PV inverter experts reveal the mystery of MPPT

Regarding the mystery of the MPPT efficiency of photovoltaic inverters, in the technical specifications of photovoltaic inverters, most manufacturers have the MPPT efficiency indicator, some marked as 99%, and some even marked as 99.9%. There is currently no reliable instrument to measure the MPPT efficiency, and its certification does not require measurement. MPPT efficiency is the most critical factor in determining the power generation of photovoltaic inverters, and its importance far exceeds the efficiency of the photovoltaic inverter itself.

At present, the power generation of domestic and foreign photovoltaic inverters under the same conditions may differ by as much as 20%. The main reason for this difference is the MPPT efficiency. Students who do not understand MPPT can first search the basic principles of photovoltaic inverter MPPT on Baidu. Photovoltaic inverter experts mainly reveal the calculation method and source of MPPT efficiency. The efficiency of MPPT is equal to the hardware efficiency multiplied by the software efficiency. The hardware efficiency is mainly determined by the accuracy of the current sensor and the accuracy of the sampling circuit. The software efficiency is mainly determined by the sampling frequency. There are many ways to implement MPPT, but no matter which method is used, the change in component power must be measured first, and then respond to the change. The most critical component is the current sensor. Its accuracy and linear error will directly determine the hardware efficiency, and the sampling frequency of the software is also determined by the accuracy of the hardware.

Currently, there are two types of current sensors: open-loop and closed-loop. The open-loop current sensor has a measurement accuracy of 99%, a linear accuracy of 99%, and a total measurement error of 2%. The closed-loop current sensor has a measurement accuracy of 99.6%, a linear accuracy of 99.9%, and a total measurement error of 0.5%. What does this mean? Let me explain to you. If an open-loop current sensor is used, the inverter cannot measure a 2% change in component power. Since the open-loop current sensor has a large error, the sampling frequency must also be reduced, otherwise oscillation will occur. Therefore, the software efficiency can only reach 99%. In other words, the inverter using an open-loop current sensor has an MPPT limit efficiency of only 97%, while the photovoltaic inverter using a closed-loop current sensor has an MPPT limit efficiency of 99.5%.

In the market, open-loop current sensors are about 30% cheaper than closed-loop current sensors. In order to reduce costs, some unscrupulous manufacturers now use low-priced open-loop current sensors, but claim that the MPPT efficiency can still exceed 99%, which seriously misleads EPCs and owners and harms people's interests. This shameful behavior will surely be spurned by people and become the first manufacturer to be eliminated from the photovoltaic market.