Power conversion device, power supply system, and method for controlling power conversion device

Abstract

STABILIZING OPERATION OF POWER CONDITIONER SOLUTION: A control unit (52) of a power conversion device (5) sets a control target value of an output voltage of a solar cell panel based on a first output voltage of the solar cell panel (1) indicated in a past operation record corresponding to an amount of solar radiation. The control unit calculates a voltage deviation that is a difference between the control target value and a current second output voltage of the solar cell panel. The control unit determines, as a command value for controlling output power of the DC-DC converter (51), a value obtained by adding, to a base value of the command value, a value obtained by converting the voltage deviation into power, the base value being calculated from current output power of the solar cell panel and a target value of input power to the power conditioner (2).SELECTED DRAWING: Figure 1

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 technology]

[0002] Patent Document 1 discloses a power conversion device that is connected to a DC bus that connects a solar panel and a power conditioner, and that charges a power storage device from the DC bus and discharges power from the power storage device to the DC bus. In the power conversion device of Patent Document 1, a control unit calculates the absolute value of the fluctuation range per unit time of the input power to the power conditioner as the rate of change of the input power to the power conditioner. The control unit determines a command value for controlling the output power of the DC-DC converter by multiplying the rate of change by a coefficient that is greater than 0 and less than 1, and sets the value obtained by multiplying the rate of change by a coefficient that is greater than 0 and less than 1 as the upper limit of the absolute value of the fluctuation range of the command value that controls the output power of the DC-DC converter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7294557 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to stabilize the operation of the power conditioner, the power conversion device of Patent Document 1 determines the command value on the assumption that the amount of solar radiation on the solar cell panel does not fluctuate. However, if the amount of solar radiation on the solar cell panel fluctuates, the control of the power conversion device of Patent Document 1 may cause the operation of the power conditioner to become unstable.

[0005] An object of one aspect of the present disclosure is to realize a power conversion device or the like that can stabilize the operation of a power conditioner. [Means for solving the problem]

[0006] A power conversion device according to one embodiment of the present disclosure is a power conversion device connected to a solar cell panel and a power conditioner, and includes a DC-DC converter and a control unit that controls the output power of the DC-DC converter. The control unit sets a control target value for the output voltage of the solar cell panel based on a first output voltage indicated in past operating results of the solar cell panel corresponding to the amount of solar radiation, calculates a voltage deviation that is the difference between the control target value and the current second output voltage of the solar cell panel, and determines, as the command value, a value obtained by adding a value obtained by converting the voltage deviation into power to a basic value of a command value for controlling the output power of the DC-DC converter, the basic value being calculated from the current output power of the solar cell panel and the input power target value to the power conditioner.

[0007] A control method for a power conversion device according to one embodiment of the present disclosure is a control method for a power conversion device connected to a solar cell panel and a power conditioner, the power conversion device comprising a DC-DC converter and a control unit that controls the output power of the DC-DC converter, and including a setting step of setting a control target value for the output voltage of the solar cell panel based on a first output voltage indicated in past operating results of the solar cell panel corresponding to the amount of solar radiation; a calculation step of calculating a voltage deviation that is the difference between the control target value and a current second output voltage of the solar cell panel; and a determination step of determining, as the command value, a value obtained by adding a value obtained by converting the voltage deviation into power to a basic value of a command value for controlling the output power of the DC-DC converter, the basic value being calculated from the current output power of the solar cell panel and an input power target value to the power conditioner. [Effects of the Invention]

[0008] According to one aspect of the present disclosure, the operation of the power conditioner can be stabilized. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a block diagram showing an example of the configuration of a power supply system including a power conversion device according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a block diagram showing an example of a specific configuration of a control unit included in the power conversion device. [Figure 3] 1 is a graph showing the correspondence relationship between output voltage and output power in a solar cell panel. [Figure 4] 10 is a graph showing a change in output power of a solar cell panel and a change in a base value of a command value for controlling the output power of a DC-DC converter. [Figure 5] 5 is a flowchart showing an example of a processing flow by a control unit according to the first embodiment of the present disclosure. [Figure 6] 1 is a graph showing the correspondence relationship between the output voltage and the output power of a solar panel corresponding to different amounts of solar radiation. [Figure 7] FIG. 10 is a block diagram showing an example of a specific configuration of a control unit included in a power conversion device according to a second embodiment of the present disclosure. [Figure 8] 10 is a flowchart showing an example of a flow of processing by a control unit according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Embodiment 1] An embodiment of the present disclosure will be described in detail below.

[0011] (Power supply system) 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 a power grid 200. As shown in FIG. 1, the power supply system 100 includes a solar cell panel 1, a power conditioner 2, a DC bus 3, a power storage device 4, and a power conversion device 5.

[0012] The solar cell 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 (Maximum Power Point Tracking) on ​​the output power of the solar cell panel 1. The DC bus 3 connects the solar cell panel 1 and the power conditioner 2.

[0013] The power storage device 4 stores electric power as energy internally and supplies the stored energy as direct current to the DC bus 3 as needed. The power storage device 4 is connected to the DC bus 3. DC power supplied from the solar cell panel 1 via the DC bus 3 is stored inside the power storage device 4. The DC power supplied from the power storage device 4 to the DC bus 3 is also supplied to the power conditioner 2.

[0014] The power storage device 4 may be a device equipped with a secondary battery such as a lithium ion battery, a sodium-sulfur (NaS) battery, a redox flow battery, or a lead acid battery. However, the power storage device 4 is not limited to a device equipped with a secondary battery. Any unit capable of storing electrical energy, such as a capacitor, a superconducting power storage unit, a flywheel power storage unit, or a compressed air power storage unit, may be used as the power storage device 4.

[0015] The power conversion device 5 is connected to the DC bus 3, and charges the power storage device 4 from the DC bus 3, and discharges power from the power storage device 4 to the DC bus 3. The power conversion device 5 is disposed between the DC bus 3 and the power storage device 4, and converts the voltage of the power supplied from one of the DC bus 3 and the power storage device 4 to the other. The power conversion device 5 includes a DC-DC converter 51, a control unit 52, a memory unit 53, an ammeter 54, and a voltmeter 55.

[0016] Based on a 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 power storage device 4, or converts the voltage of the power input from the power storage device 4 and outputs it to the DC bus 3. The command value is a command value that controls the output power of the DC-DC converter 51.

[0017] 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.

[0018] The memory unit 53 is a storage device that stores information necessary for the control unit 52 to determine a command value. The memory unit 53 may store, for example, a program for determining a command value to be input to the DC-DC converter 51. Furthermore, for example, the memory unit 53 stores information indicating the past operational performance of the solar cell panel 1. The memory unit 53 stores the output voltage and output power of the solar cell panel 1 that were measured or calculated in the past as the past operational performance, in association with the amount of solar radiation at the time of the measurement or calculation. Hereinafter, the output voltage will be referred to as the first output voltage. In other words, the past operational performance indicates the correspondence relationship between the first output voltage and the output power of the solar cell panel 1.

[0019] The storage unit 53 is not essential for the power conversion device 5. Instead of including the storage unit 53, the power conversion device 5 may be connected to an external storage device wirelessly or via a wire so as to be able to communicate with the external storage device.

[0020] 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 DC bus 3 closer to the solar cell panel 1 than the point where the power storage device 4 and the power conversion device 5 are connected.

[0021] 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 obtain the output current and output voltage of the solar cell 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.

[0022] The power converter 5 may also include a pyranometer that measures the amount of solar radiation irradiating the solar cell panel 1.

[0023] (Control unit) 2 is a block diagram showing an example of a specific configuration of the control unit 52. The control unit 52 may, for example, determine the above-mentioned command value at regular time intervals. As shown in FIG. 2, the control unit 52 includes a multiplication unit 52a, an addition unit 52b, a change rate calculation unit 52c, a subtraction unit 52d, a setting unit 52f, a calculation unit 52g, a conversion unit 52h, and a determination unit 52i.

[0024] First, an example of control will be described in which the control unit 52 sets a base value of the command value that serves as a basis for determining the command value for controlling the output power of the DC-DC converter 51. The setting of the base value of the command value involves the multiplication unit 52a, the addition unit 52b, the change rate calculation unit 52c, and the subtraction unit 52d. The control unit 52 determines the command value by adding a separately calculated value to the set base value of the command value, and an example of control for determining the command value will be described later.

[0025] (Setting control of the basic command value) The multiplication unit 52a outputs a signal obtained by multiplying the output current and the output voltage from the solar cell panel 1. The output of the multiplication unit 52a indicates the output power from the solar cell panel 1.

[0026] The adder 52b outputs a signal obtained by adding the output of the multiplier 52a and the current output power of the DC-DC converter 51. The output of the adder 52b indicates the input power to the power conditioner 2. In other words, the adder 52b calculates the value obtained by adding the output power of the solar cell panel 1 and the output power of the DC-DC converter 51 as the input power to the power conditioner 2.

[0027] The change rate calculation unit 52c calculates the absolute value of the fluctuation range per unit time of the input power to the power conditioner 2 as the change rate 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.

[0028] Specifically, the change rate calculation unit 52c calculates an absolute value ΔP1 of the fluctuation range of the current output of the adder 52b relative to the output of the adder 52b when the previous command value was determined. The change rate calculation unit 52c also calculates the length Δt of the period from the time when the adder 52b output the previous signal to the time when the adder 52b outputs the current signal. The change rate calculation unit 52c further calculates the rate of change ΔP1 / Δt of the input power to the power conditioner 2 during the period from the time when the adder 52b output the previous signal to the time when the adder 52b outputs the current signal.

[0029] The subtraction unit 52d outputs a signal obtained by subtracting the output of the multiplication unit 52a from a predetermined input power target value to the power conditioner 2. The output of the subtraction unit 52d is a signal that serves as a basis for setting a base value of a command value that controls the output power of the DC-DC converter 51.

[0030] The base value setting unit 52e sets a value obtained by multiplying the change rate ΔP1 / Δt by a coefficient that is greater than 0 and less than 1 as the upper limit of the absolute value of the fluctuation range of the base value of the command value to be output to the DC-DC converter 51. Specifically, the base value setting unit 52e calculates the 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 that is greater than 0 and less than 1. The coefficient may be, for example, 0.3, but is not limited to this.

[0031] The base value setting unit 52e sets the value of the update rate as the upper limit of the absolute value of the fluctuation range of the base value of the command value output to the DC-DC converter 51. Specifically, the base value setting unit 52e determines whether the difference between the output of the subtraction unit 52d and the base value of the previous command value is equal to or less than the value of the update rate. If the difference between the output of the subtraction unit 52d and the base value of the previous command value is equal to or less than the value of the update rate, the base value setting unit 52e sets the output of the subtraction unit 52d as the base value of the command value as is. If the difference between the output of the subtraction unit 52d and the base value of the previous command value is not equal to or less than the value of the update rate, the base value setting unit 52e sets the corrected value of the output of the subtraction unit 52d so that the difference from the base value of the previous command value is equal to or less than the value of the update rate as the base value of the command value. The basic value of the command value set by the basic value setting unit 52e specifies the magnitude of fluctuation of the next target control value relative to the current target control value of the output power of the DC-DC converter 51 when the amount of solar radiation on the solar panel 1 does not fluctuate.

[0032] Fig. 3 is a graph showing the correspondence relationship between the output voltage and the output power of the solar cell panel 1. In Fig. 3, the horizontal axis represents the output voltage, and the vertical axis represents the output power. In the example shown in Fig. 3, the power conditioner 2 performs MPPT control on the solar cell panel 1, with operating point A as the initial position.

[0033] In the example shown in FIG. 3, when the amount of solar radiation does not fluctuate, the power conditioner 2 moves the operating point of the solar cell panel 1 from operating point A to operating point B and then to operating point C, in that order. The power conditioner 2 then moves the operating point of the solar cell panel 1 to operating point D, and then moves the operating point of the solar cell panel 1 back and forth between operating point C and operating point D. In the example shown in FIG. 3, this back and forth operation occurs across a control target value for the output voltage of the solar cell panel 1 (the output voltage when the output power of the solar cell panel 1 reaches its maximum value (peak value)). As shown in FIG. 3, the absolute value of the fluctuation range of the output power when the operating point of the solar cell panel 1 is changed from A to B is denoted as ΔP1n. Furthermore, the absolute value of the fluctuation range of the output power when the operating point of the solar cell panel 1 is changed from B to C is denoted as ΔP1n+1.

[0034] 4 is a graph showing changes in the output power of the solar cell panel 1 and changes in the base value of the command value that controls the output power of the DC-DC converter 51. In FIG. 4, the horizontal axis represents time and the vertical axis represents output power. In FIG. 4, graph 401 represents the output power of the solar cell panel 1. In FIG. 4, graph 402 represents the base value of the command value that controls the output power of the DC-DC converter 51.

[0035] In Fig. 4, time T1 is the time when the operating point of solar cell panel 1 moves to operating point A. Time T2 is the time when the operating point of solar cell panel 1 moves to operating point B. Time T3 is the time when the operating point of solar cell panel 1 moves to operating point C.

[0036] 4, the length of the period from time T1 to time T2 is assumed to be Δtn. The absolute value of the fluctuation range of the output power from the solar cell panel 1 during this period is assumed to be ΔP1n. In this case, the rate of change ΔP1n / Δtn is the slope of the graph 401 during the period from time T1 to time T2.

[0037] Let ΔP2n be the fluctuation in the basic value of the command value that controls the output power of DC-DC converter 51 during the period from time T1 to time T2. In this case, the update rate ΔP2n / Δtn is the slope of graph 402 during the period from time T1 to time T2. Furthermore, the update rate ΔP2n / Δtn is a value obtained by multiplying the rate of change ΔP1n / Δtn by a coefficient that is greater than 0 and less than 1.

[0038] Furthermore, the length of the period from time T2 to time T3 is assumed to be Δtn+1. The absolute value of the fluctuation range of the output power from the solar cell panel 1 during this period is assumed to be ΔP1n+1. In this case, the rate of change ΔP1n+1 / Δtn+1 is the slope of the graph 401 during the period from time T2 to time T3.

[0039] Let us assume that the fluctuation in the basic value of the command value that controls the output power of DC-DC converter 51 during the period from time T2 to time T3 is ΔP2n+1. In this case, the update rate ΔP2n+1 / Δtn+1 is the slope of graph 402 during the period from time T2 to time T3. Furthermore, the update rate ΔP2n+1 / Δtn+1 is a value obtained by multiplying the change rate ΔP1n+1 / Δtn+1 by a coefficient that is greater than 0 and less than 1.

[0040] As described above, ΔP1 is the absolute value of the fluctuation range of the output of the adder 52b from the previous time to the current time. Therefore, even if the slope of the output power from the solar cell panel 1 is negative, the change rates ΔP1n / Δtn and ΔP1n+1 / Δtn+1 and the update rates ΔP2n / Δtn and ΔP2n+1 / Δtn+1 are positive.

[0041] (Command value determination control) Next, a description will be given of an example of control in which the control unit 52 determines a command value for controlling the output power of the DC-DC converter 51. The determination of the command value involves a setting unit 52f, a calculation unit 52g, a conversion unit 52h, and a determination unit 52i shown in FIG.

[0042] The setting unit 52f sets a control target value for the output voltage of the solar cell panel 1 based on a first output voltage indicated in past operation records of the solar cell panel 1 corresponding to the amount of solar radiation. Hereinafter, the control target value for the output voltage of the solar cell panel 1 will be simply referred to as the control target value. The reason for setting the control target value based on the first output voltage will be described later. Here, only an example of setting the control target value will be shown.

[0043] For example, the setting unit 52f sets, as the control target value, the first output voltage corresponding to the maximum value of the output power of the solar cell panel 1 in a correspondence relationship between the first output voltage corresponding to the current amount of solar radiation and the output power of the solar cell panel 1. Specifically, the setting unit 52f acquires the current amount of solar radiation from a pyranometer. The control unit 52 extracts the correspondence relationship corresponding to the acquired current amount of solar radiation from the multiple correspondence relationships stored in the storage unit 53, and sets, as the control target value, the first output voltage corresponding to the maximum value of the output power in the correspondence relationship. This allows the setting unit 52f to set the control target value using a simple method.

[0044] Furthermore, for example, the setting unit 52f sets, as the control target value, the first output voltage corresponding to the maximum value of the output power of the solar cell panel 1 in a correspondence relationship selected from a plurality of correspondence relationships corresponding to varying amounts of solar radiation. The setting unit 52f may select one of the correspondence relationships by, for example, applying a filter that defines a fluctuation range of the output power or the first output voltage of the solar cell panel 1. That is, the setting unit 52f may select one maximum value (corresponding to the first output voltage) from a plurality of maximum values ​​of the output power (corresponding to the first output voltage) corresponding to fluctuations in the amount of solar radiation by applying the filter. For example, when the amount of solar radiation fluctuates beyond a predetermined range, the setting unit 52f may select the maximum value of the output power (corresponding to the first output voltage) corresponding to an amount of solar radiation within a fluctuation range within a predetermined range.

[0045] In this case, too, the control target value can be set using a simple method, and the amount of change in the control target value can be reduced. Furthermore, depending on the weather, the amount of solar radiation can fluctuate in a relatively short period of time. For example, the amount of solar radiation may increase or decrease in a relatively short period of time, and then return to its original amount. In this case, the control unit 52 may significantly change the control target value in response to a temporary change in the amount of solar radiation. By using the above filter, the amount of change in the control target value in response to a temporary change in the amount of solar radiation can be reduced.

[0046] Calculation unit 52g subtracts the current output voltage of solar cell panel 1 measured by voltmeter 55 from the control target value set by setting unit 52f. Hereinafter, the current output voltage of the solar cell panel is referred to as the second output voltage. Through this subtraction, calculation unit 52g calculates a voltage deviation, which is the difference between the control target value and the second output voltage.

[0047] The conversion unit 52h converts the voltage deviation calculated by the calculation unit 52g into power. The conversion unit 52h converts the voltage deviation calculated by the calculation unit 52g into power by multiplying the voltage deviation calculated by the calculation unit 52g by the current output power of the solar cell panel 1 and dividing the result by the open-circuit voltage of the solar cell panel 1. When the open-circuit voltage of the solar cell panel 1 is Vm and the output power of the solar cell panel 1 is Ppv, the conversion unit 52h executes (voltage deviation) × Ppv / Vm. The units of the voltage deviation, the output power of the solar cell panel 1, and the open-circuit voltage of the solar cell panel 1 are [V], [W], and [V], respectively. Therefore, the determination unit 52i can add a power value based on the voltage deviation to the command value (power value) for controlling the DC-DC converter 51 output by the basic value setting unit 52e.

[0048] In this embodiment, the open-circuit voltage of the solar cell panel 1 used by the conversion unit 52h is the rated open-circuit voltage of the solar cell panel 1. In general, it is difficult to calculate the open-circuit voltage of the solar cell panel 1 under the solar radiation conditions (current solar radiation conditions) when measuring the output voltage and output current of the solar cell panel 1. On the other hand, the rated open-circuit voltage of the solar cell panel 1 does not differ significantly from the open-circuit voltage calculated based on the installation conditions of the solar cell panel 1. Therefore, by using the rated open-circuit voltage of the solar cell panel 1 as the open-circuit voltage of the solar cell panel 1, it is possible to reduce the processing load of the control unit 52 while obtaining results equivalent to those obtained when the open-circuit voltage of the solar cell panel 1 under the current solar radiation conditions is used.

[0049] The determination unit 52i adds the value obtained by converting the voltage deviation into power by the conversion unit 52h to a basic value of a command value for controlling the output power of the DC-DC converter 51, the basic value being calculated from the current output voltage and a predetermined input power target value to the power conditioner 2. The determination unit 52i determines this added value as a command value for controlling the output power of the DC-DC converter 51. In the present embodiment, the determination unit 52i adds the value obtained by converting the voltage deviation into power by the conversion unit 52h to the basic value of the command value set by the basic value setting unit 52e.

[0050] (Control method) Fig. 5 is a flowchart showing an example of the flow of processing by the control unit 52 (an example of a method of controlling the power conversion device 5 by the control unit 52). In the example shown in Fig. 5, the control unit 52 executes a first process shown in steps S1 to S5 and a second process shown in steps S11 to S13 in parallel. However, the control unit 52 may execute the second process after the first process, or may execute the first process after the second process.

[0051] In the first process, the multiplication unit 52a calculates the output power of the solar cell panel 1 (S1). The addition unit 52b calculates the input power to the power conditioner 2 (S2). The change rate calculation unit 52c calculates the absolute value of the fluctuation range per unit time of the input power to the power conditioner 2 as the change rate of the input power (S3).

[0052] The subtraction unit 52d subtracts the output power of the solar panel 1 calculated in step S1 from a predetermined input power target value of the power conditioner 2 (S4). The base value setting unit 52e sets the base value of the command value by multiplying the change rate calculated in step S3 by a coefficient greater than 0 and less than 1, as the upper limit of the absolute value of the fluctuation range of the base value of the command value (S5).

[0053] Note that steps S2, S3, and S4 do not necessarily have to be executed in this order. For example, step S4 may be executed first, followed by steps S2 and S3. Alternatively, one or both of steps S2 and S3 and step S4 may be executed in parallel.

[0054] In the second process, the setting unit 52f sets a control target value based on a first output voltage indicated in past operation records corresponding to the amount of solar radiation (S11; setting step). The calculation unit 52g calculates a voltage deviation, which is the difference between the control target value set by the setting unit 52f and the current second output voltage of the solar cell panel 1 (S12; calculation step). The conversion unit 52h converts the voltage deviation calculated by the calculation unit 52g into power using the current output power of the solar cell panel 1 and the open-circuit voltage of the solar cell panel 1 (S13).

[0055] Then, the determination unit 52i determines, as the command value, a value obtained by adding the value obtained by converting the voltage deviation into power by the conversion unit 52h in step S13 to the basic value of the command value set by the basic value setting unit 52e in step S5 (S14; determination step). The control unit 52 controls the power conversion device 5 by inputting the command value determined by the above series of processes to the DC-DC converter 51.

[0056] (Why do we set control targets based on past performance data?) The base value setting unit 52e sets the value of the update rate as the upper limit of the absolute value of the fluctuation range of the base value of the command value. Therefore, the base value of the command value is smaller than the absolute value of the fluctuation range per unit time of the input power to the power conditioner 2. Therefore, when the base value of the command value is used as the command value, the fluctuation of the output power of the DC-DC converter 51 can be made slower than the fluctuation of the input power to the power conditioner 2. This makes it less likely that the input power to the power conditioner 2 will become unstable due to the output power of the DC-DC converter 51. Therefore, even when the DC-DC converter 51 is controlled using the base value of the command value, the operation of the power conditioner 2 can be stabilized.

[0057] However, the base value of the command value is set taking into consideration the input power of the power conditioner 2, and does not take into account the influence of fluctuations in the amount of solar radiation. Fluctuations in the amount of solar radiation occur independently of MPPT control. Therefore, fluctuations in the amount of solar radiation cause fluctuations in ΔP1 shown in FIG. 4, which can cause the base value of the command value to fluctuate without being synchronized with MPPT control. Therefore, if the base value of the command value is used as the command value, fluctuations in the amount of solar radiation can cause the operation of the DC-DC converter 51 to become unstable.

[0058] FIG. 6 is a graph showing the correspondence relationship between the output voltage and output power of the solar cell panel 1 corresponding to different amounts of solar radiation. Graph G1 is a graph obtained when the amount of solar radiation is greater than the amount of solar radiation used to obtain graph G2. Graph G3 is a graph obtained when the amount of solar radiation is less than the amount of solar radiation used to obtain graph G2. Graph G2 in FIG. 6 corresponds to the graph in FIG. 3. In the description of FIG. 6, the output voltage of the solar cell panel 1 will be simply referred to as the output voltage, and the output power of the solar cell panel 1 will be simply referred to as the output power.

[0059] As described above, consider a case where the amount of solar radiation fluctuates while the power conditioner 2 is using MPPT control to move the operating point of the solar cell panel 1 back and forth along graph G2 around the peak of graph G2 (the control target value of the current output voltage). That is, consider a case where the amount of solar radiation fluctuates while the operating point of the solar cell panel 1 is being moved back and forth between operating points C and D shown in Fig. 3. For example, consider a case where the amount of solar radiation decreases while the output voltage is being controlled from operating point C to operating point D by MPPT control.

[0060] When the amount of solar radiation decreases, the power conditioner 2 performs MPPT control to form graph G3, which is a graph showing the correspondence relationship between the output voltage and output power of the solar cell panel 1. Therefore, the power conditioner 2 may determine that the output power corresponding to the output voltage of the solar cell panel 1 becomes a value corresponding to graph G3, exceeding the peak of graph G2. In this case, the power conditioner 2 may determine that the output voltage is at the current control target value (the peak of graph G2) or that the output power is being increased while the output voltage is being reduced (a state in which control is being performed to the right of the peak of graph G2). This means that the power conditioner 2 erroneously recognizes the current control target value.

[0061] In this case, the power conditioner 2 may reduce the output power to a value lower than the output power at operating point D (for example, operating point E in Figure 3) by setting a larger fluctuation range for the output voltage per unit time. Depending on the power conditioner 2, if the output power drops significantly, the current control target value may be lost. As a result, the power conditioner 2 may deviate from MPPT control according to graph G2 and suddenly increase the output voltage so that the output power becomes a value lower than operating point C (for example, operating point B in Figure 3).

[0062] In this state, the power conditioner 2 may fluctuate the output voltage from operating point B to operating point E along graph G2, and then rapidly repeat this control, departing from the MPPT control along graph G2 and suddenly increasing the output voltage from operating point B to operating point E. In other words, fluctuations in the amount of solar radiation may cause the MPPT control of the power conditioner 2 to fall into this type of control (control that oscillates the operating point).

[0063] The present inventors have noticed that excessive fluctuations in the output voltage of the solar cell panel 1 cause oscillations in the operating point, and have studied control methods for keeping the output voltage of the solar cell panel 1 more or less constant in order to converge the oscillations in the operating point. As a result, the present inventors have come up with the idea of ​​stabilizing the operation of the power conditioner 2 by stabilizing the voltage of the DC bus 3 in order to control the output voltage of the solar cell panel 1 more or less constant. In order to stabilize the voltage of the DC bus 3, the present inventors have come up with the idea of ​​stabilizing the operation of the DC-DC converter 51 by adjusting a command value for controlling the output power of the DC-DC converter 51 based on a control target value that takes into account fluctuations in the amount of solar radiation.

[0064] Through this idea, the inventor came up with the idea of ​​setting a control target value for the output voltage of the solar cell panel based on the first output voltage shown in the past operating performance of the solar cell panel 1 corresponding to the amount of solar radiation, as described above.

[0065] (effect) In the power conversion device 5, the setting unit 52f sets a control target value for the output voltage of the solar cell panel based on the first output voltage. Specifically, consider a case where the amount of solar radiation decreases while the power conditioner 2 is performing MPPT control according to graph G2 in FIG. 6. In this case, the setting unit 52f sets, as the control target value, the output voltage corresponding to the maximum value P32 of output power in graph G3 in FIG. 6, which shows past operation results corresponding to the amount of solar radiation. On the other hand, consider a case where the amount of solar radiation increases while the power conditioner 2 is performing MPPT control according to graph G2 in FIG. 6. In this case, the setting unit 52f sets, as the control target value, the output voltage corresponding to the maximum value P12 of output power in graph G1 in FIG. 6, which shows past operation results corresponding to the amount of solar radiation.

[0066] A calculation unit 52g calculates a voltage deviation, which is the difference between the set control target value and the current second output voltage of the solar cell panel 1. Then, a determination unit 52i determines, as the command value, a value obtained by adding a value obtained by converting the voltage deviation into power to a basic value of a command value for controlling the output power of the DC-DC converter 51.

[0067] This makes it possible to stabilize the voltage of the DC bus 3. As a result, it is possible to stabilize the operation of the power conditioner 2, i.e., the MPPT control. Specifically, as shown in FIG. 6, if the amount of solar radiation decreases while the power conditioner 2 is performing MPPT control according to graph G2, the control unit 52 can adjust the fluctuation range of the output voltage to a range equivalent to that of graph G3 (between operating points P31 and P33). Also, if the amount of solar radiation increases while the power conditioner 2 is performing MPPT control according to graph G2, the control unit 52 can adjust the fluctuation range of the output voltage to a range equivalent to that of graph G1 (between operating points P11 and P13).

[0068] Therefore, the range in which the operating point moves back and forth on graph G2 can be adjusted to the right or left of the peak of graph G2. This reduces the possibility of the operating point oscillating as described above, which occurs when the operating point moves back and forth around the peak of graph G2 when the amount of solar radiation fluctuates. This makes it possible to stabilize the output power (power generation amount) of the solar panel 1.

[0069] In the example of Fig. 6, in the MPPT control performed by the power conditioner 2, if the amount of solar radiation does not fluctuate, the output voltage corresponding to the peak of graph G2 (the operating point indicating the maximum value P22 of the output power) is set as the control target value. On the other hand, if the amount of solar radiation fluctuates, the setting unit 52f sets the control target value to a position shifted from the peak of graph G2. However, as shown in Fig. 6, near the peak of graph G2, there is only a small difference between the output power at the peak and the output power at other positions. Therefore, the reduction in output power (power generation amount) due to the setting of the control target value by the setting unit 52f is small, and there is almost no effect on the output power (power generation amount).

[0070] Here, the power conditioner 2 controls the output power of the solar cell panel 1, and the control unit 52 controls the output power of the DC-DC converter 51. Therefore, because the power conditioner 2 and the control unit 52 both control the same element, namely, power, there is a possibility that these controls may contradict each other. In this embodiment, voltage information called a control target value is used to adjust the command value that controls the output power of the DC-DC converter 51. By using a control value called voltage, which is a different element from power, it is possible to stabilize the voltage of the DC bus 3 to a certain extent using this voltage (control target value) even if the above-mentioned two power controls contradict each other. This makes it possible to stabilize the MPPT control of the power conditioner 2.

[0071] Furthermore, as described above, setting of the basic value of the command value by the basic value setting unit 52e makes it possible to make the input power to the power conditioner 2 less likely to become unstable due to the output power of the DC-DC converter 51. In other words, the above setting by the basic value setting unit 52e also makes it possible to stabilize the operation of the power conditioner 2.

[0072] [Embodiment 2] Other embodiments of the present disclosure will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0073] 7 is a block diagram showing an example of a specific configuration of the control unit 52A. The control unit 52A includes a multiplication unit 52a, a subtraction unit 52d, a setting unit 52f, a calculation unit 52g, a conversion unit 52h, and a determination unit 52i. The control unit 52A differs from the control unit 52 of the first embodiment in that it does not include the addition unit 52b, the change rate calculation unit 52c, or the basic value setting unit 52e.

[0074] In the control unit 52A, the subtraction unit 52d subtracts the current output power of the solar cell panel 1 calculated by the multiplication unit 52a from a predetermined input power target value to the power conditioner 2. The subtraction unit 52d outputs the calculation result to the determination unit 52i as a basic value of the command value. The determination unit 52i determines, as the command value, a value obtained by adding the power value output from the conversion unit 52h to the basic value of the command value.

[0075] Fig. 8 is a flowchart showing an example of the flow of processing by the control unit 52A (an example of a method of controlling the power conversion device 5 by the control unit 52A). In the example shown in Fig. 8, the control unit 52A executes the processing of steps S1 and S21 as the first processing. Furthermore, the control unit 52A executes the processing of steps S11 to S13 as the second processing. The second processing shown in Fig. 8 is the same as the second processing shown in Fig. 5, and therefore description thereof will be omitted here.

[0076] In the first process, the multiplication unit 52a calculates the output power of the solar cell panel 1 (S1). The subtraction unit 52d calculates a value obtained by subtracting the output power of the solar cell panel 1 calculated in S1 from a predetermined input power target value of the power conditioner 2, as a basic value of the command value (S21). Therefore, in the control unit 52A, the subtraction unit 52d functions as a basic value setting unit.

[0077] Then, the determination unit 52i determines the command value to be the value obtained by adding the power value calculated by the subtraction unit 52d in step S21 as the basic value of the command value to the value obtained by converting the voltage deviation into power by the conversion unit 52h in step S13 (S14).

[0078] In the control unit 52A, similarly to the control unit 52, the operation of the power conditioner 2 can be stabilized by using a control target value set based on past operation results to adjust the command value.

[0079] [Software implementation example] The functions of the power conversion device 5 (hereinafter referred to as the "device") can be realized by a program for causing a computer to function as the device, and a program for causing a computer to function as each control block of the device (particularly each part included in the control units 52, 52A).

[0080] In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., a memory) as hardware for executing the program. The control device and storage device execute the program, thereby realizing the functions described in each of the above embodiments.

[0081] The program may be non-transitory and may be recorded on one or more computer-readable recording media. The recording media may or may not be included in the device. In the latter case, the program may be supplied to the device via any wired or wireless transmission medium.

[0082] In addition, some or all of the functions of each of the control blocks can be realized by logic circuits. For example, integrated circuits in which logic circuits that function as each of the control blocks are formed are also included in the scope of the present disclosure. In addition, the functions of each of the control blocks can also be realized by, for example, a quantum computer.

[0083] Furthermore, each process described in each of the above embodiments may be executed by AI (Artificial Intelligence). In this case, the AI ​​may run on the control device or on another device (for example, an edge computer or a cloud server).

[0084] 〔summary〕 A power conversion device according to a first aspect of the present disclosure is a power conversion device connected to a solar cell panel and a power conditioner, and includes a DC-DC converter and a control unit that controls the output power of the DC-DC converter. The control unit sets a control target value for the output voltage of the solar cell panel based on a first output voltage indicated in past operating results of the solar cell panel corresponding to the amount of solar radiation, calculates a voltage deviation that is the difference between the control target value and the current second output voltage of the solar cell panel, and determines the command value to be a value obtained by adding a value obtained by converting the voltage deviation into power to a basic value of a command value for controlling the output power of the DC-DC converter, the basic value being calculated from the current output power of the solar cell panel and the input power target value to the power conditioner.

[0085] In the power conversion device of aspect 2 of the present disclosure, in aspect 1, the past operating history indicates a correspondence relationship between the first output voltage and the output power of the solar cell panel, and the control unit sets the first output voltage corresponding to the maximum value of the output power of the solar cell panel in the correspondence relationship corresponding to the current amount of solar radiation as the control target value.

[0086] In a power conversion device according to aspect 3 of the present disclosure, in aspect 1, the control unit sets as the control target value a first output voltage corresponding to the maximum value of the output power of the solar panel in the correspondence relationship selected from a plurality of the correspondence relationships corresponding to varying amounts of solar radiation.

[0087] In the power conversion device according to aspect 4 of the present disclosure, in any one of aspects 1 to 3, the control unit converts the voltage deviation into power by multiplying the voltage deviation by the current output power of the solar cell panel and dividing the result by the open-circuit voltage of the solar cell panel.

[0088] A fifth aspect of the present disclosure provides a power conversion device in accordance with the fourth aspect, wherein the open circuit voltage of the solar cell panel is a rated open circuit voltage of the solar cell panel.

[0089] In a power conversion device according to aspect 6 of the present disclosure, in any one of aspects 1 to 5, the control unit calculates the absolute value of the fluctuation range per unit time of the input power to the power conditioner as the rate of change of the input power to the power conditioner, and sets the basic value by multiplying the rate of change by a coefficient greater than 0 and less than 1 as the upper limit of the absolute value of the fluctuation range of the basic value.

[0090] The power supply system according to aspect 7 of the present disclosure includes the solar cell panel, the power conditioner, a DC bus connecting the solar cell panel and the power conditioner, a power storage device, and a power conversion device according to any one of aspects 1 to 6 that charges the power storage device from the DC bus and discharges power from the power storage device to the DC bus.

[0091] A control method for a power conversion device according to an eighth aspect of the present disclosure is a control method for a power conversion device connected to a solar cell panel and a power conditioner, the power conversion device comprising a DC-DC converter and a control unit that controls the output power of the DC-DC converter, and including a setting step of setting a control target value for the output voltage of the solar cell panel based on a first output voltage indicated in past operating performance of the solar cell panel corresponding to the amount of solar radiation, a calculation step of calculating a voltage deviation which is the difference between the control target value and the current second output voltage of the solar cell panel, and a determination step of determining, as the command value, a value obtained by adding a value obtained by converting the voltage deviation into power to a basic value of a command value for controlling the output power of the DC-DC converter, the basic value being calculated from the current output power of the solar cell panel and the input power target value to the power conditioner.

[0092] [Additional Notes] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of 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 symbols]

[0093] 1 solar panel 2 Power conditioner 3 DC bus 4. Energy storage device 5 Power conversion device 51 DC-DC converter 52 Control section 100 Power Supply System

Claims

1. A power conversion device connected to a solar panel and a power conditioner, a DC-DC converter; a control unit that controls the output power of the DC-DC converter, The control unit setting a control target value for the output voltage of the solar cell panel based on a first output voltage indicated in a past operation record corresponding to an amount of solar radiation of the solar cell panel; calculating a voltage deviation that is a difference between the control target value and a current second output voltage of the solar cell panel; A power conversion device that determines, as the command value, a value obtained by adding a value obtained by converting the voltage deviation into power to a basic value of a command value that controls the output power of the DC-DC converter, the basic value being calculated from the current output power of the solar cell panel and the input power target value to the power conditioner.

2. the past operation record indicates a correspondence relationship between the first output voltage and the output power of the solar cell panel; 2 . The power conversion device according to claim 1 , wherein the control unit sets, as the control target value, the first output voltage corresponding to a maximum value of the output power of the solar cell panel in the correspondence relationship corresponding to a current amount of solar radiation.

3. the past operation record indicates a correspondence relationship between the first output voltage and the output power of the solar cell panel; 2. The power conversion device according to claim 1, wherein the control unit sets, as the control target value, a first output voltage corresponding to a maximum value of the output power of the solar cell panel in the correspondence relationship selected from a plurality of the correspondence relationships corresponding to varying amounts of solar radiation.

4. 2. The power conversion device according to claim 1, wherein the control unit converts the voltage deviation into power by multiplying the voltage deviation by a current output power of the solar cell panel and dividing the result by an open-circuit voltage of the solar cell panel.

5. The power conversion device according to claim 4 , wherein the open-circuit voltage of the solar cell panel is a rated open-circuit voltage of the solar cell panel.

6. The control unit Calculating an absolute value of a fluctuation range per unit time of the input power to the power conditioner as a change rate of the input power to the power conditioner; The power conversion device according to claim 1 , wherein the basic value is set by multiplying the rate of change by a coefficient greater than 0 and less than 1, and setting the value as an upper limit of an absolute value of a fluctuation range of the basic value.

7. the solar cell panel; The power conditioner; a DC bus connecting the solar cell panel and the power conditioner; a power storage device; A power supply system comprising: the power conversion device according to claim 1 , which charges the power storage device from the DC bus and discharges the power storage device to the DC bus.

8. A control method for a power conversion device connected to a solar panel and a power conditioner, comprising: The power conversion device is a DC-DC converter; a control unit that controls the output power of the DC-DC converter, a setting step of setting a control target value of an output voltage of the solar cell panel based on a first output voltage indicated in a past operation record of the solar cell panel corresponding to an amount of solar radiation; a calculation step of calculating a voltage deviation that is a difference between the control target value and a current second output voltage of the solar cell panel; A control method for a power conversion device, comprising: a determination step of determining, as the command value, a value obtained by adding a value obtained by converting the voltage deviation into power to a basic value of a command value for controlling the output power of the DC-DC converter, the basic value being calculated from the current output power of the solar cell panel and a target input power value to the power conditioner.

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