A robust PLL algorithm to synchronize static power converters with polluted AC systems

A Phase Locked Loop algorithm appropriated for DSP-based control implementations where the operation of a static power converter needs to be synchronized with an AC network is presented. The operating principle of the proposed algorithm includes a multiplier, a filter, a feedback closed loop, and a Voltage Controlled Oscillator (VCO) stage. As a result, a discrete sine (and cosine) signal is generated in perfect synchronism with the fundamental component of an external reference signal. Moreover, the sampling period of the algorithm is adjusted at each sampling instant such that an integer number of sampling periods is ensured per period of the external reference signal. This is mainly achieved by using an improved discrete rectangular window filter and a discrete controller. The algorithm code is simple, stable, and presents high noise rejection. The theoretical justification and various experimental tests are included.