It is very common during the commissioning process that the solar inverters presents some fails. One of the most frequent occurrences in Brazil is the grid overvoltage and it can be caused by many reasons. Considering this, I am sharing a report of a very specific case solution.
This costumer inverter, a SUN2000L 5KTL, presented the grid overvoltage alarm (Alarm ID 2034) intermittently during all the day. We started to investigate, requesting to the local technician to check the installation of the AC output power cables – their connection, diameter, etc. – and to verify the correct parametrization of the inverter. After confirm that Brazilian grid code was correctly selected and the cables were also right, we noticed that the power consumption on the installation local was low and the distance between the inverter and the isolation transformer was long. We instructed the technician to measure the voltage on the output of the inverter and on the input of the house power grid, detecting 240V and 260V respectively, showing a voltage drop of 20V over the AC power cable.
The reduction of the cable length was impracticable in this case due the rooftop installation, but some equipment installed on the grid could be affected by the voltage increase if the problem was not fixed, so we decided to enable the voltage rise suppression and adjust the P-U curve.
The overvoltage upper limit was set at 250V; the first adjustment point of the P-U curve was adjusted to keep providing 100% of the power when the voltage reaches 235V and the second one to reduce the power generation to 60% when the voltage reaches 250V. We monitored the inverter performance during three days and it was noted that the reduction on the power generation through the voltage rise suppression was less impacting comparing with the generation losses due the constant fails. The voltage on the house power energy meter also did not overtook 230V, preserving all other installation elements.
As an alternative, we suggested to increase the AC wiring diameter if the customer wants to get back to the full power generation.
Note: The value ranges for the P-U curve adjustment that are on the inverter manual are incorrect, as shown in the pictures below.
Also, here is a picture illustrating how the P-U curve operates.
Thank you all!
