Here’s a reference design from Microchip for a 1000VA pure sine
uninterpretable uninterruptible power supply. UPS usually use 3 circuits to function. A charger for battery, a inverter to convert DC battery power to mains AC, and a controller that switches from mains to battery when the power is interrupted. This design utilizes a single dsPIC digital signal controller to handle all three functions.
A flyback switch mode dc/dc converter charges and maintains battery voltage. The inverter requires 380V DC to create the 220V AC output, the 12V DC battery supply is bootsed to 380V using another DC/DC converter in push/pull configuration. The dsPIC monitors the battery charge and directly drives the MOSFETs in both DC/DC converters.