PWM inverter for parallel operation as high quality AC source in telecommunication

This paper presents power conversion in an inverter without a 50 Hz transformer, delivering high quality line-type AC power drawn from a 48/60 V DC source. Two modes of operation of such inverters are known: single and double modulation. Advantages and disadvantages of both modes are presented and compared. Basing on this comparison an inverter has been developed which has distortion free AC voltage output, relatively small volume and weight and high efficiency. It uses IGBTs and MOSFETs controlled by an optimised PWM strategy. This inverter can synchronise with the mains and can be parallel connected to increase output power and system redundancy. By the use of a static bypass unit, a further increase in redundancy may be achieved. An example of application in a telecommunication power supply is also presented