Power conversion device

Abstract

To solve the problem that there is a risk that a system formation type inverter stops due to DC over-voltage or DC shortage voltage when fluctuation of DC voltage is large.SOLUTION: In a power conversion device which converts DC power into AC power to be output to a power system, a control unit of the power conversion device calculates a frequency command of AC voltage to be output by the power conversion device from a valid power command value and a valid power detection value. The valid power command value is calculated from a detection value of DC power, a DC voltage command value, and a valid power correction command value calculated by using deviation of a detection value of DC voltage as an input.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power conversion device. [Background technology]

[0002] In order to achieve carbon neutrality, the introduction of renewable energy sources such as solar power is progressing. As a result, the proportion of synchronous generators connected to the power grid is expected to decrease, while the proportion of inverters that connect renewable energy sources to the power grid is expected to increase.

[0003] Synchronous generators have a rotating body and are capable of supplying inertia to the power grid, but conventional inverters do not have such a capability. Therefore, as the proportion of inverters connected to the power grid increases, there is concern that the power grid will lack inertia, which will make the system frequency more susceptible to fluctuations and cause instability in the power grid.

[0004] Therefore, the concept of pseudo-inertia has been proposed, which uses inverter control to simulate the ability to supply inertia to the power grid.Inverters with the ability to supply pseudo-inertia to the power grid have attracted attention and are called grid-forming inverters.

[0005] An example of such a grid-type inverter is known from Patent Document 1. Patent Document 1 shows an example of a grid-type inverter having a DC power supply in a DC circuit. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2024-36973 Summary of the Invention [Problem to be solved by the invention]

[0007] However, for example, when a grid-connected inverter is applied to photovoltaic power generation, if the DC circuit is equipped with an unstable DC power source such as a solar panel, it is difficult to maintain a stable DC voltage of the grid-connected inverter, which poses a problem that makes it difficult to operate the grid-connected inverter stably.

[0008] If an imbalance occurs between the power input from the solar panels to the DC part of the grid-connected inverter and the power output from the grid-connected inverter to the power grid, the DC voltage of the grid-connected inverter will fluctuate according to the amount of imbalance. As a result, if the DC voltage fluctuation is large, the grid-connected inverter may stop due to DC overvoltage or DC undervoltage.

[0009] In addition, inverters for solar power generally use MPPT (maximum power point tracking) control to maximize the power generation, but this type of control becomes difficult to apply when the DC voltage fluctuates.

[0010] One example of the object of the present invention is to stabilize the DC voltage in a grid-forming inverter for photovoltaic power generation, thereby ensuring stable operation of the grid-forming inverter, and to achieve compatibility with MPPT (Maximum Power Point Tracking) control, which is called maximum power point tracking control in Japanese, in order to maximize the generated power. [Means for solving the problem]

[0011] An example of a means for solving the above problem is as follows.

[0012] In a power conversion device that converts DC power into AC power and outputs the AC power to a power grid, a control unit of the power conversion device calculates a frequency command for an AC voltage to be output by the power conversion device from an active power command value and an active power detection value, and the active power command value is calculated from a detected DC power value, a DC voltage command value, and an active power correction command value calculated using as input a deviation of the detected DC voltage value. [Effects of the Invention]

[0013] According to the present invention, in a grid-connected inverter, the DC voltage can be stabilized, and stable operation of the grid-connected inverter can be realized. Furthermore, by stabilizing the DC voltage, compatibility with MPPT control can be achieved, and the generated power can be maximized.

[0014] Further means and effects of the present invention will become apparent throughout the entire specification below. [Brief explanation of the drawings]

[0015] [Figure 1] 1 shows the configuration of a first embodiment of a power conversion device. [Figure 2] An example of the output characteristics of a solar panel is shown below. [Figure 3] An example of the output characteristics of a frequency command calculator is shown below. [Figure 4] 4 shows an example of operational waveforms in the first embodiment. [Figure 5] 4 shows an example of operational waveforms in the first embodiment. [Figure 6] 1 shows the configuration of a second embodiment of a power conversion device. [Figure 7] 10 shows an example of operating waveforms in the second embodiment. [Figure 8] 10 shows an example of operating waveforms in the second embodiment. [Figure 9] 10 shows the configuration of a third embodiment of a power conversion device. [Figure 10] 10 shows an example of operating waveforms in the third embodiment. [Figure 11] 10 shows an example of operating waveforms in the third embodiment. [Figure 12] 10 shows the configuration of a fourth embodiment of a power conversion device. [Figure 13] 10 shows an example of operational waveforms in the fourth embodiment. [Figure 14] 10 shows an example of operational waveforms in the fourth embodiment. [Figure 15] 10 shows the configuration of a power conversion device according to a fifth embodiment. [Figure 16] 10 shows the configuration of a sixth embodiment of a power conversion device. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings as needed.

[0017] In the following examples, a technology for realizing stable operation of a grid-forming inverter will be described using a power conversion device for photovoltaic power generation as an example. However, the scope of disclosure of this specification also includes cases where the technology is applied to other uses, not just photovoltaic power generation, as long as it is applied to solve the problem of stable operation of a grid-forming inverter. [Example]

[0018] 1 shows the configuration of a first embodiment of a photovoltaic power generation power converter as an example of application of the present invention. Photovoltaic power generation power converter 1 of this embodiment is connected to a three-phase AC power system 2. Photovoltaic power generation power converter 1 has a solar panel 11, a diode 12, an AC / DC converter 13, a DC capacitor 14, a DC voltage detection sensor 15, a DC current detection sensor 16, an AC voltage detection sensor 17, an AC current detection sensor 18, and a controller 19. Note that diode 12 is not essential.

[0019] Solar panel 11 is connected to the DC side of AC / DC converter 13 via diode 12, and the AC side of AC / DC converter 13 is connected to three-phase AC power grid 2. DC capacitor 14 is connected to the DC side of AC / DC converter 13, and DC voltage detection sensor 15 detects the DC voltage of DC capacitor 14. DC current detection sensor 16 is connected between diode 12 and AC / DC converter 13, and detects the DC current output from solar panel 11. AC voltage detection sensor 17 is connected to the AC side of AC / DC converter 13, and detects the three-phase AC voltage on the AC side of AC / DC converter 13. AC current detection sensor 18 is connected between AC / DC converter 13 and power grid 2, and detects the three-phase AC current output from AC / DC converter 13. The controller 19 receives as input the DC voltage detection value 500 output by the DC voltage detection sensor 15, the DC current detection value 501 output by the DC current detection sensor 16, the AC voltage detection value 502 output by the AC voltage detection sensor 17, and the AC current detection value 503 output by the AC current detection sensor 18, and outputs a pulse signal 700 that drives the switching elements that make up the AC / DC converter 13.

[0020] The controller 19 has a multiplier 190, an MPPT controller 191, a subtractor 192, a proportional integral controller 193, an adder 194, an active power calculator 195, a frequency command calculator 196, an integrator 197, a voltage command calculator 198, and a PWM calculator 199.

[0021] Multiplier 190 takes as input a DC voltage detection value 500 output by DC voltage detection sensor 15 and a DC current detection value 501 output by DC current detection sensor 16, multiplies them together to calculate the output power of the panel, and outputs the result as panel output detection value 504.

[0022] The MPPT controller 191 receives as input the DC voltage detection value 500 output by the DC voltage detection sensor 15 and the DC current detection value 501 output by the DC current detection sensor 16, and calculates a DC voltage command for the AC / DC converter 13 using MPPT (maximum power point tracking) control so that the power output by the solar panel 11 is maximized, and outputs the result as a DC voltage command value 610.

[0023] A subtractor 192 receives the DC voltage detection value 500 output by the DC voltage detection sensor 15 and the DC voltage command value 610 output by the MPPT controller 191 as inputs, and outputs the difference between them.

[0024] The proportional-plus-integral controller 193 receives the difference value output by the subtractor 192 and outputs an active power correction command value 612 by proportional-plus-integral calculation so that the difference value becomes zero.

[0025] The adder 194 receives the panel output detection value output by the multiplier 190 and the active power correction command value 612 output by the proportional-integral controller 193 as inputs, and outputs the sum of these as the active power command value 611 .

[0026] The active power calculator 195 receives as input the AC voltage detection value 502 output by the AC voltage detection sensor 17 and the AC current detection value 503 output by the AC current detection sensor 18, and outputs the active power output by the AC / DC converter 13 to the AC side as an active power detection value 510.

[0027] The frequency command calculator 196 receives the active power command value 611 output by the adder 194 and the active power detection value 510 output by the active power calculator 195 as inputs, and outputs a frequency command value 630 for the AC voltage that the AC / DC converter 13 outputs to the AC side.

[0028] The integrator 197 receives the frequency command value 630 output from the frequency command calculator 196 and outputs a phase command value 631 of the AC voltage that the AC / DC converter 13 outputs to the AC side through integration.

[0029] The voltage command calculator 198 receives as input a voltage amplitude command value 632 of the AC voltage that the AC / DC converter 13 outputs to the AC side and a phase command value 631 that the integrator 197 outputs, and outputs an output voltage command value 634 of the AC voltage that the AC / DC converter 13 outputs to the AC side.

[0030] The PWM calculator 199 receives the output voltage command value 634 output by the voltage command calculator 198 as an input, and outputs a pulse signal 700 that drives the switching elements that constitute the AC / DC converter 13 by PWM calculation.

[0031] 2 shows an example of the output characteristics of solar panel 11. With the horizontal axis representing the panel voltage and the vertical axis representing the panel output, the output characteristics of solar panel 11 generally have an upwardly convex characteristic, and the power generated by solar panel 11 can be maximized by operating at the maximum power point where the panel output is at its maximum. Therefore, MPPT controller 191 calculates the panel voltage at the maximum power point and outputs this panel voltage as DC voltage command value 610. By controlling the panel voltage in accordance with such DC voltage command value 610, the power generated can be maximized.

[0032] FIG. 3 shows an example of the output characteristics of the frequency command calculator 196. With the horizontal axis representing the active power detection value 510 output by the AC / DC converter 13 to the AC side and the vertical axis representing the frequency command value 630 of the voltage output by the AC / DC converter 13 to the AC side, the graph shows a downward drooping characteristic. When the AC / DC converter 13 outputs active power equal to the active power command value 611 to the AC side, the frequency command value 630 is set to a reference value (50 Hz or 60 Hz). On the other hand, when the AC / DC converter 13 outputs active power greater than the active power command value 611, the frequency command value 630 is set to a value smaller than the reference value, thereby reducing the phase difference between the AC end of the AC / DC converter 13 and the power grid, thereby reducing the active power output. On the other hand, when the AC power output is less than the active power command value 611, the frequency command value 630 is set to a value larger than the reference value, thereby increasing the phase difference between the AC end of the AC / DC converter 13 and the power grid, thereby increasing the active power output.

[0033] FIG. 4 shows an example of operating waveforms in the first embodiment. This case illustrates an example in which the DC voltage detection value 500 increases. When the DC voltage detection value 500 increases at time T1, the difference value output by the subtractor 192 increases, causing an increase in the active power correction command value 612 output by the proportional-integral controller 193. As a result, the active power command value 611 output by the adder 194 increases, the frequency command value 630 output by the frequency command calculator 196 increases, the frequency of the AC voltage output by the AC / DC converter 13 to the AC side increases, and the phase difference between the AC end of the AC / DC converter 13 and the power grid 2 increases, causing an increase in the active power output by the AC / DC converter 13 to the AC side. When the active power output by the AC / DC converter 13 to the AC side increases and becomes greater than the power input from the solar panel 11 to the DC side of the AC / DC converter 13, the DC voltage of the AC / DC converter 13 decreases and follows the DC voltage command value 610 at time T2.

[0034] FIG. 5 shows an example of operating waveforms in the first embodiment. This case illustrates a case where the DC voltage detection value 500 decreases. When the DC voltage detection value 500 decreases at time T1, the difference value output by the subtractor 192 decreases, causing a decrease in the active power correction command value 612 output by the proportional-integral controller 193. As a result, the active power command value 611 output by the adder 194 also decreases, causing a decrease in the frequency command value 630 output by the frequency command calculator 196. This decreases the frequency of the AC voltage output by the AC / DC converter 13 to the AC side, reducing the phase difference between the AC end of the AC / DC converter 13 and the power grid 2, thereby reducing the active power output by the AC / DC converter 13 to the AC side. When the active power output by the AC / DC converter 13 to the AC side decreases and becomes smaller than the power input from the solar panel 11 to the DC side of the AC / DC converter 13, the DC voltage of the AC / DC converter 13 increases and follows the DC voltage command value 610 at time T2.

[0035] As described above, by correcting the active power command value 611 in accordance with the deviation between the DC voltage command value 610 and the DC voltage detection value 500, the phase difference between the AC end of the AC / DC converter 13 and the power grid 2 is corrected and the active power output by the AC / DC converter 13 is adjusted, thereby making it possible to control the DC voltage of the AC / DC converter 13 to a desired value.

[0036] This makes it possible to stabilize the DC voltage, and by controlling the DC voltage to the DC voltage command value 610 given by the MPPT control, it is also possible to maximize the power generated by the solar panel 11. [Example]

[0037] 6 shows the configuration of a second embodiment of a photovoltaic power conversion device as an example of application of the present invention. The photovoltaic power conversion device 3 of this embodiment is connected to a three-phase AC power system 2. The photovoltaic power conversion device 3 has a solar panel 11, a diode 12, an AC / DC converter 13, a DC capacitor 14, a DC voltage detection sensor 15, a DC current detection sensor 16, an AC voltage detection sensor 17, an AC current detection sensor 18, and a controller 20.

[0038] Solar panel 11 is connected to the DC side of AC / DC converter 13 via diode 12, and the AC side of AC / DC converter 13 is connected to three-phase AC power grid 2. DC capacitor 14 is connected to the DC side of AC / DC converter 13, and DC voltage detection sensor 15 detects the DC voltage of DC capacitor 14. DC current detection sensor 16 is connected between diode 12 and AC / DC converter 13, and detects the DC current output from solar panel 11. AC voltage detection sensor 17 is connected to the AC side of AC / DC converter 13, and detects the three-phase AC voltage on the AC side of AC / DC converter 13. AC current detection sensor 18 is connected between AC / DC converter 13 and power grid 2, and detects the three-phase AC current output from AC / DC converter 13. The controller 20 receives as input the DC voltage detection value 500 output by the DC voltage detection sensor 15, the DC current detection value 501 output by the DC current detection sensor 16, the AC voltage detection value 502 output by the AC voltage detection sensor 17, and the AC current detection value 503 output by the AC current detection sensor 18, and outputs a pulse signal 700 that drives the switching elements that make up the AC / DC converter 13.

[0039] The controller 20 has a multiplier 190, an MPPT controller 191, a subtractor 192, a proportional integral controller 193, an adder 194, an active power calculator 195, a frequency command calculator 196, an integrator 197, a voltage command calculator 198, and a PWM calculator 199.

[0040] The multiplier 190 takes as input the DC voltage detection value 500 output by the DC voltage detection sensor 15 and the DC current detection value 501 output by the DC current detection sensor 16, multiplies them together to calculate the output power of the panel, and outputs the result as an active power command value 611.

[0041] The MPPT controller 191 receives as input the DC voltage detection value 500 output by the DC voltage detection sensor 15 and the DC current detection value 501 output by the DC current detection sensor 16, and calculates a DC voltage command for the AC / DC converter 13 using MPPT (maximum power point tracking) control so that the power output by the solar panel 11 is maximized, and outputs the result as a DC voltage command value 610.

[0042] A subtractor 192 receives the DC voltage detection value 500 output by the DC voltage detection sensor 15 and the DC voltage command value 610 output by the MPPT controller 191 as inputs, and outputs the difference between them.

[0043] The proportional-plus-integral controller 193 receives the difference value output by the subtractor 192 and outputs a frequency correction command value 640 by proportional-plus-integral calculation so that the difference value becomes zero.

[0044] The active power calculator 195 receives as input the AC voltage detection value 502 output by the AC voltage detection sensor 17 and the AC current detection value 503 output by the AC current detection sensor 18, and outputs the active power output by the AC / DC converter 13 to the AC side as an active power detection value 510.

[0045] The frequency command calculator 196 receives the active power command value 611 output by the multiplier 190 and the active power detection value 510 output by the active power calculator 195 as inputs, and outputs a frequency command value 630 for the AC voltage that the AC / DC converter 13 outputs to the AC side.

[0046] The adder 194 receives the frequency command value 630 output by the frequency command calculator 196 and the frequency correction command value 640 output by the proportional-integral controller 193 as inputs, and outputs the sum of these as the frequency command value 630 .

[0047] The integrator 197 receives the frequency command value 630 output by the adder 194 and outputs a phase command value 631 of the AC voltage that the AC / DC converter 13 outputs to the AC side by performing an integration operation.

[0048] The voltage command calculator 198 receives as input a voltage amplitude command value 632 of the AC voltage that the AC / DC converter 13 outputs to the AC side and a phase command value 631 that the integrator 197 outputs, and outputs an output voltage command value 634 of the AC voltage that the AC / DC converter 13 outputs to the AC side.

[0049] The PWM calculator 199 receives the output voltage command value 634 output by the voltage command calculator 198 as an input, and outputs a pulse signal 700 that drives the switching elements that constitute the AC / DC converter 13 by PWM calculation.

[0050] FIG. 7 shows an example of operating waveforms in the second embodiment. This case illustrates an example in which the detected DC voltage value 500 increases. When the detected DC voltage value 500 increases at time T1, the difference value output by the subtractor 192 increases, causing the frequency correction command value 640 output by the proportional-integral controller 193 to increase. As a result, the frequency command value 630 output by the adder 194 increases, the frequency of the AC voltage output by the AC / DC converter 13 to the AC side increases, and the phase difference between the AC end of the AC / DC converter 13 and the power grid 2 increases, thereby increasing the active power output by the AC / DC converter 13 to the AC side. When the active power output by the AC / DC converter 13 to the AC side increases and becomes greater than the power input from the solar panel 11 to the DC side of the AC / DC converter 13, the DC voltage of the AC / DC converter 13 decreases and follows the DC voltage command value 610 at time T2.

[0051] FIG. 8 shows an example of operating waveforms in the second embodiment. This case illustrates a case where the detected DC voltage value 500 decreases. When the detected DC voltage value 500 decreases at time T1, the difference value output by the subtractor 192 decreases, causing a decrease in the frequency correction command value 640 output by the proportional-integral controller 193. As a result, the frequency command value 630 output by the adder 194 decreases, the frequency of the AC voltage output by the AC / DC converter 13 to the AC side decreases, and the phase difference between the AC end of the AC / DC converter 13 and the power grid 2 decreases, causing a decrease in the active power output by the AC / DC converter 13 to the AC side. When the active power output by the AC / DC converter 13 to the AC side decreases and becomes smaller than the power input from the solar panel 11 to the DC side of the AC / DC converter 13, the DC voltage of the AC / DC converter 13 increases and follows the DC voltage command value 610 at time T2.

[0052] As described above, by correcting frequency command value 630 in accordance with the deviation between DC voltage command value 610 and DC voltage detection value 500, the phase difference between the AC end of AC / DC converter 13 and power grid 2 is corrected and the active power output by AC / DC converter 13 is adjusted, thereby making it possible to control the DC voltage of AC / DC converter 13 to a desired value.

[0053] This makes it possible to stabilize the DC voltage, and by controlling the DC voltage to the DC voltage command value 610 given by the MPPT control, it is also possible to maximize the power generated by the solar panel 11. [Example]

[0054] 9 shows the configuration of a third embodiment of a photovoltaic power generation power converter as an example of application of the present invention. Photovoltaic power generation power converter 4 of this embodiment is connected to a three-phase AC power system 2. Photovoltaic power generation power converter 4 has a solar panel 11, a diode 12, a DC / DC converter 21, a DC capacitor 14, a DC voltage detection sensor 15, a DC current detection sensor 16, an AC / DC converter 13, a DC capacitor 22, a DC voltage detection sensor 23, an AC voltage detection sensor 17, an AC current detection sensor 18, and a controller 24.

[0055] Solar panel 11 is connected to the primary side of DC / DC converter 21 via diode 12, the secondary side of DC / DC converter 21 is connected to the DC side of AC / DC converter 13, and the AC side of AC / DC converter 13 is connected to three-phase AC power grid 2. DC capacitor 14 is connected to the primary side of DC / DC converter 21, and DC voltage detection sensor 15 detects the DC voltage of DC capacitor 14. DC current detection sensor 16 is connected between diode 12 and DC / DC converter 21 and detects the DC current output from solar panel 11. DC capacitor 22 is connected to the DC side of AC / DC converter 13, and DC voltage detection sensor 23 detects the DC voltage of DC capacitor 22. AC voltage detection sensor 17 is connected to the AC side of AC / DC converter 13 and detects the three-phase AC voltage on the AC side of AC / DC converter 13. AC current detection sensor 18 is connected between AC / DC converter 13 and power grid 2 and detects the three-phase AC current output from AC / DC converter 13. The controller 24 receives as input the primary side DC voltage detection value 520 output by the DC voltage detection sensor 15, the primary side DC current detection value 521 output by the DC current detection sensor 16, the secondary side DC voltage detection value 522 output by the DC voltage detection sensor 23, the AC voltage detection value 502 output by the AC voltage detection sensor 17, and the AC current detection value 503 output by the AC current detection sensor 18, and outputs a pulse signal 700 for driving the switching elements that constitute the AC / DC converter 13 and a pulse signal 700 for driving the switching elements that constitute the DC / DC converter 21.

[0056] The controller 24 has a multiplier 190, an MPPT controller 191, a subtractor 192, a proportional integral controller 193, an adder 194, an active power calculator 195, a frequency command calculator 196, an integrator 197, a voltage command calculator 198, a PWM calculator 199, a primary side voltage controller 200, and a PWM calculator 201.

[0057] Multiplier 190 takes as input the primary side DC voltage detection value 520 output by DC voltage detection sensor 15 and the primary side DC current detection value 521 output by DC current detection sensor 16, multiplies them together to calculate the output power of the panel, and outputs the result as the panel output detection value.

[0058] The MPPT controller 191 receives as input the primary side DC voltage detection value 520 output by the DC voltage detection sensor 15 and the primary side DC current detection value 521 output by the DC current detection sensor 16, and calculates a primary side DC voltage command for the DC / DC converter 21 by MPPT (maximum power point tracking) control so that the power output by the solar panel 11 is maximized, and outputs the result as a primary side DC voltage command value 641.

[0059] The subtractor 192 receives the secondary side DC voltage detection value 522 output by the DC voltage detection sensor 23 and a predetermined secondary side DC voltage command value 642 as inputs, and outputs the difference between them.

[0060] The proportional-plus-integral controller 193 receives the difference value output by the subtractor 192 and outputs an active power correction command value 612 by proportional-plus-integral calculation so that the difference value becomes zero.

[0061] The adder 194 receives the panel output detection value output by the multiplier 190 and the active power correction command value 612 output by the proportional-integral controller 193 as inputs, and outputs the sum of these as the active power command value 611 .

[0062] The active power calculator 195 receives as input the AC voltage detection value 502 output by the AC voltage detection sensor 17 and the AC current detection value 503 output by the AC current detection sensor 18, and outputs the active power output by the AC / DC converter 13 to the AC side as an active power detection value 510.

[0063] The frequency command calculator 196 receives the active power command value 611 output by the adder 194 and the active power detection value 510 output by the active power calculator 195 as inputs, and outputs a frequency command value 630 for the AC voltage that the AC / DC converter 13 outputs to the AC side.

[0064] The integrator 197 receives the frequency command value 630 output from the frequency command calculator 196 and outputs a phase command value 631 of the AC voltage that the AC / DC converter 13 outputs to the AC side through integration.

[0065] The voltage command calculator 198 receives as input a voltage amplitude command value 632 of the AC voltage that the AC / DC converter 13 outputs to the AC side and a phase command value 631 that the integrator 197 outputs, and outputs an output voltage command value 634 of the AC voltage that the AC / DC converter 13 outputs to the AC side.

[0066] The PWM calculator 199 receives the output voltage command value 634 output by the voltage command calculator 198 as an input, and outputs a pulse signal 700 that drives the switching elements that constitute the AC / DC converter 13 by PWM calculation.

[0067] The primary side voltage controller 200 receives as input a primary side DC voltage detection value 520 output by the DC voltage detection sensor 15, a primary side DC voltage command value 641 output by the MPPT controller 191, and a secondary side DC voltage detection value 522 output by the DC voltage detection sensor 23, and calculates a duty ratio command value 650 for the DC / DC converter 21 so that the primary side DC voltage of the DC / DC converter 21 follows the primary side DC voltage command value 641. The PWM calculator 201 receives as input the duty ratio command value 650 output by the primary side voltage controller 200, and outputs a pulse signal 701 that drives the switching elements that constitute the DC / DC converter 21 by PWM calculation.

[0068] FIG. 10 shows an example of operating waveforms in the third embodiment. This case illustrates an example in which the secondary-side DC voltage detection value 522 increases. When the secondary-side DC voltage detection value 522 increases at time T1, the difference value output by the subtractor 192 increases, and the active power correction command value 612 output by the proportional-integral controller 193 increases. As a result, the active power command value 611 output by the adder 194 increases, the frequency command value 630 output by the frequency command calculator 196 increases, the frequency of the AC voltage output by the AC / DC converter 13 to the AC side increases, and the phase difference between the AC end of the AC / DC converter 13 and the power grid 2 increases, thereby increasing the active power output by the AC / DC converter 13 to the AC side. When the active power output by the AC / DC converter 13 to the AC side increases and becomes greater than the power input from the DC / DC converter 21 to the DC side of the AC / DC converter 13, the DC voltage of the AC / DC converter 13 decreases and follows the DC voltage command value 610 at time T2.

[0069] FIG. 11 shows an example of operating waveforms in the third embodiment. This case illustrates a case where the secondary-side DC voltage detection value 522 decreases. When the secondary-side DC voltage detection value 522 decreases at time T1, the difference value output by the subtractor 192 decreases, causing a decrease in the active power correction command value 612 output by the proportional-integral controller 193. As a result, the active power command value 611 output by the adder 194 decreases, the frequency command value 630 output by the frequency command calculator 196 decreases, the frequency of the AC voltage output by the AC / DC converter 13 to the AC side decreases, and the phase difference between the AC end of the AC / DC converter 13 and the power grid 2 decreases, causing a decrease in the active power output by the AC / DC converter 13 to the AC side. When the active power output by the AC / DC converter 13 to the AC side decreases and becomes smaller than the power input from the DC / DC converter 21 to the DC side of the AC / DC converter 13, the DC voltage of the AC / DC converter 13 increases and follows the DC voltage command value 610 at time T2.

[0070] As described above, even in a power conversion device constituted by an AC / DC converter and a DC / DC converter, by correcting the active power command value 611 in accordance with the deviation between the DC voltage command value 610 and the DC voltage detection value 500, the phase difference between the AC end of the AC / DC converter 13 and the power grid 2 is corrected and the active power output by the AC / DC converter 13 is adjusted, thereby making it possible to control the DC voltage of the AC / DC converter 13 to a desired value.

[0071] This makes it possible to stabilize the DC voltage, and by controlling the DC voltage to the DC voltage command value 610 given by the MPPT control, it is also possible to maximize the power generated by the solar panel 11. [Example]

[0072] 12 shows the configuration of a fourth embodiment of a photovoltaic power generation power converter as an example of application of the present invention. Photovoltaic power generation power converter 5 of this embodiment is connected to a three-phase AC power grid 2. Photovoltaic power generation power converter 5 has a solar panel 11, a diode 12, a DC / DC converter 21, a DC capacitor 14, a DC voltage detection sensor 15, a DC current detection sensor 16, an AC / DC converter 13, a DC capacitor 22, a DC voltage detection sensor 23, an AC voltage detection sensor 17, an AC current detection sensor 18, and a controller 25.

[0073] Solar panel 11 is connected to the primary side of DC / DC converter 21 via diode 12, the secondary side of DC / DC converter 21 is connected to the DC side of AC / DC converter 13, and the AC side of AC / DC converter 13 is connected to three-phase AC power grid 2. DC capacitor 14 is connected to the primary side of DC / DC converter 21, and DC voltage detection sensor 15 detects the DC voltage of DC capacitor 14. DC current detection sensor 16 is connected between diode 12 and DC / DC converter 21 and detects the DC current output from solar panel 11. DC capacitor 22 is connected to the DC side of AC / DC converter 13, and DC voltage detection sensor 23 detects the DC voltage of DC capacitor 22. AC voltage detection sensor 17 is connected to the AC side of AC / DC converter 13 and detects the three-phase AC voltage on the AC side of AC / DC converter 13. AC current detection sensor 18 is connected between AC / DC converter 13 and power grid 2 and detects the three-phase AC current output from AC / DC converter 13. Controller 25 receives as input primary side DC voltage detection value 520 output by DC voltage detection sensor 15, primary side DC current detection value 521 output by DC current detection sensor 16, secondary side DC voltage detection value 522 output by DC voltage detection sensor 23, AC voltage detection value 502 output by AC voltage detection sensor 17, and AC current detection value 503 output by AC current detection sensor 18, and outputs pulse signal 700 for driving the switching elements that constitute AC / DC converter 13 and pulse signal 700 for driving the switching elements that constitute DC / DC converter 21.

[0074] The controller 25 has a multiplier 190, an MPPT controller 191, a subtractor 192, a proportional integral controller 193, an adder 194, an active power calculator 195, a frequency command calculator 196, an integrator 197, a voltage command calculator 198, a PWM calculator 199, a primary side voltage controller 200, and a PWM calculator 201.

[0075] The multiplier 190 receives as input the primary side DC voltage detection value 520 output by the DC voltage detection sensor 15 and the primary side DC current detection value 521 output by the DC current detection sensor 16, multiplies them together to calculate the output power of the panel, and outputs the result as an active power command value 611.

[0076] The MPPT controller 191 receives as input the primary side DC voltage detection value 520 output by the DC voltage detection sensor 15 and the primary side DC current detection value 521 output by the DC current detection sensor 16, and calculates a primary side DC voltage command for the DC / DC converter 21 by MPPT (maximum power point tracking) control so that the power output by the solar panel 11 is maximized, and outputs the result as a primary side DC voltage command value 641.

[0077] The subtractor 192 receives the secondary side DC voltage detection value 522 output by the DC voltage detection sensor 23 and a predetermined secondary side DC voltage command value 642 as inputs, and outputs the difference between them.

[0078] The proportional-plus-integral controller 193 receives the difference value output by the subtractor 192 and outputs a frequency correction command value 640 by proportional-plus-integral calculation so that the difference value becomes zero.

[0079] The active power calculator 195 receives as input the AC voltage detection value 502 output by the AC voltage detection sensor 17 and the AC current detection value 503 output by the AC current detection sensor 18, and outputs the active power output by the AC / DC converter 13 to the AC side as an active power detection value 510.

[0080] The frequency command calculator 196 receives the active power command value 611 output by the multiplier 190 and the active power detection value 510 output by the active power calculator 195 as inputs, and outputs a frequency command value 630 for the AC voltage that the AC / DC converter 13 outputs to the AC side.

[0081] The adder 194 receives the frequency command value 630 output by the frequency command calculator 196 and the frequency correction command value 640 output by the proportional-integral controller 193 as inputs, and outputs the sum of these as the frequency command value 630 .

[0082] The integrator 197 receives the frequency command value 630 output by the adder 194 and outputs a phase command value 631 of the AC voltage that the AC / DC converter 13 outputs to the AC side by performing an integration operation.

[0083] The voltage command calculator 198 receives as input a voltage amplitude command value 632 of the AC voltage that the AC / DC converter 13 outputs to the AC side and a phase command value 631 that the integrator 197 outputs, and outputs an output voltage command value 634 of the AC voltage that the AC / DC converter 13 outputs to the AC side.

[0084] The PWM calculator 199 receives the output voltage command value 634 output by the voltage command calculator 198 as an input, and outputs a pulse signal 700 that drives the switching elements that constitute the AC / DC converter 13 by PWM calculation.

[0085] The primary side voltage controller 200 receives as input a primary side DC voltage detection value 520 output by the DC voltage detection sensor 15, a primary side DC voltage command value 641 output by the MPPT controller 191, and a secondary side DC voltage detection value 522 output by the DC voltage detection sensor 23, and calculates a duty ratio command value 650 for the DC / DC converter 21 so that the primary side DC voltage of the DC / DC converter 21 follows the primary side DC voltage command value 641. The PWM calculator 201 receives as input the duty ratio command value 650 output by the primary side voltage controller 200, and outputs a pulse signal 701 that drives the switching elements that constitute the DC / DC converter 21 by PWM calculation.

[0086] FIG. 13 shows an example of operating waveforms in the fourth embodiment. This case illustrates an example in which the secondary-side DC voltage detection value 522 increases. When the secondary-side DC voltage detection value 522 increases at time T1, the difference value output by the subtractor 192 increases, and the frequency correction command value 640 output by the proportional-integral controller 193 increases. As a result, the frequency command value 630 output by the adder 194 increases, the frequency of the AC voltage output by the AC / DC converter 13 to the AC side increases, and the phase difference between the AC end of the AC / DC converter 13 and the power grid 2 increases, thereby increasing the active power output by the AC / DC converter 13 to the AC side. When the active power output by the AC / DC converter 13 to the AC side increases and becomes greater than the power input from the DC / DC converter 21 to the DC side of the AC / DC converter 13, the DC voltage of the AC / DC converter 13 decreases and follows the DC voltage command value 610 at time T2.

[0087] FIG. 14 shows an example of operating waveforms in the fourth embodiment. This case illustrates a case where the secondary-side DC voltage detection value 522 decreases. When the secondary-side DC voltage detection value 522 decreases at time T1, the difference value output by the subtractor 192 decreases, and the frequency correction command value 640 output by the proportional-integral controller 193 decreases. As a result, the frequency command value 630 output by the adder 194 decreases, the frequency of the AC voltage output by the AC / DC converter 13 to the AC side decreases, and the phase difference between the AC end of the AC / DC converter 13 and the power grid 2 decreases, thereby reducing the active power output by the AC / DC converter 13 to the AC side. When the active power output by the AC / DC converter 13 to the AC side decreases and becomes smaller than the power input from the DC / DC converter 21 to the DC side of the AC / DC converter 13, the DC voltage of the AC / DC converter 13 increases and follows the DC voltage command value 610 at time T2.

[0088] As described above, even in a power conversion device constituted by an AC / DC converter and a DC / DC converter, by correcting frequency command value 630 in accordance with the deviation between DC voltage command value 610 and DC voltage detection value 500, the phase difference between the AC end of AC / DC converter 13 and power grid 2 is corrected and the active power output by AC / DC converter 13 is adjusted, thereby making it possible to control the DC voltage of AC / DC converter 13 to a desired value.

[0089] This makes it possible to stabilize the DC voltage, and by controlling the DC voltage to the DC voltage command value 610 given by the MPPT control, it is also possible to maximize the power generated by the solar panel 11. [Example]

[0090] FIG. 15 shows the configuration of a fifth embodiment of a photovoltaic power conversion device as an example of application of the present invention. This embodiment includes an operating status output device 26 that outputs the operating status of AC / DC converter 13 constituting the photovoltaic power conversion device. Operating status output device 26 receives inputs of detected DC voltage 500 output by DC voltage detection sensor 15, detected DC current 501 output by DC current detection sensor 16, detected AC voltage 502 output by AC voltage detection sensor 17, and detected AC current 503 output by AC current detection sensor 18, and outputs this information as well as information such as power, effective voltage, effective current, and frequency that can be calculated from this information. Outputting this information allows the user to grasp the operating status of the photovoltaic power conversion device. [Example]

[0091] FIG. 16 shows the configuration of a sixth embodiment of a photovoltaic power conversion apparatus as an example of application of the present invention. This embodiment includes an operating status output unit 27 that outputs the operating status of the AC / DC converter 13 and DC / DC converter 21 that constitute the photovoltaic power conversion apparatus. The operating status output unit 27 receives inputs including a primary-side DC voltage detection value 520 output by the DC voltage detection sensor 15, a primary-side DC current detection value 521 output by the DC current detection sensor 16, a secondary-side DC voltage detection value 522 output by the DC voltage detection sensor 23, a detected AC voltage value 502 output by the AC voltage detection sensor 17, and a detected AC current value 503 output by the AC current detection sensor 18, and outputs the inputs as well as information such as power, effective voltage, effective current, and frequency that can be calculated from the inputs. By outputting such information, the user can grasp the operating status of the photovoltaic power conversion apparatus.

[0092] The above examples illustrate the ideas and concepts of the present invention. Of course, the scope of the present invention also includes examples that are realized by combining the examples. Furthermore, as long as the disclosed ideas and concepts are used, any modifications or similar examples are also included within the scope of the present invention.

[0093] Furthermore, one example of the present invention described using the above embodiments can also be expressed as follows.

[0094] <Part 1> A power conversion device that converts DC power into AC power and outputs the AC power to a power grid, a control unit of the power conversion device calculates a frequency command of an AC voltage output by the power conversion device based on an active power command value and an active power detection value; The power conversion device calculates the active power command value from a detected value of DC power, a DC voltage command value, and a corrected active power command value calculated using as input a deviation of the detected value of DC voltage.

[0095] <Part 2> In the power conversion device described in <No. 1>, the DC voltage command is calculated from MPPT control.

[0096] <Part 3> In the power conversion device described in <Item 1>, a main circuit section of the power conversion device is configured from an AC / DC converter and a DC / DC converter.

[0097] <Part 4> The power conversion device according to any one of <Item 1> to <Item 3>, further comprising an operating state output device that outputs information obtained from a sensor provided in a main circuit section of the power conversion device.

[0098] <Part 5> The power conversion device according to any one of <Item 1> to <Item 3>, wherein the power conversion device is used as a power conversion device for photovoltaic power generation.

[0099] <Part 6> A power conversion device that converts DC power into AC power and outputs the AC power to a power grid, a control unit of the power conversion device calculates a frequency command of an AC voltage output by the power conversion device based on an active power command value and an active power detection value; the active power command value is calculated from a detected value of DC power; The power conversion device corrects the frequency command with a frequency correction command value calculated using the deviation between the DC voltage command value and the DC voltage detection value as an input.

[0100] <Part 7> <Item 6> The power conversion device according to the present invention, wherein the DC voltage command is calculated from MPPT control.

[0101] <Part 8> <Item 6> The power conversion device according to the present invention, wherein a main circuit section of the power conversion device is configured from an AC / DC converter and a DC / DC converter.

[0102] <No. 9> The power conversion device according to any one of <Item 6> to <Item 8>, further comprising an operating state output device that outputs information obtained from a sensor provided in a main circuit section of the power conversion device.

[0103] <Part 10> The power conversion device according to any one of <Item 6> to <Item 8>, wherein the power conversion device is used as a power conversion device for photovoltaic power generation. [Explanation of symbols]

[0104] 1, 3, 4, 5: Photovoltaic power generation power conversion device 2: Power system 11: Solar panels 12: Diode 13: AC / DC converter 14: DC capacitor 15: DC voltage detection sensor 16: DC current detection sensor 17: AC voltage detection sensor 18: AC current detection sensor 19, 20, 24, 25: Controller 21: DC / DC converter 22: DC capacitor 23: DC voltage detection sensor 26, 27: Operation status output device 190: Multiplier 191:MPPT controller 192: Subtractor 193: Proportional integral controller 194: Adder 195: Active power calculator 196: Frequency command calculator 197: Integrator 198: Voltage command calculator 199:PWM calculator 200: Primary side voltage regulator 201:PWM calculator 500: DC voltage detection value 501: DC current detection value 502: AC voltage detection value 503: AC current detection value 504: Panel output detection value 510: Active power detection value 520: Primary side DC voltage detection value 521: Primary side DC current detection value 522: Secondary side DC voltage detection value 610: DC voltage command value 611: Active power command value 612: Active power correction command value 630: Frequency command value 631: Phase command value 632: Voltage amplitude command value 634: Output voltage command value 640: Frequency correction command value 641: Primary side DC voltage command value 642: Secondary DC voltage command value 650: Duty ratio command value 700, 701: Pulse signal

Claims

1. A power conversion device that converts DC power into AC power and outputs the AC power to a power grid, a control unit of the power conversion device calculates a frequency command of an AC voltage output by the power conversion device based on an active power command value and an active power detection value; The power conversion device calculates the active power command value from a detected value of DC power, a DC voltage command value, and a corrected active power command value calculated using as input a deviation of the detected value of DC voltage.

2. 2. The power conversion device according to claim 1, wherein the DC voltage command is calculated from MPPT control.

3. 2. The power conversion device according to claim 1, wherein a main circuit section of said power conversion device comprises an AC / DC converter and a DC / DC converter.

4. 4. The power conversion device according to claim 1, further comprising an operating state output device for outputting information obtained from a sensor provided in a main circuit section of said power conversion device.

5. 4. The power conversion device according to claim 1, wherein the power conversion device is used as a power conversion device for photovoltaic power generation.

6. A power conversion device that converts DC power into AC power and outputs the AC power to a power grid, a control unit of the power conversion device calculates a frequency command of an AC voltage output by the power conversion device based on an active power command value and an active power detection value; the active power command value is calculated from a detected value of DC power; The power conversion device corrects the frequency command with a frequency correction command value calculated using the deviation between the DC voltage command value and the DC voltage detection value as an input.

7. 7. The power conversion device according to claim 6, wherein the DC voltage command is calculated from MPPT control.

8. 7. The power conversion device according to claim 6, wherein the main circuit section of the power conversion device comprises an AC / DC converter and a DC / DC converter.

9. 9. The power conversion device according to claim 6, further comprising an operating state output device for outputting information obtained from a sensor provided in a main circuit section of said power conversion device.

10. 9. The power conversion device according to claim 6, wherein the power conversion device is used as a power conversion device for photovoltaic power generation.

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