GreenPower UPS Technology: Bypass Design

GreenPower UPS™ Technology from CyberPower improves operating efficiency, reduce heat generation, and consume less power than conventional UPS models.

Our patented Bypass Design allows current to bypass the transformer and automatic voltage regulation (AVR) when utility power is normal, thus reducing energy consumption and associated costs. Because utility power functions normally most of the time, the bypass design allows for substantial energy savings. This technology also reduces heat generation, an important factor in decreasing operating costs.

Sine Wave Power

In the U.S., utility companies provide power to households and offices by distributing single phase alternating current (AC) power at a frequency of 60 Hz. Electrical power can be graphically depicted as a sine wave whereby the electrical signal alternates from +120 volts to -120 volts at a rate of 60 times per second (60 Hz). To enable more efficient operation of large, heavy equipment, utility companies provide commercial and industrial locations with three phase AC power which consists of three overlapping sine waves offset by 120 degrees.

Although utility companies strive to distribute 100% sine wave power, many factors can introduce electrical noise into the AC power signal in the form of sine wave distortions and as voltage sags, surges, spikes, or other irregularities. Sine wave power is important for the optimal functioning of sensitive desktop computers and related peripheral equipment. Without sine wave power output, microprocessor-based equipment can become inoperative or sustain damage from power signal distortions.

Active Power Factor Correction Supplies for IT Equipment

During the past thirty years, people have become more aware of the amount of energy used by IT equipment and devices. For many years, desktop computers and workstations inefficiently consumed power, partly due to the design of the power supplies which transformed AC power (from the wall outlet) to DC power (used by computers). This voltage transformation was relatively inefficient as reflected in low power factor ratings.

In 1992, the U.S. Environmental Protection Agency (EPA), in collaboration with advocates in the IT industry, developed the ENERGY STAR® program to prompt the development of energy-efficient products. Today this program is recognized as an international standard.

To comply with ENERGY STAR standards, manufacturers of desktop and workstation computers incorporate Active Power Factor Correction (Active PFC) as part of the engineering designs, enabling energy efficiencies of 95% or higher. Computers with Active PFC power supplies require sine wave AC power, as supplied by utility companies, for trouble-free operation. For this reason, sine wave UPS systems have become the best choice for backup power.

Simulated or stepped sine wave power, provided by entry-level UPS systems, may be problematic or incompatible with Active PFC devices. Sine wave power varies continuously from positive to negative. Simulated sine wave power mimics a sine wave by using a squared-off approximation. Due to this approximation, simulated sine wave power momentarily creates a zero power gap. When power is interrupted, a computer with an Active PFC power supply may not recognize incoming simulated sine wave power due to the zero output present in the approximated wave. This could cause the system to unexpectedly shut down or sustain system component stress.

Automatic Voltage Regulation

Automatic Voltage Regulation (AVR) in line interactive UPS systems stabilizes the incoming AC signal to maintain output power at a nominal 120 volts by controlling high and low voltages without resorting to battery power. This significantly increases battery life and lessens the likelihood of data loss, memory freezes, and system crashes.

How AVR Works in a Line Interactive UPS

A line interactive UPS includes an AVR autotransformer a special type of transformer designed to switch between powered coils of wire in response to variances in utility power input, thereby increasing or decreasing the magnetic field and the resulting output voltage to connected equipment.

This type of UPS tolerates undervoltage brownouts and overvoltage surges without consuming backup battery power by automatically selecting different power taps on the AVR autotransformer. During normal operation, incoming AC power bypasses the autotransformer (where voltage highs and lows are controlled) while also charging the battery. When the incoming voltage falls below the AVR range, the UPS switches to battery backup, and the DC-AC inverter circuitry is engaged. Power will continue to be supplied by the battery-inverter circuit until incoming voltage returns to the range manageable by the AVR.