Different types of UPS design:Line-interactive UPS design

There are three main categories of modern UPS systems: online, interactive online, or backup / stand-alone.

In a standby / stand-alone UPS system, the load is powered directly from the input power and the standby circuit is only activated when the utility power is disconnected. Most UPSs less than 1 kVA are line-interactive or standby, which is generally less expensive.

The Line Interactive Managed Ups Services keeps the inverter online and redirects the DC battery current path from normal charge mode to supply current when power is lost.

The online UPS uses a "double conversion" method to accept AC input, rectify to DC for passage through a rechargeable battery (or battery strings), and then back to 120/240 VAC to power protected equipment.

For large power supplies, dynamic uninterruptible power supplies are sometimes used. The synchronous motor / alternator is connected to the mains through a choke. Energy is stored in the flywheel. When the mains supply fails, the eddy current control system stores energy in the load. DUPS are sometimes combined or combined with a diesel generator [clarification needed] to form a Diesel Rotary Uninterruptible Power Supply, or DRUPS.

In recent years, a fuel cell UPS has been developed that uses hydrogen and a fuel cell as the power source, potentially allowing long run times in a small space.

Line-interactive UPS design

This type of UPS is capable of withstanding continuous low voltage dips and surges without consuming limited battery backup power. Instead, it compensates for this by automatically selecting different taps on the autotransformer. Changing the autotransformer tap can cause a very short interruption in the output power [citation needed], so the UPS may beep momentarily as it switches to battery power briefly before changing the selected power tap.

This has become popular with even the cheapest UPSs as it uses the components already included. The main 50/60 Hz transformer used to convert between line voltage and battery voltage must provide two slightly different turn ratios: one to convert the battery output voltage (usually a multiple of 12V) to line voltage, and the other to convert the line voltage to a slightly higher battery charge voltage (for example, multiples of 14 V). It is also easier to switch on the mains voltage side of the transformer due to the lower currents on that side.

To get the buck / kick function, all it takes is two separate switches so that the AC input can be connected to one of the two primary outputs and the load can be connected to the other, thus using the primary windings. the main transformer as an autotransformer. Note that the battery can still be charged while the impulse voltage is “lowered”, but while the low voltage is “high”, the transformer output is too low to charge the batteries.

Autotransformers can be designed to cover a wide range of AC input voltages, but this requires more taps and increases the complexity and cost of the UPS. Typically, an autotransformer only covers a range of about 90V to 140V for 120V power, and then switches to battery if the voltage is much higher or lower than that range.

Under low voltage conditions, the UPS will draw more current than normal, so it may require a circuit with a higher current than a conventional device. For example, to power a 1000 W device at 120 volts, the UPS draws 8.32 A. If a power outage occurs and the voltage drops to 100 volts, the UPS draws 10 amps to compensate. This also works in reverse so that the UPS draws less current under overvoltage conditions.