Uninterruptible power supply (UPS) is an essential component in many industrial applications. As long as the interruption of the main power supply may cause data loss, damage sensitive equipment, endanger safety or threaten life, the system needs to be equipped with UPS. When there is an external power outage, these critical systems will automatically connect the load to the battery and supply power through the battery, thus buying time for connecting another power source or ensuring safe shutdown of the equipment.
The UPS system is widely used, covering many fields such as telecommunications, hospitals, and data centers. UPS designed specifically for direct current (DC) loads can provide protection for equipment in transportation, power generation, factory and building automation, semiconductor manufacturing, security, and other fields.
Not only is it a simple switching device between external power sources and backup batteries, UPS must also manage battery health and input/output voltage. When engineers add UPS to existing or planned equipment, they need to choose products that match the load and battery requirements, while also considering the interface and safe operation requirements of the UPS.
Understand the working principle of uninterruptible power supply
The equipment designed for alternating current (AC) input uses an AC UPS, which converts the DC power from the backup battery into an AC output suitable for the load through an inverter circuit (Figure 1). During normal operation, the external AC power source will directly supply power to the load without passing through the battery and inverter. When the external power supply is interrupted, the battery will supply power to the load with the required voltage through the inverter until the battery is depleted, the external power supply is restored, or another power source is connected.
AC UPS contains a rectifier that functions when there is an AC power source. The rectifier converts some AC power into DC power and charges the battery after stabilizing it.
AC UPS will adopt bypass mode without passing through the battery
Figure 1: AC UPS will enter bypass mode when needed, without passing through the battery, and then use an inverter to convert the DC power of the battery into the AC power required by the load. The rectifier charges the battery with AC power supply. (Image source: TDK Lambda)
The DC load can be directly connected to the backup battery through DC-UPS. DC-UPS has two main functions. When there is an external power source, DC-UPS can function as an internal bidirectional DC/DC converter. In this way, the UPS can not only use the rectified DC voltage to charge the battery, but also convert the DC voltage into a voltage suitable for the DC load (Figure 2). When the external power supply is interrupted, it acts as a DC/DC converter, providing voltage stabilization from the battery to the load.
In DC-UPS, the battery directly supplies power to the load
Figure 2: In DC-UPS, the battery directly supplies power to the load. When the external power supply is restored, the rectified external AC voltage power supply supplies power to the load and charges the battery. (Image source: TDK Lambda)
The DUSH960 DC-UPS from TDK Lambda (Figure 3) is suitable for DC input voltages ranging from 12V to 60V. Under user programmable voltages ranging from 12 V to 48 VDC, this UPS can output up to 20 A of current and 960 W of power. As a programmable DC/DC converter, DUSH960 DC-UPS can be used in the input and output range of 10 V to 60 V (nominal voltage of 12 V to 48 V) without the need for batteries.
Due to the fact that the backup battery can directly supply power to the load without the need for an inverter, the efficiency of the DC-UPS system is extremely high. This DC-UPS can reliably output 96% to 98% of its electrical energy through the battery.