The Industrial Internet of Things (IIoT) relies on fast and accurate communication. Critical control systems cannot withstand momentary power interruptions, which can cause industrial PCs or controllers to crash. An uninterruptible power supply (UPS) can prevent such events from happening. Knowing the basics of UPS and the following five considerations will help you choose the right UPS power supply for industrial applications.
Define application requirements for UPS
What kind of load will the UPS power - AC or DC? Legacy systems tend to run on AC power, so retrofitting older systems also requires AC power. Over the past 20 years, the growth of the industrial PC market has shifted to DC power supplies. Power and run-time requirements should be fully considered, carefully sizing the UPS and establishing realistic expectations.
In the event of a persistent power outage, the UPS ensures a safe and orderly shutdown of the control platform, preventing data loss, system crashes or failures. When designing your system, choose an appropriate battery capacity that will allow the system to run for a while before shutting down the PC or restoring mains power in a reasonable amount of time. Oversized battery systems may take longer to charge.
Most UPS manufacturers use industry standard types. Some manufacturers only offer one technology, such as Valve Regulated Lead Acid (VRLA). Others will offer a variety of products such as valve regulated lead acid, wide temperature valve regulated lead acid and lithium iron phosphate. Different batteries vary in performance and lifespan.
Ideally, the UPS will provide multiple points of health monitoring of the battery system, so operators can take preventive action before the battery fails. Most UPSs use LEDs, and a few provide dry junction outputs with fixed threshold points. Newer UPS systems offer the above approach and integrate data into a control platform that communicates via Industrial Ethernet protocols.
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Distributed AC UPS Technology
In control systems operating on AC voltage, an AC UPS is most suitable. The offline or standby topology is very straightforward. These products are inexpensive and therefore the most common type of AC UPS. Under normal conditions, an offline UPS passes mains power from input to output with no interaction other than charging batteries in parallel with the mains circuit. If the mains power fails, the UPS will switch from the mains circuit to the battery circuit. The transition time from UPS loss of main power to battery power cannot exceed 10ms. 10ms switching, usually does not affect downstream equipment, but can protect systems sensitive to voltage fluctuations.
There are two subsets of AC UPS: modified (analog) sine wave output devices and pure sine wave output devices. The AC output of each is different.
The improved sine wave device takes the voltage from the battery pack and creates a waveform output similar to a sine wave in its simplest form. While this type of UPS is relatively inexpensive, there are some drawbacks. Large voltage steps can damage the input circuitry of downstream equipment. These large steps also result in a large number of switching transients in the UPS output. This can lead to premature failure of the mini PC and PLC power modules.
A pure sine wave UPS produces the same sine wave output as the 120/230V mains feed. Pure sine wave UPS, a better choice for sensitive control equipment such as Programmable Logic Controllers (PLCs), Distributed Control Systems (DCSs) and Industrial PCs (IPCs). Although more circuits are required, UPS-powered control equipment lasts longer, reducing total cost of ownership.
Mission critical applications require more advanced UPSs, either double conversion or online UPS. Such a UPS is never in standby mode. The battery circuit is actively connected to the system. If the mains supply is interrupted, there will be no interruptions or voltage dips at the output, allowing for seamless battery operation. The in-line system has built-in filtering and conditioning. During normal operation, it converts the input power from AC to DC and then back to AC through an inverter. Isolation protects against voltage fluctuations and minor input power disturbances. This type of UPS is more expensive and larger.
Distributed DC UPS Design
The disadvantage of an AC UPS is that all downstream equipment is AC powered and depends on the UPS. Control cabinet applications may require a very large AC UPS to power all downstream equipment. If the AC UPS fails, the downstream equipment will fail accordingly. Distributed DC UPS can save cost and space. Most control cabinets are based on DC voltage. An AC UPS provides backup at the inlet. For a DC UPS, backup power is implemented after the AC/DC transition.
Loads can be divided into buffered loads and unbuffered loads. An unbuffered load is a device that can be powered off during a loss of mains power without causing a system failure. AC/DC power supplies can directly power these loads. A DC UPS will power equipment or buffer loads that perform critical functions. This can significantly reduce the load on the DC UPS. Lower amperage means smaller UPS size and battery capacity.
DC UPS technology is simpler to design than AC UPS. DC products do not require AC-DC converters or DC-AC inverters. All voltages in the UPS, which are 24Vdc, are Safety Extra Low Voltage (SELV). This makes the power supply and battery pack more efficient. Using additional DC/DC converters for other DC voltages consumes more current in the conversion and can be parasitic on the system. In more advanced UPS systems, the only DC conversion occurs in the battery charging circuit. The DC UPS system can achieve load priority. Priority is given to powering loads connected to the UPS.
When the UPS is supplying the load in mains mode and charging the battery pack, the UPS monitors the load current. If the combination of load current and charging current overloads the main AC/DC power supply, the UPS will automatically reduce the charging current to prevent overloading. Due to the simpler circuit, DC UPS is usually smaller than AC. Some modular DC UPS systems have built-in diagnostics. With real-time monitoring information, batteries can be replaced before failure occurs, rather than guesswork.
Industrial UPS Batteries
Batteries are the backbone of a UPS system. When the power goes out, the battery will continue to work. So how do you make sure the battery isn't the weak link of the UPS? In industrial UPS applications, common battery types include VRLA, wide temperature VRLA, and lithium iron phosphate batteries.
The most common type is the standard VRLA battery, which offers the advantages of low cost, a balance of cost and capacity, but poor durability. Standard batteries have a nominal operating temperature of 0 to 40°C. They perform best in a constant temperature room around 27°C. While they are common in controlled environments, many industrial applications have a temperature range of -40 to 70°C, which can drastically reduce the life of VRLA batteries.
Wide temperature valve-regulated lead-acid batteries can operate in a temperature range of -25 to 60°C. They have a slightly longer service life than standard VRLA. They are usually used in outdoor applications. Chemical properties differ from standard VRLA, which is generally larger and more expensive. VRLA and Wide Temperature VRLA batteries can run about 250 to 300 charge cycles before failure, so VRLA lasts six months and Wide Temperature VRLA lasts a year and a half to two years. Lithium battery life and temperature range are similar to wide temperature VRLA batteries. Lithium batteries can be recharged up to 7,000 times for extended life. Lithium batteries may cost 3 times as much as wide temperature valve regulated lead acid, but perform better.
Manly Battery Co.,Ltd specializes in providing energy storage power, UPS backup power, power supply and new energy system solutions and operation and maintenance services for new energy, electric wheels, smart energy storage and green power applications. Among them, the field of network energy mainly includes communications, power, data centers, financial securities, rail transit, etc.; the field of smart energy storage mainly includes household energy storage, industrial and commercial energy storage, and microgrid energy storage systems; the field of green power mainly includes forklifts, low-speed electric vehicles, off-road vehicles, etc. At present, the main products are lithium-ion batteries and systems, lead-acid battery replacement lithium batteries and systems, and new energy system integration products and services.
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