A power tracking method and system for a string inverter

Abstract

The application discloses a power tracking method and system of a string type photovoltaic inverter. The method comprises the following steps: obtaining corresponding second power through data processing; when the corresponding second power is less than corresponding power, adjusting corresponding voltage instruction; when the power difference of each photovoltaic string is reduced to zero, the string type photovoltaic inverter is in a constant power control mode; when the corresponding second power is greater than the corresponding power, adjusting the corresponding voltage instruction; when the absolute value of the power difference of each photovoltaic string is reduced to the minimum, the string type photovoltaic inverter is in a maximum power tracking mode. Only the corresponding voltage instruction is adjusted according to the corresponding second power, so that power tracking and smooth switching between modes are realized, and the application scenarios and operation conditions of the string type photovoltaic inverter are widened. The application can integrate maximum power tracking and constant power control, and simplify the algorithm module.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic inverter technology, and in particular to a power tracking method and system for string photovoltaic inverters. Background Technology

[0002] Typically, string photovoltaic (PV) inverters need to operate in maximum power point tracking (MPPT) mode to maximize the conversion of solar energy into electrical energy. However, in certain specific operating scenarios and conditions, the output power of the PV inverter must not exceed a certain set value, thus requiring the string PV inverter to have constant power control functionality. Therefore, a single string PV inverter needs to simultaneously possess both MPPT and constant power control modes to broaden its application scenarios and adapt to different operating conditions.

[0003] In existing technologies, maximum power point tracking (MPPT) and constant power control are two different control methods for string photovoltaic (PV) inverters operating in different modes. Therefore, the software system employs different algorithms to implement them. This means that the string PV inverter needs to call different algorithm modules when switching between these two operating modes. This not only complicates the software system of the string PV inverter but also makes it difficult to achieve seamless and smooth switching between the two operating modes, which is detrimental to the stable operation of the string PV power generation system. Summary of the Invention

[0004] The purpose of this invention is to provide a power tracking method and system for string photovoltaic inverters to solve one or more technical problems existing in the prior art, and at least provide a beneficial option or create conditions.

[0005] The solution to the technical problem of this invention is to provide a power tracking method and system for a string photovoltaic inverter.

[0006] According to an embodiment of a first aspect of the present invention, a power tracking method for a string photovoltaic inverter is provided, the string photovoltaic inverter comprising N photovoltaic strings, comprising the following steps:

[0007] Obtain the current and voltage values ​​corresponding to each photovoltaic string, and calculate the actual output power of each photovoltaic string. and the total power actually output by the N photovoltaic strings ;

[0008] Obtain the first power given by the string photovoltaic inverter. ;

[0009] According to the first power Total power and the corresponding actual output power The power difference corresponding to each photovoltaic string is calculated. and the corresponding second power ;

[0010] Obtain the power corresponding to the maximum power point of each photovoltaic string. Determine the corresponding second power With corresponding power Relationship;

[0011] When the corresponding second power Greater than the corresponding power At the same time, adjust the voltage command corresponding to each photovoltaic string. This makes the corresponding power difference When the absolute value of is the smallest, the string photovoltaic inverter is in maximum power point tracking mode;

[0012] When the corresponding second power Less than the corresponding power At the same time, adjust the voltage command corresponding to each photovoltaic string. This makes the corresponding power difference When the value is zero, the string photovoltaic inverter is in constant power control mode.

[0013] Furthermore, the voltage command for adjusting each photovoltaic string... This makes the corresponding power difference The absolute value of the smallest includes:

[0014] Using the perturbation-observation method, adjust the voltage command corresponding to each photovoltaic string. ;

[0015] Input the corresponding voltage command after adjustment The output power of each photovoltaic string is directed to the corresponding second power. The offset causes the corresponding power difference to... Its absolute value is the smallest.

[0016] Furthermore, the voltage command for adjusting each photovoltaic string... This makes the corresponding power difference Zero specifically includes:

[0017] Using the perturbation-observation method, adjust the voltage command corresponding to each photovoltaic string. ;

[0018] Input the corresponding voltage command after adjustment The output power of each photovoltaic string is directed to the corresponding second power. The offset causes the corresponding power difference to... It is zero.

[0019] Furthermore, the step based on the first power Total power and the corresponding actual output power The power difference corresponding to each photovoltaic string is calculated. and the corresponding second power Specifically, it includes:

[0020] Calculate the first power With total power The difference ;

[0021] Based on the difference Total power and the corresponding actual output power The power difference corresponding to each photovoltaic string is calculated. ;

[0022] According to the corresponding power difference With the corresponding actual output power The sum of these values ​​is used to calculate the corresponding second power. .

[0023] Furthermore, the step of basing the difference on... Total power and the corresponding actual output power The power difference corresponding to each photovoltaic string is calculated. Specifically, it includes:

[0024] Based on the corresponding actual output power With total power The corresponding power ratio is obtained. ;

[0025] According to the corresponding power ratio and difference The power difference is calculated using the following formula: The power difference corresponding to each photovoltaic string is calculated. .

[0026] According to a second aspect of the present invention, a power point tracking system for a string photovoltaic inverter is provided, the string photovoltaic inverter comprising N photovoltaic strings, including:

[0027] The data acquisition module is used to acquire the current and voltage values ​​corresponding to each photovoltaic string and to acquire the first power of the string photovoltaic inverter. And obtain the power corresponding to the maximum power point of each photovoltaic string. ;

[0028] The actual output power calculation module is used to calculate the actual output power of each photovoltaic string based on the corresponding current and voltage values. and the total power actually output by the N photovoltaic strings ;

[0029] The data processing module is used to process the data based on the first power. Total power and the corresponding actual output power The power difference corresponding to each photovoltaic string is calculated. and the corresponding second power ;

[0030] The judgment module is used to determine the corresponding second power. With corresponding power Relationship;

[0031] The first adjustment module is used to adjust the corresponding second power. Greater than the corresponding power At the same time, adjust the voltage command corresponding to each photovoltaic string. This makes the corresponding power difference When the value is at its minimum, the string photovoltaic inverter is in maximum power point tracking mode;

[0032] The second adjustment module is used to adjust the corresponding second power. Less than the corresponding power At the same time, adjust the voltage command corresponding to each photovoltaic string. This makes the corresponding power difference When the value is zero, the string photovoltaic inverter is in constant power control mode.

[0033] Furthermore, the data processing module includes:

[0034] The difference calculation unit is used to calculate the first power. With total power The difference ;

[0035] A power difference calculation unit is used to calculate the power difference based on the power difference. Total power and the corresponding actual output power The power difference corresponding to each photovoltaic string is calculated. ;

[0036] The second power calculation unit is used to calculate the corresponding power difference. With the corresponding actual output power The sum of these values ​​yields the second power. .

[0037] Furthermore, the first adjustment module includes:

[0038] The first voltage regulation unit is used to adjust the corresponding second power. Greater than the corresponding power At that time, the voltage command corresponding to each photovoltaic string is adjusted using the perturbation observation method. ;

[0039] The first voltage input unit is used to input the adjusted corresponding voltage command. The output power of each photovoltaic string is directed to the corresponding second power. The offset causes the corresponding power difference to... Its absolute value is the smallest.

[0040] Furthermore, the second adjustment module includes:

[0041] The second voltage regulation unit is used to adjust the corresponding second power. Less than the corresponding power At that time, the voltage command corresponding to each photovoltaic string is adjusted using the perturbation observation method. ;

[0042] The first voltage input unit is used to input the adjusted corresponding voltage command. The output power of each photovoltaic string is directed to the corresponding second power. The offset causes the corresponding power difference to... It is zero.

[0043] Furthermore, the power difference calculation unit is specifically used to calculate the corresponding actual output power. With total power The corresponding power ratio is obtained. And according to the corresponding power ratio and difference The power difference is calculated using the following formula: The power difference corresponding to each photovoltaic string is calculated. .

[0044] The beneficial effect of this invention is: when the corresponding second power Less than the corresponding power At that time, adjust the corresponding voltage command. The power difference of each photovoltaic string When the power is reduced to zero, the string photovoltaic inverter is in constant power control mode. When the corresponding second power... Greater than the corresponding power At that time, adjust the corresponding voltage command. The power difference of each photovoltaic string When the absolute value of the voltage decreases to its minimum, the string photovoltaic inverter is in maximum power point tracking mode. This can be achieved by adjusting the voltage based on the corresponding second power input. Adjust the corresponding voltage command This enables power point tracking and smooth switching between modes, and broadens the application scenarios and operating conditions of string photovoltaic inverters. The invention integrates maximum power point tracking and constant power control, simplifying the algorithm module. Attached Figure Description

[0045] Figure 1 This is a schematic flowchart of a power tracking method for a string photovoltaic inverter provided by the present invention;

[0046] Figure 2 This is a schematic diagram of the system structure of the string photovoltaic inverter provided by the present invention;

[0047] Figure 3 This invention provides a graph showing the relationship between the output power and output voltage of a photovoltaic string under certain light intensity and temperature conditions. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and should not be construed as limiting the scope of the invention.

[0049] It should be noted that although functional modules are divided in the system diagram, in some cases, the steps shown or described may be executed in a different order than the module division or flowchart shown in the system. The terms "first," "second," etc., in the specification, claims, and the aforementioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0050] In the description of this invention, it should be noted that, unless otherwise explicitly defined, terms such as "setting," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0051] The system structure of a string photovoltaic inverter is as follows: Figure 2As shown, a basic structure employing a front-stage boost converter and a rear-stage inverter is adopted. The controller includes a voltage closed-loop controller. Specifically, the front-stage uses a DC / DC boost converter circuit for each photovoltaic string, with power coupling via a common DC bus capacitor; the rear-stage uses a common DC / AC inverter circuit to convert DC power to AC power. In some embodiments of this invention, the string photovoltaic inverter includes: N photovoltaic strings and a voltage closed-loop controller.

[0052] According to an embodiment of the first aspect of the present invention, referring to Figure 1 In some embodiments of the present invention, a power tracking method for a string photovoltaic inverter includes the following steps:

[0053] S100: Obtain the current and voltage values ​​corresponding to each photovoltaic string, and calculate the actual output power of each photovoltaic string. The total actual output power of N photovoltaic strings .

[0054] In this embodiment, the voltage and current values ​​of each photovoltaic string in the string photovoltaic inverter are collected to obtain the corresponding voltage and current values. Based on the corresponding voltage and current values, the actual output power of each photovoltaic string at that moment is calculated. And calculate the actual total output power of the N photovoltaic strings at this moment. In this embodiment, by acquiring data from each photovoltaic string, the actual operating conditions of each photovoltaic string and the actual operating conditions of N photovoltaic strings are calculated.

[0055] The system can collect the output voltage and output current values ​​of each photovoltaic string as the corresponding voltage and current values; it can also collect the input voltage and input current values ​​of each photovoltaic string as the corresponding voltage and current values.

[0056] S200, Obtain the first power given by the string photovoltaic inverter. .

[0057] In this embodiment, since the output power of a string photovoltaic inverter is difficult to keep constant at a certain value for a long time, a reference power, i.e., a first power, is obtained based on the required output power of the string photovoltaic inverter. .

[0058] S300, based on the first power Total power and the corresponding actual output power The power difference corresponding to each photovoltaic string is calculated. and the corresponding second power .

[0059] In this embodiment, the first power obtained after S200 The total power of the N photovoltaic strings obtained after passing through S100 and the corresponding actual output power of each photovoltaic string. Based on the above data, the power difference of each photovoltaic string is calculated. And the corresponding second power of each photovoltaic string .

[0060] Since there is a power loss between the output power of the N photovoltaic strings and the output power of the entire inverter, the power loss of each photovoltaic string can be obtained through the above calculation method, that is, the power difference of each photovoltaic string. And the reference power corresponding to each photovoltaic string, i.e., the second power. .

[0061] S400, obtain the power corresponding to the maximum power point of each photovoltaic string. Determine the corresponding second power With corresponding power The relationship.

[0062] In this embodiment, the power corresponding to the maximum power point of each photovoltaic module can be obtained by perturbation and observation. The second power corresponding to each photovoltaic string obtained in S300. The power corresponding to that obtained in this embodiment By comparing the two, we can determine the relationship between them.

[0063] Wherein, the power corresponding to the maximum power point Alternatively, the power corresponding to the maximum power point of each photovoltaic module can be obtained through the fixed voltage tracking method or the incremental conductance method. .

[0064] S500, when the corresponding second power Greater than the corresponding power At the same time, adjust the voltage command corresponding to each photovoltaic string. This results in the corresponding power difference. When the absolute value is at its minimum, the string photovoltaic inverter is in maximum power point tracking mode.

[0065] In this embodiment, the corresponding second power in S300 is... The corresponding power in S400 A comparison is made, and when the comparison result is the corresponding second power... Greater than the corresponding power Then the power difference of each photovoltaic string The direction of the decrease in absolute value is used to adjust and modify the voltage command of each photovoltaic string. This results in a power difference between each photovoltaic string. This is the minimum value. At this point, each photovoltaic string is actually operating at its maximum power point, thus the power point tracking algorithm achieves maximum power point tracking.

[0066] S600, when the corresponding second power Less than the corresponding power At the same time, adjust the voltage command corresponding to each photovoltaic string. This results in the corresponding power difference. When the value is zero, the string photovoltaic inverter is in constant power control mode.

[0067] In this embodiment, the corresponding second power in S300 is... The corresponding power in S400 By comparison, the corresponding second power was obtained. Less than the corresponding power Towards the power difference of each photovoltaic string The direction of decrease is used to adjust and modify the voltage command of each photovoltaic string. This results in the corresponding power difference. Decrease until it reaches zero. At this point, each photovoltaic string is actually operating at its corresponding second power level. Therefore, this power point tracking algorithm achieves constant power control.

[0068] This invention integrates maximum power point tracking (MPPT) and constant power control functions, simplifying the algorithm module. It is based on the maximum power point (MPPT) of each photovoltaic string. With the corresponding second power The relationship is used to adjust the voltage command corresponding to each photovoltaic string. The string photovoltaic inverter is operated in constant power control mode via S500, and in maximum power point tracking mode via S600. This is achieved through the corresponding second power... Adjust the corresponding voltage command This enables power tracking and smooth switching between modes, and broadens the application scenarios and operating conditions of string photovoltaic inverters.

[0069] Reference Figure 3 , Figure 3This is a curve showing the relationship between the output power and output voltage of a photovoltaic string under certain light intensity and temperature conditions, combined with... Figure 3 A detailed analysis of the string photovoltaic inverter power point tracking method of the present invention:

[0070] Obtain the voltage and current values ​​of this photovoltaic string, and calculate the actual output power of this photovoltaic string based on the voltage and current values. Actual output power The corresponding voltage value is And obtain the power corresponding to the maximum power point of the photovoltaic string along this route. ;

[0071] With second power For example, the second power The corresponding voltage value is When the second power of this photovoltaic string is Power greater than the power point of maximum power At that time, it will be based on the difference. The direction of decreasing absolute value will adjust the output voltage of this photovoltaic string, that is, the voltage value will decrease from the current value. Gradually increase to It will soon be from the current Past The voltage adjustment process can be determined according to actual needs, and can be done gradually or all at once. The voltage of the photovoltaic strings along this route will be regulated to... At this point, the difference is made The absolute value is at its minimum. At this point, the photovoltaic string is actually operating at its maximum power point, and its output power is the power corresponding to the maximum power point. Thus, the power tracking method for string photovoltaic inverters of the present invention achieves maximum power tracking functionality.

[0072] Then with the second power For example, the second power The corresponding voltage value is When the second power of this photovoltaic string is Power less than the point of maximum power At that time, it will be based on the difference. The direction of decreasing absolute value will adjust the output voltage of this photovoltaic string, that is, the voltage value will decrease from the current value. Gradually increase to It will soon be from the current Past The voltage adjustment process can be determined according to actual needs, and can be done gradually or all at once. The voltage of the photovoltaic strings along this route will be regulated to... At this point, the difference can be made The absolute value is zero. At this point, the output power of this photovoltaic string is constant, which is the second power. Therefore, the power tracking method of the string photovoltaic inverter of the present invention realizes the constant power control function.

[0073] In summary, for one of the photovoltaic strings, if the maximum power point tracking mode is switched to constant power control mode, only the changed second power needs to be obtained. This allows for smooth switching between modes. If the mode is not switched and the second power is not changed... Power point tracking (MPPT) allows string photovoltaic (PV) inverters to operate automatically in two modes: maximum power point (MPPT) mode, where the output power of each PV string is the power at the maximum power point; and constant power control (CPCC) mode, where the output power of each PV string is the second power point. .

[0074] In some embodiments of the present invention, S300 specifically includes:

[0075] S310, based on the first power obtained in S200 And the total actual output power of the N photovoltaic strings obtained in S100 Calculate the difference between the two. .

[0076] In this embodiment, there is a certain power loss between the total power output of the entire inverter and the actual total power output of the N photovoltaic strings, and the power output of the photovoltaic inverter will vary to some extent. According to S200, the first power of the entire inverter is given. And the total actual output power of the N photovoltaic strings obtained from S100 The power loss between the two is calculated, that is, the difference between the two is calculated. .

[0077] S320, the difference obtained from S310 The actual output power of each photovoltaic string obtained in S100 And the total actual output power of the N photovoltaic strings obtained in S100 The power difference of each photovoltaic string is calculated. .

[0078] In this embodiment, the power loss between the N photovoltaic strings and the string photovoltaic inverter is obtained through S310, therefore each photovoltaic string also has a certain output loss. The actual output power of each photovoltaic string is obtained through S100. The actual total output power of N photovoltaic strings and the difference obtained from S310 Calculate the power difference of each photovoltaic string. .

[0079] S330, the power difference of each photovoltaic string obtained from S320 The actual output power corresponding to the N photovoltaic strings obtained in S100 Calculations were performed to obtain the second power of each photovoltaic string. .

[0080] In this embodiment, the power difference of each photovoltaic string is obtained through S320. And the corresponding actual output power of the N photovoltaic strings obtained in S100 Calculations are performed using the following formula: The second power of each photovoltaic string is calculated. The second power obtained in this embodiment The input is sent to S400 for judgment, and then subsequent adjustments are made.

[0081] In some embodiments of the present invention, S320 specifically includes:

[0082] S321, convert the actual output power of each photovoltaic string obtained in S100. and the total actual output power of the N photovoltaic strings Calculate the ratio to obtain the corresponding power ratio. ;

[0083] S322, the power ratio obtained from S321 The difference obtained in S310 According to the power difference calculation formula: The power difference of each photovoltaic string is calculated. .

[0084] In this embodiment, in order to calculate the power difference of each photovoltaic string, the actual output power of each photovoltaic string is calculated. The total actual output power of N photovoltaic strings The value, i.e., the power ratio. The calculated ratio and the power loss are obtained. According to the power difference calculation formula: The power difference of each photovoltaic string is calculated. .

[0085] In some embodiments of the present invention, S500 specifically includes:

[0086] The S510, based on the perturbation-observation method, adjusts the voltage command corresponding to each photovoltaic string. ;

[0087] In this embodiment, the judgment result obtained in S400 is acquired, and the power corresponding to the maximum power point is... Less than the corresponding second power obtained in S330 At that time, the voltage command was adjusted by perturbation observation method. .

[0088] S520 will adjust the corresponding voltage command from S510. Input, causing the output power of each photovoltaic string to be directed towards the corresponding second power. The offset, and the corresponding power difference It changes in the direction of decreasing absolute value.

[0089] In this embodiment, for one photovoltaic string, the voltage change command and voltage command The input is fed into the voltage closed-loop controller to achieve the power difference of this photovoltaic string. The absolute value gradually decreases until it reaches its minimum, thus achieving a power output of this photovoltaic string that moves towards the second power level. Closer. Because the power corresponding to the maximum power point... Less than the second power obtained in S330 Therefore, the maximum power output of this photovoltaic string can only reach [power value missing]. And the power difference of this photovoltaic string If the power output cannot reach zero, then this photovoltaic string will operate at its maximum power point. Similarly, when all N photovoltaic strings are operating at their maximum power points, the string photovoltaic inverter is considered to be operating in maximum power point tracking (MPPT) mode, thus achieving MPPT functionality.

[0090] In some embodiments of the present invention, S600 specifically includes:

[0091] The S610, based on the perturbation-observation method, adjusts the voltage command corresponding to each photovoltaic string. ;

[0092] In this embodiment, the judgment result obtained in S400 is acquired, and the power corresponding to the maximum power point is... Greater than the corresponding second power obtained in S330 At that time, the voltage command was adjusted by perturbation observation method. .

[0093] S620, the corresponding voltage command adjusted in S610. Input, causing the output power of each photovoltaic string to be directed towards the corresponding second power. The offset, and the corresponding power difference It is zero.

[0094] In this embodiment, the corresponding voltage command is changed. and the corresponding adjusted voltage command The input is fed into the voltage closed-loop controller to achieve the power difference between each photovoltaic string. Gradually decrease until it reaches zero, and ensure that the output power of each photovoltaic string moves towards the second power. Closer. Because the power corresponding to the maximum power point... Greater than the second power obtained in S330 Therefore, the power output of each photovoltaic string can reach the second power level. And the power difference of each photovoltaic string The power output is zero, meaning that the power output of each photovoltaic string is the second power. Therefore, it is assumed that the string photovoltaic inverter operates in constant power control mode, thus achieving constant power control function.

[0095] According to an embodiment of a second aspect of the present invention, in some embodiments of the present invention, a power tracking system for a string photovoltaic inverter includes: a data acquisition module, an actual output power calculation module, a data processing module, a judgment module, a first adjustment module, and a second adjustment module.

[0096] The data acquisition module is responsible for: acquiring the voltage and current values ​​corresponding to each photovoltaic string, and sending these values ​​to the actual output power calculation module; and acquiring the first power of the string photovoltaic inverter. and the first power Send to the data processing module; obtain the power corresponding to the maximum power point of each photovoltaic string. And send it to the judgment module.

[0097] The actual output power calculation module is responsible for receiving the corresponding voltage and current values ​​sent by the data acquisition module, and calculating the actual output power of each photovoltaic string. And calculate the actual total output power of the N-channel photovoltaic strings. And the actual output power of each photovoltaic string is obtained. and the actual total output power of the N-channel photovoltaic strings. Send to the data processing module.

[0098] The data processing module's function is to receive the first power signal sent by the data acquisition module. And receive the total actual output power of the N photovoltaic strings sent by the actual output power calculation module. and the actual output power corresponding to each photovoltaic string Through the first power The actual total output power of the N-channel photovoltaic strings and the corresponding actual output power The power difference of each photovoltaic string is obtained through calculation. And the corresponding second power of each photovoltaic string The corresponding second power and the corresponding power difference Send to the judgment module.

[0099] The function of the judgment module is to receive the power corresponding to the maximum power point of each photovoltaic string sent by the data acquisition module. and the second power corresponding to the receiving data processing module. Determine the corresponding second power With corresponding power The relationship.

[0100] The function of the first adjustment module is to adjust the corresponding second power. With corresponding power By comparison, the corresponding second power was obtained. Greater than the corresponding power The power difference towards each photovoltaic string The direction of decrease is used to adjust and modify the voltage command of each photovoltaic string. This results in a power difference between each photovoltaic string. This is the minimum value. At this point, each photovoltaic string is actually operating at its maximum power point, thus the power point tracking algorithm achieves maximum power point tracking.

[0101] The function of the second adjustment module is to, in this embodiment, adjust the corresponding second power. With corresponding power By comparison, the corresponding second power was obtained. Less than the corresponding power Towards the power difference of each photovoltaic string The direction of decrease is used to adjust and modify the voltage command of each photovoltaic string. This results in the corresponding power difference. The value is zero. At this point, each photovoltaic string is actually operating at its corresponding second power level. Therefore, this power point tracking algorithm achieves constant power control.

[0102] The present invention is based on the corresponding second power Adjust the corresponding voltage command This enables power point tracking and smooth switching between modes, and broadens the application scenarios and operating conditions of string photovoltaic inverters. The present invention provides a power point tracking method for string photovoltaic inverters that integrates maximum power point tracking and constant power control, simplifying the algorithm module.

[0103] In some embodiments of the present invention, the data processing module includes: a difference calculation unit, a power difference calculation unit, and a second power calculation unit.

[0104] The function of the difference calculation unit is to receive the first power transmitted by the data acquisition module. And receive the actual total output power of the N photovoltaic strings sent by the actual output power calculation module. Calculate the difference between the two. and the difference Send to the power difference calculation unit.

[0105] In this embodiment, there is a certain power loss between the total power output of the entire inverter and the actual total power output of the N photovoltaic strings, and the power output of the photovoltaic inverter will vary to some extent. According to S200, the first power of the entire inverter is given. And the total actual output power of the N photovoltaic strings obtained from S100 The power loss between the two is calculated, that is, the difference between the two is calculated. .

[0106] The function of the power difference calculation unit is to receive the difference sent by the difference calculation unit. and receive the actual output power of each photovoltaic string. And the total actual output power of the N photovoltaic strings obtained in S100 The power difference of each photovoltaic string is calculated. .

[0107] The specific function of the power difference calculation unit is to calculate the actual output power of each photovoltaic string received. and the total actual output power of the N photovoltaic strings By taking the ratio, the corresponding power ratio can be obtained. The obtained power ratio The difference obtained in the difference calculation unit According to the power difference calculation formula: The power difference of each photovoltaic string is calculated. and the corresponding power difference It is sent to the second power calculation unit.

[0108] In this embodiment, in order to calculate the power difference of each photovoltaic string, the actual output power of each photovoltaic string is calculated. The total actual output power of N photovoltaic strings The value, i.e., the power ratio. The calculated ratio and the power loss are obtained. According to the power difference calculation formula: The power difference of each photovoltaic string is calculated. .

[0109] The function of the second power calculation unit is to receive the corresponding power difference sent by the power difference calculation unit. Through the power difference of each photovoltaic string The actual output power corresponding to N photovoltaic strings Calculations are performed to obtain the second power of each photovoltaic string. .

[0110] In this embodiment, the power difference of each photovoltaic string is used. And the actual output power corresponding to the N photovoltaic strings obtained. Calculations are performed using the following formula: The second power of each photovoltaic string is calculated. The second power obtained in this embodiment The input is fed into the judgment module for evaluation, which then leads to further adjustments.

[0111] In some embodiments of the present invention, the first adjustment module includes: a first voltage adjustment unit and a first voltage input unit.

[0112] The function of the first voltage regulation unit is to: obtain the judgment result from the judgment module, and when the corresponding maximum power point corresponds to the power... Less than the corresponding second power At that time, the voltage command was adjusted by perturbation observation method. and the adjusted voltage command It is sent to the first voltage input unit.

[0113] The function of the first voltage input unit is to receive the adjusted voltage command sent by the first voltage adjustment unit. The adjusted voltage command Input, causing the output power of each photovoltaic string to be directed towards the corresponding second power. The offset, and the corresponding power difference It changes in the direction of decreasing absolute value.

[0114] In this embodiment, for one photovoltaic string, the voltage change command and voltage command The input is fed into the voltage closed-loop controller to achieve the power difference of this photovoltaic string. The absolute value gradually decreases until it reaches its minimum, thus achieving a power output of this photovoltaic string that moves towards the second power level. Closer. Because the power corresponding to the maximum power point... Less than the second power Therefore, the maximum power output of this photovoltaic string can only reach [power value missing]. And the power difference of this photovoltaic string If the power output cannot reach zero, then this photovoltaic string will operate at its maximum power point. Similarly, when all N photovoltaic strings are operating at their maximum power points, the string photovoltaic inverter is considered to be operating in maximum power point tracking (MPPT) mode, thus achieving MPPT functionality.

[0115] In some embodiments of the present invention, the second adjustment module includes: a second voltage adjustment unit and a second voltage input unit.

[0116] The function of the second voltage regulation unit is to: obtain the judgment result from the judgment module, and when the corresponding maximum power point corresponds to the power... Greater than the corresponding second power At that time, the voltage command was adjusted by perturbation observation method. and the adjusted voltage command It is sent to the second voltage input unit.

[0117] The function of the second voltage input unit is to receive the adjusted voltage command sent by the second voltage adjustment unit. The adjusted voltage command Input, causing the output power of each photovoltaic string to be directed towards the corresponding second power. The offset, and the corresponding power difference It is zero.

[0118] In this embodiment, the corresponding voltage command is changed. and the corresponding adjusted voltage command The input is fed into the voltage closed-loop controller to achieve the power difference between each photovoltaic string. Gradually decrease until it reaches zero, and ensure that the output power of each photovoltaic string moves towards the second power. Closer. Because the power corresponding to the maximum power point... Greater than the second power obtained in S330 Therefore, the power output of each photovoltaic string can reach the second power level. And the power difference of each photovoltaic string The power output is zero, meaning that the power output of each photovoltaic string is the second power. Therefore, it is assumed that the string photovoltaic inverter operates in constant power control mode, thus achieving constant power control function.

[0119] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A power point tracking method for a string photovoltaic inverter, characterized in that, The string photovoltaic inverter includes N photovoltaic strings, including: Obtain the current and voltage values ​​corresponding to each photovoltaic string, and calculate the actual output power of each photovoltaic string. and the total power actually output by the N photovoltaic strings ; Obtain the first power given by the string photovoltaic inverter. ; According to the first power Total power and the corresponding actual output power The power difference corresponding to each photovoltaic string is calculated. And the reference power corresponding to each photovoltaic string, i.e., the second power. ; Obtain the power corresponding to the maximum power point of each photovoltaic string. Determine the corresponding second power With corresponding power Relationship; When the corresponding second power Greater than the corresponding power At the same time, adjust the voltage command corresponding to each photovoltaic string. This makes the corresponding power difference When the absolute value of is the smallest, the string photovoltaic inverter is in maximum power point tracking mode; When the corresponding second power Less than the corresponding power At the same time, adjust the voltage command corresponding to each photovoltaic string. This makes the corresponding power difference When the power is zero, the string photovoltaic inverter is in constant power control mode; Wherein, according to the first power Total power and the corresponding actual output power The power difference corresponding to each photovoltaic string is calculated. And the reference power corresponding to each photovoltaic string, i.e., the second power. Specifically, it includes: Calculate the first power With total power The difference ; Based on the difference Total power and the corresponding actual output power The power difference corresponding to each photovoltaic string is calculated. ; According to the corresponding power difference With the corresponding actual output power The sum of these values ​​is used to calculate the corresponding second power. ; Wherein, according to the difference Total power and the corresponding actual output power The power difference corresponding to each photovoltaic string is calculated. Specifically, it includes: Based on the corresponding actual output power With total power The corresponding power ratio is obtained. ; According to the corresponding power ratio and difference The power difference is calculated using the following formula: The power difference corresponding to each photovoltaic string is calculated. .

2. The power tracking method for a string photovoltaic inverter according to claim 1, characterized in that, The voltage command for adjusting each photovoltaic string This makes the corresponding power difference The absolute value of the smallest includes: Using the perturbation-observation method, adjust the voltage command corresponding to each photovoltaic string. ; Input the corresponding voltage command after adjustment The output power of each photovoltaic string is directed to the corresponding second power. The offset causes the corresponding power difference to... Its absolute value is the smallest.

3. The power tracking method for a string photovoltaic inverter according to claim 1, characterized in that, The voltage command for adjusting each photovoltaic string This makes the corresponding power difference Zero specifically includes: Using the perturbation-observation method, adjust the voltage command corresponding to each photovoltaic string. ; Input the corresponding voltage command after adjustment The output power of each photovoltaic string is directed to the corresponding second power. The offset causes the corresponding power difference to... It is zero.

4. A power point tracking system for a string photovoltaic inverter, characterized in that, The string photovoltaic inverter includes N photovoltaic strings, including: The data acquisition module is used to acquire the current and voltage values ​​corresponding to each photovoltaic string and to acquire the first power of the string photovoltaic inverter. And obtain the power corresponding to the maximum power point of each photovoltaic string. ; The actual output power calculation module is used to calculate the actual output power of each photovoltaic string based on the corresponding current and voltage values. and the total power actually output by the N photovoltaic strings ; The data processing module is used to process the data based on the first power. Total power and the corresponding actual output power The power difference corresponding to each photovoltaic string is calculated. And the reference power corresponding to each photovoltaic string, i.e., the second power. ; The judgment module is used to determine the corresponding second power. With corresponding power Relationship; The first adjustment module is used to adjust the corresponding second power. Greater than the corresponding power At the same time, adjust the voltage command corresponding to each photovoltaic string. This makes the corresponding power difference When the value is at its minimum, the string photovoltaic inverter is in maximum power point tracking mode; The second adjustment module is used to adjust the corresponding second power. Less than the corresponding power At the same time, adjust the voltage command corresponding to each photovoltaic string. This makes the corresponding power difference When the power is zero, the string photovoltaic inverter is in constant power control mode; The data processing module includes: The difference calculation unit is used to calculate the first power. With total power The difference ; A power difference calculation unit is used to calculate the power difference based on the power difference. Total power and the corresponding actual output power The power difference corresponding to each photovoltaic string is calculated. ; The second power calculation unit is used to calculate the corresponding power difference. With the corresponding actual output power The sum of these values ​​yields the second power. ; Specifically, the power difference calculation unit is used to calculate the power difference based on the corresponding actual output power. With total power The corresponding power ratio is obtained. And according to the corresponding power ratio and difference The power difference is calculated using the following formula: The power difference corresponding to each photovoltaic string is calculated. .

5. A power tracking system for a string photovoltaic inverter according to claim 4, characterized in that, The first adjustment module includes: The first voltage regulation unit is used to adjust the corresponding second power. Greater than the corresponding power At that time, the voltage command corresponding to each photovoltaic string is adjusted using the perturbation observation method. ; The first voltage input unit is used to input the adjusted corresponding voltage command. The output power of each photovoltaic string is directed to the corresponding second power. The offset causes the corresponding power difference to... Its absolute value is the smallest.

6. The power tracking system for a string photovoltaic inverter according to claim 4, characterized in that, The second adjustment module includes: The second voltage regulation unit is used to adjust the corresponding second power. Less than the corresponding power At that time, the voltage command corresponding to each photovoltaic string is adjusted using the perturbation observation method. ; The first voltage input unit is used to input the adjusted corresponding voltage command. The output power of each photovoltaic string is directed to the corresponding second power. The offset causes the corresponding power difference to... It is zero.

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