Debugging circuit and debugging method of photovoltaic string inverter

Abstract

The invention discloses a debugging method of a photovoltaic string inverter, which adopts string inverter efficiency test, and evaluates the energy conversion efficiency and performance optimization of the string inverter, thereby judging the performance of the string inverter, and improving the performance and economic benefit of a whole photovoltaic system. A string inverter power factor test is adopted to verify whether the performance and safety of the string inverter meet related standards and design requirements or not, and meanwhile, reliable data support is provided for production and application of products. A string inverter overload protection function test is adopted to verify whether a protection mechanism of the string inverter can be correctly triggered when the string inverter faces an overload condition, so that the string inverter and other equipment are protected from being damaged by electrical faults. The anti-islanding effect protection function test of the string inverter is adopted to ensure that the grid-connected photovoltaic string inverter can timely reduce the output current and avoid the islanding effect when the power grid fails, so that the safety of power maintenance personnel is ensured, and the damage to power grid equipment is avoided.

Description

Technical Field

[0001] The invention relates to a debugging method for a photovoltaic string inverter, specifically describes the debugging content, steps and methods of the photovoltaic string inverter, is suitable for distributed and centralized photovoltaic power generation devices, and belongs to the technical field of new energy photovoltaic power generation. Background Art

[0002] Photovoltaic power generation belongs to the field of new energy. The construction speed of photovoltaic power generation projects has further accelerated. At the same time, the photovoltaic construction of various petrochemical enterprises has continued to accelerate, and there are more and more photovoltaic projects. At present, the development of photovoltaic construction and commissioning technology in the petrochemical system is relatively lagging, and no corresponding technical accumulation has been formed. The technical methods and steps for photovoltaic commissioning are still unclear and are in the exploratory stage during implementation.

[0003] The prior art lacks a clear debugging method for photovoltaic string inverters. Summary of the invention

[0004] The object of the present invention is to provide a debugging method which can improve the debugging efficiency of a photovoltaic string inverter, save manpower and material resources and has a lower safety risk.

[0005] The present invention firstly discloses a debugging circuit for a photovoltaic string inverter, wherein the circuit comprises a DC input source, a string inverter, a test device, a waveform detection device, and a power grid simulator. The DC input source is connected to the string inverter, and the string inverter is connected to the waveform detection device. At the connection end between the string inverter and the waveform detection device, the power grid simulator is also connected via a first switch S1, and the test device is connected via a second switch S2.

[0006] The present invention also discloses a debugging method for a photovoltaic string inverter. Based on the debugging circuit of the photovoltaic string inverter, the debugging method includes a string inverter efficiency test, specifically:

[0007] Close the first switch S1 and the second switch S2, adjust the DC input source so that the input power is 25%, 50%, and 100% of the rated value of the string inverter, respectively, observe the output AC active power recorded by the test equipment; calculate the inverter efficiency η:

[0008]

[0009] Among them, W AC Indicates the AC active power output by the grid-connected photovoltaic power generation system, W DC Indicates the DC power output by the grid-connected photovoltaic power generation system;

[0010] η≥94.5% indicates that the efficiency of the string inverter is qualified.

[0011] Preferably, the debugging method further includes a string inverter power factor test, specifically:

[0012] Close the first switch S1 and the second switch S2, adjust the DC input source so that the string inverter outputs 100% and 50% of the rated power, observe the power factor indication value and the active and reactive power recorded by the test equipment; active power = P*t, reactive power = Q*t, calculate the average power factor PF:

[0013]

[0014] Among them, P represents active power, Q represents reactive power, and t represents time;

[0015] PF ≥ 0.9 indicates that the power factor of the string inverter is qualified.

[0016] Preferably, the debugging method further includes testing the overload protection function of the string inverter, specifically:

[0017] Close the first switch S1 and the second switch S2, adjust the DC input source so that its output power exceeds the maximum DC input power allowed by the string inverter, observe the AC active power output recorded by the test equipment, when the power output by the DC input source exceeds the maximum DC input power allowed by the string inverter, and the string inverter operates at the maximum AC output power, the current limiting operation should be automatically turned on. In any of the following cases, if the string inverter continues to operate for 7 hours or the temperature exceeds the allowable value, the string inverter should stop supplying power to the grid; then adjust the DC input source so that the string inverter is within the allowable power range, and the string inverter should be able to operate normally;

[0018] Otherwise, it is considered that the overload protection function of the string inverter is missing.

[0019] Preferably, the debugging method further includes testing the anti-islanding protection function of the string inverter, specifically:

[0020] 4.1 Open the second switch S2, close the first switch S1, start the string inverter, adjust the DC input source, make the output power P of the string inverter equal to the rated AC output power, and measure the reactive power Q output by the string inverter;

[0021] 4.2 Shut down the string inverter and disconnect S1;

[0022] 4.3 Adjust the RLC circuit in the test equipment so that its output reactive power Q EUT Equal to the rated AC output power P of the string inverter EUT ;

[0023] 4.4 Close the second switch S2 to connect to the RLC circuit in the test equipment, close the first switch S1, start the string inverter, confirm that its rated AC output power matches the input power of the grid simulator, and adjust the RLC circuit in the test equipment until the fundamental frequency current flowing through the first switch S1 is less than 1% of the rated output current of the string inverter in steady state;

[0024] 4.5 Disconnect the first switch S1, and record the time t from when the first switch S1 is disconnected to when the output current of the string inverter drops and remains below 1% of the rated output current;

[0025] The anti-islanding protection action time t≤2s indicates that when the islanding effect occurs, the inverter has the ability to quickly detect the island and immediately disconnect from the grid;

[0026] The anti-islanding protection action time t>2s indicates that the inverter cannot be disconnected from the grid in time when the islanding effect occurs, resulting in over-voltage, under-voltage, over-frequency and under-frequency abnormalities in the grid, which impacts and damages the load equipment in operation.

[0027] Specifically, in step 4.3, the RLC circuit in the test equipment is adjusted by the following steps to output a reactive power Q EUT Equal to the rated AC output power P of the string inverter EUT :

[0028] ① According to the calculation formula Q L =Q f ×P EUT =1.0×P EUT Calculate the required inductance Q for the RLC circuit L ;

[0029] ② Adjust the inductance loop in the RLC circuit to reach the calculated inductance value Q L ;

[0030] ③According to the calculation formula Q L +Q C =-Q EUT Calculate the capacitance Q required for the RLC circuit C :

[0031] ④ Adjust the capacitance loop in the RLC circuit to reach the calculated capacitance value Q C ;

[0032] ⑤Finally, adjust the resistance value R in the RLC circuit so that the reactive power Q consumed in the RLC circuit is EUT Equal to the rated AC output power P of the string inverter EUT ;

[0033] Among them, Q frepresents the quality factor, R represents the active load impedance, C represents the reactive load capacitance, L represents the reactive load inductance, Q L Indicates inductance, P EUT Indicates output power, Q C Indicates capacitance.

[0034] Preferably, when the string inverter outputs its rated AC power, the active power P deviation is ±5%, and the reactive power Q deviation is ±5%.

[0035] Preferably, the debugging method further includes performing an anti-islanding effect protection function test on the string inverter under the condition of 33% and 66% of the rated AC output power, specifically:

[0036] 5.1 Open the second switch S2, close the first switch S1, and start the string inverter; adjust the DC input source so that the output power P of the string inverter is equal to 33% of the rated AC output power, and measure the reactive power Q output by the string inverter; adjust the RLC circuit in the test equipment so that its output reactive power Q EUT Equal to the rated AC output power P of the string inverter EUT 33% of the rated AC output power; the anti-islanding protection action time t≤2s; 5.2 The second switch S2 is opened, the first switch S1 is closed, and the string inverter is started; by adjusting the DC input source, the output power P of the string inverter is equal to 66% of the rated AC output power, and the reactive power Q output by the string inverter is measured; the RLC circuit in the test equipment is adjusted so that the reactive power Q output is equal to 66% of the rated AC output power. EUT Equal to the rated AC output power P of the string inverter EUT 66%; Anti-islanding protection action time t≤2s; 5.3 Simultaneously analyze the anti-islanding test waveform of the waveform detection equipment, and determine whether the islanding effect occurs by analyzing the waveform to judge the changes in the output voltage frequency and the output current phase.

[0037] Preferred:

[0038] When the string inverter is at 33% of its rated AC output power, the active power P deviation is 0 and the reactive power Q deviation is ±5%;

[0039] When the string inverter is at 66% of its rated AC output power, the active power P deviation is 0 and the reactive power Q deviation is ±5%.

[0040] Beneficial Effects of the Invention

[0041] The string inverter overload protection function test is used to verify whether the protection mechanism of the string inverter can be correctly triggered when facing an overload situation, thereby protecting the string inverter and other equipment from damage caused by electrical faults. The string inverter anti-islanding effect protection function test is used to ensure that the grid-connected photovoltaic string inverter can reduce the output current in time when a grid fault occurs to avoid the occurrence of the islanding effect, thereby ensuring the safety of power maintenance personnel and avoiding damage to grid equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the string inverter test of the present invention;

[0043] In the figure: 1- DC input source, 2- string inverter, 3- test equipment, 4- waveform detection equipment, 5- grid simulator. DETAILED DESCRIPTION

[0044] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] The present invention provides a photovoltaic string inverter debugging circuit as follows Figure 1 As shown, the efficiency test of the string inverter in this embodiment is to close switches S1 and S2, adjust the DC input source 1 so that the input power is 25%, 50%, and 100% of the rated value of the string inverter 2, and observe the output AC active power recorded by the test equipment 3. The power calculation formula of the string inverter is as follows:

[0046]

[0047] Where η is the inverter efficiency of the power generation system, expressed as a percentage;

[0048] W AC --AC active power output by the grid-connected photovoltaic power generation system;

[0049] W DC --The DC power output by the grid-connected photovoltaic power generation system;

[0050] η≥94.5% indicates that the efficiency of the string inverter is qualified.

[0051] The present invention provides a photovoltaic string inverter debugging circuit as follows Figure 1 As shown, the power factor test of the string inverter in this embodiment is to close switches S1 and S2, adjust the DC input source 1 so that the string inverter 2 outputs the rated power of 100% and 50% respectively, observe the power factor indication value and the active and reactive power recorded by the test equipment 3, active power = P*t, reactive power = Q*t. The average power factor of the system should not be less than 0.9 (leading or lagging). The average power factor (PF) calculation formula for a period of time is as follows;

[0052]

[0053] Where PF is the average power factor over a period of time;

[0054] P--active power, in kwh;

[0055] Q--reactive power, in kvarh;

[0056] t----time, in Hour;

[0057] PF ≥ 0.9 indicates that the power factor of the string inverter is qualified.

[0058] The present invention provides a photovoltaic string inverter debugging circuit as follows Figure 1 As shown, the overload protection function test of the string inverter in this embodiment is to close the switches S1 and S2, adjust the DC input source 1 so that its output power exceeds the maximum DC input power allowed by the string inverter 2, and observe the output AC active power recorded by the test equipment 3. When the power output by the DC input source 1 exceeds the maximum DC input power allowed by the string inverter 2, the string inverter 2 should automatically start the current limiting work when it runs at the maximum AC output power. In any of the cases where it continues to work for 7 hours or the temperature exceeds the allowable value, the string inverter 2 should stop supplying power to the grid; then adjust the DC input source 1 so that the string inverter 2 is within the allowable power range, and the string inverter 2 should be able to work normally; otherwise, it is determined that the overload protection function of the string inverter 2 is missing.

[0059] The present invention provides a photovoltaic string inverter debugging circuit as follows Figure 1 As shown, the inverter anti-islanding protection function test of this embodiment is as follows: (1) disconnect the second switch S2, close the first switch S1, start the string inverter 2, adjust the DC input source 1, make the output power P of the string inverter 2 equal to the rated AC output power, and measure the reactive power Q output by the string inverter. (2) shut down the string inverter 2 and disconnect S1. (3) adjust the RLC circuit in the test equipment 3 through the following steps to make its output reactive power Q EUT Equal to the rated AC output power P of string inverter 2 EUT Q f =1.0±0.05: ①According to the calculation formula Q L =Q f ×P EUT =1.0×P EUT Calculate the required inductance Q for the RLC circuit L ; ② Adjust the inductance loop in the RLC circuit to reach the calculated inductance value Q L ; ③ and according to the calculation formula Q L +Q C=-Q EUT Calculate the capacitance Q required for the RLC circuit C ; ④ Adjust the capacitance loop in the RLC circuit to reach the calculated capacitance value Q C ⑤Finally, adjust the resistance value R in the RLC circuit so that the reactive power Q consumed in the RLC circuit is EUT Equal to the rated AC output power P of string inverter 2 EUT (4) Close S2 to access the RLC circuit in the test equipment 3, close S1, start the string inverter 2, confirm that its rated AC output power matches the input power of the grid simulator 5, and adjust the RLC circuit in the test equipment 3 until the base frequency current flowing through S1 is less than 1% of the rated output current of the string inverter 2 in steady state. (5) Disconnect S1 and record the time t from the time S1 is disconnected to the time when the output current of the string inverter 2 drops and remains below 1% of the rated output current; the anti-islanding protection action time t≤2s indicates that the inverter has the ability to quickly detect the island and immediately disconnect from the grid when the islanding effect occurs; the anti-islanding protection action time t>2s indicates that the inverter cannot be disconnected from the grid in time when the islanding effect occurs, resulting in abnormal problems such as over-voltage, under-voltage, over-frequency, etc. in the grid, which impacts the working load equipment and damages the equipment; (6) The string inverter is tested for the anti-islanding effect protection function under the conditions of 33% and 66% of the rated AC output power; ① Disconnect the second switch S2 and close the first switch S1 to start the string inverter 2; adjust the DC input source 1 so that the output power P of the string inverter 2 is equal to 33% of the rated AC output power, and measure the reactive power Q output by the string inverter 2; adjust the RLC circuit in the test equipment 3 so that its output reactive power Q EUT Equal to the rated AC output power P of string inverter 2 EUT 33% of the rated AC output power; the anti-islanding protection action time t≤2s; wherein, when the string inverter is at 33% of its rated AC output power, the active power P deviation is 0, and the reactive power Q deviation is ±5%; ② the second switch S2 is opened, the first switch S1 is closed, and the string inverter 2 is started; by adjusting the DC input source 1, the output power P of the string inverter 2 is equal to 66% of the rated AC output power, and the reactive power Q output by the string inverter 2 is measured; the RLC circuit in the test equipment 3 is adjusted so that its output reactive power Q EUT Equal to the rated AC output power P of string inverter 2 EUT 66%; anti-islanding protection action time t≤2s; wherein, when the string inverter is at 66% of its rated AC output power, the active power P deviation is 0, and the reactive power Q deviation is ±5%; ③ Simultaneously analyze the anti-islanding test waveform of the waveform detection device 4, and determine whether the islanding effect occurs by analyzing the waveform to determine the changes in the output voltage frequency and the output current phase;

[0060] Quality factor Q f The calculation formula is as follows;

[0061]

[0062] Among them, Q f represents the quality factor, R represents the active load impedance, C represents the reactive load capacitance, L represents the reactive load inductance, Q L Indicates inductance, P EUT Indicates output power, Q C Indicates capacitance.

[0063] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may modify or supplement the specific embodiments described or replace them in a similar manner without departing from the spirit of the present invention or exceeding the scope defined by the appended claims.

Claims

1. A debugging circuit for a photovoltaic string inverter, characterized in that: The circuit comprises a DC input source (1), a string inverter (2), a test device (3), a waveform detection device (4), and a power grid simulator (5); the DC input source (1) is connected to the string inverter (2), and the string inverter (2) is connected to the waveform detection device (4); the connection end between the string inverter (2) and the waveform detection device (4) is also connected to the power grid simulator (5) via a first switch S1, and connected to the test device (3) via a second switch S2.

2. A method for debugging a photovoltaic string inverter, based on the circuit of claim 1, characterized in that The method includes string inverter efficiency testing, specifically: The first switch S1 and the second switch S2 are closed, and the DC input source (1) is adjusted so that the input power is 25%, 50%, and 100% of the rated value of the string inverter (2), respectively. The output AC active power is recorded by the observation test equipment (3); and the inverter efficiency η is calculated: Among them, W AC Indicates the AC active power output by the grid-connected photovoltaic power generation system, W DC Indicates the DC power output by the grid-connected photovoltaic power generation system; η≥94.5% indicates that the efficiency of the string inverter is qualified.

3. The method according to claim 2, characterized in that The method also includes a string inverter power factor test, specifically: The first switch S1 and the second switch S2 are closed, and the DC input source (1) is adjusted so that the string inverter (2) outputs 100% and 50% of the rated power. The power factor indication value and the active power and reactive power recorded by the test equipment (3) are observed; active power = P*t, reactive power = Q*t, and the average power factor PF is calculated: Among them, P represents active power, Q represents reactive power, and t represents time; PF ≥ 0.9 indicates that the power factor of the string inverter is qualified.

4. The method according to claim 2, characterized in that The method also includes a test of the overload protection function of the string inverter, specifically: The first switch S1 and the second switch S2 are closed, and the DC input source (1) is adjusted so that its output power exceeds the maximum DC input power allowed by the string inverter (2). The AC active power output is recorded by the observation test equipment (3). When the power output by the DC input source (1) exceeds the maximum DC input power allowed by the string inverter (2), the string inverter (2) should automatically start the current limiting operation when it operates at the maximum AC output power. In any of the following cases, if the operation lasts for 7 hours or the temperature exceeds the allowable value, the string inverter (2) should stop supplying power to the grid. Then, the DC input source (1) is adjusted so that the string inverter (2) is within the allowable power range, and the string inverter (2) should be able to operate normally. Otherwise, it is determined that the overload protection function of the string inverter (2) is missing.

5. The method according to claim 2, characterized in that The method also includes a test of the anti-islanding protection function of the string inverter, specifically: 5.1 The second switch S2 is opened, the first switch S1 is closed, and the string inverter (2) is started. The DC input source (1) is adjusted so that the output power P of the string inverter (2) is equal to the rated AC output power, and the reactive power Q output by the string inverter is measured; 5.2 Shut down the string inverter (2) and disconnect S1; 5.3 Adjust the RLC circuit in the test equipment (3) so that its output reactive power Q EUT Equal to the rated AC output power P of the string inverter (2) EUT ; 5.4 Close the second switch S2 to connect to the RLC circuit in the test equipment (3), close the first switch S1, start the string inverter (2), confirm that its rated AC output power matches the input power of the power grid simulator (5), and adjust the RLC circuit in the test equipment (3) until the base frequency current flowing through the first switch S1 is less than 1% of the rated output current of the string inverter (2) in steady state; 5.5 Disconnect the first switch S1, and record the time t from when the first switch S1 is disconnected to when the output current of the string inverter (2) decreases and remains below 1% of the rated output current; The anti-islanding protection action time t≤2s indicates that when the islanding effect occurs, the inverter has the ability to quickly detect the island and immediately disconnect from the grid; The anti-islanding protection action time t>2s indicates that the inverter cannot be disconnected from the grid in time when the islanding effect occurs, resulting in over-voltage, under-voltage, over-frequency and under-frequency abnormalities in the grid, which impacts and damages the load equipment in operation.

6. The method according to claim 5, characterized in that In step 5.3, the RLC circuit in the test equipment (3) is adjusted by the following steps to make its output reactive power Q EUT Equal to the rated AC output power P of the string inverter (2) EUT : ① According to the calculation formula Q L =Q f ×P EUT =1.0×P EUT Calculate the required inductance Q for the RLC circuit L ; ② Adjust the inductance loop in the RLC circuit to reach the calculated inductance value Q L ; ③According to the calculation formula Q L +Q C =-Q EUT Calculate the capacitance Q required for the RLC circuit C : ④ Adjust the capacitance loop in the RLC circuit to reach the calculated capacitance value Q C ; ⑤Finally, adjust the resistance value R in the RLC circuit so that the reactive power Q consumed in the RLC circuit is EUT Equal to the rated AC output power P of the string inverter (2) EUT ; Among them, Q f represents the quality factor, R represents the active load impedance, C represents the reactive load capacitance, L represents the reactive load inductance, Q L Indicates inductance, P EUT Indicates output power, Q C Indicates capacitance.

7. The method according to claim 5, characterized in that When the string inverter (2) outputs its rated AC power, the active power P deviation is ±5%, and the reactive power Q deviation is ±5%.

8. The method according to claim 2, characterized in that The method also includes testing the anti-islanding protection function of the string inverter under the conditions of 33% and 66% of the rated AC output power, specifically: 8.1 The second switch S2 is opened, the first switch S1 is closed, and the string inverter (2) is started; the DC input source (1) is adjusted so that the output power P of the string inverter (2) is equal to 33% of the rated AC output power, and the reactive power Q output by the string inverter (2) is measured; the RLC circuit in the test equipment (3) is adjusted so that the reactive power Q output by the string inverter (2) is equal to 33% of the rated AC output power. EUT Equal to the rated AC output power P of the string inverter (2) EUT 33%; anti-islanding protection action time t≤2s; 8.2 The second switch S2 is opened, the first switch S1 is closed, and the string inverter (2) is started; the DC input source (1) is adjusted so that the output power P of the string inverter (2) is equal to 66% of the rated AC output power, and the reactive power Q output by the string inverter is measured; the RLC circuit in the test equipment (3) is adjusted so that the reactive power QEUT output by the RLC circuit is equal to 66% of the rated AC output power PEUT of the string inverter (2); the anti-islanding protection action time t≤2s; 8.3 Simultaneously analyze the anti-islanding test waveform of the waveform detection device (4), and determine whether an islanding effect occurs by analyzing the waveform to determine the changes in the output voltage frequency and the output current phase.

9. The method according to claim 8, characterized in that: When the string inverter is at 33% of its rated AC output power, the active power P deviation is 0 and the reactive power Q deviation is ±5%; When the string inverter is at 66% of its rated AC output power, the active power P deviation is 0 and the reactive power Q deviation is ±5%.

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