Power conversion device, power supply system, and control method

Abstract

To materialize a power conversion device which comprises a DC-DC converter and enables the DC-DC converter to be appropriately controlled.SOLUTION: A control portion (52) of a power conversion device includes a basic command value determination portion (521) that determines a basic command value on the basis of the output power of a solar cell panel, an output power reduction cause determination portion (525) that determines whether a reduction in output power of the solar cell panel has occurred due to output power suppression by a power conditioner, a corrected value calculation portion (526) that calculates a corrected value for correcting the basic command value, and a subtraction portion (527) that calculates a corrected command value.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a power conversion device, a power supply system including the power conversion device, and a control method for the power conversion device.

Background Art

[0002] Patent Document 1 discloses a power conversion device capable of stabilizing the operation of a power conditioner in a power supply system including a solar panel, a power conditioner, and a power storage device. The power conversion device includes a DC-DC converter and a control unit that controls the output power of the DC-DC converter. The control unit determines a command value for controlling the output power of the DC-DC converter by using, as an upper limit of the absolute value variation range, a value obtained by multiplying the change rate of the input power to the power conditioner by a coefficient greater than 0 and less than 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a power supply system as disclosed in Patent Document 1, in order to suppress the output power of the solar panel, a command to increase the input voltage may be issued from the power company to the power conditioner. Further, in MPPT (Maximum Power Point Tracking) control, when it is determined that the output voltage of the solar panel exceeds the peak of the P-V curve, control may be performed to greatly increase the output voltage to re-detect the MPPT. In such a case, the output power of the solar panel is intentionally suppressed.

[0005] However, if information indicating that the output power of the solar cell panel is intentionally suppressed is not transmitted to the control unit of the power conversion device, the control unit erroneously recognizes that the power generation amount by the solar cell panel has decreased due to a decrease in the amount of sunlight or the like. In this case, the control unit increases the output power of the DC-DC converter in order to compensate for the decrease.

[0006] Furthermore, in this case, since the power input to the power conditioner does not decrease, the power conditioner side recognizes that the output power of the solar cell panel is not suppressed. For this reason, the power conditioner further suppresses the output power of the solar cell panel, and the control unit of the power conversion device further increases the output power of the DC-DC converter, and ultimately the output power of the solar cell panel may become zero. As a result, an opportunity loss of power generation by the solar cell panel occurs.

[0007] Also, in this case, the voltage of the DC bus connecting the solar cell panel and the power storage device to the power conditioner is close to the open-circuit voltage of the solar cell panel, and a large amount of power is input to the power conditioner. For this reason, there is a possibility that the power conditioner may overheat and be damaged due to overvoltage.

[0008] One aspect of the present disclosure aims to realize a power conversion device or the like that can appropriately control a DC-DC converter.

Means for Solving the Problems

[0009] In order to solve the above problems, a power conversion device according to an aspect of the present disclosure is connected to a DC bus that connects a solar panel and a power conditioner, and performs charging from the DC bus to a power storage device and discharging from the power storage device to the DC bus. The power conversion device includes a DC-DC converter and a control unit that controls the output power of the DC-DC converter. The control unit includes a basic command value determination unit that determines a basic command value for controlling the output power of the DC-DC converter based on the output power of the solar panel, an output power decrease factor determination unit that determines whether or not a decrease in the output power of the solar panel due to output power suppression by the power conditioner has occurred from the output voltage and output power of the solar panel, a correction value calculation unit that calculates a correction value for correcting the basic command value based on the history of the output power of the solar panel when it is determined that a decrease in the output power of the solar panel due to output power suppression by the power conditioner has occurred, and a subtraction unit that calculates a corrected command value by subtracting the correction value from the basic command value. The DC-DC converter is controlled based on the corrected command value.

[0010] Also, a control method for a power conversion device according to an aspect of the present disclosure is a control method for a power conversion device that is connected to a DC bus connecting a solar panel and a power conditioner, and performs charging from the DC bus to a power storage device and discharging from the power storage device to the DC bus. The power conversion device includes a DC-DC converter and a control unit that controls the output power of the DC-DC converter. The method includes a basic command value determination step of determining a basic command value for controlling the output power of the DC-DC converter based on the output power of the solar panel, an output power decrease factor determination step of determining whether or not a decrease in the output power of the solar panel due to output power suppression by the power conditioner has occurred from the output voltage and output power of the solar panel, a correction value calculation step of calculating a correction value for correcting the basic command value based on the history of the output power of the solar panel when it is determined that a decrease in the output power of the solar panel due to output power suppression by the power conditioner has occurred, and a subtraction step of calculating a corrected command value by subtracting the correction value from the basic command value, and controls the DC-DC converter based on the corrected command value.

Advantages of the Invention

[0011] According to an aspect of the present disclosure, it is possible to realize a power conversion device or the like that can appropriately control a DC-DC converter.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0013] 〔Embodiment 1〕 Hereinafter, an embodiment of the present disclosure will be described in detail.

[0014] (Power Supply System) FIG. 1 is a block diagram showing an example of the configuration of a power supply system 100 including a power conversion device 5 according to an embodiment of the present disclosure. The power supply system 100 supplies power to the power grid 200. As shown in FIG. 1, the power supply system 100 includes a solar panel 1, a power conditioner 2, a DC bus 3, a power storage device 4, and a power conversion device 5.

[0015] The solar panel 1 generates DC power according to the amount of solar radiation. The power conditioner 2 controls the power supplied from the power supply system 100 to the power grid 200. The power conditioner 2 performs, for example, MPPT control on the output power of the solar panel 1. The DC bus 3 connects the solar panel 1 and the power conditioner 2.

[0016] In addition to the above MPPT control, the power conditioner 2 can be controlled based on a command value from an electric power company that operates the power supply system 100. For example, when it is necessary to suppress the output power of the solar panel 1, the electric power company inputs a command value for suppressing the output power of the solar panel 1 to the power conditioner 2. In response to the command value, the power conditioner 2 raises the voltage of the DC bus 3 above the voltage at the MPPT point of the solar panel 1. As a result, the output power of the solar panel 1 decreases below the output power at the MPPT point regardless of the variation in the power generation amount.

[0017] In addition to this, when the power conditioner 2 determines that the output voltage of the solar panel 1 has exceeded the MPPT point, it may execute control to raise the voltage of the DC bus 3 to redetect the MPPT point. Also in this case, the output power of the solar panel 1 decreases below the output power at the MPPT point regardless of the variation in the power generation amount.

[0018] The energy storage device 4 stores power as energy internally and supplies the stored energy to the DC bus 3 by DC as needed. The energy storage device 4 is connected to the DC bus 3. DC power supplied from the solar panel 1 via the DC bus 3 is stored inside the energy storage device 4. Also, the DC power supplied from the energy storage device 4 to the DC bus 3 is supplied to the power conditioner 2.

[0019] The energy storage device 4 can be a device equipped with a secondary battery such as a lithium-ion battery, a NaS (sodium-sulfur) battery, a redox flow battery, or a lead-acid battery. However, the energy storage device 4 is not limited to a device equipped with a secondary battery. As the energy storage device 4, any unit having a function of storing electrical energy, such as a capacitor, a superconducting power storage unit, a flywheel type power storage unit, or a compressed air type power storage unit, can be used.

[0020] The power conversion device 5 is connected to the DC bus 3 and performs charging from the DC bus 3 to the energy storage device 4 and discharging from the energy storage device 4 to the DC bus 3. The power conversion device 5 is disposed between the DC bus 3 and the energy storage device 4 and converts the voltage of the power supplied from one of the DC bus 3 and the energy storage device 4 to the other. The power conversion device 5 includes a DC-DC converter 51, a control unit 52, a storage unit 53, an ammeter 54, and a voltmeter 55.

[0021] Based on the command value input from the control unit 52, the DC-DC converter 51 converts the voltage of the power input from the DC bus 3 and outputs it to the energy storage device 4, or converts the voltage of the power input from the energy storage device 4 and outputs it to the DC bus 3. In the following description, regarding the output power of the DC-DC converter 51, the direction from the DC bus 3 to the energy storage device 4 is defined as positive, and the direction from the energy storage device 4 to the DC bus 3 is defined as negative.

[0022] The control unit 52 controls the output power of the DC-DC converter 51 by inputting a command value determined based on the output current and output voltage of the solar cell panel 1 to the DC-DC converter 51. The specific configuration of the control unit 52 will be described later.

[0023] The storage unit 53 is a storage device that stores information necessary for the control unit 52 to determine the command value. The storage unit 53 may store, for example, a program for determining the command value input to the DC-DC converter 51. However, in the power conversion device 5, the storage unit 53 is not essential. Instead of including the storage unit 53, the power conversion device 5 may be communicably connected to an external storage device wirelessly or wired.

[0024] The ammeter 54 outputs a signal corresponding to the output current from the solar cell panel 1. The voltmeter 55 outputs a signal corresponding to the output voltage from the solar cell panel 1. The ammeter 54 and the voltmeter 55 are provided on the side of the solar cell panel 1 rather than the point on the DC bus 3 where the energy storage device 4 and the power conversion device 5 are connected.

[0025] However, the ammeter 54 and the voltmeter 55 are not essential components of the power conversion device 5. For example, the control unit 52 may acquire the output current and output voltage of the solar panel 1 from an ammeter and a voltmeter that are not components of the power conversion device 5 and are provided on the DC bus 3.

[0026] (Control unit) FIG. 2 is a block diagram showing the configuration of the main part of the control unit 52. The control unit 52 repeatedly determines a command value for the output power of the DC-DC converter 51 at regular time intervals. As shown in FIG. 2, the control unit 52 includes a basic command value determination unit 521, a multiplication unit 522, a power recording unit 523, a voltage recording unit 524, an output power reduction factor determination unit 525, a correction value calculation unit 526, and a subtraction unit 527.

[0027] The basic command value determination unit 521 determines a basic command value for the command value input to the DC-DC converter 51. The specific configuration of the basic command value determination unit 521 will be described later with reference to FIG. 3.

[0028] The multiplication unit 522 calculates the output power of the solar panel 1 by multiplying the output current and output voltage of the solar panel 1. The power recording unit 523 stores the output power of the solar panel 1 in the storage unit 53. The voltage recording unit 524 stores the output voltage of the solar panel 1 in the storage unit 53.

[0029] The output power reduction factor determination unit 525 determines whether or not there is a reduction in the output power of the solar panel 1 due to the output power suppression by the power conditioner 2 from the output voltage and output power of the solar panel 1. The output power reduction factor determination unit 525 determines that there is a reduction in the output power of the solar panel 1 due to the output power suppression by the power conditioner 2 if both of the following equations (1) and (2) are satisfied. ·P0 - P1 ≦ -ΔPmppt (1) ·V0 - V1 ≧ ΔVth (2) In Equations (1) and (2), V1 is the output voltage of the current solar cell panel 1, and V0 is the output voltage of the solar cell panel 1 when the control unit 52 last determined the command value. Also, P1 is the output power of the current solar cell panel 1, and P0 is the output power of the solar cell panel 1 when the control unit 52 last determined the command value.

[0030] In Equation (1), ΔPmppt is the step width for varying the power in the output power control by the power conditioner 2. In Equation (2), ΔVth is the threshold value for determining the cause of the output power reduction. When Equations (1) and (2) are satisfied, it is considered that the output power of the solar cell panel 1 has decreased due to the output power suppression by the power conditioner 2.

[0031] When it is determined that the output power of the solar cell panel 1 has decreased due to the output power suppression by the power conditioner 2, the correction value calculation unit 526 calculates a correction value for correcting the basic command value based on the history of the output power of the solar cell panel 1. Specifically, the correction value calculation unit 526 calculates, as the correction value, the difference value obtained by subtracting the current value from the maximum value of the output power of the solar cell panel 1 within a period equal to the suppression period ending at the current time. The suppression period means the period from the start to the end of the output power suppression by the power conditioner 2.

[0032] When considering the control in which the power conditioner 2 suppresses the output power of the solar cell panel 1 based on a command from an electric power company, for example, the length of the specific suppression period may be about 1 hour. Also, when considering only the control for redetecting the MPPT point without considering the suppression of the output power of the solar cell panel 1 based on a command from an electric power company, it may be at most about 1 minute.

[0033] In this case, the maximum value of the output power of the solar panel 1 within a period equal to the suppression period, with the current time at the end, is the output power in the unsuppressed state before the output power suppression by the power conditioner 2. Therefore, the correction value calculated by the correction value calculation unit 526 is equal to the amount of decrease in the output power of the solar panel 1 due to the output power suppression by the power conditioner 2.

[0034] The subtraction unit 527 calculates a corrected command value by subtracting the correction value calculated by the correction value calculation unit 526 from the basic command value determined by the basic command value determination unit 521. The control unit 52 controls the DC-DC converter 51 based on the corrected command value.

[0035] In Embodiment 1, as described above, the correction value calculated by the correction value calculation unit 526 is equal to the amount of decrease in the output power of the solar panel 1 due to the output power suppression by the power conditioner 2. Therefore, the corrected command value is the value obtained by subtracting the output power of the DC-DC converter 51 for compensating the output power of the solar panel 1 that has decreased due to the output power suppression by the power conditioner 2 from the basic command value. Thus, when the cause of the decrease in the output power of the solar panel 1 is the output power suppression by the power conditioner 2, the output power of the DC-DC converter 51 is a value that does not compensate for the decrease in the output power of the solar panel 1.

[0036] (Basic Command Value Determination Unit) FIG. 3 is a block diagram showing an example of the configuration of the basic command value determination unit 521 in FIG. 2. However, the configuration of the basic command value determination unit 521 is not limited to that shown in FIG. 3, and it may have a configuration for determining a command value in a general power conversion device. In the example shown in FIG. 3, the basic command value determination unit 521 includes a multiplication unit 521a, a first subtraction unit 521b, a change rate calculation unit 521c, a second subtraction unit 521d, and a basic command value calculation unit 521e.

[0037] The multiplication unit 521a outputs a signal obtained by multiplying the output current and the output voltage from the solar panel 1. The output of the multiplication unit 521a indicates the output power from the solar panel 1.

[0038] The first subtraction unit 521b outputs a signal obtained by subtracting the current output power of the DC-DC converter 51 from the output of the multiplication unit 521a. The output of the first subtraction unit 521b indicates the input power to the power conditioner 2. That is, the first subtraction unit 521b calculates, as the input power to the power conditioner 2, a value obtained by subtracting the output power of the DC-DC converter 51 from the output power of the solar panel 1.

[0039] The change rate calculation unit 521c calculates, as the change rate of the input power to the power conditioner 2, the absolute value of the fluctuation range per unit time of the input power to the power conditioner 2. It can be said that the change rate indicates the MPPT characteristics of the power conditioner 2.

[0040] Specifically, the change rate calculation unit 521c calculates the absolute value ΔP1 of the fluctuation range of the output of the current first subtraction unit 521b with respect to the output of the first subtraction unit 521b when the previous command value was determined. Also, the change rate calculation unit 521c calculates the length Δt of the period from the time when the first subtraction unit 521b output the previous signal to the time when the current signal is output. Further, the change rate calculation unit 521c calculates the change rate ΔP1 / Δt of the input power to the power conditioner 2 during the period from the time when the first subtraction unit 521b output the previous signal to the time when the current signal is output.

[0041] The second subtraction unit 521d outputs a signal obtained by subtracting the output of the multiplication unit 521a from a predetermined input power target value for the power conditioner 2. The output of the second subtraction unit 521d indicates the basic value of the command value for controlling the output power of the DC-DC converter 51.

[0042] The basic command value calculation unit 521e determines a command value for controlling the output power of the DC-DC converter 51 by using, as the upper limit of the absolute value of the fluctuation range of the command value for controlling the output power of the DC-DC converter 51, a value obtained by multiplying a coefficient greater than 0 and less than 1 by the change rate ΔP1 / Δt. Specifically, the basic command value calculation unit 521e calculates an update rate ΔP2 / Δt by multiplying the change rate ΔP1 / Δt indicated by the output from the change rate calculation unit 52c by a coefficient greater than 0 and less than 1. The coefficient may be, for example, 0.3, but is not limited thereto.

[0043] The basic command value calculation unit 521e sets the value of the update rate as the upper limit of the absolute value of the fluctuation range of the command value output to the DC-DC converter 51. Specifically, the basic command value calculation unit 521e determines whether the difference between the basic value of the command value for controlling the output power of the DC-DC converter 51 and the previous command value is less than or equal to the value of the update rate. If the difference between the basic value of the command value and the previous command value is less than or equal to the value of the update rate, the basic command value calculation unit 521e sets the basic value of the command value as the command value as it is. If the difference between the basic value of the command value and the previous command value is not less than or equal to the value of the update rate, the basic command value calculation unit 521e sets, as the command value, a value obtained by correcting the basic value so that the difference from the previous command value is less than or equal to the value of the update rate. The basic command value determined by the basic command value calculation unit 521e defines the magnitude of the change in the next target value with respect to the current target value of the output power of the DC-DC converter 51.

[0044] (Control Method) FIG. 4 is a flowchart showing an example of a control method of the power conversion device 5 by the control unit 52. In the example shown in FIG. 4, first, the basic command value determination unit 521 determines a basic command value (S1, basic command value determination step). Next, the multiplication unit 522 calculates the output power from the solar cell panel 1 (S2). The power recording unit 523 stores the output power of the solar cell panel 1 in the storage unit 53 (S3), and the voltage recording unit 524 stores the output voltage of the solar cell panel 1 in the storage unit 53 (S4).

[0045] The output power reduction factor determination unit 525 determines whether or not there is a reduction in the output power of the solar panel 1 due to the output power suppression by the power conditioner 2 (S5, output power reduction factor determination step). When it is determined that there is a reduction in the output power of the solar panel 1 due to the output power suppression by the power conditioner 2 (YES in S5), the correction value calculation unit 526 calculates a correction value for correcting the basic command value based on the history of the output power of the solar panel 1 (S6, correction value calculation step). The subtraction unit 527 calculates a corrected command value by subtracting the correction value from the basic command value (S7, subtraction step). The control unit 52 controls the DC-DC converter 51 based on the corrected command value calculated by the above procedure.

[0046] When it is determined that there is no reduction in the output power of the solar panel 1 due to the output power suppression by the power conditioner 2 (NO in S5), the control unit 52 skips steps S6 and S7. In this case, the control unit 52 controls the DC-DC converter 51 based on the basic command value.

[0047] (Control by Conventional Power Conversion Device (1)) FIG. 5 is a timing chart showing an example of the operation of the power supply system 100 when control by a conventional power conversion device is performed. In FIG. 5, reference numeral 501 is a command value for the output power of the power conditioner 2. Reference numeral 502 is the voltage of the DC bus 3. Reference numeral 503 is the output power of the solar panel 1. Reference numeral 504 is the output power of the DC-DC converter 51. The operation example shown in FIG. 5 is an example in the case where the upper limit of the output of the DC-DC converter 51 is equal to or greater than the rated capacity of the power conditioner 2. In the following description, the command value for the output power of the power conditioner 2 is simply referred to as the command value.

[0048] Before time T11, the command value, the voltage of the DC bus 3, the output power of the solar panel 1, and the output power of the DC-DC converter 51 are all constant. At time T11, the command value starts to decrease. At this time, the power conditioner 2 increases the voltage of the DC bus 3, whereby the output power of the solar panel 1 decreases.

[0049] At this time, the conventional power conversion device increases the output power from the DC-DC converter 51 in order to compensate for the decrease in the output power of the solar panel 1. As a result, although the output power of the solar panel 1 is decreasing, the power input to the power conditioner 2 does not decrease. For this reason, the power conditioner 2 further increases the voltage of the DC bus 3. As a result, the decrease in the output power of the solar panel 1 and the increase in the output power from the DC-DC converter 51 continue.

[0050] At time T12, the command value changes from decreasing to increasing. However, since the power input to the power conditioner 2 does not decrease, the power conditioner 2 further increases the voltage of the DC bus 3. As a result, the decrease in the output power of the solar panel 1 and the increase in the output power from the DC-DC converter 51 continue further.

[0051] At time T13, the voltage of the DC bus 3 becomes approximately equal to the open-circuit voltage of the solar panel 1, and the output power of the solar panel 1 becomes 0. At this time, the power conditioner 2 stops increasing the voltage of the DC bus 3 any further. Also, at this time, the output power of the DC-DC converter 51 becomes equal to the command value.

[0052] After time T13, the conventional power conversion device increases the output power of the DC-DC converter 51 by the amount of the increase in the command value for the output power of the power conditioner 2. At time T14, the command value returns to the value before time T11 and the increase in the command value stops. At this time, the conventional power conversion device stops increasing the output power of the DC-DC converter 51.

[0053] (Control by Conventional Power Conversion Device (2)) Figure 6 is a timing chart showing another example, different from that of FIG. 5, of the operation of the power supply system 100 when control is performed by a conventional power conversion device. In FIG. 6, reference numeral 601 is a command value for the output power of the power conditioner 2. Reference numeral 602 is the voltage of the DC bus 3. Reference numeral 603 is the output power of the solar panel 1. Reference numeral 604 is the output power of the DC-DC converter 51. The operation example shown in FIG. 6 is an example in the case where the upper limit of the output power of the DC-DC converter 51 is smaller than the rated capacity of the power conditioner 2.

[0054] In the example shown in FIG. 6, the operations at times T21 and T22 are the same as the operations at times T11 and T12, respectively, in the example shown in FIG. 5. At time T23, the output power of the DC-DC converter 51 reaches the upper limit. For this reason, after time T23, the conventional power conversion device stops increasing the output power of the DC-DC converter 51. In this state, when the power conditioner 2 increases the voltage of the DC bus 3, the output power of the solar panel 1 decreases, and the power input to the power conditioner 2 also decreases. For this reason, after time T23, the power conditioner 2 starts to decrease the voltage of the DC bus 3 and increase the output power of the solar panel 1.

[0055] At time T24, the power required to compensate for the decrease in the output power of the solar panel 1 becomes smaller than the upper limit of the output power of the DC-DC converter 51. For this reason, after time T24, as the power conditioner 2 increases the output power of the solar panel 1, the conventional power conversion device decreases the output power of the DC-DC converter 51.

[0056] At time T25, the command value returns to the value before time T21. After time T25 as well, the power conditioner 2 continues to decrease the voltage of the DC bus 3 and increase the output power of the solar panel 1. Also, the conventional power conversion device decreases the output power of the DC-DC converter 51. At time T26, the voltage of the DC bus 3 returns to the value before time T21. At the same time, the output power of the solar panel 1 and the output power of the DC-DC converter 51 also return to the values before time T21.

[0057] (Control by the power conversion device of Embodiment 1) FIG. 7 is a timing chart showing an example of the operation of the power supply system 100 when the control by the power conversion device 5 is performed. In FIG. 7, reference numeral 701 is the command value. Reference numeral 702 is the voltage of the DC bus 3. Reference numeral 703 is the output power of the solar panel 1. Reference numeral 704 is the output power of the DC-DC converter 51. In FIG. 7, the period from time T31 to time T33 is the suppression period.

[0058] Before time T31, the command value, the voltage of the DC bus 3, the output power of the solar panel 1, and the output power of the DC-DC converter 51 are all constant. At time T31, the command value starts to decrease. At this time, the power conditioner 2 increases the voltage of the DC bus 3 and decreases the output power of the solar panel 1.

[0059] At this time, the basic command value increases the output power of the DC-DC converter 51 in order to compensate for the decrease in the output power of the solar panel 1. However, the output power decrease factor determination unit 525 determines that the decrease in the output power of the solar panel 1 is due to the suppression of the output by the power conditioner 2. For this reason, the corrected command value does not increase the output power of the DC-DC converter 51. Therefore, the power conversion device 5 does not increase the output power of the DC-DC converter 51 in response to the decrease in the output power of the solar panel 1. As a result, the amount of decrease in the command value and the amount of decrease in the output power of the solar panel 1 are in agreement.

[0060] At time T32, the command value changes from decreasing to increasing. Even after time T32, the output power of the DC-DC converter 51 remains constant. Therefore, after time T32, the power conditioner 2 decreases the voltage of the DC bus 3 so that as the command value increases, the output power of the solar panel 1 increases in accordance with the increase in the command value. At time T33, the command value, the voltage of the DC bus 3, and the output power of the solar panel 1 return to the values before time T31.

[0061] As described above, in the power conversion device 5, when the cause of the decrease in the output power of the solar panel 1 is the output power suppression by the power conditioner 2, the control unit 52 does not increase the output of the DC-DC converter 51. Thereby, it is possible to reduce the opportunity loss of power generation by the solar panel 1 and the possibility of overheating and destruction of the power conditioner 2 due to overvoltage. Therefore, according to the power conversion device 5, the DC-DC converter 51 can be appropriately controlled. In the above example, the suppression of the output by the power company was described. However, according to the power conversion device 5, the DC-DC converter 51 can be appropriately controlled even when re-detecting the MPPT point.

[0062] 〔Embodiment 2〕 Other embodiments of the present disclosure will be described below. For convenience of explanation, members having the same functions as the members described in the above embodiment are denoted by the same reference numerals, and the description thereof will not be repeated.

[0063] FIG. 8 is a block diagram showing an example of the configuration of a power supply system 100A including a power conversion device 5A according to Embodiment 2. As shown in FIG. 8, the power supply system 100A is different from the power supply system 100 in that it includes a power conversion device 5A instead of the power conversion device 5. The power conversion device 5A is different from the control unit 52 in that it includes a control unit 52A instead of the control unit 52.

[0064] FIG. 9 is a block diagram showing the configuration of the main part of the control unit 52A. As shown in FIG. 9, the control unit 52A is different from the correction value calculation unit 526 in that it includes a correction value calculation unit 526A instead of the correction value calculation unit 526.

[0065] The correction value calculation unit 526A is different from the correction value calculation unit 526 in the method of calculating the correction value for correcting the basic command value. The correction value calculation unit 526A calculates, as the correction value, a value obtained by multiplying a difference value obtained by subtracting the minimum value from the current value of the output voltage of the solar cell panel 1 within a period equal to the suppression period ending with the current time by a gain for converting the difference value into electric power. The suppression period is the same as that in the first embodiment. The gain is a coefficient for converting the voltage difference value into the output power of the solar cell panel 1, and is determined in consideration of the voltage-output power characteristics from the open-circuit voltage, MPPT voltage, and rated capacity of the solar cell panel 1.

[0066] In this case, the minimum value of the output voltage of the solar cell panel 1 within a period equal to the suppression period ending with the current time is the output voltage at the MPPT point before the output power suppression by the power conditioner 2. Therefore, the difference value obtained by subtracting the minimum value from the current value of the output voltage of the solar cell panel 1 is equal to the amount of decrease in the output voltage of the solar cell panel 1 due to the output power suppression by the power conditioner 2. The correction value calculated by the correction value calculation unit 526, which is calculated by multiplying the difference value by the above gain, is a value obtained by further decreasing the output power of the DC-DC converter 51 by the amount of decrease in the output voltage of the solar cell panel 1 from the value before the output power suppression by the power conditioner 2.

[0067] FIG. 10 is a timing chart showing an example of the operation of the power supply system 100A when the control by the power conversion device 5A is performed. In FIG. 10, reference numeral 1001 is a command value. Reference numeral 1002 is the voltage of the DC bus 3. Reference numeral 1003 is the output power of the solar cell panel 1. Reference numeral 1004 is the output power of the DC-DC converter 51.

[0068] Before time T41, the command value, the voltage of the DC bus 3, the output power of the solar panel 1, and the output power of the DC-DC converter 51 are all constant. At time T41, the command value starts to decrease. At this time, the power conditioner 2 increases the voltage of the DC bus 3. As a result, the output power of the solar panel 1 instantaneously increases.

[0069] However, at this time, the control unit 52A decreases the output power of the DC-DC converter 51 so as to match the decrease amount of the command value. For this reason, the power conditioner 2 immediately decreases the voltage of the DC bus 3 to the value before time T41. As a result, the output power of the solar panel 1 also increases to the value before time T41. Therefore, after time T41, the voltage of the DC bus 3 repeatedly increases slightly and decreases slightly, and becomes substantially constant. Along with this, the output power of the solar panel 1 repeatedly decreases slightly and increases slightly, and becomes substantially constant. For the sake of simplicity, in FIG. 9, these slight increases and decreases in the voltage of the DC bus 3 and the output power of the solar panel 1 do not appear, and the symbols 1002 and 1003 are shown as if they were straight lines.

[0070] At time T42, the command value changes from decreasing to increasing. After time T42, the control unit 52A increases the output power of the DC-DC converter 51 so as to match the increase of the command value. Therefore, also after time T42, the voltage of the DC bus 3 and the output power of the solar panel 1 are substantially constant.

[0071] As described above, in the power conversion device 5A, when the output power of the solar panel 1 decreases due to the suppression of the output power of the power conditioner 2, the control unit 52A decreases the output power of the DC-DC converter 51. As a result, the output power of the solar panel 1 does not substantially decrease. Therefore, the opportunity loss of power generation by the solar panel 1 is further reduced compared to the power conversion device 5 of the first embodiment. Further, since the voltage of the DC bus 3 does not substantially increase, the occurrence of an accident caused by the increase in the voltage can be prevented. Therefore, according to the power conversion device 5A, the DC-DC converter 51 can be more appropriately controlled.

[0072] 〔Example of Realization by Software〕 The functions of the power conversion devices 5 and 5A (hereinafter referred to as "devices") can be realized by a program for causing a computer to function as the device, and can be realized by a program for causing a computer to function as each control block of the device (especially each part included in the control units 52 and 52A).

[0073] In this case, the above device includes a computer having at least one control device (for example, a processor) and at least one storage device (for example, a memory) as hardware for executing the above program. By executing the above program by this control device and storage device, each function described in each of the above embodiments is realized.

[0074] The above program may be recorded on one or more computer-readable recording media, not temporarily. This recording medium may or may not be provided in the above device. In the latter case, the above program may be supplied to the above device via any wired or wireless transmission medium.

[0075] Also, part or all of the functions of each of the above control blocks can also be realized by a logic circuit. For example, an integrated circuit in which a logic circuit functioning as each of the above control blocks is formed is also included in the scope of the present disclosure. In addition to this, for example, it is also possible to realize the functions of each of the above control blocks by a quantum computer.

[0076] Also, each process described in each of the above embodiments may be executed by AI (Artificial Intelligence). In this case, the AI may operate in the above control device, or may operate in another device (for example, an edge computer or a cloud server, etc.).

[0077] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope indicated in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure.

Explanation of Reference Numerals

[0078] 1 Solar panel 2 Power conditioner 3 DC bus 4 Energy storage device 5, 5A Power conversion device 51 DC-DC converter 52, 52A Control unit 521 Basic command value determination unit 525 Output power reduction factor determination unit 526, 526A Correction value calculation unit 527 Subtraction unit 100, 100A Power supply system

Claims

1. A power conversion device connected to a DC bus that connects a solar panel and a power conditioner, and that performs charging from the DC bus to a power storage device and discharging from the power storage device to the DC bus, the power conversion device comprising: a DC-DC converter; and a control unit that controls the output power of the DC-DC converter. The control unit includes a basic command value determination unit that determines a basic command value for controlling the output power of the DC-DC converter based on the output power of the solar panel; an output power reduction factor determination unit that determines whether or not a reduction in the output power of the solar panel due to output power suppression by the power conditioner has occurred, based on the output voltage and output power of the solar panel; a correction value calculation unit that calculates a correction value for correcting the basic command value based on the history of the output power of the solar panel when it is determined that a reduction in the output power of the solar panel due to output power suppression by the power conditioner has occurred; and a subtraction unit that calculates a corrected command value by subtracting the correction value from the basic command value. A power conversion device that controls the DC-DC converter based on the corrected command value.

2. When the period until the output power suppression by the power conditioner ends is defined as a suppression period during output power suppression by the power conditioner, the correction value calculation unit according to claim 1 calculates, as the correction value, a difference value obtained by subtracting the current value from the maximum value of the output power of the solar panel within a period equal to the suppression period ending with the current time.

3. When the period until the output power suppression by the power conditioner ends is defined as a suppression period during output power suppression by the power conditioner, the correction value calculation unit according to claim 1 calculates, as the correction value, a value obtained by multiplying a difference value obtained by subtracting the minimum value from the current value of the output voltage of the solar panel within a period equal to the suppression period ending with the current time by a gain for converting the difference value into power.

4. A solar panel, a power conditioner, a DC bus, a power storage device, and a power conversion device according to any one of claims 1 to 3. A power supply system comprising the same.

5. A control method for a power conversion device that is connected to a DC bus connecting a solar cell panel and a power conditioner and performs charging from the DC bus to a power storage device and discharging from the power storage device to the DC bus. The power conversion device includes a DC-DC converter and a control unit that controls the output power of the DC-DC converter. A basic command value determination step of determining a basic command value for controlling the output power of the DC-DC converter based on the output power of the solar cell panel. An output power reduction factor determination step of determining whether or not there is a reduction in the output power of the solar cell panel due to output power suppression by the power conditioner from the output voltage and output power of the solar cell panel. A correction value calculation step of calculating a correction value for correcting the basic command value based on the history of the output power of the solar cell panel when it is determined that there is a reduction in the output power of the solar cell panel due to output power suppression by the power conditioner. A subtraction step of calculating a corrected command value by subtracting the correction value from the basic command value, including. A control method for a power conversion device that controls the DC-DC converter based on the corrected command value.

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