Hot spot prevention photovoltaic module based on power optimizer input voltage intelligent control

Abstract

The application discloses a hot spot prevention photovoltaic module based on power optimizer input voltage intelligent control, which does not need to set a bypass diode in a junction box, and avoids the problem that when the junction box fails, the whole module is treated by pouring glue, which causes the difficulty in replacing the junction box, and the great waste caused by the replacement of the whole photovoltaic module; the control unit is provided with a threshold value for the input current of the power optimizer, and different input low voltage protection values of the power optimizer are set according to the comparison between the actual input current of the power optimizer and the threshold value, so that when the low irradiation and the risk of hot spot damage occur, the MPPT tracking range is larger, and the power generation efficiency is improved; when the high irradiation and the risk of hot spot damage occur, the higher input low voltage protection value is set, the reverse bias voltage value between the two ends of the cell piece subjected to the shading is limited, and the extreme hot spot temperature is far away, and the high temperature resistance requirement of the packaging material such as the back plate and the material cost are reduced.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic power generation technology, and more specifically to a hot spot-resistant photovoltaic module based on intelligent control of the input voltage of a power optimizer. Background Technology

[0002] When photovoltaic (PV) modules installed outdoors are obstructed by dust, sand, bird droppings, or other debris, their output power will be reduced, and in severe cases, a hot spot effect may occur. The hot spot effect refers to the phenomenon where defective cells in the series circuit of a PV module, such as those that are obstructed, dirty, cracked, or have bubbles, act as a load, consuming the electrical energy generated by other cells and causing localized overheating. Severe hot spot effects can cause the module to catch fire, resulting in irreversible and serious damage. In recent years, manufacturers have been increasing the size of PV modules to improve their output power. This increase in size leads to a significant increase in current. When the current reaches 18A or higher, the electrical safety risks increase dramatically. In severe cases, hot spots and other factors can cause the junction box containing bypass diodes, backplane, and other materials to burn out, or even start a fire, resulting in huge losses to the PV power plant.

[0003] Under normal circumstances, the current Iph generated by each cell (individual cell) in a photovoltaic module due to sunlight is basically equal. If the current Iph of one or more individual cells in the photovoltaic module decreases due to shading or other reasons, it cannot match the current of the string and other individual cells. When the operating current of the photovoltaic module exceeds the current of that individual cell or several individual cells, the excess current will flow through the parallel resistor Rsh. Then, that part of the individual cells will be placed in a reverse bias state, and its function in the circuit will change from power source to load, consuming energy and generating heat, thus forming a local overheating phenomenon inside the module.

[0004] When MLPE products such as module-level power optimizers and micro-PV inverters are configured with conventional PV modules, the conventional PV modules are typically divided into 2-3 PV cell string power generation units, such as... Figure 2 The photovoltaic module 1 shown is divided into a first photovoltaic cell string power generation unit 10 and a second photovoltaic cell string power generation unit 20. To prevent some photovoltaic modules from becoming a load and suffering severe heat damage due to lack of sunlight caused by shading under strong light, it is necessary to connect them in reverse parallel to each photovoltaic cell string power generation unit, as shown below. Figure 3 , Figure 4The bypass diode shown is reverse-biased when the solar cells are operating normally, having a negligible impact on the photovoltaic module's conversion efficiency at room temperature. However, as the bypass diode's temperature rises significantly, its reverse leakage current also increases substantially, potentially having a significant impact on the photovoltaic module's power generation efficiency. Furthermore, when the photovoltaic module's junction box fails, the use of potting compound makes replacement difficult, necessitating the replacement of the entire photovoltaic module, resulting in substantial waste.

[0005] The function of a bypass diode is to constrain the voltage of mismatched sub-cell strings in a photovoltaic module, reducing the intensity of the hot spot effect. Simultaneously, the reverse bias voltage across the shaded cell is limited by the sub-cell string voltage, preventing it from exceeding the avalanche breakdown voltage and causing avalanche breakdown. When the reverse bias voltage across the cell increases to its avalanche breakdown voltage, its reverse saturation current increases rapidly, further intensifying the hot spot effect and making it prone to thermal breakdown and damage, even causing a fire. The hot spot effect still exists after the bypass diode is turned on, and it reaches its maximum when the bypass diode is active.

[0006] Individual photovoltaic (PV) modules operate at relatively low voltages. To achieve higher string voltages, PV modules are connected to PV inverters, sometimes in series with 30 or more modules. MLPE products, such as module-level power optimizers and micro-PV inverters, can isolate the connected PV modules from the PV string. This prevents other PV modules in the string from affecting the MLPE-connected module, and minor defects like dirt, cracks, and bubbles in the cells are less likely to cause hot spots, reducing the frequency of hot spots. However, current methods of connecting PV modules to MLPE products cannot completely eliminate the hot spot effect. Especially when a single cell in a sub-string is severely shaded by bird droppings, fallen leaves, etc., the bypass diode connected in parallel in the sub-string will conduct. The energy generated by the other normal cells in the sub-string will be entirely added to the shaded cell, resulting in a hot spot effect almost identical to that of a PV module without MLPE. Therefore, connecting PV modules to MLPE products cannot reduce the requirements for PV module encapsulation materials such as backsheets and encapsulants.

[0007] Our patent, CN202210506182.4, entitled "Interleaved Combined Regional Power Optimization Photovoltaic Module and Power Generation System," employs two different types of regional power optimization photovoltaic modules. It connects adjacent modules of different types in the same region in series to the same power optimizer. Compared to the previous method of using a separate power optimizer for each photovoltaic cell string unit, this significantly reduces the number of power optimizers used in the photovoltaic module, thus lowering the construction cost of the photovoltaic power generation system and shortening the length of connecting cables. Furthermore, regional power optimization effectively addresses issues such as surface dust accumulation, power loss due to shading of the front and rear rows, and mismatch between internal vertical regions, resulting in higher power conversion efficiency and better output current quality. If the two photovoltaic cell string units connected to the power optimizer in the interleaved combined regional power optimization photovoltaic module are connected to bypass diodes in reverse parallel, a severe hot spot effect can occur when one photovoltaic cell string unit experiences shading mismatch, causing the bypass diode to conduct. However, without bypass diodes, the aforementioned photovoltaic cell string units may be at risk of avalanche voltage breakdown. Therefore, how to avoid the hot spot effect that may be caused by the conduction of bypass diodes in the aforementioned interleaved combined regional power optimization photovoltaic modules, while at the same time keeping the shaded cells away from the risk of avalanche voltage breakdown, has become an urgent technical problem to be solved. Summary of the Invention

[0008] This invention aims to avoid the hot spot effect that may be caused by bypass diodes while keeping the shaded solar cells away from the risk of avalanche voltage breakdown. It provides a hot spot-resistant photovoltaic module based on intelligent control of the power optimizer input voltage.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] A hot-spot-resistant photovoltaic module based on intelligent input voltage control of a power optimizer is provided. In each photovoltaic module of a photovoltaic string, the first output terminal of the first photovoltaic cell string power generation unit and the second output terminal of the second photovoltaic cell string power generation unit are connected in series to a power optimizer. Each power optimizer is equipped with a control unit. Each control unit presets a corresponding input current threshold for the connected power optimizer. When the control unit determines that the input current of the power optimizer is less than or equal to the preset input current threshold, it sets the input low voltage protection value of the power optimizer to a first limit value and controls the input voltage of the power optimizer to be greater than or equal to the first limit value. When it determines that the input current of the power optimizer is greater than the input current threshold, it sets the input low voltage protection value of the power optimizer to a second limit value and controls the input voltage of the power optimizer to be greater than or equal to the second limit value. The second limit value of the input low voltage protection value is higher than the first limit value.

[0011] Preferably, the heat-spot-resistant photovoltaic module consists of a first photovoltaic cell string power generation unit and a second photovoltaic cell string power generation unit. Each photovoltaic cell string power generation unit includes at least one first cell string group and at least one second cell string group. Several first cell string groups and second cell string groups are connected in series to form the output terminal of the photovoltaic cell string power generation unit. The output terminal includes a positive output terminal and a negative output terminal of the photovoltaic cell string power generation unit, and the positive and negative output terminals of the output terminal are connected one-to-one to the positive and negative terminals of the input terminal of the output terminal. The first output terminal of the first photovoltaic cell string power generation unit and the second output terminal of the second photovoltaic cell string power generation unit are connected in series to the same power optimizer.

[0012] The output terminals of each power optimizer are connected in series to form a photovoltaic string, and each power optimizer is equipped with a local control unit; the control unit has a preset threshold for the local current; the control unit is used to set the input low voltage protection value of the conversion circuit to a first limit value when the local current value does not exceed the threshold value, and to set the input low voltage protection value of the conversion circuit to a second limit value when the local current value exceeds the threshold value; the control unit is also used to control the input voltage of the power optimizer to be not lower than the set input low voltage protection value.

[0013] Preferably, the number of solar cells connected in series in the first or second photovoltaic cell string power generation unit is in the range of 18-28 cells.

[0014] Preferably, the voltage Vpv between the positive and negative output terminals of the photovoltaic module is calculated using the following formula (1):

[0015] Vpv=Vmmp×(N-1)-Vbr Formula (1)

[0016] From formula (1), we can obtain: Vbr = Vmmp × (N-1) - Vpv Formula (2)

[0017] In formula (1), Vmmp represents the voltage across each cell in the photovoltaic module that has not experienced a hot spot effect;

[0018] N represents the total number of solar cells in the photovoltaic module;

[0019] N-1 represents the number of solar cells remaining in the photovoltaic module after removing one cell that has experienced a hot spot effect.

[0020] Preferably, the maximum reverse bias voltage Vbrmax at both ends of the cells in the battery string where the hot spot effect occurs is calculated by the following formula (3):

[0021]

[0022] In formula (3), Vpw represents the peak power voltage of the photovoltaic module;

[0023] T This indicates the actual operating temperature of the photovoltaic module;

[0024] This indicates the standard test temperature (STC) for photovoltaic modules, 25°C.

[0025] This represents the voltage-temperature rise coefficient of a photovoltaic module;

[0026] N This indicates the total number of solar cells in the photovoltaic module;

[0027] N- 1 represents the number of solar cells remaining in the photovoltaic module after removing the one solar cell that has experienced a hot spot effect;

[0028] This indicates the set input low voltage protection value.

[0029] Preferably, there is no need to install bypass diodes in the heat-spot-resistant photovoltaic module to protect the first photovoltaic cell string power generation unit and the second photovoltaic cell string power generation unit in the photovoltaic module, and there is no need to install bypass diodes in the first outgoing terminal and / or the second outgoing terminal of the junction box.

[0030] Preferably, the output terminals of each power optimizer in the photovoltaic string are connected in series with each other.

[0031] Preferably, the power optimizer includes a DC / DC conversion module and the control unit, wherein the DC / DC conversion module is coupled between the photovoltaic cell string power generation unit and the photovoltaic string.

[0032] Preferably, the power optimizer is a DC / DC conversion module with a main control module, and the DC / DC conversion module is a Buck type step-down type, or a Boost type step-up type, or a Boost-Buck type step-up / step-down type.

[0033] The main control module includes a maximum power point tracking (MPPT) module and a pulse width modulation (PWM) module. The MPPT module is used to acquire the electrical parameters of the input and output terminals of the DC / DC conversion module and process them to obtain the maximum power point. During the MPPT module's MPPT of the first and second photovoltaic (PV) string power generation units connected in series, when the output voltage of the MPPT module, i.e., the output voltage of the first and second PV string power generation units connected in series, reaches the set input low voltage protection value, the control unit refuses to continue to adjust the input voltage of the first PV string power generation unit, which is the target of the MPPT module's MPPT, downward.

[0034] The pulse width modulation module is used to adjust the duty cycle of the power optimizer so that the output current of the power optimizers connected in series is consistent.

[0035] Preferably, the solar cells in the battery string are any one or more of PERC solar cells, TOPCON, HJT, and ABC high-efficiency solar cells.

[0036] The present invention has the following beneficial effects:

[0037] 1. The hot spot-resistant photovoltaic module provided by the present invention does not require a bypass diode in the junction box, thus avoiding the problem of conventional photovoltaic modules where the junction box is difficult to replace due to the potting treatment of the entire module when the junction box fails, resulting in great waste.

[0038] 2. The photovoltaic module provided by this invention greatly reduces the impact of hot spot effect, avoiding the high requirements of conventional photovoltaic modules on photovoltaic module encapsulation materials such as backsheets and encapsulation films to withstand extreme hot spot temperatures. The hot spot-resistant photovoltaic module provided by this invention has an extreme hot spot temperature of less than 95°C, which can reduce the high temperature resistance requirements of encapsulation materials such as backsheets and encapsulation films, and reduce material costs;

[0039] 3. The provided control unit has a preset threshold for the input current of the power optimizer. Different input low voltage protection values ​​of the power optimizer are set by comparing the actual input current of the power optimizer with its threshold. This allows for a larger MPPT tracking range and improved power generation efficiency under low irradiance conditions when there is no risk of hot spot damage. Under high irradiance conditions and when there is a risk of hot spot damage, a higher input low voltage protection value is set to limit the reverse bias voltage value at both ends of the shaded solar cells to keep them away from extreme hot spot temperatures. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0041] Figure 1 This is a schematic diagram showing the adjacent and staggered arrangement of individual photovoltaic modules in versions A and B for regional power optimization.

[0042] Figure 2 This is a schematic diagram showing two first photovoltaic cell string power generation units in adjacent A and B region power optimization photovoltaic module units connected to the same power optimizer through a first outgoing terminal or two second photovoltaic cell string power generation units connected through a second outgoing terminal.

[0043] Figure 3 This is a schematic diagram of a battery cell connected in reverse parallel with a bypass diode;

[0044] Figure 4 This is a schematic diagram of a half-cell battery connected in reverse parallel with a bypass diode;

[0045] Figure 5 This is a schematic diagram of the connection between the photovoltaic module and the power optimizer in the existing scheme, which is a 3-part monocrystalline silicon photovoltaic module with a bypass diode junction box of the 182-72-545W type.

[0046] Figure 6 This is a schematic diagram of the connection between the photovoltaic module and the power optimizer of the 182-72-545W type two-part monocrystalline silicon photovoltaic module without bypass diode junction box in an embodiment of the present invention.

[0047] Figure 7 A schematic diagram of a 70% shading area for one cell in a 3-part monocrystalline silicon photovoltaic module with a bypass diode junction box, which is a 182-72-545W type in the existing scheme.

[0048] Figure 8This is a schematic diagram of a 70% shading area of ​​a single cell in a 182-72-545W type two-part monocrystalline silicon photovoltaic module without a bypass diode junction box, as described in this embodiment of the invention.

[0049] Figure 9 It calculates the voltage between the positive and negative output terminals of a photovoltaic module. A schematic diagram;

[0050] Figure 10 This is a diagram of the internal circuit structure of the power optimizer;

[0051] Figure 11 This is a schematic diagram of the IV and PV curves of a photovoltaic module under unshaded conditions;

[0052] Figure 12 This is a schematic diagram of the IV and PV curves of a photovoltaic module under shading conditions. Detailed Implementation

[0053] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0054] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images. They should not be construed as limiting the scope of this patent. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0055] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0056] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0057] The embodiments of the present invention are based on Figure 1 Taking the interleaved combined regional power optimization photovoltaic module shown as an example, the principle of preventing hot spot effect by adjusting the input voltage of the power optimizer and at the same time reducing the risk of avalanche voltage breakdown of the shading cell is explained in detail.

[0058] Please refer to Figure 1 and Figure 2 The staggered interconnected combined regional power optimization photovoltaic module is composed of several A-plate regional power optimization photovoltaic module units 1 and B-plate regional power optimization photovoltaic module units 2 arranged at intervals and connected to each other. Each regional power optimization photovoltaic module unit includes a first photovoltaic cell string power generation unit 10 and a second photovoltaic cell string power generation unit 20. Each photovoltaic cell string power generation unit includes at least one first cell string group 100 and at least one second cell string group 200. Several first cell string groups 100 and several second cell string groups 200 are connected in series to form the output terminal of the photovoltaic cell string power generation unit. The output terminal includes a positive output terminal and a negative output terminal of the photovoltaic cell string power generation unit. The positive and negative output terminals of the output terminal are connected one-to-one to the positive and negative terminals of the input terminal of the output terminal. The output terminal is arranged along the edge of the long side of the regional power optimization photovoltaic module unit.

[0059] The first output terminal 101 in the first photovoltaic cell string power generation unit 10 and the second output terminal 201 in the second photovoltaic cell string power generation unit 20 are located at different long side edges of the regional power optimization photovoltaic module unit. The two output terminals constitute the output terminal group of the regional power optimization photovoltaic module unit. One output terminal in the first output terminal group of the power optimization photovoltaic module unit 1 of version A and the adjacent output terminals in the second output terminal group of the regional power optimization photovoltaic module unit 2 of version B are connected in series to the same power optimizer 500.

[0060] The output terminals of each power optimizer 500 are connected in series to form a photovoltaic string. Each power optimizer 500 is equipped with a control unit. Each control unit presets a corresponding input current threshold for the connected power optimizer 500. When the control unit determines that the input current of the power optimizer 500 being configured is less than or equal to the preset input current threshold, it sets the input low voltage protection value of the power optimizer to a first limit value and controls the input voltage of the power optimizer to be greater than or equal to the first limit value. When it determines that the input current of the power optimizer 500 is greater than the input current threshold, it sets the input low voltage protection value of the power optimizer to a second limit value and controls the input voltage of the power optimizer to be greater than or equal to the second limit value. The second limit value of the input low voltage protection value is higher than the first limit value.

[0061] For example, such as Figure 5 As shown, in the existing scheme, the specification is a 182-72-545W type monocrystalline silicon photovoltaic module. The photovoltaic module of this specification has a power of 545Wp, a peak power voltage of 41.80V, a peak power current of 13.04A, an open circuit voltage of 49.65V, and a short circuit current of 13.92A. This photovoltaic module is a half-cell photovoltaic module, which is divided into 6 half-cell sub-cell string circuits. Every two half-cell sub-cell string circuits are connected in parallel to form a sub-cell string circuit connected to a junction box, forming 3 sub-cell strings. There are a total of 3 junction boxes. All 3 junction boxes are equipped with bypass diodes connected in parallel with the direction of the sub-cell strings. The 3 junction boxes are connected in series and a connecting wire is led out from the junction box to connect to the photovoltaic power optimizer.

[0062] In the solution provided in this embodiment, such as Figure 6 As shown, this is also a 182-72-545W type monocrystalline silicon photovoltaic module. This module has a power output of 545Wp, a peak power voltage of 27.86V, a peak power current of 19.56A, an open-circuit voltage of 33.10V, and a short-circuit current of 20.88A. This module is also a half-cell module, divided into six half-cell sub-cell string circuits. Every three half-cell sub-cell string circuits are connected in parallel to form one sub-cell string circuit, which is then connected to a junction box to form two sub-cell strings. There are two junction boxes in total. These two junction boxes will not have bypass diodes. The two junction boxes are connected in series, and connecting wires lead from the junction boxes to the power optimizer.

[0063] Figure 5 , Figure 6 In the two schemes shown, the boundary conditions for calculating the hot spot temperature of the photovoltaic module are as follows: the convective heat transfer coefficients of both the front and back of the photovoltaic module are set to 10 W / m²·℃, the front of the photovoltaic module receives 800 W / m² of solar irradiance, the ambient wind speed is 1 m / s, the emissivity of the glass cover of the photovoltaic module is 0.95, the emissivity of the TPT backsheet is 0.89, and the ambient temperature is 22℃.

[0064] Assumption Figure 6 and Figure 5 One of the single cells shown (half a 182-cell cell) is 70% shaded (see diagram of cell shading). Figure 7 , Figure 8 Under these conditions, the total calculated output power of the 182 solar cell is 0.5 + 0.5 * 30% = 0.65. Figure 5 In the given comparison scheme, under the maximum power point tracking (MPPT) function of its photovoltaic power optimizer, the reverse parallel diode of the sub-string where a single cell is shaded will conduct, bypassing the shaded sub-string. In this case, the overall output power of the photovoltaic module in this comparison scheme is 2 / 3 of the original power, i.e., 66.7%. However, even after the bypass diode is turned on, the hot spot effect of the photovoltaic module still exists, and the hot spot effect reaches its maximum with the conduction of the bypass diode. The energy generated by the other normal cells in the shaded sub-string will all be added to the shaded cell. The calculated heat dissipation required by the single cell with the hot spot effect through heat conduction is: 545W * 0.8 * 1 / 6 = 72.6W (where 6 in 1 / 6 refers to the photovoltaic module being divided into 6 sub-strings; 0.8 refers to the system efficiency, i.e., 80% system efficiency, 1000W / m). 2 After considering system losses under irradiation conditions, 80% of the energy is converted into electrical energy. At this time, the hot spot temperature of the shielded solar cell where the hot spot effect occurs is 123℃.

[0065] and Figure 6 The embodiment shown uses a 182-72-545W monocrystalline silicon photovoltaic module. This module has a power output of 545W, a peak power voltage of 27.86V, a peak power current of 19.56A, an open-circuit voltage of 33.10V, and a short-circuit current of 20.88A. This is a half-cell photovoltaic module, divided into six half-cell sub-cell string circuits. Every three half-cell sub-cell string circuits are connected in parallel to form one sub-cell string circuit, which is then connected to a junction box, forming two sub-cell strings. There are two junction boxes in total. No bypass diodes are installed in these junction boxes. The two junction boxes are connected in series, and a connecting wire leads from the junction box to the power optimizer. In this embodiment, the input current threshold of the power optimizer is set to 3A. When the input current of the power optimizer is lower than the 3A threshold, the input low-voltage protection value is set to 14V. When the input current is greater than or equal to the 3A threshold, the low-voltage protection value is set to 20V.

[0066] Under low current conditions, the maximum reverse bias voltage across the terminals of the single solar cell with hot spots is: 27.86*47 / 48-14=13.27V (48 is the total number of cells, of which 1 cell is shaded, and the remaining unshaded cells are 47=48-1). In the scheme provided in this embodiment, the power dissipated by the single solar cell with hot spot effect through heat conduction is: 3A*1 / 3*13.27V=13.27W (3 represents 3A current, 1 / 3 is 3 parallel sub-cell strings, and the current allocated to the cell with hot spot effect is 3A / 3=1A), which is less than 20% of the energy dissipated by the comparison scheme. At this time, the hot spot temperature is 76℃.

[0067] Under high current conditions, the photovoltaic module operates at a temperature of 45℃, with a voltage temperature rise coefficient of -0.35%. The reverse bias voltage across the individual solar cell exhibiting the hot spot effect is 27.86*(1-(45-25)*0.35%)*47 / 48-20=5.4V. At a reverse bias voltage of 10V, the maximum reverse current is 1.2A. Based on extreme conditions, the heat dissipated by the individual solar cell exhibiting the hot spot effect through heat conduction is 10V*1.2A=12W, less than 20% of the energy dissipated in the comparison scheme. At this point, the hot spot temperature is 71℃. Under extreme operating conditions of 85℃, the maximum operating point voltage of the photovoltaic module is 27.86*(1-(85-25)*0.35%)=22.0V. Therefore, even under extreme operating conditions of 85°C with medium to high irradiance, the operating voltage of the maximum power point of the photovoltaic module is still higher than the low voltage protection value of 20V set by the photovoltaic power optimizer, and it will not affect the maximum power tracking of the photovoltaic power generation unit by the photovoltaic power optimizer.

[0068] Combined with appendix Figure 9 As shown, the voltage Vpv between the positive and negative output terminals of the photovoltaic module is calculated using the following formula (1):

[0069] Vpv=Vmmp×(N-1)-Vbr Formula (1)

[0070] From formula (1), we can obtain: Vbr = Vmmp × (N-1) - Vpv Formula (2)

[0071] Where Vmmp represents the voltage across each cell in the photovoltaic module that has not experienced a hot spot effect;

[0072] N represents the total number of solar cells in the photovoltaic module;

[0073] N-1 represents the number of solar cells remaining in the photovoltaic module after removing one cell that has experienced a hot spot effect.

[0074] In summary, the maximum reverse bias voltage Vbrmax across the two ends of the cells in the battery string array where the hot spot effect occurs is calculated using the following formula (3):

[0075]

[0076] In formula (3), Vpw represents the peak power voltage of the photovoltaic module;

[0077] T This indicates the actual operating temperature of the photovoltaic module;

[0078] This indicates the operating temperature of the photovoltaic module under standard test conditions (STC), 25°C.

[0079] This represents the voltage-temperature rise coefficient of a photovoltaic module;

[0080] N This indicates the total number of solar cells in the photovoltaic module;

[0081] N- 1 represents the number of solar cells remaining in the photovoltaic module after removing the one solar cell that has experienced a hot spot effect;

[0082] This indicates the set input low voltage protection value.

[0083] The following combination Figure 11 and Figure 12 The principle of heat spot prevention in photovoltaic modules will be explained in more detail:

[0084] The 182-72-545W monocrystalline silicon photovoltaic module has the following specifications: Under standard operating conditions (STC stands for Standard Test Condition, meaning the module temperature is 25℃), the power output is 545W, the peak power voltage is 27.86V, the peak power current is 19.56A, the open-circuit voltage is 33.10V, and the short-circuit current is 20.88A.

[0085] The maximum operating point voltage temperature coefficient is -0.35% / ℃. This photovoltaic module is a half-cell photovoltaic module, also divided into 6 half-cell sub-cell string circuits. Every 3 half-cell string circuits are connected in parallel to form a solar cell string group. Two solar cell string groups are connected in series and then connected to the power optimizer through a connecting wire from the junction box. Figure 11As shown, the power optimizer of the photovoltaic power generation unit connected to the intelligent hot spot protection photovoltaic module is set with different input voltage protection values ​​according to different input currents. When the control unit determines that the input current of the power optimizer is less than or equal to the preset input current threshold of 3A, the input low voltage protection value of the power optimizer is set to the first limit value Vlvp1=14V. When the input current is greater than or equal to the input current threshold of 3A, the low voltage protection value of the power optimizer is set to Vlvp2=20V. When the solar cells of the photovoltaic module are working under consistent illumination conditions, no single solar cell suffers large mismatch loss due to shading. At this time, the voltage of the photovoltaic module at its maximum operating point is 27.86V. The maximum operating point voltage of the photovoltaic module at 85℃ = 27.86*(1+(85-25)*(-0.35%)) = 22.0V> Vlvp2. Therefore, even at the extremely high module temperature of 85℃, setting the low voltage protection value of the power optimizer will not affect its tracking of the maximum power point of the photovoltaic module.

[0086] And such Figure 12 As shown, when one of the solar cells of the photovoltaic module is shaded, its IV and PV curves will be significantly distorted compared to the curves when there is no shading, and its maximum operating point will also shift to the left to 16V.

[0087] At this time, since the power optimizer of the photovoltaic power generation unit connected to the intelligent hot spot protection photovoltaic module has different input voltage protection values ​​set according to its input current, when the control unit determines that the input current of the power optimizer is less than or equal to the preset input current threshold of 3A, the input low voltage protection value of the power optimizer is set to the first limit value Vlvp1=14V. When the input current is greater than or equal to the input current threshold of 3A, the low voltage protection value of the power optimizer is set to Vlvp2=20V. If the input current of the power optimizer is 2A, which is lower than the set current threshold of 3A, since the photovoltaic module has no risk of hot spot damage, a lower low voltage protection value Vlvp1=14V is set under the low power optimizer input current. Under the condition that the power optimizer protection value is set, the photovoltaic module can still operate at the maximum operating point of 16V, which improves the power generation output of the photovoltaic module. At this time, the problem that the maximum operating point voltage of the solar cell is lower than that under standard test conditions under low solar irradiance is also taken into account.

[0088] When the input current of the power optimizer is 4A, which is higher than the set current threshold of 3A, a higher low-voltage protection value Vlvp2=20V is set due to the greater risk of hot spot damage to the photovoltaic module at this time. When the power optimizer performs maximum power point tracking, the input voltage reaches 20V, and the controller of the power optimizer stops further reducing the input voltage and performs maximum power point tracking on the photovoltaic module. At this time, the controller makes the photovoltaic module operate at the low-voltage protection value of 20V of the power optimizer. Although the power optimizer cannot track the maximum operating point voltage of 16V of the photovoltaic module, the reverse bias voltage applied to the solar cell of the shaded solar cell is well limited to only Vbr=27.86V*(47 / 48)-20V=7.27V. The limitation of the reverse bias voltage of the shaded solar cell can limit the reverse current applied to it, completely preventing the destructive hot spot effect on the shaded solar cell, making the photovoltaic module a smart anti-hot spot photovoltaic module.

[0089] In this invention, the terms "photovoltaic power optimizer" and "power optimizer" are essentially the same.

[0090] It should be stated that the above-described specific embodiments are merely preferred embodiments of the present invention and the technical principles employed. Those skilled in the art should understand that various modifications, equivalent substitutions, and variations can be made to the present invention. However, such variations, as long as they do not depart from the spirit of the present invention, should be within the scope of protection of the present invention. Furthermore, some terminology used in this specification and claims is not limiting, but merely for ease of description.

Claims

1. A heat-spot-resistant photovoltaic module based on intelligent control of power optimizer input voltage, characterized in that, The first output terminal (101) of the first photovoltaic cell string power generation unit (10) and the second output terminal (201) of the second photovoltaic cell string power generation unit (20) in each photovoltaic module in the photovoltaic string are connected in series to a power optimizer (500). Each power optimizer (500) is equipped with a control unit. Each control unit presets a corresponding input current threshold for the connected power optimizer (500). When the control unit determines that the input current of the power optimizer (500) being configured is less than or equal to the preset input current threshold, it sets the input low voltage protection value of the power optimizer to a first limit value and controls the input voltage of the power optimizer to be greater than or equal to the first limit value. When it is determined that the input current of the power optimizer (500) is greater than the input current threshold, the input low voltage protection value of the power optimizer is set to a second limit value, and the input voltage of the power optimizer is controlled to be greater than or equal to the second limit value. The second limit value of the input low voltage protection value is higher than the first limit value. The voltage Vpv between the positive and negative output terminals of the photovoltaic module is calculated using the following formula (1): Vpv=Vmmp×(N-1)-Vbr Formula (1) From formula (1), we can obtain: Vbr = Vmmp × (N-1) - Vpv (Formula (2)) The maximum reverse bias voltage Vbrmax across the two ends of the cells in the battery string array where the hot spot effect occurs is calculated using the following formula (3): Vbrmax = Vpw × (1 - ( ) × ) × - Official (3) Where Vmmp represents the voltage across each cell in the photovoltaic module that has not experienced a hot spot effect; N This indicates the total number of solar cells in the photovoltaic module; N -1 indicates the number of solar cells remaining in the photovoltaic module after removing the one that has experienced a hot spot effect; Vbr represents the reverse bias voltage across the two ends of the cells in the battery string where the hot spot effect occurs; Vpw represents the peak power voltage of a photovoltaic module; This indicates the actual operating temperature of the photovoltaic module; This indicates the operating temperature of the photovoltaic module under standard testing conditions; This represents the voltage-temperature rise coefficient of a photovoltaic module; This indicates the set input low voltage protection value.

2. The anti-hotspot photovoltaic module based on intelligent control of power optimizer input voltage according to claim 1, characterized in that, The heat-spot-resistant photovoltaic module consists of a first photovoltaic cell string power generation unit (10) and a second photovoltaic cell string power generation unit (20). Each photovoltaic cell string power generation unit includes at least one first cell string group (100) and at least one second cell string group (200). Several first cell string groups (100) and second cell string groups (200) are connected in series to form the output terminal of the photovoltaic cell string power generation unit. The output terminal includes the positive output terminal and the negative output terminal of the photovoltaic cell string power generation unit, and the positive and negative output terminals of the output terminal are connected one-to-one to the positive and negative terminals of the input terminal of the output terminal. The first output terminal (101) in the first photovoltaic cell string power generation unit (10) and the second output terminal (201) of the second photovoltaic cell string power generation unit (20) are connected in series to the same power optimizer. The output terminals of each power optimizer are connected in series to form a photovoltaic string, and each power optimizer is equipped with a local control unit; the control unit has a preset threshold for the local current; the control unit is used to set the input low voltage protection value of the conversion circuit to a first limit value when the local current value does not exceed the threshold value, and to set the input low voltage protection value of the conversion circuit to a second limit value when the local current value exceeds the threshold value, and the control unit (22) is also used to control the input voltage of the power optimizer to be not lower than the set input low voltage protection value.

3. The anti-hotspot photovoltaic module based on intelligent control of power optimizer input voltage according to claim 2, characterized in that, The number of solar cells connected in series in the first photovoltaic cell string power generation unit (10) or the second photovoltaic cell string power generation unit (20) is in the range of 18-28 cells.

4. The heat-spot-resistant photovoltaic module based on intelligent control of power optimizer input voltage according to claim 1, characterized in that, The outputs of each power optimizer (500) in the photovoltaic string are connected in series with each other.

5. The anti-hotspot photovoltaic module based on intelligent control of power optimizer input voltage according to claim 1, characterized in that, The power optimizer includes a DC / DC conversion module and the control unit, wherein the DC / DC conversion module is coupled between the photovoltaic cell string power generation unit and the photovoltaic string.

6. The anti-hotspot photovoltaic module based on intelligent control of power optimizer input voltage according to claim 1, characterized in that, The power optimizer is a DC / DC conversion module equipped with a main control module (30). The DC / DC conversion module is a Buck type step-down converter, or a Boost type step-up converter, or a Boost-Buck type step-up converter. The main control module (30) includes a maximum power point tracking module (31) and a pulse width modulation module (32). The maximum power point tracking module (31) is used to obtain the electrical parameters of the input and output terminals of the DC / DC conversion module and process them to obtain the maximum power point. During the maximum power point tracking process of the maximum power point tracking module (31) on the first photovoltaic string power generation unit (10) and the second photovoltaic string power generation unit (20) connected in series, when the output voltage of the maximum power point tracking module (31), i.e. the output voltage of the first photovoltaic string power generation unit (10) and the second photovoltaic string power generation unit (20) connected in series, reaches the set input low voltage protection value, the control unit refuses to continue to adjust the input voltage of the first photovoltaic string power generation unit (10), which is the maximum power point tracking object of the maximum power point tracking module (31), downward. The pulse width modulation module is used to adjust the duty cycle of the power optimizer so that the output current of the power optimizers connected in series is consistent.

7. The heat-spot-resistant photovoltaic module based on intelligent control of power optimizer input voltage according to claim 1, characterized in that, The solar cells in the battery string are any one or more of PERC solar cells, TOPCON, HJT, and ABC high-efficiency solar cells.

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