Analysis on the current status and development of inverter power supply for small and medium power photovoltaic

　　In the early 1970s, the application of 20kHz PWM switching power supply caused the so-called "20kHz power supply technology revolution" in the world. This conversion idea was used in the inverter power supply system at that time, but because the power devices at that time were expensive and had large losses, the research on high-frequency and high-efficiency inverter power supply has been stagnant. After the 1980s, with the increasing maturity of power MOSFET technology and the improvement of magnetic material quality, high-frequency conversion inverter power supply entered the market.

　　The high-frequency conversion inverter power supply uses high-frequency DC/DC conversion technology to first convert low-voltage DC into high-frequency low-voltage AC, and then rectifies it into high-voltage DC after being stepped up by a pulse transformer. Since PWM technology is used in DC/DC conversion, a stable DC voltage can be obtained here, which can be used to directly drive loads such as AC energy-saving lamps, incandescent lamps, and color TVs. If the high-voltage DC is subjected to quasi-sine conversion or sine conversion, 220V, 50Hz quasi-sine wave AC or 220V, 50Hz sine wave AC can be obtained. This inverter uses high-frequency conversion (mostly 20kHz to 200kHz now), so it is small in size and light in weight. Since it uses secondary width adjustment and secondary voltage stabilization technology, the output voltage is very stable, the load capacity is strong, and the performance-price ratio is high. It is the preferred product in the current renewable energy power generation system. It is widely used in small and medium-sized AC photovoltaic systems in developed countries abroad, but in China, due to technical reasons and market chaos, some inverter power supply manufacturers have been promoting industrial frequency conversion inverter power supplies. Some even use low-silicon silicon steel sheets to reduce costs. Such inverter power supplies are flooding the market, which increases the overall cost of AC photovoltaic systems and will hinder the promotion of AC photovoltaic systems, which is very unfavorable to the development of the industry.

　　Analysis of Problems Existing in Domestic High Frequency Conversion and Small Power Inverter

　　1. Reliability

　　At present, the main problem of high-frequency conversion small power inverter power supply is low reliability. We have many years of research, production and use instructions. The main factors affecting the life of high-frequency conversion small power inverter power supply are electrolytic capacitors, photoelectric couplers and magnetic materials.

2. Efficiency

To improve the efficiency of the inverter power supply, its loss must be reduced. The losses in the inverter power supply can usually be divided into two categories: conduction loss and switching loss. To reduce these losses, it is necessary to implement zero voltage or zero current conversion on the power switch tube, that is, to adopt a resonant conversion structure.

Development Prospects of Small and Medium Power Inverters for Photovoltaic Systems

With the development of resonant switching power supplies, the idea of ​​resonant conversion has also been used in inverter power supply systems, forming a resonant high-efficiency inverter power supply. This inverter power supply uses zero voltage or zero current switching technology in DC/DC conversion, so the switching loss can be basically eliminated. Even when the switching frequency exceeds 1MHz, the efficiency of the power supply will not be significantly reduced. Experiments have shown that under the same operating frequency, the loss of resonant conversion can be reduced by 30% to 40% compared with non-resonant conversion. At present, the operating frequency of resonant power supplies can reach 500kHz to 1MHz.

It is also worth noting that the research on small and medium-power inverters for photovoltaic systems is moving towards modularization, that is, different voltage and waveform conversion systems can be constructed by using different module combinations.

Undoubtedly, the small and medium power inverters used in photovoltaic systems will adopt high-frequency conversion circuit structures. In some technical details, they will also be different from the inverters used in other occasions. For example, in addition to pursuing high reliability and high efficiency, they should also effectively combine control and inversion into one according to the characteristics of the photovoltaic industry, that is, the photovoltaic inverter should be designed with protection functions such as overvoltage, undervoltage, short circuit, overheating, and reverse polarity. Doing so not only reduces the cost of the system, but also improves the reliability of the system.

Conclusion

With the continuous standardization of photovoltaic systems, high-frequency conversion of small and medium-power inverters will be gradually recognized by the market, and its use will promote the healthy development of the photovoltaic industry.