switching contact 22 so that when normal control is being performed, the output of the integral element 21 is input to the gain 23 as the magnetization current command I0, and when interruption control is being performed, the output of the divider 27 is input to the gain 23 as the magnetization current command I0.

[0036] Gain 23 multiplies the magnetization current command I0 input from the switching contact 22 by the preset excitation inductance L of the induction motor 3. This multiplied value is output from the pattern generation unit 9 as the d-axis magnetic flux command φdp.

[0037] The switching contact 24 switches the magnetization current command holding value I0h. The pattern generation unit 9 switches the switching contact 24 so that when normal control is being performed the output of the integral element 21 is the magnetization current command holding value I0h, and when interruption control is being performed the output of the delay element 25 is the magnetization current command holding value I0h. The delay element 25 outputs the output of the switching contact 24 with a delay.

[0038] Due to the operation of the switching contact 24 and delay element 25 described above, during normal control, the magnetization current command retention value I0h is sequentially updated according to the value of the magnetization current command I0 output from the integrating element 21 and input to the gain 23. On the other hand, after switching from normal control to interruption control, the value of the magnetization current command I0 input to the gain 23 immediately before the switch is retained as the magnetization current command retention value I0h.

[0039] The multiplier 26 multiplies the d-axis current command Idp1 by the magnetization current command holding value I0h. This multiplied value is output to the divider 27.

[0040] The divider 27 divides the output of the multiplier 26 by the d-axis current command holding value Idph. This divided value is output to the switching contact 22 and the gain 28.

[0041] Gain 28 multiplies the output of the divider 27 by the pre-set second-order time constant T2 of the induction motor 3. This multiplied value is output to the differential element 29.

[0042] The differential element 29 calculates the time change of the output of gain 28. This calculated value is output to the adder 16.

[0043] In the pattern generation unit 9 of this embodiment, the operation of each component as described above determines the excitation current command Idp2 and the magnetization current command I0 based on the d-axis current command Idp1, and generates the d-axis magnetic flux command φdp based on the magnetization current command I0 and the excitation inductance L which is set in advance according to the characteristics of the induction motor 3. Specifically, during normal control, the excitation current command Idp2 is determined from the d-axis current command Idp1, and the magnetization current command I0 is determined based on the d-axis current command Idp1 and the secondary time constant T2 which is set in advance according to the characteristics of the induction motor 3. Furthermore, during interruption control, the magnetization current command I0 is determined 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 is determined based on the magnetization current command I0 and the secondary time constant T2.

[0044] Next, the operation of the power converter of this embodiment will be described below with reference to Figures 4 to 6, which show typical operating examples.

[0045] Figure 4 shows an example of commands and state variables when interruption control is performed after the d-axis magnetic flux command φdp has finished rising. Although Figure 4 shows an example of the operation of a power converter using the control device 2 described in Figures 2 and 3 as an application example of the present invention, similar results can be obtained with conventional control methods that do not apply the present invention.

[0046] When the normal command is ON, that is, during normal control, the switching contacts 15, 17, 22, and 24 in the pattern generation unit 9 are in the normal switching state, as described above. In the example in Figure 4, this state continues from the start of the rise of the d-axis current command Idp1 until it reaches a certain value and just before the cutoff. On the other hand, when the cutoff command is ON, that is, during cutoff control, the switching contacts 15, 17, 22, and 24 in the pattern generation unit 9 are in the cutoff state, as described above. In the example in Figure 4, this state continues from the fall of the d-axis current command Idp1 until it reaches zero.

[0047] In the example in Figure 4, the d-axis current command Idp1 is shown as a solid line, and the magnetization current command I0 is shown as a dashed line superimposed on it. Under normal control, the magnetization current command I0 operates as a first-order lag with a second-order time constant T2 relative to the d-axis current command Idp1 through the operation of the subtractor 19, gain 20, integral element 21, and switching contact 22.

[0048] After the d-axis current command Idp1 has finished rising and reached a certain value, and after a sufficient amount of time has elapsed, the d-axis current command Idp1 and the magnetization current command I0 will coincide, as shown in Figure 4. Therefore, in the example in Figure 4, during the execution of the interruption control, the operation of the multiplier 26, the divider 27, and the switching contact 22 causes the d-axis current command Idp1 and the magnetization current command I0 to be the same value.

[0049] On the other hand, the excitation current command Idp2, due to the operation of the switching contact 15, adder 16, gain 28, and differential element 29, is the same value as the d-axis current command Idp1 under normal control conditions, and under interruption control conditions, is the value obtained by adding the d-axis current command Idp1 to the rate of change of the magnetization current command I0 (dI0 / dt) multiplied by the second-order time constant T2.

[0050] The d-axis magnetic flux command φdp is obtained by multiplying the magnetization current command I0 by the excitation inductance L. In Figure 4, the steady-state value of the excitation current command Idp2 is defined as Idp0.

[0051] When the d-axis current command Idp1 has finished rising and reached a constant value during normal control, the value of the d-axis current command Idp1 coincides with the excitation current command Idp2 and the magnetization current command I0. At this time, the value of the d-axis magnetic flux command φdp is equal to the value obtained by multiplying the steady-state value Idp0 of the excitation current command Idp2 by the excitation inductance L. When switching from normal control to cutoff control in this state, the value of the d-axis magnetic flux command φdp changes continuously from the above multiplied value. As a result, during the period from the start of the fall-off of the d-axis current command Idp1 to zero, the d-axis magnetic flux φd can be reduced to zero without undershooting the command value due to the d-axis magnetic flux command φdp. This allows the d-axis magnetic flux φd to be attenuated without leaving any residual value when the power conversion circuit 1 is cut off.

[0052] Next, the problems in interruption control when the present invention is not applied will be explained below using the example of operation in Figure 5. Figure 5 is a diagram showing an example of each command and state variable when interruption control is performed before the rise of the d-axis magnetic flux command φdp is completed using a conventional control method. Unlike Figure 4, Figure 5 shows an example of an operation waveform in which the d-axis current command Idp1 is brought down before the d-axis magnetic flux command φdp reaches a constant value after it starts to rise. Note that the explanation of each command and state variable that behaves the same as in Figure 4 will be omitted below in Figure 5.

[0053] In conventional control methods, as shown in Figure 4, if the transition from normal control to cutoff control occurs when the rise of the d-axis magnetic flux command φdp is complete and has reached a constant value, the d-axis magnetic flux φd can be sufficiently attenuated. However, if the transition from normal control to cutoff control occurs during the rise of the d-axis magnetic flux command φdp, as shown in Figure 5, the d-axis magnetic flux command φdp becomes discontinuous, and an excessively large command value is output as the d-axis magnetic flux command φdp. As a result, the d-axis magnetic flux φd undershoots beyond zero, and the d-axis magnetic flux φd remains inside the induction motor 3 even after the power converter has stopped. If the power converter is restarted with the d-axis magnetic flux φd remaining inside the induction motor 3 in this state, it can cause excessive current and torque to be generated. To prevent this, even if the transition from normal control to cutoff control occurs during the rise of the d-axis magnetic flux command φdp, it is necessary that the d-axis magnetic flux command φdp does not become discontinuous and that the d-axis magnetic flux φd is attenuated at a constant rate of change until it reaches zero.

[0054] In this embodiment of the power converter, the above-mentioned problems are solved, and a means is provided to sufficiently attenuate the magnetic flux of the induction motor 3 when the power converter is shut off. Specifically, as explained in Figure 3, in the pattern generation unit 9 of the control device 2, the d-axis current command Idp1 immediately before switching from normal control to shut-off control is held as the d-axis current command retention value Idph by the switching contact 17 and delay element 18, and the magnetization current command I0 immediately before switching from normal control to shut-off control is held as the magnetization current command retention value I0h by the switching contact 24 and delay element 25. Then, the magnetization current command I0 during the execution of the shut-off control is calculated by multiplying the d-axis current command Idp1 by the magnetization current command retention value I0h and dividing the result by the d-axis current command retention value Idph using the multiplier 26 and divider 27.

[0055] This allows the d-axis current command Idp1 to be corrected by the ratio of the d-axis current command holding value Idph to the magnetization current command holding value I0h immediately before the transition to cutoff control, even if the d-axis magnetic flux command φdp is being raised. As a result, the magnetization current command I0 can be made a continuous value, and the continuously decreasing d-axis magnetic flux command φdp can be calculated using this magnetization current command I0. In other words, the d-axis magnetic flux φd can be attenuated at a constant rate of change until it reaches zero, preventing the d-axis magnetic flux φd from remaining inside the induction motor 3.

[0056] Furthermore, in the power converter of this embodiment, the d-axis magnetic flux command φdp is calculated based on a corrected value of the d-axis current command Idp1. Therefore, during the fall time of the d-axis current command Idp1 (d-axis current command fall time Td), the d-axis magnetic flux command φdp can be lowered at a constant rate from just before interruption to zero.

[0057] Figure 6 shows an example of commands and state variables when interruption control is performed before the d-axis magnetic flux command φdp is fully started up in a power conversion device according to the first embodiment of the present invention. In Figure 6, the commands and state variables that behave similarly to those in Figure 4 will not be explained below.

[0058] In Figure 6, similar to Figure 5, the transition from normal control to interruption control occurs during the rise of the d-axis magnetic flux command φdp. However, in the power converter of this embodiment, as described above, the d-axis current command Idp1 is corrected by the ratio of the d-axis current command holding value Idph to the magnetization current command holding value I0h, and this is used as the magnetization current command I0 to determine the d-axis magnetic flux command φdp. Due to this effect, as shown in Figure 6, the d-axis magnetic flux command φdp can be continuously changed before and after switching from normal control to interruption control, and the d-axis magnetic flux φd can be attenuated at a constant rate of change until it reaches zero. The fall time of the d-axis magnetic flux command φdp at this time coincides with the fall time Td of the d-axis current command.

[0059] During the operation of the interruption control, the value of the excitation current command Idp2 is calculated by multiplying the rate of change of the magnetization current command I0 (dI0 / dt) by the secondary time constant T2 of the induction motor 3 and adding this to the d-axis current command Idp1. Since the magnetization current command I0 decreases at a constant rate of change, the value of the excitation current command Idp2 at this time is the value obtained by shifting the d-axis current command Idp1 in the negative direction.

[0060] As explained above, in the power converter of this embodiment, even if the state transitions from normal control to shutdown control during the rise of the d-axis magnetic flux command φdp, the actual d-axis magnetic flux φd in the induction motor 3 can be lowered at a constant rate of change. As a result, the d-axis magnetic flux φd can be attenuated to zero without undershooting. In other words, the residual amount of d-axis magnetic flux φd when the power converter is shut off can be reduced to zero. Therefore, the generation of excessive current and torque when restarting the power converter can be suppressed.

[0061] According to the first embodiment of the present invention described above, the following effects are achieved.

[0062] (1) The power conversion device comprises a power conversion circuit 1 that converts DC power to AC power to drive an induction motor 3, and a control device 2 that outputs gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, Sw2 to the power conversion circuit 1 to control the power conversion circuit 1. The control device 2 determines the d-axis current command Idp1, the excitation current command Idp2, and the d-axis magnetic flux command φdp used to generate the gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, Sw2, and can also hold magnetization current command holding value I0h and d-axis current command holding value Idph according to the value of the d-axis magnetic flux command φdp immediately before the falling edge of the d-axis current command Idp1 begins. When shutting off the power conversion circuit 1, the control device 2 determines the d-axis current command Idp1, the excitation current command Idp2, and the d-axis magnetic flux command φdp based on these holding values. In this way, even if the power converter is shut off while the d-axis magnetic flux command φdp is being generated, the residual magnetic flux inside the induction motor 3 can be sufficiently attenuated.

[0063] (2) The control device 2 receives a control command cmd to operate or stop the power conversion circuit 1. Based on the control command cmd, the control device 2 performs either normal control for the period before the d-axis current command Idp1 starts to fall, or interruption control for the period after the d-axis current command Idp1 starts to fall, and can hold a value corresponding to the value of the d-axis magnetic flux command φdp immediately before switching from normal control to interruption control. Specifically, the control device 2 includes a current command generation unit 8 that generates a d-axis current command Idp1 and a q-axis current command Iqp in accordance with the control command cmd; a pattern generation unit 9 that determines an excitation current command Idp2 and a magnetization current command I0 based on the d-axis current command Idp1 and generates a d-axis magnetic flux command φdp based on the magnetization current command I0 and an excitation inductance L preset according to the characteristics of the induction motor 3; a voltage command generation 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 generation unit 14 that generates gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, Sw2 based on this voltage command. The pattern generation unit 9 holds the value of the magnetization current command I0 immediately before switching from normal control to interruption control as a magnetization current command holding value I0h. In this way, when the power converter is shut off while the d-axis magnetic flux command φdp is being generated, gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, Sw2 can be generated that are sufficient to attenuate the residual magnetic flux inside the induction motor 3.

[0064] (3) During normal control, the pattern generation unit 9 uses the switching contact 15 to obtain the excitation current command Idp2 from the d-axis current command Idp1, and the subtractor 19, gain 20, integral element 21, and switching contact 22 to obtain the magnetization current command I0 based on the d-axis current command Idp1 and a secondary time constant T2 that is set in advance according to the characteristics of the induction motor 3. During interruption control, the switching contact 24, delay element 25, multiplier 26, and divider 27 to obtain the magnetization current command I0 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 gain 28, differential element 29, and adder 16 to obtain the excitation current command Idp2 based on the magnetization current command I0 and the secondary time constant T2. In this way, the values ​​of the excitation current command Idp2 and the magnetization current command I0 required to generate the gate pulse signals Su1, Su2, Sv1, Sv2, Sw1, and Sw2 can be appropriately determined in both normal control and interruption control.

[0065] (4) The pattern generation unit 9 continues to hold the magnetization current command retention value I0h and the d-axis current command retention value Idph after switching from normal control to interruption control. Specifically, the pattern generation unit 9 uses the switching contact 24 and delay element 25, and the switching contact 17 and delay element 18 to hold the values ​​of the magnetization current command I0 and excitation current command Idp2 immediately before switching from normal control to interruption control as the magnetization current command retention value I0h and the d-axis current command retention value Idph, respectively. In addition, the multiplier 26 and divider 27 calculate the value of the magnetization current command I0 during the execution of interruption control by dividing the product of the d-axis current command Idp1 and the magnetization current command retention value I0h by the d-axis current command retention value Idph. In this way, even if the system transitions to interruption control during the rise of the d-axis magnetic flux command φdp, it is possible to calculate a continuously changing value of the magnetization current command I0. As a result, the d-axis magnetic flux φd is attenuated at a constant rate of change until it reaches zero, reliably preventing the d-axis magnetic flux φd from remaining inside the induction motor 3.

[0066] (Second embodiment) Next, a second embodiment of the present invention will be described. In this embodiment, an example will be described in which the calculation method of the magnetization current command I0 differs from that of the first embodiment. The following will focus on the differences from the first embodiment.

[0067] The power converter of this embodiment has the same configuration as the power converter shown in Figure 1 described in the first embodiment, but the functional configuration of the control device 2 is different.

[0068] Figure 7 is a functional block diagram showing details of the control device 2 according to the second embodiment of the present invention. In this embodiment, the pattern generation unit 9 is replaced by a pattern generation unit 9A, and the current command generation unit 8 outputs a d-axis current command fall time Td to the pattern generation unit 9A in addition to the d-axis current command Idp1. This is because the pattern generation unit 9A uses the d-axis current command fall time Td to calculate the magnetization current command I0 and the d-axis magnetic flux command φdp at the time of interruption.

[0069] Figure 8 is a control block diagram showing details of the pattern generation unit 9A according to a second embodiment of the present invention. The pattern generation unit 9A of this embodiment is configured to include a d-axis current command fall time Td input, and instead of the switching contact 17, delay element 18, switching contact 22, multiplier 26, divider 27, and differential element 29 in the pattern generation unit 9 of Figure 3 described in the first embodiment, it is configured to include a divider 30, a gain 31, and a switching contact 32.

[0070] The divider 30 divides the magnetization current command holding value I0h by the d-axis current command falling time Td. This divided value is output to the gain 31.

[0071] Gain 31 inverts the sign of the output of the divider 30 by multiplying it by -1, and outputs it to gain 28 and switching contact 32.

[0072] In this embodiment, the pattern generation unit 9A does not have a differential element 29 on the output side of the gain 28. Therefore, the gain 28 multiplies the output of the divider 30, whose sign has been inverted by the gain 31, by the second-order time constant T2 of the induction motor 3, and outputs it to the adder 16.

[0073] The switching contact 32 switches the value input to the integral element 21. The pattern generation unit 9A switches the switching contact 32 so that the output of gain 20 is input to the integral element 21 when normal control is being performed, and the output of gain 31 is input to the integral element 21 when interruption control is being performed. In this embodiment, instead of the d-axis current command holding value Idph described in the first embodiment, the d-axis current command fall time Td is used to calculate the excitation current command Idp2 and magnetization current command I0 at the time of interruption, and the d-axis magnetic flux command φdp is determined.

[0074] Furthermore, the pattern generation unit 9A reverses the sign of the value obtained by dividing the magnetization current command holding value I0h by the d-axis current command fall time Td using the gain 31. This process corresponds to the calculation of the time rate of change of the magnetization current command I0 performed by the differential element 29 in the first embodiment. In other words, in this embodiment, the excitation current command Idp2 at the time of interruption can be determined without using the differential element 29.

[0075] Furthermore, in the interruption control, the integral element 21 integrates the ratio of the d-axis current command fall time Td to the magnetization current command holding value I0h, so the integral element 21 can be shared between normal operation and interruption. Therefore, the continuity of the d-axis magnetic flux command φdp when transitioning from normal operation control to interruption control can be reliably guaranteed.

[0076] In the above explanation, the magnetization current command I0, which decreases at a constant rate when interrupted, is calculated by the ratio of the d-axis current command fall time Td to the magnetization current command holding value I0h. However, this embodiment is not limited to this configuration. For example, it is also possible to realize a magnetization current command I0 that decreases at a constant rate by using a rate of change limiter that lowers the magnetization current command I0 at a constant rate of change when interrupted. In this case, the input to the rate of change limiter is set to a value obtained by subtracting the magnetization current command I0 from zero, and the output is limited by the ratio of the d-axis current command fall time Td to the magnetization current command holding value I0h, thereby realizing a magnetization current command I0 that decreases at a constant rate.

[0077] According to the configuration of this embodiment, if interruption control is performed before the d-axis magnetic flux command is fully activated, it is possible to use the same commands and state variables as described in Figure 6 in the first embodiment.

[0078] As described above, in this embodiment as well, when the state transitions from normal control to shutdown control during the rise of the d-axis magnetic flux command φdp, the d-axis magnetic flux command φdp can be continuously and at a constant rate, so that the d-axis magnetic flux φd can be attenuated to zero without undershooting. In other words, the residual amount of d-axis magnetic flux φd when the power converter is shut off can be reduced to zero. Therefore, the generation of excessive current and torque when restarting the power converter can be suppressed.

[0079] Furthermore, in this embodiment, since the differential element 29 described in the first embodiment is unnecessary, even if, for example, the d-axis current command Idp1 changes abruptly due to the influence of disturbances during interruption, the excitation current command Idp2 does not diverge, and the power converter can be operated stably.

[0080] According to the second embodiment of the present invention described above, the pattern generation unit 9A continues to hold the magnetization current command holding value I0h after switching from normal control to interruption control. Specifically, the current command generation unit 8 outputs the d-axis current command fall time Td, which represents the time from the start to the end of the fall of the d-axis current command Idp1. The pattern generation unit 9A holds the value of the magnetization current command I0 immediately before switching from normal control to interruption control as the magnetization current command holding value I0h using the switching contact 24 and the delay element 25. Furthermore, the divider 30, gain 31 and integral element 21 calculate the value of the magnetization current command I0 during the execution of interruption control by integrating the value obtained by dividing the magnetization current command holding value I0h by the d-axis current command fall time Td and inverting its sign. In this way, similar to the first embodiment, even if the system transitions to interruption control during the rise of the d-axis magnetic flux command φdp, it is possible to calculate a continuously changing value of the magnetization current command I0. As a result, the d-axis magnetic flux φd is attenuated at a constant rate of change until it reaches zero, reliably preventing the d-axis magnetic flux φd from remaining inside the induction motor 3.

[0081] (Third embodiment) Next, a third embodiment of the present invention will be described. In this embodiment, an example will be described in which the method for holding the magnetization current command holding value I0h differs from that of the first and second embodiments. The following will focus on the differences from the first and second embodiments.

[0082] Figure 9 is a control block diagram showing details of the pattern generation unit 9B according to a third embodiment of the present invention. The pattern generation unit 9B of this embodiment is configured to include a switching contact 32, a minimum value limiter 33, and a gain 34 instead of the switching contact 17, delay element 18, switching contact 22, switching contact 24, delay element 25, multiplier 26, divider 27, and differential element 29 in the pattern generation unit 9 of Figure 3 described in the first embodiment.

[0083] The minimum value limiter 33 limits the output from the subtractor 19 to an upper limit of 0 and outputs it to the gain 34. That is, if the magnitude of the difference between the magnetization current command I0 and the d-axis current command Idp1 obtained by the subtractor 19 is a negative value, that value is output directly to the gain 34; if it is a positive value, the upper limit of 0 is output to the gain 34.

[0084] Gain 34 multiplies the output of the minimum value limiter 33 by the reciprocal of the preset primary time constant Tσ of the induction motor 3. This multiplied value is output from gain 34 to the switching contact 32 and gain 28.

[0085] In this embodiment, the pattern generation unit 9B, like the pattern generation unit 9A in the second embodiment, does not have a differential element 29 on the output side of the gain 28. Therefore, the gain 28 is limited to a range of 0 or less by the minimum value limiter 33, and the difference between the d-axis current command Idp1 and the magnetization current command I0, which are multiplied by the reciprocal of the primary time constant Tσ by the gain 34, is multiplied by the secondary time constant T2 of the induction motor 3 and output to the adder 16.

[0086] Furthermore, the switching contact 32 switches the value input to the integral element 21, similar to the second embodiment. The pattern generation unit 9B switches the switching contact 32 so that the output of gain 20 is input to the integral element 21 during normal control and the output of gain 34 is input to the integral element 21 during interruption control. In this embodiment, instead of the d-axis current command holding value Idph described in the first embodiment, the first-order time constant Tσ is used to calculate the excitation current command Idp2 and magnetization current command I0 at the time of interruption, and to determine the d-axis magnetic flux command φdp.

[0087] In this embodiment, the pattern generation unit 9B operates under normal conditions, similar to the first embodiment, as a first-order lag with a second-order time constant T2, via the subtractor 19, gain 20, and integral element 21 through the switching contact 32. On the other hand, during interruption, it operates as a first-order lag with an input limiter, with a first-order time constant Tσ, via the subtractor 19, minimum value limiter 33, gain 34, and integral element 21 through the switching contact 32. Here, the time constant during interruption only needs to be sufficiently short compared to the second-order time constant T2, so it is not limited to the first-order time constant Tσ of the induction motor 3, but other time constants may be used.

[0088] As described above, in the pattern generation unit 9B of this embodiment, when switching from normal control to interruption control, the time constant of the first-order lag element is switched from the second-order time constant T2 to the first-order time constant Tσ. At this time, since the first-order time constant Tσ is sufficiently shorter than the second-order time constant T2, the fall rate and fall time of the d-axis magnetic flux command φdp during interruption are approximately the same as those of the d-axis current command Idp1. Furthermore, the continuity of the d-axis magnetic flux command φdp is maintained by the integral element 21 that constitutes the first-order lag element. Therefore, even if the state transition from normal control to interruption control occurs during the rise of the d-axis magnetic flux command φdp, the d-axis magnetic flux command φdp can be continuously and at a constant rate of fall.

[0089] Furthermore, in the pattern generation unit 9B of this embodiment, the excitation current command Idp2 at the time of interruption is obtained by multiplying the output of gain 34 by the second-order time constant T2 using gain 28 and adder 16 and adding it to the d-axis current command Idp1. Since the output of gain 34 is equal to the time rate of change of the magnetization 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.

[0090] Furthermore, if the control is switched from normal operation to interruption control before the d-axis magnetic flux command φdp reaches a certain value after its initial rise, the interruption control starts with the d-axis current command Idp1 being greater than the magnetization current command I0. In this case, if the minimum value limiter 33 does not exist in the configuration of the pattern generation unit 9B shown in Figure 9, the subtractor 19, gain 34, and integral element 21 are configured as first-order lag elements. As a result, even though the d-axis current command Idp1 decreases, the output of the subtractor 19 becomes positive, and consequently, the magnetization current command I0 operates significantly in the positive direction, which is opposite to the d-axis current command Idp1. This causes the excitation current command Idp2 and the d-axis magnetic flux command φdp to be excessively large during interruption, leading to torque shock and overcurrent. To prevent this, the input to the gain 34 needs to be zero or less. Therefore, in the pattern generation unit 9B of this embodiment, a minimum value limiter 33 is provided before the gain 34, which limits the output of the subtractor 19 to a negative value of zero or less and inputs it to the gain 34.

[0091] Figure 10 shows an example of commands and state variables in a power conversion device according to a third embodiment of the present invention, when interruption control is performed before the d-axis magnetic flux command φdp is fully activated. In Figure 10, the commands and state variables that behave similarly to those in Figure 4 will not be explained below.

[0092] In the power converter of this embodiment, by using the pattern generation unit 9B with the configuration shown in Figure 9, even if a switch from normal control to interruption control occurs during the rise of the d-axis magnetic flux command φdp, the d-axis magnetic flux command φdp will not become discontinuous, as shown in Figure 10. Furthermore, by switching the time constant of the first-order lag element from the second-order time constant T2 to the first-order time constant Tσ, the rise in the d-axis magnetic flux command φdp during interruption can be suppressed.

[0093] Furthermore, in the cutoff control, during the period when the d-axis current command Idp1 is greater than the magnetization current command I0, the d-axis magnetic flux command φdp is output at a constant value, and during the period after the d-axis current command Idp1 matches the magnetization current command I0, the d-axis magnetic flux command φdp decreases at a constant rate of change. As a result, the d-axis magnetic flux command φdp can be reduced to zero within the d-axis current command fall time Td.

[0094] As explained above, in the power converter of this embodiment, when the state transitions from normal control to shut-off control during the rise-up of the d-axis magnetic flux command φdp, the actual d-axis magnetic flux φd in the induction motor 3 can be continuously lowered at a constant rate of change, so that the d-axis magnetic flux φd can be attenuated to zero without undershooting. In other words, the residual amount of d-axis magnetic flux φd when the power converter is shut off and the driving of the induction motor 3 is stopped can be reduced to zero. Therefore, the generation of excessive current and torque when restarting the power converter can be suppressed.

[0095] According to the third embodiment of the present invention described above, the pattern generation unit 9B uses an integral element 21, which is an integrator, to hold a value corresponding to the value of the d-axis magnetic flux command φdp immediately before the start of the falling edge of the d-axis current command Idp1. Specifically, the pattern generation unit 9B uses a subtractor 19 to determine the difference between the d-axis current command Idp1 and the output of the integral element 21. During normal control, the gain 20 and the switching contact 32 determine the output of the integral element 21 as the magnetization current command I0 when the product of this difference and the reciprocal of the second-order time constant T2 is input to the integral element 21. During interruption control, the gain 34 and the switching contact 32 determine the output of the integral element 21 as the magnetization current command I0 when the product of this difference and the reciprocal of the first-order time constant Tσ, which is shorter than the second-order time constant T2, is input to the integral element 21. Furthermore, the pattern generation unit 9B has a minimum value limiter 33 that limits the input to the integral element 21 to a range of 0 or less during interruption control. In this way, similar to the first and second embodiments, even if the control switches to interruption control during the rise of the d-axis magnetic flux command φdp, the value of the continuously changing magnetization current command I0 can be calculated. As a result, the d-axis magnetic flux φd is attenuated at a constant rate of change until it reaches zero, and it is possible to reliably prevent the d-axis magnetic flux φd from remaining inside the induction motor 3.

[0096] It should be noted that the present invention is not limited to the embodiments or modifications described above, and can be implemented using any components without departing from the spirit of the invention. Furthermore, each embodiment or modification may be adopted individually, or multiple embodiments may be adopted in any combination. In other words, the present invention can achieve the effects described above by arbitrarily combining the features of each embodiment.

[0097] The embodiments and modifications described above are merely examples, and the present invention is not limited to these, as long as the features of the invention are not impaired. Furthermore, although various embodiments and modifications have been described above, the present invention is not limited to these. Other embodiments conceivable within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention. [Explanation of Symbols]

[0098] 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 transformation 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... Delay element, 19... Subtractor, 20... Gain, 21... Integral element, 22... Switching contact, 23... Gain, 24... Switching contact, 25... Delay element, 26... Multiplier, 27... Divider, 28... Gain, 29... Differential element, 30... Divider, 31... Gain, 32... Switching contact, 33... Minimum value limit Ta, 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 magnetic flux command, Idf…d-axis current detection value, Iqf…q-axis current detection value, I0…magnetization current command, Idph…d-axis current command holding value, I0h…magnetization current command holding value, Idp0…steady-state value of excitation current command, ωre…estimated rotor angular frequency, ω1…primary angular frequency, Vc…modulation rate, δ…voltage command deviation, L…excitation inductance, Tσ…primary time constant, T2…secondary time constant, Td…d-axis current command rise time

Claims

1. A power conversion circuit that converts DC power to AC power to drive an induction motor, A power conversion device comprising a control device that outputs a gate pulse signal to the power conversion circuit to control the power conversion circuit, The control device receives a control command to operate or stop the power conversion circuit. The control device is A current command generation unit that generates d-axis current commands and q-axis current commands in accordance with the control command, A pattern generation unit that determines an excitation current command and a magnetization current command based on the d-axis current command, and generates a magnetic flux command based on the magnetization current command and an excitation inductance preset according to the characteristics of the induction motor, A voltage command generation unit that generates a voltage command based on the excitation current command, the magnetic flux command, and the q-axis current command, It includes a pulse command generation unit that generates the gate pulse signal based on the voltage command, The control device performs either normal control for the period before the d-axis current command starts to fall, or interruption control for the period after the d-axis current command starts to fall, based on the control command. The pattern generation unit is, During the normal control described above, the excitation current command is determined from the d-axis current command, and the magnetization current command is determined based on the d-axis current command and a secondary time constant that is set in advance according to the characteristics of the induction motor. The values ​​of the magnetization current command and the excitation current command immediately before switching from the normal control to the interruption control are retained as the first retained value and the second retained value, respectively. A power converter that, while the above-mentioned interruption control is being performed, determines the magnetization current command by dividing the product of the d-axis current command and the first holding value by the second holding value, and determines the excitation current command by adding to the d-axis current command a value obtained by multiplying the time rate of change of the magnetization current command by the second-order time constant.

2. A power conversion device according to claim 1, The pattern generation unit is a power conversion device that continues to hold the first and second holding values, respectively, after switching from the normal control to the interruption control.

3. A power conversion circuit that converts DC power to AC power to drive an induction motor, A power conversion device comprising a control device that outputs a gate pulse signal to the power conversion circuit to control the power conversion circuit, The control device receives a control command to operate or stop the power conversion circuit. The control device is A current command generation unit generates a d-axis current command and a q-axis current command in accordance with the control command, and outputs a fall time representing the time from the start to the end of the fall of the d-axis current command. A pattern generation unit that determines an excitation current command and a magnetization current command based on the d-axis current command, and generates a magnetic flux command based on the magnetization current command and an excitation inductance preset according to the characteristics of the induction motor, A voltage command generation unit that generates a voltage command based on the excitation current command, the magnetic flux command, and the q-axis current command, It includes a pulse command generation unit that generates the gate pulse signal based on the voltage command, The control device performs either normal control for the period before the d-axis current command starts to fall, or interruption control for the period after the d-axis current command starts to fall, based on the control command. The pattern generation unit is, During the normal control described above, the excitation current command is determined from the d-axis current command, and the magnetization current command is determined based on the d-axis current command and a secondary time constant that is set in advance according to the characteristics of the induction motor. The value of the magnetization current command immediately before switching from the normal control to the interruption control is retained as a retained value. During the execution of the above-mentioned interruption control, the power converter determines the magnetization current command by accumulating an inverted value obtained by inverting the sign of the value obtained by dividing the holding value by the fall time, and determines the excitation current command by adding the value obtained by multiplying the inverted value by the second-order time constant to the d-axis current command.

4. A power conversion device according to claim 3, The pattern generation unit is a power conversion device that maintains the held value after switching from the normal control to the interruption control.

5. A power conversion circuit that converts DC power to AC power to drive an induction motor, A power conversion device comprising a control device that outputs a gate pulse signal to the power conversion circuit and controls the power conversion circuit, The control device receives a control command to operate or stop the power conversion circuit. The control device is A current command generation unit that generates d-axis current commands and q-axis current commands in accordance with the control command, A pattern generation unit that determines an excitation current command and a magnetization current command based on the d-axis current command, generates a magnetic flux command based on the magnetization current command and an excitation inductance preset according to the characteristics of the induction motor, and holds the value of the magnetization current command in an integrator immediately before the fall of the d-axis current command begins. A voltage command generation unit that generates a voltage command based on the excitation current command, the magnetic flux command, and the q-axis current command, It includes a pulse command generation unit that generates the gate pulse signal based on the voltage command, The control device performs either normal control for the period before the d-axis current command starts to fall, or interruption control for the period after the d-axis current command starts to fall, based on the control command. The pattern generation unit is, During the normal control described above, the excitation current command is obtained from the d-axis current command, and the magnetization current command is obtained from the output of the integrator when the product of the difference between the d-axis current command and the output of the integrator and the reciprocal of the second-order time constant, which is set in advance according to the characteristics of the induction motor, is input to the integrator. During the execution of the aforementioned interruption control, the power converter obtains the magnetization current command from the output of the integrator when the product of the difference and the reciprocal of a primary time constant shorter than the secondary time constant is input to the integrator, and obtains the excitation current command by adding the value obtained by multiplying the product of the difference and the reciprocal of the primary time constant by the secondary time constant to the d-axis current command.

6. A power conversion device according to claim 5, The pattern generation unit is a power conversion device having a limiter that restricts the input of the integrator to a range of 0 or less while the cutoff control is being performed.

7. A control method for a power conversion circuit that converts DC power to AC power to drive an induction motor, The system receives a control command to operate or stop the power conversion circuit. The d-axis current command and q-axis current command are generated in accordance with the control command. Based on the d-axis current command, the excitation current command and magnetization current command are determined. Based on the magnetization current command and the excitation inductance, which is set in advance according to the characteristics of the induction motor, a magnetic flux command is generated. A voltage command is generated based on the excitation current command, the magnetic flux command, and the q-axis current command. A gate pulse signal is generated based on the aforementioned voltage command. The gate pulse signal is output to the power conversion circuit. Based on the control command, either normal control is performed for the period before the d-axis current command starts to fall, or interruption control is performed for the period after the d-axis current command starts to fall. During the normal control described above, the excitation current command is determined from the d-axis current command, and the magnetization current command is determined based on the d-axis current command and a secondary time constant that is set in advance according to the characteristics of the induction motor. The values ​​of the magnetization current command and the excitation current command immediately before switching from the normal control to the interruption control are retained as the first retained value and the second retained value, respectively. A control method for a power conversion circuit, during the execution of the interruption control, which determines the magnetization current command by dividing the product of the d-axis current command and the first holding value by the second holding value, and determines the excitation current command by adding to the d-axis current command a value obtained by multiplying the time rate of change of the magnetization current command by the second-order time constant.

8. A control method for a power conversion circuit according to claim 7, A control method for a power conversion circuit that continues to hold the first and second holding values ​​after switching from the normal control to the interruption control.

9. A control method for a power conversion circuit that converts DC power to AC power to drive an induction motor, The system receives a control command to operate or stop the power conversion circuit. The d-axis current command and q-axis current command are generated in accordance with the control command. Determine the fall time, which represents the time from the start to the end of the fall of the d-axis current command. Based on the d-axis current command, the excitation current command and magnetization current command are determined. Based on the magnetization current command and the excitation inductance, which is set in advance according to the characteristics of the induction motor, a magnetic flux command is generated. A voltage command is generated based on the excitation current command, the magnetic flux command, and the q-axis current command. A gate pulse signal is generated based on the aforementioned voltage command. The gate pulse signal is output to the power conversion circuit. Based on the control command, either normal control is performed for the period before the d-axis current command starts to fall, or interruption control is performed for the period after the d-axis current command starts to fall. During the normal control described above, the excitation current command is determined from the d-axis current command, and the magnetization current command is determined based on the d-axis current command and a secondary time constant that is set in advance according to the characteristics of the induction motor. The value of the magnetization current command immediately before switching from the normal control to the interruption control is retained as a retained value. A control method for a power conversion circuit, during the execution of the interruption control, which determines the magnetization current command by accumulating an inverted value obtained by inverting the sign of the value obtained by dividing the holding value by the fall time, and determines the excitation current command by adding the value obtained by multiplying the inverted value by the second-order time constant to the d-axis current command.

10. A control method for a power conversion circuit according to claim 9, A control method for a power conversion circuit that maintains the held value after switching from the normal control to the interruption control.

11. A control method for a power conversion circuit that converts DC power to AC power to drive an induction motor, The system receives a control command to operate or stop the power conversion circuit. The d-axis current command and q-axis current command are generated in accordance with the control command. Based on the d-axis current command, the excitation current command and magnetization current command are determined. Based on the magnetization current command and the excitation inductance, which is set in advance according to the characteristics of the induction motor, a magnetic flux command is generated. The value of the magnetization current command immediately before the fall of the d-axis current command begins is held in the integrator. A voltage command is generated based on the excitation current command, the magnetic flux command, and the q-axis current command. A gate pulse signal is generated based on the aforementioned voltage command. The gate pulse signal is output to the power conversion circuit. Based on the control command, either normal control is performed for the period before the d-axis current command starts to fall, or interruption control is performed for the period after the d-axis current command starts to fall. During the normal control described above, the excitation current command is obtained from the d-axis current command, and the magnetization current command is obtained from the output of the integrator when the product of the difference between the d-axis current command and the output of the integrator and the reciprocal of the second-order time constant, which is set in advance according to the characteristics of the induction motor, is input to the integrator. A control method for a power conversion circuit, during the execution of the interruption control, which involves obtaining the magnetization current command from the output of the integrator when the product of the difference and the reciprocal of a primary time constant shorter than the secondary time constant is input to the integrator, and obtaining the excitation current command by adding the value obtained by multiplying the product of the difference and the reciprocal of the primary time constant by the secondary time constant to the d-axis current command.

12. A control method for a power conversion circuit according to claim 11, A control method for a power conversion circuit that limits the input of the integrator to a range of 0 or less while the aforementioned interruption control is being performed.

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