Choosing the Right UPS Topology for IIOT and Critical Power Applications

My colleague, Daniel McGinn, provides a very good high level view of power management for IIoT devices in his recent blog, “How to Provide Power Protection in an Industrial Internet of Things Environment.”

I’d like to build on that topic, and give you a little more guidance on the types of UPS which are available for industrial applications, as well as indicating which will provide superior performance in the harsh conditions found in manufacturing. Selection becomes especially critical as companies start to lean more heavily on machine to machine (M2M) data in order to drive automated decision-making and ensure the highest efficiency.

As Daniel mentions in his piece, a centralized UPS provides the most cost-effective approach to ensuring runtime for the intelligent devices and edge compute nodes which will be part of the IIoT process. A centralized approach can reduce the cost per kilowatt for UPS protection to around a tenth of that provided by point solutions. The UPS should be situated in close proximity to the systems being protected in order to reduce electrical disturbance, losses and risk introduced by cabling infrastructure.

Ideally, the choice of UPS should only be made after a full audit of the requirements. In the first instance, the physical environment should be considered including hazards presented by airborne particles, humidity, chemicals and operational temperatures, any of which will impact the choice of UPS configuration.

Decisions about Power Availability will affect choices about system redundancy, system architecture and MTTR (mean-time-to-repair). Likewise, the need for future flexibility to upgrade may demand the use of a modular UPS to support the expansion of power or runtime requirements. Finally, the electrical environment within the facility itself needs to be considered, from the grounding network to voltage, frequency and harmonic pollution.

Since any of these four factors, physical and electrical environment, availability and flexibility will have an impact on the choice of UPS topology as well as the specification, it’s worth considering what options are available to you. IEC 62040-3 is an international standard which defines the different types of UPS, how they function and how to measure performance. It comprises three categories: Voltage Frequency Independent, Voltage Independent and Voltage Frequency Dependent.

• Voltage Frequency Independent (VFI – also known as online double conversion): The UPS output is independent of the input mains supply voltage and frequency variations, i.e., the primary power path is the UPS inverter which ensures continuity of power to the load. The UPS acts as a full filter providing voltage regulation, frequency regulation and power back-up. This type of UPS can include a static by-pass switch for maintenance and fault tolerance, and may also include a transformer. This type of UPS is specifically adapted for and common throughout industrial and harsh environment applications.
• Voltage Independent (VI or line interactive): In normal mode of operation, the continuity of load power is maintained by the use of an inverter or power interface while conditioning primary power at the input supply frequency. The load is supplied with conditioned power via a parallel connection of the AC input of the inverter and there is no frequency regulation. This UPS topology provides low power ratings and is used primarily in clean environments where there is low risk of periodic voltage fluctuations.
• Voltage Frequency Dependent (VFD – also called passive standby or offline): The UPS output is dependent on mains input voltage and frequency variations, and in normal mode the load is supplied by the utility power via a filter to eliminate power disturbances such as peaks. This type of UPS is mainly used in home and small business network applications to provide sufficient back-up time for a graceful system shut down.

In IIoT applications, supply voltage must be continuous to ensure the availability of data for critical decision-making. If you’d like to learn more about how system availability and uptime are affected by AC power outages, Schneider Electric white paper 24 “Effect of UPS on System Availability” is available as a free download from our website, and provides quantitative data regarding uptime in real-world environments.

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