Three technical solutions to improve UPS power supply reliability

Since the reform and opening up, the construction of my country's power system has been unable to meet the requirements of rapid development of various industries. In particular, the nationwide power supply shortage in recent years has led to large-scale power outages, which has seriously restricted the pace and quality of digital construction. For example, many factories cannot operate at full speed due to power restrictions, outdoor wireless communication services cannot operate normally due to power outages, financial information network systems have slowed down data transmission, abnormalities or partial suspension due to power grid quality, and the government's information construction work has to be postponed due to power outages, etc. All this shows that the power supply quality and reliability of the power system play a vital role in digital construction.

Therefore, system engineers must fully consider the reliability of the power supply system when designing digital systems. At present, the more reliable method is to use high-quality uninterruptible power supply UPS. UPS can provide high-quality AC power to various information equipment when the power grid is normal, and can convert the DC energy of the backup battery pack into a stable AC power supply for the load equipment when the power grid is abnormal. It can also ensure that there is no "interruption" in the output during the power failure of the power grid, ensuring the safe operation of information equipment. A large amount of field operation data and theoretical analysis also show that the introduction of UPS power supply can not only solve the impact of the above-mentioned AC power supply interruption, but also eliminate the harm of various high-frequency clutter, voltage surge, collapse, instantaneous power failure and other power interference in the normal AC power grid to information equipment, ensuring the safe operation of the information network at all times. It can be seen that in order to ensure the smooth progress of digital construction, the use of a highly reliable UPS power supply solution is the most effective and highly reliable power supply solution.

This article will first introduce the basic knowledge of UPS, and then analyze three system technical solutions to improve the reliability of UPS power supply, for reference by system engineers when designing power supply solutions.

1. Basic knowledge of uninterruptible power supply UPS

1. Basic concepts of UPS

UPS is a power supply device composed of a rectifier, inverter, battery and control circuit, which can provide pure and stable waveform in a limited time.

UPS has the following functions:

① When the grid voltage is normal, in addition to outputting pure, stable and continuous AC power, it can also charge the battery and store backup energy.

② When the power grid is abnormal (undervoltage, overvoltage, power failure, interference, etc.), the energy of the battery pack is used to provide uninterrupted AC output to the electrical equipment. "Uninterrupted" generally means that the output voltage waveform is zero for no more than 10ms.

Therefore, UPS can ensure that computers and other information equipment can operate safely and normally even under harsh power grid conditions.

2. Classification and main features of UPS

From the perspective of UPS technical features, UPS is generally classified based on the output inverter working mode, and can be generally divided into two types: backup type and online type. In recent years, a special case of backup power supply has been separated and called online interactive type, but strictly speaking, it is still a backup type.

Judging from the widespread use of UPS in recent years, UPS has also gradually developed from the original indoor use to the direction of all-weather application environment, and the difference between indoor UPS and outdoor UPS has emerged. Outdoor UPS has made a comprehensive quality improvement in terms of adaptability to ambient temperature, moisture resistance, waterproofness, anti-theft, etc., ensuring that UPS can work normally under various harsh outdoor environmental conditions.

The following will still explain the classification and technical characteristics of UPS from the perspective of UPS circuit topology.

(1) Online UPS:

A. Good output voltage stability ±3%

B. Small waveform distortion THD < 3%

C. Zero interruption

D. Input and output energy forms are fully isolated

Figure 5. Principle of online UPS

(2) Backup UPS:

A. The overall efficiency is high when the power grid is normal > 95%

B. No noise when the power grid is normal

C. Switching time <10ms

D. Lower price

(3) Interactive UPS: It has the same features as the backup power supply, and effectively combines the charger and inverter into one dual-purpose UPS.

Although the inverter reduces the cost of the system, it increases the control difficulty to a certain extent.

2. Three solutions to improve UPS power supply reliability

From the above principle block diagram, we can know that UPS itself has dual-circuit power supply backup, with high system reliability, which can meet the power reliability requirements of general information equipment. However, with the rapid growth and high importance of information data in recent years, in some particularly important occasions, such as provincial and above bank data centers, communication data centers, securities trading and other power consumption environments, a single UPS power supply can no longer meet customers' requirements for power reliability. A better power supply solution is necessary to ensure the security of these important data and networks.

The following are three methods that can effectively improve reliability in engineering applications: series backup power supply, output master-slave backup, and redundant parallel backup power supply. The improvement of the above three power supply schemes will improve the reliability of the power supply system by an order of magnitude, increase the MTBF value of the system exponentially, and basically achieve zero power failure in the true sense in engineering applications. Therefore, when designing a high-reliability power supply system, users can choose a suitable high-reliability power supply scheme according to the power supply requirements of the load.

1. Series backup power supply mode (bypass master-slave backup mode):

As shown in the figure above, for two UPS in online working mode, the output of the standby machine (UPS2) serves as the bypass backup input of the host machine (UPS1). In this way, when the main inverter output of the host machine fails and switches to bypass, the load is still reliably protected by the dual backup power supply mode of the standby UPS.

2. Output master-slave backup mode

As shown in the figure above, taking online UPS as an example, the outputs of two UPS or inverters are sent to the redundant converter at the same time, and then the load is powered by the redundant converter; under normal circumstances, the redundant converter allows the main input power supply (such as UPS1) to power the load. When the main input power fails, the redundant converter quickly transfers the load to the backup input power supply to complete the redundant power supply of the load; after the main input power supply is repaired and then input to the redundant converter, the redundant converter transfers the load back to the mode powered by the main input power supply. Any conversion process is uninterrupted, which can ensure the stable and safe operation of the load equipment.

3. Redundant parallel power supply mode

As shown in the figure above, the outputs of the two UPS are simultaneously sent to the parallel distribution cabinet for direct parallel connection, and the load current is shared equally, without a master-slave relationship. When a UPS fails, the machine will automatically exit the parallel system, and the load current will be 100% supplied by the remaining UPS, with uninterrupted output; after the faulty machine is repaired, the repaired UPS unit can be merged online to continue to provide redundant power supply to the load, completing the online hot maintenance of the parallel system.

3. Comparison of three solutions to improve reliability

Comparison items Series backup power supply mode Output Master-slave backup mode Redundant parallel power supply

Reliability is generally high

The master-slave logic relationship exists, and it is not easy to replace, which requires the manufacturer to complete. Yes, it is easy to replace, and the user can complete it. It depends on the parallel control method; there may be, but it cannot be replaced.

Load switching time 10ms5ms0ms

Mutual communication is not required. It is required for wired parallel operation. It is required for wireless parallel operation and can be cancelled after operation.

Capacity expansion No capacity expansion No capacity expansion Capacity expansion can be made in proportion

The system overload capacity remains unchanged, and the short-term overload capacity ratio increases; especially the starting capacity for impact loads is enhanced.

Product aging degree There is a situation where the master and slave aging are inconsistent There is a situation where the master and slave aging are inconsistent There is no situation where the master and slave aging are inconsistent

Load balancing: 100% uneven 100% uneven even, generally the current imbalance is less than 5%

Battery life generally requires regular replacement of batteries or the host to ensure that the battery life does not require replacement.

Maintainability is poor, generally shutdown is required for maintenance, online hot maintenance is possible, online hot maintenance is possible.

The backup mode is usually 1+1. It has no practical significance to increase it. It is usually 1+1 or 1+2. It can be N+m, which is more flexible.

Low system cost, generally high

Applicable occasions Load 3-10KVA Load 0.5-3KVA Load 10KVA or more

Uninterruptible power supply UPS is a reliable power supply solution for digital construction. Through the design of different UPS power supply solutions, the reliability of the AC power supply system can be improved to a new level to meet any requirements of digital construction for AC power quality.