TWI522766B - Maximum power point tracking method based on temperature variation detection for solar cell - Google Patents

Description

Solar photovoltaic maximum power point tracking method based on temperature change detection

The invention relates to a planting sun based on temperature change detection photoelectric The method of maximum power point tracking, in particular, relates to a method for accurately tracking the maximum power point of a solar cell when the sunlight changes drastically. The dramatic change of sunlight is the main cause of the wrong judgment and malfunction of the traditional maximum power point tracking method. The present invention can accurately track the maximum power point of the solar cell by utilizing the characteristic that the temperature change rate of the solar panel is higher than the atmospheric temperature change rate when the sunlight changes drastically.

Since the output power of solar cells is affected by factors such as sunlight intensity, temperature, environment, aging degradation of additional components, and materials of manufacture, solar cells can produce different power curves under different conditions, and also make the output voltage of solar cells. The current and power do not change linearly, as shown in Figures 1a and 1b. Therefore, in order to operate the solar cell at the optimum power point, Maximum Power Point Tracking (MPPT) technology must be used. Through the MPPT technology, the solar cell works at the best working point, so that it has the maximum power output. The most common power point tracking techniques currently available are: Voltage Feedback Method, Power Feedback Method, Linear Approximation, Perturb and Observe Method, Incremental Conductance Method), actual measurement method and Three Points Weighting Method, etc., but all are adjusted for power changes.

The above seven maximum power point tracking methods are basically the same in terms of their basic concepts, and the difference lies only in the judgment of the maximum power point and the implementation method. Among them, the disturbance observation method is widely applied to the maximum power point tracking because of its simple structure and less parameters to be measured. However, the disturbance observation method has a big disadvantage. When the intensity of the sunlight changes greatly, the disturbance observation method will have misjudgment and malfunction, and the result will make the working point become farther and farther away from the maximum power point. The following figure is illustrated as follows: Assume that the current operating point is point A; the operating voltage is V , and the control circuit generates a voltage disturbance value, so that the operating point voltage is from V → V + Δ V if the sunlight intensity is unchanged. Then the working point will be from point A to point B. It is known from the principle of disturbance observation that the disturbance direction is wrong (because the output power is reduced), and the control circuit will automatically perturb in the opposite direction. But unfortunately, the intensity of the solar light just becomes stronger, so that the power-voltage characteristic curve changes from P ₁ to P ₂ , so the actual working point is from point A to point C, and the output power is increased instead. The disturbance observation method is now to this end it will be disturbed in the right direction, so it will be adjusted from the operating voltage V to V + △ V, if the sun became stronger, this will continue to be the wrong direction, leading to an operating point farther and farther away from the maximum power point .

In view of the above, an object of the present invention is to provide a maximum power point tracking method for planting solar photovoltaic based on temperature change detection. When the sunlight is suddenly strong, the temperature rise of the solar panel will rise faster than the atmospheric temperature. When the sunlight is weakened, the temperature of the solar panel will drop faster than the atmospheric temperature. The rate of change of the temperature of the solar panel and the temperature of the atmosphere can be used to determine the intensity of the sunlight. Whether the change is drastic, and the working point is accurately moved to the maximum power point.

An embodiment of the maximum power point tracking method of the present invention comprises the steps of: (a) providing a solar cell comprising a solar panel for converting solar energy into electrical energy; and (b) measuring the solar cell in a The first power value P _{1 is} obtained by the power value of the first operating point TP ₁ , and the solar panel temperature and the atmospheric temperature are measured to obtain the first solar panel temperature TC ₁ and the first atmospheric temperature TA ₁ ; (c) toward the first a disturbance direction changes the output voltage of the solar cell to obtain a second operating point TP ₂ ; (d) measuring the power value of the solar cell at the second operating point TP ₂ to obtain a second power value P ₂ , simultaneously Measuring the temperature of the solar panel and the temperature of the atmosphere to obtain a second solar panel temperature TC ₂ and a second atmospheric temperature TA ₂ ; (e) when the second power value P _{2 is} less than the first power value P ₁ , A second disturbance direction opposite to the disturbance direction changes the output voltage of the solar cell to obtain another second operating point, and then measures the power value of the solar cell at the other second operating point, and measures the solar panel temperature Degree and atmospheric temperature; (f) when the second power value P _{2 is} greater than the first power value P ₁ and And moving the operating point of the solar cell from the first operating point TP ₁ to the second operating point TP ₂ , where k is a constant; (g) when the second power value P _{2 is} greater than the first power value P ₁ and At this time, the solar cell output voltage is maintained at the first voltage value V ₁ .

The value of the constant k is between 1.5 and 2. If the value of k is too large or too small, the time to adjust to the maximum power point will be longer, but no malfunction will occur.

The above and other objects, features, and advantages of the invention will be apparent from

11‧‧‧Solar battery

12‧‧‧Power Converter

13‧‧‧ Controller

14‧‧‧Surface temperature sensor

15‧‧‧Atmospheric temperature sensor

20‧‧‧ load

S1, S2, S3, S4, S5, S6, S7, S8, S9‧‧ steps

V‧‧‧ voltage

Figure 1a is a graph of voltage versus current for a conventional solar cell.

Figure 1b is a plot of power versus voltage for a conventional solar cell.

Figure 2 is a schematic diagram of a conventional perturbation observation method.

Figures 3a and 3b are flow diagrams of a maximum power point tracking method in accordance with the present invention.

Figure 4 is a schematic diagram showing the difference between the maximum power point tracking method of the present invention and the conventional disturbance observation method.

Figure 5 is a block diagram of a system of a solar cell using the maximum power point tracking method of the present invention.

The maximum power point tracking method of the present invention mainly aims to accurately determine the disturbance direction by using the difference between the temperature of the solar panel and the rate of change of the atmospheric temperature when the solar light changes drastically, thereby avoiding erroneous judgments and actions.

For convenience of explanation, the test point before any disturbance is called TP ₁ (first working point), the output power is called P ₁ (first power), the solar panel temperature TC ₁ (first solar panel temperature), atmospheric temperature TA ₁ (first atmospheric temperature); the test point after the disturbance is called TP ₂ (second operating point), the output power is called P ₂ (second power), the solar panel temperature TC ₂ (second solar panel temperature), Atmospheric temperature TA ₂ (second atmospheric temperature).

As shown in Figures 3a and 3b, the maximum power point tracking method of the present invention includes the following steps:

Step S1 : providing a solar cell including a solar panel for converting solar energy into electrical energy.

Step S2 : For the current working point of the solar cell, that is, the first operating point TP ₁ , measure the voltage value and the power value to obtain the first voltage value V ₁ and the first power value P ₁ , and measure the temperature of the solar panel The first solar panel temperature TC ₁ and the first atmospheric temperature TA _{1 are obtained at} atmospheric temperature.

Step S3 : changing the output voltage of the solar cell toward a first disturbance direction to obtain a second operating point TP ₂ .

Step S4 : measuring the voltage value and the power value of the second operating point TP ₂ to obtain the second voltage value V ₂ and the second power value P ₂ , and simultaneously measuring the temperature of the solar panel and the atmospheric temperature to obtain the temperature of the second solar panel. TC ₂ and a second atmospheric temperature TA ₂ .

Step S5 : If the second power value P _{2 is} smaller than the first power value P ₁ , the power is reduced after the disturbance, and the disturbance direction is wrong. Therefore, step S6 is performed to a second disturbance direction opposite to the first disturbance direction. The output voltage of the solar cell is changed to obtain another second operating point TP ₂ , and then returns to step S4. If the second power value P _{2 is} greater than the first power value P ₁ , step S7 is performed for further determination.

Step S7 : If , representing the temperature change rate of the solar panel Rate of change with atmospheric temperature In contrast, there is no excessive difference. It is judged that the sunshine intensity does not change drastically at this time, and the above-mentioned disturbance direction is correct. Therefore, step S8 is performed to change the output voltage of the solar cell toward the disturbance direction to make the solar cell work. Moving from the first working point TP ₁ to the second working point TP ₂ , then making the second working point TP ₂ a new first working point TP ₁ and returning to step S3; Indicates that there is a disturbance factor caused by a large change in sunshine at this time, and therefore proceeds to step S9.

Step S9 : Since the solar radiation intensity is drastically changed, a possible misjudgment may be caused. At this time, it is not preferable to make any change, so that the solar cell is maintained at the first voltage value V ₁ and the process returns to step S2.

The above k value is a proportional constant, and a reasonable k value (empirical value) is between 1.5 and 2. If the k value is too large or too small, the time to adjust to the maximum power point will be longer, but no malfunction will occur. In the period when the intensity of the sunlight changes drastically, it can be judged by step S7, and no wrong judgment or malfunction occurs, so the operating point voltage can be maintained, and the working point will move from point A to point D, as shown in Fig. 4, Wait for the sun to change and then adjust the work point.

In the control algorithm of the maximum power point tracking method of the present invention, it can be determined in step S7 whether or not it is in a period in which the intensity of the sunlight changes drastically, and no erroneous judgment or malfunction occurs. The difference between the maximum power point tracking method of the present invention and the conventional disturbance observation method is as shown in Fig. 4. In the maximum power point tracking method of the present invention, when the intensity of sunlight changes drastically, the operating point voltage can be maintained ( If it is kept at the first voltage value V ₁ ), the working point will be moved from point A to point D in Fig. 4, waiting for the sun to change and then proceeding to adjust the operating point.

Figure 5 is a block diagram showing the system of a solar cell using the maximum power point tracking method of the present invention, wherein the solar cell includes a solar panel 11 for converting solar energy into electrical energy. A surface temperature sensor 14 is attached to the solar panel 11 for sensing the temperature of the solar panel 11, and another atmospheric temperature sensor 15 is exposed to the atmosphere for sensing the temperature of the atmosphere. If the intensity of the sunlight changes drastically, the temperature change rate of the solar panel 11 will be significantly higher than the rate of change of the atmospheric temperature (ie, On the other hand, if the sunshine intensity does not change drastically, the temperature change rate of the solar panel 11 is not significantly higher than the atmospheric temperature change rate (ie, These temperature change controllers 13 can be detected via the surface temperature sensor 14 and the atmospheric temperature sensor 15. The power converter 12 supplies the output power of the solar cell 11 to the load 20, and the controller 13 is coupled to the power converter 12 to detect the voltage value V output by the solar cell 11 and according to FIG. 3a and The maximum power point tracking method of the present invention shown in FIG. 3b performs calculation and judgment to control the change of the output voltage of the power converter 12 to obtain the maximum power output, thereby improving the power generation efficiency, increasing the power generation amount, and reducing the procurement of the solar battery. And improve system reliability.

The present invention has been disclosed in the above embodiments, but it is not intended to limit the scope of the present invention. Any one skilled in the art can make some modifications and retouchings without departing from the spirit of the invention. The scope of protection is subject to the definition of the scope of the patent application attached.

S1, S2, S3, S4, S5, S7, S9‧‧ steps

Claims (2)

A method for tracking a maximum power point of a solar cell, comprising: (a) providing a solar cell comprising a solar panel for converting solar energy into electrical energy; and (b) measuring the solar cell at a first operating point TP a power value of ₁ to obtain a first power value P ₁ and a first voltage value V ₁ , and simultaneously measuring the temperature of the solar panel and the atmospheric temperature to obtain a first solar panel temperature TC ₁ and a first atmospheric temperature TA ₁ ; Changing the output voltage of the solar cell toward a first disturbance direction to obtain a second operating point TP ₂ ; (d) measuring the power value of the solar cell at the second operating point TP ₂ to obtain a second power value P ₂ Simultaneously measuring the temperature of the solar panel and the temperature of the atmosphere to obtain a second solar panel temperature TC ₂ and a second atmospheric temperature TA ₂ ; (e) when the second power value P _{2 is} less than the first power value P ₁ , a second disturbance direction opposite to the first disturbance direction changes an output voltage of the solar cell to obtain another second operating point, and then returns to step (d) to measure the solar cell at the other second operating point Power value, Simultaneously measuring the temperature of the solar panel and the temperature of the atmosphere; (f) when the second power value P _{2 is} greater than the first power value P ₁ and And moving the operating point of the solar cell from the first operating point TP ₁ to the second operating point TP ₂ , and then returning to step (c), where k is a constant; (g) when the second power value P _{2 is} greater than the first power value P ₁ and At this time, the solar cell output voltage is maintained at the first voltage value V ₁ and then returns to step (b). The solar cell maximum power point tracking method according to claim 1, wherein the constant k has a value between 1.5 and 2.