What is an Uninterruptible Power Supply?
An uninterruptible power supply, commonly referred to as UPS, is a electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS is typically used to protect hardware such as computers, data centers, telecommunications equipment or other electrical equipment where an unexpected power disruption could cause injuries, fatalities or serious business disruption.
How does a UPS work?
A Uninterruptible Power Supply has two main components – a battery backup and a voltage regulator. The UPS continuously monitors the voltage level from the utility or mains power source. During normal operation, the utility power is sent directly to the load through the UPS voltage regulator, which corrects any variations in voltage. Simultaneously, the battery inside the UPS is being charged by the utility power flowing through it.
When the utility power experiences problems such as voltage fluctuations, under voltage sag and overvoltage conditions, the UPS instantly switches to battery power seamlessly without any disruption to the critical load. The voltage regulator keeps outputting consistent voltage whether it is using utility or battery power. This enables the connected equipment to run without interruption during power anomalies at the input. Once the utility power is restored, the UPS recharges its battery and switches back to acting as a passive power distribution unit.
Types of UPS systems
There are mainly three types of UPS systems used depending on application, configuration and power rating –
Standalone UPS: As the name suggests, a standalone UPS is a self-contained unit with its own battery backup. It is optimum for powering a single computer system or networking equipment in SOHO setups. Standalone UPS are economical for low power requirements up to 800VA.
Tower/Rackmount UPS: For larger loads in office environments and small data centers, tower or rack-mounted UPS systems are commonly deployed. They have higher storage capacity lead-acid batteries and can support loads from 1000VA to 3000VA. Rackmount UPS conveniently fits in standard 19-inch server racks.
String/Modular UPS: Large scale applications like data centers, industrial plants, hospitals require centralized UPS architecture to handle very high power loads. In string or modular UPS, individual UPS modules are paralleled to increase overall power capacity. Such UPS are scalable from 10kVA to multiple MVA power ratings. String UPS utilizes common battery banks for redundancy.
Battery technologies in UPS
The battery is the core component that provides backup power during outages in a UPS. Over the years, different battery chemistries have been used –
Lead-acid battery: Conventional flooded or VRLA lead-acid batteries are most widely used in UPS due to their cost effectiveness. However, they have shorter lifespan and require periodic maintenance.
Li-ion battery: Lithium-ion battery packs are gaining traction as they offer higher energy density, faster recharging and longer operational life over 5000 cycles compared to lead-acid. Li-ion UPS are suitable for larger power-intensive applications but come at a premium.
Nickel-cadmium battery: Nickel-cadmium or NiCad batteries provided an alternate to lead-acid earlier but fell out of favor due to memory effect and disposal challenges.
Advancements in UPS Design
With growing dependence on uninterrupted power, UPS systems are undergoing numerous technological enhancements to improve efficiency, reliability and manageability. Some key developments –
Double conversion online UPS: Online UPS utilize double conversion technology, where the input AC power is converted to DC through a rectifier, and then the DC power is inverted back to pure AC output power. Such online UPS block all power disturbances effectively.
High frequency online UPS: Modern high frequency online UPS employ IGBTs or MOSFETs to operate at switching frequencies above 20 kHz instead of lower 4-8 kHz range. This significantly reduces the size of transformers and filters required.
Modular, scalable design: Modular hot-swappable components enable UPS capacity and redundancy to be expanded gradually as per changing power needs without downtime.
Higher efficiencies: Through technologies like energy saver system or ECO mode, high efficiency upto 97%, and load-based voltage regulation, today’s UPS aim for maximum power savings even at partial loads.
Green UPS: Recent eco-friendly UPS specifically target reducing heat load and noise emissions in data centers through techniques like free cooling and liquid cooling in batteries.
Remote monitoring: Connectivity options in UPS now allow remote monitoring of parameters, equipment health, diagnostics and control over Internet for centralized administration.
As the criticality of continuous power availability increases for businesses as well as individuals, uninterruptible power supply systems will continue to evolve while performing their core function of bridging power gaps flawlessly. With technological progress, future UPS are expected get smaller, lighter, greener and smarter in their functioning through integrated IoT and AI capabilities. This will further cement UPS as an indispensable link in the power distribution chain across all sectors of the modern world.