Module Level Power Electronics, Photovoltaic System including the same, and method for extracting current-voltage curve using the same

Abstract

A photovoltaic power generation system according to one embodiment of the present invention comprises: a plurality of photovoltaic (PV) modules; and a plurality of module level power electronics (MLPEs) that optimize the output voltage of the connected PV modules. Each MLPE includes a DC-DC converter; and a processor that switches from a first mode, which performs Maximum Power Point Tracking (MPPT) control by disconnecting the power connection with an inverter connected to the output terminal, to a second mode, which extracts a current (I)-voltage (V) curve, and extracts an IV curve using the output voltage and output current of each connected PV module measured while controlling the duty cycle of the DC-DC converter in the second mode.

Description

Technology Field

[0001] The present invention relates to a module-unit power conversion device, a photovoltaic power generation system including the same, and a method for extracting a current-voltage curve using the same. Background Technology

[0002] Recently, solar power generation systems have been introducing Module Level Power Electronics (MLPE) to improve the performance of PV modules under specific conditions, such as when shading occurs, and to increase power production efficiency.

[0003] Currently, functions and algorithms for diagnosing the condition of MLPEs before and after the operation of photovoltaic power generation systems are widely used, but there is a lack of technology capable of diagnosing PV (Photovoltaic) modules.

[0004] Therefore, when the power generation of a photovoltaic power generation system decreases, it is difficult to determine the exact cause, whether it is due to external factors or to the MLPE or PV modules. Since each component must be analyzed to identify the exact cause, it is not only inefficient but also frequently leads to confusion in troubleshooting.

[0005] Under these circumstances, unlike the existing method of diagnosing PV modules and MLPEs separately, there is a need for a method that can analyze the cause of the problem in an integrated manner. The problem to be solved

[0006] The objective of the present invention is to provide a photovoltaic power generation system and method capable of integratively diagnosing conditions such as power generation reduction.

[0007] The object of the present invention is to provide a photovoltaic power generation system and method capable of extracting a current-voltage curve without additional configuration. means of solving the problem

[0008] A photovoltaic power generation system according to one embodiment of the present invention comprises: a plurality of photovoltaic (PV) modules; and a plurality of module level power electronics (MLPEs) that optimize the output voltage of the connected PV modules. Each MLPE includes a DC-DC converter; and a processor that switches from a first mode, which performs Maximum Power Point Tracking (MPPT) control by disconnecting the power connection with an inverter connected to the output terminal, to a second mode, which extracts a current (I)-voltage (V) curve, and extracts an IV curve using the output voltage and output current of each connected PV module measured while controlling the duty cycle of the DC-DC converter in the second mode.

[0009] The above DC-DC converter may include a first switch and a second switch that operate on or off complementarily.

[0010] The above DC-DC converter may further include a third switch connected in parallel to the output terminal and turned on to form a current path, and a resistor connected in series with the third switch.

[0011] The above processor can control the third switch to turn on in the above second mode.

[0012] The processor can control the duty ratio of the first switch to increase stepwise from 0 to 1 starting from a second point in time after a predetermined time from a first point in time when the third switch is turned on.

[0013] The processor can identify output power using the output voltage and output current of the PV module, and extract a power (P)-voltage (V) curve using the output voltage and output power.

[0014] The above processor can identify the maximum value among the identified output powers as the Maximum Power Point (MPP).

[0015] The above processor can diagnose the state of the PV module corresponding to the IV curve extracted based on the characteristic information of the IV curve.

[0016] The above plurality of MLPEs are connected in series with one another, and each MLPE can be connected to at least one of the plurality of PV modules.

[0017] A method for extracting a current (I)-voltage (V) curve performed by a photovoltaic power generation system according to one embodiment of the present invention comprises: a step of switching from a first mode in which a module level power electronics (MLPE) that optimizes the output voltage of a connected PV module disconnects the power connection with an inverter connected to the output terminal to perform Maximum Power Point Tracking (MPPT) control to a second mode for extracting a current (I)-voltage (V) curve; and a step of extracting an IV curve using the output voltage and output current of the connected PV module measured while controlling the duty cycle of a DC-DC converter in the second mode.

[0018] The step of extracting the above IV curve may include the step of controlling the third switch to turn on in the above second mode.

[0019] The step of extracting the IV curve may include a step of controlling the duty ratio of the first switch to increase stepwise from 0 to 1 starting from a second point in time after a predetermined time from a first point in time when the third switch is turned on.

[0020] The above method may further include the step of identifying output power using the output voltage and output current of the PV module; and the step of extracting a power (P)-voltage (V) curve using the output voltage and output power.

[0021] The above method may further include the step of identifying the maximum value among the identified output powers as the Maximum Power Point (MPP).

[0022] The above method may further include a step of diagnosing the state of a PV module corresponding to the IV curve extracted based on characteristic information of the IV curve.

[0023] A module level power electronics (MLPE) according to one embodiment of the present invention comprises: a DC-DC converter; and a processor that switches from a first mode, which performs Maximum Power Point Tracking (MPPT) control by disconnecting the power connection with an inverter connected to an output terminal, to a second mode, which extracts a current (I)-voltage (V) curve, and extracts an IV curve using the output voltage and output current of each connected PV (Photovoltaic) module measured while controlling the duty cycle of the DC-DC converter in the second mode. Effects of the invention

[0024] According to one embodiment of the present invention, it is possible to extract the IV curve of a PV module without changing the topology of the photovoltaic power generation system, so that no additional costs are incurred, making it economical, and through the diagnosis of the condition of the photovoltaic power generation system, it is possible to prevent and respond to the severe deterioration of the power generation of the PV module before it occurs.

[0025] According to one embodiment of the present invention, as a result, the reduction in power generation can be prevented in advance to increase system efficiency, and operation can be performed without additional costs, thereby creating the effect of lowering the Levelized Cost of Energy (LCOE) from a system perspective.

[0026] According to one embodiment of the present invention, IV curve extraction is possible even during sunrise and sunset times when the impact on power generation is relatively minimal, thereby enabling efficient diagnosis of the condition of the photovoltaic power generation system without affecting power generation.

[0027] According to one embodiment of the present invention, it is possible to implement various functions, such as MPPT control as well as state diagnosis of a photovoltaic power generation system, through the IV curve.

[0028] According to one embodiment of the present invention, depending on the purpose, the degradation trend of PV modules and changes according to the installation environment can be analyzed, thereby enabling data collection for control optimization according to site characteristics. Brief explanation of the drawing

[0029] FIG. 1 is a schematic diagram illustrating a photovoltaic power generation system according to one embodiment of the present invention. FIG. 2 is a block diagram illustrating the configuration of an MLPE according to one embodiment of the present invention. FIG. 3 is a diagram illustrating the operation flowchart of an MLPE according to one embodiment of the present invention. FIG. 4 is a diagram illustrating an equivalent circuit of a PV module according to one embodiment of the present invention. FIG. 5 is a diagram illustrating a circuit of a DC-DC converter according to one embodiment of the present invention. FIG. 6 is a diagram illustrating a timing diagram according to an embodiment of the present invention. FIG. 7 is a diagram illustrating a current-voltage curve according to one embodiment of the present invention. Specific details for implementing the invention

[0030] Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. The detailed description disclosed below, together with the accompanying drawings, is intended to describe exemplary embodiments of the present invention and is not intended to represent the only embodiment in which the present invention can be practiced. In order to clearly explain the present invention in the drawings, parts unrelated to the description may be omitted, and the same reference numerals may be used for identical or similar components throughout the specification.

[0031] FIG. 1 is a schematic diagram illustrating a photovoltaic power generation system according to one embodiment of the present invention.

[0032] Referring to FIG. 1, the photovoltaic power generation system (1) includes a PV module (110), an MLPE (120), an inverter (130), and a grid (140).

[0033] According to one embodiment of the present invention, the PV module (110) is a module that produces electricity using sunlight and may be provided in multiple numbers.

[0034] According to one embodiment of the present invention, the MLPE (120) can be implemented as a DC optimizer, configured to be connected to each PV module (110) and to optimize the output voltage of each connected PV module (110).

[0035] The MLPE (120) can analyze various data received from the PV module (110), inverter (130), load, grid (140), etc., to monitor the status of the MLPE (120) itself or be monitored by the inverter (130).

[0036] At this time, the MLPE (120) can optimize the output voltage of each connected PV module (110) through Maximum Power Point Tracking (MPPT) control, which tracks the corresponding power and voltage when the photovoltaic power generation system (1) generates maximum power. MPPT operation is an algorithm implemented to continuously adjust the impedance received by a PV module (110) or an array composed of multiple PV modules (110) so that the photovoltaic power generation system (1) operates near the maximum power point when conditions such as solar irradiance, temperature, and load change. The specific configuration of the MLPE (120) is described with reference to FIG. 2.

[0037] At this time, the MLPE (120) can be connected to the PV module (110) in a one-to-one correspondence (n=1) as shown in FIG. 1, but depending on the structure adopted by the photovoltaic power generation system (1), it can be installed in a many-to-one or many-to-many configuration, and the installation form is not limited to any one. In another embodiment, a group consisting of n PV modules (n is a natural number greater than or equal to 2) and n MLPEs can be configured in a form in which multiple groups are connected in series.

[0038] MLPE (120) is provided in multiple numbers and connected in series with each other, and an inverter (130) is connected to both ends of the multiple MLPE (120) connected in series.

[0039] According to one embodiment of the present invention, the inverter (130) is configured to perform power conversion by being installed in the PCS (Power Conversion System) to supply power produced from the PV module (110) to a load or grid (140).

[0040] The inverter (130) monitors the operating status of the photovoltaic power generation system (1) by analyzing various data received from the PV module (110), MLPE (120), load, grid (140), etc. The inverter (130) also performs MPPT operation like the MLPE (120) and can maximize the power production efficiency of the photovoltaic power generation system (1).

[0041] In the present invention, a method is proposed that not only diagnoses the condition of the MLPE (120) itself using only the MLPE (120) without any additional configuration, but also diagnoses the condition of the PV module (110) by extracting an IV curve based on the measurement of the output voltage and output current of the PV module (110).

[0042] The IV curve can appear in various forms depending on the condition of the photovoltaic power generation system (1), and characteristics according to the shape of the curve have been established through many studies. Therefore, the IV curve is an important factor required for diagnosing the condition of the photovoltaic power generation system (1), and the condition of the photovoltaic power generation system (1) can be diagnosed by using the curve characteristics according to the extracted curve and its shape.

[0043] The extracted IV curve can be used not only for diagnosing the condition of the photovoltaic power generation system (1) but also for MPPT control.

[0044] According to one embodiment of the present invention, the IV curve of a PV module (110) can be extracted without changing the topology of various MLPEs (120) constituting a photovoltaic power generation system (1), so that no additional costs are incurred, making it economical.

[0045] According to one embodiment of the present invention, as a result, the reduction in power generation can be prevented in advance to increase system efficiency, and operation can be performed without additional costs, thereby creating the effect of lowering the Levelized Cost of Energy (LCOE) from a system perspective.

[0046] Hereinafter, the operation of a photovoltaic power generation system (1) according to one embodiment of the present invention will be described in detail with reference to the drawings.

[0047] FIG. 2 is a block diagram illustrating the configuration of an MLPE according to one embodiment of the present invention.

[0048] According to one embodiment of the present invention, the MLPE (120) may include a DC-DC converter (121) and a processor (122).

[0049] The DC-DC converter (121) can be implemented as a buck converter that steps down the voltage applied from the PV module (110) (output voltage of the PV module (110)), and an example of the DC-DC converter (121) is shown in FIG. 5.

[0050] The processor (122) may include, for example, a power control MCU (Microcontroller Unit). The processor (122) can control at least one other component (e.g., a hardware or software component) of the MLPE (120) by executing software such as a program, and can perform various data processing or operations.

[0051] The processor (122) can receive control signals necessary for power optimization by communicating serially with the inverter (130) or by performing Power Line Communication (PLC).

[0052] According to one embodiment of the present invention, the processor (122) can control the duty cycle of the DC-DC converter (121) to adjust the output voltage of the PV module (110) and the output voltage of the MLPE (120).

[0053] FIG. 3 is a diagram illustrating the operation flowchart of an MLPE according to one embodiment of the present invention.

[0054] According to one embodiment of the present invention, the processor (122) switches from a first mode, which performs MPPT control by disconnecting the power connection with the inverter (130) connected to the output terminal of the MLPE (120), to a second mode, which extracts a current (I)-voltage (V) curve (S10).

[0055] The MLPE (120) basically performs MPPT control and is electrically connected to the inverter (130) for power delivery. Meanwhile, the MLPE (120) needs to block the flow of current coming from the outside in order to measure the output voltage and output current of the PV module (110). Therefore, the processor (122) disconnects the power connection with the inverter (130) to switch from the first mode to the second mode. The processor (122) can disconnect the power connection with the inverter (130) by opening the output terminal of the MLPE (120).

[0056] At this time, the processor (122) may receive a signal requesting a transition from the first mode to the second mode, or actively perform the mode transition according to a predefined period (e.g., once a day, etc.) or a predefined time (e.g., 7:00 PM, etc.). In addition, the operation of transitioning from the first mode to the second mode can be triggered in various ways and is not limited to any one.

[0057] According to one embodiment of the present invention, the processor (122) extracts an IV curve using the output voltage and output current of the PV module (110) measured while controlling the duty ratio of the DC-DC converter (121) in the second mode (S20).

[0058] As described above, the processor (122) opens the output terminal of the MLPE (120) to disconnect the power connection with the inverter (130), thereby cutting off the current flow. However, in order to measure the output voltage and output current of the PV module (110), current must be able to flow, so the processor (122) controls the DC-DC converter (121) to form a current path. This will be explained in detail with reference to the DC-DC converter shown in FIG. 5.

[0059] The processor (122) can control the duty cycle of the DC-DC converter (121) from 0 to 1 or from 1 to 0, and can receive output voltage values ​​and output current values ​​(hereinafter also referred to as measured values) from a measuring device that measures the output voltage and output current of the PV module (110) inside the photovoltaic power generation system (1). The measured values ​​according to the duty cycle control are shown in FIG. 6.

[0060] Meanwhile, the processor (122) can receive measurement values ​​in real time according to duty cycle control and extract an IV curve in real time. However, it is not limited to this, and the output voltage and output current of the PV module (110) can be measured according to duty cycle control, and then the measurement values ​​can be received at once to extract an IV curve. The IV curve can be extracted in units of PV modules, arrays, etc., and an example of an extracted IV curve is shown in FIG. 7.

[0061] According to one embodiment of the present invention, the processor (122) can diagnose the state of a PV module corresponding to an extracted IV curve based on characteristic information of an IV curve including characteristics according to the shape of the IV curve.

[0062] According to one embodiment of the present invention, the processor (122) can obtain the power of the PV module (110) using the measured value, and can track the Maximum Power Point (MPP) using this.

[0063] According to one embodiment of the present invention, through a condition diagnosis of the photovoltaic power generation system (1), it is possible to prevent and respond to the severe deterioration of the power generation amount of the PV module (110).

[0064] According to one embodiment of the present invention, IV curve extraction is possible even during sunrise and sunset times when the influence on power generation is relatively minimal, so the condition of the photovoltaic power generation system (1) can be efficiently diagnosed without affecting power generation.

[0065] According to one embodiment of the present invention, the accuracy of the condition diagnosis is high because the actual IV curve for each PV module is extracted.

[0066] FIG. 4 is a diagram illustrating an equivalent circuit of a PV module according to one embodiment of the present invention.

[0067] According to one embodiment of the present invention, the output terminal of the PV module (110) is connected to the MLPE (120), and the voltage (V) applied to the output terminal PV ) and the current flowing at the output terminal (I PV Measures ).

[0068] According to one embodiment of the present invention, the shape of the IV curve extracted by the MLPE (120) is a shunt resistor (R) shown in the equivalent circuit diagram of the PV module (110). sh ) and series resistor (R s It can be affected by ). Therefore, depending on the shape of the extracted IV curve, the shunt resistance (R sh ) and series resistor (R s It is possible to check for abnormalities such as deterioration of ). A specific example is explained with reference to Fig. 7.

[0069] FIG. 5 is a diagram illustrating a circuit of a DC-DC converter according to one embodiment of the present invention.

[0070] The DC-DC converter (121) includes a first switch (S1) and a second switch (S2) that operate on or off complementarily. The processor (122) can control the duty cycle of the first switch (S1) to increase stepwise from 0 to 1. At this time, the processor (122) controls the second switch (S2) to operate in the opposite manner to the first switch (S1).

[0071] Meanwhile, as described above in relation to S20 of FIG. 3, in the present invention, when switching to the second mode for extracting the IV curve, the power connection with the inverter (130) is disconnected, so a current path must be formed to enable duty cycle control.

[0072] According to one embodiment of the present invention, the DC-DC converter (121) further comprises a resistor (R1) connected in parallel to the output terminal of the MLPE (120) and a third switch (S3) connected in series with the resistor (R1) to remove residual power of the inverter (130) as needed during normal operation. During normal operation (first mode performing MPPT control), the third switch (S3) is turned off so as not to affect the operation of the DC-DC converter (121). Then, when removal of residual power is required, the processor (122) turns on the third switch (S3) to consume residual power through the resistor (R1).

[0073] In the present invention, a third switch (S3) provided for this function is utilized to form a current path even after the power connection with the inverter (130) is disconnected for switching to the second mode.

[0074] According to one embodiment of the present invention, the processor (122) controls the third switch (S3) to turn on to form a current path in a second mode. When the third switch (S3) turns on, current flows through the PV module (110), and the voltage (V) changes as power is consumed through the resistor (R1). PV ) and current (I PV ) can be measured.

[0075] At this time, the DC-DC converter circuit is not limited to that shown in FIG. 5, and it is sufficient if it is designed to form a current path even after the inverter and power connection are disconnected, and so that the output voltage of the PV module (110) is controlled according to duty cycle control.

[0076] According to one embodiment of the present invention, since an IV curve can be extracted without additional elements such as equipment, systems, and circuits, cost reduction is possible.

[0077] Below, the operation over time will be explained with reference to the timing diagram of FIG. 6.

[0078] FIG. 6 is a diagram illustrating a timing diagram according to an embodiment of the present invention.

[0079] The timing diagram shown in FIG. 6 shows the gate voltage (V) of the third switch (S3) over time, sequentially from top to bottom. GS3 ), duty (D) of the first switch (S1), output voltage (V) of the PV module (110) PV ), output current (I) of the PV module (110) PV ), power (P of the PV module (110) PV It represents ).

[0080] At this time, the gate voltage (V) of the third switch (S3) GS3 When ) is 0V, the third switch (S3) operates off, and when a voltage greater than the threshold is applied to the gate, it operates on.

[0081] Below, we will examine the operation of the solar power generation system (1) over time.

[0082] First, the MLPE (120) performs MPPT control in the first mode (MPPT mode). Accordingly, the output voltage (V) of the PV module (110) PV ), output current (I PV ), power (P PV All of them are operating at the maximum power point (MPP), and the gate voltage (V) of the third switch (S3) GS3) operates off at 0V.

[0083] The processor (122) opens the output terminal of the MLPE (120) to disconnect the power connection with the inverter (130), thereby switching from the first mode (MPPT mode) to the second mode (IV Curve Extracting mode) (Output open).

[0084] The processor (122) controls the third switch (S3) to turn on in the second mode to form a current path (S3 on). At this time, the processor (122) controls the first switch (S1) to turn off by setting its duty cycle to 0, and controls the second switch (S2) to turn on as a complementary operation to the first switch (S1). At this time, the DC-DC converter (121) is placed in an open state. The output voltage (V) of the PV module (110) PV ) is measured as a constant value, but the output current (I PV ) becomes 0. This output voltage is the open-circuit voltage (V oc It is called ).

[0085] Afterward, the processor (122) performs duty cycle control while gradually increasing the duty cycle of the first switch (S1). At this time, the processor (122) does not immediately perform duty cycle control of the DC-DC converter (121) along with the ON operation control of the third switch (S3), but leaves a predetermined time interval (t2 to t3).

[0086] This is to more accurately measure the voltage and current of the PV module (110) by dissipating the residual power through the resistor (R1), as residual power may remain in the capacitors (C1, C2) or inductor (L1) inside the DC-DC converter (121).

[0087] Accordingly, the processor (122) controls the duty cycle of the DC-DC converter (121) from a point in time (hereinafter referred to as the second point in time) after a predetermined time from the point in time (hereinafter referred to as the first point in time) when the third switch (S3) turns on (start scan). In the timing diagram of FIG. 6, the first point in time is t2 and the second point in time is t3.

[0088] Specifically, the processor (122) can control the duty cycle of the first switch (S1) to increase stepwise from 0 to 1 after the second time point. When the duty cycle of the first switch (S1) is 1, the PV module (110) is short-circuited and the output voltage (V PV ) is measured as 0, and the output current (I PV ) reaches a limit value. This output current is the short-circuit current (I sc It is called ).

[0089] While the processor (122) controls the duty cycle of the DC-DC converter (121), the measuring device measures the output voltage (V) of the PV module (110). PV ) and output current (I PV ) can be measured and illustrated as shown in the timing diagram of Fig. 6.

[0090] According to one embodiment of the present invention, the processor (122) measures the output voltage (V) PV ) and output current (I PV The IV curve can be extracted using ). As previously described, the output voltage (V) in real time PV ) and output current (I PV When receiving a ) value, the processor (122) opens the voltage (V oc Short-circuit current (I) from the ) point sc You can extract an IV curve along the point.

[0091] As another example, the processor (122) can track the maximum power point (MPP) using a timing diagram. Specifically, the processor (122) can identify output power using the output voltage and output current of the PV module (110), and identify the maximum value among the identified output powers as the MPP.

[0092] Below, we examine a method for analyzing the state of a photovoltaic power generation system using the extracted IV curve.

[0093] FIG. 7 is a diagram illustrating a current-voltage curve according to one embodiment of the present invention.

[0094] According to one embodiment of the present invention, the processor (122) can diagnose the state of a PV module corresponding to an extracted IV curve based on characteristic information of the IV curve. However, it is not limited thereto, and the processor (122) can transmit the extracted IV curve to an external device, such as a server or a monitoring electronic device, so that the external device diagnoses the state of the photovoltaic power generation system (1). The monitoring electronic device may be implemented, for example, as a desktop, laptop, smartphone, etc.

[0095] The characteristics of the IV curve are as follows.

[0096] For example, as previously shown in FIG. 4, the shunt resistor (R) of the PV module (110) sh If ) decreases, just as a leakage current path is created, the IV curve becomes short-circuit current (I sc The slope of the curve can increase near ). Therefore, the IV curve is short-circuit current (I sc When the slope of the curve increases near ) (710), the shunt resistance (R) of the PV module (110) sh It can be seen that there are abnormalities such as deterioration in ).

[0097] As another example, the series resistance (R) of the PV module (110) sAs ) increases, the Fill Factor (FF) decreases, as if hindering the flow of current, so the open-circuit voltage (V oc The slope of the curve may decrease near ). Therefore, the open-circuit voltage (V oc If the slope of the curve decreases near ) (720), the series resistance (R) of the PV module (110) s It can be seen that there are abnormalities such as deterioration in ).

[0098] In this case, the curve factor is the product of the voltage and current at the maximum power point (MPP) (V mpp ХI mpp ) open-circuit voltage (V oc ) and short-circuit current (I sc It is a value divided by the product of ). That is, it can also be viewed as a value obtained by dividing the area (730) by the area (740). The closer the curve factor is to 1, the better the quality of the corresponding PV module (110) can be judged. The quality, such as the lifespan or efficiency of the PV module (110), can be determined based on the curve factor value.

[0099] As another example, depending on the shape of the IV curve near the MPP, mismatching between PV modules (110), connection errors, shading conditions, etc., can be identified.

[0100] In addition to this, the characteristics of the IV curve can be elucidated through continuous research, and various methods for diagnosing the condition of photovoltaic power generation systems using the IV curve may exist.

[0101] Although not illustrated in the drawings, according to one embodiment of the present invention, a processor (122) can extract a power (P)-voltage (V) curve using the output voltage and output current of a PV module (110). Specifically, the processor (122) can identify an output power using the output voltage and output current of a PV module (110), and extract a PV curve using the identified output voltage and output power.

[0102] According to one embodiment of the present invention, the processor (122) can identify the maximum power point using the extracted IV curve or PV curve, thereby enabling MPPT control.

[0103] According to one embodiment of the present invention, IV curve extraction is possible intermittently and actively as needed, making it efficient.

[0104] According to one embodiment of the present invention, it is possible to implement various functions, such as condition diagnosis and MPPT control, through the IV curve.

[0105] According to one embodiment of the present invention, it is possible to implement an active pre-diagnosis function by identifying the characteristics of a PV module through an extracted IV curve.

[0106] According to one embodiment of the present invention, depending on the purpose, the degradation trend of PV modules and changes according to the installation environment can be analyzed, thereby enabling data collection for control optimization according to site characteristics. Explanation of the symbols

[0107] 1: Solar power generation system 110: PV Module 120: MLPE 121: DC-DC Converter 122: Processor 130: Inverter 140: System

Claims

Claim 1 A photovoltaic power generation system comprising: a plurality of photovoltaic (PV) modules; and a plurality of module-level power electronics (MLPEs) that optimize the output voltage of the connected PV modules; wherein each MLPE comprises: a DC-DC converter; and a processor that switches from a first mode to a second mode that extracts a current (I)-voltage (V) curve by disconnecting the power connection with an inverter connected to the output terminal to perform Maximum Power Point Tracking (MPPT) control, and extracts an IV curve using the output voltage and output current of each connected PV module measured while controlling the duty cycle of the DC-DC converter in the second mode, and wherein the DC-DC converter comprises a first switch and a second switch that operate complementarily. Claim 2 delete Claim 3 A photovoltaic power generation system according to claim 1, wherein the DC-DC converter further comprises a third switch connected in parallel to the output terminal and turned on to form a current path, and a resistor connected in series with the third switch. Claim 4 In paragraph 3, the processor controls the photovoltaic power generation system to turn on the third switch in the second mode. Claim 5 In claim 4, the above processor controls the duty ratio of the first switch to increase stepwise from 0 to 1 starting from a second point in time after a predetermined time from a first point in time when the third switch is turned on. Claim 6 A photovoltaic power generation system according to claim 1, wherein the processor identifies output power using the output voltage and output current of the PV module and extracts a power (P)-voltage (V) curve using the output voltage and output power. Claim 7 In claim 6, the above processor identifies the maximum value among the identified output powers as the Maximum Power Point (MPP) in a photovoltaic power generation system. Claim 8 In claim 1, the processor is a photovoltaic power generation system that diagnoses the state of a PV module corresponding to the IV curve extracted based on characteristic information of the IV curve. Claim 9 A photovoltaic power generation system according to claim 1, wherein the plurality of MLPEs are connected in series with one another, and each MLPE is connected to at least one of the plurality of PV modules. Claim 10 A method for extracting a current (I)-voltage (V) curve performed by a photovoltaic power generation system, comprising: a step of switching from a first mode in which a Module Level Power Electronics (MLPE) that optimizes the output voltage of a connected PV module disconnects the power connection with an inverter connected to the output terminal to perform Maximum Power Point Tracking (MPPT) control to a second mode for extracting a current (I)-voltage (V) curve; and a step of extracting an IV curve using the output voltage and output current of the connected PV module measured while controlling the duty cycle of a DC-DC converter in the second mode, wherein the DC-DC converter comprises a first switch and a second switch that operate complementarily. Claim 11 delete Claim 12 A method according to claim 10, wherein the DC-DC converter further comprises a third switch connected in parallel to the output terminal and turned on to form a current path, and a resistor connected in series with the third switch. Claim 13 In claim 12, the step of extracting the IV curve comprises a step of controlling the third switch to turn on in the second mode. Claim 14 In claim 13, the step of extracting the IV curve comprises a step of controlling the duty ratio of the first switch to increase stepwise from 0 to 1 starting from a second time point after a predetermined time from a first time point when the third switch is turned on. Claim 15 A method according to claim 10, further comprising the step of identifying output power using the output voltage and output current of the PV module; and the step of extracting a power (P)-voltage (V) curve using the output voltage and output power. Claim 16 A method according to claim 15, further comprising the step of identifying the maximum value among the identified output powers as the Maximum Power Point (MPP). Claim 17 A method according to claim 10, further comprising the step of diagnosing the state of a PV module corresponding to the IV curve extracted based on characteristic information of the IV curve. Claim 18 A method according to claim 10, characterized in that the plurality of MLPEs are connected in series with one another, and each MLPE is connected to at least one of the plurality of PV modules. Claim 19 A module-level power electronics (MLPE) comprises: a DC-DC converter; and a processor that extracts a current (I)-voltage (V) curve in a first mode by disconnecting the power connection with an inverter connected to an output terminal to perform Maximum Power Point Tracking (MPPT) control, and extracts an IV curve using the output voltage and output current of each connected PV (Photovoltaic) module measured while controlling the duty cycle of the DC-DC converter in the second mode, wherein the DC-DC converter comprises a first switch and a second switch that operate complementarily.

Images