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There are many parameters and technical conditions to describe the performance of photovoltaic inverters. Here we will only briefly explain the technical parameters commonly used when evaluating inverters.
1. The operating environment conditions of the inverter, the normal operating conditions of the inverter: the altitude does not exceed 1000m, and the air temperature is 0~+40°C.
2. DC input power conditions, input DC voltage fluctuation range: ±15% of the rated voltage of the battery pack.
3. Rated output voltage, within the allowable fluctuation range of the specified input DC voltage, it indicates the rated voltage value that the inverter should be able to output. The stability and accuracy of the output rated voltage value are generally stipulated as follows:
(1) In steady state operation, the voltage fluctuation range should have a limit, for example, its deviation should not exceed ±3% or ±5% of the rated value.
(2) Under the dynamic condition of sudden load change or other interference factors, the output voltage deviation should not exceed ±8% or ±10% of the rated value.
4. Rated output frequency, the frequency of the inverter output AC voltage should be a relatively stable value, usually the power frequency is 50Hz. Under normal working conditions, the deviation should be within ±1%.
5. Rated output current (or rated output capacity), which means the rated output current of the inverter within the specified load power factor range. Some inverter products give the rated output capacity, and its unit is expressed in VA or kVA. The rated capacity of the inverter is the product of the rated output voltage and the rated output current when the output power factor is 1 (that is, purely resistive load).
6. Rated output efficiency. The efficiency of the inverter is the ratio of its output power to 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.
7. The maximum harmonic content of the inverter, the sine wave inverter, under the resistive load, the maximum harmonic content of the output voltage should be ≤ 10%.
8. The overload capacity of the inverter is the ability of the inverter to output more than the rated current value in a relatively short period of time under specified conditions. The overload capacity of the inverter should meet certain requirements under the specified load power factor.
9. The efficiency of the inverter is the ratio of the output active power of the inverter to the input active power (or DC power) under the rated output voltage, output current and specified load power factor.
10. Load power factor, which characterizes the ability of the inverter to carry inductive load or capacitive load. Under the condition of sine wave, the load power factor is 0.7~0.9 (lag), and the rated value is 0.9.
11. Load asymmetry. Under 10% asymmetric load, the asymmetry of the output voltage of the fixed-frequency three-phase inverter should be ≤ 10%.
12. The unbalance degree of the output voltage. Under normal working conditions, the unbalance degree of the three-phase voltage output by the inverter (the ratio of the reverse sequence component to the positive sequence component) should not exceed a specified value, generally expressed in %, such as 5 % or 8%.
13. Starting characteristics. Under normal working conditions, the inverter should be able to start normally for 5 consecutive times under full-load and no-load operation conditions.
14. Protection function, the inverter should be equipped with: short-circuit protection, over-current protection, over-temperature protection, over-voltage protection, under-voltage protection and phase loss protection. Among them, overvoltage protection means that for inverters without voltage stabilization measures, there should be output overvoltage protection measures to prevent the negative section from being damaged by output overvoltage. Overcurrent protection refers to the overcurrent protection of the inverter, which should be able to act in time when the load is short-circuited or the current exceeds the allowable value, so as to prevent it from being damaged by the surge current.
15. Interference and anti-interference, the inverter should be able to withstand the electromagnetic interference in the general environment under the specified normal working conditions. The anti-interference performance and electromagnetic compatibility of the inverter should meet the requirements of relevant standards.
16. Inverters that are not frequently operated, monitored and maintained should be ≤95db; inverters that are frequently operated, monitored and maintained should be ≤80db.
17. Display. The inverter should be equipped with data display of parameters such as AC output voltage, output current, and output frequency, as well as signal display of input live, energized, and fault states.
18. Communication function, remote communication function allows users to check the machine's operating status and stored data without going to the site.
19. The waveform distortion of the output voltage. When the output voltage of the inverter 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% is allowed for single-phase output).
20. Starting characteristics, which characterize the ability of the inverter to start with load and the performance of dynamic work. The inverter should ensure reliable starting under rated load.
21. Photovoltaic inverter noise, transformers, filter inductors, electromagnetic switches, fans and other components in power electronic equipment will generate noise. When the inverter is running normally, its noise should not exceed 80dB, and the noise of a small inverter should not exceed 65dB.
