Static, Modular, High-Frequency PWM Inverters for up to 15 KVA UPS

Computers are widely used in telecommunications systems as process control and management units. In this kind of utilization, computers and relevant peripherals demand an uninterruptible a.c. power supply system of high reliability, performance and flexibility. Inverters normally provide uninterruptible a.c. power from the 48/60 V d.c. power source available in telecommunication plants. SIP, the Italian telephone operating company, specified and ITALTEL developped a system with modular H.F. PWM inverters having a 2,5 KVA unit power rating. Highlights of the system are : - 48/60 V +/- 20% d.c. power supply - parallel operation of the inverters and equal load sharing between paralleled units - high diagnostic coverage and selective cut-off of failed unit, without affecting other parallel operating units - high immunity to the current-waveform distortions rejected by loads - natural cooling - static and manual by-pass, rated for the plant end-load - galvanic isolation from mains during by-pass operation. The paper describes system operation at unit level and at system level, especially during transients and on distorting loads.