off grid solar hybrid inverter From the security point of view
Temperature PV inverter protection can be divided into anti-island protection, low voltage through the station and the static power generation device, the following for everyone:
The low voltage crossing function means that the grid-connected inverter can be connected to the grid for a period of time when the grid voltage drops. The "low voltage time" (region) until the grid returns to normal; the islanding effect protection means that when the grid is powered off, The inverter should immediately stop the grid power generation, protection time does not exceed 0.2 seconds. It can be seen that the protection of islanding and low voltage crossing is contradictory, the two functions can not coexist at the same time, need to choose according to the size and requirements of power plants, the general principles are as follows:
For small-scale photovoltaic power plants, grid-connected inverter in the power grid accounts for a smaller capacity, less impact on the grid, the grid failure will not have a substantial impact on the stability of the power grid, it should have a rapid monitoring island And immediately disconnect the ability to connect with the grid, that is, grid-connected inverter should choose the island effect protection.
For large and medium-sized photovoltaic power plants, grid-connected inverter in the power grid occupies a larger capacity, the impact on the power grid in the power grid failure will not have a substantial impact on the stability of the grid, it should have a certain Low voltage through the ability, that is, when the grid inverter should choose low voltage through function.
For most of the current photovoltaic grid-connected power generation system, the inverter is configured for low voltage traversal. Large and medium-sized photovoltaic power plant low voltage tolerance requirements In order to achieve the grid-connected inverter low-voltage through function, grid-connected inverter needs to adopt a new software control algorithm, that is, static reactive power generation device, software control algorithm needs Real-time monitoring network, and determine whether the voltage drop (balanced or unbalanced fall). When the CPU found that the voltage drop occurs in the grid failure, immediately start the low voltage through function, control the output current and output power, when the grid voltage within a certain range, the inverter into the low voltage through the stage; when the grid into the voltage recovery stage, At this point the grid inverter output reactive power to play a rapid support from the grid voltage function. If the grid drop is unbalanced fall, the inverter will output the three-phase balanced current as the objective function, through the software control algorithm to achieve in the grid voltage imbalance phase, the inverter current is balanced; when the grid back to normal, Device quickly transferred to the normal state of the grid. Inverter as an important part of photovoltaic power generation, the main role is to send the PV module DC into AC power. So what are the requirements of the PV inverter for electrolytic capacitors? Today, for everyone to introduce.
1, high voltage
General high-power photovoltaic inverter, the converted AC directly into the high-voltage power grid, but from the security point of view, the photovoltaic cell output voltage is generally not higher than 900V, you can choose two 450V electrolytic capacitors in series, but In order to improve safety, you can choose two 500V electrolytic capacitors in series. A high voltage level capacitor is required to reduce the series connection of the capacitor and improve the reliability.