Uninterruptible power supply (UPS) is a device that continuously provides backup AC power for electrical load equipment and maintains the normal operation of electrical appliances in the event of abnormal power grids. In daily life, UPS uninterruptible power supply is mainly used to maintain the uninterrupted operation of key commercial equipment or precision instruments such as computers or switches, to prevent computer data loss, telephone communication network interruption or loss of control of instruments. Next, let’s take a look at the encyclopedia of UPS uninterruptible power supply with me.
1 What is UPS power supply
UPS uninterruptible power supply is a constant voltage and constant frequency power supply with inverter as the main component. It is used to provide uninterrupted power supply to a single computer, computer network system or other power electronic equipment. When the mains input is normal, the UPS will stabilize the mains and supply it to the load. At this time, the UPS is an AC mains voltage stabilizer, and it also charges the battery inside the machine. When the utility power is interrupted (accidental power failure), the UPS will immediately supply the 220V AC power to the load through the method of inverter conversion, so that the load can maintain normal operation and protect the software and hardware of the load from damage.
Before the age of batteries, uninterruptible power supplies used flywheels and internal combustion engines to provide electrical energy to loads. Such uninterruptible power supplies were called flywheel or rotary uninterruptible power supplies. Since the flywheel type uninterruptible power supply uses the internal combustion engine to provide power, it will generate larger noise and larger volume, so it is generally only used in emergency situations and some occasions with bad natural conditions, so usually UPS uninterruptible power supply will Use batteries to provide power.
2 UPS uninterruptible power supply types
1. Backup UPS
When the mains power is normal, the mains supply power to the load directly. The transfer switch turns the battery to invert power supply. Its characteristics are: simple structure, small size, low cost, but narrow input voltage range, poor output voltage stability accuracy, switching time, and the output waveform is generally square wave.
2. Online interactive UPS
When the mains is normal, the mains supply power to the load directly. When the mains is abnormal or the power is cut off, it will be converted to the battery inverter to supply power through the transfer switch. Its characteristics are: a wide input voltage range, low noise, small size, etc., but there is also a switching time.
3. Online UPS
When the mains is normal, the mains will rectify and provide DC voltage to the inverter, and the inverter will provide AC to the load. When the electricity is abnormal, the inverter is powered by the battery, and the inverter is always in working state to ensure uninterrupted output. Its characteristics are that it has an extremely wide input voltage range, no switching time and high output voltage stability accuracy, which is especially suitable for occasions with high power requirements, but the cost is high. At present, almost all UPSs with power greater than 3KVA are online UPSs.
3 The role of UPS uninterruptible power supply
UPS is the abbreviation of the English name of Uninterruptible Power System (Uninterruptible Power System). In fact, UPS is a kind of uninterruptible power supply with constant voltage and constant capacity with energy storage device and inverter as the main component. In the early days of its development, UPS was only regarded as a backup power source. Later, due to power grid quality problems such as voltage surges, voltage spikes, voltage transients, voltage sags, continuous overvoltage or undervoltage or even voltage interruptions, the electronic systems of computers and other equipment were disturbed, resulting in damage to sensitive components, loss of information, Serious consequences such as the disk program being flushed, causing huge economic losses. Therefore, UPS has been paid more and more attention, and has gradually developed into a power protection system with functions such as voltage regulation, frequency stabilization, filtering, anti-electromagnetic and radio frequency interference, and anti-voltage surge.
A wide variety of UPS power supplies are currently available in the market, with output power ranging from 500VA to 3000kVA. When there is a commercial power supply to the UPS, the UPS powers the computer after stabilizing the commercial power (220V±5%). At this time, the UPS is an AC mains voltage stabilizer, and it also charges the battery inside the machine. Due to the different design of UPS, the range of UPS adaptation is also different. The change of UPS output voltage within ±10-15% is generally a normal computer voltage. When the utility power is abnormal or interrupted, the UPS immediately converts the power of the battery in the machine to the computer system through inverter conversion, so as to maintain the normal operation of the computer system and protect the software and hardware of the computer from loss.
4 UPS uninterruptible power supply advantages
1. UPS uninterruptible power supply can automatically switch the power supply mode without manual operation, and go through different paths when there is electricity or no electricity, which is conducive to reducing energy waste.
2. The UPS power supply system starts to run when the power grid is out of power, so that it will not interfere with the normal power supply of the power grid, which is very safe.
3. During installation, you only need to connect the backup power supply to the circuit. It has a specific port for connection, which can be connected to different interfaces for different devices.
4. The UPS does not take up too much space, and it is easy to find the installation location. When the operating space of the device is small, a product similar to the size of a computer mainframe can be used.
5. The main advantage of UPS uninterruptible power supply lies in the ability of uninterruptible power supply. When the mains power is normal, the UPS AC power is rectified into DC power, and then the DC power is inverted into stable and impurity-free AC power, which is supplied to the load. . On the contrary, the direct current can be inverted into stable and impurity-free alternating current, which can continue to be used by the load.
5 How long can UPS uninterruptible power supply supply power
The power supply time of UPS uninterruptible power supply is not infinite, this time is subject to the influence of factors such as the size of the battery’s own stored energy, load size, ambient temperature, battery discharge cut-off voltage, etc. . Generally speaking, the uninterruptible power supply time of small home computer UPS can last for about 20 minutes, and the large kilowatt-level UPS can be equipped with battery packs according to requirements, and the power supply time can reach more than 1 hour, and some can even supply power for 10 hours.
How long the UPS can last depends on the actual situation. Generally speaking, UPS uninterruptible power supply manufacturers will adjust the high power and emergency time on the basis of consumer requirements, which can not only ensure the safe and stable start of the load, but also ensure the backup time. If there is an AC power failure, what the user needs to do is to quickly restore the AC power during the precious time when the UPS battery supplies power, such as enabling the backup AC circuit and enabling the diesel generator to generate electricity. Continue when the AC power returns to normal.
6 UPS uninterruptible power supply purchase
1. There are many power distribution systems for UPS uninterruptible power supplies. Large-scale UPS should adopt three-in (380V) and three-out (380V) power distribution systems.
2. Isolation transformer. In order to solve the problems of interference to the load, zero-ground voltage and isolation, generally large-scale UPSs are equipped with an output isolation transformer as standard. If the impact and interference to the power grid are considered, an input isolation transformer can be selected.
3. Output voltage unbalance. For UPS, no matter whether the input is out of phase or not, the smaller the unbalance of the output voltage, the better, and a three-phase balanced power supply should be given to the load.
4. Magnetic compatibility. Select those UPSs that have passed the electromagnetic compatibility test to reduce the pollution of electronic equipment to the power grid and the radiation to the human body, so as to avoid affecting the normal operation of other equipment. At the same time, the UPS itself must have the ability to resist interference from other equipment.
5. Output power factor. The output power factor is the ability to adapt to loads of different natures. The ideal output power factor is zero in lead and lag, which also means that it can carry loads of any nature.
6. Mean time between failures. The longer the mean time between failures, the better.
7. Monitoring software. The UPS should be equipped with monitoring software with complete functions and easy to use. For domestic users, it is also an essential requirement that the monitoring interface be in Chinese.
8. Battery. Large-scale UPS should have intelligent battery management functions, at least regular battery self-check and automatic battery maintenance, automatic conversion of equalization/floating charge, automatic temperature compensation, etc., to prolong battery life.
7 UPS uninterruptible power supply use and maintenance
1. Environmental requirements for use
1. The UPS uninterruptible power supply must be placed in a stable position and the chassis All sides must maintain sufficient ventilation distance from the wall.
2, UPS uninterruptible power supply should be kept away from heat sources, prevent direct sunlight, maintain normal temperature and humidity, keep the room clean, and prevent corrosion.
3. Overload use is prohibited. In order to prolong the service life of the UPS, the uninterruptible power supply should not run under full load for a long time. The backup UPS generally selects the load of 60% to 70% of the rated power, and the online UPS generally selects the load of 70% to 80% of the rated power.
4. Lightning strikes are the natural enemy of all electrical appliances. Be sure to ensure the effective shielding and grounding protection of the UPS. A large number of CMOS integrated circuit modules and control CPUs and other microelectronic devices are used in the UPS uninterruptible power supply. They are very sensitive to the electromagnetic pulse of lightning, so they are easily damaged. Even under the premise that the UPS has effective shielding and good protective grounding, lightning and overvoltage protection of power lines and communication lines must be done.
2. Precautions for use and maintenance
1. It is forbidden to connect inductive loads to the UPS output port. It is stipulated to ensure that the connected live wire, neutral wire and ground wire meet the requirements, and the user shall not arbitrarily change their mutual order.
2. Strictly follow the correct startup and shutdown sequence. When the load is suddenly loaded or suddenly reduced, the voltage output of the UPS power supply fluctuates greatly, and the UPS power supply cannot work normally.
3. Frequently turning off and on the UPS is strictly prohibited. It is generally required to wait at least 6 seconds before turning on the UPS power supply after turning off the UPS power supply. Otherwise, the UPS power supply may enter a state of “failure to start”, that is, the UPS power supply enters a state with neither mains output nor inverter output.
4. Generally, UPS has protective measures for battery discharge, but after discharging to protect shutdown, the battery can recover to a certain voltage, but it is not allowed to restart at this time, otherwise it will cause battery over-discharge, UPS It must be recharged before it can be put into normal use.
5. The newly purchased UPS (or the UPS that has been stored for a period of time) must be charged before it can be put into normal use, otherwise the backup time cannot be guaranteed.
6. For the UPS that has no power failure for a long time, the UPS should be discharged every 3 to 6 months, and then recharged, so as to prolong the service life of the battery, otherwise the UPS host and the battery may be damaged.
7. Regularly maintain the UPS power supply, remove the dust in the machine, measure the voltage of the battery pack, check the operation of the fan, and detect and adjust the system parameters of the UPS.
8 Troubleshooting of UPS uninterruptible power supply
1. The UPS output is normal when there is utility power, but when there is no utility power, the buzzer beeps for a long time and there is no output.
Failure analysis: It is judged from the phenomenon that the battery and inverter are partially faulty, and can be checked according to the following procedures:
Check the battery voltage to see if the battery is not sufficiently charged. It is necessary to check whether it is the fault of the battery itself or the fault of the charging circuit.
If the working voltage of the battery is normal, check whether the drive circuit of the inverter works normally. If the output of the drive circuit is normal, it means that the inverter is damaged.
If the inverter drive circuit is not working properly, check whether the waveform generation circuit has PWM control signal output. If there is a control signal output, it means that the fault is in the inverter drive circuit.
If there is no PWM control signal output from the waveform generation circuit, check whether its output is blocked due to the operation of the protection circuit, and if so, find out the reason for the protection;
If the protection circuit does not work and If the working voltage is normal, but the waveform generating circuit has no PWM waveform output, it means that the waveform generating circuit is damaged.
The above troubleshooting sequence can also be reversed, sometimes finding faults faster.
2. The battery voltage is low, but the battery voltage still cannot be charged after more than ten hours of charging.
Failure analysis: If it is judged from the phenomenon that the battery or charging circuit is faulty, you can check according to the following steps:
Check whether the input and output voltages of the charging circuit are normal;
If The input of the charging circuit is normal, but the output is abnormal. Disconnect the battery and test again. If it is still abnormal, the charging circuit is faulty;
If the input and output of the charging circuit are normal after disconnecting the battery, it means that the battery has Damaged due to long-term uncharged, over-discharged or expired life.
3. A pair of power amplifier transistors in the power stage of the inverter are damaged. After replacing the transistors of the same type, they burn out after running for a period of time.
The reason is that the current is too large, and the reasons for the excessive current are:
The overcurrent protection fails. When an overcurrent occurs at the inverter output, the overcurrent protection circuit does not work;
The pulse width modulation (PWM) component fails, and the two complementary waveforms of the output are asymmetrical, one has a long on-time, while The other one has a short conduction time, which makes the two arms work unbalanced, and even the two arms are turned on at the same time, causing damage to the two tubes;
The parameters of the power tubes are quite different. Asymmetry, the waveform passes through the output transformer, resulting in a biased magnetism, that is, the magnetic flux is unbalanced, and the accumulation leads to saturation of the transformer and a sudden increase of current, which burns out the power tube, and one burns out, and the other burns out.
