This is a general classification of grid-interactive inverters. In each category, there are many inverter brands and models with different sizes and different characteristics.
Branch inverters are used in small systems ranging from 1kWp to 11kWp. The branch inverters all contain a maximum power point tracker (MPPT), and the DC input voltage varies from extra low voltage (ELV) to 1000V (low voltage, LV). The branch inverters are connected in different ways, as shown in Figure 1, Figure 2 and Figure 3.
The multi-branch inverter is still one inverter, but has multiple MPPT input terminals. Therefore, the photovoltaic array can be divided into multiple branches, and each branch is connected to an MPPT input of the inverter.
The advantage of this type of inverter is that if the component orientations are different, the array can be divided into different branches, and all components in the same branch have the same orientation. Then each component string is connected to a dedicated MIPPT terminal, so compared with an inverter with only one MPPT terminal, the system outputs more energy. Multi-branch inverters are generally cheaper than using multiple inverters, and have the advantage of higher output energy when the various parts of the photovoltaic array have different orientations or different degrees of shielding.
Centralized inverters are very similar to branch inverters with multiple component strings. The difference is that centralized inverters are generally used in large systems (>10kWp). In these systems, the array can be divided into many sub-arrays, and each sub-array is composed of multiple component strings.
In some systems, a large inverter may be suitable for the entire photovoltaic array, or a centralized inverter may be a cabinet containing several small multi-branch inverters and exhibit an electrical output. Otherwise, many inverters will be needed, for example, a 100kW system requires 5 x20kW inverters.
Some large-scale centralized inverter manufacturers have optimized the design. For example, a centralized inverter is composed of multiple smaller inverters, and operates selectively according to the power generated by effective light. This configuration scheme improves the working efficiency of the centralized inverter, especially when operating at lower than peak load.
Component inverters are also called micro inverters, which are designed as small transformerless inverters installed on the back of photovoltaic modules (some inverters have an isolation transformer to reduce DC injection current). Many 100~300W component inverters appeared many years ago. In 2009, this product appeared again in the grid-connected photovoltaic system market. The component inverter has two main advantages: Since each component can output AC power, it is no longer necessary to draw a DC cable from the array; AC cables can be connected in parallel at each component, and then connected to the grid at a suitable location. Inverters are also small, easy to manufacture, and have the benefits of modularity (similar to photovoltaic modules), which means that more components and inverters can be integrated into the system at a very low cost in the future.
The past module inverters are usually more expensive, that is, the cost per unit power ($/W) is higher than other inverters. However, the latest module inverters on the market are related to the installation of an inverter in photovoltaic system engineering. The cost is comparable.
The disadvantage of the module inverter is related to the installation on the back of the photovoltaic module. If the inverter fails, maintenance and replacement of the inverter requires removing these components from the array to find the inverter behind the components. As discussed in Chapter 4, the temperature of photovoltaic modules rises a lot during the day, so compared with the case where the inverter is placed on a sheltered wall or indoors, the working temperature of the module inverter is higher, which increases the failure of the inverter. risks of. The manufacturer shall provide the high temperature operating characteristics of the component inverter.
The latest micro-inverters provide data recording and communication features similar to other inverters on the market, either through the local AC grid or through the website.
|Inverter type||Component inverter||Branch inverter||Multi-branch inverter||Centralized road changer|
|Power range||100 ~ 300W||700~11000W||2000 ~ 17000W||10000~30000W|
|Typical efficiency||95%||93% ~97%||97%||97%|
|Advantage||No need for DC cables; easy to integrate more components||Mature technology||Multiple MPPT, mature technology||Lowest cost ($/W), installed in one location|
|Disadvantage||Difficult to replace the faulty inverter||Only one MPPT||If the inverter fails, there is no redundancy|