Multi-reference frame based PLL for single phase systems in voltage distorted grids

The paper deals with a robust grid synchronization method for single phase highly distorted power grids. Basically, Phase Looked Loops (PLLs) are able to estimate the phase angle of the fundamental harmonic of the grid voltage used in converter control algorithm to correctly set the power transfer between the energy resource and AC grid. Moreover, PLLs also provide αβ voltage components of the grid fundamental harmonic needed to implement vector control algorithm. With the aim to generate a correct angle estimation even in grids with high distortion of the voltage waveform, a PLL algorithm is proposed that exploits a suitable harmonic decoupling network, based on multi-reference frame transformations, to estimate the amplitude and phase of both fundamental and low-order harmonics composing the ac grid voltage. Numerical simulations confirm the high harmonics rejection capability of the proposed algorithm, as well as, good dynamic response to rapid modification of grid harmonic pollution.