Uninterruptible power supply: principles of operation of different types of UPS

Uninterruptible power systems are now becoming very popular. It doesn't matter where a modern person lives - in a city apartment, in a country house, various household appliances, digital computers, life support systems have firmly entered his life.

Purpose and categories of UPS

The requirements for the quality of the power supply of all these devices are increasing. The quality of power supply of external electrical networks does not always satisfy the population. There are sharp changes in voltage, both in the direction of lowering and increasing its value. This has a very adverse effect on the operation of household equipment, and sometimes leads to its failure. Protect yourself from such troubles installation of uninterruptible power supplies helpsdevices that are most sensitive to such sudden changes.

Depending on the circuit solutions that determine the main characteristics of uninterruptible power supplies, they can be divided into several categories. Each of them ensures the smooth operation of a certain group of consumers.

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Backup UPS

They can only protect basic home appliances and desktops.

If the mains voltage is correct, consumers are connected directly to it. In case of voltage fluctuations in the network, the equipment switches to power supply from the battery, which is an integral part of the UPS. Noises and high-frequency pulses are partially suppressed, the voltage is maintained at a given level, and the battery is recharged. Stabilization of the mains voltage supplying the equipment connected to its output is not performed with uninterruptible power supplies of this category.

The need to switch to battery operation in each model of an uninterruptible power supply is determined in its own way. The limits of operation from the network are determined by the developer of the given model. They are set based on the conditions for the normal functioning of the consumer's equipment.

Battery operation will continue until the mains voltage returns to normal. After that, switching in the opposite direction occurs. The source battery must provide at least a five-minute time reserve when operating from it. This is enough to save data on a computer and shutdown consumer equipment without an emergency.

The disadvantages of uninterruptible power supplies in this category include the following:

1. Lack of mains voltage stabilizer.
2. Long switching time (~ 20 ms).
3. Stepped output voltage.
4. High frequency interference.

Switching to autonomous power supply mode occurs with any slight deviation of the mains voltage parameters from the norm. This leads to rapid deterioration of the battery.

Line-interactive sources

Models in this category are equipped with mains voltage stabilizers, which are made according to the autotransformer circuit. Switching of its windings, depending on the value of the input mains voltage, occurs in steps according to the commands of the microprocessor built into the UPS circuit. Thus, it is possible to maintain the voltage at the output of the unit close to the norm (220-230) V. Additionally, the circuit has a filter that protects the consumer from mains interference.

Connecting the battery and disconnecting from the network occurs when the voltage parameters at the input of the unit go beyond the stabilization thresholds. The number of terminals of the autotransformer is not enough to maintain the rated voltage at the output. There are also tolerances for the shape of the input signal. With large distortions, the transition to the battery mode of power supply of the consumer equipment is also carried out.

The process of switching to battery power is fairly smooth for most consumers and takes no more than 4ms.

Thus, comparing sources of this category with redundant UPSs, you can see their advantages:

1. The stabilization of the mains voltage has a stepwise nature.
2. The output voltage waveform is close to a sinusoid.
3. Filtering network interference.
4. Saving the battery life due to fewer switchings on it.

Ferroresonant power supplies

In essence, they are linear active sources. The mains voltage stabilizer in them is a ferroresonant transformer. It can store the energy of the magnetic field, which maintains the voltage in the secondary winding of the transformer at the moments of switching. The transient process lasts no more than (8-16) ms. This is acceptable for most consumers. The voltage waveform at its output is sinusoidal, protected from mains interference. The source performs its functions by the commands of its own network analysis and control unit.

Linear uninterruptible devices

This category includes double conversion UPS. They include an AC-to-DC converter (rectifier) ​​and a DC-to-AC converter (inverter). The output voltage of the inverter is used to power the equipment connected as a load. The rectifier voltage is used to recharge the internal battery. It is included in the rectifier circuit and is constantly in active mode, which depends on the quality of the input alternating voltage.

The positive qualities of a UPS in this category include:

1. Stability of the output voltage.
2. The ability to replace the battery without shutting down the UPS.

The disadvantages include:

1. Low coefficient of performance (COP).
2. The battery life is reduced due to its continuous operation.

Devices of this category are used for the operation of equipment of large organizations, on whose servers important data are stored. They must be saved in case of any drops in the network and any disruptions in its work.

Main characteristics

When purchasing a UPS, you must carefully understand the requirements for it. It is necessary to choose the model that most satisfies the criterion "price - quality".

When choosing an uninterruptible power supply, great attention should be paid to comparing the characteristics of different models. These include the following:

• UPS power.
• battery life.
• time to switch to battery operation and vice versa.
• input voltage range.
• the limits of the frequency change of the mains voltage.

The power is calculated from the total load of the source. Its value should be at least one and a half times greater than the power of consumers. The optimal power of the unit installed in the apartment is considered to be 1000 VA (1000 volt-ampere).

The switching time directly depends on the size of the load currently connected to the output of the source. The more current it draws, the shorter the battery life. The capacity of the installed battery also determines the operating time.

All UPS models have visual signaling elements. These can be bulbs of different colors, LED indicators that determine the state of the UPS at the current moment.

Steady green indicators lit are a sign of normal operation of the unit. If the LED works in a pulsed mode (its intermittent glow), then problems are possible or have already occurred. This is an attention-getting warning signal.

The constant glow of the red indicator signals the occurrence of an emergency. Its occurrence is accompanied by warning beeps in the form of intermittent beeps.

Operating rules

Correct operation of the equipment is the key to its long and reliable operation. The basic rules that must be followed when operating an uninterruptible power supply include:

• The need for constant monitoring of the light indication and sound signaling of the unit.
• Connecting consumers that really require an uninterruptible power supply.
• Ground the UPS using a three-pronged socket for the unit plug.

If a power outage occurs, you must turn off all equipment that is currently on. It is advisable to leave the UPS connected to the outlet for possible recharging of the battery after the mains failure has been eliminated. Operation of the unit with a discharged battery leads to its rapid failure. The battery life is limited and is no more than 5 years.

Compliance with these simple, but necessary rules will prolong the life of all equipment, for the operation of which uninterrupted power is required, and most importantly, it will allow save important information on hard drives of computers, which could be irretrievably lost in the event of sudden malfunctions in electrical networks.