The role of uninterruptible power supply

Program-controlled switches, data communication processing systems, computers, communication base stations, security monitoring systems and other equipment require that the AC power supply system cannot be shut down during operation. In order to improve the reliability and maintainability of these equipment, many companies have equipped them with UPS power supply (uninterruptible power supply) systems. The UPS power supply system consists of several parts such as rectifiers, energy storage devices, inverters and static switches. At present, there are many types of UPS systems on the domestic and foreign markets, and their main functions and principles are basically the same. The following is a brief introduction to their use and maintenance from several aspects.

1. The role of (UPS) uninterruptible power supply:

The use of (UPS) uninterruptible power supply is mainly in two aspects: one is emergency use to prevent sudden power outages from affecting the normal operation of equipment and causing damage to electrical equipment; the other is to eliminate "power pollution" such as surges, instantaneous high voltage, instantaneous low voltage, power line noise and frequency offset on the mains, improve power quality, and provide high-quality power for electrical equipment.

The uninterruptible power supply (UPS) is mainly composed of four parts: the rectification system, the energy storage system, the conversion system and the switch control system. When the power supply system is supplying power, the rectification system is a device that converts alternating current (AC) into direct current (DC). After filtering and voltage stabilization, it supplies the inverter or charges the energy storage system, playing the role of a charger. The energy storage system is a device used by UPS to store electrical energy. It is composed of several batteries in series. The size of the battery capacity determines the time it maintains discharge (power supply). The main function of the 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, the chemical energy is converted into electrical energy and provided to the inverter or load. The conversion system is a device that converts direct current (DC) into alternating current (AC). It consists of an inverter bridge, a control logic circuit and a filter circuit. The switch conversion control system is a contactless switch, which is an AC switch composed of thyristors (SCR) in reverse parallel. Its closing and opening are controlled by a logic controller and are divided into two types: conversion type and parallel type. The conversion switch is mainly used in systems with two power supplies, and its function is to realize automatic switching from one power supply to another; the parallel switch is mainly used in systems with parallel inverters and power supply lines or multiple inverters.

2. Use and management of (UPS) uninterruptible power supply:

The correct use of (UPS) uninterruptible power supply can not only protect it, but also help to extend its service life. Specifically, it can be started from the following aspects:

1). Regularly check the (UPS) uninterruptible power supply:

When using (UPS) uninterruptible power supply, not only should the main components be checked regularly, but also the terminal voltage and internal resistance of each battery unit of the (UPS) uninterruptible power supply battery pack should be tested. If the terminal voltage difference of a battery cell in the battery pack is found to be >0.4V or the internal resistance is >0.08Ω, the connection wire between the abnormal battery cell and the battery pack should be disconnected, and the abnormal battery cell should be charged separately using an external independent charger, and its charging voltage (for 12V batteries) should be kept between 13.5 and 13.8V, and the charging time should be controlled within 10 to 12 hours. It should be noted that during the use of the UPS power supply, the charging of each battery cell in the battery pack will be inconsistent, which may cause imbalance in the terminal voltage and internal resistance of the battery cell. These cannot be eliminated and corrected by charging the internal charging circuit of the (UPS) uninterruptible power supply. If the unbalanced battery cell is not charged offline and balanced in time, the above problems may become more serious. Therefore, charging it separately can restore the internal resistance of this battery cell to within 0.03Ω; and when the battery is fully charged, the battery cell should be connected to the battery pack in time, and the (UPS) uninterruptible power supply charging system should be used for unified charging.

2). First charge:

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

3). Choice of charging time:

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

4). When using (UPS) uninterruptible power supply, excessive discharge should be prevented:

It is well known that the number of excessive discharges of (UPS) uninterruptible power supply should be minimized during operation, because the number of excessive discharges directly affects the battery life.

When the power supply system is out of power and the (UPS) uninterruptible power supply battery pack outputs current to its inverter, the (UPS) uninterruptible power supply will generally sound an alarm every 4 to 5 seconds to remind the user that the (UPS) uninterruptible power supply is in the battery power supply state; when the alarm sound period becomes very short, it indicates that the battery has entered or is about to be over-discharged. At this time, emergency treatment should be done before the (UPS) uninterruptible power supply is over-discharged, and the generator set should be used in time to replace the power supply system to supply power to the (UPS) uninterruptible power supply, so as to avoid excessive discharge of the (UPS) uninterruptible power supply battery pack. If the excessive discharge of the (UPS) uninterruptible power supply battery pack is not repaired in a timely and effective manner, the service life of the UPS battery pack will be greatly reduced.

5). Choose a suitable charging protection working point:

The (UPS) uninterruptible power supply currently used generally uses 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, which plays a good protective role for the battery. However, the protection working point cannot be set too high or too low, because the height of the protection working point may directly lead to overcharging or undercharging of the battery. In many cases, due to improper selection of the charging protection working point, charging causes overcurrent or overvoltage to the battery, which greatly reduces the battery life. In severe cases, it will also cause the battery to swell and deform, or even explode, directly threatening the safety of people and property.

6). Maintain indoor temperature:

The working environment of the battery is closely related to the battery's storage capacity. The (UPS) uninterruptible power supply has high requirements for the ambient temperature, generally 0-40℃, and the optimal temperature is 25℃±5%. If the temperature is too high, the inverter will stop working and alarm, and it will also affect the battery life; if the temperature is too low, it will affect the output capacity of the battery. The temperature in summer 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. A working environment with too high or too low temperature will directly affect the life and working performance of the UPS power supply system.

3. Maintenance of (UPS) uninterruptible power supply:

Proper maintenance and care are very beneficial to the working life and reliability of (UPS) uninterruptible power supply.

1). Regular maintenance:

According to the above analysis, it is not difficult to find that the working environment of (UPS) uninterruptible power supply directly affects the life and working quality of (UPS) uninterruptible power supply. Therefore, when using (UPS) uninterruptible power supply, its surrounding environment should be regularly checked or tested. If the environment changes greatly, the temperature and humidity are too low or too high, which may directly affect the normal operation of (UPS) uninterruptible power supply. At the same time, the battery pack should be regularly maintained to extend the life of the UPS battery pack.

2). Do a good job of load connection:

It is very important whether the load connection of (UPS) uninterruptible power supply is correct or not, because the current of the battery pack is very large, and special tools with good insulation effect should be used during connection and maintenance. When connecting the circuit, you must comply with the relevant regulations in the product specification or user manual to ensure that the live wire, neutral wire, and ground wire meet the requirements. Users are not allowed to change their order at will. They should be connected correctly and reliably in the order of ground wire, neutral wire, and live wire.

3). Notes:

Strictly follow the correct startup and shutdown sequence to avoid large voltage output fluctuations of the (UPS) uninterruptible power supply due to sudden load loading or sudden load reduction, which may cause the (UPS) uninterruptible power supply to fail to work properly.