What’s MPPT From Solar Inverter
When people talk about solar inverter, MPPT parameters always are referred. It is pretty important when in the stage of procuring, installing and commissioning solar plant.
What’s MPPT
MPPT is the abbreviation of Max Power Point Tracking, In the PV system, the output power of solar panels is determined by many factors, such as the intensity of sunlight and ambient temperature. In different environments, the output curves of solar panels are different, and the corresponding maximum power points are also different. The stronger the sunshine is, the greater the output power of solar panels are.
Solar panel follows I-V( Green Curve ) and P-V curve( Blue Curve). In above picture, if you hope that inverter has max output power, inverter must work on max power point on P-V curve. Why does inverter track max power point constantly, like what I referred to , P-V curve will change with sunshine intensity, temperature, shileding etc. In the morning, the voltage of max power point may be 570V, at noon it may be decline until 520V, while in the afternoon, it may rise unitl 550V. That’s why inverter needs to track the max power point continuously.
For example, the voltage of Max power point is 550V, corresponding power on the P-V curve is 200W. If inverter is working on 520V, power is approximately 190W; If working voltage is 580V, power is almost 185W. Both 190 and 185 W are not greater than 200W when working on 550V. So in the situation, inverter will have the electricity loss.
MPPT Hardware Inside inverter
How does MPPT hardware work? Before we introduce the principle, we need to figure out what Boost Circuit and Duty Ratio are. They are not like what you imagine complexly.
Boost Circuit
Boost Circuti is used to convert PV voltage into Bus voltage, then Bus voltage will be converted into AC output via DC-AC circuit. It is inverter principle. Boost Circuit can promote the output voltage.
open circuit voltage is taken as the tracking voltage. The PV system is working near the maximum power point at this time.
When the open-circuit voltage of the PV system is U0, that is, the output power is P0, select a small variable ΔU, change its working voltage to U1, and the output power of the PV system is P1, compare the magnitudes of P0 and P1, and take ΔP=P1- P0.
When ΔP/ΔU=0, PV system works at the maximum power point; if it is not 0, when ΔP/ΔU>0, the working voltage of the maximum power point should be on the right, maintaining the disturbance direction (U=U0+ΔU) ; When ΔP/ΔU<0, the situation is reversed and the flow direction is changed (U=U0-ΔU).
In order to realize the tracking control of the maximum power point, it is necessary to change the output voltage of the PV system by changing the duty cycle of the MOSFET or IGBT, so as to achieve ΔP/ΔU=0, to control its operating point at the maximum power output point.