In control systems operating with AC voltage, AC UPS is the most suitable. The offline or standby topology structure is very simple and clear. These products are inexpensive, so they are the most common type of AC UPS. Under normal circumstances, offline UPS transfers the main power from the input terminal to the output terminal, without any other interaction except for charging the battery connected in parallel with the main power circuit. If the main power supply fails, the UPS will switch from the main power circuit to the battery circuit. The transition time from UPS losing main power to battery power cannot exceed 10ms. A 10ms switch usually does not affect downstream devices, but can protect systems that are sensitive to voltage fluctuations.

There are two subsets of communication UPS: improved (analog) sine wave output devices and pure sine wave output devices. Each type of communication output is different.

The improved sine wave device obtains voltage from the battery pack and creates waveform outputs similar to sine waves in the simplest form possible. Although this type of UPS has relatively low costs, there are also some drawbacks. A significant step in voltage can damage the input circuit of downstream equipment. These huge steps can also cause a large number of switching transients in the UPS output. This can cause premature failure of small PC and PLC power modules.

A pure sine wave UPS will produce a sine waveform output that is identical to the waveform fed by the 120/230V main power supply. Pure sine wave UPS is a better choice for sensitive control equipment such as programmable logic controllers (PLCs), distributed control systems (DCS), and industrial PCs (IPC). Although more circuits are required, control equipment powered by UPS has a longer lifespan, thereby reducing the total cost of ownership.

Critical task applications require more advanced UPS, namely dual conversion or online UPS. This UPS will never be in standby mode. The battery circuit is actively connected to the system. If the main power supply is interrupted, there will be no interruption or voltage drop in the output, thus achieving seamless operation of the battery. The online system has built-in filtering and regulating devices. During normal operation, it converts the input power from AC to DC, and then converts it back to AC through an inverter. Isolation can prevent voltage fluctuations and minor input power interference. This type of UPS is more expensive and larger in size.