The proper operation of the grid-connected power electronics converters usually needs using some kind of synchronization technique in order to estimate the phase of the grid voltage. The performance of this synchronization technique is of a great importance when trying to improve the quality of the consumed or delivered electric power. The synchronous reference frame phase-locked loop (SRF-PLL) synchronization algorithm has been widely used in recent years due to its ease of operation and robust behavior. However, the estimated phase can have a considerable amount of unwanted ripple if the grid voltage disturbances (e.g. harmonic distortion and unbalance) are not properly rejected. The aim of this paper is to propose an adaptive SRF-PLL which is able to strongly reject the aforementioned disturbances even if the fundamental frequency of the grid voltage varies. This synchronization method will allow the designer to easily upgrade an existing SRF-PLL, thus improving the performance of working power converters. This is accomplished by using several adaptive Infinite Impulse Response (IIR) notch filters, implemented by means of an inherently stable Schur-lattice structure. Besides the stability properties, this structure accomplished the most important topics required to be programed into the commonly used fixed point DSPs (i.e. high mapping precision, low round-off accumulation, suppression of quantization limit cycle oscillations). The proposed adaptive SRF-PLL has been tested by programing the algorithm into the fixed-point digital signal processor TI TMS320F2812. The obtained experimental results show up that the proposed synchronization method highly rejects the undesired harmonics, even if the fundamental harmonic frequency of a highly polluted grid voltage abruptly varies.