High efficiency, linear current amplifier for testing protective relays

A high efficiency, and low total harmonic distortion (THD), Class B amplifier in combination with hysteretic controlled switch mode, tracking power supplies was designed as a current generator (CG) for testing protective relays in energy distribution systems. CG simulates current disturbance in the power network system by generating different current shapes with amplitude of up to 35A and possibility of serial and parallel connection. Bandwidth depends for the most of the chosen filter inductance in tracking power supply and is compromise between efficiency and THD. In this amplifier, chosen bandwidth was 6 kHz, boosting up power supply rejection ratio. Finally, modular solution was build, integrating an LLC dc/dc power supply with amplifier/tracking power supply combination, generating high compliance voltages of up to 150V or more, contributing to high total efficiency.