JP2015109781A - System interconnection power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system interconnection power conversion device that secures stability against a sudden load change and suppresses disturbance in a system.SOLUTION: The power conversion device includes: a converter 3 for converting three-phase AC power into DC power; an inverter 4 for converting DC power into three-phase AC power; a chopper 5 connected to a DC connection part between the converter 3 and the inverter 4; and a DC power storage device 6 that is charged/discharged by operating the chopper 5. On the basis of a deviation between a DC voltage detection value Vdc in the DC connection part and a DC voltage command value Vdc, a DC current command value Idccalculated so as to keep constant a voltage of the DC connection part is distributed to a converter current command value Iconand a chopper current command value Ich, and a value resulting from moving-averaging and differentiating an inverter output current detection value Iinv with a power supply cycle is added to the chopper current command value Ich.

Description

  The present invention relates to a power conversion device linked to a system having a power storage device such as a battery, and a system that suppresses the influence on the system while responding to a sudden change in a load connected to the device. The present invention relates to an interconnected power converter.

  In power converters connected to a system that connects any load, such as an uninterruptible power supply (UPS), frequency converter, etc., it is possible to ensure the stability of the voltage to the load by improving the response to load fluctuations it can.

JP 2013-38943 A JP 2008-295160 A

  However, tracking load fluctuations can cause disturbances to the system. Therefore, how to provide a power conversion device that secures the stability of the UPS output AC voltage against sudden load changes and reduces the influence on the system becomes a problem.

  As measures against this problem, there are measures such as improving the control rate by increasing the voltage of the DC connection, and improving the stability against load fluctuations by increasing the capacity of the capacitor at the DC connection. . In these measures, the former needs to increase the breakdown voltage of the semiconductor element, and the latter has disadvantages such as an increase in the volume of the device.

  Patent Document 1 discloses a bidirectional connection to a DC power storage device (battery or the like) in order to flow a current exceeding the rating of a power conversion device (AC-AC converter) connected to a system and a load. This is a system in which a converter (DC-AC converter) is connected to a load and the excess is borne.

  However, in the case of the system configuration of Patent Document 1, since the amount exceeding the rating of the power converter including the sudden load change is always supplied from the bidirectional converter, the DC power storage device is charged by the fluctuation of the power. The discharge will be repeated. In addition, if the DC voltage of the bidirectional converter pulsates during non-linear load driving, the battery life is affected.

  As described above, in the grid-connected power conversion device, it is a problem to ensure stability against a sudden load change and to suppress disturbance in the system.

  The present invention has been devised in view of the conventional problems, and one aspect thereof is a converter that converts three-phase AC power into DC power, an inverter that converts DC power into three-phase AC power, and a converter And a DC power storage device that is charged and discharged by the operation of the chopper, the DC voltage detected value and the DC voltage command of the DC connection portion Based on the value deviation, the DC current command value calculated to keep the DC connection voltage constant is distributed to the converter current command value and the chopper current command value, and the inverter output current detection value is moved in the power cycle. A command distributor for differentiating and adding the average moving average current calculated to the chopper current command value is provided.

  Further, as one aspect thereof, the command distributor outputs a value obtained by adding the DC current command value and the moving average current as a converter current command value, and the value obtained by differentiating the moving average current during the converter operation is a chopper current. A command value is output, and when the converter is stopped, a value obtained by adding the converter current command value and a value obtained by differentiating the moving average current is output as a chopper current command value.

  As another aspect, the command distributor is a sum of the DC current command value and the moving average current if a value obtained by adding the DC current command value and the moving average current is smaller than a preset upper limit value. Is output as the converter current command value, the value obtained by differentiating the moving average current is output as the chopper current command value, and if the sum of the DC current command value and the moving average current is greater than the upper limit value, the upper limit value is converted to the converter Output as a current command value, and output as a chopper current command value a value obtained by adding the difference between the DC current command value, the addition value of the moving average current and the upper limit value, and the value obtained by differentiating the moving average current. Features.

  ADVANTAGE OF THE INVENTION According to this invention, in a grid connection power converter device, it becomes possible to ensure the stability with respect to a sudden load change, and to suppress the disturbance in a system | strain.

The block diagram which shows the main circuit of the grid connection power converter device in Embodiment 1,2. The block diagram which shows the control circuit of the grid connection power converter device in Embodiment 1,2. FIG. 3 is a block diagram illustrating a command distributor according to the first embodiment. The block diagram which shows the command distributor in Embodiment 2. FIG.

  Hereinafter, Embodiment 1 and 2 of the grid connection power converter device in this invention are demonstrated in detail based on FIGS.

[Embodiment 1]
FIG. 1 is a block diagram illustrating a main circuit of the grid-connected power conversion device according to the first embodiment. As shown in FIG. 1, a grid-connected power conversion device 1 includes a converter 3 that converts three-phase AC power output from a power source 2 into DC power using a semiconductor element, and an inverter that converts DC power into three-phase AC power. 4, a chopper (DC / DC converter) 5 connected to a DC connection between the converter 3 and the inverter 4, and a DC power storage device 6 such as a battery that is charged and discharged by the operation of the chopper 5.

  In FIG. 1, filters 8 a and 8 b are interposed between the power supply 2 and the converter 3 and between the inverter 4 and the load 7. A DC link capacitor 9 is provided at a DC connection between the converter 3 and the inverter 4, and a reactor 10 is interposed between the chopper 5 and the DC power storage device 6.

  In the grid-connected power converter configured in this way, the three-phase AC current output from the power source 2 is output to the load 7 via the filter 8a, converter 3, DC link capacitor 9, inverter 4, and filter 8b. The Further, the excess rating of the AC / DC / AC converter composed of the converter 3, the DC link capacitor 9, and the inverter 4 is output to the DC power storage device 6 through the chopper 5, and the excess is borne.

  FIG. 2 is a block diagram illustrating a control circuit of the grid-connected power conversion device according to the first embodiment.

The converter 3 controls the current so as to be in phase with the power supply voltage by the current minor loop, and at the same time controls the DC voltage to be constant. Specifically, as shown in FIG. 2, the automatic voltage regulator AVR1 performs PI (proportional integration) calculation based on the deviation between the DC voltage detection value Vdc of the DC connection portion and the first DC voltage command value Vdc1 ^*. The calculated direct current command value Idc ^* is output to the command distributor 11. The command distributor 11 will be described later.

Based on the deviation between the converter current command value Icon ^* output from the command distributor 11 and the value obtained by converting the current detection value Icon on the input side of the converter 3 by the coordinate conversion unit 13, the automatic current adjuster ACR1 PI (proportional integration) calculation is performed, and the calculated second voltage command value Vref <b> 2 is output to the PWM controller 12. The PWM controller 12 generates a PWM (pulse width modulation) signal based on the second voltage command value Vref <b> 2 by a triangular wave carrier method and outputs the PWM signal to the semiconductor element of the converter 3.

The inverter 4 controls the output voltage to be constant by a voltage minor loop. Specifically, the automatic voltage regulator AVR2 performs PI (proportional integration) calculation based on the deviation between the first output voltage command value Vout1 ^* and the value obtained by coordinate conversion of the output voltage detection value Vout by the coordinate conversion unit 15. The calculated second output voltage command value Vout2 ^* is output to the PWM controller 14. The PWM controller 14 generates a PWM signal based on the second output voltage command value Vout2 ^* by a triangular wave carrier method, and outputs the PWM signal to the semiconductor element of the inverter 4.

The chopper 5 controls charging / discharging of the DC power storage device 6 while controlling the DC voltage constant. Specifically, a value obtained by performing coordinate conversion on the inverter output current detection value Iinv output from the inverter 4 by the coordinate conversion unit 16 is subjected to moving average by the moving average unit 17 and output to the command distributor 11 as the moving average current Iave. The command distributor 11 will be described later. Based on the deviation between the chopper current command value Ich ^* output from the command distributor 11 and the detected chopper current value Ich, the automatic current regulator ACR2 performs a PI (proportional integration) operation, and the calculated chopper voltage command value Vch. ^* Is output to the PWM control unit 18. The PWM control unit 18 generates a PWM signal based on the chopper voltage command value Vch ^* by a triangular wave carrier method and outputs the PWM signal to the semiconductor element of the chopper 5.

  Note that the coordinate conversion units 13 and 16 convert the three-phase current into three-phase / two-phase conversion and dq conversion, and output a d-axis current. Further, the coordinate conversion unit 15 converts the three-phase voltage into the three-phase / two-phase conversion and the dq conversion, and outputs the d-axis voltage.

Next, the command distributor 11 will be described with reference to FIG. As shown in FIG. 3, the DC current command value Idc ^* output from the automatic voltage regulator AVR1 and the moving average current Iave output from the moving average unit 17 are added, and the addition result is converted into the converter current command value Icon ^*. And Further, the moving average current Iave output from the moving average unit 17 is differentiated by the differential compensation unit 20, the output Idif of the differential compensation unit 20 and the output of the switch 21 are added, and output as a chopper current command value Ich ^* . .

Here, the switch 21 outputs 0 during the operation of the converter 3 and outputs the converter current command value Icon ^* when the converter 3 is stopped.

  As described above, in converter 3, a current control system based on PI control is constructed, and the current is controlled to be in phase with the power supply voltage by a current minor loop. At the same time, in order to make the DC voltage constant, a major loop is formed for the current control and used as a command value for the current control.

Similarly to the converter 3, the chopper 5 also configures the DC voltage control as a major loop of the current control system in order to control the DC voltage constant. As a result, the DC voltage control major loop of the converter 3 and the chopper 5 can be shared, and the DC current command value Idc ^* generated by one DC voltage control system can be used as the two current control commands of the converter 3 and the chopper 5. It becomes possible to distribute.

  In addition, the inverter output current detection value Iinv is used as a feedforward term for DC voltage control in order to easily follow the change in the output current on the load side together with the stability of the control system.

  The AC amount handled in the control system can be converted into a DC amount by performing coordinate conversion based on the phase, and active power and reactive power can be controlled independently. However, it is known that when a non-linear load such as a capacitor input type diode rectifier load (hereinafter referred to as a rectifier load) is connected, harmonic distortion occurs in the output voltage waveform.

  Therefore, a harmonic component is also generated in the inverter output current detection value Iinv, and the odd-order ripple components (5, 7, 11, 13, 17, 19th order,...) Are superimposed on the harmonic component only by coordinate conversion. As a result, the stability of the control system of the converter 3 is hindered.

  Therefore, in order to remove this higher-order ripple component, a moving average is performed for one cycle of the power source, which is the fundamental wave of these components. However, the moving average over one cycle of the power supply can remove the harmonic component, but a delay due to the moving average processing is generated, and there is a possibility that it cannot follow a steep load fluctuation.

  In order to solve this problem, the differential compensation unit 20 incorporates a differential operation of the moving average amount to compensate for the delay due to the moving average.

  However, an excessive change due to the differential operation guarantees stability against fluctuations on the load 7 side, but on the other hand, it may cause disturbance to the input (system power supply 2) side and may cause instability.

  In the command distributor 11 described above, by adding a moving average differential operation to the command to the chopper 5, an excessive change is compensated by charging / discharging the DC power storage device 6, thereby compensating for fluctuations on the load 7 side, In addition, the stability on the input side is ensured. When the converter 3 is stopped, the load 21 is not affected even when the converter 3 is stopped by switching the switch 21 and the chopper 5 taking all current commands.

  According to the power conversion device in the first embodiment, the fluctuation of the load 7 connected to the inverter 4 is compensated by charging / discharging the DC power storage device 6 via the chopper 5. At the same time, by stabilizing the operation of the converter 3 connected to the system, it is possible to prevent disturbance to the system side.

  Further, even if the capacity of the DC link capacitor 9 is reduced, stable operation can be ensured and the apparatus can be downsized. Furthermore, since it is not necessary to increase the voltage of the DC connection portion, a semiconductor element having a low withstand voltage can be selected, and the cost can be reduced.

[Embodiment 2]
FIG. 4 shows a block diagram of the command distributor 11 in the second embodiment. Except for the command distributor 11, the second embodiment is the same as the first embodiment. Description of the same parts as those in the first embodiment is omitted.

As shown in FIG. 4, the DC current command value Idc ^* output from the automatic voltage regulator AVR1 and the moving average current Iave output from the moving average unit 17 are added, and this addition result Idc ^* + Iave is added to the limiter 22. input. An upper limit value (for example, a rated current) is set in the limiter 22. When the addition result Idc ^* + Iave is less than or equal to the upper limit value, the addition result Idc ^* + Iave is directly output as the converter current command value Icon ^*. However, when the addition result Idc ^* + Iave is greater than the upper limit value, the upper limit value is It is output as a converter current command value Icon ^* .

Further, the deviation between the input value and the output value of the limiter 22 is added to the output Idif of the differential compensation unit 20 to obtain a chopper current command value Ich ^* .

  That is, in the command distributor 11, priority can be given to the command distribution to the converter 3, and the chopper 5 can stably control the load that cannot be covered by the converter 3. Can respond.

  As described above, according to the second embodiment, the same operational effects as those of the first embodiment can be obtained.

  Although the present invention has been described in detail only for the specific examples described above, it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the technical idea of the present invention. Such variations and modifications are naturally within the scope of the claims.

DESCRIPTION OF SYMBOLS 3 ... Converter 4 ... Inverter 5 ... Chopper 6 ... DC power storage device 7 ... Load 11 ... Command distributor 17 ... Moving average part 20 ... Differential compensation part

Claims (3)

A converter that converts three-phase AC power to DC power, an inverter that converts DC power to three-phase AC power, a chopper connected to the DC connection between the converter and the inverter, and DC that is charged and discharged by the operation of the chopper A power conversion device comprising a power storage device,
Based on the deviation between the DC voltage detection value of the DC connection and the DC voltage command, the DC current command calculated to keep the voltage of the DC connection constant is distributed to the converter current command value and the chopper current command value, A grid-connected power converter comprising a command distributor that differentiates and adds a moving average current calculated by moving and averaging an inverter output current detection value in a power supply cycle to a chopper current command value. The command distributor is:
A value obtained by adding the DC current command value and the moving average current is output as the converter current command value.
During converter operation, the value obtained by differentiating the moving average current is output as the chopper current command value.
The grid-connected power converter according to claim 1, wherein a value obtained by adding the converter current command value and a value obtained by differentiating the moving average current is output as a chopper current command value while the converter is stopped. The command distributor is:
If the value obtained by adding the DC current command value and the moving average current is smaller than the preset upper limit value, the addition value of the DC current command value and the moving average current is output as the converter current command value, and the moving average current is calculated. The differentiated value is output as the chopper current command value,
If the sum of the DC current command value and the moving average current is greater than the upper limit value, the upper limit value is output as the converter current command value, and the deviation between the DC current command value and the added value of the moving average current and the upper limit value is output. The grid-connected power converter according to claim 1, wherein a value obtained by adding the value obtained by differentiating the moving average current is output as a chopper current command value.

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