Inverter drive control device and inverter drive control method

Abstract

To provide a technique capable of preventing accuracy deterioration during velocity estimation when setting the carrier frequency to be higher during asynchronous modulation mode in inverter PWM drive control.SOLUTION: The inverter drive control device includes: an inverter that inverts DC power into AC power and supplies the same to an AC motor; and a control unit that drives the inverter by a PWM control. The control unit is configured so that during the period in which the AC motor is driven at an initial speed, the carrier frequency for the PWM control is set to a frequency lower than the carrier frequency used during acceleration after the initial speed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an inverter drive control device and an inverter drive control method, and is particularly suitable for use in railway vehicles. [Background technology]

[0002] When driving induction motors for railway vehicles using sensorless vector control, a method is adopted in which the rotor rotation frequency is estimated using the induction motor current that flows through the induction motor. However, if the induction motor current contains ripple, this ripple component is also included in the estimated rotor rotation frequency, so measures to prevent this are necessary.

[0003] For example, as a countermeasure, Patent Document 1 states that "If the induction motor current contains ripples, the ripple components of the induction motor current will be included in the rotor rotation frequency estimate, making it difficult to perform accurate speed estimation. Therefore, in order to reduce the influence of the ripple components of the induction motor current, the carrier frequency of the carrier wave is increased." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-18898 A Summary of the Invention [Problem to be solved by the invention]

[0005] When an inverter device converts direct current to alternating current, it alternates between turning on and off the upper and lower arms of each phase using PWM control. When driving an induction motor using the PWM control of this inverter device, by increasing the carrier frequency used for PWM control, the switching period of the upper and lower arms becomes shorter, and an induction motor current closer to a sine wave can be obtained.

[0006] The technology described in Patent Document 1 uses a filter to remove the ripple components contained in the induction motor current, eliminating the need to set the carrier frequency of the carrier wave high, thereby preventing a decrease in the cooling performance of the electric vehicle control device and an increase in the size of the cooler.

[0007] However, if there are no constraints on element performance or associated cooling devices, the carrier frequency may be set high in order to make the induction motor current closer to a sine wave in order to reduce induction motor losses.

[0008] In addition, while the switching period can be shortened by increasing the carrier frequency, a dead time during which both the upper and lower arms are turned off is provided for the element to prevent the upper and lower arms from being turned on simultaneously and causing a short circuit.

[0009] Here, the dead time is set as a fixed value for each product, but when the carrier frequency is set high, the number of switching times increases, and the number of occurrences of dead time also increases, causing distortion in the phase voltage output of the induction motor. This may result in a decrease in estimation accuracy, especially during estimation at the initial speed in sensorless vector control.

[0010] Therefore, an object of the present invention is to provide a technique for preventing a decrease in accuracy during speed estimation when the carrier frequency is set high in an asynchronous modulation mode in PWM drive control for railway vehicles. [Means for solving the problem]

[0011] In order to solve the above problems, one representative inverter drive control device of the present invention includes an inverter that converts DC power into AC power and supplies the AC power to an AC motor, and a control unit that drives the inverter by PWM control, When the inverter is started and the modulation rate of the inverter is increased from 0% to drive the AC motor, AC motor of initial speed Estimate During this period, the carrier frequency for PWM control is Normal after that period A frequency lower than the carrier frequency used during acceleration setting This is what we do. Effect of the Invention

[0012] According to the present invention, the carrier frequency is lowered only during estimation of the initial speed, thereby reducing the number of occurrences of dead time and improving the accuracy of speed estimation. Problems, configurations and effects other than those described above will become apparent from the description of the following embodiments. [Brief description of the drawings]

[0013] [Figure 1] 1 is a block diagram showing a configuration of an inverter drive control device according to an embodiment of the present invention; [Diagram 2] 4 is a flowchart showing a control method performed by the inverter drive control device according to the embodiment. FIG. [Diagram 3] FIG. 11 is a diagram for explaining the setting of the carrier frequency when the modulation rate increases from 0% during acceleration in the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiment. In addition, in the description of the drawings, the same parts are denoted by the same reference numerals. EXAMPLES

[0015] FIG. 1 is a block diagram showing the configuration of an inverter drive control device according to an embodiment of the present invention. The inverter drive control device shown in FIG. 1 is configured to target an induction motor 11 for railroad cars as an AC motor to be driven and controlled by an inverter.

[0016] The main components are an inverter 10, an induction motor current coordinate conversion unit 13, a voltage vector calculation unit 3, an ACR 5, a speed estimation unit 7, and a PWM control unit 9. Here, the inverter 10 that drives the induction motor 11 has a two-level or three-level configuration.

[0017] Furthermore, the induction motor that is drive-controlled by an inverter is not limited to use in railway vehicles, and the induction motor may be an AC motor including a synchronous motor such as a PMSM.

[0018] A voltage vector calculation unit 3 calculates a voltage vector using an excitation / torque current command value 1 and a rotor frequency estimate value 2 output by a speed estimation unit 7. When starting to estimate the initial speed, Fslv is given as the value of the rotor frequency estimate value 2.

[0019] An induction motor current coordinate conversion unit 13 performs coordinate conversion of the detected induction motor current 12 and outputs the excitation current and torque current detection values ​​4 .

[0020] The ACR unit 5 calculates a voltage control amount 6 based on the excitation current and torque current command value 1 and the excitation current and torque current detection value 4. The calculated voltage control amount 6 includes an estimation error.

[0021] The speed estimator 7 calculates the rotor frequency estimate 2 based on the voltage control amount 6 output by the ACR unit 5 .

[0022] Here, the method for estimating the initial speed is implemented by appropriately combining a method that utilizes the deviation between the torque current command and the actual torque current caused by the error between the rotor frequency estimate and the actual rotor frequency, a method that causes the rotor frequency estimate to converge at a constant acceleration when the difference between the rotor frequency estimate and the actual rotor frequency is large, and a method that increases the magnetic flux in the motor by increasing the excitation current command when the rotor frequency estimate falls below a predetermined value.

[0023] The PWM control unit 9 performs PWM control on the inverter 10 based on a voltage command 8 obtained by adding the voltage calculated by the voltage vector calculation unit 3 and the voltage control amount 6. This controls the switching frequency at which the inverter 10 converts DC to AC.

[0024] 2 is a flow chart showing a control method performed by the vehicle drive control device according to this embodiment, which is made up of processes starting from START, passing through step 14 to step 18, and ending at END.

[0025] In step 14, the speed estimation unit 7 judges whether or not the notch command is turned on. If the notch command is turned on (YES), the process proceeds to step 15. If the notch command is not turned on (NO), the process returns to step 14 again, and thereafter the notch command on determination is periodically made.

[0026] In step 15, the speed estimator 7 starts estimating the initial speed, and the process proceeds to step 16.

[0027] In step 16, the PWM control unit 9 lowers the carrier frequency when generating the switching time. That is, the PWM control unit 9 switches the value of the carrier frequency used when generating the switching time from that used during normal acceleration in the asynchronous modulation mode (carrier frequency Fcn25 shown in FIG. 3) to a value used during initial speed estimation (carrier frequency for initial speed estimation Fcslv24 shown in FIG. 3).

[0028] In step 17, the PWM control unit 9 waits for the initial speed estimation time Tslv (initial speed estimation time Tslv23 shown in FIG. 3) to elapse from the notch command ON in step 14. After the estimation time Tslv has elapsed, the process proceeds to step 18.

[0029] In step 18, the PWM control unit 9 restores the carrier frequency. That is, the PWM control unit 9 switches (restores) the value of the carrier frequency used when generating the switching time from the value for initial speed estimation (carrier frequency Fcslv24 for initial speed estimation shown in FIG. 3) to the value for normal acceleration in the asynchronous modulation mode (carrier frequency Fcn25 shown in FIG. 3).

[0030] 3 is a diagram for explaining the setting of the carrier frequency 19 when the modulation rate increases from 0% during acceleration according to this embodiment. The horizontal axis is the time axis, and the left vertical axis indicates percentage and the right vertical axis indicates frequency.

[0031] The modulation mode when PWM controlling an induction motor consists of asynchronous modulation mode 20 and synchronous modulation mode 21, and switches according to the modulation rate 22 (dotted line in Fig. 3). When accelerating from start (start-up), the modulation rate is increased and the motor is operated in asynchronous modulation mode 20 until a specified speed is reached, and then the motor is operated in synchronous modulation mode 21 during constant speed driving after the specified speed is reached.

[0032] 3 indicates a change in carrier frequency fc in PWM control. During the asynchronous modulation mode 20, the carrier frequency fc is set to a value that takes into consideration inductive interference, temperature rise of elements, and the like.

[0033] In the case of this embodiment, in estimating the initial speed, the carrier frequency fc is set to the carrier frequency for initial speed estimation Fcslv24 during the initial speed estimation time Tslv23 during the period of the asynchronous modulation mode 20. After that, after the initial speed estimation time Tslv23 has elapsed, the carrier frequency is switched to the carrier frequency Fcn25 during normal acceleration in the asynchronous modulation mode.

[0034] As described above, the dead time is set to a value specific to the product. In the present embodiment, it is set to, for example, 10 μs. This dead time causes an error in the voltage output to the induction motor, which in turn causes distortion in the induction motor current. Therefore, during the initial speed estimation time, it is desirable to lower the carrier frequency to a range where the rotor frequency estimate is not affected by this current distortion.

[0035] As in this embodiment, the carrier frequency is switched as shown in Fig. 3, and the carrier frequency fc is lowered during the initial speed estimation. This reduces the number of switching times per second from Fcn to Fcslv (halved in Fig. 3), and the frequency of occurrence of dead time that occurs at each switching also decreases (halved in Fig. 3).

[0036] As described above, by reducing the frequency of occurrence of dead time, the waveform of the output current to the induction motor becomes closer to a sine wave, and the distortion of the current is reduced. Furthermore, the detection error of the rotor frequency is reduced, and the accuracy during speed estimation can be improved.

[0037] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present invention. [Explanation of symbols]

[0038] 1...Excitation current and torque current command values, 2...Rotor frequency estimate, 3...Voltage vector calculation unit, 4...Excitation current and torque current detection value, 5...ACR, 6...Voltage control amount, 7...Speed ​​estimation unit, 8...Voltage command, 9...PWM control unit, 10... inverter, 11... induction motor, 12... induction motor current, 13... Coordinate conversion unit for induction motor current, 19... Carrier frequency fc, 20... Asynchronous modulation mode, 21... Synchronous modulation mode, 22... Modulation rate, 23... Initial speed estimation time Tslv, 24... Carrier frequency for initial speed estimation Fcslv, 25…Carrier frequency Fcn during normal acceleration in asynchronous modulation mode

Claims

1. An inverter that converts DC power into AC power and supplies the AC power to an AC motor; A control unit that drives the inverter by PWM control; Equipped with During a period in which the inverter is started and a modulation rate of the inverter is increased from 0% to drive the AC motor, the control unit sets a carrier frequency for the PWM control to a frequency lower than a carrier frequency used during normal acceleration after the period. An inverter drive control device comprising:

2. 2. The inverter drive control device according to claim 1, The control unit performs the PWM control in an asynchronous modulation mode during a period in which the initial speed is estimated and a period until the AC motor reaches a predetermined speed by the normal acceleration. An inverter drive control device comprising:

3. 3. The inverter drive control device according to claim 1, When turning on and off the upper and lower arms constituting the inverter by the PWM control, the control unit provides a dead time during which both the upper and lower arms are turned off to prevent the upper and lower arms from being turned on simultaneously. An inverter drive control device comprising:

4. 4. The inverter drive control device according to claim 3, The control unit, when estimating a rotor frequency of the AC motor during a period in which the AC motor is driven at the initial speed, reduces the carrier frequency to a range in which the estimated rotor frequency is not affected by distortion of a current of the AC motor due to the dead time. An inverter drive control device comprising:

5. 5. The inverter drive control device according to claim 1, The control unit performs sensorless vector control on the AC motor using the PWM control. An inverter drive control device comprising:

6. 6. The inverter drive control device according to claim 1, The control unit estimates the initial speed by utilizing a deviation between a torque current command and an actual torque current caused by an error between an estimated value and an actual value of a rotor frequency of the AC motor. An inverter drive control device comprising:

7. 7. The inverter drive control device according to claim 1, The control unit increases an excitation current command for the AC motor when an estimated value of a rotor frequency of the AC motor becomes equal to or lower than a predetermined value. An inverter drive control device comprising:

8. An inverter drive control method for supplying AC power converted from DC power to an AC motor by PWM controlling an inverter, comprising: During a period in which the inverter is started and the modulation rate of the inverter is increased from 0% to drive the AC motor and an initial speed of the AC motor is estimated, a carrier frequency for the PWM control is set to a frequency lower than a carrier frequency used during normal acceleration after the period.

4. An inverter drive control method comprising:

9. The inverter drive control method according to claim 8, During the period in which the initial speed is estimated and during the period until the AC motor reaches a predetermined speed by the normal acceleration, the PWM control is performed in an asynchronous modulation mode.

4. An inverter drive control method comprising:

10. 10. The inverter drive control method according to claim 8, further comprising the steps of: Sensorless vector control is performed on the AC motor.

4. An inverter drive control method comprising:

11. 11. The inverter drive control method according to claim 8, further comprising: A deviation between a torque current command and an actual torque current caused by an error between an estimated value and an actual value of a rotor frequency of the AC motor is obtained; The deviation is utilized to estimate the initial velocity.

4. An inverter drive control method comprising:

12. 12. The inverter drive control method according to claim 8, further comprising the steps of: When an estimated value of a rotor frequency of the AC motor becomes equal to or lower than a predetermined value, an excitation current command for the AC motor is increased.

4. An inverter drive control method comprising:

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