UPS, or Uninterruptible Power Supply, is a system that connects a battery (usually a lead-acid maintenance-free battery) to a main unit, and uses the main unit's inverter and other circuit modules to convert direct current (DC) into AC power. In Europe and America, the abbreviation UPS is taken from the English prefix Uninterruptible Power System.
Classification and Principles
Based on the number of input/output phases, they can be categorized as: single-input single-output, triple-input single-output, and triple-input triple-output.
According to power rating, it is divided into: micro (<3KVA), small (3KVA~10KVA), medium (10KVA~100KVA) and large (>100KVA).
According to the circuit structure, there are standby type, online interactive type, online type, etc.
Based on the different output waveforms, there are two types: square wave and sine wave.
The circuits are now classified according to their structure, and described as follows:
2.1 Backup (Off-line or Stand-by)
1) Principle:
① When the mains power is normal, the mains power is directly output to the load after being regulated. At the same time, the AC power is converted into DC power by the rectifier to charge the battery. At this time, the inverter does not work.
② When the mains power fails, the battery provides power, which is then output to the load via the inverter. This switching time is approximately 4-10ms.
2) Features:
Power range: 300～2000VA
Operating characteristics: The mains power is directly supplied to the load after simple step-up/step-down and filtering. Battery power is only supplied when the input power does not meet the requirements. The load uses mains power most of the time.
Advantages: Simple structure, low price, small size, low noise, and high efficiency.
Disadvantages: AC power/battery power conversion time is 4-10ms, output accuracy is low, output waveform is poor, and the output waveform is a square wave.
Main application: Power outage protection for single computer systems
2.2 Online Interactive (HYBIRD)
Online interactive is also known as hybrid or three-port.
1) Principle:
① When the mains power is normal, the mains power is regulated and then output to the load through the transfer switch. At the same time, the AC power is converted into DC power by the rectifier to charge the battery. At this time, the inverter is activated but not outputting power.
②When the mains power fails, the battery provides power, which is then output to the load via the inverter.
2) Features:
Power range: 1~800KVA
Operating characteristics: The mains power is rectified and converted into DC, and then modulated into a stable sine wave by the inverter.
Advantages: The load end and the mains input end are in a state of excellent "electrical isolation", the output waveform is good, the output voltage quality is high, and it exhibits excellent load-carrying characteristics regardless of whether the load changes suddenly or is stable.
Disadvantages: Low efficiency, high cost
Main applications: power outage protection for computer and network systems, precision instruments and meters, and industrial systems.
2.3 Online:
1) Principle:
① When the mains power is normal, the mains power is converted from AC to DC by the rectifier to charge the battery. At the same time, it is output to the inverter to convert DC to sinusoidal AC, and then output to the load through the transfer switch.
② When the mains power input is abnormal, the power is output from the battery to the load via the inverter.
③ When the inverter malfunctions or its output power is insufficient (due to overload, overheating, etc.), the transfer switch will automatically switch to static bypass to continue supplying power from the mains. If the bypass is caused by overload, the UPS will trip back to normal inverter output when the load drops below 100%. If the bypass is caused by overheating, the UPS will trip back to normal output when the temperature drops below the alarm point.
2) Features:
Whether the mains power supply is normal or during a power outage when the battery inverter provides power, the inverter is always in operation, which fundamentally eliminates the impact of voltage fluctuations and interference from the grid on the load.
Since the inverter operates synchronously with the mains power, the automatic switching time between the inverter and the mains power via the transfer switch should be less than 2ms. Therefore, it has high reliability and is suitable for places with high power quality requirements.
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