Phase-locked loop for microprocessor with reduced complexity voltage controlled oscillator suitable for inverters

For grid-connected inverter applications it is necessary to produce a sinewave that is synchronised with the grid to act as a reference to produce an output waveform. The reference waveform is normally required for generating pulse width modulation (PWM) information or as a comparison waveform for the inverter controller. The phase-locked loop in this paper produces a sinusoidal output that matches phase and frequency using the zero crossing information only. This allows simplified phase detection methods to be used. The new all-digital phase-locked loop is based on a novel iterative technique to calculate the sine and cosine waveforms. This technique uses less computation to generate similar quality results to traditional multiterm Taylor series expansion techniques. A full derivation of the iterative algorithm is provided for examination. Graphs are presented that illustrate the errors of the voltage controlled oscillator and simulation results are presented for a phase-locked loop that attempts to reduce phase jitter and phase offset.