Control device for solar power generation system

Abstract

To increase the possibility of quickly returning an output voltage of a converter to a voltage at which the output power of the converter reaches a maximum when the correspondence between the output voltage of the converter and the output power of the converter changes.SOLUTION: A control apparatus 20 searches for a maximum efficiency voltage, which is an output voltage of a first converter 31 at which an output power of the first converter 31 becomes a maximum, stores the maximum efficiency voltage obtained by the search, executes voltage adjustment processing for changing the output voltage of the first converter 31 in a direction in which the output power of the first converter 31 increases with the maximum efficiency voltage as an initial value, and when the correspondence between the output voltage of the first converter 31 and the output power in response to an output voltage of a solar panel 70 changes during the voltage adjustment processing, changes the output voltage of the first converter 31 to the maximum efficiency voltage at that time and executes voltage adjustment processing again with the changed output voltage of the first converter 31 as a new initial value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control device for a solar power generation system. [Background Art]

[0002] The vehicle disclosed in Patent Document 1 includes a solar panel, a DCDC converter, and a control device. The solar panel generates power upon receiving irradiation of sunlight. The solar panel outputs the generated power to the DCDC converter. The DCDC converter converts the voltage of the output voltage from the solar panel and outputs the converted voltage.

[0003] The control device controls an output voltage of the DCDC converter. In this process, the control device determines the output voltage by a so-called hill-climbing method. In the hill-climbing method, the control device gradually increases the output voltage, for example. In this case, the control device continues increasing the output voltage if a condition that the output power increases as a result of increasing the output voltage continues to be satisfied. On the other hand, when the above condition is no longer satisfied, the control device switches the direction in which the output voltage is changed. Then, the control device gradually decreases the output voltage. In a similar manner, the control device switches the direction in which the output voltage is changed depending on whether the above condition is satisfied. By repeating such control, the control device can cause the output voltage of the DCDC converter to follow the voltage at which the output power of the DCDC converter is maximized. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Unexamined Patent Publication No. 2020-141545 [Summary of the Invention] [Problems to be Solved by the Invention]

[0005] In technologies such as Patent Document 1, which control a DC-DC converter using the hill-climbing method, the conditions surrounding the solar panel may change abruptly, for example, due to a sudden change in solar radiation. In this case, the output voltage of the solar panel may change abruptly. Consequently, the relationship between the output voltage of the DC-DC converter and the output power may also change abruptly. Under such circumstances, controlling the output voltage using the hill-climbing method requires time for the output voltage of the DC-DC converter to reach the voltage at which the output power is maximized. [Means for solving the problem]

[0006] The control device for a solar power generation system to solve the above problems is applied to a solar power generation system comprising a solar panel and a DC-DC converter that converts the output voltage of the solar panel into a voltage and outputs it, and performs a scan process to search for the maximum efficiency voltage, which is the output voltage of the DC-DC converter at which the output power of the DC-DC converter is maximized within a predetermined range, and the maximum efficiency voltage obtained by the scan process As the latest efficiency voltage Memorizing and, If the output power of the DC-DC converter corresponding to the maximum efficiency voltage obtained in the scan process is greater than or equal to a predetermined first threshold, the maximum efficiency voltage is stored as the first efficiency voltage. After the scanning process, latest A voltage adjustment process is performed to change the output voltage of the DC-DC converter in a direction that increases the output power of the DC-DC converter, using the efficiency voltage as the initial value, and during the voltage adjustment process, This determines whether the output power of the DC-DC converter has increased from below the first threshold to above the first threshold. That thing, When the output power of the DC-DC converter increases to or above the first threshold, the output voltage of the DC-DC converter is changed to the first efficiency voltage at that point. The voltage adjustment process is then performed again, using the modified output voltage of the DC-DC converter as the new initial value. [Effects of the Invention]

[0007] With the above technical concept, when the relationship between the output voltage and output power of the DC-DC converter changes, there is a higher probability that the output voltage of the DC-DC converter can be quickly returned to the voltage at which the output power of the DC-DC converter is maximized. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram of the vehicle's configuration. [Figure 2] Figure 2 is a time chart illustrating the execution timing of the scan process and the voltage adjustment process. [Figure 3] Figure 3 illustrates an example of a PV characteristic curve. [Figure 4] Figure 4 is a flowchart illustrating the processing steps for voltage adjustment. [Figure 5] Figure 5 shows an example of a case where the PV characteristic curve changes abruptly. [Figure 6] Figure 6 shows an example of a case where the PV characteristic curve changes abruptly. [Modes for carrying out the invention]

[0009] <Overall Structure> Hereinafter, one embodiment of a control device for a solar power generation system will be described with reference to the drawings. As shown in Figure 1, the vehicle 100 includes a solar panel 70, a converter unit 30, a drive battery 80, an auxiliary battery 90, and a control device 20.

[0010] The solar panel 70 is constructed by arranging multiple solar cells that generate electricity from sunlight in a panel-like configuration. The solar panel 70 is installed, for example, on the roof of the vehicle 100. The solar panel 70 may also be installed on the hood of the vehicle 100.

[0011] The converter unit 30 supplies power generated by the solar panel 70 to the drive battery 80 and the auxiliary battery 90. Details of the converter unit 30 will be described later. The drive battery 80 is a secondary battery. The drive battery 80 stores the power supplied from the converter unit 30. The drive battery 80 supplies power to a drive system (not shown) mounted on the vehicle 100. The drive system of the vehicle 100 includes one or more motors for driving the vehicle 100.

[0012] The auxiliary battery 90 is a secondary battery. The auxiliary battery 90 stores electric power supplied from the converter unit 30. The auxiliary battery 90 supplies electric power to an auxiliary machinery system (not shown) mounted on the vehicle 100. The auxiliary machinery system of the vehicle 100 is configured to include one or more auxiliary machines. The auxiliary machines are, for example, an electric oil pump, a navigation system, and lamps.

[0013] <コンバータユニット> The converter unit 30 includes a first DC-DC converter 31, a second DC-DC converter 32, a third DC-DC converter 33, and a measurement circuit 27. The converter unit 30 constitutes a solar power generation system together with the solar panel 70. Each DC-DC converter is a voltage conversion circuit that steps down or steps up a DC voltage and outputs the converted DC voltage. Hereinafter, when describing each DC-DC converter, "DC-DC" will be omitted and simply referred to as a converter. For example, the first DC-DC converter 31 is referred to as the first converter 31.

[0014] The first converter 31 is connected to the solar panel 70. The first converter 31 converts the output voltage of the solar panel 70, which is an input voltage, into a voltage based on an instruction from the control device 20, and outputs the converted voltage.

[0015] The second converter 32 is interposed between the first converter 31 and the drive battery 80. The second converter 32 converts the voltage output from the first converter 31 into a voltage within a predetermined range, and outputs the converted voltage to the drive battery 80.

[0016] The third converter 33 is interposed between the first converter 31 and the auxiliary battery 90. The third converter 33 converts the voltage output from the first converter 31 into a voltage within a predetermined range, and outputs the converted voltage to the auxiliary battery 90. Note that the voltage output by the third converter 33 is lower than the voltage output by the second converter 32.

[0017] The measurement circuit 27 repeatedly detects the output voltage of the first converter 31 and the output current of the first converter 31. The measurement circuit 27 repeatedly outputs signals corresponding to the detected output voltage and output current to the control device 20.

[0018] <Control Device> The control device 20 includes a CPU 21 and a memory 22. The memory 22 previously stores various programs describing processes to be executed by the CPU 21. The CPU 21 executes programs stored in the memory 22 to control the first converter 31, the second converter 32, and the third converter 33. When controlling the first converter 31, the CPU 21 sets a voltage instruction value Q related to the output voltage of the first converter 31. Then, the CPU 21 controls the first converter 31 so that the output voltage matching the voltage instruction value Q can be achieved. The memory 22 includes three types: RAM, ROM, and an electrically rewritable non-volatile type. In the present embodiment, these three types are collectively referred to as the memory 22.

[0019] The CPU 21 is activated as necessary not only while the start switch of the vehicle 100 is turned on, but also while the start switch is turned off. The start switch is a switch for switching the main system of the vehicle 100 between on and off. While the CPU 21 is in an activated state, it executes first converter processing for controlling the first converter 31. There are two types of first converter processing: scan processing and voltage adjustment processing. As shown in Figure 2, the CPU 21 alternately executes the scan processing and the voltage adjustment processing. The CPU 21 promptly completes the scan processing within an extremely short period of time, for example, less than one second. After that, the CPU 21 executes the voltage adjustment processing over a predetermined period of time, for example, one minute.

[0020] The PV characteristic curve, which is a prerequisite for processing for the first converter, will now be explained. As shown in Figure 3, consider a Cartesian coordinate system where the output voltage of the first converter 31 is on the X axis and the output power of the first converter 31 is on the Y axis. In this Cartesian coordinate system, the PV characteristic curve represents the correspondence between the output voltage of the first converter 31 and the output power of the first converter 31, which can be realized by the first converter 31 according to the current power generation status of the solar panel 70 and, consequently, the output voltage of the solar panel 70. The PV characteristic curve basically has a bell-shaped distribution. That is, the PV characteristic curve has a distribution with a maximum where the output power of the first converter 31 changes from increasing to decreasing. Note that the shape shown by the PV characteristic curve differs depending on the conditions in which the solar panel 70 is placed, such as the amount of solar radiation. The PV characteristic curve may also have a distribution with multiple maximums where the output power of the first converter 31 changes from increasing to decreasing. Hereafter, the correspondence between the output voltage of the first converter 31 and the output power of the first converter 31 will be referred to as the specific correspondence relationship.

[0021] <Scanning process> The scanning process will now be explained. In the scanning process, the CPU 21 searches for the maximum efficiency voltage Y by scanning the output voltage of the first converter 31 across the entire scanning range. The maximum efficiency voltage Y is the output voltage of the first converter 31 at which the output power of the first converter 31 is maximized within the scanning range. That is, in the scanning process, the CPU 21 gradually changes the output voltage of the first converter 31 within the scanning range and monitors the output power of the first converter 31 obtained at each output voltage. Then, as shown in Figure 3, the CPU 21 identifies a pair of the maximum power value W, which is the value at which the output power of the first converter 31 is maximized, and the maximum efficiency voltage Y, which is the output voltage of the first converter 31 corresponding to that maximum power value W. As described above, there may be multiple maximums of output power of the first converter 31 on the PV characteristic curve. In this case, the CPU 21 identifies multiple pairs of maximum efficiency voltage Y and maximum power value W. The CPU 21 can calculate the output power of the first converter 31 by multiplying the output current and output voltage of the first converter 31, which are obtained from the measurement circuit 27.

[0022] The scanning range is the range of output voltages, with zero as the lower limit and the characteristic voltage as the upper limit. The characteristic voltage is a value as follows. Now, let's assume that the output voltage of the first converter 31 is increased from zero on the PV characteristic line. At this time, the output power of the first converter 31 increases from zero, fluctuates, and then returns to zero again. The output voltage of the first converter 31 when the output power of the first converter 31 returns to zero is the characteristic voltage. The scanning range corresponds to a predetermined range.

[0023] <Memory Processing> The CPU 21 also performs memory processing to store the information obtained during the scan process. This memory processing will now be explained. There are two cases when the CPU 21 performs the scan: the first case where there is only one maximum output power of the first converter 31 on the PV characteristic line, and the second case where there are multiple such maximums. The following describes the processing that the CPU 21 performs in memory processing for each case.

[0024] First, let's explain the first case. As mentioned above, in the first case, there is only one set of maximum efficiency voltage Y and maximum power value W that the CPU 21 identifies during the scan process. In this case, the CPU 21 stores the maximum efficiency voltage Y obtained through the scan process in memory 22 as the latest efficiency voltage Ynew. At this time, the CPU 21 overwrites the previously stored latest efficiency voltage Ynew with the new latest efficiency voltage Ynew.

[0025] In addition to storing the latest efficiency voltage Ynew, the CPU 21 also performs the following: The CPU 21 determines whether the maximum power value W corresponding to the maximum efficiency voltage Y obtained by the scan process is greater than or equal to the first threshold U1. If the maximum power value W is greater than or equal to the first threshold U1, the CPU 21 stores the maximum efficiency voltage Y obtained by the scan process in memory 22 as the first efficiency voltage Y1. At this time, the CPU 21 overwrites the previously stored first efficiency voltage Y1 with the new first efficiency voltage Y1. If the maximum power value W is less than the first threshold U1, the CPU 21 keeps the previously stored first efficiency voltage Y1 in memory 22 as is. Details of the first threshold U1 will be described later.

[0026] Furthermore, the CPU 21 determines whether the maximum power value W corresponding to the maximum efficiency voltage Y obtained by the scan process is less than or equal to the second threshold U2. If the maximum power value W is less than or equal to the second threshold U2, the CPU 21 stores the maximum efficiency voltage Y obtained by the scan process in memory 22 as the second efficiency voltage Y2. At this time, the CPU 21 overwrites the previously stored second efficiency voltage Y2 with the new second efficiency voltage Y2. If the maximum power value W is greater than the second threshold U2, the CPU 21 retains the previously stored second efficiency voltage Y2 in memory 22 as is. Details of the second threshold U2 will be described later.

[0027] Next, let's explain the second case. In the second case, there are multiple pairs of maximum efficiency voltage Y and maximum power value W that the CPU 21 identifies during the scan process. In this second case, the CPU 21 identifies the maximum value among the multiple maximum power values ​​W obtained through the scan process as the maximum maximum value. The CPU 21 then stores the maximum efficiency voltage Y corresponding to this maximum maximum value in memory 22 as the latest efficiency voltage Ynew. At this time, the CPU 21 overwrites the previously stored latest efficiency voltage Ynew with the new latest efficiency voltage Ynew.

[0028] In addition to storing the latest efficiency voltage Ynew, the CPU 21 also performs the following: The CPU 21 determines whether the maximum value is greater than or equal to the first threshold U1. If the maximum value is greater than or equal to the first threshold U1, the CPU 21 stores the maximum efficiency voltage Y corresponding to the maximum value as the first efficiency voltage Y1 in memory 22. At this time, the CPU 21 overwrites the previously stored first efficiency voltage Y1 with the new first efficiency voltage Y1. If the maximum value is less than the first threshold U1, the CPU 21 keeps the previously stored first efficiency voltage Y1 in memory 22 as is.

[0029] Furthermore, the CPU 21 determines whether the maximum value is less than or equal to the second threshold U2. If the maximum value is less than or equal to the second threshold U2, the CPU 21 stores the maximum efficiency voltage Y corresponding to the maximum value in memory 22 as the second efficiency voltage Y2. At this time, the CPU 21 overwrites the previously stored second efficiency voltage Y2 with the new second efficiency voltage Y2. If the maximum value is greater than the second threshold U2, the CPU 21 keeps the previously stored second efficiency voltage Y2 in memory 22 as is. Here, if the maximum value is greater than the second threshold U2, the CPU 21 may also determine whether the other maximum power values ​​W among the multiple maximum power values ​​W are less than or equal to the second threshold U2. For example, the CPU 21 identifies the minimum value among the multiple maximum power values ​​W as the maximum minimum value. Then, the CPU 21 determines whether the maximum minimum value is less than or equal to the second threshold U2. Then, if the maximum minimum value is less than or equal to the second threshold U2, the CPU 21 stores the maximum efficiency voltage Y corresponding to the maximum minimum value in memory 22 as the second efficiency voltage Y2. In this way, by considering the maximum efficiency voltage Y corresponding to a maximum power value W other than the maximum maximum value as a candidate for the second efficiency voltage Y2, the opportunities to update the second efficiency voltage Y2 can be increased.

[0030] In the memory processing described above, the CPU 21 of this embodiment stores the latest efficiency voltage Ynew, the first efficiency voltage Y1, and the second efficiency voltage Y2 in non-volatile memory. The first threshold U1 and the second threshold U2 will now be explained. For example, suppose statistics are taken on the frequency distribution of the maximum power value W for various PV characteristic lines where the conditions in which the solar panel 70 is placed differ, such as different amounts of sunlight. In these statistics, the range of values ​​in which the frequency of occurrence of the maximum power value W can be considered to be relatively high is called the normal occurrence range. The first threshold U1 is predetermined as a value slightly larger than the upper limit of the normal occurrence range. The second threshold U2 is predetermined as a value slightly smaller than the lower limit of the normal occurrence range. In this embodiment, the first threshold U1 and the second threshold U2 are defined using the mean value and standard deviation of the maximum power value W obtained from the above statistics of the maximum power value W. The first threshold U1 is predetermined as a value obtained by adding 1 times the standard deviation to the mean value of the maximum power value W. The second threshold U2 is predetermined as a value obtained by subtracting 1 times the standard deviation from the mean value of the maximum power value W. Memory 22 stores the first threshold U1 and the second threshold U2 in advance.

[0031] <Voltage adjustment process> The specific processing procedure for the voltage adjustment process will now be explained. As shown in Figure 4, when the CPU 21 starts the voltage adjustment process, it first performs the process in step S100. In step S100, the CPU 21 sets the latest efficiency voltage Ynew stored in memory 22 as the voltage instruction value Q. Through this process in step S100, the CPU 21 sets the latest efficiency voltage Ynew as the initial value for controlling the output voltage of the first converter 31 in the voltage adjustment process. After this, the CPU 21 proceeds to step S110.

[0032] In step S110, the CPU 21 controls the first converter 31 so that its output voltage matches the currently set voltage instruction value Q. The CPU 21 then calculates the output power of the first converter 31 when its output voltage is controlled to match the voltage instruction value Q. In this way, the CPU 21 obtains the output power of the first converter 31 corresponding to the voltage instruction value Q. Once the CPU 21 has obtained the output power of the first converter 31, it proceeds to step S120. As described above, the CPU 21 can calculate the output power of the first converter 31 based on the detection result of the measurement circuit 27.

[0033] In step S120, the CPU 21 determines whether the elapsed time since the start of the voltage adjustment process has reached a predetermined time. The predetermined time is predetermined as the length of time for continuing one voltage adjustment process. As mentioned above, the predetermined time is, for example, 1 minute. If the result of the determination in step S120 is NO, the CPU 21 proceeds to step S130.

[0034] In step S130, the CPU 21 performs a first determination to determine whether the output power of the first converter 31 has increased from below the first threshold U1 to above the first threshold U1 within a predetermined control cycle. Hereinafter, this first determination may be referred to as the sudden change determination. The sudden change determination is a determination of whether the above-mentioned specific correspondence relationship, which is the correspondence relationship between the output voltage and output power of the first converter 31, has changed. A situation in which the sudden change determination is affirmed in step S130 is, for example, a situation in which the output power of the first converter 31 has increased rapidly, such as when the amount of solar radiation to the solar panel 70 has increased rapidly compared to the situation in which the latest efficiency voltage Ynew was detected. The control cycle mentioned above is the length of one cycle when the CPU 21 repeats the processing in step S110. The control cycle mentioned above is, for example, on a scale of less than 1 second. Now, as for the specific processing in step S130, the CPU 21 determines whether the first condition is met by referring to the latest power and the previous power of the first converter 31. The processing in step S110 is referred to as the power acquisition processing. The latest power is the output power of the first converter 31 obtained by the most recent power acquisition process. The previous power is the output power obtained by the power acquisition process performed immediately before the most recent power acquisition process. The first condition is that the previous power is less than the first threshold U1, and the latest power is greater than or equal to the first threshold U1. If the first condition is met, the CPU 21 determines that the output power of the first converter 31 has increased to greater than or equal to the first threshold U1 (step S130: YES). In this case, the CPU 21 determines that a specific correspondence has changed as a result of the sudden change determination. In this case, the CPU 21 proceeds to step S140. In step S140, the CPU 21 sets the first efficiency voltage Y1 stored in memory 22 as the voltage instruction value Q. After this, the CPU 21 returns to the process in step S110.

[0035] On the other hand, in step S130, if the first condition is not met, the CPU 21 determines that the output power of the first converter 31 has not increased to or above the first threshold U1 (step S130: NO). In this case, the CPU 21 determines, as a result of the sudden change determination, that the specific correspondence has not changed. In this case, the CPU 21 proceeds to step S150.

[0036] In step S150, the CPU 21 performs a second determination to determine whether the output power of the first converter 31 has decreased from a value greater than the second threshold U2 to a value less than or equal to the second threshold U2 within the control cycle. Hereinafter, this second determination may be referred to as the sudden change determination. A situation in which the sudden change determination is affirmed in step S150 is, for example, a situation in which the output power of the first converter 31 has decreased sharply, such as when the amount of solar radiation to the solar panel 70 has decreased sharply compared to the situation in which the latest efficiency voltage Ynew was detected. Similar to step S130, the CPU 21 performs the second determination by referring to the latest power and the previous power of the first converter 31. Specifically, the CPU 21 determines whether the latest power and the previous power of the first converter 31 satisfy the second condition. The second condition is that the previous power is greater than the second threshold U2, and the latest power is less than or equal to the second threshold U2. If the second condition is met, the CPU 21 determines that the output power of the first converter 31 has decreased to below the second threshold U2 (step S150: YES). In this case, the CPU 21 determines that the specific correspondence has changed as a result of the sudden change determination. In this case, the CPU 21 proceeds to step S160. In step S160, the CPU 21 sets the second efficiency voltage Y2 stored in memory 22 as the voltage instruction value Q. After this, the CPU 21 returns to the processing in step S110.

[0037] On the other hand, in step S150, if the second condition is not met, the CPU 21 determines that the output power of the first converter 31 has not decreased to below the second threshold U2 (step S150: NO). In this case, the CPU 21 determines, as a result of the sudden change determination, that the specific correspondence has not changed. In this case, the CPU 21 proceeds to step S170.

[0038] In step S170, the CPU 21 sets the voltage indicator value Q using the so-called hill-climbing method. Specifically, the CPU 21 sets a new voltage indicator value Q by adding or subtracting a predetermined adjustment value to the previous indicator value, which is the voltage indicator value Q set in the previous step. The adjustment value is a positive value. The adjustment value is predetermined as the optimal value for the amount of change per cycle of the output voltage of the first converter 31. Memory 22 stores the adjustment value in advance. The CPU 21 calculates the voltage indicator value Q by changing the previous indicator value in a direction that increases the output power of the first converter 31. The direction that increases the output power here means either increasing the voltage indicator value Q relative to the previous indicator value, or decreasing the voltage indicator value Q relative to the previous indicator value. The CPU 21 determines the direction in which to change the voltage indicator value Q by referring to the latest power and the previous power of the first converter 31. If the latest power of the first converter 31 is greater than or equal to the previous power, the CPU 21 sets the direction in which to change the voltage indicator value Q to the same direction as when step S170 was executed the previous time. On the other hand, if the latest power of the first converter 31 is less than the previous power, the CPU 21 reverses the direction in which it changes the voltage indicator value Q from the direction in which it performed step S170 last time. Once the CPU 21 has determined the direction in which it changes the voltage indicator value Q, it sets the new voltage indicator value Q to a value obtained by changing the previous indicator value by the adjustment value in that direction. Note that if the CPU 21 performs the process of step S170 for the first time after performing any of the processes of steps S100, S140, or S160, it sets the new voltage indicator value Q to a value obtained by adding the adjustment value to the voltage indicator value Q determined in those processes. Once the CPU 21 has set the voltage indicator value Q, it returns to the process of step S110.

[0039] As described above, the CPU 21 repeatedly sets the voltage instruction value Q through step S140, step S160, or step S170, and controls the first converter 31 through step S110. If the result of the determination in step S120 becomes YES during this repetition, that is, if the elapsed time since the start of the voltage adjustment process reaches a predetermined time, the CPU 21 terminates the series of processes of the voltage adjustment process. After this, as shown in Figure 2, the CPU 21 performs a scan process and then starts the voltage adjustment process again.

[0040] <Operation of the Embodiment> In the description of the operation and effects of the embodiments described below, the maximum efficiency voltage Y refers to the maximum efficiency voltage Y corresponding to the maximum output power of the first converter 31.

[0041] Let's assume that CPU 21 is currently performing voltage adjustment processing. Let's also assume that the judgment results in steps S120, S130, and S150 have all been NO. In this case, CPU 21 repeatedly sets the voltage instruction value Q using the hill-climbing method in step S170 and controls the first converter 31 in step S110. For example, when CPU 21 sets the voltage instruction value Q at the first timing T1, let's assume that CPU 21 sets the new voltage instruction value Q to the value obtained by adding an adjustment value to the previous instruction value. When CPU 21 controls the first converter 31 based on this voltage instruction value Q, let's assume that the latest power of the first converter 31 is greater than the previous power. In this case, when CPU 21 sets the voltage instruction value Q at the subsequent second timing T2, it sets the direction of change of the voltage instruction value Q to the same direction as at the first timing T1. That is, at the second timing T2, CPU 21 also sets the new voltage instruction value Q to the value obtained by adding an adjustment value to the previous instruction value. The CPU 21 then controls the first converter 31 based on this voltage instruction value Q. Let's assume that the latest power of the first converter 31 is lower than the previous power. In this case, when the CPU 21 sets the voltage instruction value Q at the subsequent third timing T3, it changes the direction of the voltage instruction value Q in the opposite direction to the previous time. That is, at the third timing T3, the CPU 21 sets the new voltage instruction value Q to a value obtained by subtracting the adjustment value from the previous instruction value. Then, the CPU 21 controls the first converter 31 based on this voltage instruction value Q. Through the repetition of this process, the CPU 21, in the voltage adjustment process as a whole, changes the output voltage of the first converter 31 in a direction that increases the output power of the first converter 31.

[0042] Now, during the execution of the voltage adjustment process, the specific correspondence related to the first converter 31 may change abruptly. For example, as shown by the dashed line in Figure 5, suppose that at an arbitrary fourth timing T4 during the execution of the voltage adjustment process, the maximum value of the output power on the PV characteristic line is less than the first threshold U1. Then, suppose that the output power A1 of the first converter 31 corresponding to the voltage instruction value F1 determined by the hill-climbing method at this time is less than the first threshold U1. Furthermore, suppose that at the subsequent fifth timing T5, the specific correspondence changes abruptly, as shown by the solid line in Figure 5. Then, suppose that the maximum power AM on the PV characteristic line after this abrupt change is greater than the first threshold U1. Here, immediately after the abrupt change in the PV characteristic line, the CPU 21 determines the voltage instruction value F2 by the hill-climbing method, following the fourth timing T4. The output power A2 of the first converter 31 corresponding to the voltage instruction value F2 determined at this time will be a value that reflects the PV characteristic line after the abrupt change. Now, let's assume that the output power A2 is greater than the first threshold U1, reflecting the PV characteristic curve after the sudden change. When the CPU 21 obtains this output power A2, in the first determination, which is a sudden change determination, it determines that the output power of the first converter 31 has increased from less than the first threshold U1 to greater than or equal to the first threshold U1 (step S130: YES). In this case, as shown by the arrow AX in Figure 5, the CPU 21 changes the voltage indicator Q from the previous indicator F2 to the first efficiency voltage Y1 at this point (step S140). After this, the CPU 21 sets the voltage indicator Q again using the hill-climbing method, with the changed voltage indicator Q, the first efficiency voltage Y1, as the new initial value. In other words, the CPU 21 continues the voltage adjustment process. Note that the PV characteristic curves, output powers, and voltage indicators shown in Figure 5 are examples to explain the operation of this embodiment and do not necessarily correspond to actual values.

[0043] Here, under the first condition where the maximum output power of the first converter 31 is greater than or equal to the first threshold U1 in the PV characteristic curve, the PV characteristic curves are likely to have similar distributions. Furthermore, under the first condition, the maximum efficiency voltage Y corresponding to the above maximum value is likely to always be approximately the same value. In particular, if the first conditions occur at relatively close timings, the maximum efficiency voltage Y is likely to be approximately the same. Here, the first efficiency voltage Y1 stored in memory 22 can be said to be the maximum efficiency voltage Y identified in the first condition that occurred at the timing closest to the present. And, if the result of the first judgment in step S130 is YES, the current situation is the first condition. In other words, if the result of the first judgment is YES, the current maximum efficiency voltage Y is likely to be close to the first efficiency voltage Y1 stored in memory 22. For these reasons, as in this embodiment, if the result of the first determination is YES (step S130: YES), and the voltage indicator value Q is changed to the first efficiency voltage Y1 (step S140), the following is likely to be achieved. That is, as shown in Figure 5, the output power A3 of the first converter 31 corresponding to the first efficiency voltage Y1, which is the changed voltage indicator value Q, is likely to be close to the maximum power AM on the PV characteristic line after the abrupt change.

[0044] Now, in the case of a sudden change in the specific correspondence related to the first converter 31, the following may occur. For example, as shown by the dashed line in Figure 6, suppose that at an arbitrary sixth timing T6 during voltage adjustment processing, the maximum value of the PV characteristic line was greater than the second threshold U2. And suppose that at this time, the output power B1 of the first converter 31 corresponding to the voltage instruction value G1 determined by the hill-climbing method was greater than the second threshold U2. Furthermore, suppose that at the subsequent seventh timing T7, as shown by the solid line in Figure 6, the specific correspondence changed suddenly. And suppose that the maximum power BM on the PV characteristic line after this sudden change was less than the second threshold U2. As explained in Figure 5 above, at this point, the CPU 21 determines the voltage instruction value G2 for the next timing using the hill-climbing method. And suppose that the output power B2 of the first converter 31 corresponding to this voltage instruction value G2 is a value that reflects the PV characteristic line after the sudden change. Now, suppose that this output power B2 was a value smaller than the second threshold U2. When the CPU 21 obtains the output power B2, in the second determination, which is a sudden change determination, it determines that the output power of the first converter 31 has decreased from a value greater than the second threshold U2 to a value less than or equal to the second threshold U2 (step S150: YES). In this case, as shown by the arrow BX in Figure 6, the CPU 21 changes the voltage instruction value Q from the previous instruction value G2 to the second efficiency voltage Y2 at this point (step S160). After this, the CPU 21 sets the voltage instruction value Q again using the hill-climbing method, with the changed voltage instruction value Q, which is the second efficiency voltage Y2, as the new initial value. In other words, the CPU 21 continues the voltage adjustment process. Note that the PV characteristic lines, output powers, and voltage instruction values ​​shown in Figure 6 are examples to explain the operation of this embodiment and do not necessarily correspond to actual values.

[0045] Here, as explained in the first situation above, in the second situation, where the condition is met that the maximum output power of the first converter 31 on the PV characteristic curve is less than or equal to the second threshold U2, the maximum efficiency voltage Y corresponding to that maximum value is likely to always be around the same value. And, if the result of the second judgment in step S150 is YES, the current situation is likely to be the second situation. At the same time, if the result of the second judgment is YES, the current maximum efficiency voltage Y is likely to be close to the second efficiency voltage Y2 stored in memory 22. Therefore, as in this embodiment, if the result of the second judgment is YES (step S150: YES) and the voltage instruction value Q is changed to the second efficiency voltage Y2 (step S160), the following is likely to be achieved. That is, as shown in Figure 6, the output power B3 of the first converter 31 corresponding to the second efficiency voltage Y2, which is the changed voltage instruction value Q, is likely to be close to the maximum power BM on the PV characteristic curve after the sudden change.

[0046] <Effects of the Embodiment> (1) When the CPU 21 determines that a specific correspondence has changed abruptly, it changes the output voltage of the first converter 31 to the maximum efficiency voltage Y that was previously stored. When the output voltage of the first converter 31 is changed to the maximum efficiency voltage Y, it is highly likely that the time required to bring the output voltage of the first converter 31 closer to the maximum efficiency voltage Y after the specific correspondence has changed abruptly can be shortened compared to continuing to control the first converter 31 using the hill-climbing method. Therefore, in the configuration of this embodiment, when abrupt changes occur in the specific correspondence, the output voltage of the first converter 31 can be returned to the vicinity of the maximum efficiency voltage Y at an earlier timing and the first converter 31 can be controlled.

[0047] (2) As explained in the operation of the above embodiment, if the result of the first determination is YES, the maximum efficiency voltage Y at that time is likely to be close to the first efficiency voltage Y1. Therefore, as in this embodiment, by changing to the first efficiency voltage Y1 at that time when the result of the first determination is YES, the CPU 21 is likely to be able to quickly bring the output voltage of the first converter 31 closer to the maximum efficiency voltage Y after the specific correspondence relationship has suddenly changed. This makes it easier to obtain the effect of returning the output voltage of the first converter 31 to the vicinity of the maximum efficiency voltage Y at an earlier timing, as described in (1) above.

[0048] (3) Similar to (2), if the result of the second judgment is YES, the CPU 21 changes the voltage instruction value Q to the second efficiency voltage Y2 at that point, which makes it highly likely that the output voltage of the first converter 31 will be brought closer to the maximum efficiency voltage Y after the specific correspondence has suddenly changed. As a result, similar to (2) above, the effects described in (1) above are more likely to be obtained.

[0049] <Example of changes> The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0050] The first threshold U1 is not limited to the examples of the above embodiments. Preferably, the first threshold U1 is a value suitable for detecting a sudden change in a specific correspondence to a specific correspondence having a maximum power value W that is larger than normal.

[0051] The second threshold U2 is not limited to the examples of the above embodiments. Preferably, the second threshold U2 is a value suitable for detecting a sudden change in a specific correspondence to a specific correspondence having a maximum power value W smaller than normal. The second threshold U2 is set to a value smaller than the first threshold U1.

[0052] The second judgment step may be abolished. Along with that, the second efficiency voltage Y2 may be abolished. Furthermore, the first judgment step may be abolished. Along with that, the first efficiency voltage Y1 may be abolished. If the first and second judgment steps are abolished, an appropriate sudden change judgment step may be set to replace them. The sudden change judgment step only needs to be able to determine whether or not a specific correspondence relationship has changed. For example, as a sudden change judgment step, a determination may be made as to whether or not the amount of change in output power from the previous power to the latest power is greater than a predetermined judgment value. If the amount of change is greater than the judgment value, it may be determined that the specific correspondence relationship has changed. If it is determined that the specific correspondence relationship has changed, the voltage indicator value Q may be changed to the latest efficiency voltage Ynew at that point. Even if the voltage indicator value Q is changed to the latest efficiency voltage Ynew, there is a high possibility that the time required to bring the output voltage of the first converter 31 closer to the maximum efficiency voltage Y after the sudden change in the specific correspondence relationship can be shortened compared to continuing to control the first converter 31 using the hill-climbing method.

[0053] The configuration of the solar power generation system is not limited to the examples of the embodiments described above. For example, the number of solar panels may be changed from the examples of the embodiments described above. Also, the number of DC-DC converters may be changed depending on the amount of power required, the number of power supply destinations, etc. The solar power generation system only needs to include at least one solar panel and a DC-DC converter that converts the output voltage of the solar panel into a voltage output. [Explanation of Symbols]

[0054] 20...Control device 31...First converter 70...Solar panel

Claims

[Claim 1] This is applied to a solar power generation system comprising a solar panel and a DC-DC converter that converts the output voltage of the solar panel into a voltage output. The process involves performing a scan to search for the maximum efficiency voltage, which is the output voltage of the DC-DC converter at which the output power of the DC-DC converter becomes maximum within a predetermined range. The maximum efficiency voltage obtained by the scan process is stored as the latest efficiency voltage, If the output power of the DC-DC converter corresponding to the maximum efficiency voltage obtained in the scan process is greater than or equal to a predetermined first threshold, the maximum efficiency voltage is stored as the first efficiency voltage. After the scan process, a voltage adjustment process is performed to change the output voltage of the DC-DC converter in a direction that increases the output power of the DC-DC converter, using the latest efficiency voltage as the initial value. During the voltage adjustment process, it is determined whether the output power of the DC-DC converter has increased from below the first threshold to above the first threshold, When the output power of the DC-DC converter increases to or above the first threshold, the output voltage of the DC-DC converter is changed to the first efficiency voltage at that point. The voltage adjustment process is performed again, with the modified output voltage of the DC-DC converter as the new initial value. Control device for a solar power generation system.

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