Control device for solar power generation system

Abstract

To shorten a time required to scan an entire predetermined range in search of a maximum efficiency voltage.SOLUTION: A control device 20 searches for a maximum efficiency voltage, which is an output voltage of a first converter 31 at which output electric power of the first converter 31 is maximized by scanning the output voltage of the first converter 31 within a predetermined range. At this time, the control device 20 sequentially executes: controlling the output voltage of the first converter 31 to a first voltage, and at that time, acquiring the output electric power of the first converter 31 as first electric power; controlling the output voltage of the first converter 31 to a second voltage that is changed from the first voltage by a first change width, and at that time, acquiring the output electric power of the first converter 31 as the second electric power; controlling the output voltage of the first converter 31 to a third voltage that is changed by a second change width from the second voltage; and sets when the second electric power is less than the first electric power, the second change width to a larger value than the first change width.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This 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 electricity by receiving sunlight irradiation. The solar panel outputs the generated power to the DCDC converter. The DCDC converter voltage-converts the output voltage from the solar panel and outputs it. The control device controls the output voltage of the DCDC converter.

[0003] The control device performs a scan process for determining a reference voltage that serves as a reference in controlling the DCDC converter. In the scan process, the control device monitors the output power of the DCDC converter obtained at each output voltage while gradually changing the output voltage of the DCDC converter within a predetermined range. Then, the control device determines the output voltage of the DCDC converter when the output power of the DCDC converter is maximized as the reference voltage. And the control device controls the DCDC converter so that the output voltage of the DCDC converter approaches the determined reference voltage.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a technique such as Patent Document 1 that searches for a reference voltage by a scan process, in order to start normal control as soon as possible, it is required to minimize the time required for the scan process. Patent Document 1 does not consider this point. [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 is capable of searching 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 the predetermined range by scanning the output voltage of the DC-DC converter within a predetermined range, and controlling the output voltage of the DC-DC converter to approach the maximum efficiency voltage, and in searching for the maximum efficiency voltage, the control device controls the output voltage of the DC-DC converter to a first voltage within the predetermined range, and the DC-DC converter The following steps are performed in order: first, the output power of the DC-DC converter when the output voltage of the converter is controlled to the first voltage is obtained as the first power; second, the output voltage of the DC-DC converter is controlled to a second voltage within a predetermined range obtained by changing the output voltage of the DC-DC converter by a first change amount from the first voltage; third, the output power of the DC-DC converter when the output voltage of the DC-DC converter is controlled to the second voltage is obtained as the second power; and fourth, the output voltage of the DC-DC converter is controlled to a third voltage within a predetermined range obtained by changing the output voltage of the DC-DC converter by a second change amount in the same direction as the first change amount. If the second power is smaller than the first power, the second change amount is set to a value larger than the first change amount. [Effects of the Invention]

[0007] The above technical concept reduces the time required to scan the entire predetermined range when searching for the maximum efficiency voltage. [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 scan processing and normal processing. [Figure 3]Figure 3 illustrates an example of a PV characteristic curve. [Figure 4] Figure 4 is a flowchart illustrating the processing steps of the scanning process. [Modes for carrying out the invention]

[0009] Hereinafter, one embodiment of a control device for a solar power generation system will be described with reference to the drawings. <Overall Structure> 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 the power supplied from the converter unit 30. The auxiliary battery 90 supplies power to an auxiliary system (not shown) installed in the vehicle 100. The auxiliary system of the vehicle 100 consists of one or more auxiliary devices. The auxiliary devices are, for example, an electric oil pump, a navigation system, and lamps.

[0013] <Converter Unit> The converter unit 30 comprises 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, together with the solar panel 70, constitutes a solar power generation system. Each DC-DC converter is a voltage conversion circuit that steps down or steps up a DC voltage for output. In the following, when describing each DC-DC converter, DC-DC will be omitted and it will simply be referred to as a converter. For example, the first DC-DC converter 31 will be 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 the input voltage, into a voltage based on the instructions of the control device 20 and outputs it.

[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 by the first converter 31 into a voltage within a predetermined range and outputs it 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 by the first converter 31 into a voltage within a predetermined range and outputs it to the auxiliary battery 90. 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 and output current of the first converter 31 at a predetermined control cycle. The measurement circuit 27 repeatedly outputs signals to the control device 20 corresponding to the output voltage and output current it has detected.

[0018] <Control device> The control device 20 includes a CPU 21 and a memory 22. The memory 22 stores various programs in which the processes to be executed by the CPU 21 are described in advance. The CPU 21 controls the first converter 31, the second converter 32, and the third converter 33 by executing the programs stored in the memory 22.

[0019] When controlling the first converter 31, the CPU 21 sets a voltage instruction value Q regarding the output voltage of the first converter 31. Then, the CPU 21 controls the first converter 31 so as to realize the output voltage of this voltage instruction value Q. Incidentally, when controlling the first converter 31, the CPU 21 refers to the output power of the first converter 31. The CPU 21 can calculate the output power of the first converter 31 by multiplying the output current and the output voltage of the first converter 31 acquired from the measurement circuit 27.

[0020] <Overview of the Control of the First Converter> The CPU 21 becomes activated as needed not only while the start switch of the vehicle 100 is on but also while the start switch is off. The start switch is a switch for switching the on / off of the main system of the vehicle 100. While the CPU 21 is in the activated state, it performs the first converter process for controlling the first converter 31. There are two types of the first converter process: normal process and scan process. As shown in FIG. 2, the CPU 21 performs these normal process and scan process alternately. The CPU 21 performs the normal process over a certain period such as one minute, for example. Then, the CPU 21 quickly performs the scan process within a very short time such as within one second, for example. That is, the CPU 21 basically executes the scan process by interruption while executing the normal process.

[0021] This section explains the PV characteristic curve, which is the basis for normal and scan processing. 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 that can be realized by the first converter 31 according to the current power generation status of the solar panel 70. The PV characteristic curve basically has a bell-shaped distribution. That is, the PV characteristic curve has a maximum power point where the output power of the first converter 31 is at its maximum. 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 peaks where the output power of the first converter 31 changes from increasing to decreasing. Hereafter, the regions on either side of the peak where the output power of the first converter 31 changes from increasing to decreasing will be referred to as the uphill slope region and the downhill slope region, respectively. The upward-sloping region is the region on the PV characteristic curve where the output power of the first converter 31 increases as the output voltage of the first converter 31 increases. The downward-sloping region is the region on the PV characteristic curve where the output power of the first converter 31 decreases as the output voltage of the first converter 31 increases.

[0022] In the scanning process, the CPU 21 searches for the maximum efficiency voltage Y by scanning the output voltage of the first converter 31 within the 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 maximum within the scanning range. That is, the maximum efficiency voltage Y is the output voltage of the first converter 31 corresponding to the maximum power point on the PV characteristic line. 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 has the following value. Now, let's assume that the output voltage of the first converter 31 is increased from zero on the PV characteristic line. Note that when the output voltage of the first converter 31 is zero, the output power of the first converter 31 is zero. As the output voltage of the first converter 31 is increased from zero, the output power of the first converter 31 increases and decreases and eventually returns to zero. 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] In normal processing, the CPU 21 controls the output voltage of the first converter 31 so that its output voltage approaches the maximum efficiency voltage Y. In this normal processing, the CPU 21 utilizes a known hill-climbing method. Specifically, in normal processing, the CPU 21 performs the following: At the start of normal processing, the CPU 21 controls the first converter 31 by setting the voltage instruction value Q for the first converter 31 to the maximum efficiency voltage Y identified in the scan process. After this, the CPU 21 gradually changes the output voltage of the first converter 31 in a direction that increases the output power of the first converter 31. Specifically, the CPU 21 first gradually increases the output voltage of the first converter 31. The CPU 21 continues to gradually increase the output voltage of the first converter 31 as long as the continuation condition is met. The continuation condition is that the output power of the first converter 31 is greater than the previous value. When the continuation condition is no longer met, the CPU 21 switches the direction in which it changes the output voltage of the first converter 31. In other words, the CPU 21 gradually decreases the output voltage of the first converter 31. After this, the CPU 21 continues to gradually decrease the output voltage of the first converter 31 as long as the continuation condition is met. Then, when the continuation condition is no longer met, the CPU 21 switches the direction of changing the output voltage of the first converter 31 again. In normal processing, the CPU 21 switches the direction of changing the output voltage of the first converter 31 in this manner.

[0024] <Specific details of the scanning process> Before explaining the details of the scan process, the power acquisition process will be explained. The CPU 21 performs the power acquisition process as part of the scan process. In the power acquisition process, the CPU 21 controls the first converter 31 so that its output voltage matches a pre-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. As described above, the CPU 21 can calculate the output power of the first converter 31 based on the detection results of the measurement circuit 27. The calculation of the output power of the first converter 31 by the CPU 21 is equivalent to the CPU 21 acquiring the output power of the first converter 31. When the CPU 21 acquires the output power of the first converter 31, it stores a set of the output power and the voltage instruction value Q that made this output power possible in the memory 22 as scan result information. The CPU 21 performs this series of processes in the power acquisition process. Note that each time the CPU 21 performs the power acquisition process, the amount of scan result information stored in the memory 22 increases. In the following, the group of scan result information stored in memory 22 will be referred to as the result list. The result list is a list in which multiple scan result information is arranged chronologically.

[0025] As a prerequisite for explaining the details of the scan process, the initial change range EA will be explained. The change range of the output voltage per scan when the CPU 21 scans the output voltage of the first converter 31 within the scanning range is called the voltage change range E. The initial change range EA is the initial value of the voltage change range E. Memory 22 stores the initial change range EA in advance. The initial change range EA is predetermined, for example, through experimentation or simulation, from the following perspective, for PV characteristic lines under various conditions with different amounts of sunlight. Now, let's focus on a certain upward slope region in the PV characteristic line. The minimum value of the output voltage of the first converter 31, which is the starting point of this upward slope region, will be called the minimum voltage. The initial change range EA is a value adjusted so that when the voltage instruction value Q for the first converter 31 is increased by the initial change range EA from the minimum voltage, the output power of the first converter 31 stays within the value in the upward slope region, that is, the output power does not reach the peak of its increase or decrease.

[0026] The following describes the specific processing steps for the scan process. When the CPU 21 starts the scan process, it sets the initial voltage instruction value Q and then executes the process in step S10. The CPU 21 sets the initial voltage instruction value Q to a value obtained by adding the initial change range EA to zero.

[0027] As shown in Figure 4, in step S10, the CPU 21 performs the initial power acquisition process. In this initial power acquisition process, the CPU 21 controls the first converter 31 based on the initial voltage instruction value Q, and stores the output power of the first converter 31 obtained therefrom as scan result information in the memory 22. Once the CPU 21 has finished executing the initial power acquisition process, it proceeds to step S20.

[0028] In step S20, the CPU 21 determines whether the latest power Pnew is less than the previous power Pold. The latest power Pnew is the output power of the first converter 31 obtained from the most recent power acquisition process. The previous power Pold is the output power obtained from the power acquisition process performed immediately before the most recent power acquisition process. The CPU 21 can determine the latest power Pnew and the previous power Pold by referring to the results list. Note that if the CPU 21 is executing the process in step S20 for the first time after the start of the scan process, it treats the previous power Pold as zero. If the latest power Pnew is greater than or equal to the previous power Pold (step S20: NO), the CPU 21 proceeds to step S40. The situation in which the determination result of step S20 is NO is when the control point of the first converter 31 is located in an upward sloping region on the PV characteristic line. The control point of the first converter 31 is a combination of the voltage instruction value Q for the first converter 31 and the output power corresponding to that voltage instruction value Q.

[0029] In step S40, the CPU 21 sets a new voltage change range Enew. Specifically, the CPU 21 sets the new voltage change range Enew to a value obtained by subtracting the second setting value C2 from the previous value of the voltage change range E, which is the previous change range Eold. Note that if the CPU 21 is executing the process in step S40 for the first time after the start of the scan process, the previous change range Eold is used as the initial change range EA. The second setting value C2 is predetermined to be a value that is smaller than the initial change range EA and greater than zero. For example, the second setting value C2 is 10% of the initial change range EA. Memory 22 stores the second setting value C2 in advance.

[0030] Furthermore, when the calculated value is obtained by subtracting the second setting value C2 from the previous change range Eold, if the CPU 21 sets the lower limit change range as the new voltage change range Enew instead of the calculated value if the calculated value is smaller than the lower limit change range. The lower limit change range is predetermined as a value that is smaller than the initial change range EA and greater than zero. For example, the lower limit change range is 10% of the initial change range EA. Memory 22 stores the lower limit change range in advance. The lower limit change range is predetermined, for example, by experiment or simulation, from the following perspectives, for PV characteristic lines under various conditions with different amounts of sunlight. Here, if the voltage change range E is made smaller, the maximum power point of the output power in the PV characteristic line, and thus the maximum efficiency voltage Y, can be detected with high accuracy. On the other hand, if the voltage change range E is made smaller, it takes a lot of time to scan the entire scanning range. The lower limit change range is a value that ensures that the maximum efficiency voltage Y can be detected with high accuracy, while not requiring excessive time to scan the entire scanning range. Once CPU21 sets a new voltage change range Enew, it proceeds to step S50.

[0031] On the other hand, in step S20, if the latest power Pnew is smaller than the previous power Pold (step S20: YES), the CPU 21 proceeds to step S30. The situation in which the result of the determination in step S20 is YES is when the control point of the first converter 31 is located in a downward sloping region on the PV characteristic line.

[0032] In step S30, the CPU 21 sets a new voltage change range Enew. Specifically, the CPU 21 sets the new voltage change range Enew to the previous value of the voltage change range E, which is the previous change range Eold, plus a first setting value C1. The first setting value C1 is predetermined to be smaller than the initial change range EA and greater than zero. For example, the first setting value C1 is 50% of the initial change range EA. Memory 22 stores the first setting value C1 in advance.

[0033] Furthermore, when the value obtained by adding the first setting value C1 to the previous change range Eold is used as the calculated value, if the CPU 21 finds that the calculated value is greater than the upper limit change range, it sets the upper limit change range as the new voltage change range Enew instead of the calculated value. For example, the upper limit change range is five times the initial change range EA. Memory 22 stores the upper limit change range in advance. The upper limit change range is predetermined, for example, through experiments or simulations, from the following perspectives, for PV characteristic curves under various conditions with different amounts of sunlight, etc. As mentioned above, the PV characteristic curve may have a distribution in which there are multiple peaks where the output power of the first converter 31 changes from increasing to decreasing. If the voltage change range E is made too large when the PV characteristic curve has such a distribution, there is a concern that the following may occur. That is, when the output voltage of the first converter 31 is increased by the voltage change range E, the control point of the first converter 31, which is located in the downward slope region, may reach the peak of the next upward region. The upper limit change range is determined from the perspective of preventing such a thing from happening. Once CPU21 sets a new voltage change range Enew, it proceeds to step S50.

[0034] In step S50, the CPU 21 sets a new voltage instruction value Qnew. Specifically, the CPU 21 sets the new voltage instruction value Qnew to the previous instruction value Qold, which is the previous value of the voltage instruction value Q, plus the voltage change range Enew calculated in step S30 or step S40. Once the CPU 21 has set the new voltage instruction value Qnew, it proceeds to step S60.

[0035] In step S60, the CPU 21 performs power acquisition processing. Specifically, the CPU 21 controls the first converter 31 based on the voltage instruction value Qnew set in step S50, and stores the output power of the first converter 31 obtained therefrom as scan result information in the memory 22. After this, the CPU 21 proceeds to step S70.

[0036] In step S70, the CPU 21 determines whether the latest power Pnew is zero. The latest power Pnew is the output power obtained in step S60. If the latest power Pnew is greater than zero (step S70: NO), the CPU 21 returns to the process in step S20. On the other hand, if the latest power Pnew is zero (step S70: YES), the CPU 21 proceeds to step S80. The situation in which the determination result in step S70 is YES corresponds to the situation in which the output voltage of the first converter 31 has reached the upper limit of the scanning range.

[0037] In step S80, the maximum efficiency voltage Y is identified. Specifically, the CPU 21 identifies the maximum value among multiple output powers in the result list stored in memory 22. Then, the CPU 21 identifies the voltage instruction value Q associated with this maximum value as the maximum efficiency voltage Y. After this, the CPU 21 clears the result list from memory 22 and then terminates the series of scan processes.

[0038] <Operation of the Embodiment> Let's assume that the scan process is currently running. And let's assume that CPU 21 is scanning the upstream region of the PV characteristic line. In this case, CPU 21 repeats the following processing cycle during the scan process. That is, since the latest power Pnew is greater than the previous power Pold (step S20: NO), CPU 21 sets the new voltage change range Enew to a value smaller than the previous change range Eold (step S40). Then, CPU 21 sets the new voltage instruction value Qnew to a value larger than the previous instruction value Qold by the amount of this voltage change range Enew (step S50). Then, CPU 21 performs power acquisition processing based on this voltage instruction value Qnew (step S60). By repeatedly making the new voltage change range Enew smaller than the previous change range Eold in step S40, CPU 21 gradually reduces the new voltage change range Enew. This point will be explained in detail using four consecutive timings as examples. That is, when CPU 21 searches for the maximum efficiency voltage Y, it performs the following processing in order. As shown in Figure 3, first at the first timing, the CPU 21 controls the output voltage of the first converter 31 to the first voltage V1 and acquires the output power of the first converter 31 at that time as the first power P1. At the next second timing, the CPU 21 controls the output voltage of the first converter 31 to the second voltage V2, which is changed from the first voltage V1 to a value greater than the first change range E1, and acquires the output power of the first converter 31 at that time as the second power P2. At the next third timing, the CPU 21 controls the output voltage of the first converter 31 to the third voltage V3, which is changed from the second voltage V2 to a value greater than the second change range E2, and acquires the output power of the first converter 31 at that time as the third power P3. At this time, the CPU 21 sets the second change range E2 to a value smaller than the first change range E1. Furthermore, at the fourth timing after the third timing, the CPU 21 controls the output voltage of the first converter 31 to a fourth voltage V4, which is obtained by changing the third voltage V3 to a value greater than the third change range E3, and acquires the output power of the first converter 31 at that time as the fourth power P4. At this time as well, the CPU 21 sets the third change range E3 to a value smaller than the second change range E2.

[0039] Now let's consider the situation where the CPU 21 is scanning the downstream region of the PV characteristic line. In this case, the CPU 21 repeats the following processing cycle during the scan process. That is, as shown in Figure 4, since the latest power Pnew is smaller than the previous power Pold (step S20: YES), the CPU 21 sets the new voltage change range Enew to a value larger than the previous change range Eold (step S30). Then, the CPU 21 sets the new voltage instruction value Qnew to a value larger than the previous instruction value Qold by the amount of this voltage change range Enew (step S50). Then, the CPU 21 performs power acquisition processing based on this voltage instruction value Qnew (step S60). By repeatedly increasing the new voltage change range Enew relative to the previous change range Eold in step S30, the CPU 21 gradually increases the new voltage change range Enew. This point will be explained in detail using four consecutive timings as examples. Here, we will use the 5th, 6th, 7th, and 8th timings following the 4th timing as examples. In searching for the maximum efficiency voltage Y, the CPU 21 performs the following processes in order. As shown in Figure 3, first at the fifth timing, the CPU 21 controls the output voltage of the first converter 31 to the fifth voltage V5 and acquires the output power of the first converter 31 at that time as the fifth power P5. At the next sixth timing, the CPU 21 controls the output voltage of the first converter 31 to the sixth voltage V6, which is changed from the fifth voltage V5 to the fourth change range E4, and acquires the output power of the first converter 31 at that time as the sixth power P6. At the next seventh timing, the CPU 21 controls the output voltage of the first converter 31 to the seventh voltage V7, which is changed from the sixth voltage V6 to the fifth change range E5, and acquires the output power of the first converter 31 at that time as the seventh power P7. At this time, the CPU 21 sets the fifth change range E5 to a value greater than the fourth change range E4. Furthermore, at the 8th timing after the 7th timing, the CPU 21 controls the output voltage of the first converter 31 to the 8th voltage V8, which is obtained by changing the 7th voltage V7 to the side that is larger by the 6th variation range E6, and acquires the output power of the first converter 31 at that time as the 8th power P8.Similar to the difference between the fourth change range E4 and the fifth change range E5, the CPU 21 sets the sixth change range E6 to a value greater than the fifth change range E5. Note that the voltage, power, and voltage change range at each timing shown in Figure 3 are examples to explain the operation of this embodiment and do not necessarily correspond to actual values.

[0040] <Effects of the Embodiment> (1) If the latest power Pnew is smaller than the previous power Pold (step S20: YES), the region of the PV characteristic line that the CPU 21 is currently scanning is likely to be a downward sloping region. In other words, if the latest power Pnew is smaller than the previous power Pold, the output power of the first converter 31 when the output voltage of the first converter 31 is further increased is likely to be even smaller than the latest power Pnew. And it is unlikely that this output power will be the maximum power point in the PV characteristic line. In this case, even if the voltage change range E used to set the new voltage indication value Qnew is large, it is unlikely that the CPU 21 will fail to detect the maximum power point and thus the maximum efficiency voltage Y. Therefore, if the latest power Pnew is smaller than the previous power Pold, the CPU 21 makes the new voltage change range Enew larger than the previous change range Eold (step S30). In this way, by increasing the single change range of the output voltage of the first converter 31, the time it takes for the CPU 21 to scan the entire scanning range when detecting the maximum efficiency voltage Y can be shortened.

[0041] (2) If the latest power Pnew is greater than the previous power Pold (step S20: NO), the region of the PV characteristic line that the CPU 21 is currently scanning is likely to be an upward-sloping region. In other words, if the latest power Pnew is greater than the previous power Pold, the output power of the first converter 31 when the output voltage of the first converter 31 is further increased is likely to be even greater than the latest power Pnew. And the output power of the first converter 31 at that time may be the maximum power point in the PV characteristic line. When scanning in such an upward-sloping region, if the magnitude of the change in the output voltage of the first converter 31 is made large, there is a risk of failing to detect the maximum power point and thus the maximum efficiency voltage Y in the PV characteristic line. That is, if the magnitude of the change in the output voltage of the first converter 31 is made large, there is a risk that the output power of the first converter 31 will exceed the maximum power point in the PV characteristic line and enter a downward-sloping region. Conversely, when scanning an upward-sloping region, reducing the magnitude of a single change in the output voltage of the first converter 31 allows for accurate detection of the maximum power point and, consequently, the maximum efficiency voltage Y. Therefore, if the latest power Pnew is greater than the previous power Pold, the CPU 21 reduces the voltage change E to be smaller than the previous change Eold (step S40). In this way, by reducing the magnitude of a single change in the output voltage of the first converter 31, the maximum power point and, consequently, the maximum efficiency voltage Y on the PV characteristic line can be accurately detected.

[0042] <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.

[0043] When the control point of the first converter 31 switches from an uphill slope region to a downhill slope region on the PV characteristic line, the previous change range Eold may be reset to the initial change range EA. The same applies when the control point of the first converter 31 switches from a downhill slope region to an uphill slope region on the PV characteristic line.

[0044] The method for setting the new voltage change range Enew in step S30 is not limited to the example of the above embodiment. For example, the first setting value C1 may be changed from the example of the above embodiment. The first setting value C1 may be the same as the second setting value C2. The first setting value C1 may be changed each time the process of step S30 is performed. A preferred method may be adopted as appropriate from the viewpoint of shortening the time when scanning the entire scanning range to be scanned to set the new voltage change range Enew.

[0045] The upper limit of the change range is not limited to the examples of the embodiments described above. The upper limit of the change range should be a value suitable for the upper limit of the voltage change range E when considering the downward slope region. The upper limit on the range of change may be abolished.

[0046] In the above embodiment, while the CPU 21 was scanning the downward-sloping region, the CPU 21 changed the new voltage change width Enew each time it performed the processing in step S30. This gradually changed the new voltage change width Enew. However, gradually changing the new voltage change width Enew in this way is not essential. The CPU 21 only needs to increase the new voltage change width Enew compared to the previous change width Eold at least once while scanning the downward-sloping region.

[0047] The method for setting the new voltage change range Enew in step S40 is not limited to the example of the above embodiment. For example, the second setting value C2 may be changed from the example of the above embodiment. The second setting value C2 may be changed each time the process of step S40 is performed. A method that is appropriately preferred from the viewpoint of accurately detecting the maximum efficiency voltage Y may be adopted to set the new voltage change range Enew.

[0048] The lower limit of the change range is not limited to the examples of the embodiments described above. The lower limit of the change range should be a value suitable for the lower limit of the voltage change range Enew in the upward slope region. The lower limit of the change range should be greater than zero.

[0049] In the above embodiment, while the CPU 21 was scanning the region with an upward slope, the CPU 21 changed the new voltage change width Enew each time it performed the processing in step S40. In this way, the new voltage change width Enew was gradually changed. However, it is not necessary to gradually change the new voltage change width Enew in this way. The CPU 21 only needs to make the new voltage change width Enew smaller than the previous change width Eold at least once while scanning the region with an upward slope.

[0050] It is not necessary to change the voltage change range E while the CPU21 is scanning an upward-sloping region. In other words, the same voltage change range E may always be used in the upward-sloping region.

[0051] In the above embodiment, the maximum efficiency voltage Y was searched while increasing the output voltage of the first converter 31 from zero. Conversely, the maximum efficiency voltage Y may be searched by decreasing the output voltage of the first converter 31 from the upper limit of the scanning range.

[0052] 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]

[0053] 20...Control device 31...First converter 70...Solar panel

Claims

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 scanning the output voltage of the DC-DC converter within a predetermined range 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 the predetermined range. It is possible to control the output voltage of the DC-DC converter so that it approaches the maximum efficiency voltage, In searching for the aforementioned maximum efficiency voltage, The output voltage of the DC-DC converter is controlled to a first voltage within the predetermined range. The output power of the DC-DC converter when its output voltage is controlled to the first voltage is obtained as the first power, Controlling the output voltage of the DC-DC converter to a second voltage within the predetermined range obtained by changing the first voltage by a first variation range, The output power of the DC-DC converter when its output voltage is controlled to the second voltage is obtained as the second power, The following steps are performed in order: control the output voltage of the DC-DC converter to a third voltage within the predetermined range obtained by changing the second voltage by a second change in the same direction as the first change; If the second power is less than the first power, the second change range is set to a value greater than the first change range. Control device for a solar power generation system.

2. If the second power is equal to or greater than the first power, the second change range is set to a value smaller than the first change range. A control device for a solar power generation system according to claim 1.

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