Cloud computing usage is increasing in today's world, and being connected to the internet at all times is the norm. People walk around with their smartphones, which are always connected to the Internet. Enjoying full seasons of shows on streaming services has become the preferred way to watch TV shows. The cloud has so many wide-ranging uses that it's impossible for me to list them all here. One thing is for sure. All these devices using the internet and cloud require very large storage space and infrastructure. This is the job of the data center. The data center is the heart of the Internet. To ensure that this information is available 100% of the time, data centers are designed for maximum reliability.
An Uninterruptible Power Supply (UPS) is one of the devices every data center uses to keep servers and all sensitive computing equipment safe from power line disturbances and power quality issues.
DC Power in Data Center Systems
Computing devices such as servers and routers rely on internal power supplies to provide the regulated DC power needed to run processors and peripherals. These power supplies can only handle some change in supply voltage before the computing device is prone to shutting down or overloading. The Information Technology Industry Council (ITI) has created a curve and application note describing the input voltage range that typical information technology equipment can tolerate. It is called the ITI (CBEMA) curve.
The application note defines seven power quality events described by the ITI curve. For example, the curves show that most devices can withstand voltage drops of up to 20 ms. The UPS is designed to ensure that the input voltage to the computing equipment is within the "ribbon-free" range of the voltage range.
Components of an uninterruptible power supply
There are several types of uninterruptible power supplies, which will be defined below, but all UPS systems will use the following components.
Rectifier: A rectifier converts incoming alternating current to direct current. This direct current will be used to power the energy storage system.
Energy Storage: Every UPS uses some kind of system to store energy in case of input power failure. This energy can be stored in the form of batteries, flywheels or supercapacitors and is why UPSs provide uninterrupted power.
Inverter: The inverter converts the DC power from the rectifier or energy storage system to the required AC power used by the load.
Basic system configuration of an example UPS, EatonE series DX three-phase UPS. Image courtesy of Eaton.
Types of Uninterruptible Power Supplies
Standby/Offline: Standby UPS has two modes. During normal operation, the input power is fed directly to the output load without filtering. Solid state switches are used to divert the load to battery power when a power outage is detected.
Line Interaction: Similar to a backup UPS, but with the ability to adjust output for overvoltage and undervoltage conditions without switching to battery. Solid state switches are used to divert the load to battery power when a power outage is detected.
Online/Double Conversion: Online UPS uses double conversion power electronics. In this topology, the battery system is always connected without switching to a backup power source. The power flow for normal operation is through the rectifier, the energy storage system, and through the inverter for charging.
Online Double Conversion UPS System
Critical data centers typically use online double-conversion UPS systems. We already know that an online UPS will be equipped with rectifiers, energy storage systems and inverters. To further improve system reliability, an internal automatic static transfer switch will also be included to enable transfer to bypass power. If a problem or failure is detected within the UPS, the transfer will take place automatically.
UPS systems in critical data centers also use external maintenance bypasses. This is a switchgear that allows manual transfer of critical loads from the UPS to bypass power. Manual transfer to external bypass power allows complete power cut-off for safe maintenance work inside the UPS.
UPS redundancy requires high uptime
To meet the high uptime requirements of data centers, UPS systems are often configured redundantly.
N+1 redundancy
Let's define "N" as the full UPS capacity required to handle the total load. For simple redundancy, additional modules are installed. In this multi-module system, each UPS can provide the required "N" power. This is called N+1 redundancy.
2N redundancy
Enterprise-class IT equipment typically supports dual power operation. The device can be connected to multiple power sources. In a data center, the two sources will be separate UPS systems. The "A-side" and "B-side" can power computer equipment. Each side is able to handle 100% load capacity. This is called 2N redundancy.
2(N+1) redundancy
The two concepts can also be combined. Take a redundant power distribution system with 2N as an example, not one module UPS on each side, but multiple modules. This provides N+1 redundancy on each side. This is called 2(N+1) redundancy.
Transformerless Multi-Stage UPS Topology
Today, state-of-the-art UPS systems deployed in data centers use transformerless, multi-stage topologies. This topology ensures maximum reliability and efficiency. Manufacturers are also starting to use wide bandgap transistors such as silicon carbide (SiC). This increases the efficiency of the UPS system by 98% in double conversion mode.
