What is the core principle of MPPT solar controller?? | Demuda

May 19, 2023

MPPT solar controller is an upgraded product of traditional solar charging and discharging controller. The core principle of MPPT controller is Maximum Power Point Tracking. It can detect the output voltage of solar panels in real time, track the maximum VI value, and make the system charge the battery at maximum power output. MPPT controller is the brain of the photovoltaic system, coordinating the work of solar panels, batteries and loads.

The relationship between the maximum power that solar cells can output and the environment is complex. The shape factor is defined as the ratio of the maximum power of the solar cell to the product of the open circuit voltage Voc and the short circuit current Isc. In most applications, FF, Voc and Isc can be used to approximate the electrical characteristics of the photovoltaic cell under general conditions.

Under certain operating conditions, the battery will have a working point, and the product of its current (I) and voltage (V) (electric power) will be the maximum value. This value corresponds to a specific resistance, which according to Ohm's law equals V / I. The power can be calculated using P = V * I. In the main application range of photovoltaic cells, they can be approximated as constant current sources. However, between the voltage and current of the photovoltaic cell, there is a function similar to an exponential function. According to basic circuit and calculus theory, when the slope of the I-V curve (dI/dV) and the ratio of I/V are equal, opposite in sign, dP/dV = 0, the output power is the maximum value. This position is the maximum power point (MPP), corresponding to the inflection point of the curve.

If the load resistance of a solar cell is R = V/I, which is the reciprocal of the above value, it can output the maximum power from the solar cell. Sometimes, this value is also called the "characteristic impedance" of the solar cell, which is a dynamic value related to the sunlight, temperature, and lifespan of the solar cell. If the resistance is less than or greater than this value, the power extracted will be less than the maximum power, so the solar cell will not work under the most ideal and efficient conditions. Maximum power point tracking uses several different control resistors or logic to find the maximum power point, enabling the converter to extract the maximum power from the solar cell.

To charge the battery, the output voltage of the solar panel must exceed the current voltage of the battery. If the voltage of the solar panel is lower than the voltage of the battery, the output current will be close to 0. Therefore, for safety reasons, the peak voltage (Vpp) of the solar panel is set to about 17V when it is manufactured, at a standard setting when the ambient temperature is 25°C. When the weather is very hot, the peak voltage Vpp of the solar panel drops to about 15V, but in cold weather, the peak voltage Vpp of the solar energy can reach 18V.

Now, let's compare the differences between the MPPT solar controller and the traditional solar controller. Traditional solar charging and discharging controllers are like manual gearboxes. When the engine speed increases, if the gear position of the gearbox does not increase accordingly, it will inevitably affect the vehicle speed. However, for MPPT solar controllers, the charging parameters are set before leaving the factory. That is to say, the MPPT controller can track the maximum power point of the solar panel in real-time, thereby exerting the maximum efficiency of the solar panel. The higher the voltage, the more power can be output through maximum power tracking, thereby improving charging efficiency. In theory, the solar power generation system using MPPT controllers will be 50% more efficient than traditional controllers, but according to our actual tests, due to environmental influences and various energy losses, the final efficiency can also be increased by 20%-30%.

In this sense, the MPPT solar charge controller will ultimately replace the traditional solar controller.

The main function of the MPPT controller is to detect the DC voltage and output current of the main circuit, calculate the output power of the solar array, and realize the maximum power point tracking. The disturbance resistor R and the MOSFET are connected in series. Under the condition that the output voltage is basically stable, by changing the duty ratio of MOSFET, the average current through the resistor can be changed, thereby generating a current disturbance. At the same time, the output current and voltage of the photovoltaic cell will also change. By measuring the change in the output power and voltage of the photovoltaic cell before and after the disturbance, the next disturbance direction is determined. When the disturbance direction is correct, the output power of the solar panel increases, and the next period continues to disturb in the same direction. Otherwise, disturb in the opposite direction. In this way, the disturbance and observation are repeated to make the output of the solar panel reach the maximum power point.

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