Calculation method and source of photovoltaic inverter MPPT efficiency

The MPPT efficiency indicator is marked in the technical specifications of photovoltaic inverters. 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 photovoltaic inverters at home and abroad under the same conditions may differ by as much as 20%. The main reason for this difference is MPPT efficiency. The following introduces 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 sampling circuit, while 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. This involves a key component, that is, the current sensor, whose accuracy and linear error will directly determine the hardware efficiency, and the software sampling frequency is also determined by the accuracy of the hardware.

　　At present, 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? For example, 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%.