Solar power generation system

Abstract

To provide a photovoltaic power generation system that can keep the average power generation reserve power in a desired value without necessarily requiring a plurality of solar cells.SOLUTION: A photovoltaic power generation system controls a PCS 20 so as to make a solar cell 10 perform MPPT operation in a constant control cycle TC. The constant control cycle TC has an MPPT operation period T and an output suppression period (1-T) for making the solar cell 10 operate so as to keep predetermined power generation reserve power (1-a). A control circuit 80 for the PCS 20 calculates the average output x of the solar cell 10 in the output suppression period (1-T) so that output electric energy of the solar cell in the control cycle TC, which is the total value of electric energy output from the solar cell 10 in the MPPT operation period and electric energy output from the solar cell 10 in the output suppression period (1-T), is made to be a value having desired power generation reserve power on average.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a photovoltaic power generation system that can maintain a desired power generation reserve during output suppression operation. [Background technology]

[0002] In recent years, the increasing number of solar power generation systems, a type of distributed power source, connected to the power grid has led to a decrease in the proportion of synchronous generators in the power grid, resulting in a decline in frequency stability. To address this, various technologies have been developed to improve the frequency stability of the power grid, such as power conditioning systems (PCS) equipped with pseudo-inertia control functions and so-called smart inverters.

[0003] In a solar power generation system, the output changes depending on the amount of sunlight and the temperature of the solar panels. Generally, as shown in Figure 11, the output of the solar panels is the maximum power P. M Maximum Power Point Tracking (MPPT) control is performed to search for the maximum power point and operate the PCS, etc. On the other hand, as the introduction of solar power generation equipment progresses, it is expected that there will be a need to have room to increase the output of solar cells (power generation reserve capacity) in the event of emergencies such as a decrease in the frequency of the power grid. In that case, it will not be possible to perform the above MPPT control at all times, and it will be necessary to perform output suppression operation, which suppresses the output of solar cells by a certain percentage during periods other than the MPPT operation period. However, during this period of power reduction operation, it is not possible to search for the maximum power point of the solar cells, and therefore it is not possible to maintain adequate power generation reserves.

[0004] For example, Patent Document 1 describes a technique for estimating power generation reserve by comparing a first maximum power based on a first current-voltage characteristic of a solar cell acquired in advance with a second maximum power based on a second current-voltage characteristic estimated by changing the voltage of the solar cell. Furthermore, Patent Document 2 describes a technique for identifying the solar cell operating at maximum power among multiple solar cells and estimating the power generation reserve by comparing its output voltage with the output voltages of the other solar cells. Furthermore, Patent Document 3 describes a technology in which a power conversion means installed at each consumer creates a database of the relationship between solar radiation and the maximum power that the photovoltaic power generation system can output, estimates the true maximum power from the database based on the amount of solar radiation detected by a solar radiation sensor, and calculates the amount of power generation suppression (power generation reserve) based on the difference between this maximum power and the actual generated power, so that the loss of power sales opportunities for each consumer is equal. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-9116 (

[0028] to

[0044] , Figures 6 to 8, etc.) [Patent Document 2] Japanese Patent Publication No. 2019-176561 (

[0039] to

[0041] , Figures 6 to 8, etc.) [Patent Document 3] Japanese Patent Publication No. 5372724 (

[0046] to

[0053] , Figures 5 to 7, etc.) [Overview of the project] [Problems that the invention aims to solve]

[0006] The aforementioned Patent Documents 1 to 3 do not disclose a specific method for controlling the output of a photovoltaic power generation system during a period of output curtailment based on predicted power generation reserve capacity. In particular, Patent Document 2 is based on a system with multiple solar cells, and therefore cannot be applied to a system with a single solar cell. Furthermore, Patent Document 3 aims to equalize the loss of electricity sales opportunities for multiple consumers, and does not disclose a specific method for controlling the power output of each consumer based on the calculated amount of power generation reduction.

[0007] Therefore, the problem to be solved by the present invention is to calculate the average output of a solar cell or a power conversion device during an output suppression period so as to maintain a desired power generation reserve capacity, and to control the power conversion device, and also to provide a solar power generation system that does not necessarily require a plurality of solar cells.

Means for Solving the Problems

[0008] In order to solve the above problems, the invention according to claim 1 is a solar power generation system in which a power conversion device that converts the output of a solar cell into AC power performs MPPT control on the solar cell at a predetermined control cycle, The control circuit of the power conversion device, using an MPPT operation period for performing MPPT control on the solar cell, the maximum power searched during the MPPT operation period, an output suppression period for operating the solar cell with its output suppressed to less than the maximum power, and a desired power generation reserve capacity in the control cycle, calculates the average output of the solar cell or the power conversion device during the output suppression period, and controls the power conversion device so as to obtain this average output.

[0009] Also, as described in claim 2, in the solar power generation system described in claim 1, the control circuit may calculate the average output using the output power amount of the solar cell or the power conversion device obtained from the MPPT operation period and the maximum power.

[0010] Also, as described in claim 3, in the solar power generation system described in claim 1, the control circuit may calculate the average output using the actually measured power amount obtained from the MPPT operation period and the actual output of the solar cell or the power conversion device.

[0011] Also, as described in claim 4, in the solar power generation system according to any one of claims 1 to 3, the control circuit may use the maximum power point searched by the MPPT operation in the previous control cycle as the search start point of the MPPT operation in the current control cycle.

[0012] Furthermore, as described in claim 5, in the photovoltaic power generation system described in any one of claims 1 to 3, the control circuit may calculate the average value of the operating points that fall within a predetermined range from among the multiple operating points searched by the MPPT operation of the previous multiple control cycles, and set this maximum power point as the starting point for the MPPT operation of the current control cycle.

[0013] Furthermore, as described in claim 6, in the photovoltaic power generation system described in any one of claims 1 to 3, the control circuit may shorten the original MPPT operation period and calculate the average output during the output suppression period when the search for the maximum power point by the MPPT operation of the previous control cycle is completed in a short time.

[0014] Furthermore, as described in claim 7, in the photovoltaic power generation system described in any one of claims 1 to 3, the control circuit may absorb or release the fluctuations in the output of the solar cell or power converter during the control cycle by the charging and discharging operation of the energy storage means connected to the DC input side of the power converter.

[0015] Furthermore, as described in claim 8, in the photovoltaic power generation system described in any one of claims 1 to 3, it is desirable that the power conversion device is connected to the grid power supply via the power grid.

[0016] Furthermore, as described in claim 9, the photovoltaic power generation system described in any one of claims 1 to 3 comprises a plurality of solar cells and a plurality of power converters that convert the outputs of each solar cell into alternating current power and supply it to the power grid, wherein the plurality of power converters are connected in parallel to each other to the power grid, and the control circuits of the plurality of power converters are controlled in synchronization so that the MPPT operation periods of the plurality of solar cells are staggered.

[0017] Furthermore, as described in claim 10, in the photovoltaic power generation system described in claim 9, it is desirable that the control circuits of the multiple power converters be controlled so as to cancel out fluctuations in the output of a solar cell or a power converter connected to a solar cell when the output of that solar cell or the output of a power converter connected to that solar cell gradually fluctuates during the MPPT operation period of that solar cell.

[0018] Furthermore, as described in claim 11, in the photovoltaic power generation system described in any one of claims 1 to 3, it is desirable that the control circuit set a time limit for the MPPT operation period of the current control cycle, and when the maximum power point cannot be found within this time limit, store the trend of change in the output of the solar cell and the final operating point at the end of the time limit, and set the final operating point as the starting point for searching for MPPT operation in the next control cycle. [Effects of the Invention]

[0019] According to the present invention, the average output of the solar cell or power converter during the output suppression period is calculated based on the MPPT operation control period, MPPT operation period, and desired power generation reserve capacity, and the power converter is controlled to obtain this average output, thereby enabling output suppression operation of the solar cell while maintaining the desired power generation reserve capacity. Furthermore, unlike the conventional technology mentioned above, which uses multiple solar cells to predict power generation reserves, this method allows for a simpler overall system and reduced costs. [Brief explanation of the drawing]

[0020] [Figure 1] This is an overall configuration diagram of a photovoltaic power generation system according to an embodiment of the present invention. [Figure 2] This is a timing chart illustrating the first embodiment of the present invention. [Figure 3] This is a flowchart showing the operation of the first embodiment of the present invention. [Figure 4] This is a timing chart illustrating a second embodiment of the present invention. [Figure 5]This is a flowchart showing the operation of the second embodiment of the present invention. [Figure 6] This is a timing chart illustrating a fourth embodiment of the present invention. [Figure 7] This is a timing chart illustrating a sixth embodiment of the present invention. [Figure 8] This is a timing chart illustrating a seventh embodiment of the present invention. [Figure 9] Figure 8 is a timing chart illustrating other operational examples during period ΔT2. [Figure 10] This is an overall configuration diagram of a control system for realizing the sixth and seventh embodiments of the present invention. [Figure 11] This figure shows the voltage-output characteristics of a solar cell that performs MPPT control. [Modes for carrying out the invention]

[0021] Embodiments of the present invention will be described below with reference to the figures. Figure 1 is an overall configuration diagram of a photovoltaic power generation system according to an embodiment of the present invention. In Figure 1, the DC power output from the solar cell 10 is supplied to the PCS 20 via the DC line 31. The PCS 20 converts the DC power to AC power through the operation of an inverter and outputs it to the power grid 32 to which the grid power supply 50 is connected. 40 is a load connected to the power grid 32. Furthermore, a DC / DC converter 60 that controls the charging and discharging of the energy storage means 70, which consists of a battery, a capacitor, etc., is connected to the DC line 31. These DC / DC converter 60 and energy storage means 70 are not necessarily essential components of the present invention.

[0022] The control circuit 80 consists of a computer system, for example, a CPU and a memory containing a predetermined control program, and comprehensively controls the MPPT operation and output suppression operation of the solar cell 10 by the inverter in the PCS 20, as well as the charging and discharging operation of the energy storage means 70 by the DC / DC converter 60. Note that the control circuit 80 receives the input and output voltages and currents of the PCS 20, the charge and discharge currents of the power storage means 70, etc. from a plurality of voltage and current sensors not shown.

[0023] Next, the control method according to the first embodiment of the present invention will be described while referring to FIGS. 2 and 3. FIG. 2 is a timing chart schematically showing the output of the solar cell 10, and FIG. 3 is a flowchart showing a series of operations. In the following description, the output, average output, or output power amount of the solar cell 10 is focused on, but the case where these are respectively replaced with the output, average output, or output power amount of the PCS 20 (inverter) is also included in the technical scope of the present invention.

[0024] In FIG. 2, the control cycle T of the MPPT operation C is made to correspond to the ratio 1, and the MPPT operation period within the control cycle T C is shown as the ratio T, and the output suppression period is shown as the ratio (1 - T). Also, the maximum power P during the MPPT operation M is made to correspond to the ratio 1, the desired power generation reserve for this maximum power P M with respect to the ratio 1 is shown as the ratio (1 - a), and the average output during the output suppression period is shown as the ratio x. The above a is the difference between the ratio 1 corresponding to the maximum power P M and the power generation reserve (1 - a) as a ratio, and is the average output ratio of the solar cell 10 in the control cycle T C The control cycle T of the MPPT operation C is assumed to be, for example, about 0.5 to 2 [min], but it goes without saying that it may have other lengths. Regarding the arrow y1 shown by the dashed-dotted line in FIG. 2, it will be described in the third embodiment described later.

[0025] Next, the operation of this embodiment will be described while referring to FIGS. 2 and 3. As described above, a, (1 - a), and x are ratios regarding the output of the solar cell 10, and T C ​,T,(1-T) are ratios relating to the period (time), but for convenience, below we will refer to a,(1-a),x as the output itself, and T C ,T,(1-T) are explained as the period itself.

[0026] First, in the control circuit 80, the control period T C With the MPPT operating period T and the output averaging ratio a (in other words, the power generation reserve (1-a)) set in advance, the maximum power point of the solar cell 10 is searched for over the period T using methods such as hill climbing, and MPPT control is performed (step S11 in Figure 3). Here, the maximum power point refers to the operating point where the output is maximized according to the output voltage of the solar cell 10. Then, the maximum power P found through MPPT operation M This is recorded (step S12). Note that in Figure 2, it is assumed that the output of the solar cell 10 rises up in a short time so that it can be considered to be almost linear at the start of the MPPT operation period T, and the maximum power point is searched.

[0027] Next, the control circuit 80 calculates the average output x during the output suppression period (1-T) within the MPPT operating period T shown in Figure 2 using Equation 2 based on Equation 1 below. Furthermore, the actual output of PCS20 required to maintain the average output during the output suppression period (1-T) at x is calculated as P M Calculate using ×x (Step S13). [Formula 1] 1 × T + x × (1 - T) = a × 1 [Formula 2] x = (aT) / (1 - T)

[0028] The left side of Equation 1 above is the sum of the amount of power output during the MPPT operation period T and the amount of power output during the output suppression period (1-T), and the right side of Equation 1 is the control period T C This is the amount of electrical energy required to maintain the output at a over a period of time, that is, the amount of electrical energy needed to maintain the power generation reserve at (1-a). Therefore, by controlling the PCS20 using Equation 2, which is a modified version of Equation 1, so that the average output during the output suppression period (1-T) is x, it becomes possible to maintain the desired power generation reserve (1-a) (step S14). In other words, equation 2 is equal to the control period T. C This means that the average output x required to maintain the power generation reserve at (1-a) over the entire period is calculated using time-division averaging.

[0029] For example, if the control period is T C =1, MPPT operating period T=0.1, and power generation reserve capacity P M If we maintain it at 5% (assuming 1-a=0.05), then a=0.95, and by the aforementioned equation 2, x≈0.944... Therefore, the average output x during the output suppression period (1-T) is equal to the maximum power P. M If PCS20 is controlled to be approximately 94.4% of the control period T, C On average, a power generation reserve of 5% can be maintained throughout the entire period.

[0030] Furthermore, if the MPPT operating period T is short, the PCS20 may be controlled by fixing the average output x during the output suppression period (1-T) to a, in order to avoid the complex calculations during this period T.

[0031] Next, a control method according to a second embodiment of the present invention will be described with reference to Figures 4 and 5. In the first embodiment, the maximum power P discovered at the start of the MPPT operation period T is M The average output x is calculated under the assumption that the output from the solar cell 10 is assumed to be the maximum power P over the entire period T. However, strictly speaking, the output over the entire period T is assumed to be the maximum power P. M That's not the case. Therefore, in the second embodiment, the amount of power output from the solar cell 10 during the MPPT operation period T is measured and the average output x during the output suppression period (1-T) is calculated.

[0032] Figure 4 is a timing chart schematically showing the output of the solar cell 10 in the second embodiment, and Figure 5 is a flowchart showing the series of operations. Figure 4 shows a case where the maximum power point gradually increases during the initial part of the MPPT operation period T. The amount of energy output during this MPPT operation period T (for convenience, denoted as P(t) × T [kWh]) is measured, and this amount of energy P(t) × T is used to calculate the average output x during the power suppression period (1-T). The arrow y2, indicated by a dashed line in Figure 4, and ΔP, enclosed by a dashed line, will be discussed later.

[0033] In the second embodiment, as shown in the flowchart of Figure 5, first, the output P(t) at each time point during the MPPT operation period T is measured (step S21). Next, the average value of P(t) is calculated, and this average value is used to determine the maximum power P M Convert to ratio b (step S22). Next, the control circuit 80 calculates the average output x during the output suppression period (1-T) within the MPPT operating period T using equation 4 based on equation 3 below. Note that b × T in equation 3 corresponds to the amount of energy (P(t) × T) output during the MPPT operating period T mentioned above. Furthermore, the actual output of PCS20 necessary to maintain the average output of the output suppression period (1-T) at x is P M Calculate using ×x (Step S23). [Formula 3] b × T + x × (1 - T) = a × 1 [Equation 4] x = (a - bT) / (1 - T)

[0034] As described above, if PCS20 is controlled so that the average output during the output suppression period (1-T) is x (step S24), the control period T C The power generation reserve (1-a) can be maintained over this period. In particular, in this second embodiment, since the amount of power measured during the MPPT operation period T is used, the power generation reserve (1-a) can be maintained even more accurately.

[0035] Next, a control method according to a third embodiment of the present invention will be described. In this third embodiment, the maximum power P discovered and recorded during the MPPT operation period T in the first embodiment is M The next control period T CAs the search start point during the MPPT operation (arrow y1 in FIG. 2), or the measured output P(t) during the current MPPT operation period T according to the second embodiment is used as the search start point for the next control period T C (arrow y2 in FIG. 4). Thereby, in the next control period T C it is possible to set a value with a relatively high accuracy as the maximum power as the search start point, so that the time required for searching for the maximum power point can be shortened.

[0036] Also, in the case of sudden cloudiness, etc., the maximum power point may temporarily fluctuate within the MPPT operation period T and may not be specified. For this reason, the history of the maximum power values of the MPPT operation points in a plurality of previous control periods is retained, and values not included in a predetermined width among these plurality of maximum power values are removed as noise, and the average value of the plurality of maximum power values included in the predetermined width is used as the search start point in the MPPT operation period T C of the next control period T may be used. The above average value may be obtained by, for example, performing a moving average process on a plurality of maximum power values included in a predetermined width, or by performing an averaging process by performing a first-order lag filter operation on the plurality of maximum power values. By removing the noise component and obtaining the average value as described above, the accuracy of the next search start point can be improved.

[0037] Next, the control method according to the fourth embodiment of the present invention will be described while referring to FIG. 6. In this fourth embodiment, when the search for the maximum power point by the MPPT operation ends in a short time, the original MPPT operation period T is shortened to T' as shown in FIG. 6 (T' < T), and the average output x' of the output suppression period (1 - T') relatively extended according to this period T' is calculated. As a specific method for calculating the average output x', the formula 6 based on the following formula 5 may be calculated according to the above formulas 1 and 2, or when measuring the amount of power, the formula 8 based on the following formula 7 may be calculated according to formulas 3 and 4. [Formula 5] 1 × T' + x' × (1 - T') = a × 1 [Formula 6] x'=(a-T') / (1-T') [Equation 7] b × T' + x' × (1 - T') = a × 1 [Equation 8] x'=(a-bT') / (1-T')

[0038] According to this embodiment, the average output x' during the output suppression period (1-T') is greater than the average output x during the original output suppression period (1-T). As a result, the amount of output fluctuation between the MPPT operation period T' and the output suppression period (1-T') is reduced, and power fluctuations in the power system 32 can be suppressed.

[0039] Next, a control method according to a fifth embodiment of the present invention will be described. In this fifth embodiment, the power fluctuation ΔP (power fluctuation between the MPPT operation period T and the output suppression period (1-T), and power fluctuation within the MPPT operation period T) enclosed by the dashed line in Figure 4 is charged and discharged within the capacity range of the energy storage means 70 by the operation of the DC / DC converter 60 shown in Figure 1, and as a result the control period T C It is desirable to control the PCS20 so that the internal power generation reserve is maintained at the required value (1-a). By absorbing or releasing the above-mentioned power fluctuation ΔP using the energy storage means 70, power fluctuations in the power system 32 can be avoided.

[0040] Next, a control method according to the sixth embodiment of the present invention will be described with reference to Figure 7. This embodiment relates to output control of the solar cells 10 in each power generation device when a solar power generation system is equipped with multiple solar power generation devices (units consisting of solar cells 10 and PCS 20).

[0041] For example, if a solar power generation system consists of three solar power generation devices 100A, 100B, and 100C connected in parallel to the power grid 32, then, as shown in Figure 7, one control period T CThe power grid is divided into three sections, and the respective PCS20s are controlled in synchronization so that the MPPT operation period T of each power generation device 100A, 100B, and 100C is sequentially shifted. In this case, the method for calculating the average output x during the output suppression period (1-T) is the same as in the above-described embodiments. According to this sixth embodiment, the sum of the outputs of each power generation device 100A, 100B, and 100C is controlled by the control period T. C Because it remains almost constant over a long period, fluctuations in power in the power grid 32 can be suppressed.

[0042] Next, a control method according to the seventh embodiment of the present invention will be described with reference to Figure 8. Figure 8 is a timing chart schematically showing the output of solar cells in each of the solar power generation devices 100A, 100B, and 100C when, for example, three (N=3) solar power generation devices 100A, 100B, and 100C are connected in parallel to the power grid 32, similar to the sixth embodiment.

[0043] In this embodiment, the MPPT operation period T of each power generation device 100A, 100B, and 100C is sequentially staggered. While one device is fluctuating its output for MPPT operation, the other devices adjust their output to compensate for this fluctuation, thereby controlling the total output of the entire solar power generation system so that it does not fluctuate due to MPPT operation. In the example in Figure 8, one control period T C Within this system, for example, during the MPPT operation period T of power generator 100A, the average output of the other power generators 100B and 100C is reduced to x to suppress output. Then, during the MPPT operation period T of power generator 100B, the average output of the other power generators 100A and 100C is reduced to x to suppress output. Furthermore, during the MPPT operation period T of power generator 100C, the average output of the other power generators 100A and 100B is reduced to x to suppress output.

[0044] Furthermore, in each power generation unit 100A, 100B, and 100C, the control period T CThe period (1-NT) obtained by subtracting the MPPT operation period T and the output suppression period (2T) is defined as a period during which the average output is maintained at a constant value a (the average output ratio of the solar cells 10) and all power generation devices 100A, 100B, and 100C do not operate in MPPT mode. Thus, looking at each power generation device 100A, 100B, and 100C, each device has three operating modes consisting of the MPPT operation period T, the output suppression period (2T), and the period (1-NT) during which the average output is maintained at a constant value a without MPPT operation, thereby expanding the range of operating mode options.

[0045] The method for calculating the average output x in this seventh embodiment is as follows: one control period T C The total energy (1 × a × N) of the three generators 100A, 100B, and 100C is equal to the sum of the total energy during the MPPT operating period T, the total energy during the output suppression period (2T), and the total energy during the remaining period (1-NT). Therefore, equation 9 holds true, and the average output x can be calculated using equation 10, which is based on equation 9. Here, the first term on the right-hand side of equation 9 corresponds to the "total energy consumption during the operating period T of the three MPPTs," the second term corresponds to the "total energy consumption during the output suppression period (2T)," and the third term corresponds to the "total energy consumption during the remaining period (1-NT)." All of these represent "time ratio" × "output ratio" × "number of time segments, i.e., control cycles" × "number of power generators." Note that in this example, one control cycle T C Since the target is [a specific value], and the "number of time divisions, i.e., control cycles" in the first and third terms on the right-hand side is "1", the "×1" in these terms can be omitted. [Formula 9] 1×a×N=(T×1×1×N)+{T×x×(N-1)×N} +{(1-NT)×a×1×N} [Formula 10] x = (aN-1) / (N-1)

[0046] For example, generating reserve capacity for maximum power P MIf we want to maintain it at 10% of the maximum power, that is, if we want (1-a)=0.1, then a=0.9 and N=3, and from equation 10, we get x=0.85. In other words, the average output x of each power generation device 100A, 100B, and 100C during their respective output suppression periods (2T) is equal to the maximum power P. M By controlling each PCS20 to 85%, an average power generation reserve of 10% can be maintained.

[0047] Note that the control period T in Figure 8 C The period ΔT1 within each of the power generation devices 100A, 100B, and 100C consists of an MPPT operation period T and an output suppression period (2T). Then, using the same principle as in the first embodiment, the average output x required to maintain the power generation reserve at (1-a) is calculated by x = (3a-1) / 2 such that the amount of electricity output from the solar cell 10 during period ΔT1 is the sum of the amount of electricity output from the solar cell 10 during the MPPT operation period T (1×T) and the amount of electricity output from the solar cell 10 during the output suppression period (2T) (x×2T) (T+2Tx).

[0048] In Figure 8, the outputs of the 100A, 100B, and 100C generators are all maintained at the same value a during the period (1-NT). However, if the rated outputs of the N generators are not equal, it may be difficult to equalize all outputs. In such cases, even if the outputs of each generator differ, it is sufficient if the total output of the N generators is equal to a × N.

[0049] Figure 9 is a time chart showing the case where, during the period ΔT2 in Figure 8, the output of the 100A generator operating in MPPT mode does not rise rapidly in a short time, but increases gradually, so that it can be considered to be almost linear. In this case, as shown in the diagram, if the output of the other power generators 100B and 100C is controlled to gradually decrease during the period when the output of power generator 100A gradually increases, the total output of all power generators 100A, 100B, and 100C will remain almost constant, so there is no need to worry that fluctuations in the output of each power generator will affect the power grid 32.

[0050] Next, Figure 10 is an overall configuration diagram of the control system for realizing the seventh embodiment described above, and this control system is also applicable to the sixth embodiment. In Figure 10, the main control unit 200, which is given power generation reserve (1-a) as a command, transmits ON / OFF commands for the MPPT operation of the PCS20 of the power generation units 100A, 100B, and 100C to the local control units 200A, 200B, and 200C, respectively, based on the time information.

[0051] A power generator operating in MPPT mode, for example 100A, sends the actual output of the solar cell 10 back to the main control unit 200 via the local control unit 200A. If the local control unit 200A determines that the maximum power point has been reached, it then returns the maximum output P M This is sent back to the main control unit 200. Furthermore, the main control unit 200 transmits an output command equivalent to the average output x of the solar cells 10 during the output suppression period to the local control units 200B and 200C of the other power generation units 100B and 100C that do not operate in MPPT mode, causing the power generation units 100B and 100C to operate in output suppression mode.

[0052] Alternatively, the functions of the main control device 200 described above may be implemented in each of the local control devices 200A, 200B, and 200C, with one of them set as the master and the other two as slaves. The master power generator may then be controlled in a synchronized manner so that when it is operating in MPPT mode, the other two power generators operate in output suppression mode. Alternatively, one or two (i.e., N-1) of the three power generators may be equipped with a local control device that can provide a master function, thereby designating that power generator as a local power generator with master functionality. The remaining power generators may be equipped with relatively inexpensive local control devices that cannot provide master functionality, thereby designating those power generators as local power generators without master functionality. The local power generator with master functionality may then be made to function as the master power generator, and synchronized control may be implemented so that the other local power generators without master functionality suppress output when this master power generator is operating in MPPT mode.

[0053] Next, a control method according to the eighth embodiment of the present invention will be described. In this eighth embodiment, the control circuit 80 controls the current control period T C A predetermined time limit is set for the MPPT operation period T, and if the maximum power point cannot be found within this time limit, the trend of change (increase or decrease) in the output of the solar cell 10 and the final operating point at the end of the time limit are stored. Then, the final operating point is stored in the next control cycle T. C Set this as the starting point for MPPT operation. This makes it easier to find the maximum power point, even in cloudy conditions where it is difficult to locate, and can contribute to maintaining the desired power generation reserve.

[0054] As described above, according to each embodiment of the present invention, the average output x is calculated based on the output of the solar cell 10 during the MPPT operation period, the output suppression period, the desired power generation reserve, etc., and the PCS 20 is controlled so that the output of the solar cell 10 during the output suppression period becomes the above average output x, thereby enabling the operation of the photovoltaic power generation system while maintaining the desired power generation reserve. In each embodiment, the PCS20 is connected to the grid power supply 50 via the power grid 32. However, as described in claim 7, if the PCS20 is configured to have a power storage means 70 on the DC input side, it is not necessarily required to connect the PCS20 to the grid power supply 50. In other words, even when applying the present invention to an independent photovoltaic power generation system that supplies AC output power from a PCS20 equipped with a power storage means 70 only to a load 40, maintaining a desired power generation reserve is also effective in determining how well it can cope with sudden changes in the load 40. [Explanation of symbols]

[0055] 10: Solar cells 20: Power Conditioning System (PCS) 31: DC railway 32: Power system 40: Load 50: Grid power supply 60: DC / DC Converter 70: Energy storage means 80: Control circuit 100A, 100B, 100C: Solar power generation equipment 200: Main control unit 200A, 200B, 200C: Local control unit

Claims

1. In a photovoltaic power generation system that uses a power conversion device to convert the output of solar cells into AC power, thereby controlling the solar cells with MPPT at a predetermined control cycle, The control circuit of the power converter is A photovoltaic power generation system characterized by calculating the average output of the solar cell or the power converter during the output suppression period using an MPPT operation period for MPPT control of the solar cell, the maximum power searched during the MPPT operation period, an output suppression period for operating the solar cell with its output suppressed to less than the maximum power, and a desired power generation reserve during the control cycle, and controlling the power converter so that this average output is obtained.

2. In the photovoltaic power generation system described in claim 1, The aforementioned control circuit is A photovoltaic power generation system characterized by calculating the average output using the output energy of the solar cell or the power converter obtained from the MPPT operating period and the maximum power.

3. In the photovoltaic power generation system described in claim 1, The aforementioned control circuit is A photovoltaic power generation system characterized by calculating the average output using the measured amount of power obtained from the MPPT operating period and the actual output of the solar cell or the power converter.

4. In a solar power generation system as described in any one of claims 1 to 3, The aforementioned control circuit is A photovoltaic power generation system characterized in that the maximum power point found by the MPPT operation in the previous control cycle is used as the starting point for the MPPT operation in the current control cycle.

5. In a solar power generation system as described in any one of claims 1 to 3, The aforementioned control circuit is A photovoltaic power generation system characterized by calculating the average value of operating points within a predetermined range from among the multiple operating points explored by MPPT operation in multiple control cycles up to the previous cycle, defining this as the maximum power point, and using this maximum power point as the starting point for the MPPT operation of the current control cycle.

6. In a solar power generation system as described in any one of claims 1 to 3, The aforementioned control circuit is A photovoltaic power generation system characterized by shortening the original MPPT operation period and calculating the average output during the output suppression period when the search for the maximum power point by MPPT operation in the previous control cycle is completed in a short time.

7. In a solar power generation system as described in any one of claims 1 to 3, The aforementioned control circuit is A photovoltaic power generation system characterized in that fluctuations in the output of the solar cell or the power converter during the control cycle are absorbed or released by the charging and discharging operation of a power storage means connected to the DC input side of the power converter.

8. In a solar power generation system as described in any one of claims 1 to 3, A solar power generation system characterized in that the power conversion device is connected to a grid power source via a power grid.

9. A solar power generation system according to any one of claims 1 to 3 comprises a plurality of solar cells and a plurality of power converters that convert the output of each solar cell into alternating current power and supply it to a power grid, wherein the plurality of power converters are connected in parallel to each other to the power grid, The control circuits of the aforementioned multiple power converters are as follows: A photovoltaic power generation system characterized by controlling multiple solar cells in a synchronized manner so that their MPPT operating periods are staggered.

10. In the photovoltaic power generation system described in claim 9, The control circuits of the aforementioned multiple power converters are as follows: A photovoltaic power generation system characterized by controlling the output of one solar cell or a power converter connected to it to cancel out any gradual fluctuations in the output of that solar cell or a power converter connected to it during the MPPT operation period of that solar cell.

11. In a solar power generation system as described in any one of claims 1 to 3, The aforementioned control circuit is This photovoltaic power generation system is characterized by setting a time limit for the MPPT operation period of the current control cycle, storing the trend of change in the output of the solar cell and the final operating point at the end of the time limit if the maximum power point cannot be found within the time limit, and setting the final operating point as the starting point for searching for MPPT operation in the next control cycle.

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