The Different Types Of UPS

White Paper No. 1 Version 10

Choosing the right Uninterruptible Power Supply (UPS) system is critical for ensuring continuous power supply in applications like data centres, hospitals, and airports. The IEC 62040-3 standard classifies UPS systems based on their output characteristics. This guide provides a detailed overview of the IEC standard, explains the four main types of static UPS systems, and discusses their advantages, disadvantages, and practical applications. This knowledge will help you make an informed decision about the best UPS type for your specific needs.

Types of UPS Systems

Standby UPS
- Description: Ideal for protecting individual loads like desktop computers, Standby UPS systems switch to battery/inverter power during an outage.
- Attributes: Low cost, compact size, non-sinusoidal output, high efficiency.
- IEC Classification: VFD-SY-33. Voltage and Frequency Dependent with non-sinusoidal output and up to 10 ms interruption time.
Line Interactive UPS
- Description: Suitable for small servers and networking equipment, these UPS systems use an AVR transformer for voltage regulation and an always-connected inverter.
- Attributes: High reliability, very high efficiency, sinusoidal output, handles voltage variations effectively.
- IEC Classification: VI-SS-31. Voltage Independent with sinusoidal output and up to 1 ms interruption time.
Hybrid Conversion On-Line UPS
- Description: These systems offer higher density and similar performance to double conversion UPS systems, ideal for sensitive servers in dense environments. They operate in on-line, bypass, and battery modes.
- Attributes: Excellent voltage conditioning, high power density, 0 ms transfer time, Power Factor Correction (PFC) available.
- IEC Classification: VI-SS-11 in on-line mode; VFD-SS-31 in bypass mode. Voltage Independent or Dependent with sinusoidal output.
Double Conversion On-Line UPS
- Description: Commonly used for large, critical loads like data centres, these systems operate in on-line, bypass, and PFC bypass modes.
- Attributes: Superior voltage and frequency conditioning, ease of paralleling, available in high-efficiency modes.
- IEC Classification: VFI-SS-11 in on-line mode; VFD-SS-31 in bypass mode. Voltage and Frequency Independent with sinusoidal output.

UPS Modes of Operation

Normal Mode: Powers the load using AC input, charges the energy storage device.
High-Efficiency Normal Mode: Directly powers the load from AC input to increase efficiency.
Stored Energy Mode (Battery Mode): Powers the load using DC power from the battery during input power interruption.

Summary of UPS Characteristics

UPS Type	Typical Power Range	Cost per VA	Power Density	Service Life	Load Criticality	Efficiency	IEC Classification
Standby	0.2 – 2 kVA	Low	Very High	Short	Low	Very High	VFD-SY-33
Line Interactive	0.5 – 5 kVA	Medium	Medium	Medium	Medium	Very High	VI-SS-31
Hybrid Conversion	1 – 3 kVA	High	High	Long	High	Medium High	VI-SS-11, VFD-SS-31
Double Conversion	10 – 1500 kVA	High	High	Very Long	Very High	Medium Very High	VFI-SS-11, VFD-SS-31

Conclusion

Selecting the right UPS system involves understanding the performance classifications and characteristics of different types. The IEC 62040-3 standard provides a framework to compare these systems, helping you find the optimal UPS for your application. For detailed technical specifications and further reading, refer to related white papers and the IEC standard.