Backup power systems are now part of industry DNA. They are sprinkled across data centers, telecommunications networks, manufacturing centers, and industrial plant operations—in essence, where continuous power is essential. A brief loss of power may cripple sensitive equipment, machinery, and final products. The consequent restarts can be horridly time-consuming and expensive. Uninterruptible Power Supplies (UPSs) guarantee reliable backup power and improve power quality.
A UPS is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. The primary role of a UPS in industries is to provide short-term emergency power when there's a complete mains failure or blackout. This battery backup offers enough time for either the connected equipment to safely shut down, with the minimal risk of damage or data loss, or for an alternative power source such as a backup generator to kick-in. Besides, most modern UPSs can rectify a wide range of standard power problems, including power sags, brownouts, power surges, and harmonic distortion.
For years, batteries dominated energy storage for UPSs. Ultracapacitor UPSs are an alternative source of DC power to traditional batteries. This article will review Battery and Ultracapacitor operated UPSs as backup power solutions, and examine the impact of Ultracapacitor UPSs in industrial operations.
Battery vs Ultracapacitor UPS
Both batteries and ultracapacitors store electrical energy. An electric battery is a device consisting of one or more electrochemical cells. During battery charge, the electrical energy is converted into chemical energy and stored. The movement of ions within the battery allows the current to flow out and provide power to the attached load. The voltage in batteries remains stable during discharge over a wide range of load currents, and only drops sharply at the end of the discharge process, as shown in Figure 1. Batteries offer the advantage of elevated energy content and lower cost. However, sensitivity to high current peaks can permanently damage a battery.
Figure 1. Discharge curve of battery and ultracapacitor
Unlike batteries used in vehicles, electronic devices, or other applications, batteries in industrial UPS systems are used infrequently, leaving them routinely idle. Even though the long periods of wait are preferred for batteries, and they provide sufficient power for the required period, several disadvantages regarding maintenance, size, and environmental aspects come to the fore, which leaves room for alternative solutions.
Ultracapacitors have emerged as a new alternative for batteries in UPS systems. An ultracapacitor, also known as a supercapacitor, is a term referencing a family of high-capacitance devices which combine the properties of batteries and capacitors in a single device. In many ways, an ultracapacitor is simply a larger capacitor with bigger electrode plates and less distance between them, allowing for a higher charge to be stored in the form of electrical potential energy. An ultracapacitor doesn't use a dielectric; instead, porous electrode plates are soaked in an electrolyte and separated by a paper-thin separator material, as shown in Figure 2. When a charge is passed through the electrodes, the atoms in them become polarized - giving the electrodes a positive or negative charge. These then attract electrons of opposite polarity in the electrolyte, and thus create a double electric layer. Ultracapacitors thus store a lot more power than their regular capacitor counterparts. An ultracapacitor can process a large number of charge and discharge cycles (usually several hundred thousand) compared to only a few thousand cycles for batteries.
Figure 2. Schematic illustration of an ultracapacitor (Image: Wikipedia)
Ultracapacitor-based UPSs are a relatively new alternative to battery-based UPS systems. Ultracapacitor UPSs are specifically designed for the industrial network, and solve the challenges that plague battery-based UPS devices. They are ideal devices for bridging short power outages, lasting less than a minute. Ultracapacitor UPS devices are built to endure harsh environmental conditions, have long lifespans, require no maintenance, and are compact. They are ideal for a broad range of temperatures, including applications exposed to extreme outside temperatures (-40 to 140 degrees Fahrenheit). Ultracapacitors also do not suffer heavy degradation in hotter temperatures.
More importantly, ultracapacitors reduce downtime risk, as they eliminate batteries, an unpredictable and maintenance-intensive solution, and the leading cause of UPS failure. Advanced industrial ultracapacitor-based UPS devices can also be remotely managed, minimizing the time and effort needed to monitor them, which reduces operational expenses compared to a battery-based UPS. Remote device management allows all UPS devices on the network to be monitored from a single location, such as an office laptop or a mobile device on the plant floor. This is all performed using standard tools instead of proprietary software. Battery-based devices, in contrast, require an operator or technician to manually walk the floor, open each enclosure, and inspect every battery status.
Functional Description of Uninterruptible Power Supplies (UPSs)
The following block diagram shows the behavior of UPSs in both standard operation and a case where a power disturbance occurs. When the input voltage is standard, the utility directly supports the load. The UPS, during a sag, surge, or outage, immediately transfers the load onto its inverters. Power is sourced from a battery or from ultracapacitor energy storage. In many cases, ultracapacitors are ideal for protecting the load from sags and short-term outages.
Figure 3. Functional Block Diagram of a UPS
The power to the load, during normal operation, is supplied from the primary source or main utility supply. Inverters are off, but maintain synchronization with the utility voltage to allow instant operation if there is a disturbance. When the voltage deviates from user-defined limits due to voltage sags, surges, under-voltages, over-voltages, or outage, the UPS Inverters begin supplying power to the load (discharge mode). The utility is disconnected, simultaneously isolating the UPS output and load. When the voltage again returns within user-defined limits, the UPS synchronizes with the utility voltage and closes the utility disconnect.
Industrial Network Uninterruptible Power Supply
The Panduit UPS00100DC Industrial Network Uninterruptible Power Supply (UPS) uses ultracapacitor technology. It is designed to provide backup power to a 24 VDC load in the event of a power dip or outage. The unit utilizes Electrochemical Double-Layer Capacitor cells as the energy storage device to provide a long, maintenance-free operating life sans battery replacement. The UPS accepts a 24 VDC input voltage, and offers 24 VDC output voltage to a load with a maximum output power of 100W. A bank of twelve 350F EDLCs provide energy storage of approximately 9.3 kJ, which can supply a 100W load for a run time of about 1 minute.
The UPS is intended to provide uninterrupted power for critical applications, including managed network switches, micro PLCs, and HMIs deployed on the factory floor. The device is suitable for use in extremely low-temperature environments and elevated temperatures of -40 to +60°C, without loss of performance or reduced life.
Figure 4a. Panduit UPS00100DC System Wiring Diagram
Panduit's UPS00100DC UPS can be used in a redundant power supply system or a single supply system. In a redundant power supply system, the UPS monitors the power delivered by a second supply to the load through an external load sense module (LSM) UPS003LSM. Another configuration has the UPS providing backup power to a load with a single power source. To visualize this configuration, remove the Primary Power Supply, the LSM, and the associated wiring in Figure 4a.
The UPS00100DC has a unique remote monitoring feature via Ethernet communication, instead of USB or cable. Operating status and control are provided via a web server running on the UPS. This web server can be accessed via a web browser running on a PC connected to the same network as the UPS. The UPS can monitor load current and predict Hold Time in single or dual power supply applications. It can also regularly monitor and report temperature to predict changes in capacity over its lifetime. These maintenance-free operations save expenses on battery inspections, testing, and replacement.