ONLINE UNINTERRUPTABLE POWER SUPPLY
ECS is also a distributor of industrialized online UPS. We supply UPS between 15kVA to 1000kVA to banks, hospitals and sensitive dairy
For an on-line UPS, the battery operated inverter works continuously whether the mains supply is present. or not. When the mains supply fails, the UPS supplies power only until the batteries get discharged.
A bypass switch is however provided to bypass the UPS inverter, only when a fault develops in the UPS inverter. However, once the mains power resumes, the batteries will get charged again. The switching times of these supplies is considered to be zero. Usually sealed maintenance free batteries are used and the running time of the inverter is low (approximately 10 to 30 minutes).
Uninterruptible Power Supplies (UPS) are electronic devices designed to provide power to critical mission systems. An Online UPS (OUPS) provides continuous power to the load during power outage or glitches caused by power source switching.
- The Concept of an Online UPS
The minimum components needed to design an Online UPS are the rectifier, the battery bank and the inverter. The rectifier converts the distribution line’s AC (Alternating Current) power to DC (Direct Current), the form of current suitable to store energy in a battery bank. At all times, this DC is also fed to an inverter, which reconverts the DC power to an AC waveform connected to any equipment utilizing AC that a user considers as mission critical. If the AC supply fails for any reason, the inverter will continue to draw power from the batteries
- DC-to-DC Converters
If a rectifier is connected to the AC line supply, then the DC voltage will be equal to the peak voltage of the line. (i.e., in a 120 VRMS line, the peak will be 120√2, 170V). If the battery bank is configured for 12 or 24 VDC, the UPS works by using DC-to-DC converters. For an online UPS, two power DC-to-DC converters are required. One converter operates as the battery charger, and the other boosts the battery voltage in the absence of line input and generates the appropriate DC required by the inverter.
- Phase Locked Loop (PLL)
This UPS can operate in the Free Running mode or in the Locked-to-Line mode. If the AC main line frequency is at the nominal value of 50Hz or 60Hz ± 5%, then the PLL locks the inverter output to the line. If the AC main line frequency runs out of limits for any reason, the UPS will automatically switch to run locked to the internal frequency reference. The UPS will also work in the Free Running mode if commanded to operate as a frequency converter. For example, it can connect to a 60Hz AC main line frequency and output a signal of 50Hz frequency, and vice versa. The purpose of Phase-Locking the inverter to the line input is to enable the automatic bypass feature, and to avoid signal “mixing” at the rails. These two features are detailed in the following sections.
- Bypass Operation
In order to allow a UPS bypass without loss of power at the load, two conditions must be met: • The inverter output must be locked to the frequency and phase of the AC main line • The inverter output and the AC main line’s RMS voltages must be within 10% of one another Introduction Online UPS Theory and Description, Rev. 0 Freescale Semiconductor 1-3 Preliminary When the bypass conditions are met, the bypass switch can transfer the load to the AC main line in the event of a UPS failure or when commanded by the operator during routine maintenance. It can also switch the load back to the inverter after any maintenance.