The inverter is the core of the online AC APC uninterruptible power supply(UPS), because in the online UPS system, regardless of whether the mains power is normal or not, the inverter circuit must work normally unless the inverter fails, which is determined by the characteristics of the online UPS. Therefore, the design of inverters is particularly important in the entire UPS design. Inverter is the process of converting direct current into alternating current, and the circuit that implements the inverter is called an inverter circuit. The AC output side of the APC UPS is directly connected to the load, and the inverter circuit belongs to passive inverter.
In many cases, the 50Hz power supply provided by the power grid cannot meet the special needs of the load. The load of APC UPS refers to special loads that have strict requirements for the stability of voltage and frequency, waveform distortion, etc. of the power supply, and do not allow instantaneous power outages The main function of an inverter is to convert the DC voltage output by the rectifier/charger into AC voltage with stable voltage and frequency CVCF.
Main performance parameters of inverter circuit
There are many parameters and technical conditions that describe the performance of inverters. Here, we will briefly explain the commonly used technical parameters when evaluating inverters.
(1) Environmental conditions for use
Normal operating conditions for inverters: altitude not exceeding 1000m, air temperature 0 ± 40 ° C.
(2) DC input power supply conditions
Input DC voltage fluctuation range: 15% of the rated voltage of the battery pack.
(3) Rated output voltage
The rated voltage value that the inverter should output when outputting rated current under specified input power conditions. Voltage fluctuation range: single-phase 220V ± 5%, three-phase 380 ± 5%.
(4) Rated output current
The rated current value that the inverter should output at the specified output frequency and load power factor.
(5) Rated output frequency
Under specified conditions, the rated output frequency of the fixed frequency inverter is 50Hz, with a frequency fluctuation range of 50Hz ± 2%.
(6) The maximum harmonic content of the output voltage of a sine wave inverter under resistive load should be ≤ 10%.
(7) Overload capacity
The ability of an inverter to output a current exceeding its rated value within a short period of time under specified conditions. The overload capacity of the inverter should meet certain requirements under the specified load power factor.
(8) Efficiency
The ratio of active power output to active power input (or DC power) of an inverter at rated output voltage, output, current, and specified load power factor.
(9) Load power factor
The recommended range for the allowable variation of inverter load power factor is 0.7-1.0.
(10) Asymmetric nature of load
Under 10% asymmetric load, the asymmetry of the output voltage of a fixed frequency three-phase inverter should be less than 10%.
(11) Asymmetry of output voltage
Under normal working conditions, each phase is symmetrical, and the asymmetry of the output voltage should be less than 5%.
(12) Starting characteristics
Under normal working conditions, the inverter should be able to start normally for 5 consecutive times under full load and no-load operating conditions.