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There are many UPS systems available to the home and business consumer … however many people aren’t aware of the differences. It is very common for even an experienced enthusiast to be confused over the different UPS styles or even be unaware of their existence. Additionally, a large percentage believe that there are only two types of UPS systems, “on-line” and “off-line” UPS, and they believe that UPS are designed only to protect computers.
If we were to tell you that there are at least seven different types of UPS systems and that a few of them are able to power entire buildings or industrial facilities, would you believe us?
What is a UPS?
UPS stands for “Uninterruptible Power Supply”, which is an electrical system designed to monitor and, if necessary, regulate the main power source of a load and provide emergency power to the load whenever its main power source fails without any interruption to the load's power feed.
UPS systems find use wherever power generators are ineffective. A power generator needs some time to start, ranging from some seconds to many minutes depending on its size. A UPS will provide power to the load instantaneously, allowing it to continue its normal operation.
For business/industrial applications UPS systems and generators are being used side by side because the runtime of UPS systems is very limited but nevertheless is more than sufficient to power the load until the generator (or any other auxiliary power source) come online.
Because of their instantaneous reaction, UPS systems are being used to power any critical load. Critical computers, data centers, medical and surgical equipment, emergency lighting and military equipment are but a few examples.
The technology and manufacturing advancements of the past 20 years made some battery-powered UPS types affordable by small businesses and home users, therefore it is quite common to find a sub-£70 UPS protecting a small home or office PC.
Today we are going examine the five most affordable types of battery powered UPS systems, those which are affordable by home consumers and small businesses and suitable for power computer/electronics equipment.
The Standby type is the most common and economical type of battery powered UPS system available. With this type of UPS the powered equipment is connected directly to the utility power line without any form of voltage regulation. At the same time the UPS is charging/maintaining its batteries via an AC to DC converter. When the utility power fails, the DC to AC inverter of the UPS will turn on and supply the load with power in a matter of milliseconds.
Many people believe that since the equipment is connected directly to the utility power line it can be easily damaged by a power surge or similar phenomena and the UPS works as nothing more than a short-lived battery so that you can save your files before turning off your computer. That may not be entirely untrue, because a high quality Standby UPS always has a good surge suppression circuit, fuse and also provides more than adequate noise filtration but very low cost/quality products rarely ever feature even the simplest forms of protection. The very high efficiency, simplicity, small size and low cost of the design make it ideal for home and small business users.
Many people believe that line-interactive UPS systems are “online” designs, probably confused by the design's marketing name. Actually the line interactive design is merely an upgrade of the standby UPS and it is an offline type of system.
By adding a voltage autotransformer which can regulate the output voltage, the UPS gains the ability to regulate its output voltage. The inverter of the said UPS system operates at all times, charging the batteries and power the load while the utility power is normal and draws power from the batteries to power the load once the utility power fails.
Because of the autotransformer, the UPS always regulates its output voltage and will not switch to batteries during small undervoltage/overvoltage spikes. This makes it an ideal design for home and small business computers which are powered by an unstable utility power grid. Finally, the presence of the ever-working inverter makes the switching between utility and battery power much smoother, faster and considerably reducing switching transients.
There is a sub-type of the common Standby design, the Ferrous-Resonant type of UPS. Although it is very similar to the Standby design, the Ferrous-Resonant UPS is using (as the name suggests) a Ferro-resonant transformer to filter the output. This transformer turns the Standby UPS into an “online” type of unit and has limited voltage regulation and waveform shaping.
Even though this type of UPS used to be dominant a few years ago, it is no longer being used to power high technology systems because it is relatively unstable and creates severe voltage distortions and extreme transients. The output quality of such types of UPS systems can be worse than very poor utility AC grids. Other disadvantages include the large and very heavy construction compared to other types of systems and the generation of great deals of heat because Ferro-resonant transformers are innately inefficient.
Even though this type of UPS has disadvantages which prevent it from becoming a widely used home/small business product, it has its own set of advantages which makes it relatively popular for small industrial applications.
It is a very robust design which also is considerably cheaper than any other online UPS type and offers excellent electrical isolation, making ideal for loads which are not easily affected by voltage fluctuations and/or for loads which need to be isolated by the main utility power supply. This kind of UPS did not expand a lot and even the biggest units are limited to 100-150kVA applications because it exhibits major problems while cooperating with power factor correction equipment.
The Double Conversion online UPS systems are the most common type of UPS above 10kVA and are ideal for applications where electrical isolation is necessary or for very electrically sensitive equipment. Such UPS systems a few years ago were reserved for business installations only and even though several companies made low power models available to home consumers during the past few years, the cost remains quite restrictive for the average technology enthusiast. It is an expensive type of UPS, mainly reserved for environments with very low utility power quality (industrial applications, data centers, systems running off several different and/or low quality power generators, e.t.c.).
The Double Conversion online UPS is not much different than a simple Standby UPS in terms of technology. The core design is very similar or even identical to that of a Standby UPS; however the rectifier no longer acts as a battery charger only but is designed to run continuously. This means that not only the rectifier is noticeably larger but the inverter is larger as well, since both are designed to work 24/7, and they also require improved cooling systems.
This type of UPS is called “Double Conversion” because the rectifier continuously powers the inverter, isolating the load from the utility power source even while the UPS is normally powered from it. Because of the design, a failure of the input AC load will not trigger a transfer switch since the batteries are always connected to the inverter. During a power loss the rectifier will cease to work and the batteries will keep the power feed to the inverter steady and unchanged, in no transfer time and without any switching transients. After the power is restored, the rectifier will get back to work and resume powering the inverted, as well as slowly charging the batteries at the same time.
Even though this design provides nearly ideal electrical performance and exceptional isolation (many people call Double Conversion UPS systems “electrical firewalls”, with a reason), it has several disadvantages as well. Because of the presence double conversion, where the power the load needs gets converted to DC and then back to AC again, the electrical efficiency of the design is relatively low, increasing the overall power consumption of the system and definitely increases heat generation. It is also considered to be an unreliable design compared to others because the constant wear of the power components may cause equipment failures. High reliability Double Conversion systems do exist, however the cost is extremely high and entirely out of the reach of home consumers.
This is one of the latest online UPS designs and most widely used after the simple Double Conversion UPS. It was introduced to reduce the drawbacks of the Double Conversion design and increase the electrical efficiency, which is extremely important on high power systems.
This design is very similar to the Double Conversion design, except from the fact that the Delta Transformer also contributes to the output of the UPS, assisting the ever-working inverter. The major differences do not take place at the output of the UPS but at the input. The Delta conversion UPS provides dynamic control and power factor correction at the input, resulting in a significant reduction of energy loss. It also increases compatibility with other power equipment (e.g. generators) and severely reduces the need of over-sizing wiring and generators.
We are not going to get into too much detail about Delta Conversion UPS units because they are only available in sizes above 4kVA and range up to 2000kVA, meaning that they are designed for powering anything between a small business to a small city and not for home consumers. Furthermore this design is one of the few UPS designs protected by patents, which limits its availability and increases its price far beyond the financial capabilities of typical home consumers.
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