The role of uninterruptible power supply

Programmable switches, data communication processing systems, computers, communication base stations, security monitoring systems, and other equipment require the AC power supply system to be uninterrupted during operation. In order to improve the reliability and maintainability of these devices, many enterprises have equipped them with uninterruptible power supply systems. The uninterruptible power supply (UPS) power system consists of several parts, including rectifier, energy storage device, inverter, and static switch. At present, there are many types of uninterruptible power supply systems on the domestic and international markets, whose main functions and principles are basically the same. Below is a brief introduction to their use and maintenance from several aspects.

1.The function of uninterruptible power supply:

The main purposes of uninterruptible power supply are twofold: firstly, for emergency use, to prevent sudden power outages from affecting the normal operation of equipment and causing damage to electrical equipment; The second is to eliminate "power pollution" such as surges, momentary high voltage, momentary low voltage, power line noise, and frequency offset on the mains power, improve power quality, and provide high-quality power for electrical equipment.

Uninterruptible power supply mainly consists of four parts: rectification system, energy storage system, conversion system, and switch control system. When supplying power to the power supply system, the rectification system is a device that converts alternating current (AC) into direct current (DC), filters and stabilizes it, and supplies it to the inverter or charges the energy storage system, acting as a charger. An energy storage system is a device used by an uninterruptible power supply to store electrical energy. It consists of several batteries connected in series, and the size of the batteries determines the duration of their discharge (power supply). The main function of an energy storage system is to convert electrical energy into chemical energy and store it inside the battery when the power supply system is normal; When the power supply system fails, convert chemical energy into electrical energy and provide it to the inverter or load. A transformation system is a device that converts direct current (DC) into alternating current (AC), consisting of an inverter bridge, control logic circuit, and filtering circuit. The switch conversion control system is a non-contact switch, which is an AC switch composed of a thyristor (SCR) in reverse parallel. Its closing and opening are controlled by a logic controller, and it is divided into two types: conversion type and parallel type. The conversion switch is mainly used in systems powered by two power sources, and its function is to achieve automatic switching from one power source to the other; Parallel type switches are mainly used in systems where parallel inverters are connected to power supply lines or multiple inverters.

2.Management of uninterruptible power supply usage:

Proper use of uninterruptible power supply systems can not only provide protection, but also help extend their lifespan. Specific measures can be taken from the following aspects:

(1) Regularly inspect the uninterruptible power supply:

When using an uninterruptible power supply system, it is not only necessary to regularly check the main components, but also to detect the voltage and internal resistance of each battery cell terminal of the uninterruptible power supply battery pack. If the terminal voltage difference of a certain battery cell in the battery pack is found to be greater than 0.4V or the internal resistance is greater than 0.08 Ω, the connecting wire between the abnormal battery cell and the battery pack should be disconnected, and an external independent charger should be used to charge the abnormal battery cell separately. The charging voltage (for a 12V battery) should be maintained between 13.5-13.8V, and the charging time should be controlled within 10-12 hours. It should be noted that during the use of an uninterruptible power supply, the charging of each battery cell in the battery pack may be inconsistent, which may result in an imbalance in the terminal voltage and internal resistance of the battery cells. These cannot be eliminated and corrected by relying on the internal charging circuit of the uninterruptible power supply system. If the unbalanced battery units are not charged offline in a timely manner, the above problems may become more serious. So charging it separately can restore the internal resistance of this battery cell to within 0.03 Ω; And when fully charged, promptly connect the battery unit to the battery pack and use an uninterruptible power supply charging system for unified charging.

(2) First charge:

Before using the new uninterruptible power supply, the battery should be charged directly for about 12 hours in a no-load state. If the uninterruptible power supply is in a floating charge state for a long time without discharging operation, the entire uninterruptible power supply is in a storage state. If this state is maintained for too long, the battery function may decrease due to long-term storage, and over time, the battery will gradually fail or be scrapped. It is recommended to use an uninterruptible power supply battery to supply power to the equipment once every three months, so that the uninterruptible power supply battery can discharge normally, and the battery discharge voltage should be controlled above the allowable minimum discharge voltage.

(3) Selection of charging timing:

In order to prevent the battery unit of the uninterruptible power supply from being prematurely damaged due to long-term insufficient charging, users of uninterruptible power supply should arrange the battery charging time at night as much as possible, so as to ensure that the battery has sufficient time and stable voltage to charge after discharge.

(4) The use of uninterruptible power supply should prevent excessive discharge:

As is well known, the excessive discharge frequency of uninterruptible power supply should be minimized as much as possible during operation, as the excessive discharge frequency directly affects the battery life.

When the power supply system experiences a power outage and the uninterruptible power supply battery pack outputs current to its inverter, the uninterruptible power supply generally emits an alarm sound every 4-5 seconds to indicate that the user's uninterruptible power supply is in battery powered state; When the time period of the alarm sound becomes very short, it indicates that the battery has entered or is about to enter an over discharge state. At this time, emergency measures should be taken before excessive discharge of the uninterruptible power supply, and a generator set should be used in a timely manner to replace the power supply system to supply power to the uninterruptible power supply, thereby avoiding excessive discharge of the uninterruptible power supply battery pack. If the excessive discharge of the uninterruptible power supply battery pack is not repaired in a timely and effective manner, it will greatly reduce the service life of the uninterruptible power supply battery pack.

(5) Choose a suitable charging protection working point:

The currently used uninterruptible power supplies generally use maintenance free sealed batteries. The charging system basically adopts a constant voltage load stop charging circuit, which can set an overvoltage protection working point for the battery, providing good protection for the battery. However, the protection working point should not be set too high or too low, as the high or low protection working point may directly cause overcharging or undercharging of the battery. In many cases, improper selection of charging protection points can cause overcurrent or overvoltage to the battery during charging, greatly reducing its lifespan. In severe cases, it can also lead to battery expansion, deformation, and even explosion, directly threatening personal and property safety.

(6) Maintain indoor temperature:

The working environment of batteries is closely related to their storage capacity. Uninterruptible power supplies have high requirements for environmental temperature, generally ranging from 0 to 40 ℃, with an optimal temperature of 25 ℃± 5%. If the temperature is too high, the inverter will stop working and sound an alarm, which will also affect the battery life; Low temperature will affect the output capacity of the battery. The summer temperature is very high. If the ventilation is not good, the large amount of heat generated by the operation of the equipment itself cannot be discharged in time, and the temperature will rise rapidly. If it exceeds 55 ℃, the inverter will stop working. Working environments with excessively high or low temperatures will directly affect the lifespan and performance of uninterruptible power supply systems.

3.Maintenance of uninterruptible power supply:

Proper maintenance and upkeep are highly beneficial for the service life and reliability of uninterruptible power supply systems.

(1) Regular maintenance:

Based on the above analysis, it is not difficult to find that the working environment of an uninterruptible power supply directly affects its lifespan and working quality. Therefore, when using an uninterruptible power supply, the surrounding environment should be regularly inspected or tested. If the environment changes greatly, the temperature and humidity may be too low or too high, which may directly affect the normal operation of the uninterruptible power supply. At the same time, regular maintenance of the battery pack should be carried out to extend the lifespan of the uninterruptible power supply battery pack.

(2) Make good load connections:

The correct connection of the load of the uninterruptible power supply is very important because the current of the battery pack is large, and special tools with good insulation effect should be used for connection and maintenance. When connecting circuits, it is necessary to follow the relevant regulations in the product manual or user manual to ensure that the live wire, neutral wire, and ground wire connected meet the requirements. Users must not change their mutual order arbitrarily, and should connect them correctly and reliably in the order of ground wire, neutral wire, and live wire.

(3) Attention:

Strictly follow the correct startup and shutdown sequence to avoid large voltage fluctuations in the output of the uninterruptible power supply due to sudden load loading or unloading, which may cause the uninterruptible power supply to malfunction.