1 What is UPS
UPS, also known as uninterruptible power supply, is a constant voltage and constant frequency uninterruptible power supply that contains energy storage devices and an inverter as the main component. It mainly provides uninterrupted power supply for a single computer, computer network system, or other power electronic equipment.
UPS uninterruptible power supply is an emergency power supply device that can continue to supply power to the load and ensure the quality of power supply when the main power supply fails or loses power, so that the operation of the load is not affected. It has the main functions of uninterrupted switching between dual power sources, frequency conversion, voltage conversion, isolation interference, and backup, and is widely used in fields such as big data information equipment, industrial backup power supply, shopping malls, banking systems, railway systems, and medical equipment.
UPS has gone through a development process from dynamic UPS (rotating type) to static UPS (stationary type). Early dynamic UPS used flywheel energy storage, utilizing mechanical energy and engine to achieve energy conversion. With the development of power electronics and semiconductor material technology, static UPS with thyristor as the core is gradually replacing dynamic UPS. Afterwards, static UPS devices using self turn off giant power transistors, power field-effect transistors, and insulated gate bipolar transistors as switching devices were developed. The development of electronic technology and digital control also promoted the transformation of UPS control circuits from analog circuits to digital circuits, greatly improving their performance.
UPS mainly consists of rectifiers, battery packs, inverters, and static transfer switches. When the mains power is normal, UPS stabilizes the mains power and supplies it to the load, while charging the internal battery pack; When the mains power is interrupted, UPS converts the electrical energy of the battery pack into AC power through an inverter and continues to supply power to the load, thereby achieving uninterrupted power supply.
According to different standards and characteristics, UPS can be classified based on output waveform, power capacity, input-output mode, working principle, structure, and application scenarios. The common classification methods include dynamic UPS and static UPS according to their working principles. Static UPS includes backup, interactive, online, etc; According to the power supply system, it is divided into single input and single output, three input and single output, three input and three output, etc; According to output power, it is divided into micro, small, medium, large, etc.
2 Types of UPS
Online interactive UPS
The online interactive UPS combines the high efficiency of backup UPS with the high-quality power supply advantages of online UPS. When the mains power is normal, it directly supplies power to the load from the mains power without going through a complex power conversion process, so the work efficiency is extremely high, reaching over 98%. At the same time, it also has an automatic voltage stabilization function, which can roughly stabilize the voltage and absorb some power grid interference. Its voltage stabilization method is roughly the same as the backup type, mostly using relays to change the transformer tap method. When the input voltage is high, the transformer steps down, and when the input voltage is low, the transformer steps up, with an output voltage stabilization accuracy of 5% -10%.
The inverter in this type of UPS has bidirectional conversion function, and when supplied with mains power, it serves as an AC/DC rectifier to charge the battery; When there is a power outage, it is converted to a DC/AC inverter, powered by batteries, and UPS continues to supply power to the load. The output voltage waveform can also be a quasi sine wave, but due to the high output power, there may be devices that require the input voltage to be a sine wave in the load, so the inverter output voltage of line interactive UPS is mostly a sine wave. It is also equipped with input and output high-frequency filters, which can resist high-frequency (differential and common mode) interference from grid voltage.
Line interactive UPS is suitable for small and medium-sized office and home network equipment. For these scenarios, it not only meets certain power protection requirements, but also has the advantages of low cost, simple circuit, and high reliability. And the converter also has charging function, and its charging capacity is stronger than that of the backup type. Although UPS output still has conversion time, it is shorter than backup type, usually 4-6ms. If an inductor is connected in series between the input switch and the automatic voltage regulator, the inverter can immediately supply power to the load when the mains power is cut off, which can shorten the line interactive conversion time to zero and increase anti-interference ability.
Dual conversion UPS
Dual conversion UPS ensures the stability and continuity of output voltage through two power conversions, and is widely used in key application scenarios such as data centers, medical facilities, and financial institutions.
The circuit structure of dual conversion UPS consists of rectifier/charger, inverter, battery charger (optional), battery switch, etc. The rectifier/charger converts AC input power into DC power, supplies it to the inverter, and charges the battery at the same time. When the mains power is interrupted, the inverter converts the DC power of the battery into AC power and supplies it to the load.
The circuit structure of a dual conversion UPS without bypass consists of a rectifier/charger, inverter, battery charger (optional), battery switch, etc. Modern UPS systems are often equipped with independent battery chargers, which have the advantage that the float charging voltage of the battery will not change with the load, which is beneficial for extending the life of the battery. The battery switch is used to connect or disconnect the battery from the rectifier or inverter, and can use thyristors, diodes, or mechanical switches.
The dual conversion UPS with bypass adds a UPS switch module for the UPS to switch from normal mode to energy storage mode or vice versa.
The working principle of a dual conversion UPS is that the mains AC input power is first converted into DC power by a rectifier, and then converted into AC power by an inverter. At the same time, the rectifier/charger or independent battery charger charges the battery. Under normal circumstances, the load is powered by a combination of rectifier/inverter. When the indicators of the AC input power supply of the mains exceed the predetermined capacity limit, the UPS switches to energy storage mode, that is, the battery/inverter combination supplies power to the load, and the power supply time interval is the energy storage time of the battery, or until the mains input power supply returns to the design capacity limit of the UPS, and then switches to normal mode. When the rectifier/inverter fails, or when the UPS experiences instantaneous or continuous overload, the UPS will switch to bypass operation mode, where the load is temporarily powered by the bypass power supply (AC input 3). To ensure uninterrupted conversion, the output of the inverter and the AC input 3 must be synchronized. In addition, if the input and output voltages are different, a transformer must be installed in the bypass circuit (AC input 3).
The load of the dual conversion UPS is always continuously powered by the inverter, whether the inverter is powered by a rectifier or a battery. The output voltage and frequency of UPS are not dependent on the input voltage and frequency of the mains power. The output waveform is a sine wave in both normal and energy storage modes. Due to the isolation of the load from the mains power supply by rectifiers and inverters, various interferences from the mains power supply are suppressed, which can protect against surges/spikes, line noise, undervoltage, overvoltage, lightning, frequency changes, voltage distortion, voltage harmonics, power interruptions, and other disturbances from the mains power supply. The voltage range allowed for the input power supply of a dual conversion UPS is wide, and the static and transient accuracy of the output voltage is high. When the AC input power fails, it can instantly switch from normal mode to energy storage mode without interruption of the output power during the conversion process, or in other words, the conversion time is zero. However, when the UPS fails, the transition time from normal mode to bypass mode is 1-4ms.
Online UPS
Online UPS converts input AC power into DC power and back to AC power when needed, with the highest level of power protection capability, widely used in power systems, computer data centers, and other fields.
Online UPS always keeps its inverter in working condition. It first converts external AC power into DC power through the circuit, and then converts DC power into high-quality sine wave AC power through a high-quality inverter to output to the computer. Under power supply conditions, the main function is to stabilize voltage and prevent radio wave interference; During a power outage, use a backup DC power source (battery pack) to supply power to the inverter. Due to the continuous operation of the inverter, there is no switching time issue, making it suitable for situations with strict requirements for the power supply.
Online UPS is divided into two types: bypass free and dual conversion. The circuit structure of a bypass free dual conversion UPS is relatively simple, consisting of a rectifier, inverter, battery, etc. The dual conversion UPS with bypass adds a UPS switch module for the UPS to switch from normal mode to energy storage mode or vice versa, improving the flexibility and reliability of the system.
The working mode of online UPS is as follows: when the mains power is normal, the mains power passes through the surge absorption filter circuit → AC to DC circuit → DC to AC circuit → and then converts AC power output to supply the load, while charging the battery at the same time; Once the microprocessor control circuit detects a power interruption, it immediately discharges the battery → converts DC power to AC power circuit → and converts AC power output to supply the load. If the microprocessor control circuit detects a UPS fault, the UPS will use a relay (RELAY) to trip to the bypass (BYPASS), supply power to the load from the mains, and emit an audible warning to the user.
Online UPS has many advantages, such as sine wave output. Whether in mains mode or battery mode, it can output low distortion sine wave power supply, providing the best power guarantee for users' load devices; Zero conversion time, when the mains power is cut off or restored, there is no conversion time for UPS to switch between mains mode and battery mode, effectively ensuring the reliability of load operation; Input zero wire detection function, in order to avoid UPS mains power input zero wire reverse connection, it has zero wire reverse connection detection function; Humanized bypass output, input normal mains power, default no bypass output, must be turned on to have normal inverter output, but can be changed to "mains power has bypass output" through software configuration; TVSS function, also known as TRANSIENT VOLTAGE SURGE SUPPRESS surge voltage protection function, is used for fax TELEPHONE,MODEM, Network and other conversion protection functions; Dual machine hot backup, when the most important load equipment of the user is absolutely prohibited from being powered off, models with a capacity of 6KVA or more can fully support dual machine hot backup function. Users can use two UPS for primary and backup use. When one of them fails, the other is responsible for supplying power; Input power factor correction, with input power factor correction function. Under full load conditions, the input power factor can reach 0.95 or above, so that the user's power grid environment will not be polluted; DC startup. In the event of a power outage, if a UPS is needed to start a computer or other load equipment, the battery can be directly used for DC startup, making the use of the UPS more convenient and reliable; Bypass protection and bypass power supply function greatly enhance the emergency response capability of UPS. At the same time, when the user's load equipment has special requirements for the power supply, such as voltage not being too high, bypass power supply voltage protection is provided to protect the user's load equipment from high voltage hazards; Automatic start function. When the mains power is abnormal and enters battery mode for power supply until it is cut off, the UPS will shut down. When the mains power returns to normal, the UPS will automatically start up and provide normal power without the need for users to turn on each one; Long term power supply design, providing comprehensive long-term machine options for users, equipped with suitable battery packs, can enable users to discharge for about 8 hours to meet the requirements of different power grid environments; Long lasting machines have strong charging capabilities. In addition to extending discharge time, the battery also has strong recharge ability, providing an initial charging current of about 5-10A; The self check function can simulate a power outage situation and enter battery mode for power supply. This function can be executed at any time through the self check button on the panel or in conjunction with monitoring software; Strong anti-interference, designed in accordance with international standards EN50091-2 and IEC61000-4 series standards, effectively improves the safety and reliability of UPS use; Can be used in conjunction with a generator, with a wide range of input voltage and frequency, allowing it to be used in conjunction with major brands of generators for a longer period of time. At the same time, it effectively removes the poor power generated by the generator, providing a pure, safe, and stable power source for the load; Can handle inductive loads; Download software. In order to make UPS management more convenient and effective for users, monitoring software can be downloaded for free on the website to achieve intelligent management; Slot, equipped with an Intelligent Slot. Users can choose an AS400 card to provide IBM AS400 standard communication signals. Users can use the AS400 interface for Remote Display, including sound alarms and light displays. Alternatively, you can purchase a WinPower CMC card (centralized monitoring card) and use monitoring software to enable a computer to simultaneously monitor the operational status of multiple local online UPS systems.
Other types of UPS
Including tower UPS and modular UPS. Tower UPS has an independent three-phase structure, with a low probability of internal component failure and short maintenance time, making it suitable for high-level data centers. Modular UPS achieves power module redundancy through parallel operation, which has the advantages of lower single machine cost and slightly higher efficiency, but has a higher failure rate.
High frequency machines and modular UPS power supplies have some unique advantages and disadvantages. High frequency machine UPS power supply, also known as modular high-frequency UPS, adopts a drawer style high intelligence modular design. It can meet power output input and reliability requirements by adding or removing UPS modules in the cabinet, with great flexibility and achieving the best cost-effectiveness. It has easy to plug and unplug functionality, which not only meets power output and reliability requirements by adding or removing modules inside the cabinet, but also allows for online maintenance as long as redundancy allows, achieving zero repair time. The adoption of full control technology, which gathers advanced technological achievements in the fields of power electronics and automatic control, is a milestone in the technological revolution of the UPS industry. High frequency UPS power supply has small size and light weight; Strong adaptability to fluctuations in mains voltage; The input power factor of the mains power can reach 0.99 or above, reducing the harmonic content of the mains input current to less than 5%, minimizing pollution to the mains power grid, and eliminating audible noise (including electrical and mechanical noise). But high-frequency machines must use high-frequency IGBTs that can work in 20kHz UPS. These IGBTs are expensive, have limited supply, strict voltage and current working areas, poor impact resistance, low reliability, and high failure rates.
Modular UPS is a system that separates the power components of high-frequency UPS into individual power modules, which are then output in parallel. In addition, the bypass switching module and control unit are also made into modular units, so that the entire UPS is composed of stacked modules. The biggest feature of modular UPS is that the power part can easily achieve redundancy function. As long as the surplus power of the UPS carrying capacity is greater than the power of a single module, the power part of the UPS can achieve "N+1" redundancy, thereby improving the reliability of UPS power supply. Another advantage of modular UPS is its high availability. When a module fails, it can be replaced directly, with a very short repair time and convenient maintenance. In addition, modular UPS often mentions the "grow while investing" model, which means that users can purchase fewer power modules during initial construction and then purchase power modules for UPS expansion after the number of user devices increases during business growth. The system structure of modular UPS is highly flexible, and the design concept of power modules is that they can be easily removed and installed during system operation without affecting the system's operation and output, enabling investment planning to achieve "on-demand expansion" and allowing users to achieve "dynamic growth" with business development. This not only meets the on-demand expansion of equipment in the later stage, but also reduces the initial purchase cost.