1. Input current total harmonic distortion (THD) (total harmonic distortion THD: the effective value of the harmonic current of the AC current accounts for the percentage of the effective value of the fundamental component)
The THD of the input current of the 6-pulse rectifier should be less than 33% at the full-load input current of the 6-pulse rectifier; the input filter can reduce the input current distortion to 10%.
The THD of the input current of the 12-pulse rectifier should be less than 10% when the 12-pulse rectifier is fully loaded. The input filter can reduce the total harmonic distortion of the input current to 5%.
2. AC input current limit
The rectifier/charger should have an AC input current limiting circuit, which generally limits the AC input current to 115% of the full load input current. When the generator set is supplying power (at this time, the rectifier will receive an external low-voltage signal, based on which it is judged that the generator set is supplying power), the AC input current should be limited to 100% of the full load input current.
3. Battery charging current limit
The rectifier/charger should have a battery charging current limiting circuit to limit the battery charging current to 15% of the UPS rated output capacity (KW). When the generator set is supplying power (when an external low voltage signal is received), the battery charging current should be limited to zero.
4. Battery charging voltage temperature compensation
When using a remote temperature detector, the rectifier/charger should automatically adjust the battery float voltage (generally at −5mv/pc/℃). Generally, the floating charge voltage of the battery is 2.25V/unit, and the termination voltage is 1.67V/unit. Therefore, the DC bus voltage is N×2.25V and N×1.67V at the time of floating charging and termination voltage respectively (N is the number of batteries) .
5. Gradual increase in input power
The rectifier/charger should have the ability to limit the initial power requirement to 20% of the rated load, and gradually increase the input power to 100% of the rated capacity within a 10-second interval. In the redundant UPS system, the input power of each rectifier/charger should be delayed by 5 to 300 seconds to reduce the impact on the generator set.
6. Input isolation switch
The rectifier/charger should have an input isolation switch and be protected. The isolating switch should be able to provide the current that meets the load and the recharging current of the battery at the same time, and can withstand a larger short-circuit current.
7. DC filter
The rectifier/charger should have an output filter to minimize the ripple voltage applied to the battery. The AC ripple voltage of the DC output voltage of the rectifier should be less than 1% of the float voltage (RMS). The filter should fully ensure that the DC output voltage of the rectifier/charger meets the requirements of the inverter when the battery is not connected.
8. Recharging the battery
In addition to supplying power to the load, the rectifier/charger should be able to restore the discharge power of the battery to 95% within 10 times the discharge time. After the battery is recharged, the rectifier/charger should keep the battery in a fully charged state until the next discharge.