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Some key points for UPS power inverter

Jan 27, 2021

Some key points for UPS power inverter

The inverter must be a kind of inverter device to be called that. It is directly different from a transformer, that is, it can achieve DC input and then output AC. The working principle is the same as that of a switching power supply, but the oscillation frequency is Within a certain range, for example, if the frequency is 50HZ, the output is AC 50HZ. An inverter is a device that can change its frequency.

How to choose the correct UPS power inverter mainly focuses on the following points.

1. Rated output voltage: within the allowable fluctuation range of the specified input DC voltage, it represents the rated voltage that the inverter should be able to output. The stability and accuracy of the rated output voltage are generally stipulated as follows: During steady-state operation, the voltage fluctuation range should be limited, for example, the deviation should not exceed ±3% or ±5% of the rated value. Under the dynamic conditions of sudden load changes or other interference factors, the output voltage deviation should not exceed ± 8% or ± 10% of the rated value.

2. Output voltage unbalance: Under normal working conditions, the three-phase voltage unbalance (the ratio of reverse sequence component to positive sequence component) output by the inverter should not exceed a specified value, generally expressed in %, such as 5 % Or 8%.

3. Waveform distortion of the output voltage: When the inverter output voltage is sinusoidal, the maximum allowable waveform distortion (or harmonic content) should be specified. It is usually expressed by the total waveform distortion of the output voltage, and its value should not exceed 5% (10% allowed for single-phase output).

4. Rated output frequency The frequency of the inverter's output AC voltage should be a relatively stable value, usually 50Hz. Under normal working conditions, the deviation should be within ±1%.

5. Load power factor: characterizes the ability of the inverter to carry inductive or capacitive loads. Under sine wave conditions, the load power factor is 0.7 to 0.9 (lagging), and the rated value is 0.9.

6. Rated output current: indicates the rated output current of the inverter within the specified load power factor range. Some inverter products give the rated output capacity, and the unit is expressed in VA or KVA. The rated capacity of the inverter is when the output power factor is 1 (ie pure resistive load), the rated output voltage is the product of the rated output current.

7. Rated output efficiency: The efficiency of the inverter is the ratio of its output power to the input power under specified working conditions, expressed in %. The efficiency of the inverter at the rated output capacity is the full load efficiency, and the efficiency at 10% of the rated output capacity is the low load efficiency.

8. Protection: Overvoltage protection: For inverters that do not have voltage stabilization measures, there should be output overvoltage protection measures to protect the negative intercept from output overvoltage damage.

Over-current protection: The over-current protection of the inverter should be able to ensure timely action when the load is short-circuited or the current exceeds the allowable value to protect it from surge current damage.

9. Starting characteristics: It characterizes the ability of the inverter to start with load and its performance during dynamic operation. The inverter should be guaranteed to start reliably under rated load.

10. Noise: Transformers, filter inductors, electromagnetic switches and fans in power electronic equipment will all generate noise. When the inverter is operating normally, its noise should not exceed 80dB, and the noise of a small inverter should not exceed 65dB.