A low cost reversible rectifier

A study is made of a circuit which offers a cheap, efficient four quadrant rectifier such as required for the line side of an AC motor drive. The circuit consists of a normal capacitor-filtered rectifier with SCRs connected in antiparallel with the diodes. The circuit has been described previously, but the experimental efficiency for regeneration did not exceed 40%. A mathematical model is derived for important electrical quantities by neglecting their harmonic components. The model is confirmed by both simulation and experimental work on a low power prototype. The model allows a determination of the optimum operating point for the circuit with the aim of maximizing efficiency and meeting practical constraints on the SCR extinction angle, the capacitor voltage and line current harmonics. Efficiencies of 75-80% are suggested by the model and verified experimentally. It is shown that line resistance is important in allowing the circuit to regenerate at practicable values of DC-side voltage.