Micro solar grid connected inverters are similar to AC modular system structures, but the difference between other traditional solar inverters is:
(1) The input voltage and output voltage differ greatly, so the voltage gain of micro solar grid connected inverters is generally large.
(2) Single group power is small, and micro solar grid connected inverters mostly use one solar grid connected inverter for a group of photovoltaic modules, so the power of each photovoltaic module is generally about 200W.
(3) Having communication function, due to the distributed distribution of micro solar grid connected inverters, efficient communication control function is required to achieve effective management.
Micro solar grid connected inverters have many advantages:
(1) Independent maximum power point tracking, unaffected by installation environment and photovoltaic modules.
(2) Modular design, excellent system flexibility and redundancy.
(3) A single module has a small volume and can be easily attached to photovoltaic modules without the need for additional installation.
(4) No series diodes or bypass diodes, low system losses.
However, due to its small size and distributed installation limitations, there are also some issues that urgently need to be addressed:
(1) The reliability and lifespan of solar inverter modules cannot be guaranteed.
(2) The efficiency of inverters is relatively low compared to centralized structures.
(3) The unit cost of power generation has increased.
(4) The problem of centralized control is not easy to solve.
Micro solar grid connected inverters can be classified into many types based on power conversion stages and DC bus structures, as shown in Table 1.
| Power conversion level | Single stage micro inverter |
| Power conversion level | Two stage micro inverter |
| DC bus structure | DC bus structure |
| DC bus structure | Pseudo DC bus structure |
| DC bus structure | No DC bus structure |
The DC bus structure micro solar inverter consists of a front-end high-frequency DC/DC converter and a back-end DC/AC solar inverter, and is a typical two-stage micro solar inverter; The pseudo DC bus structure micro solar inverter consists of a front-end high-frequency DC/DC converter and a back-end power frequency polarity conversion circuit, and is a typical single-stage micro solar inverter; The micro solar inverter without a DC bus structure is similar to a high-frequency link solar inverter with frequency conversion.
The comparison of the structures of three types of DC bus miniature solar inverters is shown in Table 2.
| DC bus | Pseudo DC bus | No DC bus | |
| DC/DC | Fixed D | SPWM | Frequency chain control of cyclic waves |
| DC/AC | SPWM | Power frequency square wave | Frequency chain control of cyclic waves |
| Decoupling capacitor position | DC bus | Battery side | Battery side, AC side |
| Decoupling capacitor size | Medium | Big | Big, Small |
| Control complexity | Simple | Medium | Medium, Complex |
| Cost | Middle | Low | High, High |
| Efficiency | Middle | High | Low, Low |
| Advantages | Two level independent control | Low DC/AC loss | High power density |
| Disadvantages | High DC/AC loss | Complex DC/DC control | Bidirectional switching matrix control |
Therefore, although there are still many drawbacks to micro solar grid connected inverters, their shortcomings are not overshadowed. With the development of power electronics technology, new solutions for micro solar grid connected inverters will play a crucial role in building photovoltaic power generation integrated systems.
Due to the advantages of small size, high efficiency, low power generation cost, and simple structure, a two-stage non isolated structure will be adopted as the structure of the solar grid connected inverter in this article.