A Standby Ups Continuously Powered Devices
Image credit: Alhim/Shutterstock.com
An Uninterruptible Power Supply, abbreviated as UPS, is a device whose purpose is to provide power to a system when the primary power source fails, or when the voltage level of the power source drops below acceptable performance levels. A UPS is a common element included in the design of computers, server farms, and data centers that house digital data. Depending on the demands of the application, the UPS may function to power the system long enough to allow for an orderly shutdown to be achieved, thus avoiding the issues of a system crash from sudden power loss. Or in other cases, the UPS may be configured to provide power for a much longer period, in effect, providing continual power that results in no interruption in performance by the equipment connected to the UPS.
This article will provide a review of the common types of UPS systems that are used and will discuss their configurations and operation.
Personal Computer Example
Perhaps the simplest example of a UPS with which we are familiar is the battery backup used in personal computers. Laptop and tablet computers are powered from an onboard battery technology such as Lithium-Ion that supplies the DC power to the computer's electronics. The power supply or charger unit that comes with the computer serves to recharge the battery as needed when the charge level drops off from use. If the laptop or tablet is connected to the power supply and the user is working on the computer, a sudden loss of utility power will prevent the power supply from any further recharging of the battery during the outage period, but from the perspective of the user, they do not experience any downtime or outage. The onboard battery continues to provide power to the PCBs within the computer, such as the CPU, so no loss of data occurs. Depending on the charge level of the battery at the moment that the power outage occurs, the user may be able to keep working without incident until utility power is restored and the power supply again begins recharging the computer's battery. Or, in the case of a low charge level, the user can in all likelihood still successfully save their work, close open files & applications, and perform a standard shutdown of the computer.
This example sets the framework for how the other configurations of UPS systems function, which will be outlined in the next section.
Types of Uninterruptable Power Supply Systems
UPS systems can generally be classified as being one of these five types:
- Standby UPS
- Line-interactive UPS
- Standby-ferro UPS
- Double conversion online UPS
- Delta conversion online UPS
Note that these types are based on a demand for an AC power backup for the load.
Standby UPS
A standby UPS is a configuration in which a battery backup is charged by the line voltage and is fed through an inverter to a transfer switch. When the prime power is lost, the transfer switch brings the standby power path online (represented in figure 1 below as the lower path with the dashed line). The inverter is generally not active until there is a power failure, and hence the term 'standby" is used to describe this type of UPS. The need to actively switch the power path does mean that there is a brief outage that will occur from the time that primary power is lost until the switchover is complete. The primary power path shown in Figure 1 includes an LC filter and surge protection circuitry for noise isolation.
Image credit: https://www.schneider-electric.com/
The laptop example that was presented earlier might be considered a simplified type of standby UPS where the desired output is DC instead of AC and no transfer switch is needed.
Line-interactive UPS
One of the most commonly used designs for an uninterruptable power supply is the line-interactive UPS, presented in Figure 2 below. With the line interactive design, prime power is fed through a transfer switch to an inverter and then out to the load. The inverter in this design is always active and when prime power is on, it operates in reverse to convert incoming AC power to DC which is used to keep the backup battery charged. If the line power goes out the transfer switch opens and the inverter works in the normal direction, taking the DC power from the battery and converting it to AC to supply to the load.
Image credit: https://www.schneider-electric.com/
This design which keeps the inverter active provides improved filtering and reduces the switching transients that could be present with the standby UPS configuration. Depending on the inverter design, this configuration can provide two independent power paths for the load and eliminates the inverter as a single point of failure. So even if the inverter were to fail, AC power can still flow to the output. This type of UPS offers low cost, high reliability, and high efficiency, and can support low or high voltage applications.
Standby-ferro UPS
The standby-ferro UPS uses a three winding transformer to couple the load to the power source, as shown below in Figure 3. Prime power flows through a transfer switch that is normally closed to the coils in the transformer where it couples to the secondary coil of the transformer and then supplies the power to the output load. The backup power path takes line voltage to a battery charger and maintains the backup battery, which then connects to an inverter that joins the third coil of the transformer.
Image credit: https://www.schneider-electric.com/
When the prime power fails, the transfer switch opens and the inverter supplies power to the load from the backup battery. In this design configuration, the inverter is in standby and becomes active when the prime power fails, and the transfer switch is opened.
The transformer, while providing isolation of the load from line voltage transients, can create output voltage distortion and transients of its own possibly worse than those from a poor AC connection. Additionally, the inefficiencies of the ferro transformer may result in the generation of a significant amount of heat, on top of which they are quite large and heavy, making standby-ferro UPS systems also bulky as a result.
This type of UPS is less used nowadays in powering modern computer system loads because they can become unstable. The power supplies used to power servers and routers are "power factor corrected" so as to draw only sinusoidal power from the utilities. This is accomplished by using capacitors that have a reactance such as to lead the applied AC voltage. The transformer output of the standby-ferro UPS contains coils whose inductance results in a lag in voltage compared with the AC power. This combination of an inductive and capacitive circuit results in resonance or ringing that may produce high currents and can potentially damage the load equipment.
Double-conversion online UPS
For applications above 10kVA, the double conversion online UPS is often the configuration of choice. Diagramed in Figure 4 below, the double conversion online UPS is similar to that of the standby UPS except that the inverter output represents the primary power path whereas in the standby UPS this was the secondary or backup path. The AC prime power main feeds a rectifier (AC to DC converter) and then is fed right back to the inverter that regenerates AC power from the DC power. A backup battery ties into the DC line and is charged by the rectifier.
Image credit: https://www.schneider-electric.com/
A static bypass switch is available but is not activated in the event of failure of the AC prime power. The battery power will seamlessly feed the inverter should the AC mains fail, resulting in a design that results in no transfer time in the event of a power loss. Because the inverter and rectifier are continuously active in this design, there is reduced reliability of the electrical components versus other designs. But from the perspective of the electrical power, this type of UPS delivers ideal power output performance.
Delta conversion online UPS
The delta conversion online UPS is a relatively new design that was introduced to address some of the drawbacks associated with the double conversion online UPS discussed previously. As with the double-conversion design, the delta conversion online UPS has the inverter supplying the output power to the load and hence is always operating. Figure 5 below shows the design of this type of UPS.
Image credit: https://www.schneider-electric.com/
A delta transformer couples the AC mains to the delta converter, which generates a DC power output. As with the double-conversion design, the DC output serves to maintain the charge on a backup battery and also feed the inverter, which then produces an AC output that is transmitted to the load. The prime power also has a feed that meets up with the inverter output.
The delta converter functions to minimize any harmonics that might be reflected back to the utility grid or to a connected generator system, making this UPS design compatible with generator sets and eliminating the need to oversize wiring or generators. From the perspective of output power characteristics, the delta conversion online UPS is identical to that of the double-conversion online UPS, but with a substantial reduction in energy losses or higher efficiency.
Summary
This article provided an outline of the primary types of Uninterruptible Power Supplies (UPS) Systems. For information on other topics, consult our additional guides or visit the Thomas Supplier Discovery Platform where you can locate potential sources of supply for over 70,000 different product and service categories, including over 650 suppliers of Uninterruptible Power Supplies (UPS).
Sources:
- https://www.schneider-electric.com/
- https://www.eetimes.com/the-different-types-of-ups-systems/#
- https://www.vertiv.com/
- https://www.pcmag.com/encyclopedia/term/ups
- https://www.cyberpowersystems.com/blog/how-does-a-ups-work/
Related Articles
- Types of Generators
- Best Portable Generators
- What Size Generator Do I Need For My House?
- Top Generator Manufacturers and Suppliers in the USA
- Top Transformers Manufacturers and Suppliers in the USA and Worldwide
- Top Relay Manufacturers and Suppliers in the USA and Globally
- Top Electrical Circuit Breakers Suppliers and Manufacturers in the USA and Globally
- Fireproof Electric Enclosures
- Basic Electrical Connectors
- Types of Electrical Power Supply Interference
- Electric Double-Layer Capacitors (Supercapacitors)
- How Transformer Cores Work
- Living off the Grid - Alternative Power Sources
- Types of Uninterruptible Power Supply (UPS) Systems
- Types of Electrical Switches
- What is Hydroelectric Energy? A Look at the Hydropower Process
- What is a Capacitor Used For? Variable Capacitor Types/Functions
- Basic Electrical Switch, Definition, Uses, and Applications
- Types of Electrical Power Connectors
- General Types of Transformers
- Common Types of Electrical Connectors
- All About Buck Boost Transformers
More from Electrical & Power Generation
Source: https://www.thomasnet.com/articles/electrical-power-generation/types-of-ups-uninterruptible-power-supply/
0 Response to "A Standby Ups Continuously Powered Devices"
Post a Comment