A simple three-phase variable-fraquency oscillator

The paper describes a hybrid, three-phase oscillator with variable frequency and voltage, and reversible phase sequence. The oscillator digitally generates three 120° phase shifted square waves, and mixes them in balanced modulators with a fixed frequency sine wave. The signals from the modulators are token through active filters resulting in constant amplitude, low distortion three-phase sine wave outputs. The magnitude of the output, voltage is controlled by varying the amplitude of the fixed frequency sine wave source. It has good frequency and phase stability.