Santak UPS power battery has so many characteristics?It takes a certain time for the technology of circuit structure change to mature. Of course, it also includes the adaptability of the performance and reliability of the selected devices to the new circuit structure. Therefore, the change of circuit structure has an impact on the reliability of equipment. The impact depends on the maturity of circuit technology and device level.
There are two main points in the new technology of UPS without transformer.
The first is the AC/DC high frequency rectification (PFC) technology.
The two is the output half bridge inverter technology.
These two technologies have been produced for a long time, and have become the classical technology of power electronic equipment. They are also widely used, so the maturity of technology is beyond doubt. Although the integration of these two technologies in transformerless UPS is only a matter of the last decade, there may be equipment reliability problems due to the difference of circuit setting level and parameter selection, but the fundamental reason for reliability is not the application of circuit structure and new technology.
At present, the device performance level can completely meet the higher requirements put forward by the new circuit structure.
In transformerless UPS, half-bridge inverters are the main part of the device performance requirements, and the key parameters are the voltage withstanding and output current capacity of IGBT, which can fully meet the output capacity of 400-500 kVA high-power non-output transformer UPS.
It should be noted that in the transformer-free half-bridge UPS inverters, the output voltage is directly formed by (+400V) DC bus voltage, and the RMS of input current is equal to the RMS of output current.
Compared with UPS with output transformer, UPS without output transformer requires higher voltage withstand of IGBT.
Output DC blocking problem
When an IGBT is continuously turned on due to the failure of the control link, or when an IGBT or a diode is short-circuited, the 400 V DC bus voltage will be directly output to the load end (at this time, the inductance becomes a ground wire with very small impedance). The rated voltage of DC bus after single-phase load input rectifier is 311V. Considering the allowable input ground + 15% upper limit of load, the rated voltage of DC bus is 357V. The filter capacitor withstand voltage of parallel connection at the output of rectifier circuit is usually 400V. When UPS fails, the output DC voltage will be close to 400V, and the filter capacitor and DC/DC converter will be affected by the high input voltage.
this dangerous situation occurs, even if there is no special DC component detection circuit (for example, detection circuit fault or parameter drift etc.), it can be known from the driving signal received from another IGBT that the DC voltage may be short-circuited, thus terminating the work of the inverters immediately, and disconnecting the inverters from the back negative. The connection is carried.
Reliability index of UPS without output transformer
If MTBF is not known, the reliability of UPS can be measured by the efficiency and output capability of UPS, which include the working efficiency of the whole machine, the output overload capacity, the peak coefficient of output current, the output current surge coefficient and the load power factor when starting the load.
The output capability and reliability index of UPS without output transformer are as high as those of UPS with output transformer. Reliability is no longer the key problem of UPS equipment without output transformer.