TWI676092B - Mppt for photovoltaic system and partial shading detecting method - Google Patents

Abstract

A method for tracking the maximum power point of a solar photovoltaic system and judging a part of the shading, by calculating the current solar illumination and the number of working photovoltaic cells based on the actually measured output voltage and the output current, and using the solar illumination and the work The photovoltaic cell calculates the maximum power current of the solar photovoltaic module, and whether the solar photovoltaic module is partially shaded can be judged by the sunlight and the maximum power current to determine whether the tracking process and time can be reduced, and subsequent In the maximum power point tracking, the global maximum power point can be accurately tracked.

Description

Maximum power point tracking and partial shading judgment method of solar photovoltaic system

The invention relates to a solar photovoltaic system, in particular to a method for tracking the maximum power point of a solar photovoltaic system and a method for judging partial shade.

A solar photovoltaic system is formed by connecting a plurality of solar photovoltaic modules in parallel, and each solar photovoltaic module is connected with a plurality of photovoltaic cells in series. These photovoltaic cells generate electric current when being illuminated to supply power. Because these photovoltaic cells are connected in series, in the conventional technology, when the current generated by a partially shaded photovoltaic cell is less than the current generated by a non-shaded photovoltaic cell, the shaded photovoltaic cell will generate In the case of reverse bias to change from generating power to consuming power, a bypass diode is usually connected in parallel with each photovoltaic cell to allow excess current to flow through the bypass diode of the shaded photovoltaic cell. However, this also allows the output current-voltage characteristic curve of the photovoltaic cell module under a partial shade to show a step shape, so that its power-voltage characteristic curve has multiple peaks. Such a characteristic makes it easy for the maximum power tracking to only track To the regional maximum power point instead of the global maximum power point.

The main purpose of the present invention is to provide a method for judging partial shading of a solar photovoltaic system. According to the output of the solar photovoltaic system, it is judged whether it is in a situation of partial shading, and the partial shading is obtained by tracking the maximum photovoltaic power point The global maximum power point of the next solar photovoltaic system can avoid the problem of tracking only to the regional maximum power point.

A partial shading judgment method of a solar photovoltaic system of the present invention includes: a measurement module measures an output voltage and an output current of a solar photovoltaic module of the solar photovoltaic system at two points in time; a calculation module The group calculates the daily illumination of the solar photovoltaic module and the number of working photovoltaic cells according to the output voltage and the output current; the calculation module calculates a maximum power point based on the sunshine and the number of working photovoltaic cells; a control module Controlling the solar photovoltaic module to operate at the maximum power point and measuring a maximum power point current by the measurement module; and the calculation module using the maximum power current, the sunlight, and the maximum value under a standard condition The power current and the sunlight under a standard condition determine whether the solar photovoltaic system is partially shaded.

The maximum power point tracking of a solar photovoltaic system according to the present invention includes: providing a solar photovoltaic module, the solar photovoltaic module is connected with a plurality of photovoltaic cells in series, and one characteristic curve of the solar photovoltaic module has a plurality of intervals; and an interval The prediction step includes: a measurement module measures an output voltage and an output current at one time interval of one of the solar photovoltaic modules at two time points; a calculation module is based on the output at two time points The voltage and the output current estimate the daylight intensity and the number of working photovoltaic cells in the interval of the solar photovoltaic module; the calculation module corrects the interval based on the sunlight intensity and the number of working photovoltaic cells; and the calculation module judges and corrects Whether the interval has a global maximum power point, if not, perform the interval prediction step again to correct the sunlight and the number of working photovoltaic cells in another interval, and if so, perform the global maximum power point tracking of the interval.

The present invention calculates the current illuminance and the number of working photovoltaic cells by actually measuring the output voltage and the output current, and calculates the maximum power current of the solar photovoltaic module by using the illuminance and the working photovoltaic cells , And whether the solar photovoltaic module is partially shaded can be judged by the sunlight and the maximum power current, so as to reduce the tracking time and accurately track the maximum power point in the whole region in the subsequent maximum power point tracking.

Please refer to FIG. 1, which is a flowchart of a maximum power point tracking 10 of a solar photovoltaic system 100 according to an embodiment of the present invention, which includes “providing a solar photovoltaic system 11”, “determining whether to partially shade 12”, "Interval prediction step 13", "Global maximum power point tracking 14" and "Controlling solar photovoltaic module operation at global maximum power point 15".

Please refer to Figs. 1 and 2 for providing a solar photovoltaic system 100 in "Providing Solar Photovoltaic System 11". The solar photovoltaic system 100 has a solar photovoltaic module 110, a measurement module 120, a computing module 130 and A control module 140, the measurement module 120 is electrically connected to the solar photovoltaic module 110, the calculation module 130 is electrically connected to the measurement module 120, and the control module 140 is electrically connected to the calculation module 130 And the solar photovoltaic module 110, wherein the computing module 130 may be a microprocessor or other computer device capable of performing calculations, and the control module 140 may be a power converter to actively switch by its electronic components The solar photovoltaic module 110 is operated at a maximum power point.

Please refer to FIG. 3, which is an equivalent circuit diagram of the solar photovoltaic module 110 and the measurement module 120. The solar photovoltaic module 110 has a plurality of photovoltaic cells 111 connected in series, and the photovoltaic cells 111 are exposed to light. A current is generated to supply power to a load L, and each of the photovoltaic cells 111 has a bypass diode 111a, so that excessive current can flow through the bypass diode 111a of the photovoltaic cell 111 that is shaded to avoid being bypassed. The shaded photovoltaic cell 111 is converted to consume power. The measurement module 120 has an ammeter 121 and a voltmeter 122, wherein the ammeter 121 is connected in series with the photovoltaic cells 111 to measure an output current of the solar photovoltaic module 110, and the voltmeter 122 is The photovoltaic cells 111 are connected in series to measure an output voltage of the solar photovoltaic module 110.

Please refer to FIG. 4, which is a current-voltage characteristic curve of the solar photovoltaic module 110 under a condition of partial shading. Since each of the photovoltaic cells 111 is shaded differently, the The currents are not the same, resulting in a current-voltage characteristic curve with a stepped shape, and according to the number of the photovoltaic cells 111 connected in series with the solar photovoltaic module 110, the characteristic curve can be divided into a plurality of sections with the same number. Please refer to FIG. 5, which is a power-voltage characteristic curve of the solar photovoltaic module 110 in another case of partial shading. Since each photovoltaic cell 111 is shaded differently, the power-voltage characteristic curve shows many The state of the peak.

Please refer to Figures 1 and 6 for the judgment of whether there is partial shading by the output of the solar photovoltaic module 110 in "Judgement of Partial Shade 12". Please refer to Figure 6 in this embodiment. , "Judging whether it is partially shaded 12" includes: measuring the output voltage and output current 12a, calculating the sunlight and the number of working photovoltaic cells 12b, calculating the maximum power point 12c, measuring the maximum power point current 12d, and determining whether it is partially Shade 12e.

Please refer to FIGS. 2 and 6, in step 12a, the measurement module 120 measures the output voltage and the output current of the solar photovoltaic module 110 at two points in time, and the measurement at the two points in time The output voltage and the output current are transmitted to the calculation module 130, and then in step 12b, the calculation module 130 calculates the daylight intensity of the solar photovoltaic module 110 and the number of working photovoltaic cells according to the output voltage and the output current. Wherein, the calculation module 130 takes the output voltage and the output current at two points of time into a current characteristic function to obtain the solar illumination of the solar photovoltaic module 110 and the number of working photovoltaic cells. In this embodiment, the current characteristic function is:

其中，I _o 為該輸出電流，S為該日照度，N為該工作光伏電池數，I _sc 為一短路電流，K ₀為一短路電流的溫度係數，T為一操作溫度，T _r 為一參考溫度，I _rr 為該參考溫度時的一逆向飽和電流，q為一電子電荷量，E _G 為一能隙寬度，K為一波資曼常數，A為該光伏電池之P-N接面理想參數，V _o 為該輸出電壓，V _oc 為一開路電壓。將兩個時間點下的該輸出電壓及該輸出電流代入可表示為：

其中，S ₁ ,N ₁ ,V ₁ ,I ₁分別為第一個時間點下的該日照度、該工作光伏電池數、該輸出電壓及該輸出電流，S ₂ ,N ₂ ,V ₂ ,I ₂分別為第二個時間點下的該日照度、該工作光伏電池數、該輸出電壓及該輸出電流，若兩個時間點下的該日照度及該工作光伏 電池數未改變時，藉由求解上述之聯立方程式即可求得當前之該日照度及該工作光伏電池數。 or

Among them, I _{o is} the output current, S is the sunlight, N is the number of working photovoltaic cells, I _sc is a short-circuit current, K ₀ is a temperature coefficient of a short-circuit current, T is an operating temperature, and T _r is a Reference temperature, I _rr is a reverse saturation current at the reference temperature, q is an electronic charge amount, E _G is an energy gap width, K is a wave Ziman constant, and A is an ideal parameter for the PN junction of the photovoltaic cell , V _{o is} the output voltage, and V _oc is an open circuit voltage. Substituting the output voltage and the output current at two points in time can be expressed as:

Among them, S ₁ , N ₁ , V ₁ , I ₁ are the sunlight, the number of working photovoltaic cells, the output voltage, and the output current at the first time point, respectively, S ₂ , N ₂ , V ₂ , I ₂ is the sunlight, the number of working photovoltaic cells, the output voltage, and the output current at the second time point respectively. If the sunlight and the number of working photovoltaic cells at the two time points have not changed, Solving the above simultaneous equations can obtain the current illuminance and the number of working photovoltaic cells.

Referring to FIG. 6, after obtaining the solar illumination of the solar photovoltaic module 110 and the number of working photovoltaic cells, go to step 12c. The calculation module 130 substitutes the solar illumination and the number of operating photovoltaic cells back to the current characteristics. The function obtains an estimated current function, and uses the estimated current function to obtain a power characteristic function, and differentiates the power characteristic function and sets it to 0 to calculate the maximum power point, where the power characteristic function is:

or

>C 其中，S為計算而得之該日照度，G _STC 為該標準條件下之該日照度，不同之該太陽光伏系統100的製造廠商有著不同設定，一般為1000W/m²，I _mpp 為量測而得之該最大功率電流，I _{mpp_STC} 為該標準條件下之最大功率電流，也就是在各個製造廠商於標準條件之日照度及環境溫度下所測得的最大功率電流，C為一部份遮陰門檻值，在本實施例中，該部份遮陰門檻值為3%。而若滿足上述判斷式則代表該太陽光伏系統100被部份遮陰，若未滿足上述判斷式則代表該太陽光伏系統100未被部份遮陰。 Please refer to FIGS. 2 and 6. In step 12d, the control module 140 controls the solar photovoltaic module 110 to operate at the maximum power point and measures a maximum power by the current meter 121 of the measurement module 120. Point current. Finally, step 12e is performed. The calculation module 130 judges whether the solar photovoltaic system 100 is partially shaded by the maximum power current, the sunlight, the maximum power current under a standard condition, and the sunlight under a standard condition. In this embodiment, the judgment formula for judging whether the solar photovoltaic system 100 is partially shaded can be expressed as:

> C, where S is the calculated solar illumination, G _{STC is} the solar _{illumination under} the standard conditions, different manufacturers of the solar photovoltaic system 100 have different settings, generally 1000W / m ² , I _mpp is The measured maximum power current, I _{mpp_STC} is the maximum power current under the standard conditions, that is, the maximum power current measured by various manufacturers under the standard conditions of sunlight and ambient temperature, C is a The shading threshold. In this embodiment, the shading threshold is 3%. If the above judgment formula is satisfied, it means that the solar photovoltaic system 100 is partially shaded. If the above judgment formula is not satisfied, it means that the solar photovoltaic system 100 is not partially shaded.

Please refer to FIG. 1. If it is judged that the solar photovoltaic system 100 is not partially shaded, the power-voltage characteristic curve representing the solar module 110 has only one peak, so it can be calculated by step 12c. The interval in which the maximum power point is located is taken as the interval in which the global maximum power point is located, and "the solar global maximum power point tracking 14" is performed.

Please refer to FIG. 1. If it is judged in step 12 that the solar photovoltaic system 100 is partially shaded, it represents that the power-voltage characteristic curve of the solar module 110 is in a multi-peak state, so the “interval prediction step 13” is performed. In order to obtain the power-voltage characteristic curve closer to the actual situation and the calculation and correction of the interval where the global maximum power point is located, the sunshine of the interval and the number of working photovoltaic cells, Global maximum power point.

或

中，以求得該太陽光伏模組110之該區間的該日照度及該工作光伏電池數，本發明不受限於特定電流特性函數，上述電流特性函數為本案較佳實施例。 The detailed steps of "Interval Prediction Step 13" are as follows: First, the measurement module 120 measures the output voltage and the output current at one time interval of one of the solar photovoltaic modules 110 at two points in time and transmits them to the calculation. Module 130, the calculation module 130 substitutes the output voltage and the output current at the two time points into the current characteristic function:

or

In order to obtain the solar illuminance and the number of working photovoltaic cells in the interval of the solar photovoltaic module 110, the present invention is not limited to a specific current characteristic function, and the above current characteristic function is a preferred embodiment of the present application.

或

中重新計算該區間之該功率特性曲線，最後，該計算模組130根據重新計算之該功率特性曲線判斷該區間是否有該全域最大功率點，若否則重新進行該區間預測步驟以校正另一區間之該日照度及該工作光伏電池數，若是則進行「全域最大功率點追蹤14」。 Then, the calculation module 130 corrects the interval and substitutes the power characteristic function according to the sunlight and the number of working photovoltaic cells: P ( S, N, V _o ) = V _o × ( S × ( I _sc + K ₀ × ( T - T _r ))- I _rr ×

or

Recalculate the power characteristic curve of the interval, and finally, the calculation module 130 judges whether the interval has the global maximum power point according to the recalculated power characteristic curve; if not, re-perform the interval prediction step to correct another interval If it is the daylight intensity and the number of working photovoltaic cells, if it is, then perform “Global Maximum Power Point Tracking 14”.

Please refer to Figures 1 and 2. In “Global Maximum Power Point Tracking 14”, the measurement module 120 measures the output voltage and the output at three time points in the interval where the global maximum power point is located. Current, the calculation module 120 estimates the sunlight, the number of working photovoltaic cells, and the operating temperature of the interval based on the output voltage and the output current at three time points, and obtains the interval in which the maximum power of the whole region is located. After the solar illumination, the number of working photovoltaic cells, and the operating temperature, the calculation module 130 obtains the power characteristic function of the interval in which the global maximum power is located by using the solar illumination, the number of operating photovoltaic cells, and the temperature. , And differentiating the power characteristic function to calculate the global maximum power point, the power characteristic function is:

or

Please refer to Fig. 1. After obtaining the global maximum power point, perform "control solar photovoltaic module operation at global maximum power point tracking 15". The control module 140 controls the solar photovoltaic module 110 to operate at the requested global domain. The maximum power point enables the solar photovoltaic module 110 to output the current maximum power regardless of whether it is partially shaded.

The present invention calculates the current illuminance and the number of working photovoltaic cells by actually measuring the output voltage and the output current, and calculates the maximum power of the solar photovoltaic module 110 by using the illuminance and the working photovoltaic cells. Current, and whether the solar photovoltaic module 110 is partially shaded can be judged by the solar illumination and the maximum power current, so that the maximum power point in the whole region can be accurately tracked in the subsequent maximum power point tracking.

The protection scope of the present invention shall be determined by the scope of the appended patent application. Any changes and modifications made by those skilled in the art without departing from the spirit and scope of the present invention shall fall within the protection scope of the present invention. .

10‧‧‧ Maximum Power Point Tracking of Solar Photovoltaic System

11‧‧‧ provide solar photovoltaic system

12‧‧‧ judge if it is partially shaded

12a‧‧‧Measure output voltage and output current

12b‧‧‧Calculate the sunshine and working photovoltaic cells

12c‧‧‧Calculate maximum power point

12d‧‧‧Measure the maximum power point current

12e‧‧‧ judge if it is partially shaded

13‧‧‧ interval prediction steps

14‧‧‧Global Maximum Power Point Tracking

15‧‧‧ Controls the operation of solar photovoltaic modules at the maximum power point in the world

100‧‧‧solar photovoltaic system

110‧‧‧solar photovoltaic module

111‧‧‧Photovoltaic cells

111a‧‧‧ Bypass Diode

120‧‧‧Measuring module

121‧‧‧ ammeter

122‧‧‧Voltmeter

130‧‧‧Computing Module

140‧‧‧control module

FIG. 1 is a flowchart of tracking a maximum power point of a solar photovoltaic system according to an embodiment of the present invention. FIG. 2 is a functional block diagram of a solar photovoltaic system according to an embodiment of the present invention. FIG. 3 is an equivalent circuit diagram of a solar photovoltaic module according to an embodiment of the present invention. Figure 4: A current-voltage characteristic curve of the solar photovoltaic module according to an embodiment of the present invention. Figure 5: Power-voltage characteristic curve of the solar photovoltaic module according to an embodiment of the present invention. FIG. 6 is a flowchart of a partial shading judgment method according to an embodiment of the present invention.

Claims (10)

A partial shading judgment method for a solar photovoltaic system includes: a measurement module measures an output voltage and an output current of a solar photovoltaic module of the solar photovoltaic system at two points in time; a calculation module Calculate the daily illumination of the solar photovoltaic module and the number of working photovoltaic cells based on the output voltage and the output current; calculate a maximum power point based on the solar illumination and the number of operating photovoltaic cells; a control module controls The solar photovoltaic module is operated at the maximum power point and a maximum power point current is measured by the measurement module; and the calculation module uses the maximum power current, the sunlight, and the maximum power under a standard condition. The current and the sunlight under a standard condition determine whether the solar photovoltaic system is partially shaded. According to the partial shading judgment method of the solar photovoltaic system described in item 1 of the scope of the patent application, wherein the calculation module determines whether the solar photovoltaic system is partially shaded by the expression: > C, where S is the sunlight intensity, G _STC is the sunlight intensity under the standard conditions, I _{mpp is} the maximum power current, I _{mpp_STC} is the maximum power current under the standard conditions, and C is a part of the shading threshold If the above expression is satisfied, it is judged that the solar photovoltaic system is partially shaded; if the above expression is not satisfied, it is judged that the solar photovoltaic system is not partially shaded. The method for judging the partial shading of the solar photovoltaic system as described in item 2 of the scope of patent application, wherein the threshold for the partial shading is 3%. According to the partial shading judgment method of the solar photovoltaic system described in item 1 of the scope of the patent application, wherein the calculation module calculates the output voltage and the output current at two time points into a current characteristic function to obtain the The solar intensity and the number of working photovoltaic cells in the interval of the solar photovoltaic module. The partial shading judgment method for a solar photovoltaic system as described in item 4 of the patent application scope, wherein the current characteristic function is: or Among them, I _{o is} the output current, S is the sunlight, N is the number of working photovoltaic cells, I _sc is a short-circuit current, K ₀ is a temperature coefficient of a short-circuit current, T is an operating temperature, and T _r is a Reference temperature, I _rr is a reverse saturation current at the reference temperature, q is an electronic charge amount, E _G is an energy gap width, K is a wave Ziman constant, and A is an ideal parameter for the PN junction of the photovoltaic cell , V _{o is} the output voltage, and V _oc is an open circuit voltage. According to the method for judging the partial shading of the solar photovoltaic system described in item 4 or 5 of the scope of patent application, after obtaining the solar illumination of the solar photovoltaic module and the number of working photovoltaic cells, the calculation module calculates the solar illumination and The working photovoltaic cell returns the current characteristic function several times to obtain an estimated current function, obtains a power characteristic function from the estimated current function, and differentiates the power characteristic function to calculate the maximum power point. The partial shading judgment method for a solar photovoltaic system as described in item 6 of the patent application scope, wherein the power characteristic function is: or Among them, S is the sunlight, N is the number of working photovoltaic cells, I _sc is a short-circuit current, K ₀ is a temperature coefficient of a short-circuit current, T is an operating temperature, T _r is a reference temperature, and I _{rr is} the A reverse saturation current at a reference temperature, q is an electronic charge amount, E _G is an energy gap width, K is a wave of Ziman constant, A is an ideal parameter for the PN junction of the photovoltaic cell, and V _o is an output voltage , V _oc is an open circuit voltage. A maximum power point tracking of a solar photovoltaic system includes: providing a solar photovoltaic module, the solar photovoltaic module is connected with a plurality of photovoltaic cells in series, one characteristic curve of the solar photovoltaic module has a plurality of intervals; and an interval prediction The steps include: a measurement module measures an output voltage and an output current at one time interval of the solar photovoltaic module at two time points; a calculation module is based on the output voltage and the two time points. The output current estimates the daylight intensity and the number of working photovoltaic cells in the interval of the solar photovoltaic module; the calculation module corrects the interval based on the sunlight intensity and the number of working photovoltaic cells; and the calculation module determines the corrected interval Whether there is a global maximum power point; if not, the interval prediction step is performed again to correct the solar illumination and the number of working photovoltaic cells in another interval, and if so, the global maximum power point tracking of the interval is performed. According to the maximum power point tracking of the solar photovoltaic system described in item 8 of the scope of patent application, in the step of predicting the interval, the calculation module brings the output voltage and the output current at two time points into a current In the characteristic function, the solar intensity and the number of working photovoltaic cells in the interval of the solar photovoltaic module are obtained. The current characteristic function is: or Among them, I _{o is} the output current, S is the sunlight, N is the number of working photovoltaic cells, I _sc is a short-circuit current, K ₀ is a temperature coefficient of a short-circuit current, T is an operating temperature, and T _r is a Reference temperature, I _rr is a reverse saturation current at the reference temperature, q is an electronic charge amount, E _G is an energy gap width, K is a wave Ziman constant, and A is an ideal parameter for the PN junction of the photovoltaic cell , V _{o is} the output voltage, and V _oc is an open circuit voltage. The maximum power point tracking of a solar photovoltaic system as described in item 8 of the patent application scope, wherein the global maximum power point tracking includes: the measurement module measures the interval where the global maximum power point is located at three time points The output voltage and the output current at the same time; the calculation module estimates the insolation, the number of operating photovoltaic cells, and an operating temperature of the interval based on the output voltage and the output current at three points in time; After the sunlight, the number of working photovoltaic cells, and the temperature in the interval where the maximum power is located, the calculation module obtains the global maximum power where the maximum power is located by using the sunlight, the number of working photovoltaic cells, and the temperature. A power characteristic function of the interval, and differentiating the power characteristic function to calculate the global maximum power point, the power characteristic function is: or Among them, S is the sunlight, N is the number of working photovoltaic cells, I _sc is a short-circuit current, K ₀ is a temperature coefficient of a short-circuit current, T is the operating temperature, T _r is a reference temperature, and I _{rr is} the A reverse saturation current at a reference temperature, q is an electronic charge amount, E _G is an energy gap width, K is a wave Ziman constant, A is an ideal parameter for the PN junction of the photovoltaic cell, and V _{o is} the output voltage , V _oc is an open circuit voltage.