JP2015100152A - Electric power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power conversion device capable of suppressing overshoot of a direct current voltage without impairing load response.SOLUTION: The electric power conversion device includes: a converter 2 for converting an alternate current input into a direct current; an inverter 4 for converting the direct current of the converter 2 into an alternate current to drive an alternate current motor 5; converter control means 6; and inverter control means 7 having power feedforward correction means 76. The converter control means 6 includes: voltage control means 61 which receives, as inputs, a voltage instruction and a voltage deviation of a voltage feedback being a direct current output of the converter 2, and outputs the sum of a linear amplifier 611 and an integrating amplifier 612; electric current control means 62 which compares an effective electric current reference obtained by adding the output from the power feedforward correction means 76 to the output of the voltage control means 61 with the input electric current of the converter 2 and outputs a voltage reference; switching instruction calculation means 63; and integration reset means 65 for resetting the value of integral of the integrating amplifier 612 to zero when the absolute value of the voltage deviation is equal to or less than a predetermined threshold.

Description

  The present invention relates to a power converter that controls a DC voltage by a converter and drives an AC motor by an inverter that converts the DC voltage into AC.

  A system for driving an AC motor by a power converter has been widely used.

  In a system that drives an AC motor loaded with a steel mill or the like, the power converter is composed of a converter and an inverter, and the output DC voltage of the converter is controlled to a constant value, and the inverter is controlled to a constant value by the converter. In many cases, the direct current voltage is converted into alternating current using PWM control or the like to drive the alternating current motor. In this case, a PWM control type converter is also used as the converter, and the inverter uses so-called vector control in which the output current is converted into the torque shaft and the excitation shaft of the AC motor, and the torque current and the excitation current are controlled independently. It was.

  When the above system configuration is adopted, it is important from the viewpoint of overvoltage prevention or the like to control the output voltage of the converter within a predetermined range in all operation modes. For this reason, for example, measures such as correcting the effective current reference of the converter by adding the power consumed by the inverter to the voltage control on the converter side in a feedforward manner have been implemented (see, for example, Patent Document 1).

Japanese Patent Laying-Open No. 2005-218186 (page 5-7, FIG. 1)

  The technique disclosed in Patent Document 1 feeds the power consumed by the inverter to the voltage control on the converter side in order to suppress voltage fluctuation due to a response delay when the load suddenly increases or decreases compared to the normal voltage control. The effective current reference of the converter is corrected by adding forward. This correction is called power compensation. However, when such power compensation is performed in addition to normal voltage control, the load response is improved, but the DC voltage overshoots when the load suddenly increases, undershoots when the load suddenly decreases, and the voltage fluctuation increases. There was a case.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a power converter that can suppress fluctuations such as overshoot of a DC voltage without impairing load response.

  In order to achieve the above object, a power converter according to the present invention includes a converter that converts an AC input into a DC voltage, an inverter that converts a DC output of the converter into an AC voltage, and drives an AC motor, and an output of the converter Converter control means for controlling the voltage; and inverter control means for controlling the output of the inverter, and having power feedforward correction means for detecting the output power and supplying the output to the converter control means. Has a voltage deviation obtained by subtracting a voltage feedback, which is a DC output of the converter, from a voltage command, outputs a sum of a proportional amplifier and an integral amplifier, and outputs the power feedforward correction to the output of the voltage control means The effective current reference summed with the output of the means and the input current of the converter Current control means for outputting a voltage reference, switching command calculation means for obtaining a gate signal to a switching element constituting the converter according to the voltage reference, and integration when the absolute value of the voltage deviation is equal to or less than a predetermined threshold value And an integration reset means for resetting the integral value of the amplifier to zero.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the power converter device which can suppress fluctuation | variations, such as an overshoot of DC voltage, without impairing load response.

The block block diagram of the power converter device which concerns on Example 1 of this invention. The figure explaining the behavior of the direct current voltage at the time of load increase. The block block diagram of the power converter device which concerns on Example 2 of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  A power converter according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a block diagram of a power conversion apparatus according to Embodiment 1 of the present invention.

  An AC voltage is supplied from the AC power source to the converter 2 via the input transformer 1, and the converter 2 converts this to a DC voltage and supplies it to the inverter 4 via the smoothing capacitor 3. The inverter 4 converts this DC voltage into an AC voltage and drives the AC motor 5. A speed detector 10 is mechanically connected to the rotating shaft of the AC motor 5.

  The converter 2 has a plurality of switching elements, and the output voltage is controlled by applying a gate signal from the converter control circuit 6 to these switching elements. The converter control circuit 6 includes a voltage feedback signal from a DC voltage detector 8 that detects the voltage across the smoothing capacitor 3 and a current detector 9 that detects an input current to the converter 2 and outputs an effective current. A current feedback signal is provided.

  Similarly, the inverter 4 has a plurality of switching elements, and the output thereof is controlled by applying a gate signal from the inverter control circuit 7 to these switching elements. The inverter control circuit 7 is given a speed feedback signal from the speed detector 10 and a current feedback signal from the current detector 11 that detects the output current of the inverter 4 and outputs a torque current.

  The internal configuration of the converter control circuit 6 will be described below. The voltage controller 61 amplifies the voltage deviation of the given voltage command and the voltage feedback signal from the DC voltage detector 8, and adds this output and the output of the power feedforward corrector 76 provided in the inverter control circuit 7. To obtain an effective current reference. This effective current reference is compared with the effective current feedback signal obtained from the current detector 9, and the deviation is amplified by the current controller 62 to obtain a voltage reference. This voltage reference is converted into a gate pulse by the switching command calculation circuit 63 using, for example, PWM modulation and supplied to the gate of the switching element of the converter 2. Since the voltage controller 61 and the current controller 62 perform feedback control of the outer loop and the minor loop, respectively, the former is controlled by performing the above control so that the deviation between the voltage command and the voltage feedback signal is minimized, The latter is controlled so that the deviation between the active current reference and the active current feedback signal is minimized. The voltage controller 61 is a so-called PI controller, and as shown in the figure, a proportional amplifier 611 for obtaining an output proportional to the input voltage deviation and an integrating amplifier 612 for obtaining an output obtained by integrating the inputted voltage deviation. The composition output is obtained.

  The voltage deviation which is input to the voltage controller 61 is given to the deviation confirmation device 64. The deviation checker 64 gives a command signal to the integration reset unit 65 when the absolute value of the input voltage deviation falls below a predetermined threshold value. The integration reset unit 65 resets the integration value of the integration amplifier 612 to zero when this command signal is given. That is, if the integration amplifier 612 has a circuit configuration using an integration capacitor, the integration value is reset by short-circuiting the charge of the integration capacitor. When the absolute value of the voltage deviation input to the deviation checker 64 exceeds a predetermined threshold, the command signal to the integration reset unit 65 disappears, and the integration amplifier 612 performs normal integration again.

  Next, the internal configuration of the inverter control circuit 7 will be described below.

  The difference between the given speed command and the speed feedback signal from the speed detector 10 is amplified by the speed controller 71 to obtain a torque reference. A magnetic flux reference is obtained by an automatic field weakener 72 that receives a speed feedback signal and performs field weakening when the speed is equal to or higher than the base speed. The torque current reference calculator 73 divides the torque reference by the magnetic flux reference to obtain a torque current reference. This torque current reference is compared with the torque current feedback signal obtained from the current detector 8, and the deviation is amplified by the current controller 74 to obtain a voltage reference. This voltage reference is converted into a gate pulse by, for example, PWM modulation by the switching command calculation circuit 75 and supplied to the gate of the switching element of the inverter 4. Although the torque current feedback signal is directly obtained from the current detector 8 here, the current detector 8 detects only the instantaneous current and obtains the torque current by the conversion circuit provided in the inverter control circuit 7. Anyway. The torque current reference that is the output of the torque current reference calculator 73 and the voltage reference that is the output of the current controller 74 are supplied to the power feedforward corrector 76. The power feedforward corrector 76 calculates the instantaneous power that the inverter 4 gives to the AC motor 5 and gives it to the converter control circuit 6 as a power compensation feedforward signal.

  Next, the control operation in the first embodiment will be described below with reference to FIG.

  Converter control circuit 6 performs control so that the output voltage of converter 2 becomes a predetermined voltage command. Then, the power feedforward corrector 76 corrects the response to fluctuations in the power on the load side, thereby improving the response.

  FIG. 2 shows the behavior of the DC voltage when the load suddenly increases. When the AC motor 5 is operating at a constant load and at a constant speed, when an impact load is applied at time t = T1, the torque reference changes substantially stepwise, and speed feedback (not shown) starts to decrease. In FIG. 1, when there is no power compensation by the power feedforward corrector 76 and no integration reset device 65 by the deviation checker 64 is provided, the DC voltage drops greatly as shown by a solid line waveform A at this time. On the other hand, when only the power compensation by the power feedforward corrector 76 is added, the drop is greatly improved and a dash-dot line B is obtained. However, in this case, as shown in FIG. This overshoot occurs because the integrated value of the integrating amplifier 612 remains even if the DC voltage recovers from the drop due to the impact load. In order to eliminate this overshoot, a deviation checker 64 and an integration reset unit 65 are provided, the deviation checker 64 detects that the voltage deviation of the DC voltage has become a predetermined threshold value or less, and a reset command is sent to the integration resetter 65. give. In this way, the integral value of the integrating amplifier 612 is reset to zero at time T2 in FIG. 2, and the DC voltage is statically controlled as indicated by the solid arrow C in FIG. 2, and an overvoltage due to overshoot occurs. Disappear.

  Further, if the deviation checker 64 detects that the absolute value of the voltage deviation of the DC voltage is equal to or less than a predetermined threshold value, the integration is not performed even when the load suddenly decreases as shown in FIG. It is obvious that the integration reset can be performed by the operation of the reset device 65, and the fluctuation of the DC voltage can be suppressed.

  A power conversion apparatus according to Embodiment 2 of the present invention will be described with reference to FIG. FIG. 3 is a block diagram of the power conversion apparatus according to the second embodiment of the present invention.

  About each part of this Example 2, the same part as the block block diagram of the power converter device which concerns on Example 1 of FIG. 1 is shown with the same code | symbol, and the description is abbreviate | omitted. The second embodiment is different from the first embodiment in that an output limiter 613 is provided on the output side of the integrating amplifier 612, the output of the deviation checker 64A is given to the limit processor 66, and the output of the limit processor 66 is This is the point that the limit value of the output limiter 613 is changed.

  The deviation checker 64A according to the second embodiment is configured such that when the voltage deviation of the DC voltage, that is, the voltage reference-voltage feedback value is equal to or smaller than a predetermined threshold value in a positive state, the magnitude is a predetermined threshold value in a negative state. Different commands are given to the limit processor 66 in the following state. In the former case, the limit processor 66 sets the positive limit value of the output limiter 613 to zero, and in the latter case, sets the negative limit value of the output limiter 613 to zero. In this way, it is possible to determine whether a load sudden increase or a load sudden decrease has occurred according to the sign of the voltage deviation, and the necessary limit processing can be performed according to the result, so that more accurate Control is possible.

  As mentioned above, although the Example of this invention was described, this Example is shown as an example and is not intending limiting the range of invention. The novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  For example, in order to prevent malfunction due to control disturbance or the like, in the first embodiment, only when the absolute value of the voltage deviation exceeds a predetermined threshold for a predetermined time or more and then becomes a predetermined threshold or less, the integration resetter 65 May be operated. Similarly, in the second embodiment, the limit processor 66 sets the limit value of the output limiter 613 to zero only when the absolute value of the voltage deviation exceeds a predetermined threshold for a predetermined time or more and then becomes a predetermined threshold or less. You may do it.

  In addition, the inverter controller 7 has been described as having a speed controller 73 and a current controller 74. However, the inverter controller 7 may be an application in which only the torque control is performed without the speed controller 73. Further, even when speed control is performed, it is not always necessary to obtain a speed feedback signal by the speed detector 10, and a so-called sensorless vector control method may be used to obtain the speed feedback signal indirectly by calculation.

DESCRIPTION OF SYMBOLS 1 Input transformer 2 Converter 3 Smoothing capacitor 4 Inverter 5 AC motor 6, 6A Converter control circuit 7 Inverter control circuit 8, 9 Current detector 10 Speed detector 61 Voltage controller 62 Current controller 63 Switching command calculator 64, 64A Deviation checker 65 Integral reset unit 66 Limit processor 71 Speed controller 72 Automatic field weakener 73 Divider 74 Current controller 75 Switching command calculator 76 Power feedforward corrector 611 Proportional controller 612 Integral controller 613 Output limiter

Claims (6)

A converter that converts AC input into DC voltage;
An inverter that drives the AC motor by converting the DC output of the converter into an AC voltage;
Converter control means for controlling the output voltage of the converter;
Inverter control means having power feedforward correction means for controlling the output of the inverter and detecting the output power to be supplied to the converter control means,
The converter control means includes
Voltage control means for inputting a voltage deviation obtained by subtracting voltage feedback which is a DC output of the converter from a voltage command, and outputting a sum of a proportional amplifier and an integral amplifier;
An active current reference obtained by adding the output of the power feedforward correction means to the output of the voltage control means and a current control means for comparing the input current of the converter and outputting a voltage reference;
Switching command calculation means for obtaining a gate signal to a switching element constituting the converter according to the voltage reference;
And an integration reset means for resetting the integral value of the integral amplifier to zero when the absolute value of the voltage deviation is equal to or less than a predetermined threshold value. A converter that converts AC input into DC voltage;
An inverter that drives the AC motor by converting the DC output of the converter into an AC voltage;
Converter control means for controlling the output voltage of the converter;
Inverter control means having power feedforward correction means for controlling the output of the inverter and detecting the output power to be supplied to the converter control means,
The converter control means includes
Voltage control means for inputting a voltage deviation obtained by subtracting voltage feedback which is a DC output of the converter from a voltage command, and outputting a sum of a proportional amplifier and an integral amplifier;
Output limit means for limiting the positive and negative outputs of the integrating amplifier, and
An active current reference obtained by adding the output of the power feedforward correction means to the output of the voltage control means and a current control means for comparing the input current of the converter and outputting a voltage reference;
Switching command calculation means for obtaining a gate signal to a switching element constituting the converter according to the voltage reference,
When the voltage deviation is less than a predetermined threshold in the positive state, the positive limit value of the output limit means is set to zero, and the magnitude is less than the predetermined threshold in the negative state In this case, the power conversion device is characterized in that the negative limit value of the output limit means is set to zero.   2. The power conversion device according to claim 1, wherein the integral reset unit is operated when the absolute value of the voltage deviation exceeds the predetermined threshold for a predetermined time or more.   The power converter according to claim 2, wherein when the absolute value of the voltage deviation exceeds the predetermined threshold for a predetermined time or more, the limit value of the output limit means is set to zero. The inverter control means includes
Speed control means for comparing a speed feedback obtained by directly or indirectly detecting the speed of the AC motor with a speed command and outputting a torque reference;
A current that outputs a voltage reference by comparing a torque current reference obtained by dividing the torque reference by a magnetic flux reference obtained as a function of the speed feedback and a torque current feedback obtained by detecting an output current of the inverter Control means;
5. The power conversion device according to claim 1, further comprising: a switching command calculation unit that obtains a gate signal to a switching element that constitutes the inverter according to the voltage reference. 6.   6. The power conversion apparatus according to claim 5, wherein the power feedforward correction means obtains an output by calculation from the torque current reference and the voltage reference.

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