UPS Basics

Thread Content

UPS Directory: UPS (Uninterruptible Power Supply), the components of an uninterruptible power supply, essential knowledge about UPS – UPS (Uninterruptible Power Supply). The term UPS in Chinese means “uninterruptible power supply”; it is an abbreviation for the English term “Uninterruptible Power Supply”. It enables computer systems to continue operating for a certain period of time after a power outage, allowing users to save data urgently and preventing work disruptions or data loss as a result of power outages. In computer systems and network applications, it serves two main functions: one is for emergency use, to prevent disruptions caused by sudden power outages from affecting normal operations and causing damage to the computers ； Secondly, it eliminates power supply contaminants such as surges, instantaneous high voltages, instantaneous low voltages, wire noise, and frequency shifts in the mains electricity, improving the quality of the power supply and providing high-quality power for computer systems. 　　UPS types include online and standby types, and they are classified as power-frequency or high-frequency models based on the operating frequency of their design circuits. Currently, the mainstream UPS manufacturers include Emerson. APC, EAST (EasyStar), DELTA (Delta Electronics), and others all offer UPS units of various levels to meet the needs of different user groups. [Edit this paragraph] Composition of an uninterruptible power supply 　In terms of its basic operating principle, a UPS is a power protection device that includes an energy storage unit, with an inverter as its main component, and it provides stable voltage and frequency output. It is mainly composed of components such as a rectifier, battery, inverter, and static switch. 　　Rectifier: A rectifier is a device for rectifying electricity; in simple terms, it is a device that converts alternating current (AC) into direct current (DC). It has two main functions: first, it converts alternating current (AC) into direct current (DC), which is then filtered before being supplied to the load or to the inverter ； Second, provide a charging voltage to the battery. Therefore, it also serves as a charger ； 　　Battery: The battery is a component in UPS that is used to store electrical energy; it consists of several cells connected in series, and its capacity determines the duration for which it can supply power through discharge. Its main functions are: 1. When the mains power is normal, it converts electrical energy into chemical energy and stores it inside the battery. 　　2. When the mains power fails, it converts chemical energy into electrical energy to supply the inverter or load ； 　　Inverter: Simply put, an inverter is a device that converts direct current (DC) into alternating current (AC). It consists of an inverter bridge, control logic, and filtering circuits ； 　　Static switch: Also known as a static relay, it is a contactless switch that consists of two thyristors (SCRs) connected in reverse parallel to form an AC switch, with its closing and opening controlled by a logic controller. It is divided into conversion type and parallel type. Transformer switches are primarily used in systems powered by two power sources, and their function is to enable automatic switching from one source to another ； The parallel mode switch is mainly used for connecting parallel inverters to the mains or multiple inverters. [Edit this section] Quick Guide to UPS Knowledge 1. What is UPS? 　　UPS is the abbreviation for Uninterruptible Power System; it is an important external device that provides a continuous, stable, and uninterrupted power supply. 　　In principle, a UPS is an electrical electronic device that integrates digital and analog circuits, automatic control of inverters, and a maintenance-free energy storage device ； 　　Functionally, a UPS can effectively purify the mains power in case of abnormalities in it ； It can also supply power to devices such as computers for a certain period of time in the event of a sudden power outage, giving you enough time to deal with the situation ； 　　In terms of applications, with the advent of an information-based society, UPS is widely used in all stages ranging from information collection, transmission, processing, and storage to its actual application, and its importance continues to grow as the significance of information applications increases. 　　2. What are the types of UPS? 　　Based on their working principle, UPS systems are divided into three main categories: standby, online, and online interactive. Standby UPS is the most commonly used type; it possesses the most basic and essential functions of a UPS, such as automatic voltage regulation and power failure protection. Although it generally has a conversion time of around 10 ms, and the alternating current output by the inverter is square-wave rather than sine wave, its simplicity results in advantages such as low cost and high reliability, which is why it is widely used in computers, peripherals, POS machines, and other applications ； 　　Online UPS systems have a more complex structure, but they offer excellent performance and can address all power supply issues. Their key feature is the ability to deliver pure sine wave AC power continuously without any interruptions, enabling them to handle various power problems such as spikes, surges, and frequency drift ； Due to the high investment required, it is typically used in environments with stringent power demands, such as critical equipment and network centers ； 　　Compared to standby UPS units, modular UPS systems of the online interactive type have a filtering function, offering strong resistance to power supply interference; their conversion time is less than 4 ms, and the inverter output is in the form of an analog sine wave. Therefore, they can be used with network devices such as servers and routers, or in areas with harsh electrical conditions ； In particular, the SITONG MD series of UPS units, with prices that are much lower than those of online-type UPSs, represent a much better option that should be highly recommended to users. 　　3. Why is a UPS necessary? 　　According to IDC, 45% of all computer failures are caused by power supply issues ； In China, large cities experience power outages on average 0.5 times per month, medium-sized cities 2 times per month, and small cities or towns 4 times per month. The power grid faces at least nine types of problems: power outages, lightning surges, surges, frequency fluctuations, voltage spikes, voltage variations, frequency drift, voltage drops, and pulse interference ； Therefore, from the perspective of improving power quality, it is essential to equip a computer with a UPS. 　　Furthermore, precision network and communication devices cannot tolerate any power interruptions; it goes without saying that a network center centered around servers must be equipped with UPS. Even for an ordinary computer, the value of its data files and other software after three months of use exceeds the value of its hardware, so it is also essential to have UPS to prevent data loss. 　　4. What kind of UPS should I have? 　　Depending on the condition of the equipment, the power supply environment, and the desired level of power protection, an appropriate UPS can be selected ； For example, for low-power devices equipped with built-in switching power supplies, a standby UPS is generally suitable; in environments with harsh electrical conditions, an online interactive or online UPS should be used. As for devices that cannot tolerate any interruptions or require sine wave AC power, only an online UPS will do. 　　5. What power rating should my UPS have? 　　First, you need to determine the power consumption of your device. Generally, ordinary PCs or industrial computers have a power consumption of around 200W, Apple devices are around 300W, while servers range from 300W to 600W. For other devices, you can refer to the instructions provided with that device. 　　Secondly, it is important to understand that there are two ways to express the rated power of a UPS: apparent power (in VA) and actual output power (in W). This difference arises due to the presence of reactive power. The conversion relationship between the two is as follows: Apparent power * Power factor = Actual output power. The power factor for standby and online interactive types is between 0.5 and 0.7, while the power factor for online types is generally around 0.8. 　　When equipping a device with a UPS, the actual output power of the UPS should be used as the basis for selection. Some dealers, intentionally or unintentionally, confuse the difference between (VA) and (W); users should be aware of this. 　　6. What is the difference between the “centralized” and “decentralized” configurations of UPS systems? 　　If there are many devices that require UPS power, you can choose between a \"centralized\" or \"decentralized\" setup. In a centralized approach, a single UPS with high capacity is used to supply power to all devices; if the devices are located at considerable distances from each other, separate wiring is needed. This method is commonly used in large data centers and control centers. Although it simplifies management, it comes at a higher cost. 　　“The “distributed” configuration is a popular approach these days; it involves providing the appropriate UPS units based on the needs of each device. For example, to protect the power supply of a local area network, online UPS units can be used for servers, while offline UPS units can be installed at each node. This setup results in lower costs and higher reliability. 　　The advantages and disadvantages of these two power supply methods are shown in the table below: Centralized power supply: easy to manage, requires high-level wiring, has low reliability, and high costs. 　　Decentralized power supply: difficult to manage, low wiring requirements, high reliability, low cost. 　　The selection of UPS units requires specialized knowledge; please consult professionals who will design a suitable configuration for you. 　　7. Why is it necessary to buy a branded UPS? 　　The function of UPS products is to provide protection; for users, a UPS often serves as the last line of defense to safeguard equipment and data. Compared to other products, \"reliability and quality\" are of even greater importance for UPS, and only well-established brand-name products can possess such capabilities. 　　China’s UPS market is currently very prosperous, with virtually all internationally renowned brands present there. Examples include Merlin Gerin from Europe, as well as Exide and APC from the United States. These foreign brands have certain technical advantages, but their prices are also relatively high. Their main market share is in the medium-to-high power UPS segment (10KVA and above) ； Since the 1990s, some outstanding domestic brands have emerged strongly in the UPS market. By pursuing continuous technological advancement and leveraging their advantages in localized production and services, they have achieved remarkable results and have become the main force in the low-to-medium power UPS market. 　　8. What determines the length of UPS backup time? 　　It is determined by the energy storage device of the UPS. Modern UPS units generally use fully sealed, maintenance-free lead-acid batteries as their energy storage devices. The capacity of these batteries is indicated by the figure \"ampere-hours (AH)\\", which refers to the time during which power can be delivered at a specified current level. For batteries with the same voltage, those with a higher ampere-hour rating have a greater capacity ； For batteries with the same ampere-hour rating, those with a higher voltage have a greater capacity. The capacity of a battery is usually indicated by both the voltage and the ampere-hours, for example, 12V/7AH, 12V/24AH, 12V/65AH, 12V/100AH. 　　Backup UPS units generally come equipped with 4AH or 7AH batteries, and their backup time is fixed ； Both online and online interactive UPS systems come in standard models equipped with built-in 7AH batteries, as well as long-lasting models that use larger external batteries; users can determine the capacity of the battery required based on the backup time they need to achieve. 　　The battery is an essential component of a UPS, accounting for a significant proportion of its value; moreover, its quality has a direct impact on the proper functioning of the UPS. Therefore, it is important to choose reputable batteries with guaranteed quality. 　　9. What are the precautions when using a UPS? 　　1) The environment in which the UPS is used should have good ventilation to facilitate heat dissipation, and it should be kept clean. 　　2) Do not connect inductive loads such as cash counters, fluorescent lights, air conditioners, etc., to avoid damage. 　　3) It is optimal to keep the output load of the UPS at around 60% for the highest reliability. 　　4) An undersized load on the UPS (for example, a 1000VA UPS being used with a 100VA load) can cause the battery to be deeply discharged, which reduces its lifespan; this should be avoided as much as possible. 　　5) Proper discharge helps to activate the battery. If power from the mains is not interrupted for an extended period, the mains power should be manually cut off every three months to discharge the battery using a UPS under load; this can extend the battery’s lifespan. 　　6) For most small UPS units, turn them on at the start of work; avoid starting them under load, and turn them off at the end of work ； For UPS in network data centers, since most networks operate 24 hours a day, the UPS must also run around the clock. 　　7) The UPS should be charged promptly after discharge to prevent the battery from being damaged due to excessive self-discharge. 　　Working Principle of the PS Series I. Advantages of High Frequency Operation in the PS Series First, the input section of PS series UPS units eliminates the power-frequency transformer used for isolation from the mains electricity, as well as the autotransformer used for voltage reduction; instead, SPWM technology is employed to achieve high-frequency rectification (AC/DC). On the one hand, it increases the allowable range of variation in the mains voltage ； On the other hand, digital signal processors (DSP) are used in control technologies to synchronize the input current with a sine wave and align it with the mains voltage, thereby enabling the UPS to achieve a high input power factor (PF≈1). This eliminates harmonic \"pollution\" of the mains electricity, contributing to environmental protection; it is thus a green UPS. Additionally, it significantly reduces reactive power losses, thereby lowering operating costs substantially. 　　Secondly, the traditional inverse output power-frequency transformer has been abandoned in favor of high-frequency transformers to achieve isolation between the UPS and the mains supply; this not only results in lower noise levels but also higher efficiency. The inverse control circuit in the UPS’s output stage utilizes direct sine wave feedback technology, which enables faster regulation compared to traditional analog feedback techniques. Coupled with a small output filter and SPWM modulation at frequencies above 20 kHz, this results in excellent dynamic response characteristics for the UPS, as well as a very pure and smooth sine wave output. 　　Furthermore, high-performance filtering and protection technologies are employed in the inverter protection circuit, enabling the inverter to not only have a strong overload capacity but also robust self-protection capabilities ； The battery pack inside the PS series UPS is also charged using high-frequency conversion. When the mains power fails and the UPS switches to being powered by the battery to supply power to the inverter, voltage reduction is achieved through high-frequency conversion (DC/DC) as well. 　　II. Intelligent Advantages of the PS Series The intelligence of UPS systems includes automatic identification and control of the system’s operating status, self-diagnosis of system faults, automatic monitoring and management of batteries, as well as intelligent detection and display of internal information. 　　In terms of system operation status identification and control, internal sensors and status logic are used to promptly determine the operating state of the system, assess whether the system’s operation procedures are functioning properly, thereby effectively preventing potential damage caused by incorrect operations to both the system itself and its connected loads, and enhancing the reliability of the UPS. 　　Another aspect of UPS intelligence is achieved through monitoring software that runs on a PC. The UPS is connected to the PC’s serial port via an RS232 interface, and the monitoring software for the UPS is executed on the PC. The PC sends query commands at regular intervals, and the UPS returns information regarding its operating parameters within a specified time frame. The PC then uses this information to determine the UPS’s operating status and the specific location of any faults. If necessary, it sends commands to the UPS to take corrective action and alerts maintenance personnel. Additionally, the PC automatically stops the operation of the computer or local network once the UPS’s power supply runs out, and it saves the relevant data automatically. 　　III. Network advantages of the PS series By leveraging advanced microprocessor-based monitoring technologies, the SITONG PS series enables two-way communication and control functions between UPS units and computer networks. It treats the UPS as an independent node in the wide area network, equips it with communication adapters, and assigns it a separate IP address. In this way, network administrators or authorized persons can remotely monitor the status of the UPS in real time from anywhere on the network, just as they would manage a computer. With this control function, users can monitor the operating parameters of the UPS in real time at their computer network terminals (such as input and output voltage, current, and frequency; information regarding the charging, discharging, and voltage levels of the UPS battery pack; the UPS’s output power; as well as any related fault or alarm messages). Furthermore, users can also use computer network terminals to perform timed automatic start-up and shutdown operations on the UPS output; orderly shutdown procedures will ensure the safety and reliability of the user’s software and data. 　　In summary, the Sitong PS series of UPS units utilize MOSFET and IGBT power components, which enables high frequency operation, compact design, and high efficiency; it also extends the lifespan of the batteries. Meanwhile, network intelligence technology not only provides highly reliable network power management but also offers an optimal solution for energy savings. It can be said that the Sitong PS series is in line with the latest trends in UPS technology; it is a product with excellent performance-to-price ratios, and it is bound to achieve remarkable success in China’s enterprise-grade UPS market. 　　12. What does the capacity of a battery mean? 　　The rated capacity of a battery is generally expressed in terms of the ampere-hours at a 20-hour discharge rate (C10). This means that at 25°C, the battery is discharged at a constant current for 20 hours until the termination voltage is reached (1.75V per cell); the capacity of the battery is then equal to 20 times this current value, and it is usually expressed in AH. For example, a 12V/100AH battery means that it can discharge at a constant current of 5A (0.05C) until the voltage reaches 10.5V, and it can do this for 20 hours in a row. It should also be noted that there is no linear relationship between the battery’s discharge time and the discharge current; for example, a 100AH battery cannot sustain discharge at a current of 100A for one hour, but only for a few dozen minutes ； Discharging at a current of 1A will exceed 100 hours (discharging in this manner is not recommended). 　　13. Can a standard UPS be directly connected to batteries to be used as a long-duration UPS? 　　It is not suitable; since standard UPS units have a low charging current due to their design, and are also limited by cooling conditions, using them as long-duration UPS units fails to achieve the intended purpose. Moreover, it can have adverse effects on the UPS and batteries, even leading to damage. 　　14. How to extend the power supply time of an uninterruptible power supply system? 　　There are two ways to extend the power supply time of an uninterruptible power supply system: 1. Connecting an external high-capacity battery pack: A battery pack with an appropriate capacity can be connected based on the required power supply time, but it should be noted that this method will result in a longer charging time for the battery pack. It also increases the space required and the maintenance costs, so careful consideration is necessary. 　　2. Choose an uninterruptible power supply system with a larger capacity: This approach not only reduces maintenance costs, but also ensures that the system with greater capacity can continue to function promptly in case there is an expansion in the number of connected devices. 　　15. What are the common electrical problems? What other different solutions are there? 　　There is a common misconception that the mains electricity we use is continuous and stable, aside from occasional power outages; this is not the case. As a public power grid, the mains system is connected to thousands of various types of loads. Some of these larger inductive, capacitive, and switching power supply-type loads not only draw electrical energy from the grid but also have an impact on the grid itself, thereby deteriorating the quality of power supply provided by the grid. In addition, unexpected natural and man-made accidents, such as earthquakes, fires, lightning strikes, and short circuits in power transmission and distribution systems, can all disrupt the normal supply of electricity, thereby affecting the proper operation of loads. According to tests conducted by electrical experts, the main problems that occur frequently in power grids and can cause interference or damage to computers and precision instruments are as follows: 1. Power surges: These occur when the effective value of the output voltage exceeds 110% of the rated value, and this condition persists for one or several cycles. Power surges are mainly caused by the high voltage generated in the power grid due to the sudden removal of load when large electrical devices connected to the grid are turned off. 　　2. High voltage spikes: These refer to voltages with a peak value of 6000V and a duration ranging from one ten-thousandth of a second to half a cycle (10ms). They are primarily caused by lightning strikes, arc discharges, static discharges, or the switching operations of large electrical equipment. 　　3. Transient overvoltages (switching transients): These refer to pulse voltages with peak values as high as 20,000 V, but with durations ranging from one millionth of a second to one ten-thousandth of a second. The main causes and potential damages associated with them are similar to those of high-voltage surges; however, the solutions applied to address them differ. 　　4. Voltage sags: This refers to a low-voltage condition in which the effective value of the mains voltage falls between 80% and 85% of its rated value, and this condition persists for one or several power cycles. The startup of large equipment, large electric motors, or the connection of large power transformers can all cause such problems. 　　5. Noise interference (electrical line noise): This refers to radio frequency interference (RFI), electromagnetic interference (EMI), and various other high-frequency interferences. The operation of motors, the activation of relays, the functioning of motor controllers, broadcast transmissions, microwave radiation, and electrical storms can all cause noise interference. 　　6. Frequency drift: This refers to a change in the mains frequency of more than 3 Hz, which is mainly caused by the unstable operation of emergency generators or by power supplies with unstable frequencies. 　　7. Low voltage (brownout): This refers to a situation in which the effective value of the mains voltage is below the rated value and this condition persists for an extended period of time. Causes include the startup and operation of large-scale equipment, changes in the main power supply lines, the starting of large motors, and line overloads. 　　8. Power failure: This refers to a situation where the mains power is interrupted for at least two cycles or several hours. The causes include circuit breakers tripping in the wiring, interruptions in the supply of mains power, and grid failures. 　　For the various power-related issues mentioned above, there are several different solutions; the effect is indicated as follows: ○ represents good protection, △ represents limited or condition-dependent protection, and × represents no protection. 16. Proper use and maintenance of UPS batteries During the use of uninterruptible power supply systems, people often assume that batteries require no maintenance and thus do not pay enough attention to them. However, data shows that the proportion of UPS unit failures or abnormal operation caused by battery problems is approximately 1/3. It is evident that improving the proper use and maintenance of UPS batteries is becoming increasingly important for extending their service life and reducing the failure rate of UPS systems. In addition to choosing batteries from reputable brands, proper use and maintenance of batteries should be ensured by paying attention to the following aspects: First, maintain an appropriate environmental temperature – the environmental temperature is an important factor that affects the lifespan of batteries; generally, battery manufacturers recommend an optimal temperature range of 20–25°C. Although an increase in temperature improves the battery’s discharge capacity, the cost is a **reduced lifespan** of the battery. According to experimental tests, once the ambient temperature exceeds 25°C, for every 10°C increase, the battery’s lifespan is reduced by half. Currently, the batteries used in UPS systems are generally maintenance-free sealed lead-acid batteries, with a typical design life of 5 years – a lifespan that can only be achieved under the conditions specified by the battery manufacturers. If the specified environmental requirements are not met, there is a significant difference in their lifespan. Furthermore, an increase in ambient temperature leads to increased chemical activity within the battery, resulting in the generation of a large amount of heat. This heat, in turn, causes the temperature of the surrounding environment to rise, and this vicious cycle accelerates the reduction of the battery’s lifespan. 　　II. Regular charging and discharging: The floating charge voltage and discharge voltage in a UPS are set to their rated values at the time of manufacture, while the discharge current increases as the load increases. It is necessary to adjust the load appropriately during use, for example by controlling the number of electronic devices such as computers in use. Under normal circumstances, the load should not exceed 60% of the UPS’s rated load. Within this range, the battery’s discharge current will not cause over-discharge. 　　In environments where UPS systems are connected to the mains power supply for extended periods, and where the quality of power supply is high with few outages, the batteries remain in a floating charge state for a long time. Over time, this reduces the efficiency of the conversion between chemical energy and electrical energy within the batteries, accelerating their aging and shortening their service life. Therefore, it is generally necessary to fully discharge the battery every 2–3 months, with the discharge time depending on the battery’s capacity and the level of load. After a full-discharge cycle, it must be recharged for more than 8 hours as specified. 　　III. Utilization of communication functions: At present, the vast majority of large and medium-sized UPS units possess capabilities such as communication with microcomputers and program control. By installing the appropriate software on the microcomputer, connecting the UPS via a serial/parallel port, and running the program, it is possible to communicate between the microcomputer and the UPS. It generally has functions such as information inquiry, parameter setting, timing setup, automatic shutdown, and alarm. Through information queries, it is possible to obtain information such as the mains input voltage, UPS output voltage, load utilization rate, battery capacity utilization rate, internal temperature, and mains frequency ； Through parameter settings, it is possible to define the basic characteristics of the UPS, the battery backup time, and alerts when the battery is depleted. Through these intelligent operations, **the use and management of UPS power supplies and their batteries are simplified.