A method for designing a series-parallel expansion type of photovoltaic module with extreme low temperature overvoltage protection

Abstract

This invention discloses a method for increasing the number of photovoltaic modules connected in series with extreme low-temperature overvoltage protection. The method includes: collecting photovoltaic module parameters and meteorological data of the photovoltaic power station location; and, based on the photovoltaic module parameters and meteorological data, calculating the maximum number of modules connected in series, ensuring that the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the photovoltaic cable and the maximum allowable input voltage of the inverter under extreme low temperatures. N 1 and N 2 ;calculate N = N 2 The benchmark cost per kilowatt-hour LCOE 0 Increase by the preset step size N The corresponding cost per kilowatt-hour is calculated by combining a temperature prediction model. LCOE 1 Iterative comparison LCOE 0 and LCOE 1 This invention outputs the number of photovoltaic (PV) modules connected in series when the levelized cost of electricity (LCOE) of a PV power plant is at its lowest. By allowing the inverter to shut down briefly under extremely low-probability events such as extreme temperatures, the invention achieves a greater number of PV modules connected in series with a controllable, minimal power generation loss, thereby significantly reducing the investment cost and LCOE of the PV power plant.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic power generation technology, and specifically to a method for increasing the series number of photovoltaic modules with extreme low temperature overvoltage protection. Background Technology

[0002] Driven by the clean energy strategy, photovoltaic (PV) power generation, as an important component of clean energy, has developed rapidly, with installed capacity repeatedly reaching new highs. It is expected that PV installed capacity will continue to grow significantly over the next few decades. Currently, PV power generation has entered the market-based trading stage. If PV projects cannot reduce costs and increase efficiency, it will inevitably severely restrict the development of PV projects and hinder the achievement of clean energy strategic goals.

[0003] The brackets, pile foundations, and combiner cables account for a significant portion of the overall investment in a photovoltaic (PV) power plant. Optimizing and increasing the number of PV modules connected in series can effectively reduce the workload of brackets, pile foundations, and combiner cables, decrease combiner cable losses, and save on the floor space occupied by PV modules. Currently, there are three main methods for calculating the number of PV modules connected in series: 1) the algorithm in the "Design Code for Photovoltaic Power Plants" (GB 50797-2012); 2) the algorithm in the "Modeling Guidelines for Photovoltaic Power Generation Systems" (GB / T 32826-2016); and 3) the algorithm in patent CN116545036B, "Method for Correcting the Number of PV Module Strings Based on Ambient Temperature and Solar Irradiance".

[0004] The algorithms mentioned above all share a common drawback: extreme low temperatures occur with low probability and short duration, and correspond to low solar irradiance. However, to avoid excessive open-circuit voltage of photovoltaic strings under extreme low temperatures, which could cause inverter shutdown and power generation losses, traditional algorithms are based on the principle that the open-circuit voltage of photovoltaic strings under extreme low temperatures should not exceed the maximum allowable input voltage of the inverter, and that the operating voltage of photovoltaic strings should be within the range of the inverter's MPPT voltage under all operating conditions. The maximum number of modules connected in series calculated in this way is relatively conservative, which greatly increases the amount of engineering work for pile foundations, supports, and cables, thereby increasing the cost per kilowatt-hour of photovoltaic power plants.

[0005] Therefore, there is an urgent need to provide a new design method for increasing the number of photovoltaic modules in series with extreme low temperature overvoltage protection. With the goal of minimizing the cost per kilowatt-hour, this method increases the number of photovoltaic modules in series by using inverter overvoltage shutdown protection in extreme low temperature environments, thereby reducing the amount of brackets, pile foundations and cables used. This avoids the dilemma of low probability of extreme low temperature occurrence and high cost of response, and achieves cost reduction and efficiency improvement for photovoltaic power plants. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the present invention aims to provide a design method for increasing the number of photovoltaic modules in series with extreme low temperature overvoltage protection. By allowing the inverter to shut down briefly under extremely low-probability events of extreme low temperature, a smaller amount of controllable power generation loss is exchanged for a larger number of photovoltaic modules in series, thereby reducing the amount of brackets, pile foundations and cables used, and lowering the investment cost and cost per kilowatt-hour of photovoltaic power plants.

[0007] To achieve the above objectives, the technical solution provided by this invention is: a photovoltaic module series number expansion design method with extreme low temperature overvoltage protection, comprising the following steps: Step 1: Collect the parameters of the photovoltaic modules used in the photovoltaic power station and the meteorological data of the location of the photovoltaic power station; Step 2: Based on the photovoltaic module parameters and the meteorological data, and taking into account that the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the photovoltaic cable under extreme low temperatures and that the operating voltage of the photovoltaic string is within the inverter's MPPT voltage range under all operating conditions, calculate the maximum number of modules connected in series. N 1 ; Step 3: Based on the photovoltaic module parameters and the meteorological data, and taking into account that the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the inverter under extreme low temperatures and that the operating voltage of the photovoltaic string is within the MPPT voltage range of the inverter under all operating conditions, calculate the maximum number of modules connected in series. N 2 ; Step 4: Based on the number of components connected in series N = N 2 As an initial series connection quantity, the annual power generation of the photovoltaic power station under the initial series connection quantity is calculated based on the photovoltaic module parameters and the meteorological data. E r and investment costs C Σ According to the annual power generation E r and the aforementioned investment costs C Σ Calculate the levelized cost of electricity (LCOE) of the photovoltaic power plant and use it as the benchmark LCOE. LCOE 0 ; Step 5: Follow the preset step size ΔN Increase the number of components connected in series N Based on the photovoltaic module parameters and the meteorological data, the minimum ambient temperature at which the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the inverter is calculated according to the relationship between the open-circuit voltage of the photovoltaic string and the ambient temperature. T min ; Step Six: Estimate the minimum ambient temperature based on the meteorological data and temperature prediction model. T min The probability and return period of occurrence are calculated based on the estimated probability and return period, the photovoltaic module parameters, and the meteorological data, when the ambient temperature is not lower than... T min The annual power generation of the photovoltaic power station mentioned at that time E r and investment costs C Σ According to the annual power generation E r and the aforementioned investment costs C Σ Calculate the levelized cost of electricity (LCOE) of the photovoltaic power station. LCOE 1 ; Step Seven: When LCOE 0 > LCOE 1 and N ≤ N 1 season LCOE 0 = LCOE 1 and return to step five for iterative calculation; when LCOE 0 ≤ LCOE 1 or N > N 1 When the iteration terminates and outputs, the iteration is terminated. N - ΔN This represents the number of modules connected in series when the cost per kilowatt-hour of a photovoltaic power plant is at its lowest.

[0008] Furthermore, in step one, the photovoltaic module parameters include at least the operating temperature of the photovoltaic module under standard test conditions. T ref Open-circuit voltage of photovoltaic modules under standard test conditions V ocref Temperature coefficient of open-circuit voltage of photovoltaic modules c Solar irradiance coefficient of photovoltaic modules b and rated power P max The meteorological data includes at least the solar irradiance at the location of the photovoltaic power station. S Extreme low temperatures that occur once every 30 years T L Winter hourly maximum irradiance F wmax And historical temperature data for the location of the photovoltaic power station. An extreme heat wave that occurs once every 30 years.T H As reference data, it is used to verify that the operating voltage of the photovoltaic string does not deviate from the lower limit of the inverter's MPPT voltage range under extreme high temperatures.

[0009] Furthermore, in step two, the maximum number of components connected in series... N 1 The number of cascaded components for any candidate component is calculated as follows: N Based on the negative correlation between the open-circuit voltage of the photovoltaic string and the ambient temperature, and according to the operating temperature of the photovoltaic module under standard test conditions... T ref The open-circuit voltage of the photovoltaic module V ocref The open-circuit voltage temperature coefficient of the photovoltaic module c The solar irradiance coefficient of the photovoltaic module b The solar irradiance S And the extreme low temperature that occurs once every 30 years T L Calculate the extreme low temperature T L The open-circuit voltage of the photovoltaic string described below V oc,L The N 1 For the V oc,L The maximum even number of the maximum allowable input voltage of the photovoltaic cable shall not exceed the maximum number of the specified input voltage.

[0010] Furthermore, in step three, the maximum number of components connected in series... N 2 The number of cascaded components for any candidate component is calculated as follows: N According to the above V oc,L The N 2 For the V oc,L The maximum allowable input voltage of the inverter shall not exceed the maximum even number of the inverter's maximum permissible input voltage; the maximum permissible input voltage of the photovoltaic cable is 1.2 times the rated voltage of the photovoltaic cable and is greater than the inverter's maximum permissible input voltage, therefore the... N 1 Greater than the N 2 .

[0011] Furthermore, the inverter is equipped with a voltage transformer, a current transformer, and a DC switch on its DC side. The inverter monitors the DC input voltage in real time. When the DC input voltage exceeds the inverter's maximum allowable input voltage, the DC switch is opened, and the inverter stops to prevent it from being damaged by breakdown. When the DC input voltage does not exceed the inverter's maximum allowable input voltage, the DC switch is closed, and the inverter operates normally.

[0012] Furthermore, in step five, the lowest ambient temperature T min The calculation is performed as follows: based on the negative correlation between the open-circuit voltage of the photovoltaic string and the ambient temperature, and according to the operating temperature of the photovoltaic module under standard test conditions. T ref The open-circuit voltage of the photovoltaic module V ocref The open-circuit voltage temperature coefficient of the photovoltaic module c The solar irradiance coefficient of the photovoltaic module b The solar irradiance S and the number of components connected in series. N Solve for a solution that makes the open-circuit voltage of the photovoltaic string equal to the maximum allowable input voltage of the inverter. V cmax The temperature at that time is taken as the lowest ambient temperature. T min ; with the number of components connected in series N According to the preset step size ΔN Increase, the minimum ambient temperature T min As it rises, the minimum ambient temperature... T min The probability of occurrence increases accordingly, and the lowest ambient temperature... T min The recurrence period is thus shortened; the preset step size ΔN The value is 2.

[0013] Furthermore, in step six, the minimum ambient temperature T min The probability of occurrence and the return period are estimated as follows: the historical temperature data are screened and preprocessed, the lowest winter temperature data is selected and missing and outlier values ​​are removed; the preprocessed temperature data is used as a sample, and the probability is estimated using a temperature prediction model, which is a generalized extreme value distribution model, a Gumbel distribution model, a Weibull distribution model, a Weibull survival model, or a Markov chain model; the return period is the reciprocal of the probability.

[0014] Furthermore, in step six, the annual power generation of the photovoltaic power station... E r The average annual on-grid power generation of the photovoltaic power station is calculated as follows: based on the photovoltaic module parameters and the meteorological data, without considering the power generation losses due to inverter shutdown at extreme low temperatures. E 0 Based on the historical temperature data, the lowest ambient temperature during the day was statistically analyzed. T min Duration of appearance H 1 According to the rated power P max The DC-side installed capacity of the photovoltaic power station is calculated based on the number of photovoltaic strings in the photovoltaic power station. P DC According to the above E 0 The above H 1 The maximum hourly irradiance during winter F wmax Irradiance under standard test conditions F 0 The above P DC And the number of components connected in series is N The overall efficiency coefficient at that time K N The annual power generation of the photovoltaic power station was calculated. E r The comprehensive efficiency coefficient mentioned above K N The following factors are taken into account: as the number of components connected in series... N The increase in power generation loss is due to the inverter shutdown at extreme low temperatures, the increased duration of the photovoltaic string operating voltage within the inverter MPPT voltage range during low light periods in the early morning and evening, and the decrease in cable loss of the photovoltaic string.

[0015] Furthermore, in steps four and six, the investment cost of the photovoltaic power station... C Σ The investment cost is calculated as follows: C Σ Including photovoltaic field costs C area and the cost of booster stations C station The cost of the booster station C station Regardless of the number of components connected in series N The impact of the photovoltaic field cost Carea The number of components connected in series N The cost per kilowatt-hour of the photovoltaic power station decreases as the cost increases. LCOE Based on the aforementioned investment cost C Σ The annual power generation E r Discount rate i Evaluation cycle of photovoltaic power generation system L Value-added tax deduction for projects I t Residual value of photovoltaic power plants V R and the n Annual operating costs M n The calculation yielded that the first n Annual operating costs include maintenance fees, insurance premiums, material costs, labor costs, and ancillary service fees; the benchmark cost per kilowatt-hour mentioned in step four. LCOE 0 Number of components connected in series N = N 2 The cost per kilowatt-hour of the photovoltaic power station mentioned in step six, and the cost per kilowatt-hour mentioned in step six. LCOE 1 The number of components connected in series N According to the preset step size ΔN The cost per kilowatt-hour of the photovoltaic power station after the addition.

[0016] Furthermore, in step seven, when LCOE 0 > LCOE 1 and N ≤ N 1 When, it indicates the number of components connected in series. N The increase can reduce the cost per kilowatt-hour of the photovoltaic power station, thus making LCOE 0 = LCOE 1 And return to step five to continue the iteration; when LCOE 0 ≤ LCOE 1 When, it indicates the number of components connected in series. N If further increases in efficiency cannot reduce the cost per kilowatt-hour of the photovoltaic power plant, then the iteration terminates; when... N > N 1 At that time, the number of components connected in series exceeded the maximum allowable input voltage constraint of the photovoltaic cable. N 1If the iteration terminates, the iteration ends; the number of components connected in series is output after step seven terminates the iteration. N - ΔN Located in the N 2 To the above N 1 Within the range, and ensure that the inverter performs maximum power tracking on the output power of the photovoltaic string when it is working normally.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention overcomes the limitation of traditional methods where the maximum number of photovoltaic modules connected in series is entirely constrained by the maximum allowable input voltage of the inverter under extreme low-probability events such as short-term shutdown of the inverter in extreme low-temperature conditions. By allowing the inverter to trigger overvoltage protection during short-term shutdown of the photovoltaic power plant under extremely low-probability events, this invention finds the optimal number of modules connected in series between the maximum allowable input voltage of the photovoltaic cable and the maximum allowable input voltage of the inverter. This allows for a larger number of photovoltaic modules connected in series with a controllable small amount of power generation loss, thereby significantly saving the amount of cables, supports, and pile foundations used, and reducing the investment cost and cost per kilowatt-hour of the photovoltaic power plant.

[0018] Based on the goal of minimizing the cost per kilowatt-hour, this invention comprehensively considers the power generation loss caused by inverter shutdown under extreme low temperatures, the power generation benefits brought by the increased duration of photovoltaic string operating voltage within the inverter MPPT voltage range during low light periods, and the power generation benefits brought by the reduction of photovoltaic string cable losses, thus ensuring that the obtained number of modules connected in series has the optimal economic efficiency.

[0019] This invention increases the number of photovoltaic modules connected in series, saves the floor space occupied by photovoltaic modules, reduces the amount of construction work such as piling, bracket installation, and wiring, improves construction efficiency, and is conducive to the rapid installation and grid connection of photovoltaic projects. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating a photovoltaic module series number expansion design method for extreme low temperature overvoltage protection according to the present invention. Figure 2 This is a schematic diagram of the DC-side protection circuit topology of an inverter in one embodiment of the present invention; Figure 3 This is a schematic diagram of the extreme low temperature overvoltage protection control strategy of the inverter in one embodiment of the present invention. Detailed Implementation

[0021] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0022] like Figure 1 As shown in the figure, the photovoltaic module series number expansion design method with extreme low temperature overvoltage protection provided by the present invention includes the following steps: Step 1: Collect the parameters of the photovoltaic modules used in the photovoltaic power station and the meteorological data of the location of the photovoltaic power station.

[0023] In this embodiment, the parameters of the photovoltaic modules used in the photovoltaic power station are shown in Table 1. These parameters can be obtained from the product manuals provided by the photovoltaic module manufacturers. The meteorological data of the location of the photovoltaic power station are shown in Table 2. This meteorological data can be obtained from historical records of the meteorological station in the location of the photovoltaic power station or from a professional meteorological database. In Table 1, the standard test condition of 25℃ in the "Operating Temperature Range" corresponds to the operating temperature of the photovoltaic modules under the standard test conditions described in this invention. T ref The "Open Circuit Voltage (Voc)" in Table 1 corresponds to the open circuit voltage of the photovoltaic module under the standard test conditions described in this invention. V ocref The "temperature coefficient of open-circuit voltage (Voc)" corresponds to the open-circuit voltage temperature coefficient of the photovoltaic module described in this invention. c "Maximum power (Pmax)" corresponds to the rated power described in this invention. P max The solar irradiance coefficient of the photovoltaic module b Provided separately by the photovoltaic module manufacturer; the "extreme minimum temperature" in Table 2 corresponds to the 30-year return period extreme low temperature described in this invention. T L "Extreme maximum temperature" corresponds to the extreme high temperature that occurs once every 30 years as described in this invention. T H The solar irradiance at the location of the photovoltaic power station S Winter hourly maximum irradiance F wmax Historical temperature data are obtained separately from meteorological stations or professional meteorological databases at the location of the photovoltaic power station. The photovoltaic module parameters and meteorological data mentioned above are used for numerical calculations in the formulas introduced in steps two through six.

[0024] Step 2: Based on the photovoltaic module parameters and the meteorological data, and taking into account that the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the photovoltaic cable under extreme low temperatures and that the operating voltage of the photovoltaic string is within the inverter's MPPT voltage range under all operating conditions, calculate the maximum number of modules connected in series. N 1 .

[0025] In this embodiment, the maximum allowable input voltage of the photovoltaic cable is taken as 1.2 times the rated voltage of the photovoltaic cable. That is, the photovoltaic cable is selected based on 1.2 times the rated voltage during design to reserve a certain voltage margin. Since the maximum allowable input voltage of the photovoltaic cable is greater than the maximum allowable input voltage of the inverter, the maximum number of modules in series calculated in step two is... N 1 Greater than the maximum number of components connected in series as calculated in step three. N 2 The calculated maximum number of components connected in series. N 1 Choose the largest even number that satisfies the principle in step two.

[0026] Step 3: Based on the photovoltaic module parameters and the meteorological data, and taking into account that the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the inverter under extreme low temperatures and that the operating voltage of the photovoltaic string is within the MPPT voltage range of the inverter under all operating conditions, calculate the maximum number of modules connected in series. N 2 .

[0027] In this embodiment, the maximum number of components connected in series is calculated. N 2 The largest even number that satisfies the principle in step three is selected. Maximum number of components connected in series. N 2 The number of series connections obtained by the traditional component series connection design method is the number of components connected in series that is completely constrained by the maximum allowable input voltage of the inverter under extreme low temperatures.

[0028] like Figure 2 As shown, the DC side of the inverter is equipped with a voltage transformer, a current transformer, and a DC switch. The inverter monitors the DC input voltage in real time. When the DC input voltage exceeds the inverter's maximum allowable input voltage, the DC switch opens, and the inverter shuts down to prevent damage from breakdown. When the DC input voltage does not exceed the inverter's maximum allowable input voltage, the DC switch closes, and the inverter operates normally. Figure 3As shown, the control strategy of this embodiment of the invention is as follows: when the open-circuit voltage of the photovoltaic string exceeds the maximum allowable input voltage of the inverter due to a low probability event of extreme low temperature, the inverter is temporarily shut down through the overvoltage protection mechanism on the DC side. After the extreme low temperature event ends, the inverter automatically resumes normal operation. In this way, the inverter is prevented from being damaged by breakdown, and only a very small portion of the power generation is lost.

[0029] Step 4: Based on the number of components connected in series N = N 2 As an initial series connection quantity, the annual power generation of the photovoltaic power station under the initial series connection quantity is calculated based on the photovoltaic module parameters and the meteorological data. E r and investment costs C Σ According to the annual power generation E r and the aforementioned investment costs C Σ Calculate the levelized cost of electricity (LCOE) of the photovoltaic power plant and use it as the benchmark LCOE. LCOE 0 .

[0030] The cost per kilowatt-hour of photovoltaic power plants LCOE Based on the annual power generation of photovoltaic power plants E r And investment cost calculation. Cost per kilowatt-hour. LCOE The specific calculations will be explained in detail in step six.

[0031] Step 5: Follow the preset step size ΔN Increase the number of components connected in series N , that is to say N = N + ΔN Based on the photovoltaic module parameters and the meteorological data, the minimum ambient temperature at which the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the inverter is calculated according to the relationship between the open-circuit voltage of the photovoltaic string and the ambient temperature. T min .

[0032] In this embodiment, the preset step size ΔN The value is set to 2 to ensure the number of components connected in series after each iteration. N It remains an even number. The open-circuit voltage of the photovoltaic string exhibits a negative correlation with ambient temperature, which can be described by the following formula: (1) In equation (1), T min The lowest ambient temperature at which the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the inverter. Tref The operating temperature of photovoltaic modules under standard test conditions. V cmax This is the maximum allowable input voltage of the inverter. V ocref The open-circuit voltage of the photovoltaic module under standard test conditions. c The open-circuit voltage temperature coefficient of a photovoltaic module. S This represents the actual solar irradiance received by the photovoltaic module. S ref Solar irradiance under standard test conditions. b The solar irradiance coefficient of a photovoltaic module. e It is a natural constant. N This represents the number of components connected in series.

[0033] As can be seen from formula (1), with the increase in the number of components connected in series... N The increase in ambient minimum temperature T min Increasingly higher, that is, as the number of components connected in series increases. N The increase in the ambient temperature at which the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the inverter. T min As it rises, the lowest ambient temperature T min The probability of occurrence increases accordingly, and the lowest ambient temperature T min The recurrence period is shortened accordingly. It is worth noting that, in addition to formula (1), the relationship between the open-circuit voltage of the photovoltaic string and the ambient temperature, as well as the calculation of the maximum number of modules connected in series, can also be obtained using the calculation methods disclosed in the "Design Code for Photovoltaic Power Stations" (GB 50797-2012) and patent CN116545036B. From formula (1), it can also be deduced that: given the ambient temperature, the corresponding open-circuit voltage of the photovoltaic string can be calculated, which is... V oc,L Calculation method (taking ambient temperature equal to) T L hour).

[0034] Step Six: Estimate the minimum ambient temperature based on the meteorological data and temperature prediction model. T min The probability and return period of occurrence are calculated based on the estimated probability and return period, the photovoltaic module parameters, and the meteorological data, when the ambient temperature is not lower than... T min The annual power generation of the photovoltaic power station mentioned at that time E r and investment costs C Σ According to the annual power generation Er and the aforementioned investment costs C Σ Calculate the levelized cost of electricity (LCOE) of the photovoltaic power station. LCOE 1 .

[0035] Temperature prediction models, combining meteorological data from the location of photovoltaic power plants, and after filtering and preprocessing historical temperature data, can estimate the minimum ambient temperature using generalized extreme value distribution models, Gumbel distribution models, Weibull distribution models, Weibull survival models, or Markov chain models. T min The probability of occurrence and recurrence period. This embodiment uses the Generalized Extreme Value (GEV) distribution model, whose cumulative distribution function expression is as follows: (2) In equation (2), F The cumulative distribution function of the generalized extreme value distribution. x For random variables, μ For position parameters, σ For scale parameters, ξ These are the shape parameters, and the three parameters were obtained through maximum likelihood estimation using historical temperature data. The lowest ambient temperature... T min The probability of occurrence can be expressed as follows: (3) In equation (3), P ( x ≤ T min The ambient temperature does not exceed T min Probability of occurrence. Lowest ambient temperature. T min recurrence period R It can be represented as follows: (4) In equation (4), The lowest ambient temperature T min The recurrence period, in years, characterizes the lowest ambient temperature. T min The time interval during which an event occurs on average once within a certain period. Recurrence period. R The larger the value, the lower the ambient temperature. T min The lower the probability of occurrence.

[0036] When the ambient temperature is not lower than Tmin When the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the inverter, the inverter operates normally; when the ambient temperature is lower than... T min At times, the open-circuit voltage of the photovoltaic string may exceed the maximum allowable input voltage of the inverter. The DC switch will then disconnect, and the inverter will shut down to prevent damage from breakdown and potential power generation loss. The annual power generation of the photovoltaic power station... E r It can be calculated based on the following formula: (5) In equation (5), E r This refers to the average annual on-grid electricity generated by the photovoltaic power plant, specifically the average annual on-grid electricity generated by the photovoltaic power plant after considering the power generation losses due to inverter shutdowns under extreme low temperatures. E 0 The average annual on-grid power generation of a photovoltaic power plant is calculated without considering the losses caused by inverter shutdowns at extreme low temperatures (the standard method is provided in the "Design Code for Photovoltaic Power Plants" GB 50797). H 1 The lowest daytime ambient temperature was obtained based on historical temperature data of the photovoltaic power station location. T min Duration of appearance F wmax The maximum hourly irradiance at the location of the photovoltaic power station during winter. F 0 Irradiance under standard test conditions. P DC For the DC side installed capacity of photovoltaic power plants, K N The number of components connected in series is N The overall efficiency coefficient at that time. The power loss calculated according to formula (5) is the maximum possible power loss of the photovoltaic power station. With the number of modules connected in series... N The increase in efficiency is influenced by the following factors: increased power generation losses due to inverter shutdown caused by extreme low temperatures; increased duration of photovoltaic string operating voltage within the inverter's MPPT voltage range during low light periods in the early morning and evening; and reduced cable losses of the photovoltaic strings. These factors can be comprehensively factored into the overall efficiency coefficient. K N middle.

[0037] Investment cost of photovoltaic power plants C Σ Including photovoltaic field costs C area and the cost of booster stations C station , represented as: (6) In equation (6), C Σ The investment cost of a photovoltaic power station, C area For the cost of photovoltaic field, C station Cost of the booster station. (Booster station cost) C station Regardless of the number of components connected in series N Impact; Cost of photovoltaic power plant C area As the number of components connected in series N The decrease is due to the increase in the number of components connected in series. N When the number of photovoltaic strings, the number of combiner devices, and the amount of DC side cables required for a photovoltaic power station are all reduced accordingly, thereby reducing the equipment procurement, installation, and construction costs of the photovoltaic field.

[0038] The cost per kilowatt-hour of photovoltaic power plants LCOE It can be calculated based on the following formula: (7) In equation (7), LCOE The cost per kilowatt-hour of a photovoltaic power plant; C Σ The investment cost of a photovoltaic power plant; I t Value-added tax deduction for the project; M n For the first n Annual operating costs; V R The residual value of the photovoltaic power plant; E r The average annual on-grid electricity of the photovoltaic power station is calculated according to formula (5); i The discount rate; n The number of years the system has been in operation; L The evaluation period for photovoltaic power generation systems is defined by equation (7). The cost per kilowatt-hour of a photovoltaic power station can be calculated using different numbers of modules connected in series.

[0039] Step Seven: When LCOE 0 > LCOE 1 and N ≤ N 1 season LCOE 0 = LCOE 1 and return to step five for iterative calculation; when LCOE 0 ≤ LCOE 1 orN > N 1 When the iteration terminates and outputs, the iteration is terminated. N - ΔN This represents the number of modules connected in series when the cost per kilowatt-hour of a photovoltaic power plant is at its lowest.

[0040] The iterative process in step seven is essentially about the maximum number of components connected in series. N 2 to N 1 Within a certain range, find the number of modules connected in series that minimizes the levelized cost of electricity (LCOE) of a photovoltaic power plant. LCOE 0 > LCOE 1 and N ≤ N 1 When this occurs, it indicates that the levelized cost of electricity (LCOE) of the photovoltaic power plant is lower than that of the previous iteration for the current number of components connected in series. LCOE 0 = LCOE 1 And return to step five to continue iterating; when 0 ≤ LCOE 1 When the current iteration indicates that the levelized cost of electricity (LCOE) of the photovoltaic power plant is no lower than that of the previous iteration under the current number of modules connected in series, meaning that further increasing the number of modules connected in series can no longer reduce the LCOE, the iteration terminates; when N > N 1 At that time, the number of modules connected in series exceeded the maximum number of modules connected in series under the constraint of the maximum allowable input voltage of photovoltaic cables. N 1 The iteration terminates. The output after the iteration terminates is the number of components connected in series. N - LCOE This refers to the number of modules connected in series when the cost per kilowatt-hour of a photovoltaic power plant is at its lowest. This number is located in... N 2 to N 1 Within the range, and ensure that the inverter performs maximum power tracking on the output power of the photovoltaic string when it is working normally.

[0041] The application effect of this invention is illustrated below with a specific embodiment. This photovoltaic power station project has an AC side installed capacity of 100MW, developed in 2022, and a DC side installed capacity of 135.0728MWp. The inverter used in the photovoltaic power station has a maximum allowable input voltage of 1500V, a typical 1500V inverter MPPT range of approximately 875~1500V, and an operating temperature range of -40℃ to 60℃. The main parameters of the photovoltaic modules used in the photovoltaic power station are shown in Table 1; the meteorological data for the location of the photovoltaic power station are shown in Table 2.

[0042] According to the standards "Cables for Photovoltaic Systems with Rated Voltage of 1.5 kV DC" (IEC 62930-2017) and "Cables for Photovoltaic Power Generation Systems" (NB / T 42073-2016), the maximum permissible input voltage of the photovoltaic-specific cable is 1.2 times its rated voltage. For a 1500V DC system, the maximum permissible input voltage of the photovoltaic-specific cable can reach 1800V. However, even after correction based on the negative correlation between insulation material and temperature, the maximum permissible input voltage of the inverter is unlikely to exceed 1600V. Therefore, the maximum number of modules connected in series as calculated in step two is... N 1 =36 is greater than the maximum number of components connected in series as calculated in step three. N 2 =30. Furthermore, photovoltaic modules with a maximum system voltage of 2000V have been developed, even with the maximum number of modules connected in series. N 1 The photovoltaic modules will not be damaged even when the open-circuit voltage of the photovoltaic string reaches 1800V.

[0043] Table 1 Main parameters of photovoltaic modules Table 2 Meteorological data of the photovoltaic power station location The calculations are performed according to the algorithm proposed in this invention, and the results of each step are as follows: The maximum number of components connected in series is calculated in step two. N 1 =36; The maximum number of components connected in series is calculated from step three. N 2 =30; in step four, with N 2 =30 was used as the initial number of components connected in series to calculate the baseline cost per kilowatt-hour. ΔN 0 =0.37361 yuan / kWh; in step five, follow the preset step size. LCOE N =2 Increase the number of components connected in series NDifferent results were obtained in sequence. N The lowest ambient temperature when the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the inverter. T min As shown in Table 3.

[0044] Table 3. Minimum ambient temperature for different numbers of components connected in series As shown in Table 3, with the increase in the number of components connected in series... N The minimum ambient temperature at which the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the inverter. T min The voltage subsequently increased, verifying the negative correlation between the open-circuit voltage of the photovoltaic string and the ambient temperature. Step six involves estimating the minimum ambient temperature based on a temperature prediction model. T min The probability and recurrence period of occurrence are used to calculate the levelized cost of electricity (LCOE) of a photovoltaic power plant, taking into account annual power generation and investment costs. Δ 1 Step 7: Iterative Comparison [[ID=�7]]LCOE 0 and LCOE 1 The complete iterative process and calculation results are shown in Table 4.

[0045] Table 4 Iterative Calculation Process As shown in Table 4, when the number of components connected in series... N Increasing the number of modules in series from 30 to 32, although the inverter will shut down for protection when the ambient temperature is below -20.6℃, resulting in a loss of some power generation, will increase the duration for which the photovoltaic string operating voltage remains within the inverter's MPPT voltage range during low-light periods in the early morning and evening, and will also reduce cable losses in the photovoltaic string. Therefore, the final average annual grid-connected power generation of the photovoltaic power plant will increase rather than decrease. Furthermore, the number of modules connected in series... N When the cost of photovoltaic power station was increased from 30 to 32, the construction cost was reduced by 9.4956 million yuan, and the cost per kilowatt-hour was reduced. LCOE This represents a reduction of 0.01737 yuan / kWh, equivalent to a total reduction of 57.448 million yuan in power generation costs over 25 years, demonstrating significant social and economic benefits. (The text abruptly shifts to a seemingly unrelated topic: "When the number of modules connected in series...") N When it further increases to 34, the lowest ambient temperature T min =2.8℃ is already higher than the common operating temperature. The power generation loss caused by inverter shutdown due to extreme low temperature increases sharply, and the cost per kilowatt-hour... LCOE Instead, the value increases, so step seven terminates the iteration and outputs the result. N - LCOE ΔN=34-2=32 is the number of modules connected in series when the cost per kilowatt-hour of this photovoltaic power station is at its lowest. This number is located at the maximum number of modules connected in series. N 2 =30 to N 1 The range is 36. This photovoltaic power station project is ultimately designed with 32 modules connected in series.

[0046] This invention fully utilizes the characteristics of low probability and short duration of extreme low temperatures, resulting in minimal power generation loss after curtailment. It increases the number of photovoltaic modules connected in series, significantly reducing the amount of engineering work required for cables, supports, and pile foundations, thereby lowering the levelized cost of electricity (LCOE) of photovoltaic power plants. Furthermore, by increasing the number of photovoltaic modules connected in series, this invention also saves land area, significantly reducing the amount of construction work such as piling, support installation, and wiring, improving construction efficiency, and facilitating the rapid installation and grid connection of photovoltaic projects. It is worth noting that this invention is applicable to scenarios with extremely low temperatures; when the extreme low temperatures are high, increasing the number of modules connected in series will greatly increase power generation losses caused by overvoltage protection at low temperatures, which is detrimental to reducing the overall LCOE.

[0047] Contents not described in detail in this specification are existing technologies known to those skilled in the art. The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An extreme low temperature overvoltage protected photovoltaic module string multiplication type design method, characterized by, Includes the following steps: Step 1: Collect the parameters of the photovoltaic modules used in the photovoltaic power station and the meteorological data of the location of the photovoltaic power station; Step 2: Based on the photovoltaic module parameters and the meteorological data, and taking into account that the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the photovoltaic cable under extreme low temperatures and that the operating voltage of the photovoltaic string is within the inverter's MPPT voltage range under all operating conditions, calculate the maximum number of modules connected in series. N 1 ; Step 3: Based on the photovoltaic module parameters and the meteorological data, and taking into account that the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the inverter under extreme low temperatures and that the operating voltage of the photovoltaic string is within the MPPT voltage range of the inverter under all operating conditions, calculate the maximum number of modules connected in series. N 2 ; Step 4: Based on the number of components connected in series N = N 2 As an initial series connection quantity, the annual power generation of the photovoltaic power station under the initial series connection quantity is calculated based on the photovoltaic module parameters and the meteorological data. E r and investment costs C Σ According to the annual power generation E r and the aforementioned investment costs C Σ Calculate the levelized cost of electricity (LCOE) of the photovoltaic power plant and use it as the benchmark LCOE. LCOE 0 ; Step 5: Follow the preset step size ΔN Increase the number of components connected in series N Based on the photovoltaic module parameters and the meteorological data, the minimum ambient temperature at which the open-circuit voltage of the photovoltaic string does not exceed the maximum allowable input voltage of the inverter is calculated according to the relationship between the open-circuit voltage of the photovoltaic string and the ambient temperature. T min ; Step Six: Estimate the minimum ambient temperature based on the meteorological data and temperature prediction model. T min The probability and return period of occurrence are calculated based on the estimated probability and return period, the photovoltaic module parameters, and the meteorological data, when the ambient temperature is not lower than... T min The annual power generation of the photovoltaic power station mentioned at that time E r and investment costs C Σ According to the annual power generation E r and the aforementioned investment costs C Σ Calculate the levelized cost of electricity (LCOE) of the photovoltaic power station. LCOE 1 ; Step Seven: When LCOE 0 > LCOE 1 and N ≤ N 1 season LCOE 0 = LCOE 1 Then return to the iterative calculation in step five; when LCOE 0 ≤ LCOE 1 or N > N 1 When the iteration terminates and outputs, the iteration is terminated. N - ΔN This represents the number of modules connected in series when the cost per kilowatt-hour of a photovoltaic power plant is at its lowest.

2. The photovoltaic module series number expansion design method with extreme low temperature overvoltage protection according to claim 1, characterized in that, In step one, the photovoltaic module parameters include at least the operating temperature of the photovoltaic module under standard test conditions. T ref Open-circuit voltage of photovoltaic modules under standard test conditions V ocref Temperature coefficient of open-circuit voltage of photovoltaic modules c Solar irradiance coefficient of photovoltaic modules b and rated power P max The meteorological data includes at least the solar irradiance at the location of the photovoltaic power station. S Extreme low temperatures that occur once every 30 years T L Winter hourly maximum irradiance F wmax And historical temperature data of the location of the photovoltaic power station.

3. The photovoltaic module series number expansion design method with extreme low temperature overvoltage protection according to claim 2, characterized in that, In step two, the maximum number of components connected in series N 1 The number of cascaded components for any candidate component is calculated as follows: N Based on the negative correlation between the open-circuit voltage of the photovoltaic string and the ambient temperature, and according to the operating temperature of the photovoltaic module under standard test conditions... T ref The open-circuit voltage of the photovoltaic module V ocref The open-circuit voltage temperature coefficient of the photovoltaic module c The solar irradiance coefficient of the photovoltaic module b The solar irradiance S And the extreme low temperature that occurs once every 30 years T L Calculate the extreme low temperature T L The open-circuit voltage of the photovoltaic string described below V oc,L The N 1 For the V oc,L The maximum even number of the maximum allowable input voltage of the photovoltaic cable shall not exceed the maximum number of the specified input voltage.

4. The photovoltaic module series number expansion design method with extreme low temperature overvoltage protection according to claim 3, characterized in that, In step three, the maximum number of components connected in series N 2 The number of cascaded components for any candidate component is calculated as follows: N According to the above V oc,L The N 2 For the V oc,L The maximum allowable input voltage of the inverter shall not exceed the maximum even number of the inverter's maximum permissible input voltage; the maximum permissible input voltage of the photovoltaic cable is 1.2 times the rated voltage of the photovoltaic cable and is greater than the inverter's maximum permissible input voltage, therefore the... N 1 Greater than the N 2 .

5. The photovoltaic module series number expansion design method for extreme low temperature overvoltage protection according to claim 1, characterized in that, The inverter is equipped with a voltage transformer, a current transformer, and a DC switch on its DC side. The inverter monitors the DC input voltage in real time. When the DC input voltage exceeds the inverter's maximum allowable input voltage, the DC switch is opened, and the inverter stops to prevent it from being damaged by breakdown. When the DC input voltage does not exceed the inverter's maximum allowable input voltage, the DC switch is closed, and the inverter operates normally.

6. The photovoltaic module series number expansion design method for extreme low temperature overvoltage protection according to claim 3, characterized in that, In step five, the minimum ambient temperature T min The calculation is performed as follows: based on the negative correlation between the open-circuit voltage of the photovoltaic string and the ambient temperature, and according to the operating temperature of the photovoltaic module under standard test conditions. T ref The open-circuit voltage of the photovoltaic module V ocref The open-circuit voltage temperature coefficient of the photovoltaic module c The solar irradiance coefficient of the photovoltaic module b The solar irradiance S and the number of components connected in series. N Solve for a solution that makes the open-circuit voltage of the photovoltaic string equal to the maximum allowable input voltage of the inverter. V cmax The temperature at that time is taken as the lowest ambient temperature. T min ; with the number of components connected in series N According to the preset step size ΔN Increase, the minimum ambient temperature T min As it rises, the minimum ambient temperature... T min The probability of occurrence increases accordingly, and the lowest ambient temperature... T min The recurrence period is thus shortened; the preset step size ΔN The value is 2.

7. The photovoltaic module series number expansion design method for extreme low temperature overvoltage protection according to claim 6, characterized in that, In step six, the minimum ambient temperature T min The probability of occurrence and the return period are estimated as follows: the historical temperature data are screened and preprocessed, the lowest winter temperature data is selected and missing and outlier values ​​are removed; the preprocessed temperature data is used as a sample, and the probability is estimated using a temperature prediction model, which is a generalized extreme value distribution model, a Gumbel distribution model, a Weibull distribution model, a Weibull survival model, or a Markov chain model; the return period is the reciprocal of the probability.

8. The photovoltaic module series number expansion design method for extreme low temperature overvoltage protection according to claim 7, characterized in that, In step six, the annual power generation of the photovoltaic power station E r The average annual on-grid power generation of the photovoltaic power station is calculated as follows: based on the photovoltaic module parameters and the meteorological data, without considering the power generation losses due to inverter shutdown at extreme low temperatures. E 0 ; Based on the historical temperature data, the lowest ambient temperature during the day was statistically analyzed. T min Duration of appearance H 1 According to the rated power P max The DC-side installed capacity of the photovoltaic power station is calculated based on the number of photovoltaic strings in the photovoltaic power station. P DC According to the above E 0 The above H 1 The maximum hourly irradiance during winter F wmax Irradiance under standard test conditions F 0 The above P DC And the number of components connected in series is N The overall efficiency coefficient at that time K N The annual power generation of the photovoltaic power station was calculated. E r The comprehensive efficiency coefficient mentioned above K N The following factors are taken into account: as the number of components connected in series... N The increase in power generation loss is due to the inverter shutdown at extreme low temperatures, the increased duration of the photovoltaic string operating voltage within the inverter MPPT voltage range during low light periods in the early morning and evening, and the decrease in cable loss of the photovoltaic string.

9. The photovoltaic module series number expansion design method with extreme low temperature overvoltage protection according to claim 8, characterized in that, In steps four and six, the investment cost of the photovoltaic power station C Σ The investment cost is calculated as follows: C Σ Including photovoltaic field costs C area and the cost of booster stations C station The cost of the booster station C station Regardless of the number of components connected in series N The impact of the photovoltaic field cost C area The number of components connected in series N The cost per kilowatt-hour of the photovoltaic power station decreases as the cost increases. LCOE Based on the aforementioned investment cost C Σ The annual power generation E r Discount rate i Evaluation cycle of photovoltaic power generation system L Value-added tax deduction for projects I t Residual value of photovoltaic power plants V R and the n Annual operating costs M n The calculation yielded that the first n Annual operating costs include maintenance fees, insurance premiums, material costs, labor costs, and ancillary service fees; the benchmark cost per kilowatt-hour mentioned in step four. LCOE 0 Number of components connected in series N = N 2 The cost per kilowatt-hour of the photovoltaic power station mentioned in step six, and the cost per kilowatt-hour mentioned in step six. LCOE 1 The number of components connected in series N According to the preset step size ΔN The cost per kilowatt-hour of the photovoltaic power station after the addition.

10. The photovoltaic module series number expansion design method with extreme low temperature overvoltage protection according to claim 9, characterized in that, In step seven, when LCOE 0 > LCOE 1 and N ≤ N 1 When, it indicates the number of components connected in series. N The increase can reduce the cost per kilowatt-hour of the photovoltaic power station, thus making LCOE 0 = LCOE 1 And return to step five to continue the iteration; when LCOE 0 ≤ LCOE 1 When, it indicates the number of components connected in series. N If further increases in efficiency cannot reduce the cost per kilowatt-hour of the photovoltaic power plant, then the iteration terminates; when... N > N 1 At that time, the number of components connected in series exceeded the maximum allowable input voltage constraint of the photovoltaic cable. N 1 If the iteration terminates, the iteration ends; the number of components connected in series is output after step seven terminates the iteration. N - ΔN Located in the N 2 To the above N 1 Within the range, and ensure that the inverter performs maximum power tracking on the output power of the photovoltaic string when it is working normally.

Images