UPS power supply
A UPS, or Uninterruptible Power Supply, is a system that connects a battery (usually a lead-acid maintenance-free battery) to a main unit, and uses the main unit's inverter and other circuit modules to convert DC power to AC power. It is primarily used to provide a stable and uninterrupted power supply to single computers, computer network systems, or other power electronic equipment such as solenoid valves and pressure transmitters. When the mains input is normal, the UPS stabilizes the mains power and supplies it to the load; in this state, the UPS acts as an AC voltage regulator, while simultaneously charging its internal battery. When the mains power is interrupted (power outage), the UPS immediately switches from the battery's DC power to the load via an inverter, continuing to supply 220V AC power, ensuring the load continues to operate normally and protecting the load's hardware and software from damage. UPS devices typically provide protection against both overvoltage and undervoltage.
UPS (Uninterruptible Power Supply) is a third-generation, fully online, intelligent UPS developed using cutting-edge digital technology. It addresses the reliability requirements of China's power grid environment and network monitoring and systems, as well as medical systems. It overcomes the increasingly harsh power grid environment caused by centralized power supply for medium and large-scale computer network systems. A DC power supply is a device that maintains a constant current in a circuit. Examples include dry cell batteries, storage batteries, and DC generators.
UPS and DC power supplies are crucial power supply backup equipment for enterprises. Traditional maintenance management includes: ① routine visual inspections, periodic replacement of easily damaged parts such as batteries, filter capacitors, and fans, and battery activation during major overhauls; ② upgrading or replacing equipment, and using advanced tools to test battery performance. This management approach incurs high costs for enterprises, imposes a heavy workload on maintenance personnel, makes it difficult to monitor equipment operating status and key data in real time, and has low equipment failure prevention capabilities. Implementing online maintenance management can avoid the shortcomings of traditional methods and achieve significant benefits.
UPS stands for "Uninterruptible Power Supply," an abbreviation of "Uninterruptible Power System/Uninterruptible Power Supply." It ensures that a computer system continues to operate for a period of time after a power outage, allowing users to save their work in an emergency and preventing data loss or disruption to their work due to power failure.
DCS control system
Distributed control systems (DCS) are a new generation of instrument control systems based on microprocessors, employing the design principles of decentralized control functions, centralized display and operation, and a balance between decentralized autonomy and comprehensive coordination. DCS can also be translated as "distributed control system" or "distributed computer control system."
It adopts the basic design concept of decentralized control and centralized operation and management, and uses a multi-level, hierarchical, cooperative, and autonomous structure. Its main feature is its centralized management and decentralized control. Currently, DCS has been widely used in various industries such as power, metallurgy, and petrochemicals.
DCS typically adopts a hierarchical structure, as shown in Figure 3.1. Each level consists of several subsystems, and each subsystem achieves several specific finite objectives, forming a pyramid structure.
Reliability is the lifeblood of DCS development. To ensure high reliability in DCS, three main measures are taken: first, the widespread application of highly reliable hardware and manufacturing processes; second, the extensive adoption of redundancy technology; and third, the widespread implementation of fault-tolerant technology, fault self-diagnosis, and automatic processing technology in software design. Today, most distributed control systems can achieve a MTBF (Mean Time Between Failures) of tens of thousands or even hundreds of thousands of hours.
Configuration, Use, and Maintenance of UPS Power Supplies in DCS Control Systems
The UPS system works as follows: The poor-quality factory power supply is first converted into DC power by a rectifier. One path charges the battery via a charging module, while the other path uses high-frequency pulse width modulation (SPWM) to convert the DC power back into a pure, high-quality sine wave power supply within the inverter to power the load. When the AC power supply is lost or components such as the rectifier fail, the battery pack supplies power to the inverter via a battery switch. When the inverter malfunctions, resulting in abnormal output voltage or overload, it switches to an automatic bypass switch, allowing the factory power supply to directly power the load.
For factories with fewer input and output points in their DCS systems, a single UPS with dual AC inputs is used. For factories with more input and output points in their DCS systems, a parallel power supply with dual AC inputs and dual UPSs is used.
1 Dual AC incoming line single UPS wiring
The wiring diagram for a single UPS with dual AC inputs is shown in Figure 1. Under normal circumstances, AC input 1 supplies power to the UPS. When AC input 1...
In case of a fault, the system automatically switches to AC input 2 to supply power to the UPS, with AC power supplies 1 and 2 interlocked. Under normal operating conditions, the UPS operates in the "AC input 1—rectifier—inverter—load" mode. When the rectifier module malfunctions, it operates in the "battery—inverter—load" mode. After the battery is fully discharged, the system automatically switches to direct AC power supply to the load via the automatic bypass switch. When the inverter module malfunctions, it directly supplies power to the load via the "AC input 1—automatic bypass switch—load" mode. When the UPS has a serious fault requiring repair or replacement, it supplies power to the load via the "AC input 1—manual maintenance bypass switch" mode. In this case, the UPS is short-circuited and can be handed over for repair or replacement without affecting the normal power supply to the load.
2. Dual AC incoming lines and dual UPS parallel power supply mode
The requirement is that the two UPS units connected in parallel have the same output voltage, frequency, and phase, and that the load current they carry is basically balanced. During normal operation of a dual-UPS parallel system, each UPS carries half of the load current. If one UPS fails, the other will carry the entire load, but the load must be reduced. The mean time between failures (MTBF) of this type of parallel dual-UPS system is 7 to 8 times that of a single-unit system, thus greatly improving system reliability. However, the control between the two UPS units in a dual-UPS parallel system is interconnected. It is crucial to understand the control logic of the parallel board during operation; otherwise, improper operation may cause the parallel board to misjudge, resulting in a voltage dip and adversely affecting the load.
3. UPS Usage Precautions
(1) When selecting a UPS, a certain margin should be left. For example, for a 4KVA load, the UPS should be configured to be 5KVA or higher.
(2) The UPS should avoid frequent start-up and shutdown, and should ideally be kept on for extended periods.
(3) Newly purchased UPS should be charged and discharged to extend the battery life. Constant voltage charging is generally used. The initial charging current should not exceed 0.5*C5 amperes (C5 can be calculated from the battery's rated capacity). The voltage of each battery should be controlled between 2.30 and 2.35V to avoid damaging the battery. If the charging current remains unchanged for 3 consecutive hours, it indicates that the battery is fully charged. The general charging time is 12 to 24 hours.
(4) If the power supply to the plant is always normal, the UPS will not have a chance to work. Its battery may be damaged if it is in a long-term floating charge state. The UPS should be charged and discharged regularly. This can not only activate the battery, but also check whether the UPS is in a normal working state.
(5) The UPS should be checked regularly, and the float charge voltage should be checked once a month. If the float charge voltage is lower than 2.2V, the entire battery pack should be balanced and charged.
(6) Wipe the battery with a soft cloth frequently to keep the battery surface clean.
The dual AC input dual UPS parallel power supply method is shown in Figure 2: by directly connecting the outputs of two UPSs with the same power in parallel (7) Temperature control during UPS operation, the temperature range during UPS operation is controlled within 20℃～25℃ to extend the service life of UPS batteries. In environments without air conditioning, UPS temperature control is particularly important.
(8) The UPS should be charged immediately after use to restore the battery to normal condition.
(9) The distance between the external battery pack and the UPS should be as short as possible, and the cross-sectional area of the wire should be as large as possible to increase the conductivity of the wire and reduce the power loss on the line. Especially when working with high current, the loss on the line should not be ignored.
4. Routine maintenance and troubleshooting of UPS
4.1 Routine Maintenance
(1) Check the UPS operation display screen every day to confirm whether the UPS power supply's operating status indicator lights are in normal operating condition.
(2) Listen for any abnormal noises from the UPS power supply, mainly the cooling fans of the power module and the isolation output transformer, and whether the transformer has any abnormal vibration sounds.
(3) Check if there is any blockage in the UPS power supply's exhaust vent.
(4) Check the battery float voltage, UPS output voltage and current on the UPS power supply display screen every week, and make a record. Compare the data with previous data. If the data changes significantly, the cause should be investigated in time.
4.2 General Troubleshooting
When a UPS alarm occurs during operation, do not panic and operate any switches or buttons on the UPS, as this may escalate the accident or even cause a UPS output interruption. When a UPS alarm occurs, first carefully observe the status indicator lights and the prompts on the LCD screen. The UPS has a self-diagnostic function; in the event of a fault, it will provide information such as the fault type and time of the fault through the status indicator lights and the LCD screen. After carefully observing the status indicator lights and the fault type prompts on the LCD screen, proceed with the appropriate handling based on the specific fault type. The following types of faults frequently occur during UPS operation.
(1) AC power failure, i.e., AC input power outage or large fluctuation, when the UPS issues this alarm, a battery discharge alarm will also appear. At this time, the AC input indicator light on the UPS panel will turn off, and the battery discharge indicator light will turn on. The solution is to first determine whether it is an AC power failure and check whether the UPS input switch has tripped and whether the fuse has blown. If it is indeed a power failure, and the recovery time is unknown, disconnect the unimportant loads to ensure uninterrupted power supply to the important loads.
(2) Inverter fault: If the automatic bypass switch load alarm occurs at the same time as the inverter fault alarm, first check if the inverter overload alarm is also displayed on the panel. If so, check the output current on the LCD screen. If it exceeds the rated current, shut down non-critical loads until the output current is less than the rated output current. Then press the reset button to clear the alarm and restart the inverter and output. If there is no overload alarm signal, it means that the inverter is not shut down due to inrush current, but rather that there is a fault in the IGBT device or drive control. The manufacturer should be notified in time for repair.
(3) Bypass failure. When this alarm signal appears, an inverter asynchronous alarm signal should generally appear simultaneously. This indicates that the voltage and frequency of the input plant power supply exceed the set range, but meet the rectifier requirements. At this time, the inverter will start oscillating on its own and will no longer track the bypass. At this time, large-capacity loads should not be started to avoid impacting the inverter.
5. Conclusion
With proper UPS power supply configuration and regular maintenance, and by taking preventative measures, the UPS can operate stably and reliably, thereby providing safe, reliable, and high-quality power to the DCS system and ensuring the safe, stable, and long-term operation of chemical production.
