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UPS and inverter

2019-08-16

Uninterruptible power supplies (UPS) and inverters are used to provide power, so they are often confused. However, UPS is a more complex device with a wider range of functions - in fact, UPS uses an inverter as one of its internal components.

In short, an inverter is a device that receives power from a direct current (DC) power source (such as a battery or solar module) and converts it into an alternating current (AC) power source for the appliance. The UPS unit also performs power conversion, but it adds features such as instant response and energy storage.

The best way to understand the difference between a UPS unit and an inverter is to compare them to air conditioners and compressors. Just as the compressor itself does not provide space cooling, the stand-alone inverter cannot perform all the functions of the UPS.
Determine the best backup power for your device.

How does the inverter work?

As mentioned above, the main function of the inverter is to convert power from DC to AC. Please note that the inverter can only convert power and cannot generate or store its own power. Therefore, if the inverter is disconnected from its DC power supply, the power supply will be interrupted.

Like any electrical equipment, the inverter has a rated power that can be handled. For example, in a solar photovoltaic system, most residential facilities use inverters below 10 kW, while medium commercial equipment may exceed 100 kW. In addition to the rated power, the inverter can operate with a range of DC and AC voltages.

Frequency converters (VFDs) are often referred to as "inverters" because many models can generate three-phase power from a DC input. However, this naming practice can be confusing because the main purpose of the VFD is to control the motor speed by adjusting the voltage input. Like the UPS unit, the VFD uses the inverter as one of its main components, but there are no other components and functions in the independent inverter.


How does an uninterruptible power supply (UPS) work?

The UPS is one of the devices with an unnamed name - an uninterruptible power supply, especially during power outages or grid disturbances. However, in order to be uninterrupted, the UPS must perform two important functions:

Energy storage, if the main power service is interrupted, the UPS can continue to supply power. The energy storage function is usually done by the battery and the charge controller.

Respond immediately so that all devices connected to the UPS can continue to operate in the event of a power outage. UPS equipment is typically used with computers and critical data centers to prevent loss of information during power outages or interference.

Note that the inverter can also be used as a backup power source if used in conjunction with an energy storage system. However, traditional inverters cannot be seamlessly converted by UPS. Although inverters can respond in less than a second, they are not fast enough to prevent data loss in IT equipment; UPS units are faster and respond within a few milliseconds.


Assuming the same power rating, the UPS unit is usually more expensive than the inverter because it has additional components and functions. A UPS unit is required when the application requires continuous power supply during a power outage, but an inverter with external energy storage is a more cost effective option when this function is not required. For example, you don't want to leave the data center (UPS) without a power source, but you can tolerate a brief disconnection of your lighting system (inverter with energy storage).

When using the main power service to charge the battery, please note that there are two power conversions. First convert the AC power to DC for battery charging, and when you use the battery as a power source, its output will be converted back to AC. Keep in mind that battery charging requires DC power, and AC input requires a device called a rectifier - including a UPS device, but an external charging controller is required if the battery is connected to the inverter.
Combine UPS unit and inverter.

Since the UPS unit is more expensive, it does not make sense to operate for hours without power. A smarter approach is to have short-term UPS capacity to provide time for the larger inverter system to take over the load.

Inverters with energy storage can be used as direct power sources for less critical loads such as lighting.
During a long power outage, the UPS load can remain connected, and you only need to use the inverter output to charge the UPS battery.

Please note that energy efficiency measures allow you to run longer under standby power. For example, if you replace fluorescent lamps with the same LED products, the energy consumption of these products is reduced by 50%, then you can use twice the fluorescent light with the backup power supply.

The optimal configuration will vary depending on the load in the building. For example, offices with large numbers of computers and communication devices often require higher UPS capacity. If you want konw more, please consult Daopulse.