Automatic analysis method for low voltage ride through test result of photovoltaic inverter

Abstract

The invention relates to the technical field of power system automation, and provides a photovoltaic inverter low-voltage ride-through test result automatic analysis method, which comprises the following steps: reading low-voltage ride-through test data of a photovoltaic inverter, firstly judging whether no-load test data is qualified, and further judging whether load test data is offline; if the load test data is not offline, classifying the test data into a three-phase fault, a two-phase fault and a single-phase fault according to fault types, further calculating the voltage drop depth, the drop duration, the reactive current response time, the reactive current duration, the reactive current exit time and the active power recovery rate, and if the calculation result meets the standard requirement, determining that the test data is offline. And if not, automatically storing the test waveform and the calculation result in word, and otherwise, outputting that the test waveform and the calculation result are unqualified. The method and the system do not depend on manual identification, automatically and quickly calculate the low-voltage ride-through test result of the photovoltaic inverter in batches, automatically store the test waveform and the calculation result in the word document, and are simple to implement and high in accuracy.

Description

Technical Field

[0001] The invention relates to the technical field of power system automation, and in particular to an automatic analysis method for low voltage ride-through test results of a photovoltaic inverter. Background Art

[0002] With the explosive growth of new energy, in order to ensure the stable operation of the power grid, standards such as GB / T 19964-2012 "Technical Regulations for Access of Photovoltaic Power Stations to the Power System", GB / T 40594-2021 "Technical Guidelines for Grid-Source Coordination of Power Systems", and GB / T 37408-2019 "Technical Requirements for Photovoltaic Power Generation Grid-connected Inverters" require that photovoltaic inverters must carry out low voltage ride-through tests. The test points are divided into voltage drops to 0%, 20%, 35%, 50%, 75%, and 90%Un, and no-load and load tests must be carried out. The load test is further divided into high-power and low-power conditions. Each voltage drop point must be tested at least twice under each condition.

[0003] The existing photovoltaic inverter low voltage ride-through test results rely on manual distinction between no-load and load test data, fault types, and index results. However, there are many sites, many test conditions, and a large amount of manual analysis work. It takes 5 days or more to complete the low voltage ride-through test result analysis and report writing for a photovoltaic inverter. In addition, the calculation results are affected by the level of manual ability and experience, resulting in different calculation results for different personnel, which seriously affects the accurate judgment of the photovoltaic inverter low voltage ride-through test results. Due to the long time required for calculation results, most test results are calculated and analyzed after the on-site test work is completed. If the test results are found to be unqualified, the inverter needs to be further modified. Therefore, after the on-site test is completed, it is necessary to wait for the test results to be calculated for at least 5 days or more, which seriously affects the progress of the test. Summary of the invention

[0004] The purpose of the present invention is to solve the deficiencies of the prior art and to provide a method for automatically analyzing the low voltage ride-through test results of a photovoltaic inverter, so as to automatically and quickly carry out the low voltage ride-through result analysis of the photovoltaic inverter.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for automatically analyzing low voltage ride-through test results of a photovoltaic inverter comprises the following steps:

[0007] Step 1, read the low voltage ride-through test result of the photovoltaic inverter. The low voltage ride-through test result of the photovoltaic inverter is the instantaneous data of voltage and current at the test point from 2s before the voltage drop to at least 5s after the voltage returns to normal, and includes the test data of the voltage drop to 0%, 20%, 35%, 50%, 75%, and 90% Un working conditions;

[0008] Step 2, calculating the effective value of the low voltage ride through test result of the photovoltaic inverter;

[0009] Step 3, before the voltage drops, determine whether the effective value of the three-phase current is greater than 0.1 times the rated current. If the effective value of the three-phase current is less than 0.1 times the rated current, it is no-load test data; if the effective value of the three-phase current is greater than or equal to 0.1 times the rated current, it is load test data;

[0010] Step 4, calculate the voltage drop depth and duration for the no-load test data, and determine whether the no-load test data meets the standard requirements according to the standard requirements. If not, output unqualified; if satisfied, output qualified;

[0011] Step 5, if the no-load test data meets the requirements, determine whether the load test data is off-grid based on whether the effective value of the three-phase current is greater than 0.1 times the rated current after the voltage returns to normal; if the effective value of the three-phase current is less than 0.1 times the rated current after the voltage returns to normal, the load test data is off-grid and the output is unqualified; if the effective value of the three-phase current is greater than or equal to 0.1 times the rated current after the voltage returns to normal, the load test data is not off-grid;

[0012] Step 6: If the load test data is not off-grid, the load test data is classified into three-phase fault, two-phase fault, and single-phase fault;

[0013] Step 7: Calculate the voltage drop depth U for the three-phase fault based on the fundamental positive sequence line voltage dip3 Duration t dip3 , calculate the reactive current response time t res3 Duration t last3 , exit time t ree3 , calculate the active power recovery rate P rate3 ; For two-phase faults, the voltage drop depth U is calculated based on the fundamental line voltage dip2 Duration t dip2 , calculate the active power recovery rate P rate2 ; For single-phase fault, calculate the voltage drop depth U based on the fundamental phase voltage dip1 Duration t dip1 , calculate the active power recovery rate P rate1 ;

[0014] Step 8: Determine reactive current response time t res3 Is it less than or equal to 30ms, exit time t ree3 Is it less than or equal to 30ms, the active power recovery rate P rate1 , P rate2 , P rate3Is it greater than or equal to 30% Pn / s? If it is satisfied, the output is qualified, and the test waveform and calculation results are automatically stored in the word; if it is not satisfied, the output is unqualified.

[0015] Preferably, in step 2, full-wave FFT is used to calculate the fundamental phase voltage, line voltage, phase current and the line voltage of the fundamental positive sequence component, active power, reactive power, active current and reactive current effective value.

[0016] Preferably, the no-load test data in step 4 is determined according to GB / T 19964 standard, with an allowable voltage deviation of ±5% and a duration deviation of ±20ms, specifically including the following specifications:

[0017] Voltage drop depth per unit value U dip :0.90-0.05,Duration t dip :2000±20ms;

[0018] Voltage drop depth per unit value U dip :0.75±0.05,Duration t dip : 1705±20ms;

[0019] Voltage drop depth per unit value U dip :0.50±0.05,Duration t dip : 1214±20ms;

[0020] Voltage drop depth per unit value U dip :0.35±0.05,Duration t dip :920±20ms;

[0021] Voltage drop depth per unit value U dip :0.20±0.05,Duration t dip :625±20ms;

[0022] Voltage drop depth per unit value U dip :0.00+0.05,duration t dip : 150±20ms.

[0023] Preferably, in step 6, the fault classification method is specifically:

[0024] Calculate the average fundamental phase voltage U of phases A, B, and C before the voltage drops avg ; Calculate the fundamental phase voltage average value U of phases A, B, and C respectively Aavg , U Bavg , U Cavg ; Set the judgment threshold △U to 0.8;

[0025] The judgment method is:

[0026] If U avg -U Aavg >△U and U avg -U Bavg >△U and U avg -U Cavg >△U, it is determined to be "ABC phase fault";

[0027] If U avg -U Aavg >△U and U avg -U Bavg <△UAndU avg -U Cavg >△U, it is determined to be an "AC phase fault";

[0028] If U avg -U Aavg <△UAndU avg -U Bavg >△U and U avg -U Cavg >△U, it is determined to be a "BC phase fault";

[0029] If U avg -U Aavg >△U and U avg -U Bavg >△U and U avg -U Cavg <△U, it is determined to be "AB phase fault";

[0030] If U avg -U Aavg <△UAndU avg -U Bavg <△UAndU avg -U Cavg >△U, it is determined to be a "C phase fault";

[0031] If U avg -U Aavg <△UAndU avg -U Bavg >△U and U avg -U Cavg <△U, it is determined to be a "B phase fault";

[0032] If U avg -U Aavg >△U and U avg -U Bavg <△UAndU avg -U Cavg <△U, it is determined to be "A phase fault";

[0033] ABC phase fault is a three-phase fault, AB phase fault, AC phase fault, and BC phase fault are two-phase faults, and A phase fault, B phase fault, and C phase fault are single-phase faults.

[0034] Preferably, in step 7, the test result calculation process is as follows:

[0035] S1, voltage drop depth U dip3 , U dip2 , U dip1 is: the per unit value of the voltage after the voltage drops and stabilizes;

[0036] S2, voltage drop duration t dip1 ,t dip2 ,t dip3 is: t Uend -t Ustart ;

[0037] Among them, t Ustart is the time when the voltage drop process is completed, t Uend is the moment when the voltage starts to recover; the standard deviation of the fundamental positive sequence line voltage or fundamental phase voltage is calculated respectively. After the voltage drops to 0.9Un and before the voltage rises to 0.9Un, the moment when the standard deviation is less than 0.003 is the moment when the voltage drops to 0.9Un. At the moment when the voltage drops to 0.9Un, the standard deviation is less than 0.003, which is the moment when the voltage drops to 0.9Un. Ustart During the period from the beginning of the voltage recovery to the end of the voltage rise to 0.9Un, the first time point when the standard deviation is greater than 0.003 is the time when the voltage begins to recover.

[0038] S3, reactive current response time t res1 ,t res2 ,t res3 is: t Iqstart -t 0.9start ;

[0039] Among them, t Iqstart Indicates the time when the reactive current emitted by the photovoltaic inverter continues to be greater than 90% of the reactive current injection reference value; t 0.9start Indicates the moment when the voltage drops to 0.9Un;

[0040] The reference value of reactive current injection is: 1.5*(0.9-U dip )*I n , where I n The rated current of the photovoltaic inverter, and the maximum reactive current does not exceed 1.05I n ;

[0041] S4, reactive current duration t last1 ,t last2 ,t last3 is: t Iqend -tIqstart ;

[0042] Among them, t Iqend Indicates the end time when the reactive current emitted by the photovoltaic inverter continuously exceeds 90% of the reactive current injection reference value;

[0043] S5, reactive current exit time t ree1 ,t ree2 ,t ree3 is: t Iqtuichu -t Iqend ;

[0044] Among them, t Iqtuichu Indicates that the reactive current increment is exited, that is, t Iqend After the moment, the moment when the reactive current standard deviation is less than 0.003 is the moment when the reactive current increment exits;

[0045] S6, Active power recovery rate P rate1 , P rate2 , P rate3 = start -P end ) / P n / (t Pend -t Uend );

[0046] Among them, P n Indicates the rated active power of the photovoltaic inverter; P start Indicates the active power at the time when low voltage ride-through ends and voltage begins to recover; P end Indicates that the active power is restored to the value under the current light; t Pend Indicates the time when the active power recovers to the value under the current illumination, that is, at t Uend After the time, the time point when the active power standard deviation is less than 0.003 is the time point when the active power is restored to the current light intensity.

[0047] The present invention discloses a method for automatically analyzing low voltage ride-through test results of a photovoltaic inverter, which has the following beneficial effects.

[0048] The present invention realizes automated, batch and efficient processing of photovoltaic inverter voltage ride-through test results, eliminating the reliance on manual calculations; the test result calculation efficiency is shortened from 5 days to 1 hour, and the test waveform and results can be automatically stored in a document. The method can accurately distinguish between no-load and load test data, and identify the fault type by comparing the phase voltage average values, and analyze three-phase, two-phase and single-phase faults respectively. The standard deviation method is used to accurately identify the moment when active power is restored and reactive current is exited. The analysis results are not affected by the voltage drop depth and the size of the active power, and have significant efficiency and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a flow chart of the method for automatically analyzing the low voltage ride through test results of a photovoltaic inverter according to the present invention;

[0050] Figure 2 This is a schematic diagram of the test result calculation and determination of the present invention;

[0051] Figure 3 This is a waveform diagram of the test results of the photovoltaic inverter 20%Un three-phase no-load low voltage ride-through in Application Example 1 of the present invention;

[0052] Figure 4 This is a waveform diagram of the low voltage ride-through test result of the photovoltaic inverter 20%Un three-phase load in Application Example 1 of the present invention;

[0053] Figure 5 This is a summary diagram of the test results of the photovoltaic inverter 35%Un two-phase no-load low voltage ride-through of Application Example 2 of the present invention;

[0054] Figure 6 This is a summary diagram of the low voltage ride-through test results of the photovoltaic inverter 35%Un two-phase load of the application example 2 of the present invention;

[0055] Figure 7 This is a summary diagram of the test results of the photovoltaic inverter 50%Un single-phase no-load low voltage ride-through of Application Example 3 of the present invention;

[0056] Figure 8 This is a summary diagram of the low voltage ride-through test results of a photovoltaic inverter 50%Un single-phase load in Application Example 3 of the present invention; DETAILED DESCRIPTION

[0057] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0058] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0059] The low voltage ride-through test results of photovoltaic inverters are mainly calculated manually. This embodiment of the present invention provides an automatic analysis method for the low voltage ride-through test results of photovoltaic inverters. It does not rely on manual calculations, can automatically, batch and efficiently complete the voltage ride-through test results of photovoltaic inverters, and automatically store the test waveforms and calculation results in a word.

[0060] like Figure 1 and Figure 2 As shown, a method for automatically analyzing low voltage ride-through test results of a photovoltaic inverter includes the following steps:

[0061] Step 1, read the low voltage ride-through test results of the photovoltaic inverter, specifically, the instantaneous data of voltage and current at the test point from 2s before the voltage drop to at least 5s after the voltage returns to normal, and including the test data of the voltage drop to 0%, 20%, 35%, 50%, 75%, and 90% Un conditions;

[0062] Step 2, calculating the effective value of the low voltage ride-through test result of the photovoltaic inverter, preferably using full-wave FFT to calculate the line voltage, active power, reactive power, active current, and reactive current effective value of the fundamental phase voltage, line voltage, phase current, and fundamental positive sequence component;

[0063] Step 3, before the voltage drops, determine whether the effective value of the three-phase current is greater than 0.1 times the rated current. If the effective value of the three-phase current is less than 0.1 times the rated current, it is no-load test data; if the effective value of the three-phase current is greater than or equal to 0.1 times the rated current, it is load test data;

[0064] Step 4, calculate the voltage drop depth and duration for the no-load test data, and determine whether the no-load test data meets the standard requirements according to the standard requirements. If not, output unqualified; if satisfied, output qualified;

[0065] Preferably, the no-load test data in step 4 is determined according to GB / T 19964 standard, with an allowable voltage deviation of ±5% and a duration deviation of ±20ms, specifically including the following specifications:

[0066] Voltage drop depth per unit value U dip :0.90-0.05,Duration t dip :2000±20ms;

[0067] Voltage drop depth per unit value U dip :0.75±0.05,Duration t dip : 1705±20ms;

[0068] Voltage drop depth per unit value U dip :0.50±0.05,Duration t dip: 1214±20ms;

[0069] Voltage drop depth per unit value U dip :0.35±0.05,Duration t dip :920±20ms;

[0070] Voltage drop depth per unit value U dip :0.20±0.05,Duration t dip :625±20ms;

[0071] Voltage drop depth per unit value U dip :0.00+0.05,duration t dip : 150±20ms.

[0072] Step 5, if the no-load test data meets the requirements, determine whether the load test data is off-grid based on whether the effective value of the three-phase current is greater than 0.1 times the rated current after the voltage returns to normal; if the effective value of the three-phase current is less than 0.1 times the rated current after the voltage returns to normal, the load test data is off-grid and the output is unqualified; if the effective value of the three-phase current is greater than or equal to 0.1 times the rated current after the voltage returns to normal, the load test data is not off-grid;

[0073] Step 6: If the load test data is not off-grid, the load test data is classified into three-phase fault, two-phase fault, and single-phase fault;

[0074] Preferably, in step 6, the fault classification method is specifically:

[0075] Calculate the average fundamental phase voltage U of phases A, B, and C before the voltage drops avg ; Calculate the fundamental phase voltage average value U of phases A, B, and C respectively Aavg , U Bavg , U Cavg ; Set the judgment threshold △U to 0.8;

[0076] The judgment method is:

[0077] If U avg -U Aavg >△U and U avg -U Bavg >△U and U avg -U Cavg >△U, it is determined to be "ABC phase fault";

[0078] If U avg -U Aavg >△U and U avg -U Bavg <△UAndU avg -U Cavg>△U, it is determined to be an "AC phase fault";

[0079] If U avg -U Aavg <△UAndU avg -U Bavg >△U and U avg -U Cavg >△U, it is determined to be a "BC phase fault";

[0080] If U avg -U Aavg >△U and U avg -U Bavg >△U and U avg -U Cavg <△U, it is determined to be "AB phase fault";

[0081] If U avg -U Aavg <△UAndU avg -U Bavg <△UAndU avg -U Cavg >△U, it is determined to be a "C phase fault";

[0082] If U avg -U Aavg <△UAndU avg -U Bavg >△U and U avg -U Cavg <△U, it is determined to be a "B phase fault";

[0083] If U avg -U Aavg >△U and U avg -U Bavg <△UAndU avg -U Cavg <△U, it is determined to be "A phase fault";

[0084] ABC phase fault is a three-phase fault, AB phase fault, AC phase fault, and BC phase fault are two-phase faults, and A phase fault, B phase fault, and C phase fault are single-phase faults.

[0085] Step 7: Calculate the voltage drop depth U for the three-phase fault based on the fundamental positive sequence line voltage dip3 Duration t dip3 , calculate the reactive current response time t res3 Duration t last3 , exit time t ree3 , calculate the active power recovery rate P rate3 ; For two-phase faults, the voltage drop depth U is calculated based on the fundamental line voltage dip2Duration t dip2 , calculate the active power recovery rate P rate2 ; For single-phase fault, calculate the voltage drop depth U based on the fundamental phase voltage dip1 Duration t dip1 , calculate the active power recovery rate P rate1 ;

[0086] Preferably, in step 7, the test result calculation process is as follows:

[0087] S1, voltage drop depth U dip3 , U dip2 , U dip1 is: the per unit value of the voltage after the voltage drops and stabilizes;

[0088] S2, voltage drop duration t dip1 ,t dip2 ,t dip3 is: t Uend -t Ustart ;

[0089] Among them, t Ustart is the time when the voltage drop process is completed, t Uend is the moment when the voltage starts to recover; the standard deviation of the fundamental positive sequence line voltage or fundamental phase voltage is calculated respectively. After the voltage drops to 0.9Un and before the voltage rises to 0.9Un, the moment when the standard deviation is less than 0.003 is the moment when the voltage drops to 0.9Un. At the moment when the voltage drops to 0.9Un, the standard deviation is less than 0.003, which is the moment when the voltage drops to 0.9Un. Ustart During the period from the beginning of the voltage recovery to the end of the voltage rise to 0.9Un, the first time point when the standard deviation is greater than 0.003 is the time when the voltage begins to recover.

[0090] S3, reactive current response time t res1 ,t res2 ,t res3 is: t Iqstart -t 0.9start ;

[0091] Among them, t Iqstart Indicates the time when the reactive current emitted by the photovoltaic inverter continues to be greater than 90% of the reactive current injection reference value; t 0.9start Indicates the moment when the voltage drops to 0.9Un;

[0092] The reference value of reactive current injection is: 1.5*(0.9-U dip )*I n , where I n The rated current of the photovoltaic inverter, and the maximum reactive current does not exceed 1.05I n ;

[0093] S4, reactive current duration t last1 ,t last2 ,t last3 is: t Iqend -t Iqstart ;

[0094] Among them, t Iqend Indicates the end time when the reactive current emitted by the photovoltaic inverter continuously exceeds 90% of the reactive current injection reference value;

[0095] S5, reactive current exit time t ree1 ,t ree2 ,t ree3 is: t Iqtuichu -t Iqend ;

[0096] Among them, t Iqtuichu Indicates that the reactive current increment is exited, that is, t Iqend After the moment, the moment when the reactive current standard deviation is less than 0.003 is the moment when the reactive current increment exits;

[0097] S6, Active power recovery rate P rate1 , P rate2 , P rate3 = start -P end ) / P n / (t Pend -t Uend );

[0098] Among them, P n Indicates the rated active power of the photovoltaic inverter; P start Indicates the active power at the time when low voltage ride-through ends and voltage begins to recover; P end Indicates that the active power is restored to the value under the current light; t Pend Indicates the time when the active power recovers to the value under the current illumination, that is, at t Uend After the time, the time point when the active power standard deviation is less than 0.003 is the time point when the active power is restored to the current light intensity.

[0099] Step 8: Determine reactive current response time t res3 Is it less than or equal to 30ms, exit time t ree3 Is it less than or equal to 30ms, the active power recovery rate P rate1 , P rate2 , P rate3 Is it greater than or equal to 30% Pn / s? If it is satisfied, the output is qualified, and the test waveform and calculation results are automatically stored in the word; if it is not satisfied, the output is unqualified.

[0100] Application Example 1

[0101] The 20%Un low voltage ride-through test results of a photovoltaic inverter with a rated active power of 3.15MW and a rated voltage of 35kV are automatically analyzed. First, the test data is divided into no-load test data and load test data according to the effective value of the three-phase current before the voltage drop. Among them, the waveform of the photovoltaic inverter 20%Un three-phase no-load low voltage ride-through test result is as follows Figure 3 As shown, the voltage drop depth U dip3 19.95%Un, duration t dip3 The load test data is further classified into three-phase faults, such as Figure 4 As shown, calculate the voltage drop depth U dip3 28.21%Un, duration t dip3 is 631ms, calculate the reactive current response time t res3 The duration is 34ms and t last3 is 634ms, exit time t ree3 is 8ms, the active power recovery rate P rate3 is 333.24%Pn / s, reactive current response time t res3 Greater than 30ms, exit time t ree3 Less than 30ms, active power recovery rate P rate3 If it is greater than 30% Pn / s, the result does not fully meet the requirements and an unqualified conclusion is output.

[0102] The test results of 20%Un low voltage ride-through of the photovoltaic inverter under all working conditions are shown in Table 1:

[0103] Table 1 Summary of PV inverter 20%Un low voltage ride-through test results

[0104]

[0105] Application Example 2

[0106] The 35%Un low voltage ride-through test results of a photovoltaic inverter with a rated active power of 3.15MW and a rated voltage of 35kV are automatically analyzed. First, the test data is divided into no-load test data and load test data according to the effective value of the three-phase current before the voltage drop. Among them, the waveform of the 35%Un two-phase no-load low voltage ride-through test result of the photovoltaic inverter is as follows Figure 5 As shown, the voltage drop depth U dip2 35.05%Un, duration t dip2 The load test data is further classified into two-phase faults, such as Figure 6 As shown, calculate the voltage drop depth U dip237.97%Un, duration t dip2 is 922ms, calculate the active power recovery rate P rate2 is 152.68%Pn / s, and the active power recovery rate P rate2 Greater than 30% Pn / s, the results meet the requirements; then the no-load test waveform, load test waveform and calculation results are automatically stored in Word and the Word document is saved.

[0107] The test results of 35%Un low voltage ride-through of the photovoltaic inverter under all working conditions are shown in Table 2:

[0108] Table 2 Summary of PV inverter 35%Un low voltage ride-through test results

[0109]

[0110] Application Example 3

[0111] The 50%Un low voltage ride-through test results of a photovoltaic inverter with a rated active power of 3.15MW and a rated voltage of 35kV are automatically analyzed. First, the test data is divided into no-load test data and load test data according to the effective value of the three-phase current before the voltage drop. Among them, the waveform of the 50%Un two-phase no-load low voltage ride-through test result of the photovoltaic inverter is as follows Figure 7 As shown, the voltage drop depth U dip1 50.11%Un, duration t dip1 The load test data is further classified into single-phase faults, such as Figure 8 As shown, calculate the voltage drop depth U dip1 48.53%Un, duration t dip1 is 1218ms, calculate the active power recovery rate P rate1 99.58%Pn / s, the active power recovery rate P rate1 Greater than 30% Pn / s, the results meet the requirements; then the no-load test waveform, load test waveform and calculation results are automatically saved in Word and the Word document is saved.

[0112] The test results of 50%Un low voltage ride-through of the photovoltaic inverter under all working conditions are shown in Table 3:

[0113] Table 3, Summary of PV Inverter 50%Un Low Voltage Ride Through Test Results

[0114]

[0115] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The substitution may be a substitution of a part of the structure, device, method step, or a complete technical solution. The equivalent replacement or change according to the technical solution and the inventive concept of the present invention shall be covered within the protection scope of the present invention.

Claims

1. A method for automatically analyzing low voltage ride-through test results of a photovoltaic inverter, characterized in that: The steps include: Step 1, read the low voltage ride-through test result of the photovoltaic inverter. The low voltage ride-through test result of the photovoltaic inverter is the instantaneous data of voltage and current at the test point from 2 seconds before the voltage drop to at least 5 seconds after the voltage returns to normal, and includes the test data of the voltage drop to 0%, 20%, 35%, 50%, 75%, and 90%Un conditions; Step 2, calculating the effective value of the low voltage ride through test result of the photovoltaic inverter; Step 3: Before the voltage drops, determine whether the effective value of the three-phase current is greater than 0.1 times the rated current. If the effective value of the three-phase current is less than 0.1 times the rated current, it is no-load test data; If the effective value of the three-phase current is greater than or equal to 0.1 times the rated current, it is the load test data; Step 4, calculate the voltage drop depth and duration for the no-load test data, and determine whether the no-load test data meets the standard requirements according to the standard requirements. If not, output unqualified; if satisfied, output qualified; Step 5, if the no-load test data meets the requirements, determine whether the load test data is off-grid based on whether the effective value of the three-phase current is greater than 0.1 times the rated current after the voltage returns to normal; if the effective value of the three-phase current is less than 0.1 times the rated current after the voltage returns to normal, the load test data is off-grid and the output is unqualified; if the effective value of the three-phase current is greater than or equal to 0.1 times the rated current after the voltage returns to normal, the load test data is not off-grid; Step 6: If the load test data is not off-grid, the load test data is classified into three-phase fault, two-phase fault, and single-phase fault; Step 7: Calculate the voltage drop depth U for the three-phase fault based on the fundamental positive sequence line voltage dip3 Duration t dip3 , calculate the reactive current response time t res3 Duration t last3 , exit time t ree3 , calculate the active power recovery rate P rate3 ; For two-phase faults, the voltage drop depth U is calculated based on the fundamental line voltage dip2 Duration t dip2 , calculate the active power recovery rate P rate2 ; For single-phase fault, calculate the voltage drop depth U based on the fundamental phase voltage dip1 Duration t dip1 , calculate the active power recovery rate P rate1 ; Step 8: Determine reactive current response time t res3 Is it less than or equal to 30ms, exit time t ree3 Is it less than or equal to 30ms, the active power recovery rate P rate1 , P rate2 , P rate3 Is it greater than or equal to 30% Pn / s? If it is satisfied, the output is qualified, and the test waveform and calculation results are automatically stored in the word; If not satisfied, the output is unqualified.

2. The method for automatically analyzing the low voltage ride through test results of a photovoltaic inverter according to claim 1, characterized in that: In step 2, full-wave FFT is used to calculate the fundamental phase voltage, line voltage, phase current and the line voltage, active power, reactive power, active current and reactive current effective value of the fundamental positive sequence component.

3. The method for automatically analyzing the low voltage ride through test results of a photovoltaic inverter according to claim 1, characterized in that: The judgment of the no-load test data in step 4 is based on the GB / T 19964 standard, with an allowable voltage deviation of ±5% and a duration deviation of ±20ms, including the following specifications: Voltage drop depth per unit value U dip :0.90-0.05,Duration t dip :2000±20ms; Voltage drop depth per unit value U dip :0.75±0.05,Duration t dip : 1705±20ms; Voltage drop depth per unit value U dip :0.50±0.05,Duration t dip : 1214±20ms; Voltage drop depth per unit value U dip :0.35±0.05,Duration t dip :920±20ms; Voltage drop depth per unit value U dip :0.20±0.05,Duration t dip :625±20ms; Voltage drop depth per unit value U dip :0.00﹢0.05,Duration t dip : 150±20ms.

4. The method for automatically analyzing the low voltage ride through test results of a photovoltaic inverter according to claim 1, characterized in that: In step 6, the fault classification method is specifically as follows: Calculate the average fundamental phase voltage U of phases A, B, and C before the voltage drops avg ; Calculate the fundamental phase voltage average value U of phases A, B, and C respectively Aavg , U Bavg , U Cavg ; Set the judgment threshold △U to 0.8; The judgment method is: If U avg -U Aavg >△U and U avg -U Bavg >△U and U avg -U Cavg >△U, it is determined to be "ABC phase fault"; If U avg -U Aavg >△U and U avg -U Bavg <△U and U avg -U Cavg >△U, it is determined to be "AC phase fault"; If U avg -U Aavg <△U and U avg -U Bavg >△U and U avg -U Cavg >△U, it is determined to be a "BC phase fault"; If U avg -U Aavg >△U and U avg -U Bavg >△U and U avg -U Cavg <△U, it is determined to be "AB phase fault"; If U avg -U Aavg <△U and U avg -U Bavg <△U and U avg -U Cavg >△U, it is determined to be "C phase fault"; If U avg -U Aavg <△U and U avg -U Bavg >△U and U avg -U Cavg <△U, it is determined to be "B phase fault"; If U avg -U Aavg >△U and U avg -U Bavg <△U and U avg -U Cavg <△U, it is determined to be "A phase fault"; ABC phase fault is a three-phase fault, AB phase fault, AC phase fault, and BC phase fault are two-phase faults, and A phase fault, B phase fault, and C phase fault are single-phase faults.

5. The method for automatically analyzing the low voltage ride through test results of a photovoltaic inverter according to claim 1, characterized in that: In step 7, the test result calculation process is as follows: S1, voltage drop depth U dip3 , U dip2 , U dip1 is: the per unit value of the voltage after the voltage drops and stabilizes; S2, voltage drop duration t dip1 ,t dip2 ,t dip3 is: t Uend -t Ustart ; Among them, t Ustart is the time when the voltage drop process is completed, t Uend is the moment when the voltage starts to recover; the standard deviation of the fundamental positive sequence line voltage or fundamental phase voltage is calculated respectively. After the voltage drops to 0.9Un and before the voltage rises to 0.9Un, the moment when the standard deviation is less than 0.003 is the moment when the voltage drops to 0.9Un. At the moment when the voltage drops to 0.9Un, the standard deviation is less than 0.003, which is the moment when the voltage drops to 0.9Un. Ustart During the period from the beginning of the voltage recovery to the end of the voltage rise to 0.9Un, the first time point when the standard deviation is greater than 0.003 is the time when the voltage begins to recover. S3, reactive current response time t res1 ,t res2 ,t res3 is: t Iqstart -t 0.9start ; Among them, t Iqstart Indicates the time when the reactive current emitted by the PV inverter continuously exceeds 90% of the reactive current injection reference value; t 0.9start Indicates the moment when the voltage drops to 0.9Un; The reference value of reactive current injection is: 1.5*(0.9-U dip )*I n , where I n The rated current of the photovoltaic inverter, and the maximum reactive current does not exceed 1.05I n ; S4, reactive current duration t last1 ,t last2 ,t last3 is: t Iqend -t Iqstart ; Among them, t Iqend Indicates the end time when the reactive current emitted by the PV inverter continuously exceeds 90% of the reactive current injection reference value; S5, reactive current exit time t ree1 ,t ree2 ,t ree3 is: t Iqtuichu -t Iqend ; Among them, t Iqtuichu Indicates that the reactive current increment is exited, that is, t Iqend After the moment, the moment when the reactive current standard deviation is less than 0.003 is the moment when the reactive current increment exits; S6, Active power recovery rate P rate1 , P rate2 , P rate3 For: (P start -P end ) / P n / (t Pend -t Uend ); Among them, P n Indicates the rated active power of the photovoltaic inverter; P start Indicates the active power at the time when low voltage ride-through ends and voltage begins to recover; P end Indicates that the active power is restored to the value under the current light; t Pend Indicates the time when the active power recovers to the value under the current illumination, that is, at t Uend After the time, the time point when the active power standard deviation is less than 0.003 is the time point when the active power is restored to the current light intensity.

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