Low Complexity Digital Quadrature Oscillators for Variable Frequency Applications

Switching frequency is utilized as a degree of freedom in digital control strategies for power converters. In addition to carrier-based schemes, quadrature oscillators offer an alternative method for the generation of variable frequency switching pulses. In this paper, amplitude instability in a computationally simple digital quadrature oscillator is analyzed. Algorithms for stabilizing the oscillator are developed based on this. Further implementation issues arising are addressed and a systematic comparison to carrier-based schemes is executed. It is shown that the proposed approach can be implemented with only 4 additions and 4 comparison steps without resorting to multiplication. The studies are validated in system simulation and experiments on a commercial FPGA board.