Centralized grid connection is suitable for installing solar cell arrays with the same orientation and specifications. In electrical design, a single inverter is used to realize centralized grid-connected power generation scheme.
For large grid-connected PV systems, if the orientation, inclination and shadow of solar cell array installation are basically the same, a large centralized three-phase inverter is usually used.
Centralized inverters are generally used in systems of large photovoltaic power stations (> 10MW). Many parallel PV cell strings are connected to the DC input of the same centralized inverter.
Generally, three-phase IGBT power module is used for centralized photovoltaic power system inverter with large power. Field effect transistors are used for centralized photovoltaic power system inverter with small power. DSP is also used to improve the quality of the power produced, making very close to sine wave current. The most important characteristic of the system is high power and low cost.
The master-slave structure can be adopted in large-scale photovoltaic power system. The master-slave structure is also a kind of centralized structure. This structure adopts 2 to 3 centralized inverters, and the total power is divided evenly by several inverters.
When the radiation is low, only one inverter works, which improves the efficiency of the inverter when the solar cell array outputs low power;
When the solar radiation increases and the output power of the solar cell array increases to exceed the capacity of one inverter, the other inverter is automatically put into operation.
In order to ensure the equal running time of the inverter, the inverter of the master-slave photovoltaic power system can automatically switch the master-slave configuration. The initial cost of a master-slave structure is high.
However, it can improve the efficiency of photovoltaic power system inverter in operation. For large photovoltaic power systems, the improvement of efficiency can produce great economic benefits.
Distributed grid-connected power generation is suitable for solar cell arrays installed in different orientations or different specifications. In electrical design, the solar cell array with the same orientation and specifications can be connected to the grid through a single inverter.
Large distributed systems are mainly used for the solar cell array with different orientations, inclination angles and solar shadows.
The distributed system strings together PV modules with the same orientation, inclination and no shadow. A solar cell array is formed by a string or several strings of solar cells, and a grid-connected inverter is installed to match it.
In this case, the wiring box can be omitted to reduce the cost; in addition, the grid-connected photovoltaic power system can be repaired by fragments to reduce the power generation loss during maintenance.
The photovoltaic grid-connected string inverter is to connect each photovoltaic cell module with an inverter. At the same time, there is a separate peak power tracking at each photovoltaic cell module, so that the photovoltaic cell module and the inverter can be better matched.
The string inverter has become the most popular inverter in the international market. The string photovoltaic power system inverter is based on the modular concept. Each PV series (1 kW to 5 kW) has the maximum power peak tracking at the DC end through an inverter, and is connected to the grid in parallel at the AC end.
Many large photovoltaic power plants use string inverters, because they are not affected by the differences and shadows between photovoltaic cells.
The multi-string photovoltaic power system inverter takes the advantages of the centralized inverter and string inverter but avoids the disadvantages. It can be applied to several photovoltaic power stations with kilowatts.
PV arrays of different ratings and different sizes, PV modules of different technologies, and arrays of different orientations, different inclinations or shadows can be connected to a common inverter.
At the same time, each string operates at its own peak power. The reduction of the length of the DC cable can minimize the shadow effect between arrays and the loss caused by the difference between arrays of photovoltaic power systems.