Uninterruptible power supply system rectifier unit

An Uninterruptible Power Supply (UPS) is defined as a piece of electrical equipment which can be used as an immediate power source to the connected load when there is a failure in the main input power source. In a UPS, the energy is generally stored in flywheels, batteries, or super capacitors.

The block diagram is shown below. When there is any power failure, the rectifier have no role in the circuit and the steady power stored in the batteries which is connected to the inverter is given to the load by means of transfer switch. Once the power is restored, the rectifier begins to charge the batteries.

However, during transmission and distribution, it is subject to voltage sags, spikes and outages that can disrupt computer operations, cause data loss and damage equipment. The uninterruptible power supplies protect the connected equipment from power problems and provide battery backup during power outages.

Uninterruptible Power Supplies with hybrid storage system Uninterruptible power supplies with batteries as storage source provides good performance during grid interruption and blackout by suppling instant backup energy. However batteries cannot provide backup for a very long period of time and have limited charge/discharge cycles.

According to the IEEE standard ANSI/IEEE 446–1987, minimum power factor is 0.8 at the rated load and harmonics content less than 5% is preferred for the input rectifier of the UPS system. Table 8. Typical 3-Ø UPS System Specification by ANSI/IEEE 446–1987 . Fig. 27. Input Voltage and Current waveform.

5.1.16 (Optional) Isolation transformer is required for providing neutral terminal to the UPS system. Detailed configuration of the isolation transformer shall be referred to the Particular Specification. Bypass mode. Under normal operation, the rectifier/charger unit shall convert the incoming a.c. mains power supply to d.c. power.