In the photovoltaic power generation system, an important way to improve the overall efficiency of the system is to adjust the working point of the photovoltaic cell in real time so that it always works near the maximum power point. This process is called maximum power point tracking (maximum power point). Point tracking, MPPT).
First, the basic principle of MPPTIn theory, as long as the photovoltaic cell is fully matched and directly coupled to the load (for example, the load is a charged battery), the volt-ampere characteristic curve of the load and the maximum power point trajectory curve can coincide or gradually coincide, so that the photovoltaic cell is in an efficient output. status. However, in daily applications, it is difficult to meet the direct coupling conditions of the load and the photovoltaic cell. Therefore, in order to improve the overall efficiency of the photovoltaic power generation system, an important way is to change the system load characteristics in real time, that is, adjust the working point of the photovoltaic cell so that the photovoltaic cell can always work near the maximum power point under different sunshine and temperature. This tracking process is called maximum power point tracking, as shown in Figure 1 for the MPPT basic schematic.
Figure 1 MPPT schematic
l Maximum power point A1 → maximum power point B1 (condition: change the system load characteristics from load 1 to load 2)
l Maximum power point B1 → maximum power point A1 (condition: change the load 2 back to load 1 by the system load characteristic)
It can be seen that the MPPT control strategy in the photovoltaic power generation system is based on real-time detection of the output power of the photovoltaic cell, and then through a certain control algorithm to predict the maximum power output point of the photovoltaic cell under the current working conditions, and finally by changing the current impedance. Or voltage, current, etc. to meet the maximum power output requirements.
In this way, whether due to changes in external light intensity or due to changes in the junction temperature of the internal photovoltaic cell, the output power of the photovoltaic cell is reduced, and the system can automatically operate at the optimal working state under the current working conditions to achieve maximum power output, thereby Improve the conversion efficiency of the entire photovoltaic power generation system.
Second, the factors affecting the maximum power pointAt a certain light intensity and ambient temperature, the photovoltaic cell can work at different output voltages, but only at a certain output voltage value, the output power of the photovoltaic cell can reach a maximum value, and the working point of the photovoltaic cell is reached. The highest point of the output power voltage curve is called the maximum power point. Figure 2 shows the MPPT exposure to light, and Figure 3 shows the temperature dependence of the MPPT.
Figure 2 MPPT is affected by light
Figure 3 MPPT is affected by temperature
As shown in the figure, the intensity of visible light and the temperature drop will cause the maximum power point of the photovoltaic cell to move down.
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