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With the growing rise of new energy industry, photovoltaic energy has become an industry giant, the new energy, the safe operation of the PV plant has also become an important factor in maintaining a stable power grid, protection like anti-islanding inverter protection within the power plant station, low voltage ride through and static vAR station generating apparatus of photovoltaic power plants have become an essential configuration.
Low voltage ride through function refers to the inverter with the normal period of time when the grid voltage sag, "through" the low voltage time (area) until the grid returns to normal; islanding protection means that when the power grid when the grid should immediately stop the inverter and power generation, the protection time is not more than 0.2 seconds. As can be seen, islanding protection and low voltage ride through conflicting, both functions can not coexist, we need to be selected according to plant size and requirements.
For small-scale photovoltaic power plants, grid-connected inverter grid share of smaller capacity, less impact on the power grid, and will not have a material impact on the stability of the grid when the grid failure, it should have rapid monitoring silos and the ability to immediately disconnect the grid connection, that this time should be chosen grid inverter islanding protection.
For medium and large photovoltaic power plants, grid-connected inverter grid share of larger capacity, greater impact on the grid, will not have a material impact on the stability of the grid when the grid failure, it should have a certain low voltage ride through capability, that this time should be selected inverter with low voltage ride through capabilities.
For the most current grid-connected PV systems are low voltage inverter configured through. Low and medium voltage tolerance of large photovoltaic power stations and networks in order to achieve the requirements of the low voltage inverter traversal function, grid-connected inverter need to adopt new software control algorithms, real-time monitoring network software control algorithm needs and determine whether the grid voltage drop occurs (balanced or unbalanced drop). When the CPU power grid voltage drop found fault, low voltage ride-through function starts immediately, controlling the output current and power output, when the grid voltage is within a certain range, the inverter enters a low voltage across the stage; when the grid voltage enters the recovery phase, in this case grid-connected inverter output reactive power play quickly to prop up the grid voltage. If the grid is unbalanced drop drop, the inverter output will be three-phase balanced current objective function is implemented in grid voltage unbalance phase inverter current is balanced by software control algorithm; when the grid returns to normal, the inverter It is quickly transferred to normal and network state.