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Other than the normal features of any UPS like wide input range, short circuit protection, overload protection, battery low protection etc many design modifications are done at sophisticated levels to make this design at a world-class level.
Some of the main Design highlights are:

This UPS is having a ZERO POWER SLEEP which means during the period of an off/trip condition of the UPS (irrespective of the switch position) the battery is not drained at all and the UPS may remain in the same condition for months together.
The MOSFETS are protected by switching off the gates instantaneously thereby reducing the L di/dt effect and spikes on the MOSFET drains. The spike over voltage can be further protected by Pico second speed transient diodes.
Most of the UPS available in the market does not have synchronized changeover. If the transformer core is saturated to one direction during the time of changeover and if the core is further saturated by switching ON the same side of the MOSFETs saturates the transformer core, there are chances that these MOSFETs can get damaged or derated due to excessive over current and spike voltages thus generated. This is prevented by Synchronized Changeover and in this design.
Power failure sensing is one of the complex tasks of the designer with shortest possible time and accuracy, which is very difficult to achieve by simple electronics. The normal UPS designers detect this by simple methods but may behave differently at different types of power failures or with different type of input waves like Electricity Board, Generators and Inverters. In our design the input waveform as well as the output waveform in raw form is sampled at high speeds to find out the energy as well as voltages are followed to detect correct power failure/dip/brown out. Adaptive delays are incorporated to start the Inverter (with emphasis on energy level pumping monitoring of the SMPS of the UPS) with the shortest possible delays. Five different methods are adopted to find the cause of power failures, which can never fail and guaranteed energy pump to SMPS is assured so that the computer reset never occurs in any condition.
All the voltages are measured near to RMS level accuracy so that AVR response to different types of main input like generators, Electricity Board and Inverter behaves properly and the output voltage range sticks to the specifications
Calibrating all the parameters is usually done with different presets and is usually time consuming. Here in our design we have adopted a single preset calibration for reducing costs and increasing reliability. Jumper settings are available to change parameters as well as change the functionalities like enable/disable no load sensing, battery voltage used etc…
For UPS application we have designed a MOSFET based add on charger PCB for current up to 7A. The type of charger is jumper selectable for constant voltage with current limit or, constant current charger. A battery health checkup and battery bad detection software also runs parallel. A periodic time driven battery charger restart is done than voltage based sensing to reduce electricity bills of the user. A standby mode with zero mains power is entered after full charge. The charger can be disabled to use SMPS charger if required with jumper settings. A separate program runs if charger is faulty with under or over current.
Very high levels of surge currents are allowed by pulse banking methods to satisfy the cold start requirements of bigger size monitors and power hungry computer chips with proper MOSEFET safety feature and to prevent rebooting of other computer systems connected to the UPS
Current sensing is done by software methods for no load, more load and over load sensing by taking different characteristics of transformer, battery and power devices without using and hardware detection circuits. Another capability of the circuits is to detect unbalanced load if current is taken only from one side of the transformer only.

Future upgradation

The same PCB can be upgraded to incorporate LCD/Key board interface, sensors like over temp, fan fail, mains over current, bat water low etc and advance functions like AMC/guarantee period monitoring ,periodic maintenance warning as well as service history storage without any PCB changes but with the upgradation of controller only