Solar panel power generation system

Abstract

To provide a solar panel power generation system that estimates the voltage command value of the voltage operating point with high power generation efficiency for each solar panel without using a solar radiation sensor. [Solution] The current detection means 40 detects the total current output by the upper solar panel 21 and the lower solar panel 22. Based on the detection results of the voltage detection means 60 and the detection results of the current detection means 40, the control unit 110 controls the power converter 13 to track the maximum power point, and when the power generated by the solar panel 20 decreases, it estimates a voltage command value for the solar panel 20 at a voltage operating point with high power generation efficiency based on the ratio of the total power generated by the sum of the power generated by the upper solar panel 21 and the lower solar panel 22, and the power generated by each solar panel 20 at the same solar radiation intensity, to the total rated power generated by the multiple solar panels.

Description

Technical Field

[0001] The present invention relates to a solar panel power generation system.

Background Art

[0002] Conventionally, in power generation using solar panels, when there is a change in solar radiation, a technique for controlling the solar panels to generate electricity with high efficiency based on the detection results of an ambient environment measuring instrument that measures parameters such as solar radiation amount and temperature is known (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the technique disclosed in Patent Document 1, in order to accurately measure the solar radiation amount, it is necessary to use a high-precision solar radiation sensor. Further, in the technique disclosed in Patent Document 1, control based on the detection result of a solar radiation sensor is disclosed for one solar panel. On the other hand, in the technique disclosed in Patent Document 1, in a solar panel power generation system including a plurality of solar panels connected in parallel to each other, when performing maximum power point tracking control for each solar panel, it is difficult to estimate the voltage command value of the voltage operating point with high power generation efficiency of each solar panel based on the detection result of the solar radiation sensor.

Means for Solving the Problems

[0005] A solar panel power generation system that solves the above problems comprises a plurality of solar panels connected in parallel with each other, a power converter that converts the power generated by the solar panels into a predetermined power, wherein the power converters are a plurality of the same as the number of solar panels, an electrical load or battery that receives the predetermined power converted by the power converters, a plurality of voltage detection means for detecting the voltage output by the plurality of solar panels or for detecting the voltage output by the plurality of power converters, a current detection means for detecting the current output by the solar panels or the current output by the power converters, and based on the detection results of the voltage detection means and the current detection means... In a solar panel power generation system comprising a power converter and a control unit for controlling the power converter, the current detection means detects the total current output by the plurality of solar panels, and the control unit, based on the detection result of the voltage detection means and the detection result of the current detection means, controls the power converter to track the maximum power point, and when the power generation of the solar panels decreases, estimates a voltage command value for the solar panel at a voltage operating point with high power generation efficiency based on the ratio of the total power generation obtained by summing the power generation of the plurality of solar panels and the power generation of each solar panel at the same solar radiation intensity, and the total rated power generation of the plurality of solar panels. [Effects of the Invention]

[0006] With the above configuration, it is possible to estimate the voltage command value of the voltage operating point with high power generation efficiency for each solar panel without using a solar radiation sensor. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a diagram used to explain a solar panel power generation system. [Figure 2] Figure 2 is a flowchart showing an example of the mountain climbing control process of the control device. [Figure 3] Figure 3 is a flowchart showing an example of a series of processes performed by the control unit. [Figure 4]Figure 4 is a flowchart showing an example of the scan control process of the control unit. [Figure 5] Figure 5 is a flowchart showing an example of the scan control process of the control unit. [Figure 6] Figure 6 is a diagram used to explain the first and second generated power. [Figure 7] Figure 7 is a diagram used to explain the first and second generated power. [Modes for carrying out the invention]

[0008] [Embodiment] An embodiment of the solar panel power generation system 1 will be described below with reference to the drawings. <Overall Structure> As shown in Figure 1, the solar panel power generation system 1 comprises a power conversion circuit 10, a solar panel 20, a battery 30, a current detection means 40, a capacitor 50, a voltage detection means 60, and a control device 100. The solar panel 20 comprises, for example, an upper solar panel 21 and a lower solar panel 22 connected in parallel to each other. The upper solar panel 21 and the lower solar panel 22 are stacked vertically on each other. Specifically, the upper solar panel 21 is stacked on the upper surface of the lower solar panel 22. The upper solar panel 21 and the lower solar panel 22 have the same transmittance, or the upper solar panel 21 has a structure in which the transmittance is higher than that of the lower solar panel 22. In other words, the solar panel 20 is a laminated solar panel in which multiple solar panels are stacked. In the following description, we will describe the case in which the upper solar panel 21 and the lower solar panel 22 have structures with different transmittances. Specifically, the solar panel 20 is a tandem solar panel in which the upper solar panel 21 is made of perovskite and the lower solar panel 22 is made of silicon. In this embodiment, the upper solar panel 21 is an example of a solar panel other than the bottom layer, and the lower solar panel 22 is an example of a solar panel of the bottom layer.

[0009] The solar panel power generation system 1 includes a number of power conversion circuits 10 corresponding to the number of solar panels 20 installed in the solar panel power generation system 1. In the example shown in Figure 1, the solar panel power generation system 1 is assumed to have one solar panel 20. In this case, the solar panel power generation system 1 includes one power conversion circuit 10 corresponding to the solar panel 20.

[0010] The power conversion circuit 10 has configurations corresponding to the number of solar panels that make up the solar panel 20. As described above, in this example, the solar panel 20 comprises an upper solar panel 21 and a lower solar panel 22. Therefore, the power conversion circuit 10 has the same configuration for the corresponding upper solar panel 21 and lower solar panel 22. Specifically, the power conversion circuit 10 comprises capacitors 11a, 11b, voltage detection means 12a, 12b, and power converters 13a, 13b. The power converters 13a, 13b are, for example, step-down circuits that step down the voltage output by the solar panel 20 to a predetermined voltage. The power converter 13a comprises, for example, a switching element 14a, a diode 15a connected in antiparallel to the switching element 14a, a switching element 16a, a diode 17a connected in antiparallel to the switching element 16a, and a coil 18a. Furthermore, the power converter 13b includes, for example, a switching element 14b, a diode 15b connected in antiparallel to the switching element 14b, a switching element 16b, a diode 17b connected in antiparallel to the switching element 16b, and a coil 18b. The switching elements 14 and 16 are implemented, for example, by MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors).

[0011] The upper solar panel 21 and the lower solar panel 22 each have a positive terminal and a negative terminal, and generate electricity between the positive and negative terminals. The positive terminal of the upper solar panel 21 and the power converter 13a are connected by a positive busbar LN1a. The negative terminal of the upper solar panel 21 and the power converter 13a are connected by a negative busbar LN2a. The positive terminal of the lower solar panel 22 and the power converter 13b are connected by a positive busbar LN1b. The negative terminal of the lower solar panel 22 and the power converter 13b are connected by a negative busbar LN2b.

[0012] In this embodiment, the upper solar panel 21 of the solar panel 20 is denoted by the letter "a" at the end of its reference numeral, and the lower solar panel 22 is denoted by the letter "b" at the end of its reference numeral. In the following description, when the configuration of the upper solar panel 21 and the configuration of the lower solar panel 22 are not distinguished from each other, the reference numeral at the end will be omitted.

[0013] Capacitor 11 is connected between the positive busbar LN1 and the negative busbar LN2. Specifically, one end of capacitor 11 is connected to the positive busbar LN1, and the other end of capacitor 11 is connected to the negative busbar LN2. When switching element 14a is open, the power generated by the upper solar panel 21 charges capacitor 11a. When switching element 14a is closed, capacitor 11a discharges the stored power. When switching element 14b is open, the power generated by the lower solar panel 22 charges capacitor 11b. When switching element 14b is closed, capacitor 11b discharges the stored power.

[0014] The voltage detection means 12 is connected between the positive electrode bus bar LN1 and the negative electrode bus bar LN2. Specifically, one end of the voltage detection means 12 is connected to the positive electrode bus bar LN1, and the other end of the voltage detection means 12 is connected to the negative electrode bus bar LN2. The voltage detection means 12 detects the voltage generated across both ends of the capacitor 11. In other words, the plurality of voltage detection means 12 respectively detect the voltages generated and output by the corresponding upper-layer solar panel 21 or lower-layer solar panel 22.

[0015] The switching element 14 is provided on the positive electrode bus bar LN1. When the side of the positive electrode bus bar LN1 closer to the solar panel 20 is defined as the upstream and the farther side as the downstream, the drain terminal of the switching element 14 is connected to the upstream side of the positive electrode bus bar LN1, and the source terminal of the switching element 14 is connected to the downstream side of the positive electrode bus bar LN1. The diode 15 has its cathode connected to the drain terminal of the switching element 14 and its anode connected to the source terminal of the switching element 14.

[0016] The switching element 16 is connected between the positive electrode bus bar LN1 and the negative electrode bus bar LN2. Specifically, the drain terminal of the switching element 16 is connected to the positive electrode bus bar LN1, and the source terminal of the switching element 16 is connected to the negative electrode bus bar LN2. The diode 15 has its cathode connected to the drain terminal of the switching element 16 and its anode connected to the source terminal of the switching element 16.

[0017] The coil 18 is provided on the positive electrode bus bar LN1. Specifically, one end of the coil 18 is connected to the upstream side of the positive electrode bus bar LN1, and the other end of the coil 18 is connected to the downstream side of the positive electrode bus bar LN1.

[0018] The positive bus bars LN1a and LN1b are connected downstream of the power conversion circuit 10. Specifically, the other ends of the coils 18a and 18b included in the power conversion circuit 10 and the positive bus bar LN3 are connected. Also, the negative bus bars LN2a and LN2b are connected downstream of the power conversion circuit 10. Specifically, the source terminals of the switching elements 16a and 16b included in the power conversion circuit 10 and the negative bus bar LN4 are connected.

[0019] One end of the battery 30 is connected to the positive bus bar LN3, and the other end of the battery 30 is connected to the negative bus bar LN4. The battery 30 is charged by receiving the power generated and output by the solar panel 20 included in the solar panel power generation system 1. Also, the power charged in the battery 30 is supplied to a power supply destination not shown.

[0020] The current detection means 40 is provided on the positive bus bar LN3. The current detection means 40 detects the total sum of the currents generated and output by the solar panel 20 included in the solar panel power generation system 1. In the following description, the total sum of the currents output by the solar panel 20 included in the solar panel power generation system 1 is also referred to as the total current. The current detection means 40 is realized by, for example, a shunt resistance type sensor using a resistor.

[0021] The capacitor 50 is connected between the positive bus bar LN3 and the negative bus bar LN4. Specifically, one end of the capacitor 50 is connected to the positive bus bar LN3, and the other end of the capacitor 50 is connected to the negative bus bar LN4. The capacitor 50 equalizes the fluctuations in the power output from the power conversion circuit 10 included in the solar panel power generation system 1.

[0022] The voltage detection means 60 is connected between the positive busbar LN3 and the negative busbar LN4. Specifically, one end of the voltage detection means 60 is connected to the positive busbar LN3, and the other end of the voltage detection means 60 is connected to the negative busbar LN4. The voltage detection means 60 detects the voltage generated across the capacitor 50. In other words, the voltage detection means 60 detects the voltage generated and output by the solar panel 20 of the solar panel power generation system 1.

[0023] The control device 100 comprises a control unit 110 and a storage unit 150. The control unit 110 is implemented, for example, by a hardware processor such as a CPU (Central Processing Unit) executing a program (software). Some or all of the components of the control unit 110 may be implemented by hardware (including circuits) such as an LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), or GPU (Graphics Processing Unit), or by the cooperation of software and hardware. The program may be stored in advance in a storage device (not shown) equipped with a non-transient storage medium such as an HDD (Hard Disk Drive) or flash memory provided by the storage unit 150.

[0024] The control device 100 controls the open / closed state of switching elements 14 and 16 so as to increase the power generation efficiency of the solar panel 20. Specifically, the control device 100 is connected to the gate terminals of switching elements 14 and 16 via a driver (not shown). The control device 100 controls the open / closed state by driving switching elements 14 and 16. In order to effectively extract power from the solar panel 20, the control device 100 performs Maximum Power Point Tracking (MPPT control) to operate the target solar panel among the upper solar panel 21 and lower solar panel 22 of the solar panel 20 at the operating point (maximum power point) where the output power is maximum. The details of the control of the control device 100 will be described below.

[0025] <Regarding the control of the control unit 110> The control unit 110 performs hill climbing control on the solar panel 20 at predetermined time intervals while detecting changes in solar radiation intensity. Specifically, the control unit 110 performs hill climbing control on the upper solar panel 21 to identify the maximum power point. The control unit 110 also performs hill climbing control on the lower solar panel 22 to identify the maximum power point. Based on the voltage command value at the maximum power point identified by the hill climbing control, the control unit 110 performs PI control on the power conversion circuit 10. Specifically, the control unit 110 performs PI control on the power converter 13a so that the detection result of the voltage detection means 12a matches the identified voltage command value of the upper solar panel 21. The control unit 110 also performs PI control on the power converter 13b so that the detection result of the voltage detection means 12b matches the identified voltage command value of the lower solar panel 22. The control unit 110 controls the open / closed state of the gates of the switching elements 14 and 16 by outputting gate signals for the switching elements 14 and 16 identified in conjunction with the PI control.

[0026] <Regarding the processing of the control device 100> Figure 2 is a flowchart illustrating an example of mountain climbing control by the control device 100. The process shown in Figure 2 is repeatedly executed at predetermined time intervals. Specifically, the process shown in Figure 2 relating to the upper solar panel 21 and the process shown in Figure 2 relating to the lower solar panel 22 are repeatedly executed at different timings. First, the control unit 110 acquires various values ​​(step S100). Specifically, the control unit 110 acquires the detection result of the voltage detection means 60 and the detection result of the current detection means 40. Next, the control unit 110 calculates the total power generation P of the solar panel power generation system 1 (step S102). The total power generation P is the value obtained by multiplying the voltage value detected by the voltage detection means 60 and the current value detected by the current detection means 40, and is the sum of the power generation of the upper solar panel 21 and the power generation of the lower solar panel 22. Next, the control unit 110 determines whether the total power generation P calculated in step S102 is greater than or equal to the maximum value of the total power generation P (step S104). The maximum value of the total generated power P is updated in steps S106 and S116, which will be described later. When the series of processes shown in Figure 2 is executed for the first time, the maximum value of the total generated power P is the value calculated in the previous step S102. If the control unit 110 determines that the total generated power P is equal to or greater than the maximum value of the total generated power P (step S104; YES), it updates the total generated power P to the maximum value of the total generated power P (step S106).

[0027] If the control unit 110 determines that the total generated power P is not greater than or equal to the maximum value of the total generated power P (step S104; NO), it determines whether the value obtained by subtracting the total generated power P from the maximum value of the total generated power P is greater than the threshold TH (step S108). The threshold TH is a value used to determine whether or not a change in solar radiation intensity has occurred on the solar panel 20. If the difference between the maximum value of the total generated power P and the current total generated power P is greater than the threshold TH, the control unit 110 determines that a change in solar radiation intensity has occurred. If the control unit 110 determines that the value obtained by subtracting the total generated power P from the maximum value of the total generated power P is not greater than the threshold TH (step S108; NO), it proceeds to step S118 without executing various processes associated with the change in solar radiation intensity.

[0028] If the control unit 110 determines that the value obtained by subtracting the total generated power P from the maximum value of the total generated power P is greater than the threshold TH (step S108; YES), it updates the current voltage command value as the previous voltage command value (step S110). The current voltage command value is the voltage command value immediately before the series of processes shown in Figure 2 are executed. Next, the control unit 110 calculates the estimated generated power X (step S112). The estimated generated power X is the estimated power generated by the solar panel 20 that is the subject of the series of processes shown in Figure 2. Therefore, if the process in Figure 2 is being performed on the upper solar panel 21, the estimated generated power X is the estimated power generated by the upper solar panel 21, and if the process in Figure 2 is being performed on the lower solar panel 22, the estimated generated power X is the estimated power generated by the lower solar panel 22.

[0029] Specifically, the estimated power generation X is a value based on the total power generation P, the rated power generation Pch at the same solar radiation intensity, and the total rated power generation Pall. The rated power generation Pch is the rated power generation of the solar panel 20, which is the control target of the series of processes shown in Figure 2. Therefore, when the process in Figure 2 is performed on the upper solar panel 21, the rated power generation Pch is the rated power generation of the upper solar panel 21, and when the process in Figure 2 is performed on the lower solar panel 22, the rated power generation Pch is the rated power generation of the lower solar panel 22. The total rated power generation Pall is the sum of the rated power generation of the upper solar panel 21 and the rated power generation of the lower solar panel 22. Below, we will explain the case where the estimated power generation X is the value obtained by dividing the product of the total power generation P and the rated power generation Pch by the total rated power generation Pall.

[0030] Next, the control unit 110 identifies the voltage command value of the solar panel 20, which is the control target of the series of processes shown in Figure 2, based on the estimated power generation X calculated in step S112 (step S114). The control unit 110 identifies the voltage command value, for example, based on the estimated power generation X and the calculation formula for the voltage command value.

[0031] Here, the power generated by the solar panel 20 and the voltage command value at the maximum power point for that power are correlated. Specifically, the voltage command value can be obtained by multiplying the value obtained by substituting the estimated power generated X as a variable into a logarithmic function representing the relationship between the power generated and the voltage command value at the maximum power point, by a correction value Ai, and then adding a correction value Bi. The correction value Ai represents a predetermined slope when 1 is substituted as the estimated power generated X into the logarithmic function. The correction value Bi represents a predetermined intercept when 1 is substituted as the estimated power generated X into the logarithmic function. More specifically, the voltage command value is derived by the following equation (1). In equation (1), CV represents the voltage command value, X represents the estimated power generated X, Ai represents the correction value Ai, and Bi represents the correction value Bi.

[0032] CV = Ai × log(X) + Bi …(1) The memory unit 150 pre-stores information based on correction values ​​Ai and Bi based on the characteristics of the upper solar panel 21, and information based on correction values ​​Ai and Bi based on the characteristics of the lower solar panel 22. The correction values ​​Ai and Bi of the upper solar panel 21 are determined based on an approximate formula of a logarithmic function representing the relationship between the generated power and the voltage command value at the maximum power point, based on the results of measuring the generated power at a certain solar irradiance and the voltage operating point at the maximum power point at that solar irradiance at multiple solar irradiance levels. The correction values ​​Ai and Bi of the lower solar panel 22 are determined based on an approximate formula of a logarithmic function representing the relationship between the generated power and the voltage command value at the maximum power point, based on the results of measuring the generated power at a certain solar irradiance and the voltage operating point at the maximum power point at multiple solar irradiance levels. The control unit 110 determines the voltage command value based on the estimated generated power X and the correction values ​​Ai and Bi stored in the memory unit 150. Next, the control unit 110 updates the total power generation P calculated in step S102 as the maximum value of the total power generation P (step S116).

[0033] Next, the control unit 110 determines whether the total generated power P is equal to or greater than the previous power BP (step S118). The previous power BP is updated in the process of step S128, which will be described later. In the first step S128, the value of the previous power BP (i.e., the initial value of the previous power BP) is the power value immediately before the start of scan control. If the control unit 110 determines that the total generated power P is not equal to or greater than the previous power BP (step S118; NO), it determines whether the value obtained by subtracting the previous voltage command value from the current voltage command value is 0 or greater (step S120). The current voltage command value is the voltage command value identified in step S114 if there has been a change in solar radiation intensity (i.e., step S108; YES), and the voltage command value immediately before the series of processes shown in Figure 2 are executed if there has been no change in solar radiation intensity (i.e., step S108; NO). If the control unit 110 determines that the value obtained by subtracting the previous voltage command value from the current voltage command value is 0 or greater (step S120; YES), it updates the voltage command value to the current voltage command value minus a predetermined voltage ΔV (step S122). The predetermined voltage ΔV is a voltage value that indicates the range of change in the voltage command value in hill climbing control. If the control unit 110 determines that the value obtained by subtracting the previous voltage command value from the current voltage command value is not 0 or greater (step S120; NO), it updates the voltage command value to the current voltage command value plus the predetermined voltage ΔV (step S126).

[0034] If the control unit 110 determines that the total generated power P is equal to or greater than the previous power BP (step S118; YES), it determines whether the value obtained by subtracting the previous voltage command value from the current voltage command value is 0 or greater (step S124). If the control unit 110 determines that the value obtained by subtracting the previous voltage command value from the current voltage command value is not 0 or greater (step S124; NO), it proceeds to step S122. If the control unit 110 determines that the value obtained by subtracting the previous voltage command value from the current voltage command value is 0 or greater (step S124; YES), it updates the current voltage command value by adding a predetermined voltage ΔV to it as the new voltage command value (step S126).

[0035] In other words, if the voltage command value is increased but the total generated power P has not increased (S120; YES, and S118; NO), or if the total generated power P has increased but the voltage command value has not been increased (S118; YES, and S124; NO), the control unit 110 assumes that the voltage operating point of the maximum power point is at the point where the voltage command value has been decreased, and estimates a new voltage command value that is smaller by a predetermined voltage ΔV than the current voltage command value (S122).

[0036] If the total generated power P has not increased (S118; NO) and the voltage command value has not increased (S120; NO), or if the total generated power P is increasing (S118; YES) and the voltage command value is increasing (S124; YES), the control unit 110 assumes that the voltage operating point of the maximum power point is at the point where the voltage command value has been increased, and estimates a new voltage command value that is larger by a predetermined voltage ΔV than the current voltage command value (S126).

[0037] Next, the control unit 110 updates the total generated power P calculated in step S102 as the previous power BP (step S128). [Effect of the Embodiment] The operation of the solar panel power generation system 1 according to this embodiment will be described below. The control unit 110 changes the voltage command value used as the reference for hill climbing control in accordance with the change in solar radiation intensity through the processing in steps S110 to S116 of the processing shown in Figure 2. Specifically, if there is a change in solar radiation intensity and the total power generation P is decreasing, the control unit 110 uses the voltage command value corresponding to the estimated power generation X at that solar radiation intensity as the reference for hill climbing control. On the other hand, if there is no change in solar radiation intensity, the control unit 110 uses the voltage command value that has been used until now as the reference for hill climbing control.

[0038] [Effects of the Embodiment] According to the above embodiment, the following effects can be obtained. (1) The voltage detection means 60 detects the total current output by the solar panels 20 (i.e., the upper solar panel 21 and the lower solar panel 22) of the solar panel power generation system 1. The control unit 110 performs MPPT control on the power converter 13 based on the detection result of the voltage detection means 12 corresponding to the power converter 13 to be MPPT controlled and the detection result of the voltage detection means 60. The control unit 110 also estimates the voltage command value for the solar panel 20 to be MPPT controlled when the power generation of the solar panel 20 to be MPPT controlled decreases, and based on the ratio of the rated power generation Pch to the total rated power generation Pall.

[0039] Here, as solar irradiance changes, the voltage command value at the maximum power point may deviate from the previous voltage command value. In this case, the control unit 110 may take time to identify the voltage command value corresponding to the voltage operating point where the maximum power point is maximized, based on the previous voltage command values. Specifically, in the case of general hill-climbing control, when solar irradiance decreases, the voltage command value decreases even if it increases or decreases. Therefore, during the stage when solar irradiance is decreasing, the voltage command value remains at almost the same value. Also, in the case of general hill-climbing control, the voltage command value is decreased to increase power during the stage when solar irradiance is decreasing. Therefore, at the timing when solar irradiance begins to increase, the control from the previous stage when solar irradiance was decreasing has an effect, causing the voltage command value to decrease further. Consequently, when solar irradiance increases, the voltage operating point at the voltage operating point of the maximum power point deviates from the actual voltage command value, and the generated power decreases.

[0040] The solar panel power generation system 1 of this embodiment estimates a voltage command value to be used as a reference for hill-climbing control in advance, in response to changes in solar radiation intensity. With this configuration, the solar panel power generation system 1 can quickly identify the voltage command value of the voltage operating point where the maximum power point is maximized by using the voltage command value corresponding to the change in solar radiation intensity for hill-climbing control. Therefore, the solar panel power generation system 1 can estimate the voltage command value of the voltage operating point with high power generation efficiency for each solar panel 20 without using a solar radiation sensor.

[0041] Furthermore, in this embodiment, the solar panel power generation system 1 can efficiently generate electricity by detecting the total current generated by the multiple solar panels 20 using a number of current detection means 40 that is less than the number of solar panels 20 provided in the solar panel power generation system 1 (i.e., the total number of upper solar panels 21 and lower solar panels 22).

[0042] (2) The control unit 110 estimates a value derived by substituting the estimated power generation X as the variable of a logarithmic function that shows the relationship between the power generated by the solar panel and the voltage command value at the maximum power point of said power generation, based on a correction value Ai which is a predetermined slope when the variable of the logarithmic function takes 1, and a correction value Bi which is a predetermined intercept when the variable of the logarithmic function takes 1, as the voltage command value corresponding to the voltage operating point of the maximum power point. With this configuration, the solar panel power generation system 1 can easily estimate the voltage command value by predetermined processing.

[0043] Each of the above embodiments may be modified as follows. Furthermore, the above embodiments and the following alternative examples may be combined with each other to the extent that they do not contradict the technical standards. [Example 1] The above describes a case in which the solar panel power generation system 1 estimates the voltage command value corresponding to the voltage operating point of the maximum power point of the solar panel 20 by climbing control, but it is not limited to this. The solar panel power generation system 1 may also estimate the voltage command value corresponding to the voltage operating point of the maximum power point of the solar panel 20 by using scan control in combination. Furthermore, in the above description, the control unit 110 used the estimated power generation X as the variable of the logarithmic function when estimating the voltage command value, but it may also use the power generation of each solar panel 20 identified during scan control as the variable of the logarithmic function. The following describes a case in which, while using scan control in combination, the power generation of each solar panel 20 identified during scan control is used instead of the estimated power generation X as the variable of the logarithmic function used to estimate the voltage command value.

[0044] As described above, the control unit 110 performs hill climbing control on the solar panel 20 at predetermined time intervals. The control unit 110 also performs scan control on the solar panels 20 other than the lower solar panel 22 (i.e., the upper solar panel 21) at predetermined time intervals. The control unit 110 does not perform scan control on the lower solar panel 22. The control unit 110 estimates the voltage operating point of the maximum power point of the lower solar panel 22, which does not undergo scan control, by reflecting the voltage operating point of the maximum power point identified by the scan control performed on the upper solar panel 21 and the transmittance of the upper solar panel 21.

[0045] The control unit 110 estimates the voltage operating point of the maximum power point of the lower solar panel 22 (hereinafter referred to as the fourth voltage operating point Vd) when scan control is not performed, based on the voltage operating point of the upper solar panel 21 (hereinafter referred to as the third voltage operating point Vu) when scan control is performed. Specifically, the control unit 110 estimates the value obtained by multiplying the third voltage operating point Vu by a coefficient λu as the fourth voltage operating point Vd. In this case, the fourth voltage operating point Vd is expressed by the following equation (2).

[0046] Vd = Vu × λu ... (2) The coefficient λu is a coefficient used to reflect the transmittance of the upper solar panel 21. The coefficient λu is expressed by the following equation (3).

[0047] λu = |Vu' - Vd'| / Vu' ... (3) In equation (3), Vu' represents the voltage operating point of the upper solar panel 21 at its maximum power point when mountain climbing control has been performed in advance (hereinafter referred to as the first voltage operating point Vu'), and Vd' represents the voltage operating point of the lower solar panel 22 at its maximum power point when mountain climbing control has been performed in advance (hereinafter referred to as the second voltage operating point Vd'). The information indicating the first voltage operating point Vu' and the second voltage operating point Vd' is stored in the storage unit 150 in advance.

[0048] The control unit 110 performs hill-climbing control on the upper solar panel 21 to identify the maximum power point near the third voltage operating point Vu identified by scan control. The control unit 110 also performs hill-climbing control on the lower solar panel 22 to identify the maximum power point near the estimated fourth voltage operating point Vd. Based on the voltage command value at the maximum power point identified by hill-climbing control, the control unit 110 performs PI control on the power conversion circuit 10. Specifically, the control unit 110 performs PI control on the power converter 13a so that the detection result of the voltage detection means 12a matches the identified voltage command value of the upper solar panel 21.

[0049] Furthermore, the control unit 110 performs PI control on the power converter 13b so that the detection result of the voltage detection means 12b matches the voltage command value of the identified lower solar panel 22. The control unit 110 controls the open / closed state of the gates of the switching elements 14 and 16 by outputting gate signals for the switching elements 14 and 16 identified in conjunction with the PI control.

[0050] <Processing by control device 100> Figure 3 is a flowchart showing an example of the processing of the control device 100. The processing shown in Figure 3 is executed, for example, when the control device 100 is started up or when the maximum power point is identified. First, the control unit 110 starts counting a timer that measures the execution period of scan control (step S200). Next, the control unit 110 determines whether the timer count is greater than or equal to a predetermined count T0 (step S202). The predetermined count T0 is, for example, a value that indicates a typical period for which the solar panel 20 requires scan control, and is a value that indicates a time of, for example, several minutes to several tens of minutes.

[0051] If the control unit 110 determines that the timer count is not equal to or greater than a predetermined count T0 (step S202; NO), it executes hill-climbing control for the solar panel 20 (step S204) and proceeds to step S200. The internal processing of step S204 in Modification 1 includes the execution of the series of processes shown in the flowchart in Figure 2 for the upper solar panel 21, and the execution of the same series of processes for the lower solar panel 22. Furthermore, the internal processing of step S204 is a modified version of the process shown in the flowchart in Figure 2. Details of step S204 in Modification 1 will be described later.

[0052] In step S204, the control unit 110 performs hill climbing control on the upper solar panel 21 and the lower solar panel 22, respectively, to identify the voltage command value corresponding to the voltage operating point of the maximum power point. Based on the voltage command value near the maximum power point of the upper solar panel 21 identified by the scan control described later, the control unit 110 performs hill climbing control on the upper solar panel 21. The control unit 110 also performs hill climbing control on the lower solar panel 22 based on the voltage command value near the maximum power point of the lower solar panel 22 estimated by the scan control described later. Then, the control unit 110 performs PI control on the power conversion circuit 10 so that the detection result of the voltage detection means 12 matches the voltage command value identified by the hill climbing control.

[0053] If the control unit 110 determines that the timer count is equal to or greater than a predetermined count T0 (step S202; YES), it stores information indicating the current voltage command value of the upper solar panel 21 and the current voltage command value of the lower solar panel 22 in the storage unit 150 (step S206). Next, the control unit 110 performs scan control on the upper solar panel 21 (step S208). Details of the scan control will be described later. While the control unit 110 is performing scan control on the upper solar panel 21, it controls the power converter 13b to maintain the voltage command value of the lower solar panel 22 based on the information stored in the storage unit 150. In other words, while the control unit 110 is performing scan control on the upper solar panel 21, it does not perform scan control on the lower solar panel 22. Next, the control unit 110 clears (initializes) the timer count (step S210) and proceeds to step S204. The control unit 110 repeatedly executes the processes from steps S200 to S210.

[0054] Figures 4 and 5 are flowcharts illustrating an example of the processing in step S208 shown in Figure 3. First, the control unit 110 determines whether or not it is the timing when scan control has started (step S300). In the series of processes shown in Figures 4 and 5, if it is the first step S300, the control unit 110 determines that it is the timing when scan control has started. If the control unit 110 determines that it is the timing when scan control has started (step S300; YES), it sets the duty cycle D of the switching element 14a to the initial duty cycle value D0 (step S302) and proceeds to step S304. The initial value D0 is, for example, the duty cycle D corresponding to the voltage command value of the upper solar panel 21 stored in the storage unit 150 in the processing of step S106. If the control unit 110 determines that it is not the timing when scan control has started (step S300; NO), it acquires various values ​​(step S304). Specifically, the control unit 110 acquires the detection results from the voltage detection means 60 and the detection results from the current detection means 40. Next, the control unit 110 calculates the current power PP based on the detection results acquired in step S304 (step S306). The current power PP is, for example, the value obtained by multiplying the voltage value detected by the voltage detection means 60 by the current value detected by the current detection means 40.

[0055] Next, the control unit 110 compares the current power PP calculated in step S306 with the maximum power MP to determine whether the current power PP is greater than the maximum power MP (step S308). The maximum power MP is updated in step S310, which will be described later. The value of the maximum power MP in the first step S308 (i.e., the initial value of the maximum power MP) is, for example, the current power PP calculated in the previous step S306. If the control unit 110 determines that the current power PP is greater than the maximum power MP (step S308; YES), it updates the value of the current power PP as the maximum power MP (step S310). Next, the control unit 110 updates the current duty cycle D as the maximum power duty cycle MD (step S312) and proceeds to step S314.

[0056] If the control unit 110 determines that the current power PP is not greater than the maximum power MP (step S308; NO), it determines whether the value obtained by subtracting the current power PP from the previous power BP is greater than a predetermined power difference ΔP (step S314). The predetermined power difference ΔP is a value used, for example, to identify the maximum point of the PV curve that shows the correspondence between the output voltage and the generated power, and is a value corresponding to the slope of the curve near the maximum point of the PV curve. The previous power BP is updated in the process of step S330, which will be described later. In the first step S314 process, the value of the previous power BP (i.e., the initial value of the previous power BP) is, for example, the power value immediately before starting scan control. If the control unit 110 determines that the value obtained by subtracting the current power PP from the previous power BP is not greater than a predetermined power difference ΔP (step S314; NO), it updates the duty cycle D to the value obtained by subtracting a predetermined duty cycle ΔD from the current duty cycle D (step S316). As a result, the duty cycle D becomes smaller than the current duty cycle D, and the voltage command value for the switching element 14a increases.

[0057] If the control unit 110 determines that the value obtained by subtracting the current power PP from the previous power BP is greater than a predetermined power difference ΔP (step S314; YES), it determines whether the value of the flag is 0 (step S318). The value of the flag can be 0 or 1. The flag is set to 0 at the start of the series of processes shown in Figures 4 and 5, and is updated to 1 in step S326, which will be described later. If the control unit 110 determines that the value of the flag is 0 (step S318; YES), it determines whether the duty cycle D is 0 [%] (step S320). If the control unit 110 determines that the duty cycle D is 0 [%] (step S320; YES), it updates the duty cycle D to the maximum duty cycle Dmx (step S322). The maximum duty cycle Dmx is a value that represents 100 [%]. When the duty cycle D is set to the maximum duty cycle Dmx, the switching element 14a is closed, and the detection result of the voltage detection means 60 matches the voltage across the battery 30 (i.e., the battery voltage). Next, the control unit 110 stores the current power PP in the storage unit 150 (step S324). Next, the control unit 110 updates the flag value to 1 (step S326) and proceeds to step S328.

[0058] If the control unit 110 determines that the value of the flag is not 0 (step S318; NO), or if it determines that the duty cycle D is not 0[%] (step S320; NO), it proceeds to step S328. The control unit 110 updates the duty cycle D by subtracting twice the predetermined duty cycle ΔD from the current duty cycle D (step S328). As a result, the duty cycle D becomes smaller than the current duty cycle D, and the voltage command value of the switching element 14a increases. The degree of increase in the voltage command value of the switching element 14a that occurs with the processing in step S328 is twice the degree of increase that occurs with the processing in step S316. Next, the control unit 110 updates the current power PP as the previous power BP (step S330).

[0059] Next, the control unit 110 determines whether the value of the flag is 1 or not (step S332). If the value of the flag is not 1 but 0 (step S332; NO), the control unit 110 proceeds to step S300. The control unit 110 repeatedly executes the processes in steps S300 to S330 until the value of the flag becomes 1. If the value of the flag is 1 (step S332; YES), the control unit 110 determines whether the duty cycle D is greater than the initial value D0 (step S334). If the duty cycle D is greater than the initial value D0 (step S334; YES), the control unit 110 proceeds to step S300. The control unit 110 repeatedly executes the processes in steps S300 to S332 until the duty cycle D becomes less than the initial value D0.

[0060] If the duty cycle D is less than or equal to the initial value D0 (step S334; NO), the control unit 110 estimates the voltage command value corresponding to the duty cycle D as the voltage command value for the switching element 14a at the maximum power point of the upper solar panel 21 (step S336). Next, the control unit 110 estimates the fourth voltage operating point Vd based on the third voltage operating point Vu (step S338). In this case, the third voltage operating point Vu is the voltage operating point when the switching element 14a is driven by the voltage command value converted in step S334, and is a voltage operating point with high power generation efficiency. As described above, the fourth voltage operating point Vd is calculated based on the information indicating the first voltage operating point Vu' and the second voltage operating point Vd' stored in the memory unit 150, and the third voltage operating point Vu. The control unit 110 estimates the voltage command value based on the calculated fourth voltage operating point Vd as the voltage operating point for the switching element 14b at the maximum power point of the lower solar panel 22. The control unit 110 estimates the voltage command value of the lower solar panel 22 at the maximum power point based on the estimated fourth voltage operating point Vd (step S340), and then completes the series of processes.

[0061] The following describes the details of the process in step S204 of Modification 1. In Modification 1, when the control unit 110 determines the voltage command value, it uses the power generated by the solar panel 20 (i.e., the upper solar panel 21) that is subject to scan control instead of the estimated power generated X.

[0062] The following explanation will use Figure 6 to describe the power generated by the upper solar panel 21 (hereinafter referred to as the first power generated Pa) and the power generated by the lower solar panel 22 (hereinafter referred to as the second power generated Pb). Figure 6 shows waveform W11, which indicates the voltage change of the upper solar panel 21 that is subject to scan control; waveform W12, which indicates the change in the duty cycle of the switching element 14a; waveform W13, which indicates the voltage change of the lower solar panel 22; and waveform W1, which indicates the change in the total power generated P. Specifically, waveform W11 shows the change over time of the detection result of the voltage detection means 12a. Waveform W13 shows the change over time of the detection result of the voltage detection means 12b. Waveform W1 shows the change over time of the total power generated P, which is the product of the detection result of the voltage detection means 60 and the detection result of the current detection means 40.

[0063] Figure 6 also shows the times t11 to t15 when various controls were executed. Time t11 is when the scan control of the upper solar panel 21 was started. Time t12 is when the duty cycle D of the switching element 14a of the upper solar panel 21 was set to the maximum duty cycle Dmx during the scan control. Time t13 is when the scan control of the upper solar panel 21 was completed and the voltage operating point of the lower solar panel 22 was estimated (i.e., step S338 was executed). Time t14 is when the hill-climbing control was started for the upper solar panel 21 and the lower solar panel 22 based on the voltage command value estimated by the processing in Figures 4 and 5. Time t15 is when the scan control of the upper solar panel 21 was started again (i.e., the same time as time t11). Therefore, the period TM11 from time t11 to time t13 is the scan control period for the upper solar panel 21, and the period TM12 from time t14 to time t15 is the climb control period for both the upper solar panel 21 and the lower solar panel 22.

[0064] As waveform W1 shows, the total generated power P at time t14 includes the first generated power Pa and the second generated power Pb. On the other hand, the total generated power P at time t12 contains almost no first generated power Pa. Therefore, the first generated power Pa can be derived by subtracting the total generated power P at time t12 from the total generated power P at time t14. Similarly, the second generated power Pb can be derived by subtracting the first generated power Pa from the total generated power P at time t14. Here, the total generated power P at time t14 is the current power PP stored in the storage unit 150 in the process of step S324 shown in Figure 4. The total generated power P at time t14 is an example of the starting total generated power.

[0065] If the processing in step S204 is being performed for the upper solar panel 21, the control unit 110 performs the process of calculating the first generated power Pa as the process in step S112. Specifically, the control unit 110 calculates the first generated power Pa by subtracting the current power PP stored in the storage unit 150 in the process of step S324 shown in Figure 4 from the total generated power P at the time when the mountain climbing control in step S204 of Modification 1 is started.

[0066] Furthermore, if the process in step S204 is being performed for the lower solar panel 22, the control unit 110 performs the process of calculating the second generated power Pb as the process in step S112. Specifically, the control unit 110 calculates the second generated power Pb as the value obtained by subtracting the first generated power Pa from the total generated power P at the time when the mountain climbing control in step S204 of Modification 1 is started.

[0067] In Modification 1, the control unit 110 estimates the voltage command value based on the first power generation Pa or second power generation Pb calculated in step S112 of Modification 1, and the voltage command value calculation formula, instead of the estimated power generation X.

[0068] Specifically, when the process in step S204 is performed on the upper solar panel 21, the control unit 110 estimates the voltage command value for the upper solar panel 21 by substituting the first power generation Pa for the estimated power generation X in equation (1) above. Also, when the process in step S204 is performed on the lower solar panel 22, the control unit 110 estimates the voltage command value for the lower solar panel 22 by substituting the second power generation Pb for the estimated power generation X in equation (1) above. The subsequent processes are the same as those described above, so their explanation is omitted.

[0069] Equation (1), used when estimating the voltage command value of the upper solar panel 21, is an example of a first logarithmic function, where the logarithmic function representing the relationship between the first generated power Pa and the voltage command value at the maximum power point is an example of a first logarithmic function. In this case, the correction value Ai is an example of a first slope, and the correction value Bi is an example of a first intercept. Similarly, Equation (1), used when estimating the voltage command value of the lower solar panel 22, is an example of a second logarithmic function, where the logarithmic function representing the relationship between the second generated power Pb and the voltage command value at the maximum power point is an example of a second logarithmic function. In this case, the correction value Ai is an example of a second slope, and the correction value Bi is an example of a second intercept.

[0070] [Effects of the modified example 1] The modified solar panel power generation system 1 uses a combination of scan control and hill-climbing control to estimate the voltage command value at the voltage operating point of the maximum power point of the solar panel 20. With this configuration, the solar panel power generation system 1 can estimate the voltage command value corresponding to the voltage operating point of the maximum power point with greater accuracy. Furthermore, the solar panel power generation system 1 performs scan control only on the upper solar panel 21, and does not perform scan control on the lower solar panel 22. Therefore, by shortening the time required for scan control of the solar panel 20, the solar panel power generation system 1 can ensure a longer period of time during which the solar panel 20 generates power at an appropriate third voltage operating point Vu and fourth voltage operating point Vd, which have high power generation efficiency.

[0071] Furthermore, in the modified example 1, the solar panel power generation system 1 identifies the voltage operating point of the solar panel 20 by using a first power generation Pa or a second power generation Pb instead of the estimated power generation X. With this configuration, the solar panel power generation system 1 can estimate the voltage command value corresponding to the voltage operating point of the maximum power point with greater accuracy, in accordance with the current state of the solar panel 20.

[0072] • In the above description, the solar panel power generation system 1 was described as having one upper solar panel 21 and a lower solar panel 22 that are connected in parallel and stacked vertically with each other. However, it is not limited to this. The solar panel power generation system 1 may have multiple solar panels 20, each having multiple upper solar panels 21 and a lower solar panel 22 that are connected in parallel and stacked vertically with each other. In this case, the solar panel power generation system 1 has a number of power conversion circuits 10 corresponding to the number of solar panels 20 that the solar panel power generation system 1 has. The connection between the solar panel 20, the power conversion circuit 10, the positive busbar LN3, and the negative busbar LN4 is the same as in the configuration described above, so the explanation is omitted.

[0073] The following explanation uses Figure 7 to describe how to calculate the first generated power Pa and the second generated power Pb when the solar panel power generation system 1 is equipped with multiple solar panels 20. In the following explanation, the solar panel power generation system 1 is assumed to be equipped with two solar panels 20, solar panel 20-1 and solar panel 20-2. Furthermore, the configuration of solar panel 20-1 will be described with "-1" appended to the end, and the configuration of solar panel 20-2 will be described with "-2" appended to the end. In the following explanation, if solar panels 20-1 and 20-2 are not distinguished from each other, the part after the hyphen will be omitted.

[0074] Figure 7 shows waveforms W21 showing the voltage change of the upper solar panel 21-1 being scanned and controlled, waveform W22 showing the change in the duty cycle of the switching element 14a-1, waveform W23 showing the voltage change of the lower solar panel 22-1, waveform W31 showing the voltage change of the upper solar panel 21-2 being scanned and controlled, waveform W32 showing the change in the duty cycle of the switching element 14a-2, waveform W33 showing the voltage change of the lower solar panel 22-2, and waveform W2 showing the change in total power generation P.

[0075] Specifically, waveform W21 shows the change over time of the detection result of voltage detection means 12a-1. Waveform W23 shows the change over time of the detection result of voltage detection means 12b-1. Waveform W31 shows the change over time of the detection result of voltage detection means 12a-2. Waveform W33 shows the change over time of the detection result of voltage detection means 12b-2. Waveform W2 shows the change over time of the total generated power P, which is the product of the detection result of voltage detection means 60 and the detection result of current detection means 40.

[0076] Figure 7 also shows the times t21-t25 and t31-t35 when various controls were executed. Times t21-t25 represent the control related to solar panel 20-1, and times t31-t35 represent the control related to solar panel 20-2. Times t21 and t31 are when the scan control of the upper solar panel 21 was started. Times t22 and t32 are when the power generated by the upper solar panel 21 preferably became zero during the scan control, and the open-circuit voltage of the upper solar panel 21 or the duty cycle D of the switching element 14a became zero. Times t23 and t33 are when the scan control of the upper solar panel 21 was completed and the voltage operating point of the lower solar panel 22 was estimated (i.e., when step S338 was executed). Times t24 and t34 are the times when climb control is initiated for the upper solar panel 21 and the lower solar panel 22 based on the voltage command values ​​estimated by the processing in Figures 4 and 5. Times t25 and t35 are the times when scan control for the upper solar panel 21 is initiated again (i.e., the same times as t21 and t31). Therefore, the period TM21 from time t21 to time t23 and the period TM23 from time t31 to time t33 are the scan control periods for the upper solar panel 21, and the period TM22 from time t24 to time t25 and the period TM24 from time t34 to time t35 are the climb control periods for the upper solar panel 21 and the lower solar panel 22.

[0077] As waveform W2 shows, the total generated power P during period TM24 includes the first generated power Pa and second generated power Pb from solar panel 20-1, and the first generated power Pa and second generated power Pb from solar panel 20-2. On the other hand, the total generated power P at time t22 contains almost no first generated power Pa-1, and the total generated power P at time t32 contains almost no first generated power Pa-2. Therefore, the first generated power Pa-1 can be derived by subtracting the total generated power P at time t22 from the total generated power P at time t24 (or period TM24). Similarly, the first generated power Pa-2 can be derived by subtracting the total generated power P at time t32 from the total generated power P at time t34 (or period TM24). Here, the total generated power P at times t24 and t34 is the current power PP stored in the storage unit 150 in the process of step S324 shown in Figure 4. The total power generated P at times t24 and t34 is an example of the starting total power generated.

[0078] Furthermore, the second generated power Pb is derived by the following equation (4). In equation (4), Pb is the second generated power Pb of a certain lower solar panel 22. P is the total generated power P. Pa is the first generated power Pa of the upper solar panel 21 stacked above the said lower solar panel 22. Pa' is the sum of the first generated power Pa of the upper solar panels 21 of the other solar panels 20. Pb' is the sum of the second generated power Pb of the lower solar panels 22 of the other solar panels 20.

[0079] Pb = (P - Pa') × Pa / Pa' ... (4) In other words, the control unit 110 calculates the second power generation Pb of the lower solar panel 22 to be calculated by multiplying the total power generation P by the sum of the first power generation Pa of the upper solar panels 21 provided by the solar panel power generation system 1, multiplied by the first power generation Pa of the upper solar panels 21 stacked vertically above the lower solar panel 22 to be calculated, and then dividing the result by the sum of the first power generation Pa of the upper solar panels 21 provided by the solar panel power generation system 1.

[0080] If the process in step S204 is being performed for the upper solar panel 21, the control unit 110 executes the process of calculating the first generated power Pa as the process in step S112. Also, if the process in step S204 is being performed for the lower solar panel 22, the control unit 110 executes the process of calculating the second generated power Pb as the process in step S112.

[0081] The control unit 110 estimates the voltage command value based on the first power generation Pa or second power generation Pb calculated in step S112 of the modified example 1, and the voltage command value calculation formula, instead of the estimated power generation X.

[0082] Specifically, when the process in step S204 is performed on the upper solar panel 21, the control unit 110 estimates the voltage command value for the upper solar panel 21 by substituting the first power generation Pa for the estimated power generation X in equation (1) above. Also, when the process in step S204 is performed on the lower solar panel 22, the control unit 110 estimates the voltage command value for the lower solar panel 22 by substituting the second power generation Pb for the estimated power generation X in equation (1) above. The subsequent processes are the same as those described above, so their explanation is omitted.

[0083] With this configuration, even when the solar panel power generation system 1 is equipped with multiple solar panels 20, it can estimate the voltage command value corresponding to the voltage operating point of the maximum power point with greater accuracy, in accordance with the current state of the solar panels 20.

[0084] The control unit 110 may correct the voltage operating point in relation to changes in the characteristics of the solar panel 20 over time. In this case, the memory unit 150 stores information indicating the correction value Ai and the correction value Bi corresponding to the aging of the solar panel 20. The control unit 110 calculates the estimated power generation X using the correction value Ai and the correction value Bi stored in the memory unit 150 that correspond to the current degree of aging of the solar panel 20.

[0085] The control unit 110 may estimate the voltage command value corresponding to the voltage operating point of the maximum power point for the upper solar panel 21 by using the first power generation power Pa instead of the estimated power generation power X, while for the lower solar panel 22 it may estimate the voltage command value corresponding to the voltage operating point of the maximum power point using the estimated power generation power X.

[0086] The control unit 110 may, instead of (or in addition to) estimating the voltage command value based on equation (1), estimate the voltage command value based on information that associates the estimated power generation X, the first power generation Pa, and the second power generation Pb with the voltage command value. In this case, the storage unit 150 has in advance information (table) that associates the estimated power generation X, the first power generation Pa, and the second power generation Pb with the voltage command value, and the control unit 110 searches for this information using the identified estimated power generation X, the first power generation Pa, and the second power generation Pb as search keys, and identifies the voltage command value associated with the estimated power generation X, the first power generation Pa, and the second power generation Pb as the voltage operating point of the corresponding solar panel 20.

[0087] The upper solar panel 21 and lower solar panel 22 of the solar panel 20 may not be stacked vertically on each other and may be used in a single phase configuration. In this case, the control unit 110 determines a voltage command value corresponding to the voltage operating point of the maximum power point based on the estimated power generation X of the solar panel 20 or the first power generation Pa. The processing for the lower solar panel 22 is then achieved by repeating the processing for the upper solar panel 21.

[0088] The upper solar panel 21 and the lower solar panel 22 may have the same transmittance structure. Specifically, the solar panel 20 may be a tandem solar panel in which the upper solar panel 21 and the lower solar panel 22 are made of perovskite. Furthermore, if the upper solar panel 21 and the lower solar panel 22 of the solar panel 20 are not stacked vertically on each other but are used in a single phase, the upper solar panel 21 and the lower solar panel 22 may be made of silicon.

[0089] The control unit 110 may, instead of (or in addition to) performing scan control on the upper solar panel 21 at predetermined time intervals, perform scan control based on predetermined conditions. The predetermined conditions are, for example, conditions that identify that partial shading occurs on the solar panel 20, such as the detection results of the solar radiation sensor or weather forecasts. The control unit 110 may perform scan control when it is estimated that partial shading occurs on the solar panel 20 based on the predetermined conditions.

[0090] The information indicating the coefficient λu may be calculated sequentially, or it may be stored in advance in the storage unit 150. The solar panel 20 may consist of multiple upper solar panels 21 and lower solar panels 22 stacked vertically on top of each other. In this case, the multiple upper solar panels 21 are examples of solar panels other than the bottom layer, and the lower solar panels 22 are examples of the bottom layer solar panels. Furthermore, the multiple upper solar panels 21 of the solar panel 20 may be realized with structures that have different transmittances, as long as each has a higher transmittance than the lower solar panels 22. In this case, it is preferable that the upper solar panels 21 with higher transmittances are stacked higher vertically.

[0091] Furthermore, the control unit 110 may perform MPPT control on one of the multiple upper solar panels 21 stacked as the solar panel 20, or it may perform MPPT control on each of the upper solar panels 21. When the control unit 110 performs MPPT control on one upper solar panel 21, it performs MPPT control on the upper solar panel 21 among the multiple upper solar panels 21 that has the smallest difference in output characteristics from the other upper solar panels 21. The control unit 110 then applies the estimated voltage command value for the upper solar panel 21 subject to MPPT control to the other upper solar panels 21 as well. On the other hand, when the control unit 110 performs MPPT control on each of the upper solar panels 21, it executes MPPT control based on the output characteristics of each upper solar panel 21.

[0092] The solar panel power generation system 1 was equipped with a battery 30 that received power converted by the power converter 13. The solar panel power generation system 1 may also be equipped with an electrical load such as a capacitor instead of the battery 30.

[0093] This example shows how to identify the first generated power Pa by calculating the total generated power when the duty cycle becomes zero during scan control, based on the initial total generated power when mountain climbing control is initiated. The method for identifying the first generated power Pa is not limited to setting the duty cycle to zero. The first generated power Pa can be identified by calculating the total generated power when the operating point of the solar panel being scanned is set to a non-power-generating state. In other words, the first generated power can be identified by subtracting the total generated power when the power generated by the solar panel being scanned becomes less than the power generated by the lowest layer solar panel during scan control from the initial total generated power. [Explanation of Symbols]

[0094] 1...Solar panel power generation system, 10...Power conversion circuit, 12, 12a, 12a-1, 12a-2, 12b, 12b-1, 12b-2, 60...Voltage detection means, 13, 13a, 13b...Power converter, 20, 20-1, 20-2...Solar panels, 21, 21-1, 21-2...Upper solar panels, 22, 22-1, 22-2...Lower solar panels, 30...Battery, 40...Current detection means, 50...Capacitor, 100...Control device, 110...Control unit, 150...Storage unit, P...Total generated power, Pa, Pa-1, Pa-2...First generated power, Pall...Total rated generated power, Pb...Second generated power, Pch...Rated generated power, PP...Current power, X...Estimated generated power.

Claims

1. A solar panel power generation system comprising: a plurality of solar panels connected in parallel to each other; a power converter that converts the power generated by the solar panels into a predetermined power, wherein the power converters correspond to the number of solar panels; an electrical load or battery that receives the predetermined power converted by the power converters; a plurality of voltage detection means for detecting the voltage output by the plurality of solar panels or for detecting the voltage output by each of the plurality of power converters; current detection means for detecting the current output by the solar panels or the current output by the power converters; and a control unit that controls the power converters based on the detection results of the voltage detection means and the current detection means, The current detection means detects the total current output by the multiple solar panels, The control unit, Based on the detection results of the voltage detection means and the detection results of the current detection means, the power converter is controlled to track the maximum power point, and if the power generated by the solar panel decreases, the voltage command value for the solar panel at a voltage operating point with high power generation efficiency is estimated based on the ratio of the total power generated by the sum of the power generated by the multiple solar panels and the power generated by each solar panel at the same solar radiation intensity, to the total rated power generated by the multiple solar panels. Solar panel power generation system.

2. The control unit estimates the voltage command value of the voltage operating point as the value derived by substituting the ratio as the variable into a logarithmic function that shows the relationship between the power generated by the solar panel and the voltage command value of the maximum power, the logarithmic function having a predetermined slope and a predetermined intercept when the variable of the logarithmic function takes the value of 1. The solar panel power generation system according to claim 1.

3. The multiple solar panels constitute a stacked solar panel, stacked vertically on top of each other, and among the solar panels constituting the stacked solar panel, all solar panels except the bottom layer have a structure with a transmittance equivalent to or higher than that of the bottom layer solar panel. The control unit, The power converter corresponding to the solar panels to be scanned is controlled to perform a scan control to estimate the voltage operating point for some of the solar panels to be scanned among the multiple solar panels, For some of the solar panels targeted for mountain climbing control, a first generated power is identified by subtracting the total generated power when the power generated by the power converter becomes less than the power generated by the lowest-level solar panel when scan control is performed on the solar panels targeted for scan control, from the initial total generated power, which is the total generated power when mountain climbing control is started on some of the solar panels targeted for mountain climbing control. The second power generation is determined by subtracting the first power generation from the total power generation at the start, When the power generation of the solar panel decreases, the voltage command value of the voltage operating point is estimated by substituting the first power generation into a first logarithmic function that shows the relationship between the power generation of the solar panel being scanned and the voltage command value of the maximum power, wherein the first logarithmic function has a first slope and a first intercept when the variable of the first logarithmic function takes 1. Simultaneously, the voltage command value of the voltage operating point is estimated by substituting the second power generation into a second logarithmic function that shows the relationship between the power generation of other solar panels (other than the solar panel being scanned) and the voltage command value of the maximum power, wherein the second logarithmic function has a second slope and a second intercept when the variable of the second logarithmic function takes 1. The solar panel power generation system according to claim 1.

4. The multiple solar panels constitute a stacked solar panel arranged vertically on top of each other, and among the solar panels constituting the stacked solar panel, the solar panels other than the bottom layer have a structure with a transmittance equivalent to or higher than that of the bottom layer solar panel. The control unit, The power converter corresponding to the solar panels to be scanned is controlled to perform a scan control to estimate the voltage operating point for some of the solar panels to be scanned among the multiple solar panels, For some of the solar panels targeted for mountain climbing control, a first generated power is identified by subtracting the total generated power when the power generated by the power converter becomes less than the power generated by the lowest-level solar panel when scan control is performed on the solar panels targeted for scan control, from the initial total generated power, which is the total generated power when mountain climbing control is started on some of the solar panels targeted for mountain climbing control. As the second generated power, which is the power generated by the lowest layer solar panel, the value obtained by subtracting the sum of the first generated power from the initial total generated power and the first generated power of the solar panel that is the target of scan control and is stacked vertically above the lowest layer solar panel is calculated by dividing the result by the sum of the first generated power. The solar panel power generation system according to claim 1.

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