Module level power electronics device, and operation method of solar power generation system comprising same

Abstract

According to an embodiment of the present invention, provided is an operation method of a solar power generation system comprising a plurality of module level power electronics (MLPE) devices, the method comprising the operations of: performing maximum power point tracking (MPPT) control in a first mode of the MLPE devices; switching the first mode to a second mode by disconnecting a power connection between an inverter and output terminals of the plurality of MLPE devices; controlling a duty ratio of a DC-DC converter provided in the MLPE devices after switching to the second mode; and extracting an output voltage and an output current of each of PV modules connected to the plurality of MLPE devices in the second mode.

Description

Module unit power conversion device and method of operation of a solar power generation system including the same

[0001] The present invention relates to a module unit power conversion device and an operating method of a solar power generation system including the same.

[0002] Recently, solar power generation systems are introducing module-level power conversion devices (or module-level power conditioning devices) (MLPE) to improve the performance of PV modules under specific conditions, such as when there is shading, and to increase power generation efficiency.

[0003] Currently, functions and algorithms for diagnosing the status of MLPE before and after operation of solar power generation systems are widely used, but there is a lack of technology that can diagnose PV (Photovoltaic) modules.

[0004] Therefore, when power generation in a solar power generation system declines, it is difficult to determine the exact cause—whether it is due to external factors or the MLPE or PV modules. Identifying the exact cause requires analyzing each component, which is not only inefficient but also often leads to confusion during troubleshooting.

[0005] In this situation, there is a need for a method that can comprehensively analyze the cause of the problem, unlike the existing method of diagnosing the PV module and MLPE separately.

[0006] The purpose of the present invention is to provide a solar power generation system and method capable of comprehensively diagnosing conditions such as a decrease in power generation.

[0007] An object of the present invention is to provide a solar power generation system and method capable of extracting a current-voltage curve without additional configuration.

[0008] According to one embodiment of the present invention, a method for operating a solar power generation system including a plurality of module level power electronics (MLPEs) is provided, the method including: performing maximum power point tracking (MPPT) control in a first mode of the MLPEs; disconnecting power connections between output terminals of the plurality of MLPEs and an inverter to convert the first mode to a second mode; controlling a duty ratio of a DC-DC converter provided in the MLPE after conversion to the second mode; and extracting an output voltage and an output current of each PV module connected to the plurality of MLPEs in the second mode.

[0009] In the present invention, the operation of switching the first mode to the second mode may be an operation of opening the output terminals of the plurality of MLPEs at a first time point to disconnect the power connection between the output terminals of the plurality of MLPEs and the inverter.

[0010] In the present invention, the DC-DC converter additionally includes a third switch that is connected in parallel to the output terminal and in series with the first resistor, and operates to form a current path by operating on for a predetermined period of time from a second time point after the first time point, thereby dissipating residual power present at the first time point, and the third switch can operate off in the first mode.

[0011] In the present invention, a method for operating a solar power generation system, wherein the first switch and the second switch of the DC-DC converter of the MLPE are controlled from a third point in time after the second point in time, and the first switch and the second switch are controlled so that the duty ratio of the DC-DC converter gradually increases.

[0012] In the present invention, the DC-DC converter includes a first switch and a second switch that operate complementarily on or off, and the first switch and the second switch can be turned on or off so as to adjust the duty ratio of the DC-DC converter.

[0013] In the present invention, the operation of controlling the duty ratio of the DC-DC converter can control the duty ratio of the DC-DC converter so that the duty ratio increases to a preset value each time the duty cycle of the DC-DC converter elapses.

[0014] In the present invention, as the duty ratio is controlled to gradually increase from the third point in time of the second mode, the output voltage of the PV module can decrease and the output current can increase.

[0015] In the present invention, the DC-DC converter includes a capacitor connected in parallel with both output terminals of the solar module, a first switch and a second switch connected in parallel with the capacitor, and when the first switch is turned off, the second switch is turned on to open the DC-DC converter, and when the first switch is turned on, the second switch is turned off to short-circuit both output terminals of the PV module.

[0016] In the present invention, at the third point in time when the third switch of the DC-DC converter is turned on, the slope of the IV curve can correspond to the loss of the shunt resistance in the equivalent circuit diagram of the PV module.

[0017] In the present invention, as the duty ratio gradually increases, the slope of the IV curve when the open circuit voltage becomes 0 can correspond to the loss of the series resistance in the equivalent circuit diagram of the PV module.

[0018] According to one embodiment of the present invention, in a solar power generation system, a module level power electronics (MLPE) of the solar power generation system is provided, the MLPE including a DC-DC converter; and a processor that controls the MLPE to perform maximum power point tracking (MPPT) control by disconnecting power from an inverter connected to an output terminal in a first mode, extract a current (I)-voltage (V) curve in a second mode, and extract an IV curve using output voltage and output current of a PV module measured while controlling a duty ratio of the DC-DC converter in the second mode.

[0019] In the present invention, the processor can control the MLPE to switch the mode of the MLPE from the first mode to the second mode at a first time point, and to open the output terminals of the plurality of MLPEs at the first time point so that the power connection between the output terminals of the plurality of MLPEs and the inverter is released.

[0020] In the present invention, the DC-DC converter may include a first switch and a second switch that operate complementarily on or off.

[0021] In the present invention, the DC-DC converter may include a third switch connected in parallel to the output terminal and operating to form a current path, and a first resistor connected in series with the third switch.

[0022] In the present invention, the processor can control the third switch to operate on in the second mode.

[0023] In the present invention, the processor can control the duty ratio of the first switch to gradually increase from 0 to 1 from a third point in time, which is a predetermined time after the second point in time when the third switch is turned on.

[0024] In the present invention, the processor can identify the output power using the output voltage and output current of the PV module in the second mode, and extract a power (P)-voltage (V) curve using the output voltage and output power.

[0025] In the present invention, the processor can identify the maximum value among the identified output powers as a maximum power point (MPP).

[0026] In the present invention, the processor can diagnose the status of a PV module corresponding to the IV curve extracted based on characteristic information of the IV curve.

[0027] In the present invention, it may be characterized in that the plurality of MLPEs are connected in series with each other, and each MLPE is connected to at least one PV module among the plurality of PV modules.

[0028]

[0029] According to one embodiment of the present invention, since the IV curve of a PV module can be extracted without changing the topology of the solar power generation system, it is economical because no additional cost is incurred, and through diagnosis of the status of the solar power generation system, prevention and response can be taken before the power generation of the PV module is seriously deteriorated.

[0030] According to one embodiment of the present invention, it is possible to prevent a decrease in power generation in advance, thereby increasing system efficiency, and to operate without additional costs, thereby creating an effect of lowering the Levelized Cost of Energy (LCOE) from a system perspective.

[0031] According to one embodiment of the present invention, IV curve extraction is possible even during sunrise and sunset times, which have a relatively small effect on power generation, so that the status of a solar power generation system can be efficiently diagnosed without affecting power generation.

[0032] According to one embodiment of the present invention, it is possible to implement various functions such as MPPT control as well as status diagnosis of a solar power generation system through an IV curve.

[0033] According to one embodiment of the present invention, it is possible to analyze the deterioration tendency of PV modules and changes according to the installation environment according to the purpose, thereby enabling data collection for control optimization according to site characteristics.

[0034] FIG. 1a and FIG. 1b are schematic diagrams illustrating an example of a solar power generation system according to one embodiment of the present invention.

[0035] FIG. 2 is a block diagram illustrating the configuration of an MLPE according to one embodiment of the present invention.

[0036] FIG. 3 is a diagram illustrating an operation flow diagram of MLPE according to one embodiment of the present invention.

[0037] FIG. 4 is a drawing showing an equivalent circuit diagram of a PV module according to one embodiment of the present invention.

[0038] FIG. 5 is a circuit diagram of a DC-DC converter according to one embodiment of the present invention.

[0039] FIG. 6 is a drawing illustrating a timing diagram according to one embodiment of the present invention.

[0040] FIGS. 7a and 7b are diagrams illustrating current-voltage curves according to one embodiment of the present invention.

[0041]

[0042] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The detailed description set forth below, together with the accompanying drawings, is intended to explain exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. In the drawings, portions irrelevant to the description may be omitted for clarity in describing the present invention, and the same reference numerals may be used throughout the specification for identical or similar components.

[0043] FIG. 1a and FIG. 1b are schematic diagrams illustrating an example of a solar power generation system according to one embodiment of the present invention.

[0044] As illustrated in FIG. 1a, a solar power generation system according to an embodiment of the present invention may be configured to include a plurality of PV modules (10), an inverter (400) including a main controller (100), a plurality of MLPEs (Module Level Power Electronics) (200), and a server (300). Alternatively, as illustrated in FIG. 1b, a solar power generation system according to another embodiment of the present invention may be configured to include a plurality of PV modules (10), a main controller (100), a plurality of MLPEs (Module Level Power Electronics) (200), an inverter (400), and a server (300).

[0045] That is, a solar power generation system according to one embodiment may be configured to include a main controller (100) in an inverter (400) as in FIG. 1a, or according to another embodiment, may be configured to include an inverter (400) between the main controller (100) and the grid (20) as in FIG. 1b. Here, the inverter (400) may convert direct current power generated from a plurality of PV modules (10) into alternating current power and transmit the converted alternating current power to the grid (20). Hereinafter, for convenience of explanation, the description will be based on an embodiment in which the main controller (100) is included in the inverter (400) as in FIG. 1a. In addition, although a plurality of PV modules (10) and a plurality of MLPEs (200) are collectively referred to below, the PV modules (10) and the MLPEs (200) are separate from each other and may be configured as different types or models.

[0046] According to one embodiment, each of the plurality of PV modules (10) may mean a solar power generation panel in module unit. In addition, the plurality of suns and panels (10) may be connected in at least one of series and parallel, and the plurality of MLPEs (200) may be provided in each of the plurality of PV modules (10). In addition, one MLPE (200) may be connected to one PV module (10), or one MLPE (200) may be connected to multiple PV modules (10). The MLPE (200) may transmit power generation information including power generation amount, temperature, and failure information of the PV module (10) to the main controller (100), and receive an operation command for optimizing power efficiency from the main controller (100).

[0047] According to one embodiment of the present invention, the MLPE (200) is connected to each PV module (10) and is configured to optimize the output voltage of each connected PV module (10), and can be implemented as a DC optimizer. More specifically, the MLPE (200) is a device that is connected to each solar panel (10) and optimizes the output power (output voltage) of each connected solar panel (10). The MLPE (200) can optimize and output the output voltage of each connected PV module through the MPPT operation described below. To this end, the MLPE (200) analyzes various data received from the PV module (10), the inverter (400), the load, the grid (20), etc., and can monitor the status of the MLPE (200) by itself or be monitored by the inverter (400).

[0048] At this time, the MLPE (200) can optimize the output voltage of each connected PV module (10) through Maximum Power Point Tracking (MPPT) control that tracks the corresponding power and voltage when the solar power generation system (1) generates maximum power. The MPPT operation is an algorithm implemented to continuously adjust the impedance received by a PV module (10) or an array composed of multiple PV modules (10) so that the solar 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 (200) is described with reference to FIG. 2.

[0049] At this time, MLPE (200) can be connected to PV module (10) in one-to-one correspondence (n=1) as shown in Fig. 1, but can be installed in many-to-one or many-to-many manner depending on the structure adopted by the solar power generation system (1), and the installation form is not limited to any one. In another embodiment, one group composed 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 PV modules are connected in series.

[0050] MLPE (200) is provided in multiple numbers and connected in series with each other, and an inverter (400) or a main controller (100) is connected to both ends of the multiple MLPE (200) connected in series.

[0051] According to one embodiment of the present invention, an inverter (400) is a configuration that is installed in a PCS (Power Conversion System) to perform power conversion to supply power generated from a PV module (10) to a load or a grid (20). As described above, the inverter (400) may be provided to include a main controller (100) as illustrated in FIG. 1A, or may be provided separately from the main controller (100) as illustrated in FIG. 1B. Hereinafter, for convenience of explanation, the description will be made based on an embodiment in which the inverter (400) includes a main controller (100) as illustrated in FIG. 1A, and the operation of the inverter (400) may also be understood as the operation of the main controller (100).

[0052] According to one embodiment, an inverter (400) analyzes various data received from a PV module (10), an MLPE (200), a load, a grid (20), etc. to monitor the operating status of a solar power generation system (1). The inverter (400) also performs MPPT operation like the MLPE (200) and can maximize the power production efficiency of the solar power generation system (1).

[0053] According to one embodiment of the present invention, not only can the status of the MLPE (200) itself be diagnosed using only the MLPE (200) without any additional configuration, but the status of the PV module (10) can also be diagnosed by extracting an IV curve based on measurements of the output voltage and output current of the PV module (10).

[0054] In addition, the IV curve can appear in various forms depending on the state of the solar power generation system (1), and the characteristics according to the shape of the curve have been established through many studies. Therefore, the IV curve is an important factor necessary for diagnosing the state of the solar power generation system (1), and according to one embodiment of the present invention, the IV curve can be extracted by the operation of the MLPE (200), and the state of the solar power generation system (1) can be diagnosed using the extracted curve and the curve characteristics according to the shape.

[0055] The extracted IV curve can be used not only for diagnosing the status of the solar power generation system (1) but also for MPPT control.

[0056] According to one embodiment of the present invention, it is possible to extract the IV curve of a PV module (10) without changing the topology of various MLPEs (200) constituting a solar power generation system (1), and thus, it is economical because no additional cost is incurred.

[0057] According to one embodiment of the present invention, it is possible to prevent a decrease in power generation in advance, thereby increasing system efficiency, and to operate without additional costs, thereby creating an effect of lowering the Levelized Cost of Energy (LCOE) from a system perspective.

[0058] Hereinafter, the operation of a solar power generation system (1) according to one embodiment of the present invention will be specifically described with reference to the drawings.

[0059] FIG. 2 is a block diagram illustrating the configuration of an MLPE according to one embodiment of the present invention.

[0060] According to one embodiment of the present invention, the MLPE (200) may include a DC-DC converter (210) and a processor (220).

[0061] The DC-DC converter (210) can be implemented as a buck converter that steps down the voltage applied from the PV module (10) (the output voltage of the PV module (10)), and an example of the DC-DC converter (210) is illustrated in FIG. 5. According to one embodiment of the present invention, the duty ratio, which is the ratio at which the DC-DC converter (210) operates on in one duty cycle, can be controlled by the processor (220).

[0062] The processor (220) may include, for example, a microcontroller unit (MCU) for power control. The processor (220) may execute software such as a program to control at least one other component (e.g., hardware or software component) of the MLPE (200) and perform various data processing or operations.

[0063] The processor (220) can perform serial communication with the inverter (400) or power line communication (PLC) to receive control signals necessary for power optimization.

[0064] According to one embodiment of the present invention, the processor (220) can control the duty ratio of the DC-DC converter (210) to adjust the output voltage of the PV module (10) and the output voltage of the MLPE (200). According to one embodiment of the present invention, the processor (220) can control the duty ratio of the DC-DC converter (210) according to a shutdown signal to convert (regulate) the output voltage of the MLPE (200). At this time, the duty ratio control of the DC-DC converter (210) can be performed directly by the processor (220) or according to a command of the main controller (100) or the inverter (400).

[0065] FIG. 3 is a diagram illustrating an operation flow diagram of MLPE according to one embodiment of the present invention.

[0066] According to one embodiment of the present invention, the processor (220) switches from a first mode for performing MPPT control by disconnecting power from an inverter (400) connected to an output terminal of the MLPE (200) to a second mode for extracting a current (I)-voltage (V) curve (S10).

[0067] According to one embodiment of the present invention, the first mode may be a mode in which the processor (220) performs MPPT control in a general situation, and the second mode may be a mode in which the output terminals of the plurality of MLPEs and the power connection of the inverter are disconnected to extract the output voltage and output current of each PV module connected to the plurality of MLPEs.

[0068] The MLPE (200) basically performs MPPT control and is electrically connected to the inverter (400) for power transmission. Meanwhile, the MLPE (200) needs to block the current flow coming from the outside in order to measure the output voltage and output current of the PV module (10). Therefore, the processor (220) disconnects the power connection with the inverter (400) in order to switch from the first mode to the second mode. The processor (220) can disconnect the power connection with the inverter (400) by opening the output terminal of the MLPE (200).

[0069] At this time, the processor (220) may receive a signal requesting a transition from the first mode to the second mode, or may actively perform the mode transition according to a predefined cycle (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 may be triggered in various ways and is not limited to any one.

[0070] According to one embodiment of the present invention, the processor (220) extracts an IV curve using the measured output voltage and output current of the PV module (10) while adjusting and controlling the duty ratio of the DC-DC converter (210) in the second mode (S20).

[0071] As described above, the processor (220) opens the output terminal of the MLPE (200) to disconnect the power connection with the inverter (400), thereby cutting off the current flow. However, in order to measure the output voltage and output current of the PV module (10), current must be able to flow, and thus the processor (220) controls the DC-DC converter (210) to form a current path. This will be described in detail with reference to the DC-DC converter illustrated in FIG. 5 below.

[0072] The processor (220) can control the duty ratio of the DC-DC converter (210) from 0 to 1 or from 1 to 0, and can receive the output voltage value and output current value (hereinafter, also referred to as measured values) of the PV module (10) connected to the MLPE (200) from a measuring device that measures the output voltage and output current of the PV module (10) inside the solar power generation system (1). The measured values ​​in the first mode and the second mode according to the duty ratio control according to one embodiment of the present invention are illustrated in FIG. 6 below.

[0073] Meanwhile, the processor (220) can receive measurement values ​​in real time according to duty ratio control and extract the IV curve in real time. However, it is not limited thereto, and the output voltage and output current of the PV module (10) can be measured according to duty ratio control and then the measurement values ​​can be received at once to extract the IV curve. The IV curve can be extracted by PV module unit, array unit, etc., and an example of the extracted IV curve is illustrated in FIG. 7 below.

[0074] According to one embodiment of the present invention, the processor (220) can diagnose the state of a PV module corresponding to an IV curve extracted based on characteristic information of the IV curve including characteristics according to the shape of the IV curve.

[0075] According to one embodiment of the present invention, the processor (220) can obtain the power of the PV module (10) using the measured value, and can use this to track the maximum power point (MPP).

[0076] According to one embodiment of the present invention, it is possible to diagnose the status of a solar power generation system (1) to prevent and respond before the power generation of a PV module (10) is seriously deteriorated.

[0077] According to one embodiment of the present invention, since IV curve extraction is possible even during sunrise and sunset times when the influence on power generation is relatively small, the status of a solar power generation system (1) can be efficiently diagnosed without affecting power generation.

[0078] According to one embodiment of the present invention, the accuracy of condition diagnosis is high because the actual IV curve for each PV module is extracted.

[0079] FIG. 4 is a drawing showing an equivalent circuit diagram of a PV module according to one embodiment of the present invention.

[0080] According to one embodiment of the present invention, the output terminal of the PV module (10) is connected to the MLPE (200). In addition, the voltage (V) applied to the output terminal of the PV module (10) PV ) and the current flowing in the output terminal (I PV ) can be measured by MLPE (200).

[0081] According to one embodiment of the present invention, the shape of the IV curve extracted by the MLPE (200) may be influenced by the shunt resistance (Rsh) and the series resistance (Rs) shown in the equivalent circuit diagram of the PV module (10). Therefore, depending on the shape of the extracted IV curve, it is possible to check for abnormalities such as deterioration of the shunt resistance (Rsh) and the series resistance (Rs). A specific example will be described with reference to FIG. 7.

[0082] FIG. 5 is a circuit diagram of a DC-DC converter according to one embodiment of the present invention.

[0083] The DC-DC converter (210) includes a first switch (S1) and a second switch (S2) that operate complementarily on or off. The processor (220) can control the duty ratio of the first switch (S1) to increase in steps from 0 to 1. At this time, the processor (220) controls the second switch (S2) to operate in the opposite direction to the first switch (S1).

[0084] According to one embodiment of the present invention, the duty ratio may be controlled to increase by a constant value for each duty cycle. According to a specific embodiment, the processor (220) may control the first switch (S1) so that the duty ratio gradually increases by a constant value in the duty cycle after the third time point (t3, the time point at which IV curve extraction begins) described below in the second mode.

[0085] Meanwhile, as described above with respect 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 (400) is released, so a current path must be formed to enable duty ratio control.

[0086] According to one embodiment of the present invention, the DC-DC converter (210) further includes a third switch (S3) connected in parallel to the output terminal of the MLPE (200) and connected in series with the first resistor (R1) to remove residual power of the inverter (400) as needed during normal operation. During normal operation (the first mode in which MPPT control is performed), the third switch (S3) is turned off and does not affect the operation of the DC-DC converter (210). Then, when removal of residual power is required, the processor (220) turns on the third switch (S3) to consume residual power through the resistor (R1). That is, the third switch (S3) can be turned on at a second time point (t2, the time point at which the third switch is turned on) after a predetermined time has elapsed from the first time point (t1, the time point at which the first mode is switched to the second mode) described below, thereby forming a current path and operating to consume the remaining power present at the first time point (t1).

[0087] In more detail, the present invention utilizes the third switch (S3) provided for this function to form a current path even after the first time point (t1) when the power connection with the inverter (400) is disconnected for the second mode transition.

[0088] According to one embodiment of the present invention, the processor (220) controls the third switch (S3) to be turned on to form a current path in the second mode. When the third switch (S3) is turned on, current flows through the PV module (10), and the voltage (VPV) and current (IPV) that change as power is consumed through the resistor (R1) can be measured.

[0089] 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 so that a current path can be formed even after the inverter and power connection are disconnected, and the output voltage of the PV module (10) is regulated according to duty ratio control.

[0090] 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.

[0091] Below, the operation according to time is explained with reference to the timing diagram of Fig. 6.

[0092] FIG. 6 is a drawing illustrating a timing diagram according to one embodiment of the present invention.

[0093] The timing diagram illustrated in Fig. 6 represents, from top to bottom, the gate voltage (VGS3) of the third switch (S3), the duty (D) of the first switch (S1), the output voltage (VPV) of the PV module (10), the output current (IPV) of the PV module (10), and the power (PPV) of the PV module (10) over time. Referring to Fig. 6, the first mode according to one embodiment of the present invention may be an MPPT mode, and the second mode may be an IV mode.

[0094] At this time, when the gate voltage (VGS3) of the third switch (S3) is 0 V, the third switch (S3) operates off, and when a voltage higher than the threshold value is applied to the gate, the third switch (S3) operates on.

[0095] Below, we examine the operation of the solar power generation system (1) over time.

[0096] First, the MLPE (200) performs MPPT control in the first mode (MPPT mode). Accordingly, the output voltage (VPV), output current (IPV), and power (PPV) of the PV module (10) are all operating at the maximum power point (MPP), and the gate voltage (VGS3) of the third switch (S3) is in off operation at 0 V.

[0097] The processor (220) opens the output terminal of the MLPE (200) at a first time point (t1) to disconnect the power connection with the inverter (400), thereby switching from the first mode (MPPT mode) to the second mode (IV Curve Extracting mode) (Output open).

[0098] In addition, the processor (220) controls the third switch (S3) to turn on in the second mode at the second time point (t2) to form a current path (S3 on). At this time, the processor (220) sets the duty ratio of the first switch (S1) to 0 to control the first switch (S1) to turn off, 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 (210) is placed in an open state. The output voltage (VPV) of the PV module (10) is measured at a constant value, but the output current (IPV) becomes 0. This output voltage is called the open-circuit voltage (Voc).

[0099] Thereafter, the processor (220) performs duty ratio control while gradually increasing the duty ratio of the first switch (S1). According to one embodiment of the present invention, the processor (220) can control the duty ratio of the DC-DC converter so that the duty ratio increases to a preset value each time the duty cycle of the DC-DC converter elapses. At this time, the processor (220) does not immediately perform the duty ratio control of the DC-DC converter (210) together with the on operation control of the third switch (S3), but sets a predetermined time interval (t2 to t3).

[0100] This is to measure the voltage and current of the PV module (10) more accurately by consuming the residual power through the resistor (R1), as residual power may remain in the capacitor (C1, C2) or inductor (L1) inside the DC-DC converter (210).

[0101] Accordingly, the processor (220) controls the duty ratio of the DC-DC converter (210) from a point in time (hereinafter referred to as a third point in time (t3)) a predetermined time after the point in time (hereinafter referred to as a second point in time (t2)) when the third switch (S3) is turned on (Start scan).

[0102] Specifically, the processor (220) can control the duty ratio of the first switch (S1) to gradually increase from 0 to 1 after the third time point (t3). When the duty ratio of the first switch (S1) is 1, the PV module (10) is short-circuited, the output voltage (VPV) is measured as 0, and the output current (IPV) reaches a limit value. This output current is called short-circuit current (Isc).

[0103] While the processor (220) controls the duty ratio of the DC-DC converter (210), the measuring device can measure the output voltage (VPV) and output current (IPV) of the PV module (10) as shown in the timing diagram of FIG. 6.

[0104] According to one embodiment of the present invention, the processor (220) can extract an IV curve using the measured output voltage (VPV) and output current (IPV). As described above, when receiving the output voltage (VPV) and output current (IPV) values ​​in real time, the processor (220) can extract an IV curve from an open circuit voltage (Voc) point to a short circuit current (Isc) point.

[0105] As another example, the processor (220) can track the maximum power point (MPP) using a timing diagram. Specifically, the processor (220) can identify the output power using the output voltage and output current of the PV module (10), and identify the maximum value of the identified output power as the MPP.

[0106] Below, we will examine a method for analyzing the status of a solar power generation system using the extracted IV curve.

[0107] FIG. 7a and FIG. 7b are diagrams illustrating current-voltage curves according to one embodiment of the present invention.

[0108] According to one embodiment of the present invention, the processor (220) can diagnose the status of the PV module (10) corresponding to the extracted IV curve based on the characteristic information of the IV curve. However, the present invention is not limited thereto, and the processor (220) can transmit the extracted IV curve so that an external device, such as a server or a monitoring electronic device, can diagnose the status of the solar power generation system (1). The monitoring electronic device can be implemented as, for example, a desktop, a laptop, a smart phone, or the like.

[0109] Fig. 7a is an example of an IV curve extracted according to one embodiment of the present invention. Referring to Fig. 7a, an IV curve extracted from a third time point (t3) is illustrated, and the scan direction may mean a time-series order direction of the extracted values ​​over time. As described above, at the first time point, the output voltage is an open-circuit voltage (Voc) and the output current is 0. In addition, when the duty ratio of the first switch (S1) of the DC-DC converter (210) gradually increases to 1 and finally becomes 0, the output current when the output voltage becomes 0 is a short-circuit current, and the output voltage becomes 0.

[0110] Referring to Fig. 7a, points on the graph may be points indicating the starting point of each duty cycle. According to one embodiment of the present invention, the IV curve can be extracted by obtaining the output voltage and output current values ​​of the PV module (10) at the starting point or the ending point of each duty cycle. In Fig. 7a, the intervals between points are shown to be spaced apart for convenience of explanation, but according to an embodiment of the present invention, the duty cycle for controlling the first switch (S1) of the DC-DC converter (210) can be sufficiently short so that an IV curve close to continuous can be extracted.

[0111] Below, the characteristics of the IV curve are examined with reference to Fig. 7b, as follows.

[0112] For example, as shown in FIG. 4 above, when the shunt resistance (Rsh) of the PV module (10) is lowered, the slope of the IV curve may increase near the short-circuit current (Isc), similar to the occurrence of a leakage current path. Accordingly, when the slope of the IV curve increases near the short-circuit current (Isc) (710), it can be seen that there is an abnormality, such as deterioration, in the shunt resistance (Rsh) of the PV module (10).

[0113] As another example, when the series resistance (Rs) of the PV module (10) increases, the fill factor (FF) decreases, as if the flow of current is impeded, and thus the slope of the curve may decrease near the open circuit voltage (Voc). Accordingly, if the slope of the curve decreases near the open circuit voltage (Voc) (720), it can be seen that there is an abnormality, such as deterioration, in the series resistance (Rs) of the PV module (10).

[0114] At this time, the curve factor is the product of voltage and current (VmppХImpp) at the maximum power point (MPP) divided by the product of open circuit voltage (Voc) and short circuit current (Isc). In other words, it can also be viewed as the value of area (730) divided by area (740). The closer the curve factor is to 1, the better the quality of the corresponding PV module (10) can be determined. Depending on the curve factor value, the quality such as the lifespan and efficiency of the PV module (10) can be determined.

[0115] As another example, mismatching, connection errors, shading conditions, etc. between PV modules (10) can be identified based on the shape of the IV curve near the MPP.

[0116] In addition, the characteristics of the IV curve can be revealed through continuous research, and there can be various methods of diagnosing the status of solar power generation systems using the IV curve.

[0117] Although not shown in the drawing, according to one embodiment of the present invention, the processor (220) can extract a power (P)-voltage (V) curve using the output voltage and output current of the PV module (10). Specifically, the processor (220) can identify the output power using the output voltage and output current of the PV module (10), and extract the PV curve using the identified output voltage and output power.

[0118] According to one embodiment of the present invention, the processor (220) can identify the maximum power point using the extracted IV curve or PV curve, thereby enabling MPPT control.

[0119] According to one embodiment of the present invention, it is efficient to intermittently and actively extract IV curves as needed.

[0120] According to one embodiment of the present invention, various functions such as MPPT control as well as status diagnosis can be implemented through the IV curve.

[0121] 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.

[0122] According to one embodiment of the present invention, it is possible to analyze the deterioration tendency of PV modules and changes according to the installation environment according to the purpose, thereby enabling data collection for control optimization according to site characteristics.

[0123] [Explanation of symbols]

[0124] 1: Solar power generation system

[0125] 10: PV module

[0126] 200: MLPE

[0127] 210: DC-DC converter

[0128] 220: Processor

[0129] 400: Inverter

[0130] 20: Grid

Claims

1. A method for operating a solar power generation system including a plurality of module level power conversion devices (Module Level Power Electronics, MLPE), An operation of performing Maximum Power Point Tracking (MPPT) control in the first mode of the above MLPE; An operation of switching the first mode to the second mode by disconnecting the power connection between the output terminals of the plurality of MLPEs and the inverter; An operation for controlling the duty ratio of the DC-DC converter provided in the MLPE after switching to the second mode; and An operation of extracting the output voltage and output current of each PV module connected to the plurality of MLPEs in the second mode; A method of operating a solar power generation system including:

2. In paragraph 1, A method for operating a solar power generation system, wherein the operation of switching the first mode to the second mode is an operation of opening the output terminals of the plurality of MLPEs at a first point in time to disconnect the power connection between the output terminals of the plurality of MLPEs and the inverter.

3. In paragraph 2, The above DC-DC converter, A method of operating a solar power generation system, further comprising a third switch connected in parallel to the output terminal and connected in series with the first resistor, and operating to form a current path by operating on for a predetermined period of time from a second time point after the first time point, thereby dissipating residual power existing at the first time point, wherein the third switch operates off in the first mode.

4. In paragraph 2, An operating method of a solar power generation system, wherein the first switch and the second switch of the DC-DC converter of the MLPE are controlled from a third point in time after the second point in time, and the first switch and the second switch are controlled so that the duty ratio of the DC-DC converter gradually increases.

5. In paragraph 1, The above DC-DC converter, An operating method of a solar power generation system, comprising a first switch and a second switch that operate complementarily on or off, wherein the first switch and the second switch are turned on or off so as to adjust the duty ratio of the DC-DC converter.

6. In paragraph 1, The operation of controlling the duty ratio of the DC-DC converter is as follows: An operating method of a solar power generation system, which controls the duty ratio of a DC-DC converter so that the duty ratio increases to a preset value each time the duty cycle of the DC-DC converter elapses.

7. In paragraph 6, An operating method of a solar power generation system, wherein the output voltage of the PV module decreases and the output current increases as the duty ratio is controlled to gradually increase from the third point in time of the second mode.

8. In paragraph 1, The above DC-DC converter, A capacitor connected in parallel with both output terminals of the above solar module, It includes a first switch and a second switch connected in parallel with the capacitor, When the first switch is turned off, the second switch is turned on and the DC-DC converter is opened. An operating method of a solar power generation system, wherein when the first switch is turned on, the second switch is turned off so that both output terminals of the PV module are short-circuited.

9. In paragraph 1, A method of operating a solar power generation system, wherein at a third point in time when the third switch of the above DC-DC converter is turned on, the slope of the IV curve corresponds to the loss of the shunt resistor in the equivalent circuit diagram of the PV module.

10. In paragraph 1, A method of operating a solar power generation system, wherein the slope of the IV curve when the open circuit voltage becomes 0 as the above duty ratio increases corresponds to the loss of the series resistance in the equivalent circuit diagram of the PV module.

11. In solar power generation systems, As a module level power conversion device (MLPE) of a solar power generation system, DC-DC converter; and The above MLPE performs Maximum Power Point Tracking (MPPT) control by disconnecting the power connection with the inverter connected to the output terminal in the first mode, and controls to extract the current (I) - voltage (V) curve in the second mode. An MLPE of a solar power generation system including a processor for extracting an IV curve using the measured output voltage and output current of the PV module while controlling the duty ratio of the DC-DC converter in the second mode.

12. In paragraph 11, An MLPE of a solar power generation system, wherein the processor controls the MLPE to switch the mode of the MLPE from the first mode to the second mode at a first time point, and to open the output terminals of the plurality of MLPEs at the first time point so that the power connection between the output terminals of the plurality of MLPEs and the inverter is disconnected.

13. In paragraph 11, The above DC-DC converter, MLPE of a solar power generation system comprising a first switch and a second switch that operate complementarily on or off.

14. In paragraph 13, The above DC-DC converter, An MLPE of a solar power generation system, comprising a third switch connected in parallel to the output terminal and operating to form a current path, and a first resistor connected in series with the third switch.

15. In paragraph 14, The above processor, MLPE of a solar power generation system, which controls the third switch to operate on in the second mode.

16. In paragraph 15, The above processor, An MLPE of a solar power generation system that controls the duty ratio of the first switch to increase in steps from 0 to 1 from a third point in time, which is a predetermined time after the second point in time when the third switch is turned on.

17. In paragraph 11, The above processor, In the second mode, the output power is identified using the output voltage and output current of the PV module, MLPE of a solar power generation system, which extracts a power (P)-voltage (V) curve using the above output voltage and output power.

18. In paragraph 17, The above processor, MLPE of a solar power generation system, which identifies the maximum value among the identified output powers as the maximum power point (MPP).

19. In paragraph 11, The above processor, MLPE of a solar power generation system that diagnoses the status of a PV module corresponding to the IV curve extracted based on characteristic information of the IV curve.

20. In paragraph 11, An MLPE of a solar power generation system, characterized in that the plurality of MLPEs are connected in series with each other, and each MLPE is connected to at least one PV module among the plurality of PV modules.

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