Easy to understand UPS uninterruptible power supply

The role of UPS

UPS in Chinese is " uninterruptible power supply ". It is an energy storage device, with rectifiers and inverters as the main components. It provides uninterruptible power supply with constant voltage and frequency for monitoring systems, automation instruments, remote communication systems and other equipment in substations.

The main role of the UPS system is twofold:

(1) As an AC power supply for important equipment, to prevent sudden power outages from affecting normal work and causing damage to the equipment;

(2) Eliminate "power pollution" such as surges, instantaneous high / low voltages, power line noise, and frequency offsets in the city power, improve power quality, and provide high-quality power for computers and the like.

Classification of UPS

There are three main types of UPS systems: backup , interactive, and online .

(1) Backup type: It has functions such as automatic voltage stabilization and power failure protection. The conversion time is about 10ms. The AC power output by the inverter is a square wave. The structure is simple and the price is cheap.

(2) Interactive: with filtering function, strong ability to resist mains interference, conversion time is less than 4ms, inverter output is analog sine wave, and the price is much lower than online;

(3) On-line: more complex structure, perfect performance, can continuously output pure sine wave AC power, can solve all power supply problems such as spikes, surges, frequency drifts; high price, usually used in key computers and network equipment, etc. In demanding environments.

Structure of UPS

The UPS system in the substation is generally composed of three parts: the main power UPS, the bypass voltage stabilization cabinet, and the output feeder cabinet (three in one can also be used at low power).

Rectifier:

There are two main functions:

First, change the alternating current (AC) into direct current (DC) and supply it to the inverter after filtering;

Second, it provides a charging voltage to the battery, and acts as a charger;

Inverter:

Converting direct current (DC) into alternating current (AC) for the load;

Battery:

The UPS is used as a device for storing electric energy, so that when the mains power fails, the direct current can be inverted to provide uninterruptible power for the load. Its capacity determines the duration of its sustain discharge (power supply);

Static switch:

Also known as a static switch, it is an AC switch composed of two thyristors (SCR) connected in antiparallel. Its closing and opening are controlled by a logic controller;

Isolation transformer, voltage regulator:

Isolate AC and DC in the input or output part. In addition to isolation, the regulator also has the function of stabilizing voltage;

Four operating modes of UPS

(1) Normal operation mode:

Under normal AC power supply, the rectifier converts AC power to DC power, eliminates "power pollution" in the city power, and charges the battery at the same time. The inverter is then supplied to convert DC power to AC power, providing a more stable power supply to the load.

(2) Power failure mode:

When the AC power source is abnormal or the rectifier or reactor is faulty, the battery pack provides DC power to the inverter, so that the AC output will not be interrupted, thereby protecting the load.

(3) Standby power mode:

When abnormal conditions such as the inverter fuse blown or short circuit occur, the inverter will automatically cut off to prevent damage. If the bypass AC power is normal at this time, the static switch will switch the power supply to bypass The backup power output is used by the load.

(4) Maintenance bypass mode:

When the UPS is to be repaired or the battery is replaced and the load power supply cannot be interrupted, the inverter switch can be cut off first, then the maintenance bypass switch is activated, and then the rectifier and the bypass switch are cut off. The AC power continues to supply AC power to the load through the maintenance bypass switch. At this time, maintenance personnel can safely perform maintenance on the UPS.