UPS Basic Knowledge Summary- Basic topology of UPS

Time of issue:2023-03-15


Basic topology of UPS:

GB/T7260.3 describes three classification methods and topological structures of UPS:

VFD level-passive backup (Passive Standby-"Off-line"): the voltage V and frequency F of the load depend on the grid power supply (Depends); the voltage and frequency are not adjusted.

Level VI - Line Interactive (Line Interactive): The voltage V of the load has nothing to do with the grid power (Independent); the frequency has not been adjusted.

VFI level-double conversion (Double Conversion-"On-Line"): the voltage V and frequency F of the load are independent of the grid power supply (Independent); the voltage and frequency of the load are adjusted by "regeneration" (re-generated ).


IEC 62040-3/GB 7260.3 definition:


(1) Passive backup-VFD (Passive Standby, also known as offline OFF-Line)

Composition: charger, inverter, battery, filter/voltage regulator;

Application: UPS less than 2KVA;

Advantages: simple circuit and cheap price; Disadvantages: the frequency cannot be adjusted, and there is a break when switching.


(2) Line Interactive-VI (Line Interactive)

Composition: static switch, bidirectional inverter, battery, bypass switch.

Application: This configuration is not very suitable for medium-high power and for supplying sensitive loads, because frequency adjustment is not possible.

Advantages: simple circuit, high efficiency; Disadvantages: the frequency cannot be adjusted, and the dynamic characteristics are poor. For intermittently sensitive loads, there is another UPS structure, specifically referring to the static switching action (to prevent the current from the inverter from entering the grid).


(3) Double-conversion-VFI (Double-Conversion, also known as online On-Line) basic

Composition: rectifier/charger, inverter, static bypass switch, manual maintenance bypass switch, battery. The inverter is connected in series between the AC input and the load. By way of operation, the concept of bypass is introduced. If the mains is normal and the inverter is broken, the load cannot be delivered, and a static bypass is required. If it fails, a manual bypass is introduced.

Application: In this configuration, due to the use of static switches, the time required to switch the load to the inverter is negligible; moreover, the voltage and frequency of the output are completely independent of the input voltage and frequency. This means that this type of UPS can be designed to work as a frequency converter. In fact, this type is the main configuration for medium and high power (above 10KVA). Note: This type of UPS is often referred to as "on-line," which means that the load is continuously powered by the inverter regardless of the state of the AC input power.

Advantages: stable voltage and frequency, switching without interruption; Disadvantages: expensive.