A Design Basis for Ferro-Resonant Parallel Inverters with Silicon Controlled Rectifiers

Abstract

The paper describes the operation and design basis of medium power S. C. R. parallel inverter in which magnetic ferro-resonance has been utilised to achieve some desirable properties. Example of a specific system which consists of a 500 VA parallel inverter providing 220V, 50 Hz a.c. from a 48 volts d.c. input using ferro-resonant transformer and a constant frequency trigger circuit with crystal control and associated transistorised scale-down circuit has been discussed. The main advantages of such an inverter are economy in components and cost, inherent output voltage stabilization within ± 10% for variation in the input d.c. voltage as well as load changes, short circuit/overload protection, sinewave output with harmonic distortion less than 5% without using any additional filter and frequency stabilization accuracy of about 0.5 parts per million. The applications of such an inverter are in standby a.c. power supply for computers, frequency stabilizer/master clock control system for electric clocks, a.c. power supply for mobile use, and power supply systems where a highly stable constant frequency supply is required in specific applications.