AVR

What Is an AVR?

Automatic Voltage Regulation (AVR) is a technology designed to stabilize voltage. It is commonly used in Uninterruptible Power Supply (UPS) systems. Also referred to as an Automatic Voltage Stabilizer (AVS), its primary function is to adjust unstable power input to a safe output range, protecting connected devices from voltage fluctuations such as overvoltage, undervoltage, or sudden drops.

AVR regulates voltage through internal mechanisms that boost (increase) or buck (decrease) the voltage when minor fluctuations occur. This process does not consume battery power, helping extend battery life while reducing risks like data loss, system crashes, and hardware failures caused by voltage instability.

How Does AVR Work on a UPS?

1. AVR in Line Interactive UPS Systems

In a line interactive UPS system, AVR operates using an autotransformer—a special type of transformer that automatically switches between different power taps in response to voltage changes.

• Boost Function: When the input voltage drops below a certain threshold (e.g., 207V in a 230V system), the AVR switches to a "boost" tap, increasing the output voltage by approximately 15% to return to a safe range.

• Buck Function: When the input voltage exceeds a certain level (e.g., 253V in a 230V system), the AVR switches to a "buck" tap, reducing the output voltage by around 15% to maintain stability.

The AVR in a line interactive UPS automatically manages voltage highs and lows without switching to battery power, effectively extending the battery lifespan. Additionally, AVR systems use Hysteresis to prevent frequent switching, known as "chatter." For instance, the buck function may activate at 253V but only deactivate when the input voltage drops below 244V.

2. AVR in Online Double Conversion UPS Systems

In an online double conversion UPS system, AVR works differently. Instead of mechanical switches and transformers, this system uses an inverter to control the output voltage electronically. Regardless of fluctuations in input voltage, the output remains stable and precisely regulated.

Online double conversion UPS systems offer true AVR with more accurate and consistent voltage control than line interactive systems.

Benefits and Limits of AVR

AVR plays a critical role in maintaining voltage stability in UPS systems but has certain limitations. The following table outlines its key benefits and limitations: