Cascade three-phase PLL for unbalance and harmonic distortion operation (CSRF-PLL)

This paper presents a phase-locked loop (PLL) method aimed to provide an estimation of the phase angle and the amplitude of the fundamental positive sequence component of a three-phase reference signal subject to severe unbalance and high harmonic distortion. In addition the proposed scheme provides the estimation of the angular frequency, and both the positive and negative sequences of the fundamental component of the reference signal. The proposed method is referred as CSRF-PLL and consists of a cascade interconnection of two recently reported PLL schemes, namely, UH-PLL reported in [1] and the conventional SRF-PLL reported in [2]. In the CSRF-PLL, the UH-PLL is used as a pre-filter to extract the positive-sequence component of the reference signal which is fed to the SRF-PLL. Recall that the proper operation of the SRF-PLL can only be guaranteed if its input is a pure sinusoidal and balanced signal, which in this case is represented by the fundamental positive sequence delivered by the UH-PLL. The SRF-PLL is used, in its turn, to estimate the fundamental frequency which is necessary for the proper operation of the UH-PLL. Simulations are provided to evaluate the performance of the proposed solution. Experimental evidence will be provided in the final version of the paper.