AN2946 datasheet(24/38 Pages) STMICROELECTRONICS

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Firmware design

AN2946

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Doc ID 15473 Rev 2

steady state. Since the resulted power at point B is higher than the power at point A,

the MCU continues to increase the duty cycle.

Step 2: The MCU increases the duty cycle from DC(B) to DC(C). During steady state

the charger operates at point C. Because the power at point C is still higher than the

power at point B, the MCU keeps the same trend and increases the duty cycle.

Step 3: The charger now moves to point D after the MCU increases the duty cycle from

DC(C) to DC(D). Since the power at point D is lower than the power at point C, the

MCU reverses the direction. At the next step, it decreases the duty cycle and moves to

Step 4: The MCU keeps decreasing duty cycle from DC(C) to DC(B). After detecting

that the power at B point is lower than that at C point, MCU reverses direction again.

Then system comes back to step 2.

The P&O tracing route can be described as shown in Figure 30. This tracing route explains

that the MPPT algorithm is dynamic. The charger does not operate at a fixed point, and it

works within a certain range that the maximum power point locates.

Figure 30.

P and O tracing route

The P&O method is based on the fact that the P-V curve remains almost unchanged during

a very short time period. Generally, the MCU executes each P&O step in several

milliseconds, while the P-V curve drift caused by environmental change usually takes a few

seconds or even several minutes, which is much longer. The P&O method is a feasible

method to achieve MPP tracking.

AN2946 датащи(PDF) 24 Page - STMicroelectronics