An uninterruptible power supply or uninterruptible power source ( UPS ) is an electrical device that provides emergency power to the load when the input or power source failed. UPS is different from backup or emergency power systems or standby generators as it will provide almost immediate protection from input power interruptions, by supplying energy stored in batteries, supercapacitors, or stywe wheels. Most uninterrupted resource battery runtime is relatively short (only minutes) but enough to start the standby resource or turn off the well-protected equipment.
UPS is typically used to protect hardware such as computers, data centers, telecommunications equipment or other electrical equipment where unexpected power failures can cause injury, death, serious business interruption or data loss. UPS units vary in size from units designed to protect a single computer without a video monitor (about 200 volt amperes) to large units that drive entire data centers or buildings. The world's largest UPS, the 46-megawatt Battery Electric Storage System (BESS), in Fairbanks, Alaska, drives entire towns and rural communities nearby during outages.
Video Uninterruptible power supply
Common power problems
The main role of any UPS is to provide short-term power when input resources fail. However, most UPS units are also capable of varying degrees of fixing common equipment power problems:
- Spike voltage or voltage is more sustainable
- Diminution of occasional or continuous input voltage
- Noise, defined as transients or high-frequency oscillations, is usually injected into the channel by the nearest equipment
- Mainstream instability
- Harmonic distortion, defined as the departure of the ideal sinusoidal waveform expected on the line
UPS units are divided into categories based on the above issues that they handle, and some manufacturers categorize their products according to the number of power related issues they handle.
Maps Uninterruptible power supply
Technology
The three general categories of modern UPS systems are on-line, line-interactive and standby. The on-line UPS uses the "double conversion" method to receive AC input, aligning to DC to bypass the rechargeable battery (or battery), then revert back to AC 120 V/230 V to power the protected equipment. A line-interactive UPS maintains an inverter in line and redirects the DC battery current path from normal charging mode to supply current when power is lost. In standby system ("off-line"), the load is turned on directly by the input power and the backup power circuit is only called when the power fails. Most UPSs under 1 kVA are from interactive or standby lines that are usually cheaper.
For large power units, Dynamic Uninterruptible Power Supplies (DUPS) are sometimes used. The synchronous motor/alternator is connected to electricity through the choke. Energy is stored in a flywheel. When the power fails, the current eddy current setting maintains the power on the load as long as the flywheel energy is not exhausted. DUPS are sometimes combined or integrated with a diesel generator that is turned on after a short delay, forming an uninterruptible diesel rotary (DRUPS) power supply.
A fuel cell UPS has been developed in recent years using hydrogen and fuel cells as a resource, potentially providing long-term time in small spaces.
Offline/standby
Offline/standby UPS (SPS) offers only the most basic features, providing surge protection and battery backup. Protected equipment is usually connected directly to incoming power. When the incoming voltage falls below or rises above a predetermined level, SPS turns on its internal DC-AC inverter circuit, powered from an internal storage battery. The UPS then mechanically diverts equipment connected to the output of a DC-AC inverter. The transition time can be as long as 25 milliseconds depending on the amount of time it takes the standby UPS to detect the lost utility voltage. UPS will be designed to power certain equipment, such as a personal computer, without dip or brownout to the device.
Line-interactive
UPS interactive lines are similar in operation to UPS standby, but with the addition of multi-tap variable-voltage autotransformer. This is a special type of transformer that can increase or decrease the wire reel powerless, thereby increasing or decreasing the magnetic field and the transformer output voltage. This can also be done by different buck-boost transformers than autotransformers, because the former can be transferred to provide galvanic isolation.
This type of UPS is able to tolerate continuous undervoltage brownouts and overvoltage surge without consuming limited backup battery life. This even offset by automatically selecting different power taps on autotransformer. Depending on the design, changing the autotransformer faucet may cause a very short output power interruption, which may cause the UPS to be equipped with a power-lost alarm for "chirp" for a moment.
It has become popular even in the cheapest UPS as it takes advantage of the components already included. The main 50/60 Hz transformer used to convert between line voltage and battery voltage needs to provide two slightly different rotation ratios: One to change the output voltage of the battery (usually a multiple of 12 V) to the drain voltage, and the second to convert the voltage to the charging voltage slightly higher battery (like a multiple of 14 V). The difference between the two voltages is that the battery charge requires a delta voltage (up to 13-14 V for 12 V battery charge). Furthermore, it is easier to switch on the voltage-line side of the transformer because of the lower current on that side.
To get the buck/boost feature, all that is required are two separate switches so that the AC input can be connected to one of the two main taps, while the load is connected to the other, thus using the main winding of the main transformer as an autotransformer. The battery can still be charged while "bucking" the excess voltage, but while "increasing" an undervoltage, the transformer output is too low to charge the battery.
Autotransformer can be engineered to cover a wide range of input voltages, but this requires more taps and increases complexity, and sacrifices the UPS. It is common for autotransformer to cover ranges from only about 90 V to 140 V for 120 V power, and then switch to batteries if the voltage is much higher or lower than that range.
Under low voltage conditions, the UPS will use more current than normal so it may require a higher current circuit than a normal device. For example, to power a 1000-W device at 120Ã,V, the UPS will draw 8.33 A. If the brownout occurs and the voltage drops to 100Ã,V, the UPS will pull 10Ã, A to compensate. It also works in reverse, so in overvoltage conditions, the UPS will require less current.
Online/double conversion
In the online UPS, the battery is always connected to the inverter, so there is no need for a power transfer switch. When a power loss occurs, the rectifier simply descends from the circuit and the battery keeps the power stable and unchanged. When power is recovered, the rectifier brings most of the load and starts charging the battery, although the charging current may be limited to prevent the high power rectifier from overheating the battery and boiling the electrolyte. The main advantage of on-line UPS is its ability to provide "electrical firewalls" between incoming power and sensitive electronic equipment.
The online UPS is ideal for environments where electrical isolation is required or for equipment that is highly sensitive to power fluctuations. Although it was at one time reserved for very large installations of 10 kW or more, technological advancements now allow it to be available as a common consumer device, supplying 500 W or less. Initial online UPS costs may be higher, but the total cost of ownership is generally lower due to longer battery life. Online UPS may be required when the power environment is "noisy", when other sags, outages and other anomaly power equipment is frequent, when sensitive load-bearing IT equipment is required, or when the operation of an extended-run backup generator is required.
The basic technology of UPS online is the same as in standby or line-interactive UPS. But it usually costs much more, because it has a much larger AC-to-DC charger/current charger, and with rectifier and inverter designed to keep running with an improved cooling system. This is called UPS double conversion because the direct rectifier is driving the inverter, even when it is turned on from the normal AC current.
Other designs
This hybrid Rotary UPS design has no official designation, although one name used by UTL is "double conversion on request". This UPS style is targeted for high efficiency applications while retaining the features and levels of protection offered by double conversion.
Hybrid (double conversion on request) UPS operates as an off-line/standby UPS when power conditions are in a preset window. This allows the UPS to achieve a very high efficiency rating. When power conditions fluctuate outside a predetermined window, the UPS switches to online/double conversion operations. In dual conversion mode, the UPS can adjust for voltage variations without having to use battery power, can filter out channel noise and control frequency.
Ferroresonant
The Ferroresonant unit operates in the same way as a standby UPS unit; However, they are online with the exception that the ferroresonant transformer, used to filter the output. This transformer is designed to hold energy long enough to cover the time between switching from power to battery and effectively eliminating the transfer time. Many UPS ferroresonant are 82-88% efficient (AC/DC-AC) and offer excellent isolation.
The transformer has three reels, one for ordinary electric power, the second for improved battery power, and a third for AC power output to the load.
This is the dominant UPS type and limited to 150 kVA range. These units are still widely used in some industrial settings (oil and gas, petrochemicals, chemicals, utilities, and heavy industrial markets) due to UPS's strong natural properties. Many ferroresonant UPSs that use controlled ferro technology may not interact with power factor correction tools.
DC power
A UPS designed to power DC equipment is very similar to an online UPS, except that it requires no inverter output. In addition, if the UPS battery voltage is adjusted to the required voltage of the device, the device's power supply will also not be required. Because one or more power conversion steps are eliminated, this improves the efficiency and processing time.
Many of the systems used in telecommunications use the extra-low 48-volt DC "general battery" voltage, because they have less stringent security regulations, such as those installed in channels and connection boxes. DC is usually the dominant resource for telecommunications, and AC is usually the dominant source for computers and servers.
There have been many experiments with 48 V DC power for computer servers, in the hope of reducing the possibility of failure and cost of equipment. However, to supply the same amount of power, the current will be higher than equivalent 115 V or 230 V circuits; larger currents require a larger conductor, or more energy is lost as heat.
The laptop computer is a classic example of a PC with built-in DC UPS.
The DC high voltage (380 V) is found in use in some data center applications, and allows for small electrical conductors, but is subject to more complex electrical code rules for safe detention of high voltage.
Rotary
A rotating UPS uses the inertia of a high-spinning flywheel (crazy flywheel energy) to provide short-run ride-through in the event of a power loss. The crazy wheel also acts as a buffer against power surges and sag, because such short-term power events can not affect the speed of high-gear rotation of the mass. It is also one of the oldest designs, preceded vacuum tubes and integrated circuits.
This can be considered as online as it rotates continuously under normal conditions. However, unlike battery-based UPS, a wheel-based UPS system typically provides 10 to 20 seconds of protection before the flywheel slows and the power output stops. It is traditionally used in conjunction with standby generators, providing backup power for only a short period of time the engine needs to start running and stabilize its output.
Rotary UPS is generally reserved for applications requiring more than 10,000 W of protection, to justify the costs and benefits of a rotary UPS system advantage. A larger crazy wheel or some flywheel that operates in parallel will increase the backup time or capacity.
Because the force wheel is a source of mechanical power, it is not necessary to use an electric motor or generator as an intermediary between the engine and a diesel engine designed to provide emergency power. By using gearbox transmission, flywheel rotation inertia can be used to directly power a diesel engine, and once running, a diesel engine can be used to spin the flywheel directly. Some flywheels can also be connected in parallel through mechanical countershafts, without the need for separate motors and generators for each flywheel.
They are usually designed to provide very high current output compared to pure electronic UPS, and are better able to provide current surge currents for inductive loads such as motor startup or compressor loads, as well as medical equipment MRI and lab labs. It is also able to tolerate short-circuit conditions up to 17 times larger than the electronic UPS, allowing one device to fuse the fuse and fail while other devices are still being supported from the rotary UPS.
Its life cycle is usually much larger than pure electronic UPS, up to 30 years or more. But they do require periodic stoppages for mechanical maintenance, such as the replacement of ball bearings. In larger systems the system redundancy ensures the availability of processes during this maintenance. The battery-based design does not require any time to stop if the battery can be hot-swapped, which usually applies to larger units. The newer rotary units use technologies such as magnetic bearings and air evacuated enclosures to increase standby efficiency and reduce maintenance to very low levels.
Typically, high-speed flywheels are used in conjunction with a motor generator system. These units can be configured as:
- A motor that drives a mechanically connected generator,
- Combined synchronous motors and generator devices in alternating rotor and single stator slots,
- A hybrid rotary UPS, designed similar to an online UPS, except that it uses a flywheel instead of a battery. The rectifier drives the motor to rotate the flywheel, while the generator uses a flywheel to power the inverter.
In the case of No. 3 motor generator can be synchronous/synchronous or induction/sync. The motor side of the unit in case No. 2 and 3 can be driven directly by an AC power source (usually when in an inverter bypass), a 6-step motor drive, or a 6-pulse inverter. Case No. 1 uses integrated flywheel as a short-term energy source rather than a battery to allow time for external electrical generators to start and be brought online. Case No. 2 and 3 may use electrically coupled batteries or gears that are freely coupled as short-term energy sources.
Establish factor
UPS systems have several different shapes and sizes. However, the two most common forms are towers and rack mounts.
Model tower
The tower model stands upright on the ground or on a table/shelf, and is usually used on network workstations or desktop computer applications.
The rack-mount model
The rack-mount model can be mounted on a standard 19 "rack rack and can require anywhere from 1U to 12U (rack space).Usually used in server and network applications.
Apps
N 1
In large business environments where reliability is critical, a large UPS can also be a single point of failure that can interfere with many other systems. To provide greater reliability, multiple UPS modules and smaller batteries can be integrated together to provide excessive power protection equivalent to a very large UPS. "N 1" means that if the load can be given by module N, the installation will contain N module 1. In this way, failure of one module will not affect system operation.
Lots of redundancy
Many computer servers offer the option of excessive power supply, so if there is a failure of one power supply, one or more other power supplies are capable of switching on the load. This is a critical point - every power supply should be able to turn on the whole server by itself.
Redundancy is further enhanced by inserting each power supply into a different circuit (ie to a different circuit breaker).
Redundant protection can be extended further by connecting each power supply to the UPS itself. It provides both dual protection from power supply failure and UPS failure, so sustainable operation is assured. This configuration is also referred to as 1 1 or 2N redundancy. If the budget does not allow for two identical UPS units then it is a common practice to connect one power supply to the mains and the other to the UPS.
Outdoor use
When the UPS system is placed outdoors, it must have some special features that guarantee that it can tolerate weather without any effect on performance. Factors such as temperature, humidity, rain, and snow among others should be considered by the manufacturer when designing outdoor UPS systems. The operating temperature range for outdoor UPS systems can be around -40 ° C to 55 ° C.
The outdoor UPS system can be a pole, ground (base), or host installed. External environments can mean extreme cold, in which case an external UPS system should include battery heater mats, or extreme heat, in this case an external UPS system should include a fan system or air conditioning system.
A solar inverter , or inverter PV , or solar converter , converts the direct current output (DC) from the photovoltaic solar panel (PV) to alternating current the frequency of utilities (AC) that can be incorporated into a commercial grid or used by a local power grid outside the network. It is a critical BOS component in photovoltaic systems, enabling the use of regular air-conditioning equipment. The solar inverter has a special function that is customized for use with photovoltaic arrays, including maximum power point tracking and anti-island protection.
Power factor
The problem in the combination of dual conversion UPS and generator is the voltage distortion made by UPS. The input of a dual conversion UPS is basically a large rectifier. The current drawn by the UPS is non-sinusoidal. This may cause the voltage from AC power or generator to be non-sinusoidal. Voltage distortions can then cause problems in all electrical equipment connected to the power source, including the UPS itself. This will also cause more power lost in the cable that supplies power to the UPS due to current current surge. This "noise" level is measured as a percentage of "total current harmonic distortion" (THD I ). The classical UPS rectifier has a 25% -30% THD I level. To reduce voltage distortion, this requires a larger electrical wire or generator two times larger than the UPS.
There are several solutions to reduce THD I in double conversion UPS:
Classical solutions such as passive filters reduce THD I to 5% -10% at full load. They are reliable, but large and only work with full load, and present their own problems when used together with the generator.
An alternative solution is an active filter. Through the use of such devices, THD I can fall by up to 5% above the full power range. The latest technology in a double conversion UPS unit is a rectifier that does not use the classical rectifier components (thyristors and diodes) but uses high frequency components instead. A double conversion UPS with an investigator â € <â €
Communications
Power management (PM) requires
- UPS to report its status to a computer it owns via communication links such as serial port, Ethernet and Simple Network Management Protocol, GSM/GPRS or USB
- The subsystem in the OS that processes the report and generates a notification, PM event, or command that orders it to close. Some UPS manufacturers publish their communication protocols, but other manufacturers (such as APC) use proprietary protocols.
The basic computer-to-UPS control method is intended for one-to-one signaling from one source to a target. For example, one UPS can connect to a single computer to provide status information about the UPS, and allow the computer to control the UPS. Similarly, USB protocols are also meant to connect one computer to multiple peripheral devices.
In some situations it is useful for one large UPS to be able to communicate with multiple protected devices. For traditional serial or USB controls, signal replication devices can be used, which for example allows one UPS to connect to five computers using a serial or USB connection. However, separation is usually only one way from the UPS to the device to provide status information. The return control signal can only be allowed from one of the protected systems to the UPS.
Because Ethernet has increased in general usage since the 1990s, control signals are now commonly sent between one UPS and many computers using standard Ethernet data communication methods such as TCP/IP. The status and control information are usually encrypted so that for example an external hacker can not control the UPS and instruct it to close.
UPS state distribution and control data requires that all intermediate devices such as Ethernet switches or serial multiplexers be supported by one or more UPS systems, in order for UPS warnings to reach the target system during a power outage. To avoid dependence on Ethernet infrastructure, UPS can connect directly to the main control server by using GSM/GPRS channels as well. SMS or GPRS data packets sent from UPS trigger software to shut down PC to reduce load.
Battery
The time period for battery-operated UPS depends on battery type and size and discharge rate, and inverter efficiency. The total capacity of lead-acid batteries is a function of the level at which it is disposed, which is described as Peukert's law.
Manufacturers provide run-time ratings in minutes for packaged UPS systems. Larger systems (such as for data centers) require detailed load calculations, inverter efficiency, and battery characteristics to ensure the required resistance is achieved.
General battery characteristics and load testing
When a lead-acid battery is charged or discharged, it initially affects only the reacting chemical, which is at the interface between the electrode and the electrolyte. With time, the charge stored in chemicals in the interface, often called "interface cost", is spread by the diffusion of these chemicals throughout the volume of active ingredients.
If the battery is completely discharged (eg, the car's lamp is left overnight) and then is given a quick charge for just a few minutes, then during that short charge time it only develops a charge near the interface. The battery voltage can rise to close to the charger voltage so that the charging current decreases significantly. After a few hours, the cost of this interface will spread to the volume of the electrode and electrolyte, which causes the interface charge so low that it may not be enough to start the car.
Because of the cost of the interface, a short duration UPS self-test function may not accurately reflect the actual runtime capacity of the UPS, and instead an extended or < i> rundown very draining battery test is required.
The inner debit test itself damages the battery because the chemicals in the discharged battery start crystallizing into a highly stable form of molecule that will not come back late when the battery is recharged, permanently reducing the charge capacity. In these lead acid batteries are known as sulfation but also affect other types such as nickel cadmium batteries and lithium batteries. Therefore, it is generally recommended that rundown tests be rare, as every six months to a year.
Test the battery/cell string
A multi-kilowatt commercial UPS system with a large, accessible battery bank can isolate and test individual cells in string battery , which consists of a composite battery cell unit (such as a 12-V lead acid battery) or cell individual chemical cells connected in series. Isolating a single cell and installing a jumper instead allows one battery to be tested while the remaining battery is charged and available to provide protection.
It is also possible to measure the electrical characteristics of individual cells in the battery string, using intermediate sensor cables attached to each cell-to-cell connection, and monitored individually or collectively. Battery strings can also be transferred as series-parallel, for example two sets of 20 cells. In such situations it is also necessary to monitor the flow of currents between parallel strings, since currents can circulate between strings to balance the effects of weak cells, dead cells with high resistance, or short cells. For example, a stronger string can flow through a weaker string until the voltage imbalance is equalized, and this must be taken into account in the measurement of individual intercellular cells in each string.
Parallel-series battery interactions
Parallel series-paired battery cables can develop an unusual failure mode because of the interaction between multiple parallel strings. Batteries that are damaged in one string may affect the operation and good or new battery life in other strings. These problems also apply to other situations where parallel string-series is used, not only in UPS systems but also in electric vehicle applications.
Consider setting the parallel-series batteries with all the good cells, and one being shorted or off:
- A failed cell reduces the maximum voltage developed for the entire string of strings contained within it.
- The other series series coupled in parallel with the degraded string will now be discarded via a string that is degraded until the voltage corresponds to the degraded string voltage, the possibility of overcharging and causing the boiling electrolyte and the outgassing of the good cells remaining in the string degraded. This parallel string is now completely non-rechargeable, as the voltage increase will decrease through the string containing the failed battery.
- The charging system may try to measure the capacity of the battery string by measuring the overall stress. Due to the overall voltage drop of the strings due to the dead cells, the charging system can detect this as a discharge state, and will continue to attempt to fill the parallel string-string, causing overload and continuous damage to all cells in the series of degraded series containing damaged batteries.
- If lead-acid batteries are used, all cells in a previously good parallel string will start sulfate because of their inability to fully recharge, so the storage capacity of these cells is permanently damaged, even if the damaged cell in one string is degraded eventually found and replaced with new ones.
The only way to prevent this smooth parallel-series string interaction is to not use any parallel strings at all and to use separate charge and inverters for each string.
New/series serial battery interactions
Even just one string of batteries connected in series can have an adverse interaction if the new battery is mixed with the old battery. Older batteries tend to have reduced storage capacity, and both will eject faster than new batteries and also charge up to maximum capacity faster than new batteries.
As a series of new and old battery mixes are exhausted, the string voltage will drop, and when the old battery runs out the new battery still has the available charge. The newer cells can continue to flow through the rest of the string, but because of the low voltage this energy flow may be useless, and may be wasted in old cells as a warming resistance.
For cells that are supposed to operate in a certain exhaust window, new cells with more capacity can cause old cells in series strings to keep flowing outside the safe lower threshold of the exhaust window, damaging the old cells.
When recharged, the old cells recharge faster, leading to a rapid voltage rise near the fully charged state, but before new cells with more capacity are fully charged. The charge controller detects the high voltage of the fully loaded strings and reduces the flow of current. New cells with larger capacities now fill very slowly, so slowly that the chemicals begin to crystallize before it reaches a fully charged state, reducing the capacity of new cells over several charging/discharging cycles until its capacity is better suited to the old cells in series strings..
Source of the article : Wikipedia
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