Photovoltaic MPPT (Maximum Power Point Tracking) method based on environmental change identification

Abstract

The invention provides a photovoltaic MPPT (Maximum Power Point Tracking) method based on environmental change identification, and the control method comprises the following steps: 1, judging a working state before prediction is started, and obtaining data for subsequent judgment; 2, identifying scene change according to the laws of the next working point and the current maximum power point when the temperature and the light intensity of the photovoltaic characteristic curve change; thirdly, different modulation strategies are completed through an MPPT controller according to the recognized scene changes; 4, the output efficiency of the photovoltaic cell is maximized by controlling the duty ratio output by the MPPT controller, prediction is carried out according to the voltage and current value sampled last time, and the photovoltaic cell can quickly reach the vicinity of the maximum power point; and step 5, performing small-step tracking to complete maximum power point tracking. The technical problems that temperature and light intensity changes are difficult to distinguish and a tracking strategy is difficult to design in a targeted manner in the prior art are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photovoltaic power generation, and particularly to a photovoltaic MPPT method based on environment change identification. BACKGROUND

[0002] With the continuous growth of global energy demand and the increasing severity of environmental problems, light energy, as a clean and renewable energy source, plays a crucial role in mitigating global climate change by reducing carbon emissions and other greenhouse gas emissions. Therefore, the progress and popularization of solar energy technology not only meet future energy demand, but also promote the realization of sustainable development and environmental protection goals. Photovoltaic (PV) systems convert solar energy into electricity, providing a sustainable solution to meet energy demand. The energy production of photovoltaic systems depends on various parameters, including environmental parameters such as temperature and solar irradiance. Therefore, it is necessary to use MPPT control technology to track the maximum power point to obtain as much solar energy as possible.

[0003] Many maximum power point tracking (MPPT) methods have been proposed, of which the most commonly used are the perturb and observe (P&O) method and the incremental conductance (INC) method. Fast MPPT techniques use internal parameters of photovoltaic modules to achieve good performance under uniform and partially shaded solar irradiance conditions. However, most studies ignore the effects of temperature changes, which limits their performance. The judgment of light intensity changes by fast MPPT techniques is based on ΔP and ΔI, where temperature rise and light intensity drop have the same characteristics, so temperature changes and light intensity changes cannot be distinguished, and the use of a common duty cycle modulation method reduces efficiency. SUMMARY

[0004] The present application aims to provide a photovoltaic MPPT method based on environment change identification, which can solve the technical problem that temperature and light intensity changes are difficult to distinguish, and then it is difficult to design a targeted tracking strategy.

[0005] The technical solution adopted by the present application to solve its technical problems is: The present application provides a photovoltaic MPPT method based on environment change identification, the control system of the control method includes a photovoltaic panel, an MPPT controller that distinguishes temperature and light intensity changes, a load, and a DC-DC circuit connected to the load, including the following steps: Step one: judge the working state before starting prediction, get data for subsequent judgment; Step two: identify scene changes according to the law of the next working point and the current maximum power point when temperature and light intensity change according to the photovoltaic characteristic curve; Step three: different modulation strategies are completed by the MPPT controller for the identified scene changes; Step four: through controlling the duty cycle of the MPPT controller output to make the photovoltaic cell output efficiency maximum, according to the last sampling voltage and current value to predict, quickly reach the maximum power point near; Step five: small step tracking is carried out again, and the maximum power point tracking is completed.

[0006] Further, the working state is judged before starting prediction, and the scene change is identified according to the rule of the next working point and the current maximum power point when the temperature and light intensity change. When the temperature rises, the next working point reached along the load curve is on the right side of the current maximum power point. When the light intensity decreases, the next working point is on the left side of the current maximum power point. When the photovoltaic system runs under uniform light intensity, the next working point and the maximum power point characteristics are the same when the temperature rises. When the light intensity decreases, the relationship between the next working point and the maximum power point depends on whether the voltage interval of the maximum power point before and after the light intensity change is similar. When the voltage interval is similar, the situation is the same as that under uniform light intensity. When the voltage interval is far apart, the relationship between the next working point and the maximum power point is opposite to that under uniform light intensity. And because the working point voltage difference before and after the change is obvious, a voltage threshold can be used to distinguish the above-mentioned situation, and the load value of the MPPT controller is calculated through the measured values of current and voltage.

[0007] Further, the light intensity and temperature judgment method includes: according to the past , and positive and negative to judge the temperature, light intensity and load change method is optimized especially the scene identification when the temperature rises and the light intensity decreases.

[0008] Further, the photovoltaic system I-V curve characteristic maximum power point finding method includes: under uniform light intensity, the maximum power point is regularly distributed, under local shading condition, the maximum power point distribution has similarity only the voltage interval has difference, so that the next working point along the load curve changes and the maximum power point between the temperature change and the light intensity change has a certain relationship.

[0009] Further, the temperature and light intensity are distinguished, including: judging whether it is less than 0, if yes, it is light intensity reduction, if If greater than 0, it is judged whether the variables UIC (uniform light intensity) and PSC (local shadow) are 1, the values of the variables UIC and PSC are distinguished by the collected photovoltaic module voltage, if UIC is 1, it indicates that the current is temperature rise, otherwise, PSC is 1, it is further judged whether the difference between the output voltage of the last sampling and the output voltage of the present sampling is greater than the threshold β, if it is satisfied, it is light intensity drop, if it is not satisfied, it is temperature rise, then different strategies are taken for different cases, the voltage and current values of the last sampling are predicted to quickly reach the maximum power point.

[0010] Further, the photovoltaic MPPT method taking different strategies for different cases comprises: different prediction control modes are taken for different environmental changes, and the current and voltage values measured are used for prediction when the light intensity and temperature change.

[0011] In summary, the beneficial effects of the present application are: The photovoltaic MPPT method based on environmental change identification of the present application analyzes the working state of the controller according to the sampling voltage and current values obtained by the controller in each sampling period, can predict the voltage and current values of the maximum power point on the output characteristic curve of the battery under the corresponding light intensity when the light intensity and temperature change, and thus calculates the optimal output duty ratio, so that the system quickly reaches the optimal power point. BRIEF DESCRIPTION OF DRAWINGS

[0012] The present application is further described below in combination with the drawings and embodiments.

[0013] Figure 1 It is the composition principle diagram of the MPPT control system of the present application; Figure 2 It is the working flow chart of the MPPT control system of the present application; Figure 3 It is the I-V characteristic curve diagram of the photovoltaic module output under different temperature effects and solar radiation levels under uniform light intensity; Figure 4 It is the P-V characteristic curve diagram of the photovoltaic module output under different temperature effects and solar radiation levels under uniform light intensity; Figure 5 It is the I-V characteristic curve diagram of the photovoltaic module output under different temperature effects and solar radiation levels under local shadow; Figure 6 It is the P-V characteristic curve diagram of the photovoltaic module output under different temperature effects and solar radiation levels under local shadow; Figure 7 It is the MPPT control diagram in the embodiment when facing temperature rise and light intensity drop; Figure 8Simulation results of several MPPT control methods under uniform light intensity in an embodiment; Figure 9 Simulation results of several MPPT control methods under partial shading in an embodiment. DETAILED DESCRIPTION

[0014] The application will now be described in further detail with reference to the drawings. These drawings show only the basic structure of the application and therefore only show the components relevant to the application.

[0015] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "connected" and "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0016] Please refer to Figures 1-9 The application discloses a photovoltaic MPPT method based on environmental change identification. The control system of the control method comprises a photovoltaic cell panel, an MPPT controller distinguishing temperature and light intensity changes, a load, and a DC-DC circuit connected with the load, and comprises the following steps: Step one: judging the working state before starting prediction, obtaining 、 、 , PSC, UIC data, for subsequent judgment; Step two: according to the law of the next working point and the current maximum power point when the temperature and light intensity change, the scene change can be identified as: light intensity increases, light intensity decreases, temperature rises and falls; Step three: for the identified scene changes: light intensity increases, light intensity decreases, temperature rises and falls, different modulation strategies are completed through the MPPT controller respectively; Step four: the duty cycle output by the MPPT controller can make the photovoltaic cell output efficiency reach the maximum, and because there is the following relationship between the external load and the internal resistance of the photovoltaic cell at this time: ; The voltage and current values sampled last time can be predicted to quickly reach the vicinity of the maximum power point; Step five: small step tracking is performed again to complete the maximum power point tracking.

[0017] Further, the working state is judged before starting prediction, and according to the rule of the next working point and the current maximum power point when the temperature and light intensity change, the scene change is identified, which is divided into: light intensity increase, light intensity decrease, temperature rise and decrease, including: finding the maximum power point according to the I-V curve characteristics of the photovoltaic system, the judgment principle is to analyze the rule of the next working point and the current maximum power point when the temperature and light intensity change, specifically: when the photovoltaic system runs under uniform light intensity, when the temperature rises, the next working point reached by the working point along the load curve is all on the right side of the current maximum power point; when the light intensity decreases, the next working point is all on the left side of the current maximum power point. When the photovoltaic system runs under local shading, when the temperature rises, the characteristics of the next working point and the maximum power point are the same as under uniform light intensity; when the light intensity decreases, the relationship between the next working point and the maximum power point depends on whether the voltage interval of the maximum power point before and after the light intensity change is similar, when the voltage interval is similar, the case is the same as under uniform light intensity, and when the voltage interval is far apart, the relationship between the next working point and the maximum power point is opposite to that under uniform light intensity, and because the voltage gap between the working points before and after the change is obvious, a voltage threshold can be used to distinguish the above cases. The load value of the MPPT controller is calculated by the measured values of current and voltage R load， The calculation formula is: ; In one embodiment, the light intensity and temperature judgment method includes: optimizing the past method of judging temperature, light intensity and load change according to the 、 and , especially the scene identification when the temperature rises and the light intensity decreases. Because the temperature rise and light intensity decrease in the past method are the same in the characteristics of 、 and , it is difficult to design a suitable fast modulation strategy according to the specific situation, which reduces the efficiency.

[0018] In one embodiment, the method of finding the maximum power point of the I-V curve characteristics of the photovoltaic system includes: under uniform light intensity, the maximum power point is regularly distributed, and under local shading conditions, the maximum power point distribution has similarity only with the difference in voltage interval, so that there is a deterministic relationship between the next working point and the maximum power point along the load curve when the temperature and light intensity change.

[0019] In one embodiment, distinguishing temperature and light intensity includes: judging whether it is less than 0, if so, it is light intensity decrease. If If greater than 0, then determine whether the variables UIC (uniform light intensity) and PSC (partial shadow) are 1, the values of the variables UIC and PSC are distinguished by the collected photovoltaic module voltage, if UIC is 1, it indicates that the current is temperature rise; otherwise, PSC is 1, further determine whether the difference between the output voltage of the last sampling and the output voltage of the current sampling is greater than the threshold β, if it is satisfied, it is light intensity drop. If it is not satisfied, it is temperature rise. Since the maximum power point voltage distribution under the condition of local shading has obvious difference, β only needs to be less than the maximum voltage difference, so the design range is relatively loose. Then different strategies are taken for different situations, the voltage and current values of the last sampling are predicted to quickly reach the vicinity of the maximum power point.

[0020] In one embodiment, the photovoltaic MPPT method taking different strategies for different situations includes: different prediction control modes are taken for different environmental changes, and the current value and voltage value measured are used to predict when the light intensity changes and the temperature changes, for example, when the light intensity rises, the voltage of the predicted MPPT point is approximately equal to the voltage value of the last sampling, and the current value is estimated by using the reference value voltage . The calculation of can be expressed as: ; The voltage and current values of the predicted MPP point are substituted into the calculation formula of the duty cycle to quickly reach the predicted GMPP point, and the expression is: ; When the light intensity decreases, the voltage value of the MPP point can be predicted to be approximately equal to the voltage value of the last sampling, and the current value , so the calculation expression of the duty cycle is: ; When the temperature rises, the current value of the MPP point can be predicted to be approximately equal to the current value of the last sampling, and the voltage value , so the calculation expression of the duty cycle is: ; When the temperature drops, the current value of the MPP point can be predicted to be approximately equal to the current value of the last sampling, and the voltage value , so the calculation expression of the duty cycle is: ; Specifically, Figure 3 is a photovoltaic module output I-V characteristic curve diagram under different temperature effects and solar radiation levels under uniform light intensity, Figure 4The graph shows the PV characteristic curves of photovoltaic modules under different temperature effects and solar irradiance levels under uniform light intensity. It can be seen that the nonlinear relationship between the photovoltaic panel output parameters and atmospheric variables is highly dependent on changes in solar irradiance and ambient temperature. The short-circuit current of the photovoltaic cell (…) The PV current increases quasi-linearly with increasing solar radiation, while the open-circuit voltage of the photovoltaic panel increases slightly. The maximum power of the photovoltaic panel is highly proportional to the solar irradiance. With increasing temperature, the PV current increases slightly, but the PV open-circuit voltage... The power level is significantly reduced. Furthermore, it can be observed that due to the inherent characteristics of the photovoltaic system's IV curve, the maximum power point exhibits a regular distribution under uniform light intensity. Figure 5 This is a graph showing the output IV characteristic curves of photovoltaic modules under different temperature effects and solar irradiance levels under partial shading. Figure 6 This diagram shows the PV characteristic curves of photovoltaic modules under different temperature effects and solar irradiance levels under partial shading. Similarly, the maximum power point distribution under partial shading conditions is similar, only the voltage range differs. Therefore, there is a deterministic relationship between the next operating point and the maximum power point as the load curve changes with temperature and light intensity. Specifically, when the photovoltaic system is operating under uniform light intensity, when the temperature rises, the next operating point reached along the load curve is always to the right of the current maximum power point; when the light intensity decreases, the next operating point is always to the left of the current maximum power point. When a photovoltaic system operates under partial shade, if the temperature rises, the characteristics of the next operating point are the same as under uniform light intensity. If the light intensity decreases, the relationship between the next operating point and the maximum power point depends on whether the voltage range of the maximum power point is close before and after the light intensity change. When the voltage ranges are close, the situation is the same as under uniform light intensity. However, when the voltage ranges are far apart, the relationship between the next operating point and the maximum power point is the opposite of that under uniform light intensity. Since the voltage difference of the operating point before and after the change is significant, a voltage threshold can be used to distinguish it from the above situation.

[0021] Figure 7 To implement the MPPT control chart for conditions of rising temperature and decreasing light intensity, the method involves obtaining the relationship between the operating point and the current maximum power point after an environmental change, using a step size. It also distinguishes between general and special cases based on UIC and PSC conditions. For the special case where the maximum power point distribution range differs significantly under partial shading conditions, due to the large voltage range difference and the significant difference in voltage changes between the operating points under rising temperature and decreasing light intensity, a voltage threshold is used to handle this special case. Specifically, in conjunction with… Figure 8Under uniform light intensity conditions and temperature changes, when the temperature rises from 25°C to 50°C, the PV panel operating point first moves from point A (MPP is 25°C) along load line 1 to point B, and then reaches point C through a step adjustment. The calculation yields... This indicates that the next operating point after the change in conditions is located to the right of the current maximum power point. Furthermore, since the current light intensity is uniform, i.e. The current condition change is determined to be a temperature change. To quickly reach the operating point E, which is closer to the new maximum power point F, the new duty cycle is calculated using the previously obtained current. First, the circuit is rapidly modulated to point D, then automatically and quickly moves along load line 2 to point E. Afterward, a small-step tracking method is used, and the new maximum power point F (MPP at 50°C) can be tracked in a few steps. When the light intensity decreases under uniform light conditions, as... Figure 9 The PV panel operation point moves from point A along load curve 1 to point G, then reaches point H in one step. , It can be determined that the current change is a decrease in light intensity. Since point G is approximately located in the constant current source region, the ISC is approximately equal to the maximum power point current. Therefore, the current at point G is used to obtain a new duty cycle to quickly reach the vicinity of the maximum power point. Then, by adjusting the step size, the maximum power point is reached.

[0022] Figure 8 The graph shows the output power curve of the photovoltaic cell under uniform light intensity, with the temperature set to first increase from 25℃ to 50℃ and then decrease back to 25℃. The solar irradiance level increases from 400W / m2 to 1000W / m2 and then decreases to 500W / m2 and 400W / m2 respectively.

[0023] Figure 9For local shading, the output power curve of the photovoltaic cell is set to change from 25℃ to 50℃ and then to 25℃. The solar radiation level changes from case 1: 700W / m2, 800W / m2, 900W / m2, 1000W / m2 to case 2: 500W / m2, 600W / m2, 700W / m2, 1000W / m2 to case 3: 350W / m2, 600W / m2, 700W / m2, 1000W / m2 to case 4: 150W / m2, 300W / m2, 700W / m2, 1000W / m2 to case 5: 220W / m2, 360W / m2, 640W / m2, 850W / m2. The Simulink simulation shows that compared with the traditional INC method and the MINC method proposed in the paper Xu L, Cheng R, Yang J. A modified INC method for PV string under uniform irradiance and partially shaded conditions. IEEE Access. 2020 Jul 16;8:131340-51., the overall tracking efficiency of the proposed method is increased by 3.89% and 0.25% under uniform light intensity, and is increased by 3.65% and 0.13% under local shadow condition.

[0024] The photovoltaic MPPT method based on environment change recognition, the photovoltaic cell group, the MPPT controller distinguishing temperature and light intensity change, the load and the DC-DC circuit connected with the load of the application, through the research on the output characteristics of the photovoltaic module, the relationship between the current working point and the maximum power point before and after the environmental change is obtained, and the voltage threshold processing is set for special cases, a method for accurately distinguishing temperature and light intensity change is proposed, and after detecting the temperature change, the known point current is used for fast modulation, so that the working point quickly reaches the maximum power point, and then small step tracking is carried out, the application not only avoids the wrong identification of the previous method when facing environmental change, especially temperature rise and light intensity drop, but also considers the response speed and steady accuracy of the MPPT controller.

[0025] The photovoltaic MPPT method based on environment change recognition, according to the sampling voltage and current value obtained by the controller in each sampling period, the working state of the controller is analyzed, when the light intensity changes and the temperature changes, the voltage and current value of the maximum power point (MPP point) on the output characteristic curve of the battery under the corresponding light intensity can be predicted, so as to calculate the optimal output duty ratio, so that the system quickly reaches the optimal power point (GMPP point).

[0026] The above merely describes the preferred embodiment of the present application, but the present application is not limited to other forms, any person skilled in the art can use the disclosed technical content to make changes or equivalent embodiments of equivalent changes applied to other fields, but as long as it does not deviate from the technical scheme of the present application, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present application still belongs to the protection scope of the technical scheme of the present application, and in the description of the present application, it should be pointed out that unless otherwise specified and limited, the terms "mounting", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

Claims

1. A photovoltaic MPPT method based on environmental change identification, characterized in that: The control system of the control method includes a photovoltaic panel, an MPPT controller that distinguishes between temperature and light intensity changes, a load, and a DC-DC circuit connected to the load, and includes the following steps: Step 1: Before starting the prediction, assess the working status and obtain data for subsequent judgment; Step 2: Identify scene changes based on the pattern of the next operating point and the current maximum power point when temperature and light intensity change in the photovoltaic characteristic curve; Step 3: For each identified scene change, different modulation strategies are implemented using the MPPT controller; Step 4: By controlling the duty cycle of the MPPT controller, the output efficiency of the photovoltaic cell is maximized. Based on the voltage and current values ​​sampled previously, a prediction is made to quickly reach the vicinity of the maximum power point. Step 5: Perform small-step tracking again to complete maximum power point tracking.

2. The photovoltaic MPPT method based on environmental change identification according to claim 1, characterized in that: Before initiating prediction, the operating status is assessed. Based on the pattern of the next operating point and the current maximum power point when temperature and light intensity change according to the photovoltaic characteristic curve, scene changes are identified. When the photovoltaic system is operating under uniform light intensity, when the temperature rises, the next operating point reached along the load curve is always to the right of the current maximum power point. When the light intensity decreases, the next operating point is always to the left of the current maximum power point. When the photovoltaic system is operating under partial shading, when the temperature rises, the characteristics of the next operating point and the maximum power point are the same as under uniform light intensity. When the light intensity decreases, the relationship between the next operating point and the maximum power point depends on whether the voltage range of the maximum power point is close before and after the light intensity change. When the voltage range is close, the situation is the same as under uniform light intensity. However, when the voltage range is far apart, the relationship between the next operating point and the maximum power point is the opposite of that under uniform light intensity. Furthermore, since the voltage difference of the operating point before and after the change is significant, a voltage threshold can be used to distinguish it from the above situations.

3. The photovoltaic MPPT method based on environmental change identification according to claim 1, characterized in that: Methods for determining light intensity and temperature include: based on previous... , and The method of using positive and negative values ​​to determine changes in temperature, light intensity, and load has been optimized to enable scene identification when temperature rises and light intensity decreases.

4. The photovoltaic MPPT method based on environmental change identification according to claim 1, characterized in that: Methods for finding the maximum power point (MPP) based on the characteristics of the photovoltaic system's IV curve include: under uniform light intensity, the MPP is distributed in a regular pattern; under partial shading conditions, the MPP distribution is similar, only the voltage range differs. Therefore, there is a deterministic relationship between the next operating point and the MPP as the load curve changes with temperature and light intensity.

5. The photovoltaic MPPT method based on environmental change identification according to claim 1, characterized in that: Distinguishing between temperature and light intensity includes: judging If it is less than 0, then the light intensity has decreased; if not... If the value is greater than 0, then it is determined whether the variables UIC (uniform light intensity) and PSC (local shading) are 1. The values ​​of variables UIC and PSC are identified by the collected photovoltaic module voltage. If UIC is 1, it indicates that the current temperature is rising; otherwise, PSC is 1. It is further determined whether the difference between the output voltage sampled last time and the output voltage sampled now is greater than the threshold β. If it is satisfied, it indicates that the light intensity is decreasing; if it is not satisfied, it indicates that the temperature is rising. Then, different strategies are adopted for different situations. Based on the voltage and current values ​​sampled last time, predictions are made to quickly reach the vicinity of the maximum power point.

6. The photovoltaic MPPT method based on environmental change identification according to claim 1, characterized in that: Photovoltaic MPPT methods that adopt different strategies for different situations include: adopting different predictive control modes for different environmental changes, and making predictions based on measured current and voltage values ​​when light intensity and temperature change.

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