Strictly speaking, the distributed inverter is not a specific inverter type, but a centralized inverter and a combiner box with MPPT function to form a distributed inverter solution. This solution refers to the solution of decentralized MPPT optimization and centralized grid-connected power generation. By adding the DC/DC boost conversion hardware unit and the MPPT control software unit inside the traditional photovoltaic combiner box, the distributed tracking function of 1 MPPT corresponding to each 2~4 series of PV modules is realized, which greatly reduces the inconsistency of module parameters, partial shadows, and Loss of efficiency caused by differences in elevation angles, etc. At the same time, after the output voltage of the improved photovoltaic combiner box (photovoltaic controller) is increased to 820V, it is concentrated in the inverter room, and the AC output voltage of the inverter is increased to 520V, thereby reducing the transmission loss of AC and DC cables and The self-heating loss of the inverter.
Different from the traditional centralized grid-connected power station, the DC combiner box is replaced with an intelligent combiner box with MPPT optimization function. Each 1MW distributed power generation system has multiple independent MPPT optimization units to solve the problem of dust occlusion, shadow occlusion, Power generation loss caused by component mismatch such as inconsistent DC line loss, component degradation, and inclination difference.
In the actual photovoltaic power generation system, due to the problem of component mismatch, it is difficult to keep the IV curve of each string completely consistent. The traditional single-channel MPPT centralized power generation solution will cause each string to fail to work effectively at its maximum power point. , And the cascade-level MPPT distributed power generation solution can maximize the independent MPPT optimization function of each string. Take the distributed inverter scheme of a certain company as an example, the schematic diagram of its system connection is shown in Figure 1.
The main advantages of the distributed inverter are:
①Compared with centralized type, “decentralized MPPT tracking” reduces the probability of mismatch and increases power generation;
②Compared with the string type, the distributed inverter has a boost function, which reduces the line loss;
③Compared with string type, “centralized inverter” has more advantages in terms of construction cost;
④The cascade-level MPPT and centralized grid-connected scheme combine the advantages of the two, reducing the harmonic oscillation and grid-connected circulating current problems that may be caused by multiple inverters in parallel.
The main disadvantages of the distributed inverter are:
① With little engineering experience, there are still few applications in engineering projects;
②Because of the use of “centralized inverter”, the shortcomings of requiring a dedicated machine room are also present in the distributed inverter;
③The combiner box needs an additional MPPT module, which is complicated in structure and difficult to protect.