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January 2022

Hello Reader

Happy New Year. I hope everyone is healthy and ready to take on 2022.

I wanted to start this year by going back to the basics of Uninterruptible Power Supply (UPS) systems, UPS 101.

As we progress we will also learn about the major components of UPS, their topologies, and how each protects against power problems. We will discuss what a maintenance bypass is, the different types, and why one is important. And finally, we will wrap up with types of parallel systems.

This month we will begin with the building blocks of a Static UPS system. What makes a UPS?

An Uninterpretable Power Supply system, or UPS, is a device that ensures electrical power is always available to a critical load.

I often explain a UPS system as a black box. This particular black box has two inputs and one output. The main AC input, often utility power, a DC input, and an AC output.

If the main AC input power is lost, as occurs when there is a utility power outage, the DC input provides electricity to an inverter. This ensures power is always available to the load.

But what’s inside this black box and how does it work? This is the tricky part. But don’t worry, we will keep it simple.

All UPS systems have the following components to some degree. Its topology will determine how and to what degree the

components are used. Next month we will learn more about UPS system topologies.

The figure shows a block diagram of a double-conversion UPS and can be used as we discuss the following components.

Rectifier-Every UPS system must have a rectifier, sometimes called a charger. Its purpose is to transform AC power into DC power. It keeps them charged so they are ready to use when needed and recharges them after a discharge. Depending on the UPS topology, it also provides DC power to the inverter through the DC bus.

Inverter-Most of today’s critical loads are powered by AC power. An inverter is used to transform the DC power supplied by either a battery or rectifier to AC.

Static Switch-A static switch is a device using semiconductors to transfer critical load from the inverter to a bypass source if there is a failure of the UPS system. It is also used to allow the load to remain on when maintenance is performed. Bypass power is usually utility power.

Energy Storage Device-In static UPS systems some type of energy storage device is needed to power the inverter when the main input power is not available. Lead-acid batteries have been primarily used and they are still the prominent source today. But in specific applications, a flywheel is sometimes used.

The past few years Lithium-Ion batteries have entered the UPS market. As the cost of Lithium-Ion decreases and their reliability is proven, they will likely replace Lead Acid as the go-to for UPS systems.

There are additional components used in UPS systems, including input and output filters, that help “clean” up the power. Control Logic is needed to control the UPS. However, these are outside the scope of this newsletter.

If you want to jump ahead of the series, or crave a more in-depth explanation of UPS systems, including the additional components mentioned above, check out my book, "UPS Handbook, A Layman's Guide to Uninterruptible Power Supply Systems."

Until next month, best of luck with your New Year’s Resolutions.

Thanks again for reading.

Rob

​Rob@robdelauter.com ​

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