Abstract
A novel phase-locked loop (PLL) with simple structure is proposed in the present work for three-phase power converters under adverse grid conditions. Based on a synchronous rotating frame PLL (SRF-PLL), multi-resonant harmonic compensators with the ability of accommodating frequency deviations are employed in the feedback path of a pre-filter. As a result, the negative-sequence component and harmonic distortions of grid voltage can be attenuated. Different from existing methods, only classical regulators are used, avoiding complicated networks for the decoupling of unbalance and harmonics and thus greatly simplifying the control algorithm. The proposed method is analysed and designed in both the continuous s-domain and discrete z-domain, whereby stable, fast, accurate, and robust responses are achieved. Simulation results have been obtained to show the improved performance of the proposed PLL compared with two widely used methods.
Highlights
Grid synchronisation is crucial for a number of power conversion devices, e.g. grid-connected inverters, active power filters, and static synchronous compensator etc. [1, 2]
The advantage in the synchronous reference frame (SRF) is that the fundamental positive sequence component of grid voltage can be transformed into DC signals while harmonics at two different frequencies could result in the same frequency, which facilitates the realisation of closed-loop regulators [8]
The 5th and 7th harmonics decoupling units are included in the DSOGI-phase-locked loop (PLL) according to the design in [11]
Summary
Grid synchronisation is crucial for a number of power conversion devices, e.g. grid-connected inverters, active power filters, and static synchronous compensator etc. [1, 2]. A repetitive learning-based PLL in which a Lyapunov technique was used to improve the performance was proposed in [21], but it occupied extra computation space and burden Many other strategies such as modified SRF-based digital PLL [22], two-phase stationary frame enhanced PLL [23], and rotor PLL [24] have been reported, to name but a few. The negative-sequence component and harmonic distortions of grid voltage can be eliminated Compared with those existing methods, complicated unbalance and harmonics decoupling network is not needed, which greatly simplifies the control algorithm. Simulated results have been obtained which show the advantages of the simple but novel PLL
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