JP7487402B2 - Driving device and driving method for induction motor - Google Patents

Description

The present invention relates to a driving device and driving method for an induction motor using speed sensorless control.

Generally, driving devices that drive induction motors for railway vehicles at variable speeds use a distributed power system that uses several dozen induction motors in one train. If a configuration is applied to such driving devices that controls the induction motors using rotational speed sensors, the control device will become larger due to the need to secure space to install the sensors and the increase in sensor wiring. For this reason, speed sensorless control methods that do not use rotational speed sensors are increasingly being adopted for driving devices for induction motors.

Prior art for speed sensorless control is disclosed in, for example, Patent Document 1 and Patent Document 2. The method described in Patent Document 1 stores the pulse mode at the time of starting and uses it as the initial value when restarting to estimate the speed. The method described in Patent Document 2 estimates the secondary magnetic flux by passing a direct current, and estimates the speed from the average value of the slope of the derivative value.

JP 2017-055626 A JP 2018-011474 A

In the speed sensorless control method, when switching from a power cut state such as coasting to power running or regenerative driving, it is necessary to instantly estimate the rotation speed and smoothly restart. In addition, if the station is on a slope, the vehicle starts to move slightly from the moment the brakes are released at start-up, so it is also necessary to estimate the minute speed at that time.

In addition, by using the methods described in Patent Documents 1 and 2, it is possible to restart the device from a power-cut state when there is no speed sensor.

However, the method described in Patent Document 1 has the problem that if the speed fluctuates during the coasting period, torque fluctuations increase at start-up. Also, the method described in Patent Document 2 has the problem that the initial speed estimation time is long because recent highly efficient induction motors have small slip and the magnetic flux rises slowly.

The object of the present invention is to provide a control device that enables initial speed estimation in a short period of time even using speed sensorless control.

In order to solve the above problems, a representative configuration of a driving device for an induction motor according to the present invention includes an inverter for driving an induction motor, a current detection circuit for detecting a current flowing through the induction motor, and a control device for controlling the inverter based on a current value detected by the current detection means, and the control device is characterized in that it applies a pulse voltage of a very short duration from the inverter and short-circuits the terminals of the induction motor after the application of the pulse voltage, thereby estimating the initial speed of the induction motor using the current value of the current flowing through the induction motor.

According to the present invention, the initial speed is estimated using the current value generated in the induction motor when a pulse voltage of a very short duration is applied, making it possible to estimate the initial speed in a short period of time. By using this estimated initial speed, smooth restart is possible without causing speed or torque fluctuations.

1 is a block diagram showing a schematic configuration of a drive device for an induction motor according to the present invention; 1 is a block diagram showing a configuration of a driving device for an induction motor according to a first embodiment; FIG. 13 is a diagram showing a schematic waveform of a current behavior when a pulse voltage is applied. FIG. 1 is a diagram showing a schematic waveform of a current behavior when a pulse voltage is applied by a conventional method. FIG. 11 is a block diagram of an initial speed estimator that uses a q-axis current amplitude value as a feature. FIG. 11 is a block diagram of an initial speed estimator that uses the current ratio between the d-axis and q-axis as a feature. FIG. 11 is a block diagram of an initial speed estimator that uses a data set obtained by analyzing the time course of d-axis current and q-axis current as feature quantities. 13 is a diagram showing a schematic waveform when an offset occurs in a detected current; FIG. FIG. 11 is a block diagram of an initial speed estimator that uses a rate of change of a q-axis current as a feature. FIG. 13 is a diagram showing schematic waveforms when the q-axis current is small when the rotation speed is low. FIG. 11 is a block diagram of an initial speed estimator that uses an integrated value of a q-axis current as a feature. FIG. 11 is a block diagram showing a configuration of a driving device for an induction motor according to a second embodiment. FIG. 13 is a diagram showing a schematic waveform when a current is sampled at a period approximately equal to a switching period. FIG. 11 is a diagram showing a schematic waveform when a current is sampled at a short sampling period according to the second embodiment. FIG. 11 is a block diagram showing a configuration of a vector control unit 21 according to a third embodiment. FIG. 13 is a diagram showing schematic waveforms from initial speed estimation to vector control by PLL control after switching. FIG. 13 is a diagram showing an outline of the overall configuration of a railway vehicle according to a fourth embodiment. 4 is a diagram showing the switching state of a switching element and a current path when a pulse voltage is applied in Example 1. FIG. 11A and 11B are diagrams illustrating states of switching elements and current paths during a dead time period. 13 is a diagram illustrating the on/off states of switching elements and current paths when a three-phase short circuit is performed in accordance with the fifth embodiment. FIG.

Hereinafter, as a form for implementing the present invention, examples 1 to 5 of the present invention will be described with reference to the drawings. Examples 1 to 5 are examples in which an induction motor 1 is driven by a control device 2 according to the present invention.

Prior to describing the first to fifth embodiments, the gist of the present invention will be described.
FIG. 1 is a block diagram showing a schematic configuration of a driving device for an induction motor according to the present invention.
As a schematic configuration, the control device 2 has a vector control unit 21 that calculates a voltage command value based on a current value detected by a current detection circuit 4 that detects a current flowing through an induction motor 1 .

The PWM pulse generating unit 22 generates a PWM pulse signal from this voltage command value, and the inverter 3 outputs an output voltage corresponding to the command voltage.

The vector control unit 21 controls the drive of the induction motor using general vector control and does not specify a control method.

As mentioned above in the "Problems to be Solved by the Invention" section, when controlling induction motors for railway vehicles without using a rotational speed sensor, it is necessary to instantly estimate the rotational speed from a power-cut state such as coasting, and to restart the motor smoothly. Also, if the station is on a slope, the moment the brakes are released at start-up, the vehicle begins to move slightly, and it is necessary to instantly estimate the minute speed at that time and restart the motor.

For this reason, the control device 2 switches between a configuration for performing initial speed estimation for restart and a configuration for performing vector control after start-up, using the control changeover switches 25 and 26. When the control changeover switches 25 and 26 are switched to side A, initial speed estimation is performed, and when they are switched to side B, vector control after start-up is performed.

When the control changeover switches 25 and 26 are switched to side A to perform initial speed estimation, a pulse voltage of a very short duration is generated by the pulse voltage generator 23 and output to the PWM pulse generating unit 22. This causes a pulse voltage of a very short duration to be applied from the inverter 3 to the induction motor 1. The current flowing through the induction motor 1 due to the applied pulse voltage is detected by the current detection circuit 4, and the initial speed estimator 24 estimates the initial speed from the detected current value and outputs it to the vector control unit 21 as an initial speed estimate value.

After the initial speed estimation is completed, the control changeover switches 25 and 26 are switched to side B, and the vector control unit 21 performs vector control after startup.

Here, a description will be given of the behavior of the current when a pulse voltage is applied to the induction motor 1. The voltage equation for the induction motor is expressed as shown in Equation 1 when using an orthogonal coordinate system.

When a pulse voltage v _1d (the fifth term on the right side of the first line of Equation 1) is applied to the d-axis by the pulse voltage generator 23, a d-axis current i _1d (the first term on the left side of the first line of Equation 1) is generated. A d-axis secondary magnetic flux φ _2d (the first term on the left side of the third line of Equation 1) is induced by an interference term component Mi _1d (the first term on the right side of the third line of Equation 1) of the induction motor. As a result, a disturbance component ω _r Mφ _2d /L ₂ (the third term on the right side of the second line of Equation 1) proportional to the rotation speed is generated on the q-axis, and a q-axis current i _1q (the first term on the left side of the second line of Equation 1) is generated.

As described above, the behavior of the q-axis current _i1q flowing due to the d-axis pulse voltage _v1d has a strong correlation with the rotation speed _ωr at that time. In addition, although the above describes the case where a pulse voltage is applied to the d-axis, the q-axis current _i1q generated by applying a pulse voltage _v1q to the q-axis may also be used.

The present invention focuses on this correlation and provides a control device that performs speed sensorless control by estimating the rotation speed of an induction motor from the current value flowing through the induction motor using a short duration pulse voltage.

The detailed operation of the first embodiment of the present invention will be described with reference to Figures 2 and 3. Figure 2 is a block diagram showing the configuration of the induction motor drive device according to the first embodiment of the present invention, and Figure 3 is a diagram showing a schematic waveform of the current behavior when a pulse voltage is applied.

As in the case of the schematic configuration shown in Figure 1, in the drive device configuration shown in Figure 2, initial speed estimation is performed by setting the control changeover switches 25 and 26 to side A. During initial speed estimation, the pulse voltage generator 23 outputs a pulse voltage VdA of minute period Th to the d-axis as shown in Figure 3(a), and applies it to the induction motor 1 via the inverter 3. Here, the minute period Th has a length of less than half the carrier period.

The current flowing through the induction motor due to the application of this pulse voltage of the minute period Th is detected by the current detection circuit 4, and the detected current (for example, Iu and Iw shown in FIG. 2) is taken into the control device 2 through the sample-and-hold unit 9 and the AD conversion unit 8. The taken-in detected current is converted into dq-axis orthogonal coordinates by the orthogonal coordinate conversion unit 27, making it possible to detect the d-axis current IdA and the q-axis current IqA. The currents to be detected may be any two of the three phases as shown in FIG. 2, or all three phases.

3(c) and (d), the d-axis current IdA and the q-axis current IqA have waveforms that are strongly correlated with the rotation speed ωr (ωr1 to ωr3) at the time when the pulse voltage VdA of the short period Th is applied. Therefore, the initial speed estimator 24 is configured to perform initial speed estimation based on the current value of at least one of the d-axis current IdA and the q-axis current IqA generated by the pulse voltage VdA of the short period Th.

Here, in order to provide sensitivity for the initial speed estimation, it is desirable to set the crest value of the applied pulse voltage VdA to a value such that the peak value Idp of the d-axis current IdA shown in (c) of Figure 3 is approximately the rated current.

A comparison with a conventional method will be described with reference to FIG.
In the conventional method, the application time Tz of the pulse voltage is lengthened to estimate the initial speed by utilizing the periodicity that appears in the current waveform. Therefore, when the rotation speed ωr is low, the time for initial speed estimation becomes long in order to obtain the periodicity of the waveform, which is a problem in itself.

However, as explained above, in this embodiment, the correlation between the characteristics of the rising portions of the d-axis current IdA and the q-axis current IqA in response to the pulse voltage VdA of the very short period Th (the area surrounded by the dotted frame in Figure 4) and the rotation speed ωr is utilized, making it possible to perform initial speed estimation in a short period of time.

Next, a method for estimating the initial velocity will be described.
As described above, the d-axis current IdA and q-axis current IqA flowing through the induction motor due to the pulse voltage VdA of the short period Th have a strong correlation with the rotation speed ωr at that time, so a data set storing this correlation is prepared and the initial speed is estimated using this data set. This makes it possible to estimate the initial speed of the rotation speed ωr of the induction motor by measuring at least one of the d-axis current IdA and the q-axis current IqA when the pulse voltage VdA of the short period Th is applied.

Specific aspects of the data set are shown below as (1) to (5).
By preparing data that indicates the relationship between the rotation speed ωr of the induction motor and the d-axis current IdA or the q-axis current IqA, it is possible to create a data set.

(1) Using the Current Amplitude Value (Peak Value) FIG. 5 is a block diagram of the initial speed estimator 24 that uses the q-axis current amplitude value as a feature value.
Based on the waveform diagram of the q-axis current IqA shown in (d) of Figure 3, the initial speed (rotation speed ωrini) can be estimated using a data set 241 that indicates the relationship between information in which the current amplitude value (peak value) Iqp of the q-axis current IqA is a characteristic parameter and the rotation speed ωrini, as shown in the initial speed estimator 24 of Figure 5.

(2) Using the Current Ratio of the d-axis and the q-axis FIG. 6 is a block diagram of an initial speed estimator 24B that uses the current ratio of the d-axis and the q-axis as a feature value.
As shown in the initial speed estimator 24B of Figure 6, in order to suppress the dependency on the magnitude of each of the d-axis and q-axis currents and improve robustness, the initial speed (rotation speed ωrini) can be estimated using a data set 241B that shows the relationship between information in which the ratio between the d-axis current IdA and the q-axis current IqA (Iqn calculated by the multiplier/divider 242 shown in Figure 6) is a feature and the rotation speed ωrini.

(3) Using a Function FIG. 7 is a block diagram of an initial speed estimator 24C that uses a data set obtained by analyzing the time course of the d-axis current and the q-axis current as feature quantities.
As shown in the initial speed estimator 24C in FIG. 7, the initial speed (rotation speed ωrini) can be estimated using a data set 241C in which the relationship between the time course of the current waveforms of the d-axis current IdA and the q-axis current IqA and the rotation speed ωrini is learned as a function using regression analysis, a neural network, or the like, with the d-axis current IdA and the q-axis current IqA as variables.

(4) Using the Rate of Change of Current FIG. 8 is a diagram showing a schematic waveform when an offset occurs in the detected current, and FIG. 9 is a block diagram of an initial speed estimator 24D that uses the rate of change of the q-axis current as a feature.
As shown in Fig. 8, the d-axis current IdA and the q-axis current IqA flowing through the induction motor due to the pulse voltage VdA of the short period Th tend to have steep waveforms. Therefore, as shown in (c) and (d) of Fig. 8, the current sensor used in the current detection circuit 4 becomes susceptible to offsets due to temperature, etc.

Therefore, in order to suppress the influence of offset due to temperature, etc., the initial speed (rotation speed ωrini) can be estimated using a data set 241D that indicates the relationship between the rotation speed ωrini and information that features the rate of change of the q-axis current IqA, such as the differential value dIqA of the q-axis current IqA shown in (e) of Fig. 8, or the difference value of the q-axis current IqA (corresponding to dIqA) calculated by a difference block as shown in the initial speed estimator 24D of Fig. 9. The rate of change of the d-axis current IdA can also be used, but it is preferable to use the one with the larger rate of change.

(5) Use of the Integrated Value of Current FIG. 10 is a diagram showing a schematic waveform when the q-axis current becomes minute when the rotation speed is low, and FIG. 11 is a block diagram of an initial speed estimator 24E that uses the integrated value of the q-axis current as a feature.
As shown in (d) of Fig. 10, when the rotation speed ωr1 of the induction motor 1 becomes small, the q-axis current IqA generated by the interference term component proportional to the rotation speed ωrini may become an extremely small value. In this case, in order to improve the detection accuracy of the extremely small current value, the initial speed (rotation speed ωrini) can be estimated using the integrated value (integral value) SIqA of the q-axis current IqA shown in (e) of Fig. 10, that is, the data set 241E indicating the relationship between the rotation speed ωrini and information having as its feature the integrated value (integral value) SIqA of the q-axis current IqA calculated by the integrator 213 of the initial speed estimator 24E in Fig. 11.

In addition, the initial speed (rotation speed ωrini) can be estimated by combining the initial speed estimator 24D shown in Figure 9 and the initial speed estimator 24E shown in Figure 11, or by appropriately switching between the initial speed estimator 24D shown in Figure 9 and the initial speed estimator 24E shown in Figure 11.

FIG. 12 is a diagram showing the configuration of a control device according to the second embodiment of the present invention.
The control device 2 according to the second embodiment is configured such that a sample-and-hold unit 9', an AD conversion unit 8', and a current moving average unit 29 are added to the control device 2 according to the first embodiment.

FIG. 13 is a diagram showing schematic waveforms when current is sampled at a period similar to the switching period, and FIG. 14 is a diagram showing schematic waveforms when current is sampled at a short sampling period according to the second embodiment.
The pulse time of the minute period Th of the pulse voltage VdA shown in the previous embodiment 1 has a time width approximately equal to the switching period Ts of the PWM pulse generating unit 22. For this reason, if sampling is performed by operating the sample-and-hold unit 9 and the AD conversion unit 8 with the same switching period Ts as the PWM pulse generating unit 22 (FIGS. 2 and 12), it may not be possible to obtain current values that indicate the characteristics of the d-axis current IdA and q-axis current IqA, which change sharply, as shown in (a) and (b) of FIG.

Furthermore, when the rotation speed ωr decreases and the q-axis current IqA becomes small, this current value may be significantly affected by noise and become buried in the noise, making it difficult to perform initial speed estimation.

14A and 14B, a sample-and-hold unit 9' and an AD conversion unit 8' are used that have a sampling period Tms that is shorter than the switching period Ts of the PWM pulse generation unit 22. The d-axis current IdA and the q-axis current IqA sampled at this short sampling period Tms are averaged by a current moving average unit 29 (performing so-called filtering) to determine IdAm and IqAm, which are used as inputs to the initial speed estimator 24.
Here, the initial speed estimator 24 in the second embodiment can also use the data sets 241 to 241C described in (1) to (3) in the first embodiment.

This makes it possible to suppress the effects of noise caused by sudden changes in current and small currents, improving the accuracy of initial speed estimation.

Figure 15 is a diagram showing the configuration of a vector control unit in a control device of Example 3 of the present invention, and Figure 16 is a diagram showing the schematic waveforms from initial speed estimation to vector control by PLL control after switching.

The vector control unit 21 of the control device 2 of Example 3 is configured to have a PLL (Phase Locked Loop) control unit 215 instead of the speed estimator 211, as compared to the vector control unit 21 of the control device 2 of Examples 1 and 2.

In Example 3, similar to Examples 1 and 2, when an initial speed estimation is performed using the A side of the control changeover switches 25 and 26, the control changeover switches 25 and 26 are changed from the A side to the B side to perform vector control after startup. However, as shown in FIG. 16, in order to further improve the accuracy of the estimated speed after the initial speed estimation is performed, an operating mode is incorporated in which speed estimation is performed using the PLL control unit 215 before transitioning to normal driving.

In speed estimation using PLL control performed by the PLL control unit 215, as shown in Figure 16, the d-axis current Id is increased while the q-axis current Iq is observed, and the rotation speed ωr is adjusted so that the q-axis current Iq becomes zero.

As described above, in addition to the initial speed estimation performed in Example 1 or 2, the vector control unit 21 shown in Figure 15 performs speed estimation using PLL control as shown in Figure 16, and by starting the induction motor 1 using two-stage speed estimation, it is possible to perform a smooth restart.

FIG. 17 is a diagram showing an outline of the overall configuration of a railway vehicle according to a fourth embodiment of the present invention.
Example 4 is a railway vehicle 100 equipped with any one of the control devices 2 according to Examples 1 to 3. By applying any one of the control devices 2 according to Examples 1 to 3 to the inverter 3 that drives the induction motors 1a to 1d used for running the railway vehicle 100, it becomes possible to instantly estimate the rotation speed from a power cut state such as coasting control, and to smoothly restart the train without generating speed and torque fluctuations.

In addition, if the station is on a slope and the vehicle starts to move slightly the moment the brakes are released at start-up, it is possible to quickly estimate the speed and restart smoothly.

The relationship between the switching state and the current path of the inverter device according to the fifth embodiment of the present invention will be described with reference to FIGS.
FIG. 18 is a diagram showing the switching states and current paths of switching elements constituting power conversion device 32 connected to DC voltage source 31 in inverter 3 when the pulse voltage shown in FIG. 3 described in the previous Example 1 is applied.

In the section Th where the pulse voltage shown in Figure 3 is applied, if a pulse voltage is applied based on the U phase, for example, the switching elements of the U phase + side element (321P), V phase - side element (322N) and W phase - side element (323N) are turned ON, as shown in Figure 18, and a + current flows in the U phase and a - current flows in the V phase and W phase.

Figure 19 shows the state of the switching elements and the current path during the dead time period when the three elements on the P side and the three elements on the N side are turned on with a duty of 50% when the section Th in which the pulse voltage shown in Figure 3 is applied ends and the voltage is turned off. Here, the dead time period refers to the state in which all switching elements are turned off when switching from the P side to the N side or from the N side to the P side.

During such dead time periods, a return current is generated by the return configuration of the return diodes and other components included in the elements. For this reason, as shown in Figure 19, if a positive current flows through the U phase and a negative current flows through the V and W phases, a return current is generated in the return configuration of the positive sides of the V and W phases and the negative side of the U phase during the dead time.

Here, in the state shown in Figure 19, the switching elements on the positive side of the V and W phases and the negative side of the U phase are in the on state, so current flows from the DC power supply from the positive side of the V and W phases to the negative side of the U phase. In other words, due to the influence of the current from the DC power supply, the currents in the UVW phases do not flow according to the characteristics of the induction motor.

Railway inverters generally use switching elements that handle high voltages and large currents, resulting in long dead times. This means that they are easily affected by current from the DC power supply, making it difficult to obtain a current waveform that matches the characteristics of an induction motor, leading to a deterioration in the accuracy of speed (rotation speed) estimation.

Therefore, in the fifth embodiment of the present invention, a method is provided for obtaining a current waveform that matches the characteristics of an induction motor. To achieve this, a configuration is adopted in which the switching elements on the P side or N side are kept on for all three phases (hereinafter referred to as "three-phase short circuit") when the section Th in which the pulse voltage shown in Figure 3 is applied ends and the voltage is turned off. In other words, the mode in which the terminals of the three phases of the induction motor are short circuited is implemented during the speed estimation period. Moreover, the fifth embodiment is applicable to the first to fourth embodiments shown above.

Figure 20 is a diagram showing the on/off states of the switching elements and the current paths when performing this three-phase short circuit. Here, Figure 20 shows an example of performing a three-phase short circuit by turning on all of the N-side switching elements, but a three-phase short circuit may also be performed by turning on all of the P-side switching elements.

In addition, the manner in which the three-phase terminals of an induction motor are short-circuited is not limited to turning on the P-side or N-side switching elements for all three phases, and a separate means for short-circuiting the three phases may be used.

As a result, no dead time period occurs during which all switching elements are turned off. Therefore, as shown in Figure 20, if all switching elements on the N-side are kept on, the return current will flow from the negative side of the V and W phases to the negative side of the U phase due to the N-side switching elements. In other words, since there is no influence from the current from the DC power supply, the current will flow according to the characteristics of the induction motor.

As described above, by placing the terminals of the induction motor in a three-phase short-circuit state after applying a pulse voltage, it is possible to suppress the influence of current from the DC power supply and prevent deterioration in the accuracy of estimating the speed (rotation speed), even in railway inverters that use switching elements with a long dead time period.

The present invention is not limited to the above-described embodiments, but includes various modified examples. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those having all of the configurations described. It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

1...induction motor, 2...control device, 3...inverter, 4...current detection circuit, 5...vector control switching unit, 6...current subtraction unit, 7...zero command output unit, 8...AD conversion unit, 9...sample hold unit, 21...vector control unit, 211...speed estimator, 212...ACR control unit, 213...integrator, 214...current command generator, 215...PLL control unit, 22...PWM pulse generation unit, 23, 231...pulse voltage generator, 24...initial speed estimator, 241...data set, 25, 26...control switching switch, 27, 28...orthogonal coordinate conversion unit, 29...current moving average unit, 31...DC voltage source, 32...power conversion device, 321, 322, 323...switching elements

Claims (21)

an inverter that drives an induction motor;
a current detection circuit for detecting a current flowing through the induction motor;
A drive device for an induction motor comprising: a control device that controls the inverter based on the current detected by the current detection circuit,
The control device includes:
A drive device for an induction motor, comprising: a pulse voltage for a very short period of time applied from the inverter; and a terminal of the induction motor is short-circuited after the application of the pulse voltage, thereby estimating an initial speed of the induction motor using a current value of the current flowing through the induction motor. 2. The induction motor drive device according to claim 1,
11. An induction motor driving device according to claim 10, wherein the short period is equal to or shorter than a half period of an actual rotation frequency of the induction motor driven by the pulse voltage. 3. The driving device for an induction motor according to claim 1 or 2,
a terminal of the induction motor being short-circuited by turning on all switching elements on a positive side or all switching elements on a negative side of the inverter, said ... A driving device for an induction motor according to any one of claims 1 to 3,
The current value is at least one of the current values of two current components obtained by dividing the current flowing through the induction motor by the pulse voltage into two orthogonal axes. A driving device for an induction motor according to any one of claims 1 to 3,
The current value is a value obtained by filtering a current detection value sampled over a period shorter than a switching period of the inverter for the current flowing through the induction motor due to the pulse voltage. A driving device for an induction motor according to any one of claims 1 to 5,
The control device includes:
A driving device for an induction motor, characterized in that the initial speed is estimated based on a data set indicating a relationship between at least one of a rate of change of the current value and an integrated value of the current value and a rotation speed of the induction motor. A driving device for an induction motor according to any one of claims 1 to 5,
The control device includes:
A driving device for an induction motor, characterized in that the initial speed is estimated based on a data set showing a relationship between the current value and the rotation speed of the induction motor or a function showing the relationship. an inverter that drives an induction motor;
a current detection circuit for detecting a current flowing through the induction motor;
A drive device for an induction motor comprising: a control device that controls the inverter based on the current detected by the current detection circuit,
The control device includes:
A drive device for an induction motor, characterized in that an initial speed of the induction motor is estimated based on a data set indicating the relationship between at least one of a rate of change of a current value of the current flowing through the induction motor due to a short duration pulse voltage applied from the inverter and an integrated value of the current value, and the rotation speed of the induction motor. an inverter that drives an induction motor;
a current detection circuit for detecting a current flowing through the induction motor;
A drive device for an induction motor comprising: a control device that controls the inverter based on the current detected by the current detection circuit,
The control device includes:
estimating an initial speed of the induction motor using a current value of the current flowing through the induction motor due to a pulse voltage of a short duration applied from the inverter;
a drive device for an induction motor, the drive device comprising: a drive circuit for driving the induction motor, the drive circuit for driving the induction motor being controlled by a PLL circuit; A driving device for an induction motor according to any one of claims 1 to 8,
The control device includes:
a drive device for an induction motor, the drive device comprising: a drive circuit for driving the induction motor, the drive circuit for driving the induction motor being controlled by a PLL circuit; A railway vehicle equipped with an induction motor drive device according to any one of claims 1 to 10. A first step of applying a short duration pulse voltage from an inverter to an induction motor;
a second step of detecting a current flowing through the induction motor by shorting terminals of the induction motor after the application of the pulse voltage;
and a third step of estimating an initial speed of the induction motor using the detected current value of the current and starting the induction motor. A method for driving an induction motor according to claim 12, comprising the steps of:
A method for driving an induction motor, wherein the very short period applied in the first step is a period not exceeding half a period of an actual rotational frequency of the induction motor driven by the applied pulse voltage. A method for driving an induction motor according to claim 12 or 13, comprising the steps of:
A method for driving an induction motor, wherein in the second step, all of the switching elements on the positive side or all of the switching elements on the negative side of the inverter are turned on to short-circuit terminals of the induction motor. A method for driving an induction motor according to any one of claims 12 to 14, comprising the steps of:
a current value used in the third step being at least one of the current values of two current components obtained by dividing the current flowing through the induction motor by the pulse voltage into two orthogonal axes. A method for driving an induction motor according to any one of claims 12 to 14, comprising the steps of:
a current detection value sampled for a period shorter than a switching period of the inverter, for the current flowing through the induction motor due to the pulse voltage, being filtered to obtain the current value used in the third step. A method for driving an induction motor according to any one of claims 12 to 16, comprising the steps of:
The third step includes estimating the initial speed based on a data set indicating a relationship between at least one of a rate of change of the current value and an integrated value of the current value and a rotation speed of the induction motor. A method for driving an induction motor according to any one of claims 12 to 16, comprising the steps of:
The method for driving an induction motor, wherein the third step estimates the initial speed based on a data set indicating a relationship between the current value and the rotation speed of the induction motor or a function indicating the relationship. A first step of applying a short duration pulse voltage from an inverter to an induction motor;
a second step of detecting a current flowing through the induction motor due to the pulse voltage;
and a third step of estimating an initial speed of the induction motor based on a data set indicating a relationship between at least one of a rate of change of the detected current value and an integrated value of the current value, and the rotation speed of the induction motor, and starting the induction motor. A first step of applying a short duration pulse voltage from an inverter to an induction motor;
a second step of detecting a current flowing through the induction motor due to the pulse voltage;
a third step of estimating an initial speed of the induction motor using the detected current value of the current, and after estimating the initial speed, estimating a speed of the induction motor subsequent to the initial speed using PLL control to start the induction motor. A method for driving an induction motor according to any one of claims 12 to 19, comprising the steps of:
a third step of estimating the initial speed and then estimating a speed of the induction motor subsequent to the initial speed using PLL control to start the induction motor.

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