“Uninterruptible power supply UPS (Uninterruptible Power System) is a constant voltage and constant frequency uninterruptible power supply with energy storage device and Inverter as the main component.
1. Classification and characteristics of UPS power supply
Uninterruptible power supply UPS (Uninterruptible Power System) is a constant voltage and constant frequency uninterruptible power supply with energy storage device and inverter as the main component.
There are many types of UPS power supplies, generally static conversion, which can be divided into three categories: backup, online, and online interactive. The most commonly used is online UPS. When the on-line UPS power supply has mains input, it supplies power to the load in the manner of “AC-rectifier-inverter”, and at the same time charges the battery in the machine; when the mains is interrupted, it uses the “battery inverter” inverting conversion method. The pole mode provides 220V AC power to the load. Its characteristic is to truly realize the interference-free voltage stabilization power supply to the load, switching from the mains power supply to the battery power supply in zero time, so that the load maintains normal operation and protects the load software and hardware from damage. UPS efficiency, power factor, conversion time, output voltage, frequency range, etc. are all important parameters that characterize UPS performance. In general, online UPS can solve almost all common power problems.
2. The necessity of UPS power supply
Some large inductive, capacitive, switching power supply and other loads in the public grid will cause distortion or frequency drift of the grid voltage waveform, deteriorating the power supply quality of the grid, unexpected natural and man-made accidents, such as earthquakes, lightning strikes, open circuits in transmission and transformation systems, or Short circuit will also affect the normal operation of the load. According to tests, the main problems that often occur in the power grid and interfere with or damage computers and precision instruments are power surges, high-voltage spikes, transient overvoltages, voltage sags, wire noise, frequency deviations, power failures, and so on.
Computers have higher requirements for power, especially memory. If the power is cut off abnormally, the information in the memory will not be able to be saved to storage devices such as hard disks. This will cause the information to be lost or become incomplete and lose its value, and waste a lot of work and energy. Time may even cause huge economic losses. For operating systems like UNIX, if the system information in the memory is not written back to the hard disk, it may also cause the system to crash. Although the hard disk in the computer is a magnetic storage medium, there is no loss of information due to power failure, but a sudden power failure will damage the physical head of the hard disk that is reading and writing, or the system file will cause a file allocation table error when the file system is maintained. And cause the entire hard disk data to be lost. Most of the existing operating systems are equipped with virtual memory. Due to the sudden power failure, the system has no time to cancel the virtual memory, resulting in “information fragmentation” in the hard disk, which not only wastes hard disk storage space, but also causes the machine to run slowly.
The computer power supply is a rectifier power supply. Excessive voltage may cause the rectifier to burn out. Interferences such as voltage spikes, tube state overvoltage, and power noise may enter the motherboard through the rectifier, affecting the normal operation of the machine, and even burning the host circuit. With the widespread use of computers and networks, safe and reliable power has become an important issue that computer managers must face seriously.
Three, the choice of UPS
Not all electrical equipment needs to use UPS. When choosing UPS, the main consideration should be the size of the load, the characteristics and importance of the load, and the discharge time.
(1) The characteristics of the load. Computers and their peripheral devices are mostly capacitive rectifier loads, and there are inrush currents when starting. Even in normal operation, the peak value of the current is 23 times its effective value. Therefore, this should be taken into consideration when choosing a UPS. One feature, leaving a certain margin for UPS.
(2) Calculation of load size and UPS capacity. The load power factor of the computer equipment is between 0.65DD0.7, and the total power can be calculated by accumulating the rated power vector of each load. The UPS capacity is selected according to the following formula: UPS capacity≥load capacity/0.8.
That is, taking into account the inrush current at the start of the load, the load capacity should be less than 80% of the UPS rated capacity.
(3) The configuration of discharge time. Generally, the backup time of long-term UPS is mainly limited by factors such as battery cost, installation space, and battery recharging time. In areas where the power environment is poor and power outages are frequent, UPS and generators are used to supply power. In the event of a power failure, the UPS battery supplies power first. If the power failure lasts for a long time, the backup generator can be started to continue supplying power to the UPS. When the mains power is restored, it will switch to the mains power supply.
(4) Calculation of battery power supply time. The battery power supply time is mainly affected by factors such as load size, battery capacity, ambient temperature, and battery discharge cut-off voltage. For UPS battery power supply time, the battery discharge current can be calculated first, and then the discharge time can be found according to the battery discharge curve.
The battery discharge current can be calculated according to the empirical formula:
Discharge current = UPS capacity (VA) × power factor / battery discharge average voltage × efficiency;
If you want to calculate the actual load discharge time, you only need to replace the UPS capacity with the actual load capacity.
Fourth, the working principle of UPS
(1) AC-DC conversion: the alternating current from the grid is reduced by an autotransformer, full-wave rectification, and filtering into a direct current voltage, which is then supplied to the inverter circuit. The AC-DC input has a soft start circuit, which can avoid the impact on the power grid when it is turned on.
(2) DC-AC inverter circuit: adopts high-power IGBT module full-bridge inverter circuit, which has a large power margin, and the output impedance is particularly small in the output dynamic range, and it has a fast response characteristic. Due to the use of high-frequency modulation current-limiting technology and fast short-circuit protection technology, the inverter can work safely and reliably whether it is a transient supply voltage, a load impact or a short-circuit.
(3) Control drive: Control drive is the core to complete the function control of the whole machine. In addition to providing detection, protection, synchronization, and various switch and Display drive signals, it also completes the control of SPWM sinusoidal pulse width modulation, due to the use of static and dynamic Double voltage feedback. Greatly improve the dynamic characteristics and stability of the inverter. The working principle block diagram of the uninterruptible power supply is shown in the figure below.
Five, UPS installation
The quality of UPS installation directly affects the long-term operation of the UPS system in the future, so UPS should be standardized from the planning to the installation process. Mainly consider the following factors: grid conditions, load capacity and characteristics, use environment, grounding conditions, wiring and switching capacity, etc.
(1) Grid situation. It mainly includes the equipment that has determined the UPS standby time, such as the range of grid voltage fluctuations and the frequency of power outages. If necessary, other protection measures can be added to the front stage of the UPS. When using UPS power supply, you must comply with the relevant regulations of the manufacturer’s product manual to ensure that the live, neutral, and ground wires are in compliance with the requirements, and the mutual order must not be changed at will.
(2) Use environment. The operating environment of the UPS power supply should be protected from direct sunlight, and sufficient ventilation space should be reserved to facilitate heat dissipation and ensure that the engineers have a certain amount of space when the UPS is maintained. The temperature requirement is 0℃-40℃, and the humidity requirement is 10%-90%. The surrounding environment should be kept clean to reduce the corrosion of harmful dust to the internal circuit of the UPS. When the UPS is configured with a long time delay, the battery is heavier and the floor unit should be considered. The area load-bearing problem.
(3) Grounding conditions. In order to ensure the stable and reliable operation of the computer system, prevent parasitic capacitive coupling interference, and protect the equipment and personal safety, it is necessary to have a good grounding system. Generally, the grounding resistance is less than 4Ω.