The frequency converter, whether frequency control type or vector control type or torque control type, has a variable frequency soft start function, that is, when the motor starts, because the output voltage and frequency can be started from zero, it limits the starting current of the motor, and even less than the rated current can be started normally. The capacity of the inverter, in the 380V voltage level, the power range from 2,2 to 1500kW products can cover almost all the current application range.

At present, the commonly used inverters are AC-DC-AC voltage source type inverters, among which the voltage of the DC link is about 510 ~ 620V, which is obtained after the three-phase AC voltage through the three-phase uncontrolled rectification. If another 510 ~ 620V DC power supply can be provided for the intermediate link of the inverter after the mains power failure, the IGBT inverter can output three-phase sinusoidal AC voltage uninterrupted, and its voltage is 0~380V, the frequency is O ~ 50Hz continuously adjustable, to achieve soft start of the load or reach the output voltage of 380(1±3%)V. Output frequency 50(1±I%)Hz accuracy. For example, a set of batteries can achieve uninterrupted power supply to the load. Based on this idea, a new type of UPS is developed, which can become a frequency conversion type AC uninterruptible power supply, so that the frequency converter can be applied in new application fields. Because the UPS output is three-phase sine wave and voltage and frequency stabilization, in order to increase the reliability of the equipment and avoid interference to the load, transformers and LC low-pass filters are added to the output of the inverter.