Method and circuit arrangement for obtaining characteristic curves of a PV power generation device
Patent Information
- Application Number
- JP2023580446
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-03-22
- Filing Date
- 2023-02-17
- Publication Date
- 2026-02-24
AI Technical Summary
Existing methods for obtaining the characteristic curve of a PV generator in power generation facilities are complex and lead to increased control-related and communication requirements, as well as potential power fluctuations and overload risks.
A method and circuit device that reduce the accumulated output power of DC-DC converters not involved in the scan, while maintaining constant voltage or current, to ensure the sum of the reduced output power and the expected maximum power of the scanned PV generator does not exceed the nominal power of the DC-AC converter, thereby simplifying the process and reducing power loss.
The method allows for the efficient acquisition of the characteristic curve with negligible power loss, avoiding overloading of the DC-AC converter and maintaining power generation at an acceptable level, even during scans.
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Abstract
Description
[Technical field]
[0001] The present application relates to a method and a circuit arrangement for obtaining a characteristic curve of a photovoltaic power generation device, or PV power generation device for short, and a power generation installation having such a circuit arrangement. Obtaining the characteristic curve of a PV power generation device can also be called scanning the characteristic curve of a PV power generation device, or scanning the PV power generation device. [Background technology]
[0002] In the power plant, the PV generators may be connected to a power converter via a DC-DC converter (DC voltage converter), and the PV generators may comprise a number of PV strings that may be connected in series and / or in parallel. The PV strings may in turn comprise a number of PV modules. The power converter may in particular be a DC-AC converter (inverter) connected to an AC grid (in particular an AC supply grid) for exchanging power with the AC grid (in particular for feeding power into the AC grid).
[0003] A PV generator has a voltage-current characteristic curve, UI characteristic curve for short, which shows the dependence of the DC current generated by the PV generator on the PV voltage present at the PV generator. It may be desirable to obtain the UI characteristic curve of a PV generator during operation. It is known from documents WO2014 / 118059A1 and US2020 / 0220357A1 that when an individual DC-DC converter of the generator analyzes the UI characteristic curve, it compensates for the resulting fluctuations in the total power by compensatingly controlling one or more other DC-DC converters of the generator, keeping the total power as constant as possible. This compensating control action increases the control-related and communication demands on the generator.
[0004] US 11,171,489 B2 also describes a method for obtaining a UI characteristic curve of, for example, a PV power plant of a power plant, in which a converter not involved in obtaining the UI characteristic curve compensates for power fluctuations of a converter which obtains the UI characteristic curve. It is further disclosed that in an extreme case, during the acquisition of the characteristic curve, the power of the converter not involved in the acquisition is reduced to zero. Summary of the Invention
[0005] The present application is based on the object of presenting an improved method for obtaining a characteristic curve of a PV power generation device. Furthermore, it is an object of presenting a circuit arrangement for obtaining a characteristic curve of a PV power generation device.
[0006] This object is achieved by a method having the features of claim 1 or by a method having the features of claim 2. This object is further achieved by a circuit arrangement having the features of independent patent claim 7 or by a circuit arrangement having the features of independent patent claim 8. Preferred embodiments are specified in the dependent patent claims.
[0007] In a power plant with several PV generators, each PV generator is connected to the DC-AC converter via an assigned DC-DC converter. The output side of these DC-DC converters is connected to the DC link as an input element of the DC-AC converter. The PV generator comprises at least one PV string, preferably several PV strings. Several PV strings of PV generators can be connected in parallel, in series or in a combination of series and parallel circuits. Correspondingly, the input side of the DC-DC converter can be connected to one PV string or to several PV strings that can be connected to the DC-DC converter in parallel, in series or in a combination thereof.
[0008] The PV power plants can be connected in a parallel circuit to the DC link as input elements of a DC-AC converter via a respectively assigned DC-DC converter, or alternatively, the PV power plants can be connected in series to the DC link as input elements of a DC-AC converter via a respectively assigned DC-DC converter.
[0009] The characteristic curve of one of the PV generators can be obtained by performing a so-called scan, which may also be called scanning of the PV generator. During a scan of the PV generator, for example, various voltage values at the output of the PV generator are regulated by the assigned DC-DC converter and the current supplied by the PV generator is measured against the regulated voltage values. Alternatively, it is also possible to regulate the current flowing through the PV generator and measure the resulting voltage. The UI characteristic curve of the PV generator can be obtained by plotting the measured current values against the regulated voltage values.
[0010] A method for acquiring characteristic curves of PV power generation devices scanned from a plurality of PV power generation devices in such a power generation facility includes: a) reducing the cumulative output power of a DC-DC converter for which the associated PV power plant is not intended to obtain a characteristic curve as a function of the maximum power expected at the output side of the DC-DC converter connected to the scanned PV power plant during the acquisition of the characteristic curve of the scanned PV power plant, to ensure that the sum of the reduced cumulative output power and the maximum expected power of the scanned PV power plant does not exceed the nominal power of the DC-DC converter; b) thereafter obtaining a characteristic curve of the scanned PV power plant; Includes.
[0011] In a power plant having a DC-DC converter connected in parallel with the input of a DC-AC converter, the method comprises: c) During the acquisition of the characteristic curve: it further comprises a step of keeping the DC-link voltage constant using a DC-AC converter. In this case, the DC-link voltage corresponds to the voltage on the output side of the DC-DC converter. In this case, the value of the DC-link voltage in this step preferably corresponds to a value equal to or greater than the open circuit voltage of the PV generator to be scanned, which is guaranteed if the DC-DC converter used is a boost converter. This voltage is preferably kept constant by controlling a clock semiconductor switch of the DC-AC converter.
[0012] In a power plant where the DC-DC converter is connected in series with the DC link at the input of the DC-AC converter, this method c1) During characteristic curve acquisition: Using a DC-AC converter, a current flowing through the series circuit of the DC-DC converter is kept constant, preferably by controlling a clock semiconductor switch of the DC-AC converter.
[0013] The method according to the invention is characterized by its simplicity of implementation and by the negligible power losses that may occur due to the execution of the scan, while at the same time avoiding overloading of the DC-AC converter, which is dangerous especially in installations where the nominal power potential of the installed PV power generation equipment is significantly greater than the nominal power of the DC-AC converter, so that these installations always operate at the nominal power of the DC-AC converter and therefore also immediately before the method according to the invention is executed.
[0014] While scanning one of the PV generators, the output power of the scanned PV generator fluctuates because it passes through different points on the UI characteristic curve, and each of these different points indicates a different output power of the scanned PV generator. Here, the fluctuating output power of the scanned PV generator has a maximum power at a maximum power point (MPP) on the UI characteristic curve of the scanned PV generator. Overall, to avoid damage to the DC-AC converter and support grid compatibility with the AC grid, the sum of the output power of the scanned PV generator and the cumulative output power of the remaining PV generators should not exceed the nominal power of the DC-AC converter.
[0015] An expected maximum power of the PV power generating equipment involved in the scan can be determined by the method prior to reducing the cumulative output power, where the expected maximum power can be based on an empirical value, such as from a previous scan or an otherwise known maximum power of PV power generating equipment not involved in the scan, and can further depend on or be determined from temperature, sunlight, and similar environmental factors.
[0016] The above method can achieve this because the cumulative output power of the PV generators not involved in the scan is lowered during the scan to the extent that the sum of the output powers of all PV generators does not exceed the nominal power of the DC-AC converter being scanned. At the same time, this allows to continue to generate as much power as possible and output this through the DC-AC converter even during the scanning of the characteristic curve of one of the PV generators. This is advantageous because it allows the power generation to continue to be maintained at an acceptable level. A sufficient distance from the nominal power of the DC-AC converter is maintained so that the characteristic curve of the scanned PV generator can be passed through it preferably completely. It may not even be necessary to reduce the output power of the individual DC-DC converters and associated PV generators not involved in the scan, or to reduce it significantly.
[0017] The advantage of this method is that it is simple to implement, as the accumulated output power of DC-DC converters not involved in the scan does not need to be changed during the scan but can be kept at a constant level, yet still generate an acceptable level of active power to be supplied to the AC grid.
[0018] According to the invention, during the acquisition of the characteristic curves, the individual output powers of the DC-DC converters, whose associated PV generators are not intended to acquire characteristic curves, are kept constant. In this case, in order to lower the cumulative output power of the DC-DC converters not involved in the scan, the individual output powers can be lowered with respect to the output powers at the respective maximum power points of the associated PV generators. However, these PV generators continue to generate power, albeit at a reduced level. In this case, keeping the individual output powers constant has the advantage that the method is simplified and the regulation-related expenses can be reduced.
[0019] In one embodiment of the method, the characteristic curve of the scanned PV generator is obtained during an open-loop operation of the DC-DC converter assigned to the scanned PV generator. In this case, the open-loop operation has the advantage over the closed-loop operation that a control loop with feedback can be omitted, making the method simpler and faster. In comparison with the closed-loop operation, in which the voltage value is adjusted in a targeted manner, for example with the voltage value present at the PV generator being fed back, the open-loop operation simply adjusts something without feedback. For example, at least one parameter of the DC-DC converter can be adjusted and the DC-DC converter can be controlled in this way. In the case of a scan, this adjustment or this parameter is changed continuously in order to obtain the characteristic curve, for example by the fact that by changing the parameter, the voltage present at the PV generator is changed and measured and the current output by the PV generator at the current voltage is measured. This parameter can in particular be the duty cycle controlling the DC-DC converter. Particularly preferably, the parameter or the duty cycle is changed over a predefined period of time, which results in an improved reproducibility of the scan and a simplified correction calculation thereafter.
[0020] In one embodiment of the method, the open-loop operation includes a current limiting to avoid exceeding the permissible input current of the DC-DC converter assigned to the scanned PV generator. The current limiting serves to protect the DC-DC converter and can be implemented, for example, as a protection circuit or as a superimposed regulation action operating in a limiting manner. Only if the permissible input current of the DC-DC converter is exceeded does the protection circuit operate or the superimposed control action intervene in a limiting manner. Otherwise, the current limiting has no effect on the scanning process. In response to the operation, the scanning is interrupted and can then be continued with modified control, for example to avoid re-operation of the protection circuit or the superimposed regulation action.
[0021] In one embodiment of the method, the controlled parameter is the duty cycle of the DC-DC converter. Thus, in open-loop operation, the duty cycle of the DC-DC converter assigned to the scanned PV power plant is controlled and continuously changed. In this case, the scan to obtain the characteristic curve can be performed in particular using a predefined curve of the duty cycle.
[0022] In one embodiment, after obtaining the characteristic curve of the scanned PV power plant, the method includes: d) terminating the reduction of the accumulated output power of the DC-DC converter for which the associated PV power generation device is not intended to obtain a characteristic curve.
[0023] This allows the output power to be reduced only during the scan, and then output at unreduced levels again after the scan is completed.
[0024] A circuit device for acquiring characteristic curves of PV power generation devices scanned from a plurality of PV power generation devices in a power generation facility, comprising: adjusting a DC-DC converter, the associated PV power generator of which is not intended to obtain a characteristic curve, as a function of the maximum power expected at the output side of the DC-DC converter connected to the scanned PV power generator, such that the cumulative output power of the DC-DC converter is reduced during the acquisition of the characteristic curve of the scanned PV power generator, to ensure that the sum of the cumulative output power and the maximum expected power of the scanned PV power generator does not exceed the nominal power of the DC-DC converter; It is intended and configured to obtain a characteristic curve of a scanned PV power plant.
[0025] In a first embodiment of the power generation installation, in which the output side of each of the PV power generation arrangements is connected in parallel to a DC link as an input element of a DC-AC converter, in each case via an assigned DC-DC converter, the circuit arrangement is intended and configured to keep constant, during acquisition of the characteristic curve, the voltage of the DC link and the individual output power of the DC-DC converter (12) for which the associated PV power generation arrangement (2) is not intended to acquire a characteristic curve.
[0026] In a second embodiment of the power generation installation, in which the output side of the PV power generation arrangement is in each case connected in series with the DC link as an input element of a DC-AC converter via an assigned DC-DC converter, the circuit arrangement is intended and configured to keep constant during acquisition of the characteristic curve the current flowing through the series circuit of the DC-DC converters and the individual output power of the DC-DC converters (12) for which the associated PV power generation arrangement (2) is not intended to acquire a characteristic curve.
[0027] The circuit arrangement can be used to determine the expected maximum power of the DC-DC converter involved in the scan before reducing the accumulated output power. In this case, the expected maximum power can be based on empirical values, for example from previous scans, and can further depend on temperature, sunlight, and similar environmental factors. The required reduction can also be determined in a traditional way from nominal variables of the scanned DC-DC converter, for example from nominal current and nominal power.
[0028] In one embodiment, the circuit arrangement is arranged in the DC-AC converter and / or the DC-DC converter and is designed and configured in particular to additionally realize closed-loop and / or open-loop control tasks of the DC-AC converter and / or the DC-DC converter. In particular, the circuit arrangement may be in the form of at least one computing unit arranged in the DC-AC converter and / or the DC-DC converter. The at least one computing unit may then be optionally configured and designed to additionally perform closed-loop and / or open-loop control tasks of the DC-AC converter and / or the DC-DC converter.
[0029] A power plant having a DC-AC converter and having a plurality of PV power plants can comprise the circuit arrangement described above, in which the output side of the PV power plants is connected in parallel or in series to the DC link as an input element of the DC-AC converter, in each case via an assigned DC-DC converter. The PV power plants can be scanned according to one of the above methods. After a PV power plant has been scanned, another PV power plant of the plurality of PV power plants can be scanned according to the described method. Using the described method, it is possible to scan some or all of the plurality of PV power plants of the power plant one after the other. [Brief description of the drawings]
[0030] The present application is explained and described in more detail below on the basis of exemplary embodiments shown in the figures.
[0031] [Figure 1] FIG. 1 shows a schematic diagram of a method for obtaining a characteristic curve of a PV power plant. [Diagram 2] FIG. 2 shows diagrammatically the curves of characteristic electrical variables in a power plant. [Diagram 3] FIG. 3 shows a schematic diagram of an example of a power plant comprising DC-DC converters connected in parallel. [Figure 4]FIG. 4 shows a schematic diagram of an example of a power generation installation comprising DC-DC converters connected in series. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] FIG. 1 shows a schematic diagram of a method for acquiring characteristic curves of PV power generation devices 2 scanned from a plurality of PV power generation devices 2 in a power generation facility 10. The method includes: a) reducing the accumulated output power KA of a DC-DC converter 12 for which the associated PV generator 2 is not intended to obtain a characteristic curve. This reduction is made as a function of the maximum power Pscan expected at the output of the DC-DC converter 12 connected to the scanned PV generator 2 during the acquisition of the characteristic curve of the scanned PV generator 2. This reduction is selected such that the sum of the accumulated output power KA and the expected maximum power Pscan does not exceed the nominal power PN of the DC-AC converter 20. This method comprises: b) Subsequently, acquiring the characteristic curve of the scanned PV power plant 2.
[0033] If the power plant 10 is embodied as shown in FIG. 3, the output of each of the PV power plants 2 is connected in parallel, in each case via an assigned DC-DC converter 12, to a DC link 14 as an input element of a DC-AC converter 20, c) During the acquisition of the characteristic curve, the voltage UZK on the DC link 14 is kept constant using the DC-AC converter 20.
[0034] In an alternative embodiment, if the power plant 10 is embodied as shown in FIG. 4, the output side of the PV power plant 2 is connected in series with the DC link 14 as an input element of a DC-AC converter 20, in each case via an assigned DC-DC converter 12, c1) During acquisition of the characteristic curve, the current in the series circuit of the DC-DC converter 12 is kept constant using the DC-AC converter 20.
[0035] In this case, the circuit arrangement 16, which may optionally be in the form of a regulating unit of the DC-AC converter 20, can be used to keep the voltage of c) or the current of c1) constant.
[0036] After obtaining the characteristic curve of the PV power generation device to be scanned, d) Finish reducing the accumulated output power KA of a DC-DC converter 12 for which the associated PV power plant 2 is not intended to obtain a characteristic curve.
[0037] This allows for after the scan to return to the same power output as before the scanning process.
[0038] 2 shows, by way of example, electrical variables within the power plant 10 before, during and after the scanning process. The process of scanning the PV power plant begins at time t1 and ends at time t2.
[0039] At the top, the nominal power PN of the DC-AC converter 20 is plotted. Below that is shown the accumulated output power KA of the DC-DC converter 12, which is not involved in the scanning process since the associated PV generator is not intended for scanning. During the scanning process, i.e. between t1 and t2, this accumulated output power KA is reduced and kept constant at the reduced value.
[0040] The DC-DC converter involved in the scan is preferably operated in an open-loop manner, i.e. its duty cycle is varied so that in the connected PV generators to be scanned the voltage is changed so that a characteristic curve can be obtained. In particular, the duty cycle can be changed in a ramp manner. The current Iscan output by the PV generator during the scan is shown in the lower part of FIG. 2. In the upper part of FIG. 2 the power Pscan output during the scan by the DC-DC converter involved in the scan is plotted against the accumulated output power KA. It can be seen that the reduction of the accumulated output power KA is selected such that the sum of the maximum powers of the output power Pscan of the PV generators 2 involved in the scan and the accumulated output power during the scan process remains below the nominal power PN of the DC-AC converter 20.
[0041] In one embodiment of the power plant 10 as shown in Fig. 3, the DC link voltage UZK is kept constant during the scanning process. This is shown in the center of Fig. 2. In this case, the DC link voltage UZK preferably corresponds to the open circuit voltage of the PV power plant 2 being scanned.
[0042] In one embodiment of the power plant 10 as shown in FIG. 4, the current through the series connected DC-DC converters is kept constant during the scanning process.
[0043] 3 shows an embodiment of a power plant 10 having a number of PV power plants 2 each having a number of PV modules 4 connected in series and each having a DC-AC converter 20. The outputs of the PV power plants 2 are connected in parallel to a DC link 14 as input elements of the DC-AC converter 20 via respectively assigned DC-DC converters 12. The power plant 10 supplies power to an AC grid 30 via the DC-AC converters 20. The power plant 10 comprises a circuit arrangement 16 designed and arranged to perform the above-mentioned method.
[0044] In particular, the circuit arrangement 16 is designed and configured to adjust the DC-DC converter 12, for which the associated PV generator 2 is not intended to obtain a characteristic curve, as a function of the expected maximum power Pscan at the output side of the DC-DC converter 12 connected to the scanned PV generator 2 during the acquisition of the characteristic curve of the scanned PV generator 2, so that the accumulated output power KA is reduced, thereby ensuring that the sum of the accumulated output power KA and the expected maximum power Pscan does not exceed the nominal power PN of the DC-AC converter 20. Furthermore, the circuit arrangement 16 is designed and configured to obtain the characteristic curve of the scanned PV generator 2, by controlling the DC-DC converter assigned to the scanned PV generator 2 such that the duty cycle is kept the same over several clock periods. As a result, the voltage of the scanned PV generator 2 is given and the associated measured value, i.e. the current output by the scanned PV generator 2, can be determined in a targeted manner. The duty cycle can then be changed and maintained over several clock periods and the next measured value of the characteristic curve can be determined. This process can be repeated until the entire characteristic curve from the open circuit point to the short circuit point has been passed.
[0045] In the power plant 10 of FIG. 3, the circuit arrangement 16 is further intended and arranged to keep the voltage of the DC link constant during the acquisition of the characteristic curve.
[0046] FIG. 4 shows an embodiment of a power plant 10 with a number of PV power plants 2 each with a number of PV modules 4 connected in series, with a DC-AC converter 20. The output side of the PV power plants 2 is connected in series to a DC link 14 as an input element of the DC-AC converter 20 via a respectively assigned DC-DC converter. The power plant 10 supplies power to an AC grid 30 via the DC-AC converter 20. The power plant 10 comprises a circuit arrangement 16 designed and configured to perform the above-mentioned method. In particular, the circuit arrangement 16 is designed and configured to adjust the DC-DC converter 12, for which the associated PV power plant 2 is not intended to obtain a characteristic curve, as a function of the maximum power Pscan expected at the output side of the DC-DC converter 12 connected to the scanned PV power plant 2 during the acquisition of the characteristic curve of the scanned PV power plant 2, so that the accumulated output power KA is reduced, ensuring that the sum of the accumulated output power KA and the expected maximum power Pscan does not exceed the nominal power PN of the DC-AC converter 20. Furthermore, the circuit arrangement 16 is designed and configured to acquire the characteristic curve of the scanned PV power plant 2. This characteristic curve is obtained in the same manner as described above with respect to FIG.
[0047] In the power plant 10 of FIG. 4, the circuit arrangement 16 is further intended and configured to keep the current through the series circuit of the DC-DC converter constant during the acquisition of the characteristic curve.
[0048] As shown in Figs. 3 and 4, the circuit arrangement 16 may be in the form of a separate unit (e.g., a computing unit) and may exchange information with the DC-AC converter 20 and the DC-DC converter, for example via a communication line. Likewise, the circuit arrangement 16 may be arranged in the DC-AC converter 20 and / or in the DC-DC converter 12. In particular, it may be designed and configured to additionally realize closed-loop and / or open-loop control tasks of the DC-AC converter 20 and / or the DC-DC converter 12. In particular, the circuit arrangement 16 may be in the form of at least one computing unit arranged in the DC-AC converter 20 and / or the DC-DC converter 12. The at least one computing unit may, for example, be in the form of or part of a regulation unit of the DC-AC converter 20. In particular, the circuit arrangement 16 may be configured and designed to additionally perform closed-loop and / or open-loop control tasks of the DC-AC converter 20 and / or the DC-DC converter 12.
[0049] The multiple PV power plants 2 of the power plant 10 may be scanned in sequence, one PV power plant at a time, in which case the described method may be used to scan some or all of the multiple PV power plants of the power plant 10 in sequence. [Explanation of symbols]
[0050] t time t1 Start Scan t2 Scan end Nominal power of PN DC-AC converter KA Accumulated output power UZK DC link voltage Iscan The output current of the PV generator being scanned Pscan Output power during scanning 2 PV power generation equipment 4 PV Module 10 Power generation facilities 12 DC-DC converter 14 DC Link 16 Circuit device 20 DC-AC converter 30 AC Grid a), b), c), d) Method steps
Claims
1. A method for obtaining a characteristic curve of a PV power plant (2) scanned from a plurality of PV power plants (2) in a power generation installation (10), the output side of each of the PV power plants (2) being connected in parallel to a DC link (14) as an input element of a DC-AC converter (20) via an in each case assigned DC-DC converter (12), said method comprising: a) reducing the cumulative output power (KA) of the DC-DC converter (12) for which the associated PV power plant (2) is not intended to acquire the characteristic curve as a function of the maximum power (Pscan) expected at the output side of the DC-DC converter (12) connected to the scanned PV power plant (2) during acquisition of the characteristic curve of the scanned PV power plant (2) to ensure that the sum of the reduced cumulative output power (KA) and the expected maximum power (Pscan) of the scanned PV power plant (2) does not exceed the nominal power (PN) of the DC-AC converter (20); b) then obtaining the characteristic curve of the scanned PV power plant (2); c) maintaining the voltage (UZK) of the DC link (14) constant using the DC-AC converter (20) during acquisition of the characteristic curve; d) maintaining constant the individual output power of the DC-DC converters (12) for which the associated PV power plants (2) are not intended to obtain the characteristic curves during the acquisition of the characteristic curves; A method comprising:
2. A method for obtaining characteristic curves of scanned PV power plants (2) from a plurality of PV power plants (2) in a power generation installation (10), the output sides of the PV power plants (2) being connected in series to a DC link (14) as input elements of a DC-AC converter (20) via an in each case assigned DC-DC converter (12), the method comprising: a) reducing the cumulative output power (KA) of the DC-DC converter (12) for which the associated PV power plant (2) is not intended to acquire the characteristic curve as a function of the maximum power (Pscan) expected at the output side of the DC-DC converter (12) connected to the scanned PV power plant (2) during acquisition of the characteristic curve of the scanned PV power plant (2) to ensure that the sum of the reduced cumulative output power (KA) and the expected maximum power (Pscan) of the scanned PV power plant (2) does not exceed the nominal power (PN) of the DC-AC converter (20); b) then obtaining the characteristic curve of the scanned PV power plant (2); c1) maintaining a constant current in the series circuit of the DC-DC converter (12) using the DC-AC converter (20) while acquiring the characteristic curve; d) maintaining constant the individual output power of the DC-DC converters (12) for which the associated PV power plants (2) are not intended to obtain the characteristic curves during the acquisition of the characteristic curves; A method comprising:
3. 3. The method according to claim 1, wherein the characteristic curve of the PV power plant (2) being scanned is obtained during open-loop operation of the DC-DC converter (12) assigned to the PV power plant (2) being scanned.
4. The method of claim 3 , wherein the open loop operation includes current limiting to prevent the allowed input current of the DC-DC converter assigned to the scanned PV power plant from being exceeded.
5. 4. The method of claim 3, wherein the open-loop operation comprises setting a duty cycle of the DC-DC converter (12) assigned to the PV power plant (2) to be scanned, and the scanning to obtain the characteristic curve is performed using in particular the duty cycle curve.
6. After obtaining the characteristic curve of the scanned PV power plant (2), the method comprises:
4. The method of claim 3, further comprising the step of: d) terminating the reduction of the cumulative output power (KA) of the DC-DC converter (12) for which the associated PV power plant (2) is not intended to obtain the characteristic curve.
7. A circuit device for acquiring characteristic curves of PV power generation devices (2) scanned from a plurality of PV power generation devices (2) in a power generation installation (10), the output side of each of the PV power generation devices (2) being connected in parallel to a DC link (14) as an input element of a DC-AC converter (20) via an assigned DC-DC converter (12) in each case, the circuit device comprising: adjusting the DC-DC converter (12) for which the associated PV power plant (2) is not intended to acquire the characteristic curve as a function of the maximum power (P scan ) expected at the output side of the DC-DC converter (12) connected to the scanned PV power plant (2) so that the cumulative output power (K A ) of the DC-DC converter (12) is reduced during acquisition of the characteristic curve of the scanned PV power plant (2), ensuring that the sum of the reduced cumulative output power (K A ) and the expected maximum power (P scan ) does not exceed the nominal power (P N ) of the DC-AC converter (20); Obtaining the characteristic curve of the PV power plant (2) being scanned; A circuit arrangement intended and configured to maintain constant, during acquisition of the characteristic curve, the voltage (UZK) of the DC link (14) and the individual output power of the DC-DC converter (12) for which the associated PV power generation plant (2) is not intended to acquire the characteristic curve.
8. A circuit device for acquiring characteristic curves of PV power generation devices (2) scanned from a plurality of PV power generation devices (2) in a power generation installation (10), the output sides of the PV power generation devices (2) being connected in series to a DC link (14) as input elements of a DC-AC converter (20) via an assigned DC-DC converter (12) in each case, the circuit device comprising: adjusting the DC-DC converter (12) for which the associated PV power plant (2) is not intended to acquire the characteristic curve as a function of the maximum power (P scan ) expected at the output side of the DC-DC converter (12) connected to the scanned PV power plant (2) so that the cumulative output power (K A ) of the DC-DC converter (12) is reduced during acquisition of the characteristic curve of the scanned PV power plant (2), ensuring that the sum of the reduced cumulative output power (K A ) and the expected maximum power (P scan ) does not exceed the nominal power (P N ) of the DC-AC converter (20); Obtaining the characteristic curve of the PV power plant (2) being scanned; A circuit device intended and configured to maintain constant, during acquisition of the characteristic curve, the current flowing through the series circuit of the DC-DC converters (12) and the individual output power of the DC-DC converters (12) whose associated PV power generation devices (2) are not intended to acquire the characteristic curve.
9. The circuit arrangement according to claim 7 or 8, wherein the circuit arrangement is arranged in the DC-AC converter (20) and / or the DC-DC converter (12).
10. 10. The circuit arrangement according to claim 9, wherein the circuit arrangement is intended and configured for open-loop and / or closed-loop control of the DC-AC converter (20) and / or the DC-DC converter (12).
11. A power generation installation (10) having a DC-AC converter (20) and having a plurality of PV power generation devices (2), the output sides of which are connected in parallel or in series to a DC link (14) as input elements of the DC-AC converter (20) via in each case an assigned DC-DC converter (12), the power generation installation (10) comprising a circuit arrangement according to claim 7 or 8.