There are three common types of high-frequency machines. In the late 1990s, one type added a BOOST boost chopper circuit to the SCR rectifier backend to boost the DC to the voltage required for UPS output, thus eliminating the need for an output transformer. It can be simply understood as replacing the AC boost of the previous power frequency UPS transformer with DC boost, which not only reduces the cost, but also greatly reduces the size and weight of the UPS. It can be said to be a major technological innovation in the UPS industry. This type of UPS without a transformer, although the first half of the rectifier is still an SCR device, the second half of its rectifier contains an IGBT high-frequency boost chopper circuit. From the definition in China, this also belongs to high-frequency machines. At present, this BOOST boost chopper high-frequency model is becoming increasingly rare, and only some small and medium power UPS will continue to be used.
With the continuous development of power electronic power devices and UPS control technology, there have been two models: full IGBT models and full IGBT+output isolation transformer models, namely IGBT rectifier+IGBT inverter transformerless models and IGBT rectifier+IGBT inverter transformer models. Their rectifiers use high-frequency adjustment methods, and the modulation frequency is generally thousands of Hz.
According to the definition of rectifier modulation frequency for UPS models, the schematic diagrams of three high-frequency machines are as follows:
The biggest feature of high-frequency machines is the absence of transformers, small size and light weight, high power density, high overall efficiency, and low input harmonic current. Therefore, their development prospects are more promising, and high-frequency is the trend of power electronics development. However, in terms of application, high-frequency machines still lack environmental adaptability and impact resistance compared to more mature power frequency machines.