MPPT ALGORITHM

MPPT (Maximum Power Point Tracker) is a detection method for work point with optimal capacity of the solar power system by controlling electronic locks (IGBT) cycle of the inverter. MPPT is originally a power electronic equipment coupling power source PV to load to amplify the power supply from the power solar cells when working conditions change and thus may improve performance of the system.

MPP control is an internal control with a microprocessor that uses the maximum power point detection algorithm to make the solar panel absorb the maximum solar radiation energy to convert into power source (DC/AC).

  • For connection to solar panel: The microprocessor uses MPPT algorithm to track the working current – voltage curve of solar panel, forcing it to work at the current and voltage of the maximum power point MPP.
  • For battery connection, MPP charge control includes a DC – DC bộ chuyển đổi: It receives DC power from solar panel, converts into AC power and reconverts DC power afterwards to charge battery. MPP charge control performs active and separate control for both input (solar panel) and output (battery), it requires two different DC power to ensure optimal charging current features:
    + When the current from solar panel is low, MPPT charge control increases the current to charge battery.
    + When the current from solar panel is high, MPPT charge control decreases the current to protect battery.

When the weather changes, the amount of solar radiation varies, which shows that charge control plays a vital role in the system. Therefore, MPPT charge control is most useful for independent solar energy system using battery and having no connection to grid. It is also necessary for water pump system using solar energy.

Figure 1.Characteristic line I – V and power characteristic line of PV

Shown in Figure 1, the two endpoints of the I – V graph correspond with two points ISC and VOC with P = 0. The maximum power point (MPP) is the point at which the product of the maximum voltage and current values. Voltage and current value at MPP point in general case is denoted Vm and Im. In standard conditions, MPP will get the nominal current IR and nominal voltage VR.

Figure 2. I – V and P – V curves of PV change under radiation conditions

The maximum power point sticking system is used to define the maximum capacity point that is normally located at the elbow of I – V characteristics with each PV. Then, a signal will be defined to control the inverter so as to achieve this maximum working point.

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