An online UPS (Uninterruptible Power Supply) continuously powers the connected equipment from its battery, ensuring a seamless transition in case of a power outage. Here's a breakdown of how they work:
Key Components
- Rectifier/Charger: Converts incoming AC power to DC power.
- Battery: Stores DC power for backup.
- Inverter: Converts DC power back to AC power to supply the load.
- Static Switch (Bypass): Allows the load to be directly connected to the AC mains in case of UPS failure or during maintenance.
Operational Stages
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Normal Operation:
- The incoming AC mains supply is fed to the rectifier/charger.
- The rectifier/charger converts the AC power to DC power.
- This DC power then serves two purposes: it charges the battery, and it powers the inverter.
- The inverter converts the DC power back into a clean, regulated AC power supply, which is then fed to the connected equipment (the load).
- Crucially, the load is always powered by the inverter, which is receiving its power from the DC bus.
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Power Outage (Mains Failure):
- When the AC mains power fails, the rectifier/charger stops receiving power.
- The battery immediately begins to supply DC power to the inverter.
- The inverter continues to convert the DC power to AC power, ensuring that the load remains powered without any interruption.
- Because the load was already running off the inverter, there is no switch-over time. This is the key characteristic of an "online" UPS.
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Static Bypass (Optional):
- If the UPS experiences a critical failure (e.g., inverter malfunction), the static switch can automatically or manually switch the load directly to the AC mains.
- This bypass mode protects the load from a complete power loss, although it removes the power conditioning and backup capabilities of the UPS.
Advantages of Online UPS
- Zero Transfer Time: The connected equipment experiences no interruption during a power outage.
- Power Conditioning: The inverter constantly regenerates a clean and stable AC power supply, protecting the load from voltage fluctuations, surges, and noise on the mains.
- Superior Power Quality: Provides a more consistent and reliable power supply compared to other types of UPS.
Disadvantages of Online UPS
- Higher Cost: Typically more expensive than other UPS types.
- Lower Efficiency: Due to the continuous double conversion (AC to DC and then DC to AC), online UPS tend to be less energy-efficient.
- Higher Heat Generation: The double conversion process also generates more heat.
In summary, online UPS provide the highest level of power protection by continuously powering the load from the inverter, ensuring a seamless transition to battery power during outages and providing power conditioning benefits at all times.
