How to protect photovoltaic inverters?

With the rise of the new energy industry, photovoltaic power generation has become a giant in the new energy industry. The safe operation of photovoltaic power stations has also become an important factor in maintaining the stability of the power grid. The in-station protection of the power station, such as the anti-islanding protection of the inverter, low voltage ride-through, and the static reactive power generation device in the station have become indispensable configurations of photovoltaic power stations.

The low voltage ride-through function means that when the grid voltage drops, the grid-connected inverter can be connected to the grid normally for a period of time, "traveling through" this low voltage time (area) until the grid returns to normal; the islanding effect protection means that when the grid is powered off, the grid-connected inverter should immediately stop grid-connected power generation, and the protection time shall not exceed 0.2 seconds. It can be seen that the islanding effect protection and low voltage ride-through are contradictory, and the two functions cannot coexist at the same time, and need to be selected according to the scale and requirements of the power station.

For small photovoltaic power stations, the grid-connected inverter occupies a small capacity in the power grid and has little impact on the power grid. In the event of a power grid failure, it will not have a substantial impact on the stability of the power grid. Therefore, it should have the ability to quickly monitor the island and immediately disconnect from the grid. That is, the grid-connected inverter should select the island effect protection function at this time.

For large and medium-sized photovoltaic power stations, the grid-connected inverter occupies a large capacity in the power grid and has a greater impact on the power grid. In the event of a power grid failure, it will not have a substantial impact on the stability of the power grid. Therefore, it should have a certain low voltage ride-through capability, that is, the grid-connected inverter should select the low voltage ride-through function at this time.

For most of the current photovoltaic grid-connected power generation systems, the inverter is configured with low voltage ride-through. Low voltage tolerance requirements for large and medium-sized photovoltaic power stations In order to realize the low voltage ride-through function of the grid-connected inverter, the grid-connected inverter needs to adopt a new software control algorithm. The software control algorithm needs to monitor the grid in real time and determine whether the grid has a voltage drop (balanced or unbalanced drop). When the CPU finds that the grid has a voltage drop fault, it immediately starts the low voltage ride-through function to control the output current and output power. When the grid voltage is within a certain range, the inverter enters the low voltage ride-through stage; when the grid enters the voltage recovery stage, the grid-connected inverter outputs reactive power to quickly support the grid voltage. If the grid drop is an unbalanced drop, the inverter will use the output three-phase balanced current as the objective function, and use the software control algorithm to achieve that the current of the inverter is balanced in the unbalanced grid voltage stage; when the grid returns to normal, the inverter quickly switches to the normal grid-connected state.