Recently, the customer asked why the inverter shuts down after the night.
From the perspective of the inverter principle, the inverter may not be connected to the grid at night.
Therefore, the inverter is disconnected from the power grid and no reactive power is emitted. This is a misunderstanding. After the inverter stops generating power at night, the single-phase current 0.29A is measured at the AC output end of the inverter.
This is because the EMI filter capacitor exists at the output end of the inverter, and the EMI capacitor generates reactive power on the power grid. The following figure shows the schematic diagram of the SUN2000-36KTL inverter user manual.
The inverter has an output EMI filter (as shown in the following figure) to prevent high-frequency EMI interference from entering the power grid. At night, the inverter does not work, the output isolation relay is disconnected, and the LCL filter is disconnected.
However, the EMI filter capacitor C is not removed from the power grid.
The capacitor C is still in the power grid and generates reactive power.
However, the reactive power value is small. We can calculate the following: Calculation method: Qc=2πfcU^2. The competitor's inverter has reactive power on the filter capacitor. For details about the actual data, see the following table. In the lab test, the 47.5kw inverter standby reactive power is 336var.
The onsite server is SUN2000-36KTL, and the measured AC voltage is 400Vac. It is estimated that the standby reactive power of an inverter is 233 var. At night, the current measured by the clamp meter at the output end of the inverter is generated by the EMI capacitor of the inverter. The reactive power at night is much smaller than the output power of the inverter, which has little impact on the power factor and even slightly helps reduce the reactive power consumption of the power plant. In the market, all PV inverters of all manufacturers and models have reactive power at night, but the power consumption of power plants is not consumed.
