Photovoltaic current detection method and inverter

Abstract

The invention discloses a photovoltaic current detection method and an inverter. The method comprises the following steps: constructing a current-voltage output characteristic curve of a photovoltaic array; sampling voltage is obtained, wherein the sampling voltage is used for representing the output current of the photovoltaic array; based on the sampling voltage, in combination with a current-voltage output characteristic curve, obtaining an output current of the photovoltaic array; wherein the current-voltage output characteristic curve at least comprises a first fitting curve, the first fitting curve comprises a current zero point of the photovoltaic array, and the first fitting curve is obtained at least through the following steps: obtaining at least two current points in the first fitting curve; obtaining a voltage value corresponding to each current point to obtain coordinates corresponding to at least two current points in the first fitting curve; and performing linear fitting based on the coordinates of the current points to obtain a first fitting curve of the current-voltage output characteristic curve. The low-current sampling precision can be improved, and the sampling accuracy is ensured.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic power generation technology, and in particular to a photovoltaic current detection method and an inverter. Background Art

[0002] The photovoltaic storage hybrid inverter plays an important role in the household independent photovoltaic storage power generation system. The inverter charges the battery with the DC power generated by the photovoltaic module, and can also convert it into AC power. Since the output power of solar cells is affected by external factors such as light intensity and environment, the inverter will have the MPPT (Maximum power point tracking) maximum power tracking function. The MPPT function mainly collects voltage and current signals, and through algorithms, allows the system to work at the maximum power point. Therefore, improving the current sampling accuracy can enable the system to work at the maximum power point and improve the power generation efficiency of the system.

[0003] However, in the related art, photovoltaic current detection will produce a large deviation when collecting small currents, making the system unable to operate at the maximum power point, resulting in unstable power control, inaccurate power generation, and energy loss.

[0004] Therefore, it is necessary to provide a technical solution to solve the problem of large detection error in photovoltaic current detection under low current conditions. Summary of the invention

[0005] In order to solve the problem of large detection error of photovoltaic current detection under low current conditions in the related art, in a first aspect, the present application provides a photovoltaic current detection method, the method comprising: Construct the current-voltage output characteristic curve of the photovoltaic array; Obtaining a sampled voltage, wherein the sampled voltage is used to characterize an output current of the photovoltaic array; Based on the sampled voltage and in combination with the current-voltage output characteristic curve, the output current of the photovoltaic array is obtained; Wherein, the current-voltage output characteristic curve includes at least a first fitting curve, the first fitting curve includes a current zero point of the photovoltaic array, and the first fitting curve is obtained by at least the following steps: obtaining at least two current points in the first fitting curve; Obtaining a voltage value corresponding to each current point to obtain coordinates corresponding to at least two current points in the first fitting curve; A linear fit is performed based on the coordinates of the current points to obtain a first fitting curve of the current-voltage output characteristic curve.

[0006] According to the above description, in the photovoltaic current detection method provided in the embodiment of the present application, linear fitting is performed near the current zero point, and a first fitting curve including the current zero point of the photovoltaic array is constructed by linear fitting. Then, the output current of the photovoltaic array can be obtained based on the collected sampling voltage representing the output current of the photovoltaic array and combined with the first fitting curve. In this way, the sampling accuracy of the photovoltaic array under low current conditions can be improved.

[0007] Furthermore, the current-voltage output characteristic curve of the photovoltaic array also includes a second fitting curve and a third fitting curve; the current value corresponding to the first fitting curve is less than or equal to the current value of the second fitting curve; the current value of the second fitting curve is less than or equal to the current value of the third fitting curve.

[0008] Furthermore, the maximum current value corresponding to the first fitting curve is less than or equal to a preset current threshold; the preset current threshold satisfies: greater than or equal to 0.16 times the maximum output current of the photovoltaic array, and less than or equal to 0.24 times the maximum output current of the photovoltaic array.

[0009] Further, performing linear fitting based on the coordinates of the current point to obtain a first fitting curve of the current-voltage output characteristic curve includes: Obtain three current points within the first fitting curve; Obtaining the voltage value corresponding to each current point to obtain the coordinates corresponding to the three current points in the first fitting curve; Construct a linear system of equations, which is expressed by the following formula: , Where Y is an n*1 column vector containing the voltage values ​​of all current points; X is an n*2 matrix, the first column contains the current values ​​of all current points, and the second column is a constant 1; θ is an n*1 column vector containing the fitting weight parameters to be determined; Calculate it by the following formula θ The optimal solution is: ; Where, X T represents the transposed matrix of X; based on θ The optimal solution of is obtained, and the linear equation of the first fitting curve is obtained.

[0010] Furthermore, the voltage value under the zero current condition is collected to determine whether the voltage value under the zero current condition is within a preset range. If it exceeds the preset range, the current zero point calibration is performed on the first fitting curve.

[0011] Further, performing current zero point calibration on the first fitting curve includes: Perform voltage sampling under zero current conditions at least twice, and average the obtained voltage sampling results to obtain a voltage average under zero current conditions; It is judged whether the voltage value under the zero current condition is within the preset range, and it is judged whether the voltage mean under the zero current condition is within the preset range. If it exceeds the preset range, the first fitting curve is calibrated, and the fitting formula after calibration is as follows: ; In the formula, y Indicates the voltage value, x Indicates the current value, k represents the linear fitting parameter of current-voltage, b x is the voltage mean; If it is within the preset range, the fitting formula of the first fitting curve is not changed.

[0012] Furthermore, the method also includes: Acquire system time, determine whether the current time is in a preset time interval based on the system time, and in response to being in the preset time interval, start a process of performing current zero point calibration on the linear fitting result of the first fitting curve; The preset time interval is configured to satisfy: In response to the system time being in a preset time interval, the output current of the photovoltaic array substantially meets the zero current condition; The preset range is between 0.8 times and 1.2 times the voltage value corresponding to the zero current before correction.

[0013] In a second aspect, the present application further provides an inverter, comprising a photovoltaic current detection device, wherein the photovoltaic current detection device is used to execute the photovoltaic current detection method as described above.

[0014] In this technical solution, since the photovoltaic current detection device executes any photovoltaic current detection method in the above technical solutions, it has all the beneficial effects of the photovoltaic current detection method, which will not be described in detail here.

[0015] Furthermore, the photovoltaic current detection device includes a voltage acquisition module and a processing module, and the voltage acquisition module includes: A current transformer, wherein the primary side of the current transformer is electrically connected to the output end of the photovoltaic array, and the secondary side of the current transformer is electrically connected to the sampling resistor; A filter circuit, the filter circuit is configured to filter the voltage signal converted by the sampling resistor; A processing circuit, the processing circuit is configured to receive a voltage signal across the sampling resistor transmitted by the filter circuit, and amplify the voltage signal to obtain a sampling voltage representing an output current of the photovoltaic array; The processing module is used to construct a current-voltage output characteristic curve of the photovoltaic array, and obtain the output current of the photovoltaic array according to the sampled voltage and the current-voltage output characteristic curve of the photovoltaic array.

[0016] Further, the processing circuit includes: A first operational amplifier U2 and a gain resistor R5, wherein the in-phase and inverting input terminals of the first operational amplifier U2 are connected to two ends of the sampling resistor through the resistor R6 and the resistor R1 respectively, the first operational amplifier U2 is connected to the gain resistor R5, and the first operational amplifier U2 is configured to change the gain of the first operational amplifier U2 by adjusting the resistance value of the gain resistor R5; The processing circuit also includes a second operational amplifier U3, a resistor R2, a resistor R3, a resistor R7, a resistor R8 and capacitors C1, C2, C5 and C9, wherein the output end of the first operational amplifier U2 is connected to the in-phase input end of the second operational amplifier U3 through the resistor R2 and the capacitor C2 in sequence, the connection node between the resistor R2 and the capacitor C2 is grounded through the capacitor C5, and the connection node between the resistor R2 and the capacitor C2 is connected to the output end of the second operational amplifier U3 through the resistor R3, the connection node between the capacitor C2 and the second operational amplifier U3 is grounded through the resistor R9, the positive end of the power supply of the second operational amplifier U3 is grounded through the capacitor C1, the negative end of the power supply is grounded through the capacitor C9, and the output of the second operational amplifier U3 is used as the output of the voltage acquisition module BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A flowchart of a photovoltaic current detection method provided in one embodiment of the present application; Figure 2 A flowchart of the steps of current zero point calibration in a photovoltaic current detection method provided in an embodiment of the present application; Figure 3 A schematic diagram of the composition of a voltage acquisition module in a photovoltaic current detection device provided in an embodiment of the present application; Figure 4 A schematic diagram of the circuit connection of a voltage acquisition module in a photovoltaic current detection device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0018] The present application will be described in detail below in conjunction with the specific implementation modes shown in the accompanying drawings, but these implementation modes do not limit the present application. Structural, methodological, or functional changes made by ordinary technicians in the field based on these implementation modes are included in the protection scope of the present application.

[0019] In order to solve the shortcomings of the prior art, firstly, Figure 1 As shown, the present application provides a photovoltaic current detection method, the method comprising the following steps: Step S11, constructing a current-voltage output characteristic curve of the photovoltaic array; Step S12, obtaining a sampled voltage, which is used to characterize the output current of the photovoltaic array. Specifically, it can be obtained through a hardware circuit module, such as first sampling the output current of the photovoltaic array through a current transformer to obtain a sampled current, and then processing the sampled current through a processing circuit to obtain a sampled voltage.

[0020] Step S13, based on the sampled voltage and in combination with the current-voltage output characteristic curve, the output current of the photovoltaic array is obtained.

[0021] In step S11, constructing the current-voltage output characteristic curve at least includes constructing a first fitting curve, that is, the current-voltage output characteristic curve includes a first fitting curve, the first fitting curve includes a current zero point of the photovoltaic array, and the first fitting curve is constructed and obtained by at least the following steps: Step S111, obtaining at least two current points in the first fitting curve; Step S112, obtaining a voltage value corresponding to each of the current points to obtain coordinates corresponding to at least two current points in the first fitting curve; Step S113: performing linear fitting based on the coordinates of the current point to obtain a first fitting curve of the current-voltage output characteristic curve.

[0022] According to the above description, in the photovoltaic current detection method provided in the embodiment of the present application, linear fitting is performed for the small current interval near the current zero point, and a first fitting curve including the current zero point of the photovoltaic array is constructed by linear fitting. Then, the output current of the photovoltaic array can be obtained based on the collected sampling voltage representing the output current of the photovoltaic array and combined with the first fitting curve. In this way, the sampling accuracy of the photovoltaic array under small current conditions can be improved.

[0023] Furthermore, the current-voltage output characteristic curve of the photovoltaic array also includes a second fitting curve and a third fitting curve; the current value corresponding to the first fitting curve is less than or equal to the current value of the second fitting curve; the current value of the second fitting curve is less than or equal to the current value of the third fitting curve.

[0024] Specifically, the maximum output current of the photovoltaic array can be used to divide the intervals, so as to obtain three adjacent and non-overlapping fitting intervals, and the sample points in each fitting interval are linearly fitted to obtain the first fitting curve, the second fitting curve and the third fitting curve. Among them, the first fitting curve represents the photovoltaic low current output condition, the second fitting curve represents the photovoltaic medium output current condition, and the third fitting curve represents the photovoltaic high current output condition. By segmentally fitting the current-voltage output characteristic curve, a more accurate current-voltage output characteristic curve is constructed. Segmented fitting is conducive to improving the sampling accuracy in the full current range of large, medium and small currents.

[0025] As an optional implementation, the maximum current value corresponding to the first fitting curve is less than or equal to a preset current threshold; the preset current threshold satisfies: greater than or equal to 0.16 times the maximum output current of the photovoltaic array, and less than or equal to 0.24 times the maximum output current of the photovoltaic array.

[0026] Exemplarily, in the embodiment of the present application, the maximum current value corresponding to the first fitting curve is less than or equal to 0.2 times the maximum output current of the photovoltaic array. In the current interval from zero current to 0.2 times the maximum output current of the photovoltaic array, three (two or more) current points are given, and voltage sampling is performed on each current point. A linear fit is performed based on the three sampling points to obtain the first fitting curve.

[0027] The construction method of the second fitting curve and the third fitting curve is similar to the construction method of the first fitting curve, except that the positions of the sampling points are different, which will not be described in detail here.

[0028] As an optional implementation, in the photovoltaic current detection method provided in the present application, performing linear fitting based on the coordinates of the current point to obtain a first fitting curve of the current-voltage output characteristic curve includes the following steps: Obtaining three current points within the first fitting curve; Obtaining a voltage value corresponding to each of the current points to obtain coordinates corresponding to three current points in the first fitting curve; A linear system of equations is constructed, which is represented by the following formula: , Wherein, Y is an n*1 column vector, containing the voltage values ​​of all the current points; X is an n*2 matrix, the first column contains the current values ​​of all the current points, and the second column is a constant 1; θ is an n*1 column vector containing the fitting weight parameters to be determined; Calculate it by the following formula θ The optimal solution is: ; Where, X T represents the transposed matrix of X; based on θ The optimal solution of the first fitting curve is obtained.

[0029] Specifically, the fitting of the first fitting curve is taken as an example for explanation below. Three current points are given in the current interval corresponding to the first fitting curve: X1, X2, and X3. The voltage acquisition module is used to obtain the voltage values ​​corresponding to the three current points: Y1, Y2, and Y3, thereby obtaining a set of sampling point arrays: (X1, Y1), (X2, Y2), and (X3, Y3).

[0030] Construct the following linear equations: (1); Where Y is an n*1 column vector containing all Yi values. The expression of Y is as follows: (2); In formula (1), X is an n*2 matrix, and the matrix X is expressed as follows: (3); In the formula, the first column is the horizontal coordinate Xi of all sampling points, and the second column is the constant 1; In formula (1), θ is a 2*1 column vector, θ contains parameters k and b, k represents the linear fitting parameter of current-voltage, b is the voltage value under zero current condition, and the expression of column vector θ is as follows: (4); Calculate it by the following formula θ The optimal solution is: (5); Where, X T represents the transposed matrix of X; based on θ The optimal solution of , so that the linear equation of the first fitting curve can be obtained, the expression is as follows: (6); In the formula, y represents the voltage value, x represents the current value, k represents the linear fitting parameter of current-voltage, and b represents the voltage value under zero current conditions. Among them, the current points: X1, X2, and X3 can be the current points given by the manufacturer, which are used to construct the photovoltaic current-voltage output characteristic curve.

[0031] It is easy to understand that the construction method of the second fitting curve and the third fitting curve is similar to the construction method of the first fitting curve, the difference is that the positions of the sampling points are different, and no further description is given here. The function expression of the first fitting curve is: y1=k1*x1+b1 ; The function expression of the second fitting curve is: y2=k2*x2+b2 ; The function expression of the third fitting curve is: y3=k3*x3+b3 By fitting the current-voltage output characteristic curve of each current interval in a piecewise manner, the current-voltage output characteristic curve of the photovoltaic array is obtained, the calculation error is reduced, and the sampling accuracy of the current is improved. Specifically, the above fitting method can be the least squares method.

[0032] As an optional implementation method, in order to further improve the sampling accuracy under low current, the photovoltaic current detection method provided in the present application also includes: collecting the voltage value under zero current conditions, judging whether the voltage value under zero current conditions is within a preset range, and if it exceeds the preset range, performing current zero point calibration on the first fitting curve.

[0033] Specifically, as time goes by, the electronic components of the sampling circuit will age and the current zero point will shift, that is, the fitting curve function The b value in will be offset. At this time, under the condition of zero current, the sampling voltage corresponding to the zero current is obtained, and it is determined whether the voltage value under the zero current condition (i.e., the sampling voltage) is within the preset range. If the voltage value under the zero current condition exceeds the preset range, it means that the b value is offset, and the first fitting curve is calibrated to zero point to achieve high-precision current sampling. In an embodiment of the present application, in order to improve the accuracy of small current sampling, the linear fitting result of the small current fitting interval close to zero current (i.e., the first fitting curve) is calibrated to zero point.

[0034] It should be noted that the "zero current condition" described in the embodiments of the present application refers to the condition where the output current of the photovoltaic array is 0. In practical applications, it can also be a current value close to 0, for example, it can be less than 1.5%*I max The value of I max Indicates the maximum output current of the photovoltaic array.

[0035] Further, as an implementation method, Figure 2 As shown, performing current zero point calibration on the first fitting curve includes the following steps: Step S21, performing voltage sampling under zero current conditions for at least two times, performing average processing on the obtained voltage sampling results, and obtaining a voltage average under zero current conditions.

[0036] Step S22, determining whether the voltage mean under the zero current condition is within the preset range, if it exceeds the preset range, calibrating the first fitting curve, after calibration, the first fitting curve is represented by the following formula: (7); Wherein, y represents the voltage value, x represents the current value, k represents the linear fitting parameter of current-voltage, and bx is the mean voltage under zero current conditions.

[0037] Specifically, according to the fitting curve function expression , under zero current conditions, the sampled voltage value of the photovoltaic array is substantially equal to the b value. The preset range of the b value is set to be between 0.8 times and 1.2 times the voltage value corresponding to the zero current before correction. For ease of explanation, for example, b1 is 0.8 times the b value, and b2 is 1.2 times the b value.

[0038] If the voltage value Y0 under the zero current condition satisfies that it is greater than or equal to b1 and less than or equal to b2, the current b value is continued and the current fitting curve is retained.

[0039] If the voltage value Y0 under zero current condition is less than b1 or greater than b2, perform at least two voltage samplings under zero current condition, calculate the voltage mean of the voltage value Y0 and determine whether the obtained voltage mean is within the preset range of the b value. If the voltage mean meets the range of greater than or equal to b1 to less than or equal to b2, continue the current b value and retain the current fitting curve. Otherwise, replace the original b value in the fitting curve function corresponding to the first fitting interval with the voltage mean to obtain a new fitting curve. The function expression of the new fitting curve is as follows: (8); In the formula, y represents the voltage value, x represents the current value, k represents the linear fitting parameter of current-voltage, and bx represents the voltage mean under zero current conditions. It should be noted that the voltage value under zero current conditions refers to the sampled voltage collected when the output current of the photovoltaic array is 0 or close to 0.

[0040] As an optional implementation method, after the first fitting curve is calibrated for current zero point, the second fitting curve and the third fitting curve can also be linearly fitted again according to the photovoltaic current detection method provided in the embodiment of the present application to obtain a new current-voltage output characteristic curve of the photovoltaic array within the maximum output current range, thereby ensuring the accuracy of current sampling.

[0041] As an optional implementation, the photovoltaic current detection method provided by the present application further includes: acquiring system time, judging whether the current moment is in a preset time interval based on the system time, and in response to being in the preset time interval, starting a process of performing current zero point calibration on the linear fitting result of the first fitting curve; The preset time interval is configured to satisfy: in response to the system time being in the preset time interval, the output current of the photovoltaic array substantially meets the zero current condition.

[0042] For example, the preset time interval can be set from 8 pm to 4 am the next day. During this preset time interval, the photovoltaic array is in a lightless (or weak light) environment. At this time, the output current of the photovoltaic array is basically zero, which meets the zero current condition, thereby ensuring the accuracy of b value detection. By automatically adjusting the b value, the zero point self-learning function is realized, which can effectively improve the small current sampling accuracy of the product in the middle and late stages and improve the power generation efficiency of the system.

[0043] According to the above description, the photovoltaic current detection method provided by the present application performs linear fitting near the current zero point, and constructs a first fitting curve including the current zero point of the photovoltaic array by linear fitting, and then the output current of the photovoltaic array can be obtained based on the sampling voltage that characterizes the output current of the photovoltaic array and combined with the first fitting curve. In this way, the sampling accuracy of the photovoltaic array under low current conditions can be improved. In addition, by calibrating the current zero point, the problem of inaccurate sampling caused by the voltage offset corresponding to the current zero point is solved, and the sampling accuracy within the full life cycle of the low current interval is further guaranteed.

[0044] In a second aspect, the present application further provides an inverter, which includes a photovoltaic current detection device, and the photovoltaic current detection device is used to execute the photovoltaic current detection method described above, which can improve the current sampling accuracy.

[0045] As an optional implementation, the photovoltaic current detection device includes a voltage acquisition module and a processing module, such as Figure 3As shown, the voltage acquisition module includes: a current transformer 11, a filter circuit 12, and a processing circuit 13. The processing module is used to construct the current-voltage output characteristic curve of the photovoltaic array, and obtain the output current of the photovoltaic array according to the sampled voltage representing the output current of the photovoltaic array and the current-voltage output characteristic curve of the photovoltaic array. The processing module may include processing chips such as DSP and MCU, which are loaded with an execution program. In one embodiment, the processing module divides the photovoltaic current into three sections for processing, and each section of the current is fitted in the above manner to obtain the relationship between the voltage and the current. The photovoltaic current can be calculated by the sampled voltage. The three-section linear fitting can achieve accurate measurement of small current, medium current and large current, and multi-point fitting can be used to effectively reduce the system error and improve the sampling accuracy. On the other hand, since the fitting curve is a linear function, the b value is the system zero point. Since the aging of the device will cause the zero point to offset, the processing module is further set to perform zero point self-learning when the photovoltaic system is not working, and the zero point self-learning is achieved through multiple sampling to ensure the accuracy of the zero point and achieve high-precision current sampling.

[0046] like Figure 4As shown, the primary side of the current transformer 11 is electrically connected to the output end of the photovoltaic array P1, and the secondary side of the current transformer 11 is electrically connected to the sampling resistor R4. The filter circuit 12 includes a common mode filter circuit and a differential mode filter circuit, and the common mode filter circuit and the differential mode filter circuit are composed of a resistor R1, a resistor R6, a capacitor C4, a capacitor C6 and a capacitor C7. Among them, the capacitor C4 and the capacitor C7 are connected in series at both ends of the sampling resistor R4, and the connection node between the capacitor C4 and the capacitor C7 is grounded. The resistor R1 is arranged between the sampling resistor R4 and the capacitor C4, and the resistor R6 is arranged between the sampling resistor R4 and the capacitor C7. The capacitor C6 is connected in series at both ends of the sampling resistor R4, thereby forming the filter circuit 12. The processing circuit 13 includes an operational amplifier U2 and a gain resistor R5, wherein the gain resistor R5 is connected to the operational amplifier U2, and the gain of the operational amplifier U2 can be changed by adjusting the resistance value of the gain resistor R5. The in-phase and inverting input terminals of the operational amplifier U2 are connected to the two ends of the sampling resistor R4 through the resistor R6 and the resistor R1 respectively. The processing circuit 13 also includes an operational amplifier U3, a resistor R2, a resistor R3, a resistor R7, a resistor R8 and capacitors C1, C2, C5 and C9, wherein the output end of the operational amplifier U2 is connected to the non-inverting input end of the operational amplifier U3 through the resistor R2 and the capacitor C2 in sequence, the connection node between the resistor R2 and the capacitor C2 is grounded through the capacitor C5, and the connection node between the resistor R2 and the capacitor C2 is connected to the output end of the operational amplifier U3 through the resistor R3, the connection node between the capacitor C2 and the operational amplifier U3 is grounded through the resistor R9, the positive power supply end of the operational amplifier U3 is grounded through the capacitor C1, and the negative power supply end is grounded through the capacitor C9, and the output of the operational amplifier U3 serves as the output of the voltage acquisition module.

[0047] When the photovoltaic array P1 is illuminated, a current is generated. The current flows through the primary side of the current transformer 11 and generates a current on the secondary side of the current transformer 11. The current on the secondary side of the current transformer 11 is converted into a voltage signal through the sampling resistor R4. The voltage signal is filtered by the filter circuit 12 and enters the processing circuit 13. The processing circuit 13 is configured to receive the voltage signal across the sampling resistor R4 transmitted by the filter circuit 12 and amplify the voltage signal. The processing circuit 13 has the characteristics of high input impedance and low noise, and can effectively suppress noise and common-mode signals. After amplifying the voltage signal, the processing circuit 13 filters out the high-frequency signal in the amplified voltage signal to ensure the stability of the voltage signal and obtain the adopted voltage representing the output current of the photovoltaic array P1.

[0048] Optionally, the processing circuit 13 includes a second-order bandpass filter, whose attenuation frequency can reach -40dB / 10 times, effectively filtering out interference and noise, and improving the sampling accuracy of the current. The cutoff frequency of the bandpass filter can be expressed as follows: (9); Wherein, f is the cut-off frequency of the band-pass filter, C2 and C5 represent the capacitance values ​​of the corresponding capacitors, and R2, R3, and R9 represent the resistance values ​​of the corresponding resistors.

[0049] The gain of a second-order bandpass filter can be expressed as follows: (10); In the formula, G represents the gain of the bandpass filter, and R7 and R8 represent the resistance values ​​of the corresponding resistors respectively.

[0050] According to the above description, a photovoltaic current detection device provided by the present application adopts a processing circuit 13 to effectively amplify the voltage signal, filter out interference in the signal, reduce system noise, and improve current sampling accuracy; and adopts a current transformer to reduce the cost of the device.

[0051] The photovoltaic current detection device provided in the present application is achieved through a combination of software and hardware. On the one hand, the hardware part realizes the signal acquisition, amplification and filtering functions to ensure the accuracy of the voltage signal. On the other hand, the software algorithm part adopts a three-stage fitting curve to reduce accidental errors and ensure the accuracy of the current in each stage. At the same time, the current zero-point self-learning improves the current sampling accuracy in the later stage of the photovoltaic product life cycle. The above two aspects can effectively ensure the current sampling accuracy of the photovoltaic product throughout its entire life cycle, which is beneficial for the photovoltaic system to work at the maximum power point and improve the power generation efficiency of the photovoltaic system.

[0052] It will be appreciated that the word "exemplary" as used herein means "serving as an example, instance, or illustration". Any embodiment described as "exemplary" is not necessarily preferred or superior to other embodiments and / or does not exclude the combination of features of other embodiments. It will be appreciated that certain features of the present application described in the context of separate embodiments for the sake of clarity may also be provided in a single embodiment by combination. Conversely, various features of the present application described in the context of a single embodiment for the sake of clarity may also be provided individually or in any suitable combination or as any other described embodiment of the present application.

[0053] The above disclosure is only the preferred embodiment of the present application, but it is not intended to limit the scope of rights of the present application. A person of ordinary skill in the art can understand that without departing from the spirit and scope of the present application and the appended claims, changes, modifications, substitutions, combinations, and simplifications should all be equivalent replacement methods and still fall within the scope of the invention.

Claims

1. A photovoltaic current detection method, characterized in that: The method comprises: Construct the current-voltage output characteristic curve of the photovoltaic array; Obtaining a sampled voltage, wherein the sampled voltage is used to characterize an output current of the photovoltaic array; Based on the sampled voltage and in combination with the current-voltage output characteristic curve, an output current of the photovoltaic array is obtained; The current-voltage output characteristic curve at least includes a first fitting curve, the first fitting curve includes a current zero point of the photovoltaic array, and the first fitting curve is obtained by at least the following steps: obtaining at least two current points in the first fitting curve; Obtaining a voltage value corresponding to each of the current points to obtain coordinates corresponding to at least two current points in the first fitting curve; A linear fit is performed based on the coordinates of the current point to obtain a first fitting curve of the current-voltage output characteristic curve.

2. The photovoltaic current detection method according to claim 1, characterized in that: The current-voltage output characteristic curve of the photovoltaic array also includes a second fitting curve and a third fitting curve; the current value corresponding to the first fitting curve is less than or equal to the current value of the second fitting curve; the current value of the second fitting curve is less than or equal to the current value of the third fitting curve.

3. The photovoltaic current detection method according to claim 2, characterized in that: The maximum current value corresponding to the first fitting curve is less than or equal to a preset current threshold; the preset current threshold satisfies: greater than or equal to 0.16 times the maximum output current of the photovoltaic array, and less than or equal to 0.24 times the maximum output current of the photovoltaic array.

4. The photovoltaic current detection method according to claim 1, characterized in that: Performing linear fitting based on the coordinates of the current point to obtain a first fitting curve of the current-voltage output characteristic curve includes: Obtaining three current points within the first fitting curve; Obtaining a voltage value corresponding to each of the current points to obtain coordinates corresponding to three current points in the first fitting curve; A linear system of equations is constructed, which is represented by the following formula: ， Wherein, Y is an n*1 column vector, containing the voltage values ​​of all the current points; X is an n*2 matrix, the first column contains the current values ​​of all the current points, and the second column is a constant 1; θ is an n*1 column vector containing the fitting weight parameters to be determined; Calculate it by the following formula θ The optimal solution is: ； Where, X T represents the transposed matrix of X; based on θ The optimal solution of the first fitting curve is obtained.

5. The photovoltaic current detection method according to any one of claims 1 to 4, characterized in that: The method further comprises: The voltage value under the zero current condition is collected to determine whether the voltage value under the zero current condition is within a preset range. If it exceeds the preset range, current zero point calibration is performed on the first fitting curve.

6. The photovoltaic current detection method according to claim 5, characterized in that: The current zero point calibration of the first fitting curve comprises: Perform voltage sampling under zero current conditions at least twice, and average the obtained voltage sampling results to obtain a voltage average under zero current conditions; The step of judging whether the voltage value under the zero current condition is within the preset range is judging whether the voltage mean value under the zero current condition is within the preset range. If it exceeds the preset range, the first fitting curve is calibrated. The fitting formula after calibration is as follows: ； In the formula, y Indicates the voltage value, x Indicates the current value, k represents the linear fitting parameter of current-voltage, b x is the voltage mean value; If it is within the preset range, the fitting formula of the first fitting curve is not changed.

7. The photovoltaic current detection method according to claim 6, characterized in that: The method further comprises: Acquiring system time, determining whether the current moment is in a preset time interval based on the system time, and in response to being in the preset time interval, starting a process of performing current zero point calibration on the linear fitting result of the first fitting curve; The preset time interval is configured to satisfy: In response to the system time being in a preset time interval, the output current of the photovoltaic array substantially meets the zero current condition; The preset range is between 0.8 times and 1.2 times the voltage value corresponding to the zero current before correction.

8. An inverter, comprising a photovoltaic current detection device, characterized in that: The photovoltaic current detection device is used to execute the photovoltaic current detection method according to any one of claims 1 to 7.

9. The inverter according to claim 8, characterized in that: The photovoltaic current detection device includes a voltage acquisition module and a processing module, and the voltage acquisition module includes: A current transformer, wherein the primary side of the current transformer is electrically connected to the output end of the photovoltaic array, and the secondary side of the current transformer is electrically connected to the sampling resistor; A filter circuit, wherein the filter circuit is configured to filter the voltage signal converted by the sampling resistor; a processing circuit, the processing circuit being configured to receive the voltage signal across the sampling resistor transmitted by the filter circuit, and amplify the voltage signal to obtain a sampling voltage representing the output current of the photovoltaic array; The processing module is used to construct a current-voltage output characteristic curve of the photovoltaic array, and obtain the output current of the photovoltaic array according to the sampled voltage and the current-voltage output characteristic curve of the photovoltaic array.

10. The inverter according to claim 9, characterized in that: The processing circuit comprises: A first operational amplifier U2 and a gain resistor R5, wherein the in-phase and inverting input terminals of the first operational amplifier U2 are connected to the two ends of the sampling resistor through the resistor R6 and the resistor R1 respectively, the first operational amplifier U2 is connected to the gain resistor R5, and the first operational amplifier U2 is configured to change the gain of the first operational amplifier U2 by adjusting the resistance value of the gain resistor R5; The processing circuit also includes a second operational amplifier U3, a resistor R2, a resistor R3, a resistor R7, a resistor R8 and capacitors C1, C2, C5 and C9, wherein the output end of the first operational amplifier U2 is connected to the non-inverting input end of the second operational amplifier U3 through the resistor R2 and the capacitor C2 in sequence, the connection node between the resistor R2 and the capacitor C2 is grounded through the capacitor C5, and the connection node between the resistor R2 and the capacitor C2 is connected to the output end of the second operational amplifier U3 through the resistor R3, the connection node between the capacitor C2 and the second operational amplifier U3 is grounded through the resistor R9, the positive power supply end of the second operational amplifier U3 is grounded through the capacitor C1, the negative power supply end is grounded through the capacitor C9, and the output of the second operational amplifier U3 serves as the output of the voltage acquisition module.

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